DESIGN AND DEVELOPMENT OF CONSTRAINED LINER FOR PREVENTING HIP JOINT DISLOCATION USING POLYMERIC MATERIALS

Most Materials used for orthopedic implants in Total Hip Replacement (THR) surgeries are: Titanium based alloys, Cobalt Chrome based alloys and Ultra High Molecular Weight Polyethylene (UHMWPE). However, implants made of these materials increase the risk of dislocation due to their design and to wear of materials (third body particles), restrict the patient`s hip range of motion (ROM). A new polymeric Constrained Liner, which provide high lever out resisting moment to dislocations and full ROM, was developed.

Block copolymer made from blocks of Polyurethane and Polycarbonate was selected as the material for the device (DSM Bionate II). The Bionate family has been used as materials for orthopedic implants for many years that has the needed characteristics for device constrain liner i.e. large elasticity ranges and high strength and is approved for use by the FDA. In this project we investigate the influence of different material hardness (material types A80, A90 and D55) on the performance of different constrain liners designs.

The project goals:

• Characterization of the product geometry;
• Preforming stress simulation to evaluate different product designs;
• Manufacturing product prototypes;
• Testing the prototypes using Lever-out and Pull-out tests (dynamic and static) and validating the theoretical calculations;

A computational Force model that simulates the forces that are applied on an implanted constrained liner during different hip movements was developed. Since the constrain liner is made of polymeric elastomeric material, which has a non-linear Young’s Modulus, physical properties such as force impact and force magnitude, have great influence on the material’s stress distribution. These models and others finite element calculations were used to test these parameters on the selected materials and designs.