= Biomaterial
{wiki}
In biomedical engineering, a <biomaterial> is a material selected or designed to interact with a biological system for a medical purpose. Its defining feature is this intended interaction, rather than whether it originated in an organism. A synthetic <polymer>, a <metal> or a <ceramic> can therefore be a <biomaterial>; natural <collagen> can also be processed for such a use. The biomedical meaning should be distinguished from the broader use of “bio” to mean material obtained from biomass.<Terminology for biorelated polymers and applications (IUPAC Recommendations 2012) by Michel Vert and others>[Entry 30 and its notes; the biomaterial entry is also reproduced in the IUPAC Gold Book]{ref}
A <biomaterial> has both a material function and a biological environment. A load-bearing component must transmit <forces> without unacceptable deformation, but its surface also contacts fluid, <proteins> and <biological cells>. <Biocompatibility> consequently concerns an appropriate host response for a particular application; it is not a universal label that guarantees identical behavior at every site or for every exposure duration.<Terminology for biorelated polymers and applications (IUPAC Recommendations 2012) by Michel Vert and others>[Entry 106, biocompatibility in biomedical therapy]{ref}
An illuminating historical example is the 1971 work of <L. L. Hench> and colleagues on a bone-bonding glass-ceramic. They compared laboratory measurements of glass-ceramic solubility and interfacial <hydroxyapatite> crystallization with <histology> and ultrastructure observations around implants in rat femurs. The important question was how the material–<bone> interface developed, rather than merely whether the bulk <ceramic> was strong.<Bonding mechanisms at the interface of ceramic prosthetic materials by L. L. Hench and others>[Primary abstract: comparison of in-vitro interfacial studies and in-vivo implant observations]{ref}
To separate bulk behavior from an interface effect in a model experiment, one could compare specimens with identical dimensions and bulk <Young's modulus> but different surface treatments, while holding the <cell culture> conditions fixed. Measure both the mechanical response and <cell adhesion>, instead of substituting one for the other. Conversely, changing specimen thickness while retaining the same surface can change bending resistance without changing the nominal surface chemistry. These controlled comparisons show why evaluating a <biomaterial> requires specifying the material, its geometry, its interface and the biological setting together.
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