Microfluidic Production of Ultrathin, Handleable Collagen Sheets Exhibiting Toe-heel Tensile Behavior.

The extracellular matrix (ECM) of cardiovascular tissues displays a non-linear, strain-dependent elastic modulus, attributed to the hierarchical organization of collagen. At low loads, these tissues exhibit compliance, permit contraction or dilation, while at high loads, they stiffen and increase their mechanical strength at least tenfold. Although collagen gels are widely used in 3D cell culture, tissue engineering, and biofabrication, current engineering techniques fail to replicate this hierarchical organization at the microscale. As a result, they lack both the non-linear tensile behavior and the physiologically relevant strength of native tissues. To address this limitation, we prepare ultrathin, templated collagen sheets (1.8 microns thin and 10 mm wide) from an acidic collagen solution using a microfluidic wet spinning process, incorporating and later removing microscale oil droplets at 2.25% volume concentration. Templated collagen sheets exhibit a two-fold increase in fibril alignment dispersion compared with non-templated ones. When assessed along their length, the Young's modulus of the templated sheets increases 62-fold at 90% failure strain, recapitulating the tensile behavior of native load-bearing tissues. We anticipate that these ultrathin templated collagen sheets will find broad applications as substrate materials for the bottom-up fabrication of load-bearing biomaterials and tissue structures for in vitro applications and implantation.