3D Cryoprinting for the Manufacture of Large-Scale, Interface-Free and Interconnected Porous Biopolymeric Scaffolds

3D cryoprinting is a technique that utilises a low-temperature surface to improve the manufacturability of soft materials that are difficult to process in other ways due to low shape fidelity. Typical approaches to 3D printing of soft and low-viscosity materials require modifications to the material’s chemistry following printing to facilitate solidification, including the incorporation of photopolymerization additives and cross-linking agents or baths, or heat-assisted solvent evaporation. For several biological materials, these approaches have been shown to limit the range of biochemistries or mechanics achievable in the final printed structure, limiting the ability to successfully integrate with biological tissues. Cryoprinting techniques can maintain the bioactivity of natural biopolymers by preserving the original polymer chemistry while controlling the printed geometry by near-immediate freezing of the viscous slurry following deposition, eliminating the need to adapt or heat the material during manufacture.

This study explores combining cryoprinting with a multi-material deposition system to incorporate and control local spatial variations of biomaterial composition for biological implants. By using a pneumatic extrusion 3D printing system, we show that we can precisely deposit viscous bioinks to create complex 3D biomimetic geometries and architectures. Highly porous structures produced from collagen suspensions have been manufactured through controlled platen temperatures and, thus, well-defined growth of ice crystals. We demonstrate the ability to create gradation in structural properties within a single construct through the incorporation of multiple materials, geometric tuning, as well as thermal control of the deposition surface. Construct architectures imaged using X-ray Computed Tomography (XCT) were assessed for their pore size and pore interconnectivity, exploring the effects of processing parameters on the structural attributes of the final printed constructs, to ensure that cell migration is facilitated. Thus, we show that large, 3D, interface-free and interconnected mesoporous scaffolds can be successfully produced from dilute aqueous suspensions of structural biopolymers (1-2 wt%), offering significant potential for improved scaffold biointegration.