Microfluidic Synthesis of Collagen‐Based Microgels for Tissue Engineering Applications

ABSTRACT To expand the use of collagen‐based biomaterials beyond their current applications in three‐dimensional (3D) cell culture, tissue engineering, and biofabrication, limitations such as poor shear‐thinning behavior and poor control over porosity during gelation need to be overcome. Granular biomaterials promise to address these constraints, however their uniform and scalable preparation from extracellular matrix materials is challenging. To address this need, we employed a droplet microfluidic approach and prepared irregularly shaped microgels of fibrillar collagen and collagen‐glycosaminoglycan (GAG) copolymer in a continuous oil phase, at rates of up to 5500 s−1. The approach allowed us to tune the average microgel size from 40 to 170 µm. Microgels obtained after removal of the oil phase were found to promote the attachment and proliferation of human fibroblasts and mesenchymal stromal/stem cells. Granular materials prepared with packing densities exceeding 65 vol% exhibited shear‐thinning rheological behavior, a requirement for use as injectable biomaterials and bioinks. Cell‐containing granular biomaterials contracted 2.8 times less than thermally gelled matrices of comparable collagen and cell concentration. In a case study, a skin tissue model prepared from a fibroblast containing collagen‐GAG (CG) microgels layer covered with an epithelium revealed immunohistochemical markers associated with intact human skin after month‐long air–liquid interface (ALI) culture.