In surgery, a biomaterial is a synthetic material used to replace part of a living system or to function in intimate contact with living tissue. Compare this definition to that of bio-based material.

The Clemson University Advisory Board for Biomaterials defined a biomaterial as "a systemically and pharmacologically inert substance designed for implantation within or in corporation with living systems".

In 1986, the Consensus Conference of the European Society for Biomaterials defined a biomaterial as "a nonviable material used in a medical device, intended to interact with biological systems".

Another definition of biomaterial is "any substance (other than drugs) or combination of substances synthetic or natural in origin, which can be used for any period of time, as a whole or as a part of a system which treats, augments, or replaces any tissue, organ, or function of the body".

A biomaterial is different from a biological material such as bone that is produced by a biological system. Artificial hips, vascular stents , artificial pacemakers, and catheters are all made from different biomaterials.

Biomimetic materials are not made by living things but have similar compositions and properties to living things. The calcium hydroxyapatite coating found on many artificial hips is a sort of fake bone that allows for easier attachment of the implant to the living bone.

Surface functionalization may provide a way to transform a bio-inert material into a biomimetic or even bio-active material by coupling of protein layers to the surface. Different approaches to functionalization of biomaterials exist. Plasma processing has been successful applied on chemically inert materials like polymers or silicon to graft various functional groups to the surface.

All details are given in the definition and processing of biomaterials.