Strategy to improve the mechanical properties of bioabsorbable materials based on chitosan for orthopedic fixation applications

Bioabsorbable polymeric fixation devices have been used as an alternative to metallic implants in orthopedics, preventing the stress shielding effect and avoiding a second surgery for implant removal. However, several problems are still associated with current bioabsorbable implants, including the limited mechanical stiffness and strength, and the adverse tissue reactions generated. To minimize or even eliminate the problems associated with these implants, strategies have been developed to synthesize new implant materials based on chitosan. To overcome the brittle behavior of most 3D chitosan-based structures, glycerol and sorbitol were blended to chitosan and the effect of these plasticizers in the produced specimens was analyzed by flexural tests, Berkovich tests, scanning electron microscopy (SEM) and micro-CT analyzes. The improvement of the mechanical properties was also tested by adding ceramics, namely hydroxyapatite powder and biphasic mixtures of hydroxyapatite (HA) and beta-tricalcium phosphate (β-TCP). In the plasticizers group, the best combination of the measured properties was obtained for chitosan with 10% glycerol (flexural strength of 53.8 MPa and indentation hardness of 19.4 kgf/mm2), while in the ceramics group the best mechanical behavior was obtained for chitosan with 10% HA+β-TCP powder (flexural strength of 67.5 MPa and indentation hardness 28.2 kgf/mm2). All the tested material compositions were dense and homogeneous, fundamental condition for a good implant performance. These are encouraging results, which support the continued development of chitosan-based materials for orthopedic fixation applications.