Regenerative Approaches to Support Osseointegration Implants: Optimizing and Eliminating the Skin-Implant Interface

This work will develop new treatment options for combat- and blast-related amputees. Current prosthetics rely on the soft tissues to support the forces associated with prosthesis wear. For many reasons, combat- and blast-related amputees have difficulty wearing a traditional prosthesis. Heterotopic ossification (bone forming in the muscles), split thickness skin grafts used to help preserve limb length, and chronic pain can all serve as barriers in this regard. Still more amputees have very short residual bones, which cannot adequately control a traditional socket-based prosthesis. The inability to successfully wear a prosthesis can mean the difference between functional independence and wheelchair dependency. Osseointegration technology stands to dramatically improve the lives of this subset of combat- and blast-related amputees.

Unfortunately, all current osseointegrated solutions must pass through the skin. This 'transdermal' interface presents unique challenges, since bacteria from the outside world may migrate deep inside the body causing a severe infection. This is the most feared complication of osseointegration and usually requires additional surgeries, removal of the implant, and the loss of precious bone and soft tissues. However, the unique challenges associated with the 'transdermal' interface is precisely why we chose to focus our efforts on optimizing it or eliminating it entirely.

Current osseointegration designs rely on stabilizing the skin onto the implant. In this fashion, normal motion at the skin interface is minimized, but never eliminated. Our first aim is to design a biologic collar around the implant to accommodate normal motion at the transdermal interface. We plan to do this using existing tissue engineering and bioprinting technology, with which we have considerable expertise. The mechanical features of this living implant will then be tested in our existing animal model for osseointegration. The second aim of this proposal is designed to eliminate the transdermal portion of the prosthesis entirely, thereby minimizing the risk of deep infection. Using similar, existing, tissue engineering and bioprinting technology, we will coat a weight-bearing titanium implant with living bone, soft tissue and skin, then implant it in our animal model. We see this as the first step to coating a functional prosthesis or rudimentary artificial limb with living tissue.

It is possible that the innovations contained within this proposal will benefit not only the implant designed for this study, but also all future osseointegration devices.