Composite Materials for Use in Orthopaedic Applications: Fracture Behavior of Acrylic Bone Cement Reinforced with High Toughness Organic Fibers

Abstract

A study of the fracture behavior of poly(methyl methacrylate) bone cement reinforced with short ultra-high strength polyethylene fibers is presented. The flexural strength and modulus are apparently not improved by the incorporation of polyethylene fibers in the PMMA cement, probably because of the presence of voids, the poor mixing practice and the weakness of the fiber/matrix inter facial bond. Linear elastic and nonlinear elastic fracture mechanics techniques are used to assess the ultimate behavior of the unreinforced and reinforced cements. Both techniques yield similar trends for the fracture toughness, indicating that a significant reinforcing effect is obtained at fiber content as low as 1% by weight, but beyond that concentration a plateau value is reached and the fracture toughness becomes insensitive to fiber content. The present polyethylene/PMMA composite presents several advantages as compared to other composite cements, but overall the mechanical performance of this system resembles that of Kevlar 29/PMMA cement, with a few differences. Scanning electron microscopy reveals characteristic m icromechan isms of energy absorption in PE/ PMMA bone cement, including plastic bending and kinking of the PE fibers, pull-out and possibly some splitting. More fundamental modeling treatments are needed to obtain a quantitative estimate of such m icromechan isms, within the framework of the fracture behavior of short fiber composites with weakly bonded constituents as well as to optimize the various mechanical properties with respect to structural parameters and cement preparation techniques.