INTERFACIAL FRICTIONAL BEHAVIOR: CANCELLOUS BONE, CORTICAL BONE, AND A NOVEL POROUS TANTALUM BIOMATERIAL

Abstract

A laboratory test was undertaken to evaluate the interfacial frictional characteristics of cortical and cancellous bone, as well as a novel porous tantalum biomaterial (Hedrocel®, Implex Corp.). Three sets of tests were conducted to measure the friction coefficients of (1) bovine cancellous bone against bovine cortical bone; (2) net-shape formed porous tantalum against bovine cortical and cancellous bone; and (3) electron-discharge-machine formed (EDM'd) porous tantalum against bovine cortical and cancellous bone. The bovine cortical bone was tested in three conditions: periosteum-intact, periosteum-denuded and surface-flattened. An inclined plane apparatus was used to determine the coefficients of friction. By gradually increasing the substrate tilt, the angle of slippage was determined, and the friction coefficient was calculated.The average friction coefficients of cancellous bone against periosteum-intact, periosteum-denuded and surface-flattened cortical bone were 0.91±0.14, 0.61± 0.07 and 0.58±0.06, respectively. Porous tantalum specimens prepared from a preshaped vitreous carbon skeleton, when tested against periosteum-intact, periosteum-denuded and surface-flattened cortical bone, and against cancellous bone, had average friction coefficients of 1.10±0.18, 0.82±0.15, 0.86±0.11, and 0.98±0.17, respectively. Porous tantalum specimens prepared by electron-discharge machining, when tested against periosteum-intact cortical bone, periosteum-denuded cortical bone and cancellous bone, had average friction coefficients of 1.75±0.33, 0.74±0.07, and 0.88±0.09, respectively. The friction coefficient of the porous tantalum material was very high in comparison to natural bone autografts or allografts, and to conventional orthopedic implant coating materials (sintered beads and wire mesh). Other factors being equal, this high-friction characteristic would be expected to translate into higher initial stability of a porous tantalum implant, as compared to natural bone grafts.