Fabrication of bionanocomposites comprising flat nanocrystals of calcium in collagen fibers exhibiting hardness comparable to metal

Abstract

In nature's biomineralization process, living organisms naturally incorporate insoluble mineral compounds into their nano and molecular scale biological structures which results in formation of unusually hard but significantly less brittle biominerals. Mimicking nature's biomineralization process, here we present a novel nanoscale design of a brick–mortar type structure constructed at room temperature that consists of two-dimensional nanocrystals of calcite and calcium polyphosphate (bricks) bound together with an amorphous soft biopolymer phase (mortar). The resulting mesocrystalline-like biomineralized nanocomposite scaffolds combine both the properties of thin calcium containing nanocrystals and the organic phase surrounding them, and accurately replicate the micro- and lamellar-level mechanical and structural properties of bone. The flat morphology of calcium containing nanocrystals (<50 nm) is shown to dramatically enhance the mechanical properties of bioscaffolds that exhibit hardness comparable to biomedical tantalum and titanium. By changing the ratio of hard to soft phases within the bionanocomposites, we demonstrate tunable hardness and modulus (stiffness) from average values of 0.21 GPa (standard deviation ∼ 0.12) to 1.2 GPa (standard deviation ∼ 0.82) and 0.24 GPa (standard deviation ∼ 0.12) to 6.6 GPa (standard deviation ∼ 6.3) respectively that are suitable for high- or low-stress environment applications of bone substitutes and tissue regeneration. This presents a promising strategy to design and synthesize advanced engineered biocomposites with exceptional mechanical properties.