Synergistic Prestress and Interfacial Interactions Reinforce Layered Brushite/Sodium Alginate Composites

As a laminated composite, the robust interface between aragonite platelets and organic matrices imparts nacre with superior mechanical properties. Additionally, the prestressing strategy, which involves compressing hydroxyapatite platelets through the contraction of collagen molecules, is employed to enhance bone strength. Inspired by these natural materials, layered brushite/sodium alginate composite bulks (BSPE) are fabricated with high performance through synergistic interfacial interactions and prestress processing. The bulks are prepared by stacking and hot-pressing BSPE films, which are obtained via unidirectional freeze-casting and pressing. To strengthen the interfacial interactions, brushite platelets are surface-modified with polyvinyl alcohol molecules, forming strong hydrogen bonds with sodium alginate chains. Furthermore, megapascal-level contractile prestresses are generated by soaking surface-modified films in ethanol, inducing the shrinkage of sodium alginate chains through dehydration. Consequently, the specific strength and specific toughness of the composites reach 137.5 MPa/(Mg m −3 ) and 3.8 MPa m 1/2 /(Mg m −3 ), respectively, representing 2.0 and 2.5 times the values of natural nacre. Moreover, the energy absorption capacity of the BSPE bulk is approximately 2.5 times higher than that of the control bulk. The synergistic approach provides new insights for designing and manufacturing high-performance composites under mild conditions.