Apatite-Based Coating of Percutaneous Osseointegrated Implants for Improving Epidermal Integration at the Skin-Device Interface

Percutaneous osseointegrated prosthetic docking devices offer an alternative to traditional socket suspension systems. These devices consist of a titanium endoprosthesis within the medullary canal and a percutaneous post traversing the skin barrier, providing a stable connection platform for docking an artificial limb. They are reported to offer faster donning and doffing, obviate “socket pain,” and extend wear time. Because epithelium does not recognize titanium as a biologically active material, these devices create an open wound that is prone to infection at the implant exit site (“stoma”). Persistent healing cascades in this stomal region are thought to result from both foreign body responses and chronic wound healing phenomena. A seal between the epidermis and the implant surface is important to minimize infection risk. However, there are no effective clinical solutions to address this challenge. Understanding established knowledge of gingival mucosal integration with the enamel tooth surface through “hemidesmosomes (HD),” we hypothesized that bioactive implant surfaces could stimulate specific epithelial cellular responses to enhance surface integration. To test this, implant surfaces coated with fluorapatite (FA)—the primary component of enamel—were evaluated for their ability to promote epidermal hemidesmosome expression, facilitate integration with the implant surface, and limit epithelial down-growth. Using two in vivo models, we investigated the ability of FA-coated Ti surfaces to enhance wound healing around a percutaneous device. First, in vitro studies were undertaken. Second, coated and uncoated percutaneous implants were examined over four weeks in a non-load-bearing rat back model. The histological analysis measured epithelial downgrowth and granulation tissue area, while protein and gene expression were assessed using immunohistochemistry (IHC) and RT-qPCR, respectively. Third, a 12-week amputation and implantation load-bearing sheep model is in process to confirm these findings. The histological analysis will quantify areas of epithelial downgrowth and granulation tissue for statistical comparison. While the data from the cell-culture study showed HD over-expression, rat studies demonstrated that FA-coated surfaces significantly enhanced stomal wound healing and improved skin marsupialization by reducing downgrowth. FA-coated implants showed the statistically significant least downgrowth compared titanium devices. Gene expression analysis of the granulation tissue indicated progression toward healing, and IHC confirmed these findings. Data analysis from the load-bearing sheep model is ongoing; however, preliminary histological results appear to align with the conclusions of the rat studies. The rat back model supported our hypothesis that FA-coated surfaces promote wound healing at the stoma of a percutaneous device.