Bond strength of resin cement to zirconia treated in pre-sintered stage J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-20 Kamal Ebeid, Sebastian Wille, Tarek Salah, Marwa Wahsh, Maged Zohdy, Matthias Kern
PurposeAim of this study was to evaluate the tensile bond strength (TBS) between resin cement and zirconia surface treated in different sintering stages.Materials and MethodsEighty zirconia discs having final dimensions of 12 mm diameter and 3.2 mm thickness were milled then divided into three main groups according to the type of surface treatment performed (group 1: air abrasion using 50 µm Al2O3 particles, group 2: silica coating using Rocatec soft, and group 3: a control group receiving no surface treatment). Groups 1 and 2 were divided into two subgroups each according to the stage in which the surface treatment was performed (subgroup A; surface treatment performed in the pre-sintered stage and subgroup B; surface treatment performed in the post-sintered stage). Discs were later bonded to composite core materials using resin cement then tested for TBS either being subjected to 3 days of water storage or 150 days of water storage and 37,500 thermal cycles.ResultsLong-term aging caused a significant decrease in TBS of all subgroups except the subgroup air-abraded in the post-sintered stage. After long-term aging, the group silica coated in the pre-sintered stage showed the significantly lowest TBS compared to all other groups. There was also no significant difference between the subgroups air-abraded and silica coated in the pre-sintered stage. All specimens in the control group debonded during long-term aging.SignificanceAir-abrading zirconia with Al2O3 at a reduced pressure in the pre-sintered stage may result in durable bond strength to resin cement.
Effect of Grinding on Subsurface modifications of Pre-Sintered Zirconia under Different Cooling and Lubrication Conditions J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-20 P. Suya Prem Anand, N. Arunachalam, L. Vijayaraghavan
Pre-Sintered zirconia is preferred as a restoration material in dental applications due to its excellent strength and fracture toughness. When abrasive processes were used to obtain the required shape of (Y-TZP) yttria-stabilized tetragonal pre-sintered zirconia, it resulted in material strength degradation in the presence of coolant. Therefore, experiments were carried out on pre-sintered zirconia with diamond grinding wheel to evaluate the performance of cooling conditions such as dry, wet and minimum quantity lubrication (MQL). The effects of different environments on the grinding performance were studied based on the temperature distribution, phase transformation, flexural strength, microhardness and edge chipping damage. The Raman spectroscopy and X-ray diffraction analysis were used to estimate the quantity of monoclinic phase in pre-sintered zirconia. The temperature rise of the workpiece material during the grinding experiment was not higher and insufficient to cause the thermal stresses. The microstructural changes induced by grinding under different cooling strategies were associated with the quantitative assessment of monoclinic phase. The flexural strength of ground components was improved in the dry condition compared to the other process due to the absence of the defective layer and the occurrence of Y3+ ions segregation. After grinding, there was a slight decrease in the hardness value by (1 to 8 HV), which was due to the formation of microcracks in the subsurface layer of the ground surface. In addition, to ensure the presence of microcracks, the edge chipping depth was measured. The damage depth obtained from the wet condition showed a higher value of 30 µm compared to the dry and MQL conditions.
Validation of Finite Element models of the Mouse Tibia using Digital Volume Correlation J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-18 S. Oliviero, M. Giorgi, E. Dall'Ara
A FINITE ELEMENT ANALYSIS OF DIAPHRAGMATIC HERNIA REPAIR ON AN ANIMAL MODEL J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-15 N. de Cesare, C. Trevisan, E. Maghin, M. Piccoli, P.G. Pavan
The diaphragm is a mammalian skeletal muscle that plays a fundamental role in the process of respiration. Alteration of its mechanical properties due to a diaphragmatic hernia contributes towards compromising its respiratory functions, leading to the need for surgical intervention to restore the physiological conditions by means of implants. This study aims to assess via numerical modeling biomechanical differences between a diaphragm in healthy conditions and a herniated diaphragm surgically repaired with a polymeric implant, in a mouse model. Finite Element models of healthy and repaired diaphragms are developed from diagnostic images and anatomical samples. The mechanical response of the diaphragmatic tendon is described by assuming an isotropic hyperelastic model. A similar constitutive model is used to define the mechanical behavior of the polymeric implant, while the muscular tissue is modelled by means of a three-element Hill’s model, specifically adapted to mouse muscle fibers. The Finite Element Analysis is addressed to simulate diaphragmatic contraction in the eupnea condition, allowing the evaluation of diaphragm deformation in healthy and herniated-repaired conditions. The polymeric implant reduces diaphragm excursion compared to healthy conditions. This explains the possible alteration in the mechanical functionality of the repaired diaphragm. Looking to the surgical treatment of diaphragmatic hernia in human neonatal subjects, this study suggests the implementation of alternative approaches based on the use of biological implants.
Study on design and cutting parameters of rotating needles for core biopsy J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-15 Marco Giovannini, Huaqing Ren, Jian Cao, Kornel Ehmann
Core needle biopsies are widely adopted medical procedures that consist in the removal of biological tissue to better identify a lesion or an abnormality observed through a physical exam or a radiology scan. These procedures can provide significantly more information than most medical tests and they are usually performed on bone lesions, breast masses, lymph nodes and the prostate. The quality of the samples mainly depends on the forces exerted by the needle during the cutting process. The reduction of these forces is critical to extract high-quality tissue samples. The most critical factors that affect the cutting forces are the geometry of the needle tip and its motion while it is penetrating the tissue. However, optimal needle tip configurations and cutting parameters are not well established for rotating insertions. In this paper, the geometry and cutting forces of hollow needles are investigated. The fundamental goal of this study is to provide a series of guidelines for clinicians and surgeons to properly select the optimal tip geometries and speeds. Analytical models related to the cutting angles of several needle tip designs are presented and compared. Several needle tip geometries were manufactured from a 14-gauge cannula, commonly adopted during breast biopsies. The needles were then tested at different speeds and on different phantom tissues. According to these experimental measurements recommendations were formulated for rotating needle insertions. The findings of this study can be applied and extended to several biopsy procedures in which a cannula is used to extract tissue samples.
Experimental and analytical evaluation on the mass transfer performance of braided stent-grafts J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-15 Wen Xue, Liheng Gao, Xuan Fang, Fan Zhao, Jing Gao, Guoping Guan, Jing Lin, Fujun Wang, Lu Wang
On Incorporating Osmotic Prestretch/Prestress in Image-Driven Finite Element Simulations of Cartilage J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-15 Xiaogang Wang, Thomas S.E. Eriksson, Tim Ricken, David M. Pierce
Growth and in vivo stresses traced through tumor mechanics enriched with predator-prey cells dynamics J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-15 A.R. Carotenuto, A. Cutolo, A. Petrillo, R. Fusco, C. Arra, M. Sansone, D. Larobina, L. Cardoso, M. Fraldi
Mechanical stress accumulating during growth in solid tumors plays a crucial role in the tumor mechanobiology. Stresses arise as a consequence of the spatially inhomogeneous tissue growth due to the different activity of healthy and cancer cells inhabiting the various districts of the tissue, an additional piling up effect, induced by stress transferring across the scales, contributing to determine the total stress occurring at the macroscopic level. The spatially inhomogeneous growth rates accompany nonuniform and time-propagating stress profiles, which constitute mechanical barriers to nutrient transport and influence the intratumoral interstitial flow, in this way deciding the starved/feeded regions, with direct aftereffects on necrosis, angiogenesis, cancer aggressiveness and overall tumor mass size. Despite their ascertained role in tumor mechanobiology, stresses cannot be directly appraised neither from overall tumor size nor through standard non-invasive measurements. To date, the sole way for qualitatively revealing their presence within solid tumors is ex vivo, by engraving the excised masses and then observing opening between the cut edges. Therefore, to contribute to unveil stresses and their implications in tumors, it is first proposed a multiscale model where Volterra-Lotka (predator/prey–like) equations describing the interspecific (environment-mediated) competitions among healthy and cancer cells are coupled with equations of nonlinear poroelasticity. Then, an experimental study on mice injected subcutaneously with a suspension of two different cancer cell lines (MiaPaCa-2 and MDA.MB231) was conducted to provide experimental evidences that gave qualitative and some new quantitative confirmations of the theoretical model predictions.
High-velocity micro-particle impact on gelatin and synthetic hydrogel J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-14 David Veysset, Steven E. Kooi, A.A. Мaznev, Shengchang Tang, Aleksandar S. Mijailovic, Yun Jung Yang, Kyle Geiser, Krystyn J. Van Vliet, Bradley D. Olsen, Keith. A. Nelson
The high-velocity impact response of gelatin and synthetic hydrogel samples is investigated using a laser-based microballistic platform for launching and imaging supersonic micro-particles. The micro-particles are monitored during impact and penetration into the gels using a high-speed multi-frame camera that can record up to 16 images with nanosecond time resolution. The trajectories are compared with a Poncelet model for particle penetration, demonstrating good agreement between experiments and the model for impact in gelatin. The model is further validated on a synthetic hydrogel and the applicability of the results is discussed. We find the strength resistance parameter in the Poncelet model to be two orders of magnitude higher than in macroscopic experiments at comparable impact velocities. The results open prospects for testing high-rate behavior of soft materials on the microscale and for guiding the design of drug delivery methods using accelerated microparticles.
Dynamic Properties of Hydrogels and Fiber-reinforced Hydrogels J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-07 Nicholas Martin, George Youssef
Hydrophilic polymers, or hydrogels, are used for a wide variety of biomedical applications, due to their inherent ability to withhold a high-water content. In recent years, a large effort has been focused on tailoring the mechanical properties of these hydrogels to become more appropriate materials for use as anatomical and physiological structural supports. A few of these such methods include using diverse types of polymers, both natural and synthetic, varying the type of molecular cross-linking, as well as combining these efforts to form interpenetrating polymer network hydrogels. While multiple research groups have characterized these various hydrogels under quasi-static conditions, their dynamic properties, representative of native physiological loading scenarios, have been scarcely reported. In this study, an E-glass fiber reinforced family of alginate/PAAm hydrogels cross-linked by both divalent and trivalent cations are fabricated and investigated. The effect of the reinforcement phase on the dynamic and hydration behaviors is then explicated. Additionally, a micromechanics framework for short cylindrical chopped fibers is utilized to discern the contribution of the matrix and fiber constituents on the hydrogel composite. The addition of E-glass fibers resulted in the storage modulus exhibiting a ~50%, 5%, and ~120%, increase with a mere addition of 2 wt. % of the reinforcing fibers to Na-, Sr-, and Al-alginate/PAAm, respectively. In studying the cross-linking effect of various divalent (Ba, Ca, Sr) and trivalent (Al, Fe) cations, it was noteworthy that the hydrogels were found to be effective in dissipating energy while resisting mechanical deformation when they are cross-linked with higher molecular weight elements, regardless of valency. This report on the dynamic properties of these hydrogels will help to improve their optimization for future use in biomedical load-bearing applications.
Displacement of teeth without and with bonded fixed orthodontic retainers: 3D analysis using triangular target frames and optoelectronic motion tracking device J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-06 Firas Chakroun, Vera Colombo, Dave Lie Sam Foek, Luigi Maria Gallo, Albert Feilzer, Mutlu Özcan
PurposeThe objective of this study was to evaluate the anterior tooth movement without and with bonded fixed orthodontic retainers under incremental loading conditions.Materials and MethodsSix extracted mandibular anterior human teeth were embedded in acrylic resin in True Form I Arch type and 3D reconstruction of Digital Volume Tomography (DVT) images (0.4 mm3 voxels) were obtained. The anatomy of each tooth was segmented and digitally reconstructed using 3D visualization software for medical images (AMIRA, FEI SVG). The digital models of the teeth were repositioned to form an arch with constant curvature using a CAD software (Rhinoceros) and a base holder was designed fitting the shape of the roots. The clearance between the roots and their slot in the holder was kept constant at 0.3 mm to replicate the periodontal ligament thickness. The holder and the teeth were then manufactured by 3D printing (Objet Eden 260VS, Stratasys) using a resin material for dental applications (E=2–3 GPa). The 3D-printed teeth models were then positioned in the holder and the root compartments were filled with silicone. The procedure was repeated to obtain three identical arch models. Each model was tested for tooth mobility by applying force increasing from 5 to 30 N with 5 N increments applied perpendicular on the lingual tooth surface on the incisal one third (crosshead speed: 0.1 mm/s). The teeth on each model were first tested without retainer (control) and subsequently with the bonded retainers (braided bonded retainer wire; Multi-strand 1×3 high performance wire, 0.022” x 0.016”). Tooth displacement was measured in terms of complicance (F/Δ movement) (N/mm) using custom-built optoelectronic motion tracking device (OPTIS) (accuracy: 5 μm; sampling rate: 200 Hz). The position of the object was detected through three LEDs positioned in a fixed triangular shape on a metal support (Triangular Target Frame). The measurements were repeated for three times for each tooth. Data were analysed using mixed model with nesting (alpha=0.05).ResultsThe use of retainer showed a significant effect on tooth mobility (0.008±0.004) compared to non-bonded teeth (control) (0.014±0.009) (p<0.0001). The amount of displacement on the tooth basis was also significantly different (p=0.0381) being the most for tooth no. 42 (without: 0.024±0.01; with: 0.012±0.002) (p=0.0018). No significant difference was observed between repeated measurements (p=0.097) and the incremental magnitude of loading (5–30 N: 0.07±0.01- 0.09±0.02) (p>0.05).ConclusionMandibular anterior teeth showed less tooth mobility when bonded with stainless steel wire as opposed to non-bonded teeth but the tooth mobility varied depending on the tooth type. Intermittent increase in loading from 5 to 30 N did not increase tooth displacement.
Sliding Wear and Friction Characteristics of Polymer Nanocomposite PAEK-PDMS with nano-hydroxyapatite and nano-carbon fibres as fillers J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-06 Suman B. Iyer, Anshuman Dube, N.M. Dube, Pratik Roy, R.R.N. Sailaja
The development of a suitable polymeric bioactive composite with hydroxyapatite as a filler is one of the very actively pursued areas in bioapplications. This report concerns development of such a novel polymeric biocomposite viz. poly (aryl ether) ketone-poly (dimethylsiloxane) with a small percentage of nano carbon fibres and varying percentages of nanohydroxyapatite particulates as fillers. The earlier characterization of this material involving mechanical, thermal and bio-compatibility studies showed optimum improved behaviour at about 7% nanohydroxyapatite loading as reported elsewhere. In this study, the wear and friction response of this biocomposite was tested in air under dry sliding conditions against hard steel using a pin-on-disc apparatus. Interestingly, the adhesive wear characteristics of this nanocomposite with varying nanohydroxyapatite percentages showed a trend similar to that in other characteristics with lowest wear occurring around the same nanohydroxyapatite percentage. It was observed that the specific wear rate in this novel nanocomposite was exceptionally low [~ 10-8 (mm3/N-m)] compared to that in other similar polymer composites. The origin of this very low wear rate can be associated with the multiple strategies used in the preparation of this nanocomposite such as the use of poly (dimethylsiloxane) which is known to provide a cushioning effect in the matrix. In addition, the phosphate grafting of poly (dimethylsiloxane), the nanonature of both the fillers and their specific surface treatments using aminosilane for enhancing the matrix- filler interfacial bonding all of them seem to have played their expected beneficial roles resulting in the above very low wear rate. The earlier studies on this nanocomposite have shown improvement of the mechanical compressive strength with the addition of carbon nanofibres. Interestingly, here the friction coefficient of the nanocomposite with carbon nanofibres is consistently higher than that without carbon nano fibres for different nanohydroxyapatite percentages samples, for both low (5 N) as well as high (30 N) applied load. It could possibly be due to dislodged carbon nano fibres acting as a third body abrasive or fibres acting as weak links in the matrix filler network affecting the friction response. These wear and friction measurements have clearly brought out the various interesting aspects of the tribological response of the nanocomposite material and the intricate roles played by its matrix component poly (dimethylsiloxane) and the surface treated nano fillers nanohydroxyapatite and nano carbon fibre.
Radiation therapy affects the mechanical behavior of human umbilical vein endothelial cells J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-06 Alireza Mohammadkarim, Mohammad Tabatabaei, Azim Parandakh, Manijhe Mokhtari-Dizaji, Mohammad Tafazzoli-Shadpour, Mohammad-Mehdi Khani
Utilization of a robotic mount to determine the force required to cut palatal tissue J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-06 Kimia Sorouri, Dale J Podolsky, Annie M Q Wang, David M Fisher, Karen W Wong, Thomas Looi, James M Drake, Christopher R Forrest
Features of the Volume Change and a New Constitutive Equation of Hydrogels under Uniaxial Compression J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-05 Y.R. Zhang, X.K. Jia, Y.L. Bai, L.Q. Tang, Z.Y. Jiang, Y.P. Liu, Z.J. Liu, L.C. Zhou, X.F. Zhou
For high-water content hydrogels in compression, the water inside of hydrogels contributes to the response of hydrogels to external loads directly, but part of the water is expelled from hydrogels in the meantime to change the volume of the hydrogel and reduce the contribution. In order to consider the contribution of the water in the constitution equation, PVA (polyvinyl alcohol) hydrogels with high-water content were used as examples, and compressive experiments were carried out to measure both the stress-strain relation and the change of the volume in the meantime. By considering the effect of the difference of the contribution of water in different directions of the hydrogel, we deduced a new constitutive equation, which can pretty well depict the stress-strain of hydrogels with different water contents. The results showed that the contribution of water to the total stress increases with the compression strain and even exceed that of the polymer, although the expelled water reduces the contribution at the early loading stage, which well explains the difference of elastic moduli of hydrogels in compression and tension.
Electromyography activity of triceps surae and tibialis anterior muscles related to various sports shoes J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-05 Andrea Roca-Dols, Marta Elena Losa-Iglesias, Rubén Sánchez-Gómez, Ricardo Becerro-de-Bengoa-Vallejo, Daniel López-López, Patricia Palomo-López, David Rodríguez-Sanz, César Calvo-Lobo
Triceps surae (TS) and tibialis anterior (TA) activation patterns have not yet been studied under different types of sport shoes. We hypothesized that sports shoes may reduce the activity patterns of these muscles in relation to barefoot condition. Thus, our main aim was to evaluate the activity patterns of TS and TA muscles in healthy people during all gait phases using five types of sport shoes with respect to barefoot condition. A total sample of thirty healthy participants, mean age 36.20±8.50, was recruited in a podiatry laboratory following an observational research design. During walking and running, electromyography signals were recorded from TS and TA muscles using surface electrodes in the following experimental situations: 1.) barefoot, 2.) minimalist, 3.) pronated control, 4.) air chamber, 5.) ethyl-vinyl-acetate and 6.) boost. The TS and TA showed significant reductions (P<0.05) in the peak amplitude of different sport shoes types with respect to the barefoot condition in different phases of the gait cycle during walking and running. Nevertheless, the boost sport shoe produced statistically significant increases in the peak amplitude of the gastrocnemius medialis muscle in comparison with the barefoot condition in the midstance phase of the gait cycle during running (P=0.047). In addition, the pronation control and air chamber sport shoes produced statistically significant increases in the peak amplitude of the TA muscle with respect to the barefoot condition in the contact phase of the gait cycle (P=0.021; P=0.013), respectively, during running. Despite TS and TA muscles activity patterns seem to be reduced using different sport shoes types with respect to the barefoot condition in different phases of the gait cycle during walking and running, some sport shoes may increase this muscular activity in specific phases of the gait cycle during running.
Physico-mechanical properties of resin cement light cured through different ceramic spacers J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-04 Sérgio Kiyoshi Ishikiriama, Paula Minatel Locatelli, Thiago Soares Porto, Ana Flávia Sanches Borges, Rafael Francisco Lia Mondelli, Fabio Antonio Piola Rizzante
The purpose of this in vitro study was to compare the micro hardness, color stability/ΔE, and degree of conversion/DC of a resin cement light cured through different ceramic spacers. Lithium-disilicate ceramic samples were obtained from IPS E-max CAD blocks (HT A1) and IPS in-Ceram (transparent neutral); and divided in 7 groups (n=8 for each test): CTR/control group; 06 M/0.6 mm monolithic; 12 M/1.2 mm monolithic; 20 M/2.0 mm monolithic; 06B/0.4+0.2 mm bilayered; 12B/1.0+0.2 mm bilayered; 20B/1.8+0.2 mm bilayered. The resin cement (Variolink veneer) was light cured through the ceramic spacers. The resin cement samples were evaluated for ΔE using a spectrophotometer after 24 hours, 7days and after aging (24 h in water at 60 °C). Knoop microhardness and DC tests were conducted immediately after light curing, after 24 hours and 7days. All experimental groups showed similar microhardness values, although being lower than CTR group. Similar results were observed after 7days. ΔE was similar between all groups after 24 hours (except for 12B and 20B), and increased for all groups after 7days and after artificial aging, especially for thicker and bilayer groups. Only 06 M showed values similar to CTR group. DC values were similar to all groups immediately after light curing, increasing after 24 h and 7days. After 7days, only group 20B showed lower DC than CTR group. A tendency of higher DC could be observed for monolithic and thinner ceramics. All test results showed strong correlation (0.9987). Ceramic interposition can reduce mechanical and physical properties of resin cements, especially with thicker and bilayered ceramics. Group 06 M showed the best ΔE overtime.
Cervical fusion cage computationally optimized with porous architected Titanium for minimized subsidence J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-06-02 Ahmed Moussa, Michael Tanzer, Damiano Pasini
Bone Healing Response in Cyclically Loaded Implants: Comparing Zero, One, and Two Loading Sessions per Day J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-31 Renan de Barros e Lima Bueno, Ana Paula Dias, Katia J. Ponce, Rima Wazen, John B. Brunski, Antonio Nanci
Comparison of five viscoelastic models for estimating viscoelastic parameters using ultrasound shear wave elastography J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-30 Boran Zhou, Xiaoming Zhang
The purpose of this study is to compare five viscoelastic models (Voigt, Maxwell, standard linear solid, spring-pot, and fractional Voigt models) for estimating viscoelastic properties based on ultrasound shear wave elastography measurements. We performed the forward problem analysis, the inverse problem analysis, and experiments. In the forward problem analysis, the shear wave speeds at different frequencies were calculated using the Voigt model for given shear elasticity and varying shear viscosity. In the inverse problem analysis, the viscoelastic parameters were estimated from the given wave speeds for the five viscoelastic models using the least-square regression. The experiment was performed in a tissue-mimicking phantom. A local harmonic vibration was generated via a mechanical shaker on the phantom at five frequencies (100, 150, 200, 250, and 300 Hz) and an ultrasound transducer was used to capture the tissue motion. Shear wave speed of the phantom was measured using the ultrasound shear wave elastography technique. The parameters for different viscoelastic models for the phantom were identified. For both analytical and experimental studies, ratios of storage to loss modulus as a function of excitation frequency for different viscoelastic models were calculated. We found that the Voigt and fractional Voigt models fit well with the shear wave speed - frequency and ratio of storage to loss modulus – frequency relationships both in analytical and experimental studies.
Tensile biomechanical properties and constitutive parameters of human corneal stroma extracted by SMILE procedure J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-30 Yaoqi Xiang, Min Shen, Chao Xue, Di Wu, Yan Wang
The biomechanical behavior of human corneal stroma under uniaxial tension was investigated by the experimental analysis of cornea stromal lenticules taken out by corneal refractive surgery. Uniaxial tests were conducted to determine their stress-strain relationship and tensile strength. The Gasser-Ogden-Holzapfel (GOH) model was used to describe biomechanical behavior of the corneal stroma. The theoretical stress-strain relationship of the GOH model in the uniaxial tensile test was deduced. The corneal specimens were collected from ten patients (4 male and 6 female), aged from 17 to 36. The differences between corneal stress-strain relationship in the horizontal and vertical direction were compared. The constitutive parameters C10, k1 and k2 were evaluated through least squares curve-fitting of experimental data.
New microscale constitutive model of human trabecular bone based on depth sensing indentation technique J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-30 Marek Pawlikowski, Krzysztof Jankowski, Konstanty Skalski
A new constitutive model for human trabecular bone is presented in the present study. As the model is based on indentation tests performed on single trabeculae it is formulated in a microscale. The constitutive law takes into account non-linear viscoelasticity of the tissue. The elastic response is described by the hyperelastic Mooney-Rivlin model while the viscoelastic effects are considered by means of the hereditary integral in which stress depends on both time and strain. The material constants in the constitutive equation are identified on the basis of the stress relaxation tests and the indentation tests using curve-fitting procedure. The constitutive model is implemented into finite element package Abaqus® by means of UMAT subroutine. The curve-fitting error is low and the viscoelastic behaviour of the tissue predicted by the proposed constitutive model corresponds well to the realistic response of the trabecular bone.
An Investigation of the Viscoelastic Properties and the Actin Cytoskeletal Structure of Triple Negative Breast Cancer Cells J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-30 Jingjie Hu, Yuxiao Zhou, John D. Obayemi, Jing Du, Winston O. Soboyejo
Effects of postmortem time and storage fluid on the material properties of bovine liver parenchyma in tension J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-31 Kristin M. Dunford, Tanya LeRoith, Andrew R. Kemper
In motor vehicle collisions (MVCs), liver injuries are one of the most frequently reported types of abdominal organ trauma. Although finite element models are utilized to evaluate the risk of sustaining an abdominal organ injury in MVCs, these models must be validated based on biomechanical data in order to accurately assess injury risk. Given that previous studies that have quantified the tensile failure properties of human liver parenchyma have been limited to testing at 48hrs postmortem, it is currently unknown how the material properties change between time of death and 48hrs postmortem. Therefore, the objective of this study was to quantify the effects of postmortem degradation on the tensile material properties of bovine liver parenchyma with increasing postmortem time when stored in DMEM or saline. A total of 148 uniaxial tension tests were successfully conducted on parenchyma samples of fourteen bovine livers acquired immediately after death. Liver tissue was submerged in DMEM or saline and kept cool during sample preparation and storage. Twelve livers were stored as large blocks of tissue, while two livers were stored as small blocks and slices. Tension tests were performed on multiple dog-bone samples from each liver at three time points: ~6hrs, ~24hrs, and ~48hrs postmortem. The data were then analyzed using a Linear Mixed Effect Model to determine if there were significant changes in the failure stress, failure strain, and modulus with respect to postmortem time. The results of the current study showed that the failure strain of bovine liver parenchyma decreased significantly between 6hrs and 48hrs after death when stored as large blocks in saline and refrigerated. Conversely, neither the failure stress nor failure strain changed significantly with respect to postmortem time when stored as large blocks in DMEM. The modulus did not significantly change for tissue stored as large blocks in either saline or DMEM. Cellular disruption increased with postmortem time for tissue stored as large blocks, with tissue stored in saline showing the greatest increase at each time point. In addition, preliminary results indicated that reducing the tissue storage size had a negative effect on the material properties and cellular architecture. Overall, this study illustrated that the effects of postmortem liver degradation varied with respect to the preservation fluid, storage time, and storage block size.
Uncertainty quantification for constitutive model calibration of brain tissue J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-31 Patrick T. Brewick, Kirubel Teferra
The results of a study comparing model calibration techniques for Ogden's constitutive model that describes the hyperelastic behavior of brain tissue are presented. One and two-term Ogden models are fit to two different sets of stress-strain experimental data for brain tissue using both least squares optimization and Bayesian estimation. For the Bayesian estimation, the joint posterior distribution of the constitutive parameters is calculated by employing Hamiltonian Monte Carlo (HMC) sampling, a type of Markov Chain Monte Carlo method. The HMC method is enriched in this work to intrinsically enforce the Drucker stability criterion by formulating a nonlinear parameter constraint function, which ensures the constitutive model produces physically meaningful results. Through application of the nested sampling technique, 95% confidence bounds on the constitutive model parameters are identified, and these bounds are then propagated through the constitutive model to produce the resultant bounds on the stress-strain response. The behavior of the model calibration procedures and the effect of the characteristics of the experimental data are extensively evaluated. It is demonstrated that increasing model complexity (i.e., adding an additional term in the Ogden model) improves the accuracy of the best-fit set of parameters while also increasing the uncertainty via the widening of the confidence bounds of the calibrated parameters. Despite some similarity between the two data sets, the resulting distributions are noticeably different, highlighting the sensitivity of the calibration procedures to the characteristics of the data. For example, the amount of uncertainty reported on the experimental data plays an essential role in how data points are weighted during the calibration, and this significantly affects how the parameters are calibrated when combining experimental data sets from disparate sources.
A modular inverse elastostatics approach to resolve the pressure-induced stress state for in vivo imaging based cardiovascular modeling J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-28 Mathias Peirlinck, Matthieu De Beule, Patrick Segers, Nuno Rebelo
Patient-specific biomechanical modeling of the cardiovascular system is complicated by the presence of a physiological pressure load given that the imaged tissue is in a pre-stressed and -strained state. Neglect of this prestressed state into solid tissue mechanics models leads to erroneous metrics (e.g. wall deformation, peak stress, wall shear stress) which in their turn are used for device design choices, risk assessment (e.g. procedure, rupture) and surgery planning. It is thus of utmost importance to incorporate this deformed and loaded tissue state into the computational models, which implies solving an inverse problem (calculating an undeformed geometry given the load and the deformed geometry). Methodologies to solve this inverse problem can be categorized into iterative and direct methodologies, both having their inherent advantages and disadvantages. Direct methodologies are typically based on the inverse elastostatics (IE) approach and offer a computationally efficient single shot methodology to compute the in vivo stress state. However, cumbersome and problem-specific derivations of the formulations and non-trivial access to the FE code, especially for commercial products, refrain a broad implementation of these methodologies. For that reason, we developed a novel, modular IE approach and implemented this methodology in a commercial FEA solver with minor user subroutine interventions. The accuracy of this methodology was demonstrated in an arterial tube and porcine biventricular myocardium model. The computational power and efficiency of the methodology was shown by computing the in vivo stress and strain state, and the corresponding unloaded geometry, for two models containing multiple interacting incompressible, anisotropic (fiber-embedded) and hyperelastic material behaviors: a patient-specific abdominal aortic aneurysm and a full 4-chamber heart model.
A transverse isotropic constitutive model for the aortic valve tissue incorporating rate-dependency and fibre dispersion: application to biaxial deformation J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-26 Afshin Anssari-Benam, Yuan-Tsan Tseng, Andrea Bucchi
This paper presents a continuum-based transverse isotropic model incorporating rate-dependency and fibre dispersion, applied to the planar biaxial deformation of aortic valve (AV) specimens under various stretch rates. The rate dependency of the mechanical behaviour of the AV tissue under biaxial deformation, the (pseudo-) invariants of the right Cauchy-Green deformation-rate tensor C ̇ associated with fibre dispersion, and a new fibre orientation density function motivated by fibre kinematics are presented for the first time. It is shown that the model captures the experimentally observed deformation of the specimens, and characterises a shear-thinning behaviour associated with the dissipative (viscous) kinematics of the matrix and the fibres. The application of the model for predicting the deformation behaviour of the AV under physiological rates is illustrated and an example of the predicted σ−λ σ − λ curves is presented. While the development of the model was principally motivated by the AV biomechanics requisites, the comprehensive theoretical approach employed in the study renders the model suitable for application to other fibrous soft tissues that possess similar rate-dependent and structural attributes.
Dynamic rheological comparison of silicones for podiatry applications J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-26 Ana-María Díaz-Díaz, Bárbara Sánchez-Silva, Javier Tarrío-Saavedra, Jorge López-Beceiro, Julia Janeiro-Arocas, Carlos Gracia-Fernández, Ramón Artiaga
Purpose This work shows an effective methodology to evaluate the dynamic viscoelastic behavior of silicones for application in podiatry. The aim is to characterize, compare their viscoelastic properties according to the dynamic stresses they can be presumably subjected when used in podiatry orthotic applications. These results provide a deeper insight which extends the previous creep-recovery results to the world of dynamic stresses developed in physical activity. In this context, it shoulod be taken into account that an orthoses can subjected to a set of static and dynamic shear and compressive forces. Methods Two different podiatric silicones, Blanda-blanda and Master, from Herbitas, are characterized by dynamic rheological methods. Three kinds of rheological tests are considered: shear stress sweep, compression frequency sweep and shear frequency sweep, all the three with simultaneous control of the static force at three different levels. The static force represents a static load like that produced by the weight of a human body on a shoe insole. In a practical sense, dynamic stresses are related to physical activity and are needed to evaluate the frequency effect on the viscoelastic behavior of the material. It is considered that the dynamic stresses can be applied in compression and shear since, in practice, the way the stresses are applied in real life depends on the orthoses geometry and its exact location with respect to the foot and shoe. The effects of static and dynamic loads are individualized and compared to each other through the relations between the elastic constants for isotropic materials. Conclusions The overall proposed experimental methodology can provide very insightful information for better selection of materials in podiatry applications. This study focuses on the rheological characterization to choose the right silicone for each podiatric application, taking into account the dynamic viscoelastic requirements associated to the physical activity of user. Accordingly, one soft and one hard silicones of common use in podiatry were tested. Each of the two silicones exhibit not only different moduli values, but also, a different kind of dependence of the dynamic moduli with respect to the static load. In the case of the soft sample a linear trend is observed but in the case of of the hard one the dependence is of the power law type. Moreover, these samples exhibit very different Poisson's coefficient values for compression stresses lower than 20 kPa, and almost the same values for stresses above 40 kPa. That different dependence of the Poisson's ratio on the static load should also be taken into account for material selection in customized podiatry applications, where static and dynamic loads are strongly dependent on the individual weight and activity.
Development of biomimetic in vitro fatigue assessment for UHMWPE implant materials J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-26 Ronja Scholz, Marina Knyazeva, Dario Porchetta, Nils Wegner, Fedor Senatov, Alexey Salimon, Sergey Kaloshkin, Frank Walther
An important research goal in the field of biomaterials lies in the progressive amendment of in vivo tests with suitable in vitro experiments. Such approaches are gaining more significance nowadays because of an increasing demand on life sciences and the ethical issues bound to the sacrifice of animals for the sake of scientific research. Another advantage of transferring the experiments to the in vitro field is the possibility of accurately control the boundary conditions and experimental parameters in order to reduce the need of validation tests involving animals.. With the aim to reduce the amount of needed in vivo studies for this cause, a short-time in vitro test procedure using instrumented load increase tests with superimposed environmental loading has been developed at TUD to assess the mechanical long-term durability of ultra-high molecular weight polyethylene (UHMWPE) under fatigue loading in a biological environment.
Influence of post coating heat treatment on microstructural, mechanical and electrochemical corrosion behaviour of vacuum plasma sprayed reinforced hydroxyapatite coatings J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-24 Amardeep Singh, Gurbhinder Singh, Vikas Chawla
In the present study, reinforced hydroxyapatite (HA) coatings (HA + 10 wt% Al2O3 and HA + 10 wt% ZrO2) were deposited on SS-316L substrate with an intermediate layer (bond coat) of zirconia by vacuum plasma spray technique. The so-formed reinforced HA coatings were heat treated at 700 °C for 1 h. The influence of post coating heat treatment on phase composition, microstructure, mechanical and electrochemical corrosion properties were investigated. As-sprayed and heat treated coatings were characterized by x-ray diffraction, scanning electron microscope, surface roughness, porosity and crystallinity. Results showed that after post coating heat treatment, the structural integrity of HA has been completely re-established. Moreover, significant drop in porosity has been observed due to the sintering effect produced by heat treatment. Considerable improvement in nanohardness and shear strength was witnessed; however, the nanohardness of top layer was decreased after annealing due to the weak bonding of partially melted and un-melted particles with fully melted splats caused by diffusion process. As-sprayed coatings exhibited higher wear resistance compared to heat treated coatings. Nevertheless, post coating heat treatment effectively enhanced the corrosion resistance of coatings, since, the heat treatment lead to densification of coatings microstructure which further reduces the active sites for dissolution.
Mechanical reliability, fatigue strength and survival analysis of new polycrystalline translucent zirconia ceramics for monolithic restorations J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-23 Gabriel KR Pereira, Luís F Guilardi, Kiara S Dapieve, Cornelis J Kleverlaan, Marília P Rippe, Luiz Felipe Valandro
This study characterized the mechanical properties (static and under fatigue), the crystalline microstructure (monoclinic - m, tetragonal - t and cubic - c phase contents) and the surface topography of three yttrium-stabilized zirconia (YSZ) materials with different translucent properties, before and after aging in an autoclave (low temperature degradation). Disc-shaped specimens were produced from second generation (Katana ML/HT – high-translucent) and third generations (Katana STML – super-translucent and UTML – ultra-translucent) YSZ ceramics (Kuraray Noritake Dental Inc.), following ISO 6872-2015 guidelines for biaxial flexural strength testing (final dimensions: 15 mm in diameter and 1.2 ± 0.2 mm in thickness), and then subjected to the respective tests and analyses. ML was mainly composed of tetragonal crystals, while STML and UTML presented cubic content. Aging increased the monoclinic content for ML and did not affect STML and UTML. Topographical analysis highlights different grain sizes on the ceramic surface (UTML > STML > ML) and aging had no effect on this outcome. Weibull analysis showed the highest characteristic strength for ML both before and after aging, and statistically similar Weibull moduli for all groups. ML material also obtained the highest survival rates (ML > STML > UTML) for both fatigue strength and number of cycles to failure. All fractures originated from surface defects on the tensile side. Third generation zirconia (Katana STML and UTML) are fully stabilized materials (with tetragonal and cubic crystals), being totally inert to the autoclave aging, and presented lower mechanical properties than the second-generation zirconia (Katana ML - metastable zirconia).
Stiffness and energy dissipation across the superficial and deeper third metacarpal subchondral bone in Thoroughbred racehorses under high-rate compression J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-22 Fatemeh Malekipour, R. Chris Whitton, Peter Vee-Sin Lee
Subchondral bone injury due to high magnitude and repetition of compressive loading is common in humans and athletic animals such as Thoroughbred racehorses. Repeated loading of the joint surface may alter the subchondral bone microstructure and initiate microdamage in the bone adjacent to the articular cartilage. Understanding the relationship between microdamage, microstructure and mechanical properties of the subchondral bone adjacent to the articular cartilage is, therefore, essential in understanding the mechanism of subchondral bone injury. In this study, we used high-resolution µCT scanning, a digital image-based strain measurement technique, and mechanical testing to evaluate the three-dimensional pre-existing microcracks, bone volume fraction (BVF) and bone mineral density (BMD), and mechanical properties (stiffness and hysteresis) of subchondral bone (n=10) from the distopalmar aspect of the third metacarpal (MC3) condyles of Thoroughbred racehorses under high-rate compression. We specifically compared the properties of two regions of interest in the subchondral bone: the 2 mm superficial subchondral bone (SSB) and its underlying 2 mm deep subchondral bone (DSB). The DSB region was 3.0±1.2 times stiffer than its overlying SSB, yet it dissipated much less energy compared to the SSB. There was no correlation between structural properties (BVF and BMD) and mechanical properties (stiffness and energy loss), except for BMD and energy loss in SSB. The lower stiffness of the most superficial subchondral bone in the distal metacarpal condyles may protect the overlying cartilage and the underlying subchondral bone from damage under the high-rate compression experienced during galloping. However, repeated high-rate loading over time has the potential to inhibit bone turnover and induce bone fatigue, consistent with the high prevalence of subchondral bone injury and fractures in athletic humans and racehorses.
Time-elapsed Synchrotron-light Microstructural Imaging of Femoral Neck Fracture ☆ J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-22 Saulo Martelli, Egon Perilli
Time-elapsed micro-computed-tomography (μCT) imaging allows studying bone micromechanics. However, no study has yet performed time-elapsed μCT imaging of human femoral neck fractures. We developed a protocol for time-elapsed synchrotron μCT imaging of the microstructure in the entire proximal femur, while inducing clinically-relevant femoral neck fractures. Three human cadaver femora (females, age: 75−80 years) were used. The specimen-specific force to be applied at each load step was based on the specimens’ strength obtained using finite-element analysis of clinical CT images. A radio-transparent compressive stage was designed for loading the specimens while recording the applied load during synchrotron μCT scanning. The total μCT scanning field of view was 146 mm wide and 132 mm high, at 29.81 μm isotropic pixel size. Specimens were first scanned unloaded, then under incremental load steps, each equal to 25% of the estimated specimens’ strength, and ultimately after fracture. Fracture occurred after 4 to 5 time-elapsed load steps, displaying sub-capital fracturing of the femoral neck, in agreement with finite-element predictions. Time-elapsed μCT images, co-registered to those of the intact specimen, displayed the proximal femur microstructure under progressive deformation up to fracture. The images showed (1) a spatially heterogeneous deformation localized in the proximal femoral head; (2) a predominantly elastic recovery, after load removal, of the diaphyseal and trochanteric regions and; (3) post-fracture residual displacements, mainly localized in the fractured region. The time-elapsed μCT imaging protocol developed and the high resolution images generated, made publicly available, may spur further research into human femur micromechanics and fracture.
Calibration of colloidal probes with atomic force microscopy for micromechanical assessment J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-17 Lukas Kain, Orestis G. Andriotis, Peter Gruber, Martin Frank, Marica Markovic, David Grech, Vedran Nedelkovski, Martin Stolz, Aleksandr Ovsianikov, Philipp J. Thurner
Botulinum Toxin Type-A Affects Mechanics of Non-injected Antagonistic Rat Muscles J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-17 Filiz Ateş, Can A. Yucesoy
Botulinum toxin type A (BTX-A) effects on the mechanics of non-injected antagonistic muscles are unknown. The aim was to test the following hypotheses in a rat model: BTX-A injected into gastrocnemius medialis (GM) and lateralis (GL) (1) decreases forces of the antagonistic tibialis anterior (TA) and extensor digitorum longus (EDL), (2) reduces length range of force exertion and (3) increases passive forces of the TA, and (4) changes inter-antagonistic and inter-synergistic epimuscular myofascial force transmission (EMFT). Two groups of Wistar rats were tested: BTX (0.1 units of BTX-A were injected to the GM and GL, each) and Control (saline injected). Five-days post, TA, EDL, GM-GL, and soleus distal and EDL proximal isometric forces were measured after TA lengthening. BTX-A exposure caused forces of all muscles to decrease significantly. TA and EDL active force drops (maximally by 37.3%) show inter-compartmental spread. Length range of force exertion of the TA did not change, but its passive force increased significantly (by 25%). The percentages of intramuscular connective tissue content of the TA and EDL was higher (BTX: 20.0±4.9% and 19.3±4.1% vs. control: 13.1±5.4% and 14.5±4.0%, respectively). Calf muscles’ forces were not affected by TA length changes for both groups indicating lacking inter-antagonistic EMFT. However, BTX-A altered EDL proximo-distal force differences hence, inter-synergistic EMFT. A major novel finding is that BTX-A affects mechanics of non-injected antagonistic muscles in test conditions involving only limited EMFT. The effects indicating a stiffer muscle with no length range increase contradict some treatment aims, which require clinical testing.
Influence of laser structuring of PEEK, PEEK-GF30 and PEEK-CF30 surfaces on the shear bond strength to a resin cement J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-10 Bruno Henriques, Douglas Fabris, Joana Mesquita-Guimarães, Anne C. Sousa, Nathalia Hammes, Júlio C.M. Souza, Filipe S. Silva, Márcio Fredel
Objectives The aim of this study was to evaluate the influence of a surface conditioning technique using laser ablation on PEEK substrate on its bonding strength to a resin cement, comparing this method with the traditional treatment using acid etching. Materials and methods Samples of unfilled PEEK, 30% glass fibre reinforced PEEK and 30% carbon fibre reinforced PEEK were separated in four groups according to the following surface treatments: acid etching with H2SO4, laser ablation with 200 μm holes spaced 400 μm apart (D2E4), laser ablation with 200 μm holes spaced 600 μm apart (D2E6) and laser ablation (D2E4) followed by acid etching. A resin cement (Allcem CORE) was then applied to the PEEK surface and cured using UV light. The samples were aged in distilled water at 37 °C for 24 hours. Shear bond strength tests were performed to the fracture of the samples. Two-way ANOVA statistical analysis was performed with a significance level of 0.05. Scanning electron microscopy analysis was performed both before and after the failure to analyse the conditioned and fracture surfaces, respectively. Results Micrographs show that the surface treatments were effective. The interface images show that there is no proper bonding between the resin and the PEEK. The resin cement did not penetrate the holes created by the laser ablation on the PEEK surface. Laser conditioning did not increase the shear bond strength as hypothesized. Indeed, there was a statistical significant decrease in unfilled PEEK samples. In carbon or glass reinforced PEEK, the change was not significant. The fracture micrographs show that the failure mode was mainly adhesive. Conclusions Laser treatment did not created the desired mechanical interlocking, thus it did not increase the shear bonding strength of PEEK to the resin. Further studies should be carried out to increase the bonding between PEEK and resin cements.
The Rib Cage Stiffens the Thoracic Spine in a Cadaveric Model with Body Weight Load under Dynamic Moments J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-16 Erin M. Mannen, Elizabeth A. Friis, Hadley L. Sis, Benjamin M. Wong, Eileen S. Cadel, Dennis E. Anderson
The thoracic spine presents a challenge for biomechanical testing. With more segments than the lumbar and cervical regions and the integration with the rib cage, experimental approaches to evaluate the mechanical behavior of cadaveric thoracic spines have varied widely. Some researchers are now including the rib cage intact during testing, and some are incorporating follower load techniques in the thoracic spine. Both of these approaches aim to more closely model physiological conditions. To date, no studies have examined the impact of the rib cage on thoracic spine motion and stiffness in conjunction with follower loads. The purpose of this research was to quantify the mechanical effect of the rib cage on cadaveric thoracic spine motion and stiffness with a follower load under dynamic moments. It was hypothesized that the rib cage would increase stiffness and decrease motion of the thoracic spine with a follower load. Eight fresh-frozen human cadaveric thoracic spines with rib cages (T1-T12) were loaded with a 400 N compressive follower load. Dynamic moments of ±5 N·m were applied in lateral bending, flexion/extension, and axial rotation, and the motion and stiffness of the specimens with the rib cage intact have been previously reported. This study evaluated the motion and stiffness of the specimens after rib cage removal, and compared the data to the rib cage intact condition. Range-of-motion and stiffness were calculated for the upper, middle, and lower segments of the thoracic spine. Range-of-motion significantly increased with the removal of the rib cage in lateral bending, flexion/extension, and axial rotation by 63.5%, 63.0%, and 58.8%, respectively (p<0.05). Neutral and extension zones increased in flexion/extension and axial rotation, and neutral zone stiffness decreased in axial rotation with rib cage removal. Overall, the removal of the rib cage increases the range-of-motion and decreases the stiffness of cadaveric thoracic spines under compressive follower loads in vitro. This study suggests that the rib cage should be included when testing a cadaveric thoracic spine with a follower load to optimize clinical relevance.
Integrating MRI-based geometry, composition and fiber architecture in a finite element model of the human intervertebral disc J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-17 Marc A. Stadelmann, Ghislain Maquer, Benjamin Voumard, Aaron Grant, David B. Hackney, Peter Vermathen, Ron N. Alkalay, Philippe K. Zysset
Mechanical properties of the human scalp in tension J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-17 Lisa Falland-Cheung, Mario Scholze, Pamela F Lozano, Benjamin Ondruschka, Darryl C Tong, Paul A Brunton, J Neil Waddell, Niels Hammer
Mechanical properties of the human scalp have not been investigated to a great extent with limited information available. The purpose of this study was to provide new baseline material data for human scalp tissue of various ages, which can be applied to experimental and constitutive models, such as in the area of impact biomechanics. This study used specimens from the left and right temporal, fronto-parietal and occipital regions of the human scalp. It investigated the tensile behavior of scalp tissue using tissues harvested from unfixed, fresh cadavers. These samples were subjected to an osmotic stress analysis and upon testing, cyclic loading followed by stretching until failure in a universal testing machine. Strain evaluation was conducted using digital image correlation in a highly standardized approach. Elastic modulus, tensile strength, strain at maximum load and strain to failure were evaluated computationally. No significant differences were observed comparing the tensile strength between males and females. In contrast to that, a sex-dependent difference was found for the elastic modulus of the occipital scalp region and for the elongation properties. Additionally, regional differences within the male group, as well as an age dependent correlation for females were found in the elastic modulus and tensile strength. Scanning electron microscope analyses have shown the ultrastructural failure patterns, indicated by damaged keratin plates, as well as partially disrupted and retraced collagens at the failure site. The novel data obtained in this study could add valuable information to be used for modelling purposes, as well as provide baseline data for simulant materials and comparisons of tissue properties following head injury or forensic investigations.
Factors Influencing the Effectiveness of Occupant Retention under Far-side Impacts: A Parametric Study J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-12 Sagar Umale, Narayan Yoganandan, Frank A. Pintar, Mike W.J. Arun
The occupant retention and injuries under far-side impact are invariably dependent upon the effectiveness of the seatbelt restraint system, which is largely driven by parameters such as seatbelt pre-tensioner limiting load, D-ring position above and behind the shoulder, and friction coefficient between the torso and the seatbelt. The cumulative effect of systematic variation of these parameters on occupant kinematics under far-side is rarely studied in the literature. In this study, a systematic and detailed analysis was performed to understand the effect of these parameters on occupant retention. A rigid buck assembly with Global Human Body Model Consortium Human Body Model, validated with post mortem human surrogate experiments was used under two different impact scenarios—lateral and oblique. A simulation matrix of 16 cases was designed by varying the magnitude of the parameters for each impact scenario. Each case was graded as good, moderate, or poor retention based on the position of the shoulder seatbelt at the time of rebound. Head accelerations and excursions, chest compression, rib fractures, and neck moments of the HBM were analyzed to understand the effect of improved retention on occupant kinematics. Results showed that higher pre-tensioner limiting load, higher seatbelt friction, and backward position of D-ring improved retention in both lateral and oblique scenarios. Head acceleration, and excursions and chest compression decreased from poor retention cases to good retention cases for both impact scenarios. Rib fractures were higher in cases with poor retention as compared to those with good retention. The peak lateral neck moments changed marginally from poor to good retention; however, the rate of loading of the neck was significantly higher in good retention. Thus, the current study suggested that the backward D-ring position coupled with higher pretensioner limiting load and friction is likely to improve retention in far-side impacts and prevent injuries from the occupant slipping out of the restraint system. Better retention reduced occupant acceleration, excursion, chest compression and number of rib fractures, on the contrary it might instill higher injury vulnerability to neck and brain.
Simultaneous Magnetic Resonance and Optical Elastography Acquisitions: Comparison of Displacement Images and Shear Modulus Estimations using a Single Vibration Source J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-08 Spencer Brinker, Steven P. Kearney, Thomas J. Royston, Dieter Klatt
Composite self-expanding bioresorbable prototype stents with reinforced compression performance for congenital heart disease application: computational and experimental investigation J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-08 Fan Zhao, Wen Xue, Fujun Wang, Laijun Liu, Haoqin Shi, Lu Wang
Stents are vital devices to treat vascular stenosis in pediatric patients with congenital heart disease. Bioresorbable stents (BRSs) have been applied to reduce challenging complications caused by permanent metal stents. However, it remains almost a total lack of BRSs with satisfactory compression performance specifically for children with congenital heart disease, leading to importantly suboptimal effects. In this work, composite bioresorbable prototype stents with superior compression resistance were designed by braiding and annealing technology, incorporating poly (p-dioxanone) (PPDO) monofilaments and polycaprolactone (PCL) multifilament. Stent prototype compression properties were investigated. The results revealed that novel composite prototype stents showed superior compression force compared to the control ones, as well as recovery ability. Furthermore, deformation mechanisms were analyzed by computational simulation, which revealed bonded interlacing points among yarns play an important role. This research presents important clinical implications in bioresorbable stent manufacture and provides further study with an innovative stent design.
Zebrafish as a model to study bone maturation: nanoscale structural and mechanical characterization of age-related changes in the zebrafish vertebral column J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-03 Zhuo Chang, Po-Yu Chen, Yung-Jen Chuang, Riaz Akhtar
Zebrafish (Danio rerio) is a useful model for understanding biomedical properties of bone and are widely employed in developmental and genetics studies. Here, we have studied the development of zebrafish vertebral bone at the nanoscale from adolescence (6 months), early adulthood (10 months) to mid-life (14 months). Characterization of the bone was conducted using energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and Peakforce QNM Atomic force microscopy (AFM) techniques. SEM and AFM revealed a lamellar structure with mineralized collagen fibrils. There was a significant increase in the wall thickness from 6 to 10 months (76%) and 10 months to 14 months (26%), which is positively correlated with nanomechanical behavior. An increase in the Ca/P ratio was found which was also positively correlated with nanomechanical properties. The change in mechanical properties and Ca/P are similar to those expected in humans when transitioning from adolescence to mid-life. We suggest that zebrafish serve as a suitable model for further studies on age-related changes in bone ultrastructure.
Relationships of Bone Characteristics in MYO9B Deficient Femurs J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-03 Do-Gyoon Kim, Yong-Hoon Jeong, Brooke K. McMichael, Martin Bähler, Kyle Bodnyk, Ryan Sedlar, Beth S. Lee
The objective of this study was to examine relationships among a variety of bone characteristics, including volumetric, mineral density, geometric, dynamic mechanical analysis, and static fracture mechanical properties. As MYO9B is an unconventional myosin in bone cells responsible for normal skeletal growth, bone characteristics of wild-type (WT), heterozygous (HET), and MYO9B knockout (KO) mice groups were compared as an animal model to express different bone quantity and quality. Forty-five sex-matched 12-week-old mice were used in this study. After euthanization, femurs were isolated and scanned using microcomputed tomography (micro-CT) to assess bone volumetric, tissue mineral density (TMD), and geometric parameters. Then, a non-destructive dynamic mechanical analysis (DMA) was performed by applying oscillatory bending displacement on the femur. Finally, the same femur was subject to static fracture testing. KO group had significantly lower length, bone mineral density (BMD), bone mass and volume, dynamic and static stiffness, and strength than WT and HET groups (p<0.019). On the other hand, TMD parameters of KO group were comparable with those of WT group. HET group showed volumetric, geometric, and mechanical properties similar to WT group, but had lower TMD (p<0.014). Non-destructive micro-CT and DMA parameters had significant positive correlations with strength (p<0.015) without combined effect of groups and sex on the correlations (p>0.077). This comprehensive characterization provides a better understanding of interactive behavior between the tissue- and organ-level of the same femur. The current findings elucidate that MYO9B is responsible for controlling bone volume to determine the growth rate and fracture risk of bone.
Engineering Mesenchymal Stem Cell Spheroids by Incorporation of Mechanoregulator Microparticles J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-03 Fatemeh Abbasi, Mohammad Hossein Ghanian, Hossein Baharvand, Bahman Vahidi, Mohamadreza Baghaban Eslaminejad
Mechanical forces throughout human mesenchymal stem cell (hMSC) spheroids (mesenspheres) play a predominant role in determining cellular functions of cell growth, proliferation, and differentiation through mechanotransductional mechanisms. Here, we introduce microparticle (MP) incorporation as a mechanical intervention method to alter tensional homeostasis of the mesensphere and explore MSC differentiation in response to MP stiffness. The microparticulate mechanoregulators with different elastic modulus (34 kPa, 0.6 MPa, and 2.2 MPa) were prepared by controlled crosslinking cell-sized microdroplets of polydimethylsiloxane (PDMS). Preparation of MP-MSC composite spheroids enabled us to study the possible effects of MPs through experimental and computational assays. Our results showed that MP incorporation selectively primed MSCs toward osteogenesis, yet hindered adipogenesis. Interestingly, this behavior depended on MP mechanics, as the spheroids that contained MPs with intermediate stiffness behaved similar to control MP-free mesenspheres with more tendencies toward chondrogenesis. However, by using the soft or stiff MPs, the MP-mesenspheres significantly showed signs of osteogenesis. This could be explained by the complex of forces which acted in the cell spheroid and, totally, provided a homeostasis situation. Incorporation of cell-sized polymer MPs as mechanoregulators of cell spheroids could be utilized as a new engineering toolkit for multicellular organoids in disease modeling and tissue engineering applications.
Attachment and spatial organisation of human mesenchymal stem cells on poly(ethylene glycol) hydrogels J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-03 Aman S. Chahal, Manuel Schweikle, Catherine A. Heyward, Hanna Tiainen
Strategies that enable hydrogel substrates to support cell attachment typically incorporate either entire extracellular matrix proteins or synthetic peptide fragments such as the RGD (arginine–glycine–aspartic acid) motif. Previous studies have carefully analysed how material characteristics can affect single cell morphologies. However, the influence of substrate stiffness and ligand presentation on the spatial organisation of human mesenchymal stem cells (hMSCs) have not yet been examined. In this study, we assessed how hMSCs organise themselves on soft (E = 7.4 – 11.2 kPa) and stiff (E = 27.3 – 36.8 kPa) poly(ethylene glycol) (PEG) hydrogels with varying concentrations of RGD (0.05 – 2.5 mM). Our results indicate that hMSCs seeded on soft hydrogels clustered with reduced cell attachment and spreading area, irrespective of RGD concentration and isoform. On stiff hydrogels, in contrast, cells spread with high spatial coverage for RGD concentrations of 0.5 mM or higher. In conclusion, we identified that an interplay of hydrogel stiffness and the availability of cell attachment motifs are important factors in regulating hMSC organisation on PEG hydrogels. Understanding how cells initially interact and colonize the surface of this material is a fundamental prerequisite for the design of controlled platforms for tissue engineering and mechanobiology studies.
Effects of different surface treatments on the cyclic fatigue strength of one-piece CAD/CAM zirconia implants J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-03 Qian Ding, Lei Zhang, Rui Bao, Gang Zheng, Yuchun Sun, Qiufei Xie
Objectives The effects of different surface treatments on cyclic fatigue strengths of computer-aided design and computer-aided manufacturing (CAD/CAM) zirconia implants and its mechanisms were evaluated. Material and methods One-piece cylindrical screw-type zirconia (Y-TZP) implants with diameters of 4.1-mm were fabricated using CAD/CAM technique; they were divided into four groups according to the type of surface treatment: (i) sintering (control group, CTRL), (ii) sandblasting (SB), (iii) sandblasting and etching with an experimental hot etching solution (SB-ST), and (iv) sandblasting and etching with hydrofluoric acid (SB-HF). The surface morphology and roughness of the implants were evaluated. Tetragonal to monoclinic transformation was measured on the surface by micro Raman spectroscopy. Static and fatigue tests were carried out at room temperature following the ISO 14801:2014 Standard. The cyclic fatigue strength of each group was determined using the staircase method. Specimens that survived the fatigue test were statically loaded to measure the residual fracture strength. Results Among the four groups, SB-HF exhibited the highest surface roughness. Compared with the CTRL group, the surface monoclinic content was higher after all three types of surface treatments, amongst which, SB-HF had the highest content (39.14%), significantly more than the other three groups (P＜0.01). The cyclic fatigue strengths of CTRL, SB, SB-ST, and SB-HF implants were 530 N, 662.5 N, 705 N, and 555 N, respectively. The fracture strength after fatigue loading was higher than that before fatigue loading with no significant difference (P＞0.05). Conclusions SB and SB-ST remarkably enhanced the fatigue resistance of zirconia implants, while SB-HF did not. One-piece 4.1-mm diameter CAD/CAM zirconia implants have sufficient durability for application in dental implants.
OPTIMIZATION OF COLLAGEN-ELASTIN-LIKE POLYPEPTIDE COMPOSITE TISSUE ENGINEERING SCAFFOLDS USING RESPONSE SURFACE METHODOLOGY J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-02 Bhuvaneswari Gurumurthy, Jason A. Griggs, Amol V. Janorkar
The ability of a tissue-engineered scaffold to regenerate functional tissues depends on its mechanical and biochemical properties. Though the commonly used collagen scaffolds have good biochemical properties, they fail due to their poor mechanical and physical properties. We have reinforced the collagen matrix with elastin-like polypeptide (ELP) to improve the mechanical and physical properties and optimized the composite composition using a novel statistical method of response surface methodology (RSM). RSM used a central composite design to correlate the 2 input factor variables (collagen and ELP concentrations) and 3 output objectives (tensile strength, elastic modulus, and toughness) using a second order polynomial equation. Upon uniaxial tensile testing and subsequent RSM optimization, a composite prepared using 6 mg/mL collagen and 18 mg/mL ELP was identified as having an optimal combination of all the three tensile properties. Physical properties of the 6:18 mg/mL composite versus the 6:0 mg/mL collagen-only hydrogel characterized by swelling ratio, differential scanning calorimetry, and FTIR spectroscopy revealed that the addition of ELP reduced the residual water content in the composites and provided evidence of the presence of collagen-ELP interactions. Scanning electron microscopy images of the collagen-only hydrogel showed porous fibrillar and dense afibrillar collagenous microstructure, but the collagen-ELP composite showed a dense collagenous microstructure with characteristic ELP aggregates. We surmise that because of the low water content and dense microstructure, the 6:18 mg/mL collagen-ELP composite had improved mechanical properties. Taken together, the composites prepared in this research can form good quality, rigid porous structures required for tissue engineering applications.
A comparative analysis of the avian skull: Woodpeckers and chickens J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-05-02 Jae-Young Jung, Andrei Pissarenko, Nicholas A. Yaraghi, Steven E. Naleway, David Kisailus, Marc A. Meyers, Joanna McKittrick
Woodpeckers peck at trees without any reported brain injury despite undergoing high impact loads. Amongst the adaptations allowing this is a highly functionalized impact-absorption system consisting of the head, beak, tongue and hyoid bone. This study aims to examine the anatomical structure, composition, and mechanical properties of the skull to determine its potential role in energy absorption and dissipation. An acorn woodpecker and a domestic chicken are compared through micro-computed tomography to analyze and compare two- and three-dimensional bone morphometry. Optical and scanning electron microscopy with energy dispersive X-ray spectroscopy are used to identify the structural and chemical components. Nanoindentation reveals mechanical properties along the transverse cross-section, normal to the direction of impact. Results show two different strategies: the skull bone of the woodpecker shows a relatively small but uniform level of closed porosity, a higher degree of mineralization, and a higher cortical to skull bone ratio. Conversely, the chicken skull bone shows a wide range of both open and closed porosity (volume fraction), a lower degree of mineralization, and a lower cortical to skull bone ratio. This structural difference affects the mechanical properties: the skull bones of woodpeckers are slightly stiffer than those of chickens. Furthermore, the Young's modulus of the woodpecker frontal bone is significantly higher than that of the parietal bone. These new findings may be useful to potential engineered design applications, as well as future work to understand how woodpeckers avoid brain injury.
Uncoupled poroelastic and intrinsic viscoelastic dissipation in cartilage J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-26 Guebum Han, Cole Hess, Melih Eriten, Corinne R. Henak
This paper studies uncoupled poroelastic (flow-dependent) and intrinsic viscoelastic (flow-independent) energy dissipation mechanisms via their dependence on characteristic lengths to understand the root of cartilage's broadband dissipation behavior. Phase shift and dynamic modulus were measured from dynamic microindentation tests conducted on hydrated cartilage at different contact radii, as well as on dehydrated cartilage. Cartilage weight and thickness were recorded during dehydration. Phase shifts revealed poroelastic- and viscoelastic-dominant dissipation regimes in hydrated cartilage. Specifically, phase shift at a relatively small radius was governed by poroviscoelasticity, while phase shift at a relatively large radius was dominantly governed by intrinsic viscoelasticity. The uncoupled dissipation mechanisms demonstrated that intrinsic viscoelastic dissipation provided sustained broadband dissipation for all length scales, and additional poroelastic dissipation increased total dissipation at small length scales. Dehydration decreased intrinsic viscoelastic dissipation of cartilage. The findings demonstrated a possibility to measure poroelastic and intrinsic viscoelastic properties of cartilage at similar microscale lengths. Also they encouraged development of broadband cartilage like-dampers and provided important design parameters to maximize their performance.
EFFECT OF TWO-STEP AND ONE-STEP SURFACE CONDITIONING OF GLASS CERAMIC ON ADHESION STRENGTH OF ORTHODONTIC BRACKET AND EFFECT OF WATER EXPOSURE ON ADHESION STRENGTH J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-26 Moshabab A. Asiry, Ibrahim AlShahrani, Samer M. Alaqeel, Bangalore H. Durgesh, Ravikumar Ramakrishnaiah
Purpose The adhesion strength of orthodontic brackets bonded to dental glass ceramics was evaluated after ceramic surface was treated with two-step and one-step surface conditioning systems, and subjecting to thermo-cycling. Materials and Method A total of forty specimens were fabricated from silica based glass ceramic (lithium disilicate) by duplicating the buccal surface of maxillary first premolar. The specimens were randomly assigned to two experimental groups (n=20), group one specimens were treated with two-step surface conditioning system (IPS ceramic etching gelTM and Monobond plusTM) and group two specimens were treated with one-step surface conditioning system (Monobond etch and primeTM). The surface roughness of the specimens after treatment with two-step and one-step surface conditioning system was measured using non-contact surface profilometer. Ten randomly selected specimens from each group were subjected to thermo-cycling and the remaining ten served as baseline. The shear bond strength of the specimens was measured using universal material testing machine. The adhesive remnant index score was calculated, and the results of surface roughness and bond strength were tabulated and subjected to analysis of variance and post hoc tukey's test at a significance level of p<0.05. Results The results of the study showed that the specimens treated with two-step conditioning system had higher surface roughness and bond strength than one-step conditioning system. The maximum specimens treated with both two-step and one-step conditioned specimens showed adhesive failure after subjecting thermo-cycling. Conclusions Traditional two-step conditioning provides better bond strength and the clinical importance of the study is that, the silane promoted adhesion significantly reduces on exposure to water over a period of time.
Enhancing the mechanical and in vitro performance of robocast bioglass scaffolds by polymeric coatings: Effect of polymer composition J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-25 Azadeh Motealleh, Siamak Eqtesadi, Antonia Pajares, Pedro Miranda
The effect of different polymeric coatings, including natural and synthetic compositions, on the mechanical performance of 45S5 bioglass robocast scaffolds is systematically analyzed in this work. Fully amorphous 45S5 bioglass robocast scaffolds sintered at 550 °C were impregnated with natural (gelatin, alginate, and chitosan) and synthetic (polycaprolactone, PCL and poly-lactic acid, PLA) polymers through a dip-coating process. Mechanical enhancement provided by these coatings in terms of both compressive strength and strain energy density was evaluated. Natural polymers, in general, and chitosan, in particular, were found to produce the greater reinforcement. The effect of these coatings on the in vitro bioactivity and degradation behavior of 45S5 bioglass robocast scaffolds was also investigated through immersion tests in simulated body fluid (SBF). Coatings from natural polymers, especially chitosan, are shown to have a positive effect on the bioactivity of 45S5 bioglass, accelerating the formation of an apatite-like layer. Besides, most coating compositions reduced the degradation (weight loss) rate of the scaffold, which has a positive impact on the evolution of their mechanical properties.
Preliminary female cervical spine injury risk curves from PMHS tests J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-24 Narayan Yoganandan, Sajal Chirvi, Frank A. Pintar, Jamie L. Baisden, Anjishnu Banerjee
The human cervical spine sustains compressive loading in automotive events and military operational activities, and the contact and noncontact loading are the two primary impact modes. Biomechanical and anatomical studies have shown differences between male and female cervical spines. Studies have been conducted to determine the human tolerance in terms of forces from postmortem human subject (PMHS) specimens from male and female spines; however, parametric risk curves specific to female spines are not available from contact loading to the head-neck complex under the axial mode. This study was conducted to develop female-spine based risk curves from PMHS tests. Data from experiments conducted by the authors using PMHS upright head-spines were combined with data from published studies using inverted head-spines. The ensemble consisted of 20 samples with ages ranging from 29 to 95 years. Except one, all specimens sustained neck injuries, consisting of fractures to cervical vertebrae, and disruptions to the intervertebral disc and facet joints, and ligaments. Parametric survival analysis was used to derive injury probability curves using the compressive force, uncensored for injury and right censored for noninjury data points. The specimen age was used as the covariate. Injury probability curves were derived using the best fit distribution, and the ± 95% confidence interval limits were obtained. Results indicated that age is a significant covariate for injury for the entire ensemble. Peak forces were extracted for 35, 45, and 63 (mean) years of age, the former two representing the young (military) and the latter, the automobile occupant populations. The forces of 1.2kN and 2.9kN were associated with 5% and 50% probability of injury at 35 years. These values at 45 years were 1.0kN and 2.4kN, and at 63 years, they were 0.7kN and 1.7kN. The normalized widths of the confidence intervals at these probability levels for the mean age were 0.74 and 0.48. The preliminary injury risk curves presented should be used with appropriate caution. This is the first study to develop risk curves for females of different ages using parametric survival analysis, and can be used to advance human safety, and design and develop manikins for military and other environments.
A Catheter Friction Tester Using Balance Sensor: Combined Evaluation of the Effects of Mechanical Properties of Tubing Materials and Surface Coatings J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-24 Troels Røn, Kristina Pilgaard Jacobsen, Seunghwan Lee
In this study, we introduce a new experimental approach to characterize the forces emerging from simulated catherization. This setup allows for a linear translation of urinary catheters in vertical direction as controlled by a micro-actuator. By employing silicone-based elastomer with a duct of comparable diameter with catheters as urethra model, sliding contacts during the translation of catheters along the duct is generated. A most unique design and operation feature of this setup is that a digital balance was employed as the sensor to detect emerging forces from simulated catherization. Moreover, the possibility to give a variation in environment (ambient air vs. water), clearance, elasticity, and curvature of silicone-based urethra model allows for the detection of forces arising from diverse simulated catherization conditions. Two types of commercially available catheters varying in tubing materials and surface coatings were tested together with their respective uncoated catheter tubing. The first set of testing on the catheter samples showed that this setup can probe the combined effect from flexural strain of bulk tubing materials and slipperiness of surface coatings, both of which are expected to affect the comfort and smooth gliding in clinical catherization. We argue that this new experimental setup can provide unique and valuable information in preclinical friction testing of urinary catheters.
Brain stiffens post mortem J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-22 J. Weickenmeier, M. Kurt, E. Ozkaya, R. de Rooij, T.C. Ovaert, R.L. Ehman, K. Butts-Pauly, E. Kuhl
Alterations in brain rheology are increasingly recognized as a diagnostic marker for various neurological conditions. Magnetic resonance elastography now allows us to assess brain rheology repeatably, reproducibly, and non-invasively in vivo. Recent elastography studies suggest that brain stiffness decreases one percent per year during normal aging, and is significantly reduced in Alzheimer's disease and multiple sclerosis. While existing studies successfully compare brain stiffnesses across different populations, they fail to provide insight into changes within the same brain. Here we characterize rheological alterations in one and the same brain under extreme metabolic changes: alive and dead. Strikingly, the storage and loss moduli of the cerebrum increased by 26% and 60% within only three minutes post mortem and continued to increase by 40% and 103% within 45 minutes. Immediate post mortem stiffening displayed pronounced regional variations; it was largest in the corpus callosum and smallest in the brainstem. We postulate that post mortem stiffening is a manifestation of alterations in polarization, oxidation, perfusion, and metabolism immediately after death. Our results suggest that the stiffness of our brain–unlike any other organ–is a dynamic property that is highly sensitive to the metabolic environment. Our findings emphasize the importance of characterizing brain tissue in vivo and question the relevance of ex vivo brain tissue testing as a whole. Knowing the true stiffness of the living brain has important consequences in diagnosing neurological conditions, planning neurosurgical procedures, and modeling the brain's response to high impact loading.
A computational parametric study on edge loading in ceramic-on-ceramic total hip joint replacements J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-22 Feng Liu, Li Feng, Junyuan Wang
Edge loading in ceramic-on-ceramic total hip joint replacement is an adverse condition that occurs as the result of a direct contact between the head and the cup rim. It has been associated with translational mismatch in the centres of rotation of the cup and head, and found to cause severe wear and early failure of the implants. Edge loading has been considered in particular in relation to dynamic separation of the cup and head centres during a gait cycle. Research has been carried out both experimentally and computationally to understand the mechanism including the influence of bearing component positioning on the occurrence and severity of edge loading. However, it is experimentally difficult to measure both the load magnitude and duration of edge loading as it occurs as a short impact within the tight space of hip joints. Computationally, a dynamic contact model, for example, developed using the MSC ADAMS software for a multi-body dynamics simulation can be particularly useful for calculating the loads and characterising the edge loading. The aim of the present study was to further develop the computational model, and improve the predictions of contact force and the understanding of mechanism in order to provide guidance on design and surgical factors to avoid or to reduce edge loading and wear. The results have shown that edge loading can be avoided for a low range of translational mismatch in the centres of rotation of the cup and head during gait at the level of approximately 1.0 mm for a cup at 45 °inclination, keeping a correct cup inclination at 45 °is important to reduce the edge loading severity, and edge loading can be avoided for a certain range of translational mismatch of the cup and head centres with an increased swing phase load.
Application of the time-strain superposition - Part I: Prediction of the nonlinear constant shear rate response of brain tissue J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-21 Barbara Zupančič
Modern surgical training, better understanding of the biomechanics of traumatic brain injury, and precise quantification of the difference between mechanical response of healthy and disease-modified brain tissue, require reliable experimental data and efficient mathematical/computational models. In this paper, a new methodology is proposed for prediction of the nonlinear viscoelastic behaviour of porcine brain. Time-strain superposition is applied to the brain stress relaxation data for construction of the overall master curve. The nonlinear internal-clock viscoelastic model, which is based on the free volume concept, is utilized to predict the constant shear rate (CSR) response, based on the known stress relaxation master curve. Demonstrated theoretical procedure is evaluated on the porcine brain experimental data available from the literature. Results show good agreement between the predicted CSR response and the previously published CSR measurements. We may justifiably speculate that the proposed approach serves well for prediction of the nonlinear CSR behaviour of the porcine brain tissue. Since the methodology is strongly supported by the physical background, it exhibits the potential to be utilized for prediction of nonlinear behaviour in other loading modes, as well as of other tissues or viscoelastic materials.
Development and Clinical Verification of Numerical Simulation for Laser in Situ Keratomileusis J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-19 FangJun Bao, JunJie Wang, Si Cao, Na Liao, Bao Shu, YiPing Zhao, YiYu Li, XiaoBo Zheng, JinHai Huang, ShiHao Chen, QinMei Wang, Ahmed Elsheikh
To develop and validate numerical models of the laser in situ keratomileusis (LASIK) procedure through considering its effect on corneal biomechanical behavior. 3D finite element models of the human eye were developed to simulate LASIK. The models’ predictions of post-operative corneal elevation, corneal refractive power with vector decomposition (M-c-pos, J0-c-pos, J45-c-pos) and refractive error correction (M-rec, J0-rec, J45-rec) were compared against clinical data obtained for 28 eyes of 28 patients. A parallel exercise was conducted to estimate the post-operative corneal shape using a shape subtraction method (SSM) – which does not consider the effects of LASIK on corneal mechanical behavior – and the results are compared with the finite element method (FEM). A significant decrease in elevation differences between FEM predictions and clinical data was found compared with the differences between SSM results and clinical data (p= 0.000). In addition, there were no significant differences in post-operative equivalent sperical corneal refractive power between FEM results and corresponding clinical data (M-c-pos: p= 0.501), while SSM showed significant differences with clinical data (M-c-pos: p= 0.000). Further, FEM achieved a predicted value of M-c-pos within ±1.00D accuracy in 100% of cases, compared with 57% achieved by the SSM. M-rec predicted by FEM was not significantly different from clinical results (p= 0.085), while SSM overestimated it (p= 0.000). The match between LASIK numerical model predictions with clinical measurements improved significantly when the procedure's effect on corneal biomechanical behavior was considered. This outcome has important implications on efforts to develop planning tools for refractive surgery.
Osteogenesis of 3D printed porous Ti6Al4V implants with different pore sizes J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-18 Qichun Ran, Weihu Yang, Yan Hu, Xinkun Shen, Yonglin Yu, Yang Xiang, Kaiyong Cai
Selective laser melting (SLM) is one of the three-dimensional (3D) printing techniques that manufacturing versatile porous scaffolds with precise architectures for potential orthopedic application. To understand how the pore sizes of porous Ti6Al4V scaffolds affect their biological performances, we designed and fabricated porous Ti6Al4V implants with straightforward pore dimensions (500, 700, and 900 μm) via SLM, termed as p500, p700, and p900 respectively. The morphological characteristics of Ti6Al4V scaffolds were assessed showing that the actual pore sizes of these scaffolds were 401 ± 26 μm, 607 ± 24 μm, 801 ± 33 μm, respectively. The mechanical properties of Ti6Al4V scaffolds were also evaluated showing that they were comparable to that of bone tissues. Meanwhile, the effect of pore size on biological responses was systematically investigated in vitro and in vivo. It was verified that 3D printing technique was able to fabricate porous Ti6Al4V implants with proper mechanical properties analogous to human bone. The in vitro results revealed that scaffolds with appropriate pore dimension were conducive to cell adhesion, proliferation and early differentiation. Furthermore, the porous Ti6Al4V scaffolds were implanted into the rabbit femur to investigate bone regeneration performance, the in vivo experiment showed the p700 sample was in favor of bone ingrowth into implant pores and bone-implant fixation stability. Taken together, the biological performance of p700 group with actual pore size of about 600 μm was superior to other two groups. The obtained findings provide basis to individually design and fabricate suitable porous Ti6Al4V with specific geometries for orthopedic application.
Packing of muscles in the rabbit shank influences three-dimensional architecture of M. soleus J. Mech. Behav. Biomed. Mater. (IF 3.11) Pub Date : 2018-04-07 Carolin Wick, Markus Böl, Florian Müller, Reinhard Blickhan, Tobias Siebert
Isolated and packed muscles (e.g. in the calf) exhibit different three-dimensional muscle shapes. In packed muscles, cross-sections are more angular compared to the more elliptical ones in isolated muscles. As far as we know, it has not been examined yet, whether the shape of the muscle in its packed condition influences its internal arrangement of muscle fascicles and accordingly the contraction behavior in comparison to the isolated condition. To evaluate the impact of muscle packing, we examined the three-dimensional muscle architecture of isolated and packed rabbit M. soleus for different ankle angles (65°, 75°, 85°, 90°, and 95°) using manual digitization (MicroScribe® MLX). In general, significantly increased values of pennation angle and fascicle curvature were found in packed compared to isolated M. soleus (except for fascicle curvature at 90° ankle angle). On average, fascicle length of isolated muscles exceeded fascicle lengths of packed muscles by 2.6%. Reduction of pennation angle in the packed condition had only marginal influence on force generation (about 1% of maximum isometric force) in longitudinal direction (along the line of action) although an increase of transversal force component (perpendicular to the line of action) of about 26% is expected. Results of this study provide initial evidence that muscle packing limits maximum muscle performance observed in isolated M. soleus. Besides an enhanced understanding of the impact of muscle packing on architectural parameters, the outcomes of this study are essential for realistic three-dimensional muscle modelling and model validation.
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