Bioinspired coacervate-based bioinks for construction of multiscale tissue engineering scaffolds

Engineering hydrogels that resemble biological tissues of various lengths via conventional fabrication techniques remains challenging. Three-dimensional (3D) bioprinting has emerged as an advanced approach for constructing complex biomimetic 3D architectures, which are currently restricted by the limited number of available bioinks with high printability, biomimicry, biocompatibility, and proper mechanical properties. Inspired by ubiquitous coacervation phenomena in biology, we present a unique mineral-biopolymer coacervation strategy that enables the hierarchical assembly of nanoclay and recombinant human collagen (RHC). This system was observed to undergo a coacervation transition (liquid‒liquid phase separation) spontaneously. The formed dense phase separated from its supernatant is the coacervate of clay-RHC-rich complexes, where polymer chains are sandwiched between silicate layers. Molecular dynamics simulation was first used to verify and explore the coacervation process. Then, the coacervates were demonstrated to be potential bioinks that exhibited excellent self-supporting and shear-thinning viscoelastic properties. Through extrusion-based printing, the versatility of the bioink was demonstrated by reconstructing the key features of several biological tissues, including multilayered lattice, vascular, nose, and ear-like structures, without the need for precrosslinking operations or support baths. Furthermore, the printed scaffolds were cytocompatible, elicited minimal inflammatory responses, and promoted bone regeneration in calvarial defects.