Precoating of ultrahigh molecular weight polyethylene with polymethylmethacrylate: interfacial strength.

Abstract

Fixation of polymeric implants, especially an ultrahigh molecular weight polyethylene (UHMWPE) acetabular cup, to a host bone site has been a challenge since its first conception from the Charnley low friction total hip arthroplasty. Destabilization of the acetabular cup, similar to the well-documented cases of femoral stems, is caused mainly by aseptic loosening; the mobile loosened particles further contribute to the progression of aseptic loosening. Although the obvious fixation problems lie in the bone-bone cement interface, little work has been done to reduce the loosening by improving the acetabular components as a whole in cemented procedures. Most of the grooved outer surface, external fixation devices, and metal backings have been introduced to avoid problematic fixation of the cup to bone cement; nevertheless, the designs themselves to some degree became the source of the loosening problems. One possible way to improve the adhesion of acrylic bone cement to the UHMWPE acetabular cup is precoating the surface with polymethylmethacrylate (PMMA). This study successfully precoated the UHMWPE surface with PMMA, showing good chemical and mechanical stability, and suggests the optimal conditions of variables involved in the newly developed precoating process. The highest interfacial tensile strength was 11.51 +/- 0.65 MPa, which is stronger than those of UHMWPE and metal in metal-backed cups (6.3 MPa) and bone-bone cement (8.5 MPa). Further chemical analysis and mechanical testing are in progress, yet the present result of the mechanical tensile strength test showed that the precoating process for the UHMWPE surface could be a viable means toward stable fixation of the polymeric implants by using PMMA bone cement.