In vitro and In vivo Comparisons of the Porous Ti6Al4V Alloys Fabricated by the Selective Laser Melting Technique and A New Sintering Technique J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-12-10 Ji Li, Zhongli Li, Yueyi Shi, Haoran Wang, Ruiling Li, Jiangping Tu, Gong Jin
A new sintering technique using Ti6Al4V powder suspension was performed to prepare porous Ti6Al4V alloy with 75% porosity. Porous Ti6Al4V alloy with the same porosity fabricated by selective laser melting technique was used as the control. The characteristics, mechanical and biological properties of the two types of porous Ti6Al4V alloys were evaluated by mechanical tests, in vitro cell analysis and implantations. Results indicated that both groups showed good biocompatibility and osteogenic ability. However, microstructure and mechanical properties of the sintered porous Ti6Al4V were more similar to the cancellous bone without obvious stress shielding, and the new type of sample may be more effective in achieving early stability after implantation. Therefore, under the study conditions, this new type of porous alloy prospects a good candidate for biomaterials, especially for repairing bone defects and arthroplasty in orthopedics.
Magnesium phosphate based cement with improved setting, strength and cytocompatibility properties by adding Ca(H2PO4)2·H2O and citric acid J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-12-10 Suchun Yu, Langlang Liu, Chao Xu, Honglian Dai
Inorganic phosphate cements have become prevalent as bone filling materials in clinical applications, owing to beneficial properties such as self-setting, biodegradability and osteoconductivity. However, the further development of phosphate cements with higher strength and improved cytocompatibility is expected. In this paper, we reported the preparation of a novel magnesium phosphate based cement (MPBC), which has similar compositions with magnesium phosphate cement (MPC) but Ca(H2PO4)2·H2O and citric acid were additionally added to modulate the performance. The physicochemical and biological properties of MPBC were investigated, the influences of the added Ca(H2PO4)2·H2O and citric acid on the performances of MPBC were analyzed, and the differences of performance between MPBC and MPC were discussed. Experimental results show that the setting time and compressive strength of MPBC were effectively enhanced by the addition of citric acid. In vitro biological degradation indicates that about 15 wt% of MPBC was reduced in 4 weeks. Compared with MPC, MPBC has weaker alkalinity and less dissolution of phosphate, leading to better suitability for cell proliferation and adhesion. These results suggest that as a bone filling material, MPBC shows better performance than MPC in many key indicators and has promising application prospects.
On multiscale boundary conditions in the computational homogenization of an RVE of tendon fascicles J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-12-10 Thiago André Carniel, Bruno Klahr, Eduardo Alberto Fancello
Present study provides a numerical investigation on multiscale boundary conditions in the computational homogenization of a representative volume element (RVE) of tendon fascicles. A three-dimensional hexagonal-helicoidal finite element RVE composed of two material phases (collagen fibers and cells) and three finite strain viscoelastic models (collagen fibrils, matrix of fibers and cells) compose the multiscale model. Due to the unusual helical geometry of the RVE, the performance of four multiscale boundary conditions is evaluated: the linear boundary displacements model, the minimally constrained model and two mixed boundary conditions allying characteristics of both, linear and minimal models. Numerical results concerning microscopic kinematic fields and macroscopic stress-strain curves point out that one of the mixed models is able to predict the expected multiscale mechanics of the RVE, presenting sound agreement with experimental facts reported in literature, for example: characteristic non-linear shape of the stress-strain curves; macroscopic energy loss by hysteresis; axial rotation of fascicles observed in tensile tests; collagen fibrils are the main load-bearing components of tendons; cells contribute neither to the stiffness nor to the macroscopic energy loss. Moreover, the multiscale model provides important insights on the micromechanics of tendon fascicles, predicting a non-homogeneous and relevant strain localization on cells, even under physiological macroscopic strain amplitudes.
Mechanical behavior of in vivo degraded second generation resorbable magnesium scaffolds (RMS) J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-12-11 Christoph Brandt-Wunderlich, Philipp Ruppelt, Philine Zumstein, Wolfram Schmidt, Daniela Arbeiter, Klaus-Peter Schmitz, Niels Grabow
Resorbable magnesium scaffolds are used for the treatment of atherosclerotic coronary vascular disease and furthermore, for vascular restoration therapy. Recently, the first-in-man clinical studies with Magmaris showed promising results regarding the target lesion failure as well as vasomotion properties after 12 and 24 month. The consistency of in vivo degraded magnesium alloys in a cardiovascular environment is qualitatively described in literature, but only little has been disclosed about the actual change in mechanical properties and the behavior of the magnesium alloy degradation products. In the present study, uncoated magnesium scaffolds 3.0 ×20 mm were implanted in coronary arteries of two healthy Goetinnger mini-swine. The scaffolds were explanted to evaluate the mechanical properties of the degraded magnesium scaffolds after 180 days in vivo. Ex vivo sample preparation and test conditions were adapted to a customized compression test setup which was developed to investigate the micro-scale scaffold fragments (width 225 ± 75 µm, thickness 150 µm). As reference bare undegraded magnesium scaffold fragments were tested. Mechanical parameters relating to force as a function of displacement were determined for both sample groups. The undegraded samples showed no fracturing at the maximum applied force of 8 N, whereas the in vivo degraded test samples showed forces of 0.411 ± 0.197 N at the first fracturing and a maximum force of 0.956 ± 0.525 N. The deformation work, calculated as area beneath the force-displacement curve, of the in vivo degraded test samples was reduced by approximately 87–88% compared to the undegraded samples (5.20 mN·mm and 40.79 mN·mm, both at 7.5% deformation). The indication for a complete loss of structural integrity through a reduction of mechanical properties after a certain degradation time increases the chance to restore vascular function and physiological vasomotion in the stented vessel compartment.
Biomechanical aspects of reinforced implant overdentures: a systematic review J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-12-11 Mona Fathy Gibreel, Ahmed Khalifa, Mohamed Mostafa Said, Fatma Mahanna, Nesma El-Amier, Timo O. Närhi, Leila Perea-Lowery, Pekka K. Vallittu
Purpose The purpose of this systematic review was to investigate the effect of the reinforcement on the mechanical behavior of implant overdenture (IOD) bases and its cumulative biological effect on the underlying supporting structures (implants and residual ridge). Material and methods The required documents were collected electronically from PubMed and Web of Science databases targeting papers in English with denture base reinforcement for IOD in order to recognize the principal outcomes of reinforcement on the mechanical and biological properties of overdenture. Such biological outcomes as: strains on implants, peri-implant bone loss, residual ridge resorption, and strain on the residual alveolar ridge. Results A total of 269 citations were identified. After excluding any repeated articles between databases and the application of exclusion and inclusion criteria, only 13 publications fulfilled the inclusion criteria. Three publications investigated the mechanical properties of fiber and/or metal- reinforced implant overdenture while another 3 articles investigated the effect of metal reinforcement on stress distribution and strains transmitted to the underlying implants. In addition, 3 in vitro studies investigated the effect of metal reinforcement on overdenture base strain and its stresses. Stress distribution to the residual ridge and strain characteristics of the underlying tissues were investigated by 2 in vitro studies. Five clinical studies assisting the clinical and prosthetic maintenance of metal-reinforced IOD were included. Data concerning the denture base fracture, relining, peri-implant bone loss, probing depth, and implant survival rates during the functional period were extracted and considered in order to evaluate the mechanical properties of the denture base, residual ridge resorption and implant preservation rate, respectively. Conclusion The use of a denture base reinforcement can reduce the fracture incidence of IOD by enhancing its flexural properties and reducing the overdenture base deformation. Strains on the underlying supporting structures of overdenture prosthesis including dental implants and the residual ridge can be decreased and evenly distributed by using a metal reinforcement.
Mechanical properties and microstructure of Ti-Mn alloys produced via powder metallurgy for biomedical applications J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-12-08 Y. Alshammari, F. Yang, L. Bolzoni
Titanium and especially its alloys are highly employed materials in biomedical applications because of their balanced mechanical properties and biocompatibility. Ti-Mn alloys (1, 5, and 10 wt%. Mn) were produced by powder metallurgy as a potential alternative material for biomedical applications. Two sets of samples were produced, one set as-sintered and the other was beta (β) forged. For the as-sintered samples with a content of up to 10 wt% Mn, the tensile strength ranged from 606–1070 MPa. On the other hand, for the β forged alloys the tensile strength ranged from 728–1224 MPa and the maximum value was for Ti-5Mn. Forged Ti-5Mn exhibits a good balance of mechanical properties such as ultimate tensile strength (1224 MPa), elongation (4.6%) and Vickers hardness (415 HV). The purely elastic properties of the Ti-10Mn alloy is attributed to the effects of the omega (ω) phase, the formation of which is due to the high amount of beta stabiliser added to Ti.
Stored potential energy increases and elastic properties alterations are produced after restoring dentin with Zn-containing amalgams J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-12-06 Manuel Toledano, Estrella Osorio, Fátima S. Aguilera, Manuel Toledano-Osorio, Modesto T. López-López, Raquel Osorio
The aim of this research was to ascertain the mechanical and chemical behavior of sound and caries-affected dentin (CAD), after the placement of Zn-free vs containing amalgam restorations. Peritubular and intertubular dentin were evaluated using, a) nanoindenter in scanning mode; the load and displacement responses were used to perform the nano-Dynamic mechanical analysis and to estimate the complex (E⁎) and storage modulus (E'); b) Raman spectroscopy was used to describe the hierarchical cluster analysis (HCA). Assessments were performed before restoration placement and after restoring, and after 3 months of storage with thermocycling (100,000cy/5 °C and 55 °C). When CAD was treated with Zn-containing restorations, differences between E⁎ and E' at both peritubular and intertubular dentin augmented, with energy concentration and production of implications in the mechanical performance of the restored teeth. E⁎ and E' were very low at intratubular dentin of CAD restored with Zn-containing restorations. The relative presence of minerals, the phosphate crystallinity and the crosslinking of collagen increased their values at both types of dentin (peritubular and intertubular) when CAD was treated with Zn-containing restorations. The nature and secondary structure of collagen improved in CAD treated with Zn-containing amalgams. Different levels of dentin remineralization were revealed by hierarchical cluster analysis.
Strength limits in mesoscaled 3Y-TZP ceramics for micro-surgical instruments J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-12-04 N. Antolino, C. Muhlstein, G. Hayes, J. Adair, R. Bermejo
Micro-surgical instruments are a new application for mesoscale ceramics formed using the lost mold-rapid infiltration forming (LM-RIF) process. Instrument strength and reliability are the foremost concerns for this sensitive application. It is hypothesized that increasing grain size can improve the damage tolerance of the parts associated with the transformation toughening in the 3Y-TZP material, while retaining high strength. In this work, mesoscale bend bars (314×22×18 μm) of 3Y-TZP fabricated using the LM-RIF process were heat treated at 1400 °C for 1 h, 8 h, or 16 h, respectively, to obtain samples with different grain sizes. Strength tests were performed under three-point bending and results were evaluated using Weibull statistics. Fractographic and confocal Raman spectroscopic analyses were carried out to interpret the data.Experimental findings showed that the characteristic strength decreased with increasing grain size contrary to the damage tolerance hypothesis. An Orowan-Petch model was recalled to correlate the strength with the flaw size to grain size ratio. At fine grain sizes the strength was controlled by the flaws introduced by the LM-RIF process, whereas at large grain sizes the strength become more grain size controlled. Although larger-grained samples did have a higher propensity to transform, and thus increase toughening, exaggerated grain growth in some of the specimens tested caused an additional flaw population which led to an overall lower strength. Finally, based on the experimental observations and fracture mechanics considerations, we believe that an upper bound of ∼2.5 GPa exists for the strength of mesoscale as-fabricated 3Y-TZP ceramic parts.
The viscoelastic behaviors of several kinds of cancer cells and normal cells J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-30 Yongfang Xie, Mingling Wang, Min Cheng, Zhiqin Gao, Guohui Wang
The purpose of this study was to investigate the viscoelastic behaviors of cancer cells and normal cells using the micropipette aspiration technique combined with the standard linear viscoelastic solid model. The viscoelastic behaviors of pairs of cell lines (human skin cells and human skin cancer cells, human fetal lung fibroblasts and human lung cancer cells, human mammary fibroblasts and human breast cancer cells, and human hepatocyte cells and human hepatocellular carcinoma cells) were tested by the micropipette aspiration technique. The cellular viscoelastic parameters (the instantaneous modulus E0, the equilibrium modulus associated with long term equilibrium E∞, and the apparent viscosity μ) were calculated using a Kelvin standard linear viscoelastic solid model. The present results indicate that the cancer cells were easier to deform, and the viscoelastic parameters (E0, E∞, μ) of the cancer cells were significantly lower than their corresponding normal cells (P<0.0001). The viscoelastic parameters (E0, E∞, μ) among some normal cells showed significant differences (P<0.05), while the different cancer cells showed no significant differences (P>0.05). These findings may be relevant for the identification and diagnosis of cancer cells as well as providing an explanation of this occurrence mechanism in cancer cells and cancer treatment.
Fabrication of alumina-PSZ composites via spark plasma sintering and their mechanical properties J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-29 Tomoyuki Fujii, Keiichiro Tohgo, Pandoyo Bayu Putra, Yoshinobu Shimamura
Alumina-partially stabilized zirconia (PSZ) composites were fabricated via spark plasma sintering (SPS) technique to produce biocompatible materials with superior mechanical properties. The volume fraction of the composites covered from 100% alumina to 100% PSZ. Their sintering state was examined by optical microscopy, density measurement, and X-ray diffraction, and dense composites without any reaction phases could be fabricated, irrespective of PSZ content. Then, three-point bending tests and hardness tests were conducted. The hardness and elastic modulus agreed with the predictions based on the Voigt model and the Eshelby's equivalent inclusion model combined with the Mori-Tanaka's mean field concept, respectively. While the bending strength of the composites ranged from that of monolithic alumina to that of monolithic PSZ, the fracture toughness of the composites improved as compared with the monoliths of alumina and PSZ. We concluded that the use of alumina and PSZ was effective to fabricate the composites with high mechanical performances.
Full-field analysis of epicardial strain in an in vitro porcine heart platform J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-30 Paolo Ferraiuoli, Benjamin Kappler, Sjoerd van Tuijl, Marco Stijnen, Bas A.J.M. de Mol, John W. Fenner, Andrew J. Narracott
The quantitative assessment of cardiac strain is increasingly performed to provide valuable insights on heart function. Currently, the most frequently used technique in the clinic is ultrasound-based speckle tracking echocardiography (STE). However, verification and validation of this modality are still under investigation and further reference measurements are required to support this activity.The aim of this work was to enable these reference measurements using a dynamic beating heart simulator to ensure reproducible, controlled, and realistic haemodynamic conditions and to validate the reliability of optical-based three-dimensional digital image correlation (3D-DIC) for a dynamic full-field analysis of epicardial strain.Specifically, performance assessment of 3D-DIC was carried out by evaluating the accuracy and repeatability of the strain measurements across multiple cardiac cycles in a single heart and between five hearts. Moreover, the ability of this optical method to differentiate strain variations when different haemodynamic conditions were imposed in the same heart was examined.Strain measurements were successfully accomplished in a region of the lateral left ventricle surface. Results were highly repeatable over heartbeats and across hearts (intraclass correlation coefficient = 0.99), whilst strain magnitude was significantly different between hearts, due to change in anatomy and wall thickness. Within an individual heart, strain variations between different haemodynamic scenarios were greater than the estimated error of the measurement technique.This study demonstrated the feasibility of applying 3D-DIC in a dynamic passive heart simulator. Most importantly, non-contact measurements were obtained at a high spatial resolution (~ 1.5 mm) allowing resolution of local variation of strain on the epicardial surface during ventricular filling. The experimental framework developed in this paper provides detailed measurement of cardiac strains under controlled conditions, as a reference for validation of clinical cardiac strain imaging modalities.
EFFECT OF EPIGALLOCATECHIN-3- GALLATE SOLUTIONS ON BOND DURABILITY AT THE ADHESIVE INTERFACE IN CARIES-AFFECTED DENTIN J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-30 Melissa Proença Nogueira Fialho, Viviane Hass, Rodrigo Proença Nogueira, Fabiana Mantovani Gomes França, Cecilia Pedroso Turssi, Roberta Tarkany Basting, Flávia Lucisano Botelho Amaral
Hydrolytic and enzymatic degradation by matrix metalloproteinases (MMPs) reduces the durability of composite resin restorations on caries-affected dentin (CAD). The use of MMP inhibitors such as epigallocatechin-3-gallate (EGCG) could increase the longevity of the bond to dentin. This study aimed to evaluate the use of EGCG at different aqueous concentrations on the resin-dentin microtensile bond strength (μTBS), fracture pattern and nanoleakage (NL) in immediate (IM) time interval and after 12-months of water storage (1Y) when using a two-step etch-and-rinse adhesive system on CAD. Dentin surfaces of 40 human molars were submitted to a microbiological caries induction protocol and randomized into 5 groups (n = 8) (0.02% EGCG; 0.2% EGCG; 0.5% EGCG; 2% Chlorhexidine [CHX] and no treatment as Control Group - [NT]). After acid etching, the solutions were applied for 60 s followed by application of dental adhesive (Adper Single Bond 2, 3 M ESPE) to CAD surfaces. Subsequently, a resin composite (4 mm) block was built on the dentin. After 24 h, the teeth were sectioned into beam-shaped specimens (cross-sectional area of 1 mm2 and 8-mm high). Half of the specimens were tested in IM and the other half after 1Y. Two samples per tooth were submitted to SEM for NL evaluation. Data were statistically analyzed by two-way ANOVA and Tukey tests (α = 0.05). The results showed that use of EGCG and CHX did not affect μTBS in IM (p> 0.05). After 1Y, there was a reduction in μTBS for all experimental groups (p < 0.05). Adhesive fractures predominated in IM in all groups, except for 0.05% EGCG and NT. After 1Y, there was an increase in these adhesive fractures in all groups. For NL, all agents applied reduced NL in comparison with CT (p < 0.001). CHX showed lower NL (p < 0.001), followed by 0.02% and 0.5% EGCG. NT showed highest NL for both time intervals (p < 0.001). Thus, although the use of EGCG at different concentrations and CHX reduced the NL, they were unable to reduce degradation of μTBS to CAD over time.
Influence of nano-hydroxyapatite containing desensitizing toothpastes on the sealing ability of dentinal tubules and bonding performance of self-etch adhesives J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-28 Dandan Pei, Yuchen Meng, Yuncong Li, Jie Liu, Yi Lu
ObjectivesTo evaluate the dentinal tubular occlusion of nano-hydroxyapatite (nHAp) containing desensitizing toothpastes and their influence on the resin-dentin bonding performance of two mild self-etch adhesives.Materials and MethodsMid-coronal dentin specimens were prepared from obtained intact human third molars. They were immersed in 1% citric acid for 20 s to expose the dentinal tubules to simulate sensitive teeth and then randomly divided into four groups. The control group received no desensitizing treatment. Experimental groups were treated with two commercial nHAp containing desensitizing toothpastes (Biorepair and Dontodent) and an experimental pure nHAp paste respectively. Each group was further divided into two subgroups and bonded with either G-Bond or Clearfil S3 Bond. The micro-tensile bond strength was tested and failure mode distribution was analyzed. Moreover, the effect of desensitizers on dentinal tubular occlusion was observed by the field-emission scanning electron microscope (FESEM). Resin infiltration of the adhesives labeled by fluorescent Rhodamin B was evaluated under confocal laser scanning microscopy (CLSM).ResultsFESEM revealed that all the desensitizers noticeably occluded the dentinal tubules, and the extents were completer after application for 7 days. The majority of the occlusion still preserved even after acid challenge with cola or adhesive. CLSM demonstrated shorter resin tags were produced in the desensitized groups. When bonding with G-Bond, the pure nHAp group showed comparable bond strength to the control group, while Biorepair and Dontodent treatment decreased the bond strength. For groups bonded with Clearfil S3 Bond, all the desensitizers reduced the bond strengths compared to the control and no significant difference was found among the three groups.ConclusionNano-hydroxyapatite containing desensitizing toothpastes could occlude dentinal tubules effectively with a certain degree of acid resistance, which contributes to the relief of dentin hypersensitivity. While, the application of these nHAp desensitizers comprised the resin infiltration of G-Bond and Clearfil S3 Bond, resulting in decreased bond strengths of the resin-dentin bonding.
Bacterial leakage and bending moments of screw-retained, composite-veneered PEEK implant crowns J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-28 Andreas Wachtel, Tycho Zimmermann, Mona Sütel, Ufuk Adali, Mohamad Abou-Emara, Wolf-Dieter Müller, Sven Mühlemann, Andreas Dominik Schwitalla
Due to its elastic modulus close to bone, the high-performance material PEEK (polyetheretherketone) represents an interesting material for implant-supported dental prostheses. Besides a damping effect of masticatory forces, it might have a sealing effect against bacterial leakage of the implant-abutment interface (IAI). So far, PEEK has only been used for provisional implant crowns. Therefore, the aim of the study was the evaluation of the bacterial tightness of screw-retained PEEK crowns on titanium implants with conical IAI during masticatory simulation and subsequent bending moment testing.Ten screw-retained implant crowns in the shape of an upper central incisor consisting of a PEEK crown framework veneered with composite were connected to NobelActive RP titanium implants (4.3 ×11.5 mm, Nobel Biocare AB, Göteborg, Sweden) with a tightening torque of 15 Ncm.Prior to tightening, the interior of the implant was inoculated with a bacterial suspension of Enterococcus faecium. The specimens were overmolded with indicating agar (Kanamycin-Aesculin-Azid-Agar (KAAA), Oxoid Limited, Basingstoke United Kingdom), that turns black in contact with E. faecium. The specimens were subjected to a cyclic masticatory simulation whereby a force of 50 N · cm was applied at an angle of 30° to the implant axis for 1.2 million cycles. Afterwards, the specimens were subjected to a static loading test according to ISO 14801:2007 to determine the bending moment.During masticatory simulation neither a loosening of the implant screws nor any damage to the veneer or the PEEK framework occurred. Furthermore, no bacterial leakage could be observed in any of the specimens. The average maximum bending moment was measured at 352.13 ± 48.96 N∙cm.Regarding masticatory forces, PEEK implant crowns seem to be applicable as definitive implant-supported restorations. Furthermore, the bacterial tightness of the IAI of screw-retained one-piece PEEK implant crowns is advantageous compared to superstructures of conventional materials. Further studies are necessary to substantiate the clinical significance of these findings.
Optimization of bio-inspired bi-directionally corrugated panel impact-resistance structures: Numerical simulation and selective laser melting process J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-27 Jiankai Yang, Dongdong Gu, Kaijie Lin, Ying Yang, Chenglong Ma
The telson (tail plate) of Stomatopoda (mantis shrimp) shows excellent impact resistance properties, and its special structure is an ideal prototype to mimic. In this paper, a series of bi-directionally corrugated panel (DCP) structures inspired by the telson of mantis shrimp was designed. The crush simulation of DCP structures with different structural parameters, namely wavelength (λ) and amplitude (A), was carried out using ANSYS LS-NYNA. In order to verify the simulation results, AlSi10Mg components with DCP structures were fabricated by selective laser melting and the out-of-plane compression tests were conducted to investigate the compression performance. The numerical simulation results indicated that the influence of wavelength of DCP structure on the energy absorption (EA) and specific energy absorption (SEA) capability was greater than that of the amplitude, and the DCP structure with A = 8 mm and λ = 6 mm possessed the best impact resistance performance. The SLM-processed AlSi10Mg components with DCP structures showed high surface quality and good forming accuracy, and the relation between experimental compression behavior and the DCP structure parameter was in good agreement with the numerical results.
Decellularisation affects the strain rate dependent and dynamic mechanical properties of a xenogeneic tendon intended for anterior cruciate ligament replacement J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-26 Jennifer Helen Edwards, Eileen Ingham, Anthony Herbert
Development of new replacement grafts for anterior cruciate ligament (ACL) repair requires mechanical testing to ensure they can provide joint stability following implantation. A decellularised porcine superflexor tendon (pSFT) has been developed previously as an alternative to current reconstruction methods and subjected to biomechanical analysis. The application of varied strain rates to biological tissues is known to alter their biomechanical properties, however the effects of decellularisation on strain rate dependent and dynamic mechanical behaviour of tissues have not been explored. This study utilised tensile testing to investigate the material properties of native and decellularised pSFTs at three different strain rates (1%.s−1, 10%.s−1 and 100%.s−1). In addition, dynamic mechanical analysis (DMA) was used to ascertain the relative contributions of the solid and fluid phase components of the tissues.Ultimate tensile strength was significantly reduced in decellularised compared with native untreated pSFTs but was unaffected by strain rate. In contrast, toe region moduli increased with increasing strain rate for native tissues, but this effect was not observed in decellularised pSFTs. Linear region moduli were unaffected by strain rate, but were significantly reduced in decellularised pSFT compared with native tissue.Following DMA, significant reductions in dynamic modulus, storage modulus and loss modulus were seen in decellularised compared with native pSFT. Interestingly, the damping ability of the tendons was unaffected by decellularisation, suggesting that solid and fluid phases of the tissue were affected equally. These results, alongside previous studies, suggest that decellularisation affects collagen crimp, tissue swelling and collagen fibre sliding. However, despite these findings, the biomechanical properties of decellularised pSFT remain sufficient to act as an off-the-shelf solution for ACL reconstruction.
How much force is required to perforate a colon during colonoscopy? An experimental study J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-26 Steve Johnson, Michael Schultz, Mario Scholze, Troy Smith, John Woodfield, Niels Hammer
IntroductionColonoscopy is a commonly-performed procedure to diagnose pathology of the large intestine. Perforation of the colon is a rare but feared complication. It is currently unclear how much force is actually required to cause such injury nor how this is altered in certain diseases. Our aim was to analyze the forces required to perforate the colon in experiments using porcine tissues.MethodsUsing 3D printing technology, models of two commercially available colonoscope heads were printed under three configurations: straight (I), 90°- bent (L) and fully bent (U). Samples of porcine colon were assessed with the models and configurations under perpendicular and angular load application and these data compared to the maximum force typically exerted by experienced colonoscopists.ResultsThe force required for perforation was significantly lower for the I compared to the L of the larger colonoscope head configuration under angular loading (14.1 vs. 46.5 N). Similar differences were found for linear stiffness when loaded (I vs. L small when loaded perpendicular: 0.80 vs. 2.41 N/mm; I vs. L large when loaded angled 0.70 vs. 2.06 N/m). The mode and site of failure varied significantly between the scopes, with delamination of the mucosa/submucosa below the sample (96%) for the I, blunt mucosa/submucosa/muscularis failure adjacent to the loading site (77%) for the L, and failure of all colon layers lateral to the loading site (59%) for the U configuration, respectively. Perpendicular and angulated loading resulted in similar load-deformation values. Maximum forces typically exerted by colonoscopists averaged 13.9 to 27.9 N, depending on the colonoscope model and head configuration.DiscussionThe force required for colon perforation varies depending on the type mode of loading and is likely lower than the force an experienced colonoscopist would exert in daily practice. There is a real risk of perforation, especially when the end of the scope is advancing directly into the colonic wall. The given experimental setup allowed to obtain reliable data of the colon in a standardized scenario, forming the basis for further experiments.
Optimization method for the determination of Mooney-Rivlin material coefficients of the human breasts in-vivo using static and dynamic finite element models J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-22 Yue Sun, Lihua Chen, Kit-lun Yick, Winnie Yu, Newman Lau, Wanzhong Jiao
It has been a long-standing problem in the engineering design of bra for optimal support and shaping due to the difficulty of quantifying the hyper-elastic properties of human breasts. The objective of this study is to determine an optimal approach to obtain the non-linear properties of breast soft tissues and the corresponding deformations during motions. The Mooney-Rivlin material parameters of the breasts in-vivo were verified through an optimization process that involved iteratively changing the material coefficients with the integration of static and dynamic finite element models. Theoretical equations of a rigid-flexible coupled system during the motion of forward-leaning were established with gravitational, centrifugal and Coriolis forces to simulate the dynamic deformation of the flexible breasts. The resultant, optimally generated, coefficients of the Mooney-Rivlin hyperelastic material type for the breast were found. This new set of breast material coefficients was verified by finite element analysis of the breast deformation during forward-leaning and running movement. The method proposed in this study provides an effective way to determine the breast properties for predicting breast deformation and analysis of the bra-breast contact mechanism and thus, improving the design of bras.
Antibiotic Elution and Mechanical Property of TiO2 Nanotubes Functionalized PMMA-based Bone Cements J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-23 Shou-Cang Shen, Kumaran Letchmanan, Pui Shan Chow, Reginald Beng Hee Tan
To overcome the disadvantage of current antibiotic bone cements with low drug elution efficiency, the hollow nanostructured titanium-dioxide (TiO2) nanotubes (TNTs) were formulated with antibiotic loaded bone cement to create nano diffusion networks, enabling enhanced release of antibiotic. By incorporation of TNTs into Poly(methyl methacrylate) (PMMA) based bone cement, more than 50% of loaded antibiotic (such as gentamicin or vancomycin) could be released in two months. As comparison, only about 5% of total drug release was achieved in the absence of TNTs. The mechanical properties of PMMA-based bone cements were well preserved after incorporation of TNTs. Furthermore, the compression strength and bending modules of TNTs formulated antibiotic bone cements could be maintained after the drug release for 70 days or aging in PBS buffer for 3 months. The insoluble TNTs in bone cement is believed to support the mechanical properties after wet aging.
Fretting damage of Ni-rich ultrafine grained NiTi superelastic wires J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-20 S.R. Soria, C.E. Callisaya, H. Soul, S. Claramonte, A. Yawny
The effects of fretting on Ni-rich ultra-fine grained NiTi superelastic wires have been characterized. Fretting tests have been performed using wire on wire in 90° cross-cylinder configuration until 105 cycles in air at 25 °C. Constant displacement amplitude of 50 µm and normal loads of 10, 20 and 50 N were considered. For a normal load of 10 N, the tribosystem performed in Gross Slip Regime and the predominance of wear damage was observed. Mixed Fretting Regime was instead observed for normal loads of 20 N and 50 N. In these cases, the predominant damage mechanism was crack formation with the cracks oriented normal to the displacement direction. Occurrence of martensitic transformation in the contact region was inferred from the particular shape of the fretting loops. Due to their possible impact on biocompatibility, the debris detached from the tribosystem during the different experiments were collected and characterized by TEM. They consisted in agglomerations of nano-crystalline TiO2 (rutile) and NiO oxide particles sized between 10 and 20 nm.
Characterization of Resilin-like Proteins with Tunable Mechanical Properties J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-20 Renay S.-C. Su, Emily E. Gill, Yeji Kim, Julie C. Liu
Resilin is an elastomeric protein abundant in insect cuticle. Its exceptional properties, which include high resilience and efficient energy storage, motivate its potential use in tissue engineering and drug delivery applications. Our lab has previously developed recombinant proteins based on the resilin-like sequence derived from Anopheles gambiae and demonstrated their promise as a scaffold for cartilage and vascular engineering. In this work, we describe a more thorough investigation of the physical properties of crosslinked resilin-like hydrogels. The resilin-like proteins rapidly form crosslinked hydrogels in physiological conditions. We also show that the mechanical properties of these resilin-like hydrogels can be modulated simply by varying the protein concentration or the stoichiometric ratio of crosslinker to crosslinking sites. Crosslinked resilin-like hydrogels were hydrophilic and had a high water content when swollen. In addition, these hydrogels exhibited moderate resilience values, which were comparable to those of common synthetic rubbers. Cryo-scanning electron microscopy showed that the crosslinked resilin-like hydrogels at 16 wt% featured a honeycomb-like structure. These studies thus demonstrate the potential to use recombinant resilin-like proteins in a wide variety of applications such as tissue engineering and drug delivery due to their tunable physical properties.
The Denticulate Ligament – Tensile Characterisation and Finite Element Micro-scale Model of the Structure Stabilising Spinal Cord J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-20 Katarzyna Polak-Kraśna, Sandra Robak-Nawrocka, Sylwia Szotek, Marcin Czyż, Daniel Gheek, Celina Pezowicz
BackgroundDamage to the spinal cord is one of the most debilitating pathologies with considerable health, economic and social impact. Improved prevention, treatment and rehabilitation after spinal cord injury (SCI) requires the complex biomechanics of the spinal cord with all its structural elements and the injury mechanism to be understood. This comprehensive understanding will also allow development of models and tools enabling better diagnosis, surgical treatment with increased safety and efficacy and possible development of regenerative therapies. The denticulate ligaments play an important role in stabilising spinal cord within the spinal canal. They participate in spinal cord movements and play a role in determining the stress distribution during physiological but also traumatic loading. We present detailed tensile characterisation of the denticulate ligaments and a Finite Element micro-scale model of the ligament relating its structure with the distribution of stress under physiological loading.MethodDenticulate ligaments were dissected from cervical spinal levels from 6 porcine cervical specimens with fragments of the pia and dura mater and characterised in terms of their geometry and response to uniaxial tensile loading. The stress-strain characteristics were recorded until rupture of the ligament, ultimate parameters and Young's moduli were determined. The parametric micro-structural Finite Element model was constructed based on literature microscope and histological images of a denticulate ligament as a phenomenological representation of the complex microstructure of a soft tissue. The model was validated against the experimental data.ResultsStress-strain characteristics obtained in tensile test were typical for a soft tissue behaviour. No statistically relevant differences in ultimate strength, strain and Young's moduli were observed between the ligaments harvested from different vertebral levels. Average ultimate tensile stress was 1.26 ± 0.20 MPa at strain 0.51 ± 0.00, rupturing force (1.01 ± 0.21 N) was in agreement with results obtained previously. The Finite Element model accurately predicted the extension-load behaviour of the denticulate ligament in elastic regime. The micro-scale structural representation enabled capturing deformation modes representative of the experimentally observed behaviour.ConclusionsThe presented stress-strain characteristics of the denticulate ligaments add valuable data to the understanding of the biomechanics of the spinal cord and enable development of more accurate models. The developed micro-scale model was capable of capturing biomechanical response of collagenous tissue under tensile loading, it can be applied for the prediction of other soft tissues behaviours. The denticulate ligament model should be included into future spinal cord models to fully represent the complex system's biomechanics and enable development of surgical aid tools to improve patient outcomes and future regenerative therapies.
Functional polyhedral oligomeric silsesquioxane reinforced poly(lactic acid) nanocomposites for biomedical applications J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-19 Lin Huang, Jianwang Tan, Wenqiang Li, Lin Zhou, Zhibin Liu, Binghong Luo, Lu Lu, Changren Zhou
Polyhedral oligomeric silsesquioxane reinforced poly (L-lactic acid) nanocomposites (PLLA/POSS) were prepared to overcome the insufficient mechanical properties of PLLA. In order to improve the compatibility between the nanofillers and matrix, PLLA chains were grafted onto the POSS nanoparticles via microwave-assisted ring opening polymerization (ROP). Herein, a series of interface-modified polyhedral oligomeric silsesquioxane (POSS-(PLLA)32) nanoparticles with various PLLA tail lengths were synthesized and the influence of the structure and additional amount of POSS nanoparticles on the properties of PLLA based nanocomposites were studied. POSS nanoparticles exhibit effective nucleation activity and lead to a significant improvement in the mechanical strength, thermal stability and biocompatibility of the resulting nanocomposites. The addition of 6 wt% POSS-(PLLA)32 600 shows the optimal mechanical properties owing to has the longest PLLA tail length on POSS core, which possesses the optimal interfacial compatibility between POSS nanoparticles and PLLA. The Young's modulus improved by 57% and the tensile strength increased by 26.5% compared with neat PLLA. Moreover, the introduction of POSS nanoparticles lead to a porous fiber structure when processed by electrospinning and the nanofibrous scaffold effectively promoted cells adhesion and spreading. These results demonstrate the potential applications of the PLLA/POSS nanocomposites in tissue engineering and regenerative medicine.
EVALUATION OF THE SINTERING TEMPERATURE ON THE MECHANICAL BEHAVIOR OF β-TRICALCIUM PHOSPHATE/CALCIUM SILICATE SCAFFOLDS OBTAINED BY GELCASTING METHOD J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-17 Lilian de Siqueira, Cynthia Guimarães de Paula, Rubia Figueredo Gouveia, Mariana Motisuke, Eliandra de Sousa Trichês
Scaffolds have been studied during the last decades as an alternative method to repair tissues. They are porous structures that act as a substrate for cellular growth, proliferation and differentiation. In this study, scaffolds of β-tricalcium phosphate with calcium silicate fibers were prepared by gel casting method in order to be characterized and validated as a better choice for bone tissue treatment. Gel-casting led to scaffolds with high porosity (84%) and pores sizes varying from 160 to 500 µm, which is an important factor for the neovascularization of the growing tissue. Biocompatible and bioactive calcium silicate fibers, which can be successfully produced by molten salt method, were added into the scaffolds as a manner to improve its mechanical resistance and bioactivity. The addition of 5 wt.% of calcium silicate fibers associated with a higher sintering temperature (1300 °C) increased by 64.6% the compressive strength of the scaffold and it has also led to the formation of a dense and uniform apatite layer after biomineralization assessment.
Linear viscoelastic and microstructural properties of native male human skin and in vitro 3D reconstructed skin models J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-17 Deepika Malhotra, Sharadwata Pan, Lars Rüther, Thomas B. Goudoulas, Gerrit Schlippe, Werner Voss, Natalie Germann
The study reports first ever account of measurements of linear viscoelastic moduli under small amplitude oscillatory shear deformations, for commercially available juvenile and aged in vitro 3D reconstructed skin models. The results were compared with those of native male whole human and dermis-only foreskin samples, catering to a wide age group from 0.5 to 68 years, including samples from a 23-year-old male abdomen. In the strain sweep tests, the dermis of the juvenile/young age group assumed a higher intrinsic elastic modulus than the whole skin. A reverse qualitative trend was noted for the adult/aged age group. Confirmed by the histological examination of the stained cross-sections, this is attributed to the nascent epidermal differentiation and the high fiber density of dermal collagen. The oscillation frequency sweeps exposed a greater dependence of the elasticity on the frequency for the native male dermis foreskin samples as compared to the whole skins, irrespective of age. This is anticipated since the extremely structured epidermis confers higher resistance to the whole skins towards intracycle deformations compared to the dermis, thereby storing smaller elastic energy. The 3D skin models examined in this work exhibited a broader linear viscoelastic region, a larger viscoelasticity, and much higher dynamic moduli, compared to the native skin. The rheological trends are a significant addition to the literature and may be used as a reference for the design of next generation of scaffolds.
Quantifying Machining Outputs of Pristine Human Teeth Relevant to Dental Preparation Procedures J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-16 James F. Nowak, Johnson Samuel
Minimally-assisted tooth repair (MaTR) systems are envisioned to be capable of substituting for the skill of a dentist. If successfully developed, MaTR systems could enable lower-skilled dental technicians to provide dental care at a fraction of the overall medical cost. This paper explores a key initial step towards the development of such systems by quantifying the machining responses of pristine human teeth relevant to dental preparation procedures. The working hypothesis of the study is that such findings will enable the benchmarking of key process planning and control metrics relevant for the future development of MaTR systems. To this end, pristine human cadaver teeth were cut using a computer-controlled motion platform and dental hand-piece. Relevant cutting responses, such as cutting forces, in-process rotational speed of the dental bur, teeth morphology, and bur wear were captured. The trends in cutting forces show the potential for implementing region-specific process parameters for cutting the enamel and dentin regions of the tooth. A feed-per-tooth value of 0.1 µm at rotational speeds of 8 krpm and 50 krpm is seen to cut both the enamel and dentin regions at cutting forces lower than patient discomfort thresholds identified in literature. Cutting force signals were also successfully mapped against the CT-scan data of the tooth. This mapping indicates a clear identification of the enamel/dentin regions, and a transition region that is dependent on cutting parameters, tooth/tool geometry and tool pose. The trends in the in-process rotational speed of the dental bur indicate that stalling of the dental bur occurs at feed per tooth values greater than 0.25 μm. The evidence of stalling can be detected by both a drop in the cutting force signal and by surface morphology changes on the cut surface of the tooth. MaTR systems should be designed to avoid bur stalling regions by either operating at feed per tooth values ≤ 0.25 μm or by the use of dental spindles with higher torque capacity. Lastly, the type of fit present on the shank of the bur is seen to result in differences in the cutting force signals and wear of the cutting edges (flutes) of the dental bur. In general, a right-angle (RA) fit on the shank of the dental bur results in a larger tool runout leading to uneven loads on the flutes and increased tool wear. The friction grip (FG) fit avoids these problems and may be more suited for MaTR systems.
Development of graphene oxide/calcium phosphate coating by pulse electrodeposition on anodized titanium: biocorrosion and mechanical behavior J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-16 Leila Fathyunes, Jafar Khalil-Allafi, Maryam Moosavifar
In this work, graphene oxide (GO) reinforcement was used to improve the strength and fracture toughness of the calcium phosphate (CaP) coating applied on the anodized titanium using pulse electrodeposition. The results showed that the CaP coating consisted of mixed phases of octa-calcium phosphate (OCP), dicalcium phosphate dehydrate (DCPD) and hydroxyapatite (HAp); however, compositing of this coating with GO caused deposition of the pure HAp phase. Moreover, the nanohardness and elastic modulus for the CaP-GO coating increased over 52% and 41%, respectively, as compared to those measured for the GO-free coating. An improvement of about 16% in the adhesion strength of the CaP coating composited with GO to the anodized titanium was also arisen from improving integrity, crystallinity and decreasing the elastic modulus mismatch of this coating with titanium substrate. Finally, uniformity in the microstructure and more biostability of the CaP-GO coating led to its better protection against the corrosion of anodized titanium.
A Shear Assay Study of Single Normal/Breast Cancer Cell Deformation and Detachment from Poly-Di-Methyl-Siloxane (PDMS) Surfaces J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-15 C.J. Ani, J.D. Obayemi, V.O. Uzonwanne, Y. Danyuo, O.S. Odusanya, J. Hu, K. Malatesta, W.O. Soboyejo
This paper presents the results of a combined experimental and analytical/computational study of viscoelastic cell deformation and detachment from poly-di-methyl-siloxane (PDMS) surfaces. Fluid mechanics and fracture mechanics concepts are used to model the detachment of biological cells observed under shear assay conditions. The analytical and computational models are used to compute crack driving forces, which are then related to crack extension during the detachment of normal breast cells and breast cancer cells from PDMS surfaces that are relevant to biomedical implants. The interactions between cells and the extracellular matrix, or the extracellular matrix and the PDMS substrate, are then characterized using force microscopy measurements of the pull-off forces that are used to determine the adhesion energies. Finally, fluorescence microscopy staining of the cytosketelal structures (actin, micro-tubulin and cyto-keratin), transmembrane proteins (vimentin) and the ECM structures (Arginin Glycine Aspartate – RGD) is used to show that the detachment of cells during the shear assay experiments occurs via interfacial cracking between (between the ECM and the cell membranes) with a high incidence of crack bridging by transmembrane vinculin structures that undergo pull-out until they detach from the actin cytoskeletal structure. The implications of the results are discussed for the design of interfaces that are relevant to implantable biomedical devices and normal/cancer tissue.
Enhanced corrosion resistance and bonding strength of Mg substituted β-tricalcium phosphate/Mg(OH)2 composite coating on magnesium alloys via one-step hydrothermal method J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-12 Yishu Lin, Shu Cai, Song Jiang, Dongli Xie, Rui Ling, Jiayue Sun, Jieling Wei, Kaier Shen, Guohua Xu
To overcome the defect of high degradation rate of magnesium (Mg), bioactive coatings with compact structure, sufficient bonding strength and enhanced corrosion resistance are essential for Mg-based biodegradable implants. In this study, a dense Mg-substituted β-tricalcium phosphate and magnesium hydroxide (β-TCMP/Mg(OH)2) composite coating was prepared on AZ31 alloy via one-step hydrothermal method. The influences of hydrothermal temperature on its composition, microstructure of the surface and interface, bonding strength and corrosion behavior were evaluated. The results showed that the compact composite coating synthesized at 140 °C not only possessed a crack-free bilayered structure with an adequate bonding strength (more than 20.88 ± 1.60 MPa), but also got an extreme high impedance (1197.003 ± 152.817 kΩ·cm2) so that significantly enhanced the corrosion resistance and inhibited the formation of pitting corrosion. Furthermore, the in vitro immersion test suggested that the composite coating slower the initial degradation rate of Mg alloys and enhanced its surface bioactivity to some extent.
Edge chipping resistance of ceramics bonded to a dentine analogue J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-12 Cristiano Taufer, Alvaro Della Bona
Objective To evaluate the edge chip resistance ( R eA ) of two CAD/CAM monolithic ceramics (GC- IPS e.max CAD and YZ- Zenostar Zr Translucent) bonded to a dentine analogue substrate (G10- NEMA G10). Methods Plate-shaped specimens were prepared from GC and YZ ceramics and were either bonded (B) to G10 or attached (NB) to a universal testing machine for edge chipping test. Samples from all groups (GC-B, GC-NB, YZ-B and YZ-NB) were indented (n = 25) at different edge distances (d= 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 mm) to produce chips. Force (F, in N) and d values were recorded and R eA (in N/mm) were calculated. Data were statistically analyzed using Pearson´s correlation, Student t, ANOVA and Tukey tests (α=0.05). Results A strong correlation (R≥ 0.98) was found between F and d values for all groups. R eA values increased with increasing d, irrespective of ceramic type (GC and YZ) or fixation method (B and NB). Significant differences (p<0.05) in mean R eA values were found between B and NB ceramics at lower d (0.1 − 0.3 mm) that did not persist (p>0.05) at greater d (0.5 and 0.6 mm), meaning, bonding (B) to G10 protected both materials against chipping close to the edge. Conclusions The larger the distance from the occlusal contact to the restoration edge, the greater the chance to avoid ceramic chipping in monolithic restorations. For d ≤ 0.3 mm, such F vs d relation is less critical for edge resistance of YZ and for resin bonded monolithic ceramics.
Load-bearing capacity under fatigue and survival rates of adhesively cemented yttrium-stabilized zirconia polycrystal monolithic simplified restorations J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-12 Camila Pauleski Zucuni, Andressa Borin Venturini, Catina Prochnow, Gabriel Kalil Rocha Pereira, Luiz Felipe Valandro
This study aims to evaluate the fatigue failure load, number of cycles for failure and survival probability of 2nd and 3rd generation yttrium-stabilized zirconia (YSZ) adhesively cemented to a dentin analogue substrate. Disc-shaped specimens (n = 10; Ø = 10 mm; thickness = 1.0 mm) were produced from four 2nd generation YSZs (Lava Plus, 3 M ESPE; Vita In-Ceram YZ-HT, VITA Zahnfabrik; Zirlux FC, IvoclarVivadent; Katana ML-HT, Kuraray) and two 3rd generation YSZs (Katana UTML and Katana STML, Kuraray). Each YSZ disc was adhesively cemented (Multilink Automix System) onto its dentin analogue pair (epoxy resin, Ø = 10 mm; thickness = 2.5 mm). Fatigue tests were conducted through step-stress approach (load ranging from 400 to 2600 N; step-size of 200 N; 20,000 cycles per step, 20 Hz) and the obtained data were analyzed using Kaplan Meier and Mantel-Cox tests. Surface topography and phase transformation (m-, t-, and c-phases) inspections after particle air-abrasion of the YSZs were performed, as well as fractographic analysis of the failed specimens. Second-generation zirconia materials presented higher fatigue failure load, number of cycles for failure, and survival probability than 3rd generation. Similar topographical characteristics of the YSZs could be noted. Phase transformation (t- to m-phase) after YSZ air-abrasion was only observed for 2nd generation materials. All failures started from the surface/sub-surface defects located at the cementation interface. 2nd generation zirconia presented higher load-bearing capacity in cyclic loading than 3rd generation materials.
Controlled mercerization of bacterial cellulose provides tunability of modulus and ductility over two orders of magnitude J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-06 Mousa Younesi, Xinyu Wu, Ozan Akkus
Effects of mercerization process on plant-based cellulose is well studied in the literature whereas the effects of mercerization on mechanical properties of bacterial cellulose is not investigated. In this work bacterial cellulose (BC) was mercerized in NaOH solution with different molar concentrations of 0, 1.50, 1.75, 2.00, 2.13, 2.25, 5.00, 7.00 and 10.00 M. The BC samples shrunk substantially with increasing NaOH concentration. At the same concentration, NaOH treatment resulted in significantly larger shrinkage than KOH treatment. Mercerization of BC samples in 7 M NaOH resulted in an order of magnitude increase in elongation from 5.4 ± 1.6% to 50.8 ± 5.7% along with about 30-fold reduction in Young's modulus. Mercerized samples in 4 M NaOH had maximum toughness among all groups at a value of 64.0 ± 15.8 MJ•m−3. Changes in BC crystalline structure from cellulose I to cellulose II were characterized and confirmed semiquantitatively by using X-ray diffraction (XRD) and Raman spectroscopy. Results of this work demonstrated mercerization as a method to tune the mechanical properties of BC precisely. Mercerized BC as a biocompatible material with tunable mechanical properties shows potential to be utilized in tissue engineering and regenerative medicine in the future.
Characterization of Perfused & Sectioned Liver Tissue In A Full Indentation Cycle Using A Visco-hyperelastic Model J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-06 Ling Li, Ashkan Maccabi, Ahmad Abiri, Yen-Yi Juo, Wenyang Zhang, Yi-Jui Chang, George Saddik, Lihua Jin, Warren Grundfest, Erik Dutson, Jeff Eldredge, Peyman Benharash, Robert Candler
Realistic modeling of biologic material is required for optimizing fidelity in computer-aided surgical training and assistance systems. The modeling of liver tissue has remained challenging due to its nonlinear viscoelastic properties and high hysteresis of the stress-strain relation. While prior studies have described the behavior of liver tissue during the loading status (in elongation, compression, or indentation tests) or unloading status (in stress relaxation or creep tests), a hysteresis curve with both loading and unloading processes was incompletely defined. We seek to use a single material model to characterize the mechanical properties of liver tissue in a full indentation cycle ex vivo perfused and then sectioned. Based on measurements taken from ex-vivo perfused porcine livers, we converted force-displacement curves to stress-strain curves and developed a visco-hyperelastic constitutive model to characterize the liver's mechanical behavior at different locations under various rates of indentation (1, 2, 5, 10, and 20 mm/s). The proposed model is a mixed visco-hyperelastic model with up to 6 coefficients. The normalized root mean square standard deviations of fitted curves are less than 5% and 10% in low ( < 0.05 ) and high strain ( > 0.3 ) conditions respectively.
Compressibility of arterial wall – direct measurement and predictions of compressible constitutive models J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-05 Pavel Skacel, Jiri Bursa
Volumetric compressibility and Poisson's ratios of fibrous soft tissues are analyzed in this paper on the basis of constitutive models and experimental data. The paper extends the previous work of Skacel and Bursa (J Mech Behav Biomed Mater, 54, pp. 316–327, 2016), dealing with incompressible behaviour of constitutive models, to the area of compressibility. Both recent approaches to structure-based constitutive modelling of anisotropic fibrous biomaterials (based on either generalized structure tensor or angular integration) are analyzed, including their compressibility-related aspects. New experimental data related to compressibility of porcine arterial layer are presented and compared with the theoretical predictions of analyzed constitutive models. The paper points out the drawbacks of recent models with distributed fibres orientation since none of the analyzed constitutive models seems to be capable to predict the experimentally observed Poisson's ratios and volume change satisfactory.
Designed for Resistance to Puncture: The Dynamic Response of Fish Scales J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-02 S. Ghods, S. Murcia, E.A. Ossa, D. Arola
Natural dermal armors are serving as a source of inspiration in the pursuit of “next-generation” structural materials. Although the dynamic strain response of these materials is arguably the most relevant to their performance as armors, limited work has been performed in this area. Here, uniaxial tension and transverse puncture tests were performed on specimens obtained from the scales of Asian carp over strain rates spanning seven decades, from 10−4 to 103 s−1. The importance of anatomical variations was explored by comparing the performance of scales from the head, middle and tail regions. In both loading orientations, the scales exhibited a significant increase in the resistance to failure with loading rate. The rate sensitivity was substantially higher for transverse loading than for in-plane tension, with average strain rate sensitivity exponents for measures of the toughness of 0.35 and 0.08, respectively. Spatial variations in the properties were largest in the puncture responses, and scales from the head region exhibited the greatest resistance to puncture overall. The results suggest that the layered microstructure of fish scales is most effective at resisting puncture, rather than in-plane tension, and its effectiveness increases with rate of loading. X-ray microCT showed that delamination of plies in the internal elasmodine and stretching of the fibrils were key mechanisms of energy dissipation in response to puncture loading. Understanding contributions from the microstructure to this behavior could guide the development of flexible engineered laminates for penetration resistance and other related applications.
The effect of different preconditioning protocols on repeatability of bovine ACL stress-relaxation response in tension J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-02 Mohammadhossein Ebrahimi, Ali Mohammadi, Aapo Ristaniemi, Lauri Stenroth, Rami K. Korhonen
Mechanical characterization of soft tissues such as ligaments remains challenging. There is variability in the measured material parameters of ligaments, most of which is related to natural tissue variability, but some of it can be a result of using different testing protocols. Generally preconditioning (cyclic loading-unloading) is performed prior to actual tests to reduce the experimental variability. Commonly, preconditioning protocols for ligaments with a small strain level and 10 sinusoidal loading-unloading cycles are used. The effect of preconditioning and its parameters including strain level, number of cycles and number of preconditioning repetitions on the repeatability of tensile stress-relaxation tests are poorly known for knee ligaments. In the present study, forty-eight dumbbell-shaped bovine anterior cruciate ligament (ACL) samples were used to evaluate the repeatability of stress-relaxation response. Different preconditioning protocols with 2% and 6% strain levels and 1, 5 or 10 preconditioning repetitions were applied. After preconditioning, one-step stress-relaxation test was carried out twice with an hour resting period in between the tests. The equilibrium stress showed no systematic bias when only one preconditioning repetition was applied (2.0±3.1% difference and p>0.05 between repeated tests). Systematic bias in the peak-to-equilibrium stress ratio was not observed when higher strain level and number of repetitions were used (0.5±1.6% difference and p>0.05 between repeated tests). In conclusion, the commonly used preconditioning protocol is capable of producing repeatable equilibrium stress levels of bovine ACLs from stress-relaxation tests in tension. However, if repeatable peak-to-equilibrium stress ratio is desirable, higher strain and number of preconditioning repetitions are recommended.
Mechanical and Surface Chemical Analysis of Retrieved Breast Implants from a Single Centre J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-02 Louise J Magill, Aleksandra Tanksa, Mohammed Keshtgar, Ashfin Mosahebi, Gavin Jell
Introduction Breast implants are associated with complications such as capsular contracture, implant rupture and leakage often necessitating further corrective surgery. Re-operation rates have been reported to occur in up to 15.4% of primary augmentation patients and up to 27% in primary reconstructions patients within the first three years . The aim of this study was to examine the mechanical and surface chemical properties as well as the fibroblast response of retrieved breast implants in our unit to determine the in vivo changes which occur over time. Methods Ethical approval was obtained. 47 implants were retrieved. Implantation time ranged from 1 month to 388 months (Mean 106.1 months). Tensile strength, elongation, Young's modulus and tear strength properties were measured using Instron 5565 tensiometer on anterior and posterior aspects of the implant. Attenuated total reflectance-fourier transform infra-red spectroscopy (ATR-FTIR), wettability and scanning electron microscopy (SEM) analysis was performed on the shell surfaces. Bicinchoninic acid assay was performed to determine shell protein content. The fibroblast response was determined by seeding HDFa cells on the retrieved implants and cell metabolism measured using Alamar Blue™ assay. Results Mechanical properties fall with increasing duration of implantation. There were no significant changes in ATR-FTIR spectra between ruptured and intact implants nor significant changes in wettability in implants grouped into 5 year categories. SEM imaging reveals surface degradation changes with increasing duration of implantation. Conclusions With increasing duration of implantation, mechanical properties of the breast implants fall. However this was not associated with surface chemical changes as determined by ATR-FTIR and wettability nor protein content of the shells. Thus the reduction in mechanical properties is associated with breast implant failure but further research is required to elucidate the mechanisms.
Effect of tribochemical silica coating or multipurpose products on bonding performance of a CAD/CAM resin-based material* J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-02 Xinyi Wu, Haifeng Xie, Hongliang Meng, Lu Yang, Bingzhuo Chen, Ying Chen, Chen Chen
Gating and Inactivation of Mechanosensitive Channels of Small Conductance: A Continuum Mechanics Study J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-02 Liangliang Zhu, Qiang Cui, Hang Xiao, Xiangbiao Liao, Xi Chen
Surface functionalization of polylactic acid fibers with alendronate groups does not improve the mechanical properties of fiber-reinforced calcium phosphate cements J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-03 Daniela-Geta Petre, Nathan W. Kucko, Anna Abbadessa, Tina Vermonden, Alessandro Polini, Sander C.G. Leeuwenburgh
Calcium phosphate cements (CPCs) are frequently used as synthetic bone substitute, but their intrinsic low fracture toughness impedes their application in highly loaded skeletal sites. However, fibers can be used to reduce the brittleness of these CPCs provided that the affinity between the fibers and cement matrix facilitates the transfer of loads from the matrix to the fibers. The aim of the present work was to improve the interface between hydrophobic polylactic acid (PLA) microfibers and hydrophilic CPC. To this end, calcium-binding alendronate groups were conjugated onto the surface of PLA microfibers via different strategies to immobilize a tunable amount of alendronate onto the fiber surface. CPCs reinforced with PLA fibers revealed toughness values which were up to 50-fold higher than unreinforced CPCs. Nevertheless, surface functionalization of PLA microfibers with alendronate groups did not improve the mechanical properties of fiber-reinforced CPCs.
Effect of carbon fiber type on monotonic and fatigue properties of orthopedic grade PEEK J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-03 Noah Bonnheim, Farzana Ansari, Marco Regis, Pierangiola Bracco, Lisa Pruitt
Carbon-fiber reinforced (CFR) PEEK implants are used in orthopedic applications ranging from fracture fixation plates to spinal fusion cages. Documented implant failures and increasing volume and variety of CFR PEEK implants warrant a clearer understanding of material behavior under monotonic and cyclic loading. To address this issue, we conducted monotonic and fatigue crack propagation (FCP) experiments on orthopedic grade unfilled PEEK and two formulations of CFR PEEK (PAN- and pitch-based carbon fibers). The effect of annealing on FCP behavior was also studied. Under monotonic loading, fiber type had a statistically significant effect on elastic modulus (12.5 ± 1.3 versus 18.5 ± 2.3 GPa, pitch versus PAN CFR PEEK, AVG ± SD) and on ultimate tensile strength (145 ± 9 versus 192 ± 17 MPa, pitch versus PAN CFR PEEK, AVG ± SD). Fiber type did not have a significant effect on failure strain. Under cyclic loading, PAN CFR PEEK demonstrated an increased resistance to FCP compared with unfilled and pitch CFR PEEK, and this improvement was enhanced following annealing. Pitch CFR PEEK exhibited FCP behavior similar to unfilled PEEK, and neither material was appreciably affected by annealing. The improvements in monotonic and FCP behavior of PAN CFR PEEK is attributed to a compound effect of inherent fiber properties, increased fiber number for an equivalent wt % reinforcement, and fiber aspect ratio. FCP was shown to proceed via cyclic modes during stable crack growth, which transitioned to static modes (more akin to monotonic fracture) at longer crack lengths. The mechanisms of fatigue crack propagation appear similar between carbon-fiber types.
Mechanical behaviour of extremely tough TZP bioceramics J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-03 Frank Kern, Helen Reveron, Jérôme Chevalier, Rainer Gadow
Tetragonal Zirconia Polycrystals (TZP) is attractive for structural biomedical applications because of their excellent mechanical properties at room-temperature, which include high strength, fracture toughness and wear resistance. In this work, zirconia stabilized with Y or Yb or Yb+Nd, all containing 0.5 vol.% Al2O3, were prepared by hot-pressing (HP) at 50–60 MPa and sintered at 1300–1350 °C for 1 h. Microstructural features, phase composition and mechanical properties were investigated. The strength was measured by 4-point bending (4P-B), piston-on-three-balls (P-3B) and three-balls-on-three-balls (3B-3B) biaxial methods. Toughness was determined by indentation strength in bending (ISB). Vickers hardness (Hv) and the Young modulus (E) were also estimated. Preliminary aging behaviour (LTD) was also here considered. Measured biaxial strength was significantly higher (until 1.83 times) than the uniaxial one because of the tetragonal to monoclinic (t-m) zirconia phase transformation which is strongly influenced by the loading configuration. The variation of the strength with the testing method is attributed to the compressive stresses generated by the phase transformation which is particularly favoured under P-3B tests and also to the calculation of the stresses from elastic theories. LTD preliminary tests showed excellent aging resistance of 3Yb-0.5 A ceramics.
Structural Analysis of the Frontal and Parietal Bones of the Human Skull J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-01 Stephen L. Alexander, Karin Rafaels, C Allan Gunnarsson, Tusit Weerasooriya
Tuning strain-induced γ-to-ε martensitic transformation of biomedical Co–Cr–Mo alloys by introducing parent phase lattice defects J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-01 Kenta Yamanaka, Manami Mori, Shigeo Sato, Shinki Tsubaki, Kozue Satoh, Masayoshi Kumagai, Muneyuki Imafuku, Takahisa Shobu, Akihiko Chiba
In vitro experimental and numerical study on biomechanics and stability of a novel adjustable hemipelvic prosthesis J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-01 Dongxu Liu, Zikai Hua, Jianfeng Jiang, Lei Wang, Jie Liu, Zhongmin Jin, Leiming Gao
Mechanical performance of conical implant-abutment connections under different cyclic loading conditions J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-11-01 Kuang-Ta Yao, Hung-Chan Kao, Cheng-Kung Cheng, Hsu-Wei Fang, Chang-Hung Huang, Ming-Lun Hsu
The Mechanical Response of Commercially Available Bone Simulants for Quasi-Static and Dynamic Loading J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-30 A.D. Brown, J.B. Walters, Y.X. Zhang, M. Saadatfar, J.P. Escobedo-Diaz, P.J. Hazell
Bone is a complex hierarchal structured material with varying porosity and mechanical properties. In particular, human cranial bone is essentially a natural composite consisting of low porosity outer and inner tables and a cancellous interior, or diploë. Experimental studies of biomechanically accurate cranial bone analogues are of high importance for biomechanical, forensics, and clinical researchers, which could improve the understanding and prevention of traumatic injury. Many reported studies use commercially available bone surrogates to draw biomechanical and forensics conclusions; however, their mechanical properties are not tabulated over a range of strain rates. This study elucidates the mechanical viability of three leading commercially available bone surrogates, i.e. Synbone, Sawbone, and Bonesim, over a large range of strain rates (10−3 to 103 s−1). Quasi-static compression testing was conducted using a universal testing machine and a Split-Hopkinson Pressure bar system equipped with high-speed video was used to determine the dynamic mechanical behavior of these materials. Micro-computed X-ray tomography (XRT) were performed on each material to investigate their pore structures and distributions. All materials exhibited strain rate dependent strength behavior, particularly at high loading rates (≥103 s−1). The Young's modulus was found to increase with strain rate from 10−3 to 10−1 s−1 for transversely and longitudinally loaded surrogate materials except for Synbone and the higher density Bonesim. The higher density Bonesim was determined to be the most suitable cranial bone simulant tested based on a combination of transverse Young's Modulus (1500 MPa), yield strength (19 MPa), ultimate strength (49 MPa), and ultimate strain (17%). These materials show limited promise for applications where the measured elastic properties and strengths are of interest.
Tribological behavior of Ti-6Al-4V against cortical bone in different biolubricants J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-29 Chenchen Wang, Gangqiang Zhang, Zhipeng Li, Xiangqiong Zeng, Yong Xu, Shichang Zhao, Hongxing Hu, Yadong Zhang, Tianhui Ren
Do endodontic retreatment techniques influence the fracture strength of endodontically treated teeth? A systematic review and meta-analysis J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-26 Ricardo Schestatsky, Gustavo Dartora, Rodrigo Felberg, Aloísio Oro Spazzin, Rafael Sarkis-Onofre, Ataís Bacchi, Gabriel Kalil Rocha Pereira
One of the major concerns about endodontically retreated teeth (ERT) is undoubtedly its loss of remnant structure, which could lead to consequently greater fracture risk. Therefore, the objective of this systematic review is to assess the influence of endodontic retreatment on the fracture strength of the dental tooth remnant. In vitro studies assessing the influence of mechanical retreatment on the mechanical properties (static or under fatigue) of restored teeth were searched in PubMed and SCOPUS databases. Three independent reviewers screened titles/abstracts of articles and the full-text of potentially eligible studies. The risk of bias was independently assessed by one researcher and verified by another two. Comparison between the mean load to fracture of teeth after endodontic treatment and after endodontic retreatment were estimated using pairwise random effects meta-analysis to calculate pooled mean differences. Three studies were included for the systematic review and 2 for the meta-analysis. The pooled effect indicated a statistical difference (Mean difference: −121.03 95%CI: −183.02, −59.05) between conditions favoring the endodontically treated teeth. However, the low number of studies combined with their heterogeneity made it difficult to prove such phenomenon. ERT might present lower fracture strength than endodontically treated teeth. However, more coherent laboratory tests may provide better evidence and quantitative parameters on how much reliability can be attributed to an endodontic retreatment, in addition to which technique can provide more predictable results in this conservative approach.
Dentin pretreatment with 45S5 and niobophosphate bioactive glass: Effects on pH, antibacterial, mechanical properties of the interface and microtensile bond strength J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-25 José Bauer, Allana Silva e Silva, Edilausson Moreno Carvalho, Paulo Vitor Campos Ferreira, Ceci Nunes Carvalho, Adriana Pigozzo Manso, Ricardo Marins de Carvalho
Objectives The aim of the study was to evaluate the effect of bioactive glass (45S5 and NbG) suspensions on bond strength (µTBS), hardness, modulus of elasticity, pH and antibacterial activity of the resin-dentin interfaces after 3 months. Methods Groups with different concentrations (5% and 20%) of two types of glass (45S5 and NbG), and a control group (distilled water) were studied. Twenty-five extracted human third molars were etched with phosphoric acid. The means of the two-way ANOVA and Holm-Sidak tests (α=5%). The antimicrobial activity data were analyzed by the Kruskal-Wallis test (α=5%). Results The interactions were significant among groups for µTBS (p=0.033). Significant reductions in µTBS were observed after 3 months storage in PBS for the Control and 5% NbG Groups. Suspensions with 5% and 20% 45S5 glass and 20% NbG resulted in stable µTBS values and increased hardness after 3 months. Both 20% suspensions (45S5 and NbG) increased the elastic modulus. A significant greater reduction in bacterial growth was observed with the use of 20% 45S5. Conclusion Rewetting dentin with the suspension of 20% 45S5 glass prevented the reduction in bond strength; increased hardness; modulus of elasticity of the resin-dentin interface, and demonstrated antibacterial activity against Streptococcus mutans.
Effect of light-curing protocols on the mechanical behavior of bulk-fill resin composites J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-25 João Felipe Besegato, Eduardo Inocente Jussiani, Avacir Casanova Andrello, Ricardo Vignoto Fernandes, Fabio Martins Salomão, Bruno Luiz Santana Vicentin, Cássia Cilene Dezan-Garbelini, Márcio Grama Hoeppner
Objective To investigate the effect of two light-curing protocols on mechanical behavior of three bulk-fill resin composites (BFRC) considering their optical properties. Methods One increment of 4 mm thickness of the bulk-fill resin composites Opus Bulk Fill, Tetric N-Ceram and Filtek Bulk Fill Flow were submitted to two different light-curing protocols: Sp - irradiance of 1000 mW/cm2 (20 s); Xp - irradiance of 3200 mW/cm2 (6 s). To assess the influence on the mechanical behavior it was studied polymerization shrinkage by X-ray microtomography (n = 3), Vickers hardness (n = 10) at the top and bottom surfaces of the samples, irradiance reaching the bottom surface (n = 3) and absorbance spectrum during the light-curing time interval (n = 3). Data were analyzed by two-way ANOVA test for parametric data and Kruskal Wallis test, followed by Wilcoxon or Mann-Whitney U post-test, for non-parametric data. Results All BFRCs contracted when light-cured, with greater contraction for Xp. Filltek Bulk Fill Flow showed highest polymerization shrinkage, for both Sp and Xp. All BFRCs showed minor hardness values on the bottom surface, with greater reduction for Xp. All BFRCs exhibited a decrease in irradiance at 4mm depth. A decrease in absorbance intensity throughout the light-cure was observed, except for Opus Bulk Fill. Conclusions Regardless BFRCs composition, the light-curing protocol with lower irradiance and longer exposure time results in lower polymerization shrinkage and higher hardness. The higher irradiance in a shorter time interval compromises the mechanical behavior of the resin composites, which may result in undesirable clinical outcomes.
Dynamics of a capsule flowing in a tube under pulsatile flow J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-25 Jorge Maestre, Jordi Pallares, Ildefonso Cuesta, Michael A. Scott
We analyze numerically the behavior of a deformable micro-capsule confined in a pipe under a pulsatile flow. The capsule moves and is deformed by the action of a pulsatile flow inside the tube with a non-null mean velocity. This configuration can be found in the nature and in many bioengineering systems where artificial capsules are driven by micro-pumps through micro-channels. The capsule is considered as a thin hyperelastic membrane, which encloses an internal fluid. As it has been demonstrated in the literature, this model represents a wide range of artificial capsules, for example, the alginate-based capsules, typically used in bioengineering applications. A hybrid isogeometric finite element method and boundary element method based on a T-spline discretization and formulated in the time domain is used to solve the mechanical and hydrodynamical equations. The influence of the relative rigidity of the membrane, frequency and amplitude of the pulsatile flow is studied. Results show that the behavior of the capsule differs from steady flows and it depends strongly on the frequency of the flow and mechanical characteristic of the capsule.
Multiscale Modeling for the Heterogeneous Strength of Biodegradable Polyesters J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-19 Taohong Zhang, Geyu Jin, Xiaoxiao Han, Yue Gao, Qingfeng Zeng, Binbin Hou, Dezheng Zhang
A heterogeneous method of coupled multiscale strength model is presented in this paper for calculating the strength of medical polyesters such as polylactide (PLA), polyglycolide (PGA) and their copolymers during degradation by bulk erosion. The macroscopic device is discretized into an array of mesoscopic cells. A polymer chain is assumed to stay in one cell. With the polymer chain scission, it is found that the molecular weight, chain recrystallization induced by polymer chain scissions, and the cavities formation due to polymer cell collapse play different roles in the composition of mechanical strength of the polymer. Therefore, three types of strength phases were proposed to display the heterogeneous strength structures and to represent different strength contribution to polymers, which are amorphous phase, crystallinity phase and strength vacancy phase, respectively. The strength of the amorphous phase is related to the molecular weight; strength of the crystallinity phase is related to molecular weight and degree of crystallization; and the strength vacancy phase has negligible strength. The vacancy strength phase includes not only the cells with cavity status but also those with an amorphous status, but a molecular weight value below a threshold molecular weight. This heterogeneous strength model is coupled with micro chain scission, chain recrystallization and a macro oligomer diffusion equation to form a multiscale strength model which can simulate the strength phase evolution, cells status evolution, molecular weight, degree of crystallinity, weight loss and device strength during degradation. Different example cases are used to verify this model. The results demonstrate a good fit to experimental data.
Influence of nanocellulose on mechanics and morphology of polyvinyl alcohol xerogels J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-19 R. Pramanik, B. Ganivada, Farsa Ram, Kadhiravan Shanmuganathan, A. Arockiarajan
Unravelling the viscoelastic, buffer-like mechanical behavior of tendons: A numerical quantitative study at the fibril-fiber scale J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-19 Nikolaos Karathanasopoulos, Georgios Arampatzis, J-Francois Ganghoffer
We investigate the capacity of tendons to bear substantial loads by exploiting their hierarchical structure and the viscous nature of their subunits. We model and analyze two successive tendon scales: the fibril and fiber subunits. We present a novel method for bridging intra-scale experimental observations by combining a homogenization analysis technique with a Bayesian inference method. This allows us to infer elastic and viscoelastic moduli at the embedded fibril scale that are mechanically compatible with the experimental data observed at the fiber scale. We identify the rather narrow range of moduli values at the fibrillar scale that can reproduce the mechanical behavior of the fiber, while we quantify the viscoelastic contribution of the embedding, non-collagenous matrix substance. The computed viscoelastic moduli suggest that a great part of the stress relaxation capacity of tendons needs to be attributed to the embedding matrix substance of its inner components, classifying it as a primal load relaxation constituent.
A novel micro-grooved collagen substrate for inducing vascular smooth muscle differentiation through cell tissue arrangement and nucleus remodeling J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-21 Kazuaki Nagayama, Keiichi Uchida, Akiko Sato
Fluid load support does not explain tribological performance of PVA hydrogels J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-21 Elze Porte, Philippa Cann, Marc Masen
Control of Bacterial Attachment by Fracture Topography J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-21 Amar Velic, Asha Mathew, Peter Hines, Prasad K.D.V Yarlagadda
Characterization of low-shrinkage dental composites containing methacrylethyl-polyhedral oligomeric silsesquioxane (ME-POSS) J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-18 Talita Angelina Tavares Canellas, Aline de Almeida Neves, Ingrid Kimberly Bezerra dos Santos, Amanda Ramos Pereira de Rezende, Carlos Eduardo Fellows, Eduardo Moreira da Silva
Strontium doped hydroxyapatite from Mercenaria clam shells: Synthesis, mechanical and bioactivity study J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-10-17 Anindya Pal, Purnendu Nasker, Sudeep Paul, Amit Roy Choudhury, Arijit Sinha, Mitun Das
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