(B-62) Interleukins, Keratins, and Homeobox genes are differentially expressed around Keratin-Coated Percutaneous Devices

Introduction:: Percutaneous devices are routinely used to treat a plethora of medical conditions. These devices, which link the intra and extracorporeal regions of the body, require a biologically stable skin-device interface to ensure long-term success. Most attempts to improve this interface focus primarily on device surface modifications such as physical topography or biomimetic coatings. Although some of these strategies have produced minor improvements in terms of the skin-device integration and inhibiting epithelial downgrowth, an effective solution to a stable interface is still lacking. In the current study, we used RNA sequencing to investigate the molecular pathways associated with healing cascades around implanted devices coated with keratin nanomaterials. We hypothesized that the addition of keratin-derived coatings to titanium devices, representing a fingernail-skin interface, could improve soft-tissue integration/attachment at the skin-device interface.


Materials and Methods:: Percutaneous devices were made of titanium alloy (Ti6AL4V) and consisted of a percutaneous post and a subdermal fixation surface. Half of the devices were then coated with a 1mm thick, commercially pure titanium, porous-textured coating on the subdermal fixation surface and lower portions of the post. Subsets of these smooth- and porous-textured devices were then further coated with 2 different types of keratin-nanomaterial coating, keratose (gKOS) or keratiene (iKTN). These percutaneous devices were then implanted in Yucatan miniature pigs under the skin on either side of the dorsal midline. Each pig received 6 devices; three smooth-textured devices (1 uncoated control, 1 gKOS-coated) and 1 iKTN-coated, and three porous-textured devices (1 uncoated control, 1 gKOS-coated and 1 iKTN-coated). Each animal was assigned to one of three groups based on time from surgery (n = 6/group) and sacrificed at either 4 weeks (Group 1), 8 weeks (Group 2), or 16 weeks (Group 3) following implantation. Thin tissue slices were collected from the device interface for immunohistochemical analyses and RNA-sequencing. The remaining tissue was embedded in poly(methyl methacrylate) (PMMA) for histological analyses. The DESeq2 software package was used to fit a generalized linear model to the RNA sequencing data to identify statistically significant differentially expressed genes. T-tests were used to test for significance for the remaining continuous variables.


Results, Conclusions, and Discussions:: Significant differences in granulation tissue area, epidermal downgrowth, capsule thickness and gene expression were observed based on the type of texture/coating applied to the implanted percutaneous devices. Significantly less granulation tissue area was observed in porous gKOS devices compared to their porous-textured control in Group 3 (16 weeks). Most changes in epidermal downgrowth were observed at 16 weeks, where porous-textured devices exhibited significantly less epidermal downgrowth than smooth-textured devices (Figure 1). A similar trend was observed for capsular thickness at 8 and 16 weeks regardless of the keratin coating applied (Figure 2). A differential expression analysis between smooth and porous-textured devices revealed 540, 37, and 442 significant genes for Groups 1, 2, and 3. In Group 1 (4 weeks), multiple keratin, serpin, solute carrier, and interleukin genes were significantly upregulated. Many of these genes likely play a role in the initial stages of wound healing including KRT6A (5-fold increase), which has been observed in previous studies to be upregulated in the migrating epithelium during the wound-healing response. In Group 3 (16 weeks), KRT222 was downregulated greater than 2-fold. Additionally, interleukin genes IL2, IL7R, IL12B, and IL22RA2 were upregulated, indicating a greater inflammatory response in porous-textured devices compared to smooth-textured devices at this time point. A comparison between controls and keratin-coated devices is in progress but initial comparisons between the porous-textured control and the corresponding keratin-coated devices have identified the upregulation of HOXA10 and HOXC12 which are known to provide locational cues to the surrounding tissue during development and wound healing. In summary, we have shown that device surface texturing significantly impacts epidermal downgrowth and fibrous capsule thickness. Additionally, granulation tissue area measurements indicate that porous-textured, keratin-coated devices may promote faster resolution of inflammation at the skin-device interface.


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