Implications of the acute and chronic inflammatory response and the foreign body reaction to the immune response of implanted biomaterials

Abstract

In vivo implantation of medical devices, prostheses, biomaterials, and tissue-engineered scaffolds initiates the innate immune response consisting of acute inflammation, chronic inflammation, and the foreign body reaction (FBR) within the first 2 weeks following implantation. This chapter focuses on these humoral and cellular events occurring at the implant site immediately following implantation. Following injury/implantation, blood-material interactions occur and the provisional matrix is formed. Acute inflammation consisting predominantly of polymorphonuclear leukocytes follows but resolves quickly, usually within the first week if not sooner, depending on the extent of injury at the implant site. Chronic inflammation consisting of monocytes, macrophages, and lymphocytes follows acute inflammation. This process also resolves quickly with biocompatible materials leaving monocytes and macrophages to interact at the interface of the implanted device or material. The FBR at the interface with biomaterials is composed of macrophages, which may fuse together to form foreign body giant cells (FBGCs). Outside the FBR at the biomaterial interface, fibrosis and fibrous encapsulation occur in the final stages of the healing response to the implanted biomaterial. Numerous challenges including lack of understanding of these responses in vivo currently limit projection to clinical application of the respective medical device, prosthesis, or biomaterial. The end-stage of the innate immune response consisting of the FBR at the interface with fibrous encapsulation has received extensive attention over the past decade. Numerous efforts have been made to downregulate the activity of macrophages and FBGCs at the interface and to decrease/eliminate the fibrous capsule formation. Ultimately, the success or failure of medical devices, implants, biomaterials, and tissue-engineered constructs is modulated by the interaction between their characteristics, patient conditions, and surgical technique.