The innate response to biomaterials

Physical barriers, such as skin, nails, lips, and mucous membranes, are the first line of defense against pathogen invasion and irritants and are fairly effective in our daily defense against exposure to microbes. However, the barriers can be compromised by disease or a physical breach such as the surgical implantation of biomaterials. Once breached, there are several strategies used by the human body to respond to the presence of foreign materials and material breakdown products. Traditionally, these response methods have been segregated into “innate” (also called nonspecific) and “acquired” (also called adaptive or specific) immune responses. This article reviews these responses and the current knowledge of innate responses and pathways that are activated by biomaterials and biomaterial breakdown products. These include initial cellular responses (such as inflammation to both inert and resorbable materials as well as inflammatory and giant cell responses to resorbable materials) and the inflammasome, the proposed mechanism for innate responses to particulate biomaterials. This article also reviews strategies implemented to alter biomaterial surfaces as a means to increase the biocompatibility of implantable devices (eg, vascular stents) and how the innate response to particulate biomaterials has been harnessed to improve efficacy of vaccines and serve as a platform for novel therapeutic strategies.