A hip replacement that lasts 20 years. A dissolvable stitch that disappears after a wound heals. A contact lens that lets oxygen through to the cornea. These are biomaterials, materials designed to interact with biological systems for medical use. They can be natural or synthetic, permanent or biodegradable. The common requirement is biocompatibility: they must not harm the body, and the body must not destroy them.

Biomaterials fall into several categories. Metals like titanium and cobalt-chrome are strong and corrosion-resistant, ideal for joint replacements and dental implants. Ceramics like hydroxyapatite mimic bone mineral and bond directly to bone. Polymers like PLGA are biodegradable and used for sutures, drug delivery, and tissue scaffolds. Composites combine materials to get the best properties of each.

Designing a biomaterial is a balancing act. It must have the right mechanical properties for the application. A bone implant must bear load without flexing too much. A vascular graft must be flexible and non-clotting. The material must also resist infection, wear, and degradation. And it must be manufacturable and sterilizable.

The field is moving toward smarter materials. Drug-eluting stents release medication to prevent restenosis. Shape-memory alloys expand at body temperature. Self-healing hydrogels repair themselves after damage. The material is no longer passive. It is part of the therapy.