An Investigation on the Polymer Composite Medical Device - External Fixator

Abstract

Primary impetus for the development of composite materials for medical usage came from orthopedic implant application. In case of metal alloys stiffness mismatch causes stress shielding in applications such as bone plates, total hip replacement, and total knee replacement. Moreover, the metal alloys and ceramics are radio opaque, and in some cases they result in undesirable artifacts in X-ray radiography. In the case of polymer composite materials the radio transparency can be adjusted by adding contrast medium to the polymer. More over the polymer composite materials are fully compatible with the modern diagnostic methods such as computed tomography (CT) and magnetic resonance imaging (MRI) as they are non-magnetic. The current study reports the development of a radiolucent fiber reinforced polymer composite material for a biomedical device, Ilizarov external fixator. Material fabrication and characterization are described. Quantitative X-ray radiographic analysis was carried out to choose the best from the probable materials. The Finite Element Method (FEM) was employed to determine the worst possible in service loading condition, and the ring dimensions were modified accordingly. Half ring prototypes were produced using two types of composite materials: knitted aramid fiber fabric reinforced epoxy and random short carbon (RSC) fiber reinforced epoxy. The in-plane compressive strength and axial stiffness of the complete frame were measured according to ASTM specifications. The performance was evaluated and compared to an existing system in simulated in-service conditions.