Superelastic Orthopedic Implant Coatings

Contemporary orthopedic hip implants are static (fixed in dimension), thereby leading to persistent implant loosening problems that have led to annual double digit implant failure rates for the past decade.   Today’s hip implants are inserted between the lateral and medial cortices of the femoral canal.  Upon insertion, the tapered portion of the implant stem creates a wedge effect in the medullary canal, leaving large gaps between the implant and bone tissue.   These gaps limit the opportunity for implant-to-bone contact, thereby limiting osseointegration (bone growth). Moreover, wear particle debris due to implant use accumulates in these gaps, causing osteolysis and aseptic implant loosening.    In contrast, orthopedic hip implants that utilize a superelastic Nitinol spacer fabric (NSF) implant coating are dynamic and “space filling” in nature.  NSF is a multi-layer, porous construct  engineered to expand in vivo to close the gaps at the implant and bone interface.  By applying controlled, chronic, pressure to the bone tissue, NSF stimulates bone remodeling and enhances osseointegration to improve longer-term implant apposition.   NSF is composed of two separate fabric faces knit independently and connected by separate, vertical, filler spacer fibers.  The three layers have different functions: the top (outermost) layer is engineered for optimal bone in-growth; the middle, vertical, fiber layer for elasticity; and the bottom layer for brazing to the Titanium implant.  The three-ply structure is porous and crush resistant.  NSF can be 95% porous, with pores ranging from 300-500 microns to allow for optimal bone in-growth with a 1.6 GPa modulus of elasticity to closely match the trabecular bone.    NSF represents the first “dynamic” orthopedic coating which will provide performance advantages by addressing persistent implant loosening problems. NSF will offer a clear market differentiation from the various static coatings on the market today.