Mechanical and morphological characterization of polyamide bone analogues

This research was an investigation for finding a suitable materials to model the mechanical properties of human bone. Polymer/ceramic particulate filled composites were used to achieve these objectives. The resin used as a matrix was nylon 6 and the particulate fillers were calcium and phosphate salts, CaCl₂ and hydroxyapatite (Ca₅(PO₄)₃OH). An analysis of the thermal and morphological properties was performed and these findings were related to the results of the mechanical data. Blend compositions ranged from a weight percent of 0.5 to 10% salt in the polymer matrix. Most analysis was performed on blends created by a solution mixing method, which facilitated interaction of the two phases. The results from the mechanical data were fitted to theoretical predictions for particulate composites. The theories used included the Sato-Furukawa prediction for reduced modulus, (E/E₁), the Kerner model for ultimate tensile stress, and the Nielsen prediction for breaking strain. All blend samples exhibited a reduction in modulus from that of the pure material. The hydroxyapatite blends agreed well with the Sato-Furukawa prediction for this reduced modulus as a result of cavitation. CaCl₂ blends exhibited an increase in tensile strength, which was contrary to that of the hydroxyapatite samples. Thermal properties showed that the 5.0% and 6.0% CaCl₂ blends exhibited little, or no crystallization behavior. Comparisons of the 10.0% hydroxyapatite to that of reported values for trabecular bone agree favorably in the areas of tensile strength, strain to break, and to a lesser degree, elastic modulus. From these findings and previous research the composition of a full bone analogue is proposed and discussed.