No abstract

No abstract

More than 285,000 total hip replacement surgeries are performed in the US each year. Most prosthetic hip joints consist of a cobalt-chromium (CoCr) femoral head that articulates with a polyethylene acetabular component, lubricated with synovial fluid. The statistical survivorship of these metal-on-polyethylene prosthetic hip joints declines significantly after 10 to 15 years of use, primarily as a result of polyethylene wear and wear debris incited disease. The current engineering paradigm to increase the longevity of prosthetic hip joints is to improve the mechanical properties of the polyethylene component, and to manufacture ultra-smooth articulating surfaces. In contrast, we show that adding a patterned microtexture to the ultra-smooth CoCr femoral head reduces friction when articulating with the polyethylene acetabular liner. The microtexture increases the load-carrying capacity and the thickness of the joint lubricant film, which reduces contact between the articulating surfaces. As a result, friction and wear is reduced. We have used a lubrication model to design the geometry of the patterned microtexture, and experimentally demonstrate reduced friction for the microtextured compared to conventional smooth surrogate prosthetic hip joints.

We numerically investigate the influence of interfacial deformations on the drag force exerted on a particle straddling a fluid interface. We perform finite element simulations of the two-phase flow system in a bounded two-dimensional geometry.The fluid interface is modeled with a phase-field method which is coupled to the Navier-Stokes equations to solve for the flow dynamics. The interfacial deformations are caused by the buoyant weight of the particle, which results in curved menisci.We compute drag coefficients as a function of the three-phase contact angle, the viscosity ratio of the two fluids, and the particle density. Our results show that, for some parameter values, large drag forces are not necessarily correlated with large interfacial distortions and that a lower drag may actually be achieved with non-flat interfaces rather than with unperturbed ones.

It has long been known that articular cartilage exhibits a surface microtexture with shallow indentations. By contrast, prosthetic joints consist of ultra-smooth bearing surfaces, the longevity of which does not reach that of natural cartilage. We show that adding a microtexture to the smooth femoral component of a prosthetic knee joint reduces friction by increasing the lubricant film thickness between the bearing surfaces of the knee. We have implemented an elastohydrodynamic lubrication model to optimize the geometry of the microtexture, while taking into account the deformation of the polyethylene tibial insert. We have manufactured several microtexture designs on a surrogate femoral component, and experimentally demonstrate that the microtexture reduces friction between the surrogate femoral component and tibial insert.