Medical applications for composite materials
Fibre-reinforced polymer composites (FRPs) are finding more applications in the medical sector because of their light-weight, high-stiffness characteristics and bio-compatibility. External components such as artificial limbs use the high specific properties, fatigue resistance and flexibility of manufacture of composites to advantage. The chemical inertness of carbon fibre has led to a number of surgical applications where the material is used in conjunction or instead of metallic or polymeric materials.
Early designs of artificial limbs employed press-moulded carbon-fibre composites as the main load-bearing structure. More recent developments incorporate a wider use of carbon-fibre to include load-carrying links in the joint mechanisms, foot keels with sprung energy return, and hybrid designs incorporating elastomers to dampen shock loads.
The behaviour of artificial joints, which conventionally consist of an ultra-high molecular weight polyethylene, UHMWPE, component articulating against a polished steel part can be improved by enhancing the wear characteristics of the polymer. The UHMWPE can be reinforced by a random distribution of short (~3 mm) carbon fibres to provide the desired. tribological properties.
Carbon composites are being implanted into cartilage to promote biological resurfacing of damaged areas. The open weave structure of the material promotes cell growth along and between individual fibres ultimately resulting in a suitable repair.
Carbon fibre tows, either used individually or in plaits, are also being employed in the repair of damaged ligament. Loops of material are passed through holes drilled in the adjacent bone structures and then their length adjusted to achieve the correct tension for the particular patient.
The mechanical properties of bone repair materials, often a self-curing acrylic, can be enhanced by the addition of carbon fibres. Tensile, compressive and shear strengths as well as creep and fatigue performance are all improved and this could lead to wider clinical use of the material.