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

Project Details


Background: Many combat- and blast-related amputees have difficulty with prosthesis wear. This affects functional mobility and often means the difference between wheelchair dependence and independent ambulation. Difficulties are due, in large part, to the manner in which prostheses attach to the body. Modern prostheses require a socket that transfers the ground reactive force to the patient's skin, soft tissues, and muscle before loading the appendicular skeleton. The high rate of wound complications observed in blast wounds also adds to the problem. Heterotopic ossification (HO), the formation of lamellar bone in soft tissues, occurs in the vast majority of combat amputees, causes ulcerations and pain, and limits function. Additionally, many amputees have very short residual limbs, which also limits their ability to don a prosthesis. Osseointegrated prostheses eliminate the need for traditional sockets and stand to benefit patients who have difficulty with prosthesis wear. In addition, by attaching the prosthesis directly to the bone, amputees regain proprioception, which improves balance and helps avoid falls. Furthermore, by using the Compress implant, which transmits compression stresses directly to the bone, we reduce fracture risk by inducing bone hypertrophy, thereby eliminating stress shielding, common in stem-based implants, and reversing osteopenia that plagues lower extremity amputees. As such, this project addresses multiple Focus Areas, including:(1) Improving the functional utility of assistive devices related to the human-device interface (prostheses, orthoses, and other assistive devices).(2) Improving the ability to predict, identify and reduce secondary health effects that develop after severe primary neuromusculoskeletal injury.(a) Intervention strategies to diminish falls and decrease fracture risk.(b) Strategies to improve treatment and rehabilitation of heterotopic ossification(3) Optimizing treatment strategies and sequence of progression throughout the rehabilitation process following severe extremity trauma.Though the means by which implants attach to the bone may vary, all current osseointegrated devices must pass through the skin. This presents unique challenges, as deep infection remains the most common and devastating complication. In most cases, the treatment of these infections requires implant removal, thorough debridement, and loss of residual bone length. Importantly, the innovations contained within this proposal focus on the skin-implant interface. As such, this work may benefit not only the implant being used for this work, but perhaps all future osseointegration devices.Objective/Hypothesis: Given that osseointegration depends heavily on the skin-implant interface, we hypothesize that the transcutaneous portion of an osseointegrated implant can be optimized, or eliminated entirely, using existing tissue engineering methods.Specific Aims: Aim 1: Investigate strategies for improving the transdermal interface in osseointegrated devices -- Development of a biologic collar. Current implant designs focus on tethering the skin and minimizing motion at the skin-implant interface. The biologic collar is designed to accommodate motion. Bone and extracellular matrix (ECM) will be printed directly onto a porous titanium backbone at the transdermal portion of the implant using existing 3D bioprinting technology. Histologic, molecular, and mechanical testing will be assessed in five implants and compared to five all-metal devices after implantation in our existing osseointegration model using Yorkshire swine.Aim 2: Investigate strategies for eliminating the transdermal interface -- Development of a weight-bearing biologic post. It is possible that the transdermal portion of an osseointegration implant may be eliminated entirely. Using current tissue engineering and bioprinting technology, we will coat five weight-bearing titanium implants with living bone, ECM, fat, and glabrous skin, then implant them using our osseointegration model. Histologic, molecular, and mechanical testing will be performed in a similar fashion to that described in Aim 1.Study Design: This project involves in vitro 3D bioprinting onto a titanium matrix, maturation of tissues in a bioreactor, then implanting in an in vivo animal model.Military Benefit: This work will develop new treatment options for combat casualties who have difficulty with prosthesis wear due to HO and/or efforts to preserve residual limb length such as split thickness skin grafts. Still more patients have very short residual limbs, which renders them ineffective for use with traditional socket-based prostheses. The inability to successfully don a prosthesis can mean the difference between functional independence and wheelchair dependency. The proposed osseointegration technology stands to dramatically improve the lives of this subset of combat amputees, while remaining applicable to all osseointegrated implants currently in development.

Effective start/end date1/03/1528/02/18


  • Congressionally Directed Medical Research Programs: $1,240,000.00


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