Hydrogels as biomimetic mineralisation scaffolds

Biominerals are exquisite materials displaying a diversity of length scales and structural patterns. Formed by biological organisms, their physicochemical properties often show little correlation with their mineral cousins. The hierarchical structure results in, for example, superior ageing, durability and strength compared with the constituent components. Inherently, biominerals are hybrid materials made from organic and inorganic components. Nacre for example is formed from calcium carbonate, chitin and proteins. Analysis of biominerals and their mechanism of formation allow determination of the relative importance of each component. This leads to the formulation of synthetic strategies and enable materials scientists to develop biomimetic materials with new properties. A major component of many biominerals is a three-dimensional organic insoluble matrix. This matrix can be replicated synthetically using hydrogels. Acting as the mineralisation scaffold, and hydrogels, which are porous, allow diffusion of mineralisation solutions and/or gases in and out of the scaffold, are typically biocompatible thereby enabling the formation of intimately interpenetrated composite materials to be synthesized. In this review, the current state of knowledge in this area is summarized and literature pertaining to the use of hydrogels as substrates and scaffolds to form organic/inorganic composites is discussed. The use of the resulting materials as implantable and injectable hybrid materials for medical applications is also discussed.