HYDROGELS AS AN INTERFACE BETWEEN BONE AND AN IMPLANT

The use of fully hydrated hydrogels in the body has been well establis hed. The forces a hydrogel generates on swelling when it is placed in a constrained space were investigated with a view to providing a mecha nism for fixing a prosthesis in the intramedullary cavity. A cross-lin ked poly(2-hydroxyethyl methacrylate) [p(HEMA)] hydrogel was investiga ted as a potential material. In vitro mechanical tests were carried ou t to determine the stresses generated in the p(HEMA) when it was place d in water and not allowed to swell. Pull out loads of up to 375 N ind icated that the system could be used successfully in vivo. Consequentl y, the material was placed intraosseously at two sites in a rabbit ani mal model, in the mid-shaft (diaphysis) and the lower end (metaphysis) of the femur. Histological examination showed there was no adverse bo ne response; bone was growing from the endosteal surface up to and int o the hydrogel in the diaphyseal implants and surrounded the hydrogel in the metaphysis. As a result of the shape and size variations in the rabbit femur, in vivo mechanical tests were found to give lower value s than those obtained in vitro.