within the host animal to that tissue response recognised and established as suitable with control materials" - ASTM "Refers to the ability of a biomaterial to perform its desired function with respect to a medical therapy, without eliciting any undesirable local or systemic effects in the recipient or beneficiary of that therapy, but generating the most appropriate beneficial cellular or tissue response in that specific situation, and optimising the clinically relevant performance of that therapy". "Biocompatibility is the capability of a prosthesis implanted in the body to exist in harmony with tissue without causing deleterious changes". Comments on the above five definitions The Dorland Medical definition not recommended according to Williams Dictionary since it only defines biocompatibility as the absence of host response and does not include any desired or positive interactions between the host tissue and the biomaterials. This is also called the “Williams definition” or “William’s definition”. It was defined in the European Society for Biomaterials Consensus Conference I and can more easily be found in ‘The Williams Dictionary of Biomaterials’. The ASTM is not recommended according to Williams Dictionary since it only refers to local tissue responses, in animal models. The fourth is an expansion or rather more precise version of the first definition noting both that low toxicity and the one should be aware of the different demands between various medical applications of the same material. All these definitions deal with materials and not with devices. This is a drawback since many medical devices are made of more than one material. Much of the pre-clinical testing of the materials is not conducted on the devices but rather the material itself. But at some stage the testing will have to include the device since the shape, geometry and surface treatment etc. of the device will also affect its biocompatibility. ‘Biocompatible’ In the literature, one quite often stumbles upon the adjective form, ‘biocompatible’. However, according to Williams’ definition, this does not make any sense because biocompatibility is contextual, i.e. much more than just the material itself will determine the clinical outcome of the medical device of which the biomaterial is a part. This also points to one of the weaknesses with the current definition because a medical device usually is made of more than one material. Metallic glasses based on magnesium with zinc and calcium addition are tested as the potential biocompatible metallic biomaterials for biodegradable medical implants