Coaxial temperature controlled cryoprinting: A biomimetic technology inspired by the freezing survival mechanisms of...

Inspired by the freeze-survival mechanism of the frog Rana sylvatica, we developed a co-axial, self-crosslinking approach to be used when fabricating frozen scaffolds. Soft biomaterial can be fabricated into scaffolds using methods such as Temperature Controlled Cryoprinting (TCC), which uses a freezing plate to freeze the biomaterial as it is extruded. However, it remains a challenge to uniformly crosslink the scaffolds during thawing without them losing their shape. In this paper, we use coaxial printing to generate locally variable phase-transition compositions, mimicking the frog's glucose distribution during freezing, and electrical Joule heating to simulate metabolic heat production. Unlike previous methods, in our novel approach the crosslinker is located already within the frozen scaffold, and there is no need to submerge the scaffold in a bath. Both mathematical modeling and experimental validation confirmed the concept. A finite thawing-diffusion-crosslinking model was developed to analyze parameters such as temperature, thawing interface, concentration, and crosslinking interface. Experimental evaluations, including mechanical testing, heating test, swelling performance and electron microscope, demonstrated that coaxial self-crosslinking enables controlled thawing and crosslinking of frozen scaffolds. Results demonstrated that coaxial TCC self-crosslinking scaffolds are feasible, allowing for a more controlled thawing and crosslinking process in cryoprinted scaffolds.