CNT and rGO reinforced PMMA based bone cement for fixation of load bearing implants: Mechanical property and biological response

https://doi.org/10.1016/j.jmbbm.2021.104320Get rights and content

Highlights

  • Novel PMMA-based bone cement containing various amounts of rGO and CNT is prepared.

  • Incorporation of rGO and CNT into PMMA-based cement increases its compressive, tensile and bending strength.

  • Toughening and cell interactions mechanism of PMMA-based cement containing rGO and CNT is proposed.

Abstract

Polymethyl methacrylate (PMMA) bone cements (BCs) have some drawbacks, including limited bioactivity and bone formation, as well as inferior mechanical properties, which may result in failure of the BC. To deal with the mentioned issues, novel bioactive polymethyl methacrylate-hardystonite (PMMA-HT) bone cement (BC) reinforced with 0.25 and 0.5 wt% of carbon nanotube (CNT) and reduced graphene oxide (rGO) was synthesized. In this context, the obtained bone cements were evaluated in terms of their mechanical and biological characteristics. The rGO reinforced bone cement exhibited better mechanical properties to the extent that the addition of 0.5 wt% of rGO where its compressive and tensile strength of bioactive PMMA-HT/rGO cement escalated from 92.07 ± 0.72 MPa, and 40.02 ± 0.71 MPa to 187.48 ± 5.79 MPa and 64.92 ± 0.75 MPa, respectively. Besides, the mechanisms of toughening, apatite formation, and cell interaction in CNT and rGO encapsulated PMMA have been studied. Results showed that the existence of CNT and rGO in BCs led to increase of MG63 osteoblast viability, and proliferation. However, rGO reinforced bone cement was more successful in supporting MG63 cell attachment compared to the CNT counterpart due to its wrinkled surface, which made a suitable substrate for cell adhesion. Based on the results, PMMA-HT/rGO can be a proper bone cement for the fixation of load-bearing implants.

Introduction

Acrylic bone cements have been mainly used as a cementing material for transferring the load between the bone and prosthetic implant in joint replacement surgeries (Pahlevanzadeh et al., 2018). This type of material offers many advantages like quick polymerization reaction, effortlessness in preparation and application, and fast patient recovery (Marrs et al., 2006). The failure rate after 16 years has been recorded as high as 67%, in patients younger than 45 years old (Marrs et al., 2006). Two reasons for the mentioned failures are inferior mechanical properties, and lack of bioactivity of PMMA (Pahlevanzadeh et al., 2019a). The acrylic BCs do not directly stick to the bone. The indirect surface adhesion increases the possibility of the formation of the gap between the bone/cement and cement/implant (Pahlevanzadeh et al., 2018, 2019a; Marrs et al., 2006), which can result in the loosening of the implant and can provide optimal sites for the colonization of bacteria (Cole et al., 2020). For improving the adhesion of cement to the bone, the approaches have mainly paid attention to using additional additives, particularly some bioactive ceramics like hydroxyapatite (Gonçalves et al., 2012), fluorapatite (Pahlevanzadeh et al., 2018), akermanite (Chen et al., 2015), baghdadite (Pahlevanzadeh et al., 2019b), and monticellite (Pahlevanzadeh et al., 2019a). Nevertheless, incorporating the additives can change the properties of the composite, particularly the mechanical properties, which are essential if the cement is applied for load-bearing usages (Cole et al., 2020; Yang et al., 2020). Investigations show that for having a bioactive BC to exhibit osteoconductivity after setting, the concentration of bioactive filler should be higher than 60 wt/wt.% (approximately 35 vol/vol%) (Tsukeoka et al., 2006).

Based on the previous research, hardystonite (Ca2ZnSi2O7), as a bioactive ceramic, has shown acceptable biological and mechanical properties. The mechanical characteristics of HT are close to that of natural bone, including Young's modulus (37 GPa), fracture toughness (1.24 MPa m1/2) and the bending strength (136 MPa) (Pahlevanzadeh et al., 2019b; Tsukeoka et al., 2006). Besides, in a physiological environment, HT has superior chemical stability compared to calcium silicates. HT has shown anti-bacterial and anti-inflammatory properties due to the release of Zn from its network (Pahlevanzadeh et al., 2020; Wu et al., 2005). Hence, HT has been utilized to achieve a bioactive cement in this study, but it led to the decline of mechanical properties, predictably. To deal with this problem, the incorporation of carbon-based materials (CBMs) such as graphene and its derivatives could be an effective method to compensate for the reduction of mechanical properties (Pahlevanzadeh et al., 2020; Wu et al., 2005; Abdallah et al., 2020).

In this respect, CNTs as a category of CBMs are rolled-up graphene sheet layers in a tubular structure (Abdallah et al., 2020). CNTs show unique chemical and physical properties, which are highly dependent on different manufacturing routes. As the chemical bonding of CNTs is based upon the sp2 orbital bond, they have the hardest and strongest material documented in terms of modulus of elasticity and tensile strength, respectively (Abdallah et al., 2020). Applications of graphene and its nanomaterials family, like GO and rGO, the same as many novel materials, offer various technological opportunities because of outstanding thermal, electrical, optical, and mechanical properties of them (Lee et al., 2015). The questions about short-term and long-term cytotoxicity of graphene-based materials have raised because of growing biomedical applications of these materials (Abdallah et al., 2020; Lee et al., 2015). In this regard, an essential factor is the quantity of attached oxygen functional groups to the surface in which for a higher C/O levels, flakes are less cytotoxic, which can be attributed to the partially rGO structures (Tadyszak et al., 2018). So, rGO was used in this study to improve the BCs' mechanical properties without sacrificing the biocompatibility. In recent years, both CNT (Halim et al., 2018; Qian et al., 2019) and rGO (Zhang and Gurunathan, 2016) have been utilized in various applications in the biomedical field, such as tissue engineering (Liu et al., 2020; Li et al., 2020; Prakash et al., 2020), drug delivery (Abdallah et al., 2020; Lu et al., 2020), and properties improvement of BCs (Gonçalves et al., 2012; Ormsby et al., 2010a, 2010b). The homogenous dispersion of graphene-based reinforcement into the polymeric matrix is essential for having an appropriate interfacial bonding between the reinforcement and matrix and resulting in an optimal enhancement in mechanical properties (Ormsby et al., 2010a). For example, Ormsby et al., 2010a, 2010b revealed that the most efficient method for producing PMMA containing CNT BCs is dispersing the MWCNT reinforcement in the liquid monomer ingredient utilizing ultrasonic disintegrating before its introduction into the polymer powder. Accordingly, they showed that acrylic BCs containing 0.1 to 0.25 wt% of MWCNT reinforcement resulted in a remarkable enhancement in both static and fatigue properties, while the levels of cytotoxic response were low (Ormsby et al., 2010a, 2010b).

Herein, we developed bioactive BC containing 60 wt% of HT, which was effective in achieving appropriate bioactivity and apatite-like layer formation on specimens' surfaces. Furthermore, we aimed to create well-dispersed CNT, and rGO reinforced bioactive cements by ultraviolet dispersing in MMA liquid. There are many studies (Pahlevanzadeh et al., 2018, 2019a; Marrs et al., 2006; Cole et al., 2020; Gonçalves et al., 2012) for improvement of PMMA based cements features; however, a few of them have investigated incorporating carbon-based materials in PMMA-based cements. In addition to the effect of CNT and rGO incorporation on the mechanical and cytotoxic properties of BC, comparing their effectiveness was examined in this study, which is scarcely studied before. The formation of the apatite-like layer, favorable compressive, tensile and bending strength, and high MG63 cell viability and proliferation demonstrated PMMA/HT/rGO BC could be an appropriate replacement for commercial PMMA.

Section snippets

Preparation of the BCs

The powders of calcium carbonate (CaCO3, Merck, 98% purity), zinc oxide (ZnO, Merck, 99% purity), and silicon dioxide (SiO2, Aldrich, 99% purity) were provided in order to the mechanochemical synthesis of HT. The MMA liquid monomer (containing MMA: 84.4%, butyl methacrylate: 13.2%, N–N dimethyl-p-toluidine: 2.4%, and hydroquinone: 20 ppm), and PMMA powder (containing PMMA: 87.7%, benzoyl peroxide: 2.4% and barium sulfate: 10% as radio-opaque filler) were purchased from Teknimed, France (CEMFIX1

Characterizations of HT

Fig. 1a depicts the XRD pattern of the HT after synthesis. As can be seen, only characteristic peaks of HT (XRD JCPDS data file No. 1219075–0916) were detected, and no impurities peak was observed. Hence, the process, including 20 h milling of the ingredients and raising the temperature to 900 °C, is sufficient for the synthesis of HT powder (Ormsby et al., 2010b). According to the Williamson–Hall method, the crystallite size of HT powder was measured equal to 85 ± 4 nm. The TEM images in the

Conclusion

In this research, the effects of two nanostructured carbon reinforcements (rGO and CNTs), when incorporated into the PMMA/HT bone cement have been compared on an extensive group of properties of the cements. Both CNT and rGO in PMMA-based BC display the capability to tailor their compressive, tensile, and bending strength of the cement. Nevertheless, for the rGO-reinforced bone cement, some mechanical properties were higher compared to the corresponding values for the non-reinforced cement.

Credit author statement

F. Pahlevanzadeh: Writing—original draft preparation, methodology, formal analysis; H.R. Bakhsheshi-Rad: Conceptualization, supervision, formal analysis, writing—review and editing; M. Kharaziha: Conceptualization, supervision, writing—review and editing; M. Kasiri-Asgarani: Conceptualization, writing—review and editing; M. Omidi: Conceptualization, writing—review and editing; M. Razzaghi: Conceptualization, writing—review and editing; A. F. Ismail: Conceptualization, supervision,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. The authors declare that the work described has not been published previously (except in the form of an abstract, a published lecture or academic thesis, see ‘Multiple, redundant or concurrent publication’ for more information), that it is not under consideration for publication elsewhere, that its publication is approved by

Acknowledgments

The authors would like to thank the Universiti Teknologi Malaysia (UTM) and Islamic Azad University, Najafabad and Norwegian University of Science and Technology for providing the facilities of this research.

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