Encapsulation of ePTFE in prevascularized collagen leads to peri-implant vascularization with reduced inflammation

During the typical healing response to an implanted biomaterial, vascular-rich granulation tissue forms around the implant and later resolves into a relatively avascular, fibrous capsule. We have previously shown that a microvascular construct (MVC) consisting of isolated microvessel fragments suspended in a collagen I gel forms a persistent microcirculation in lieu of avascular scar when implanted. The current study evaluated the potential for microvascular constructs to maintain a vascularized tissue environment around an implanted biomaterial. An analysis of the peri-implant tissue around bare expanded polytetrafluoroethylene (ePTFE), ePTFE embedded within a microvascular construct, or ePTFE embedded within collagen alone revealed that the presence of the MVC, but not collagen alone, promoted vascular densities comparable to that of the granulation tissue formed around bare ePTFE. The vessels within the microvascular construct surrounding the ePTFE were perfusion competent, as determined by India ink perfusion casting, and extended into the interstices of the polymer. In contrast to bare ePTFE, the presence of the MVC or collagen alone significantly reduced the number of activated macrophages in association with ePTFE. Similar results were observed for ePTFE modified to increase cellularity and prevent the formation of an avascular scar. The microvascular construct may prove effective in forming vascularized tissue environments and limiting the number of activated macrophages around implanted polymers thereby leading to effective implant incorporation.