Biological and nano-indentation properties of polybenzoxazine-based composites reinforced with zirconia particles as a novel biomaterial

Introduction The biological and mechanical properties of substances are relevant to their application as biomaterials and there are many efforts to enhance biocompatibility and mechanical properties of bio-medical materials. Objectives In this study, to achieve a low rate of shrinkage during polymerization, good mechanical properties, and excellent biocompatibility, benzoxazine based composites were synthesized. Methods Benzoxazine monomer was synthesized using a solventless method. FTIR and DSC analysis were carried out to determine the appropriate polymerization temperature. The low viscosity of the benzoxazine monomer at 70°C attract us to use in situ polymerization after high speed ball milling of the benzoxazine and it mixture with different weight fractions of zirconia particles. Dispersion and adhesion between the ceramic and polymer components were evaluate by SEM. To evaluate the biological properties and toxicity of the polybenzoxazine-based composite samples reinforced with zirconia particles, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay was conducted. The micromechanical properties of each composite were evaluated by more than 20 nanoindentation tests and 3 nanoscratching tests. Surface topography of scratched regions was investigated using Atomic Force Microscopy. Shrinkage was simulated by Materials Studio software. Results SEM images showed good dispersion and adhesion between the ceramic and polymer components. Biocompatibility assay showed excellent in vitro biocompatibility. Nano-indentation force-displacement curves showed matrix, reinforcement and interphase regions in specimens and excellent homogeneity in mechanical properties. The nanoindentation results showed that the addition of zirconia particles to the polybenzoxazine matrix increased the modulus and hardness of the neat polybenzoxazine; however, by adding more than an optimum level of reinforcement particles, the mechanical properties decreased due to the agglomeration of reinforcement particles and weak interphase that cause inappropriate load transferring between matrix and reinforcement particles. Results of nano-scratching tests showed effects of zirconia particles as reinforcement on the coeffiecient of friction of the synthesized composites. Shrinkage simulation showed a low rate of shrinkage for polybenzoxazine in comparison with other low shrinkage polymers, such as Bis-GMA. Conclusion Polybenzoxazine based composites that reinforced with an optimum amount of zirconia particles (60% wt micro and 10% wt nano-particles) could be used as a novel biomaterial duo to its excellent biocompatibility, good mechanical properties, appropriate viscosity and low rate of polymeization shrinkage.