A pore way to heal and regenerate: 21st century thinking on biocompatibility.

This article raises central questions about the definition of biocompatibility, and also about how we assess biocompatibility. We start with the observation that a porous polymer where every pore is spherical, ∼40 microns in diameter and interconnected, can heal into vascularized tissues with little or no fibrosis and good restoration of vascularity (i.e., little or no foreign body reaction). The same polymer in solid form will trigger the classic foreign body reaction characterized by a dense, collagenous foreign body capsule and low vascularity. A widely used definition of biocompatibility is 'the ability of a material to perform with an appropriate host response in a specific application'. With precision-porous polymers, in direct comparison with the same polymer in solid form, we have the same material, in the same application, with two entirely different biological reactions. Can both reactions be 'biocompatible?' This conundrum will be elaborated upon and proposals will be made for future considerations and measurement of biocompatibility.