| The performance and reliability of cemented femoral components in total hip replacements are strongly influenced by the interfacial adhesion and resistance to debonding of the bone/PMMA and prosthetic/PMMA interfaces. Progressive failure of either of these typically weak interfaces, followed by extensive cracking of the cement mantle under normal physiological loads, has been implicated in the loss of structural integrity of cemented components. Recently developed interface fracture mechanics techniques provide an appropriate mechanics framework from which debonding characteristics may be quantitatively studied, Using interface fracture mechanics, debonding of the constituent interfaces can be quantified in terms of the strain energy release rate, G (J/m2), which represents the macroscopic energy required to separate the interface. In addition, subcritical debonding characteristics associated with mechanisms of cyclic fatigue crack growth are particularly relevant considering that these systems will experience over 1,000,000 physiological loading cycles per year. At these interfaces, as in other bulk polymer material systems, crack growth under fatigue loading conditions is expected to occur at stresses well below those required for catastrophic failure. To date, little information about the subcritical debond-growth behavior at or near these interfaces is available. Therefore, accurate predictions of the long-term reliability of these interfaces have not been possible.;Accordingly, the focus of this work was to provide a quantitative characterization of the interface adhesion and the subcritical debond behavior of the prosthetic/PMMA interface. Adhesion was determined from the debond fracture resistance behavior (R-curve) measured under monotonic loading and reported in terms of the energy required to initiate debonding, Go, and the steady state interfacial fracture energy, Gss. Subcritical debond behavior was determined from the fatigue debond growth-rate curve behavior measured under cyclic loads and reported in terms of debond growth per cycle, da/dN, as a function of applied debond driving energy, ΔG. Mechanisms of failure were quantitatively identified and related to salient variables such as prosthetic surface morphology, mixed mode loading conditions, cement layer thickness, interfacial chemistry and environmental factors. Implications for progressive debonding under physiological loads in vivo and design considerations for engineering interfaces to promote adhesion and fatigue resistance are discussed. |
