材料の生体適合性

Biocompatibility is a dynamic and context-dependent concept, not a static, inherent property of a material. The ‘appropriate host response’ varies significantly with the intended function of the device. For instance, a material for a permanent hip implant should be bioinert, eliciting minimal reaction and integrating stably with bone. In contrast, a material for a biodegradable suture should elicit a controlled inflammatory response that facilitates healing and then safely degrades. The cascade of events at the biointerface begins seconds after implantation with the 吸着 of a layer of host proteins (e.g., albumin, fibrinogen, fibronectin), a phenomenon known as the Vroman effect. The composition and conformation of this protein layer dictates the subsequent cellular attachment, activation, and signaling. This initial phase is followed by an inflammatory response, involving the recruitment of neutrophils and then macrophages to the implant site. If the material is perceived as foreign and cannot be phagocytosed, macrophages may fuse to form foreign body giant cells (FBGCs). This chronic inflammatory state leads to the final stage: the formation of a dense, avascular fibrous capsule that isolates the implant from the host body. While this encapsulation can be acceptable for some passive implants, it is detrimental for devices requiring biological integration, like sensors or tissue scaffolds. Understanding and controlling these interactions through surface modification—by altering wettability, charge, topography, or grafting specific biomolecules—is a central goal of biomaterials science to ensure long-term device success and patient safety.