Bioprinting of light-crosslinkable neutral-dissolved collagen to build implantable connective tissue with programmable cellular orientation

Fabricating connective tissue with printing fidelity, structural stability, biocompatibility, and cellular orientation remains a challenge for bioink. Collagen, as inherent fibers to provide strengthin vivo, should be the ideal material for tissue printing. However, current collagen-bioink exhibits poor printability and mechanical properties. Here, the light-crosslinkable norbornene-collagen (NorCol) is developed to solve this dilemma. NorCol with complete collagen structure exhibits outstanding shear-thinning properties and light-crosslinking strength, realizing the construction of complicated constructs with excellent printing fidelity and structural stability. Neutral-dissolved NorCol with different concentrations is directly integrated to print pure collagen structure with composite modulus, providing top-class biocompatibility that mimics the heterogeneous microarchitecture of the extracellular matrix (ECM). This composite structure also permits extensive infiltration of host tissue and capillaries during subcutaneous transplants. By the designed tight interface of printed filaments, a geometric-guided and modulus-independent anisotropic mechanical environment is constructed, realizing cellular orientation. Furthermore, the cellular orientation is in the same direction as the printed high-concentration NorCol, which is the same case of cells and collagen fibersin vivo. This capability of NorCol breaks new ground for printing pure ECM protein-based, implantable and functional constructs, applicable in connective tissue engineering for human applications.