Functionality of porous titanium improved by biopolymer filling

Metallic biomaterials with a higher Young's modulus than that of a bone adversely affect bone healing and remodeling. Therefore, it is important to develop the metallic biomaterials having a low Young's modulus. Porous materials are advantageous from this viewpoint because the Young's modulus decreases with increasing porosity. However, with an increase in porosity, the other mechanical properties start deteriorating simultaneously. In comparison with metallic biomaterials, polymers exhibit lower Young's moduli; therefore, a polymer filling is a possible option to improve the mechanical properties of porous materials by preventing the stress concentration at the pores without increasing the Young's modulus. Furthermore, certain polymers exhibit intrinsic biofunctionalities. Thus, a polymer filling is expected to prevent an increase in the Young's modulus and impart biofunctionalities to porous materials without deteriorating their mechanical properties. In this study, porous pure titanium (pTi) with a porosity of 22%-50% and filled with a medical polymer (polymethylmethacrylate: PMMA) (pTi/PMMMA) was firstly fabricated. The effects of the PMMA filling on the tensile strength of pTi were then investigated. However, the deterioration of mechanical properties was not satisfactorily prevented because of the poor interfacial adhesiveness between the titanium particles and the medical polymer. Therefore, in the present study, silane-coupling treatment was employed in order to improve the interfacial adhesiveness, and silane-coupling-treated (Si-treated) pTi filled with PMMA (Si-treated pTi/PMMA) was fabricated. The effect of the silane-coupling treatment on the mechanical properties of pTi/PMMA was investigated. It is found that the PMMA filling improves the tensile strength of pTi that has a porosity of over 40%. The tensile strengths of Si-treated pTi/PMMA are greater than those of pTi and pTi/PMMA. In the fractographs of pTi/PMMA obtained after the tensile test, the detachment of titanium particles from PMMA is observed; this occurs because of poor interfacial adhesiveness between titanium particles and PMMA. However, in the case of Si-treated pTi/PMMA, the interfacial adhesiveness between titanium particles and PMMA is improved by the silane-coupling treatment. This leads to the dispersion of the stress concentration at the necks between particles, resulting in an improvement in the tensile strength of pTi. On the other hand, the PMMA filling hardly affects the Young's modulus of pTi because the Young's modulus of PMMA is lower than that of pTi.