Thermal and mechanical behavior of ultra-high molecular weight polyethylene/collagen blends

Bone defects or diseases significantly affect quality of life, thus the development of materials with improved performance that can be used as bone substitutes is increasingly studied. As an alternative, ultra-high molecular weight polyethylene (UHMWPE) has been employed for orthopedic applications since it combines high wear resistance, high impact resistance and low friction coefficient. However, it is a bioinert material and difficult to process. In the present work, the addition of collagen (hydrolyzed or type II), one of the constituents of natural bone, to UHMWPE was studied aiming to improve its processability and possibly its biocompatibility. The blends were prepared by compression and twin-screw extrusion. The results show that addition of higher amounts of both collagens to UHMWPE reduced the degree of crystallinity. However, crystallization and melting temperatures were not affected. The thermogravimetric analysis exhibited two thermal events correlated to the degradation of collagens (Tmax~300 °C) and of UHMWPE (Tmax~480 °C), corroborating the FTIR analysis that presented bands corresponding to these materials. The extrusion process promoted a better dispersion of the collagens, especially the hydrolyzed one. In addition, the obtained materials presented better mechanical properties when extruded. Torque reduction during extrusion showed that hydrolyzed collagen aid processing, even more than collagen due to its smaller molecular weight.