Biomimetic Mineralization via Polymer-Induced Liquid Precursors*

The hallmark of biomineralization is the ability of organisms to form non-equilibrium crystal morphologies. Our group has been using in vitro model systems to examine the physicochemical mechanisms that might be involved in biomineralization, with emphasis on the role that biopolymers play. We have discovered that many of the long-standing enigmatic biomineral features can be reproduced in the beaker using a non-classical crystallization process we call the Polymer-Induced Liquid-Precursor (PILP) process. This process entails adding charged polymers to supersaturated salt solutions which then sequester ions/clusters/phases to induce phase separation of a hydrated amorphous mineral precursor. Interaction of these PILP colloids with various organic templates and matrices leads to a variety of non-equilibrium morphologies and composite textures, many of which emulate those seen in biominerals. We argue that a PILP type process may lie at the foundation of biomineralizing systems ranging from invertebrate exoskeletons to vertebrate bones and teeth. This argument is based on the diversity of features that can be emulated, and their distinct mineralogical signatures of formation mechanism, such as incorporation of high magnesium into calcite, transition bars and shrinkage patterns, and remnant colloidal textures within single-crystalline composites. Through this enhanced understanding of biomineralization processes, we are now developing biomimetic processing methods that enable the fabrication of hard-tissue biomaterials which emulate bone.