Complex Coacervate as a Novel Platform for non-classical Crystallization

Complex coacervation is a liquid–liquid phase separation process in which oppositely charged polyelectrolytes form a dense, polymer-rich phase that coexists in equilibrium with a dilute supernatant. This phenomenon has been related to various intracellular mechanisms due to its ability to compartmentalize, sequester, and selectively concentrate ions and biomolecules. We hypothesize that coacervates can act not only as microenvironments for molecular concentration but also as dynamic platforms that promote the crystallization of inorganic ions. Our results show that coacervates formed by poly(diallyl dimethylammonium) and poly(acrylate) effectively concentrate calcium and oxalate ions, facilitating crystallization with uniform size distribution, controlled morphology, and polymorph selectivity. Calcium oxalate growth was found to be strongly influenced by parameters such as polymer concentration, composition, and system pH.. Furthermore, replacing poly(acrylate) with other polyanions, such as poly(hyaluronate) or poly(phosphate), enabled selective control over polymorph formation or complete inhibition of crystallization, respectively. We propose that these effects arise from variations in calcium–polyanion strength of interactions, in addition to modulating local Ca–Ca spacing and ultimately guide nucleation and crystal growth within the coacervate phase. Overall, these findings highlight the potential of complex coacervates as versatile, biomimetic platforms for controlling mineralization processes with implications in both biological systems and designing new materials.