Tissue-Material Characteristics Determine Fibrous Encapsulation Dynamics Across Common Polymeric Surgical...

Common polymeric surgical biomaterials are susceptible to dysregulated fibrous encapsulation, which contributes to failure in 10% of implantable medical devices. While biomaterial factors influencing the underlying foreign body response have been extensively studied, the role of the implantation site-specifically the tissue microenvironment-remains poorly understood. Here, we explore the tissue-specificity of the foreign body response by evaluating fibrous encapsulation around clinically-relevant synthetic non-biodegradable polymers across distinct tissue microenvironments. We first characterize the physicochemical properties of PDMS, PP, PTFE, HDPE and nylon, and develop a mouse model that enables direct within-animal comparisons of fibrous capsule formation next to skin, bone, fat, fascia and muscle. Using this model and these biomaterials, we histologically assess the extent and quality of fibrous encapsulation at 7 and 28 days for all biomaterial-tissue combinations. At 7 days, capsules adjacent to muscle are the thickest, but-at 28 days-capsules in contact with bone and fascia reach comparable thicknesses, which are significantly greater than those of capsules adjacent to skin. Although PTFE and nylon elicit less fibrous encapsulation at 28 days than some of the other biomaterials, adjacent tissue type has a substantially greater influence on fibrous encapsulation than stiffness, roughness or wettability. Interestingly, more vascularized tissues (i.e., skin and muscle) do not show significant differences in capsule thickness over time, suggesting that they may promote a more rapid initiation and stabilization of the foreign body response. Together, these findings identify adjacent tissue type as a dominant predictor of fibrous encapsulation for common polymeric surgical biomaterials.