Novel, injection molded all-polyethylene composites for potential biomedical implant applications

This study aimed to create a self-reinforced composite material that can be processed by injection molding and other standard thermoplastic processing techniques and can be potentionally used as implant material. Self-reinforcement in biomaterials is desirable because it does not compromise biocompatibility and improves biofunctionality through improved mechanical performance. Self-reinforced composites can be currently processed by specialized, expensive and unproductive methods; hence we aimed to create a simpler processing alternative that works with biocompatible materials. We combined a high-density polyethylene matrix with high-performance polyethylene (Dyneema®) fibers. Before making the composite structure, the fibers were cross-linked by gamma irradiation to prevent their melting and maintain their structural integrity. The cross-linked fibers withstood the compounding by twin-screw extrusion and the subsequent injection molding. The effect of the irradiation dose on the processability, crystallinity, morphology, mechanical performance and cytotoxicity was investigated. We found that adding 20 m% of 200 kGy irradiated Dyneema® fibers increased the tensile modulus by 22.0%, the tensile strength by 71.1%, while both the composite and its constituents were all found to be biocompatible. The 41.1 MPa tensile strength, the 1.62 GPa tensile modulus, and the 64 Shore D hardness is quite similar to those of ultra-high molecular weight polyethylene, which is widely used in implants. Still, the material introduced in this paper shows no issues with the melt flow characteristics. These achievements are similar to other self-reinforcing methods, but the manufacturing method presented here can be economically realized on widely available processing technologies and machines.