Hydroxyapatite: an Eco-Friendly Material for Enzyme Immobilization

Biocatalysis has emerged in the last decade as a valuable and eco-friendly tool in chemical synthesis, allowing in several instances to reduce or eliminate the use of hazardous reagents, environmentally dangerous solvents and harsh reaction conditions. Enzymes are indeed able to catalyse chemical transformations on non-natural substrates under mild reaction conditions, still maintaining their high chemo-, regio-, and stereoselectivity. Enzyme immobilization, i.e. the grafting of enzymes on solid supports, can be viewed as an enabling technology, as it allows a better control of the reaction and the recycling of the biocatalyst, thus rendering economically viable the use of expensive enzymes also on a large scale. To pursue a sustainable approach, the supports for enzyme immobilization should be eco-friendly and possibly renewable. This review highlights the use of hydroxyapatite (HAP), an inorganic biomaterial able to confer strength and stiffness to the bone tissue in animals, as carrier for enzyme immobilization. HAP is a cheap, non-toxic and biocompatible material, with high surface area and protein affinity. Different enzyme classes, immobilization strategies, and the use of diverse HAP-based supports will be discussed, underlining the immobilization conditions and the properties of the obtained biocatalysts.