Bioprinted hASC-laden structures with cell-differentiation niches for muscle regeneration

The development of an in situ (or in vivo) bioprinting system could lead to surgical devices that can directly print cells/tissues on the damaged anatomical location. Such devices would require tissue-specific bioinks, a bioreactor system, and an appropriately designed multiple-axis machine system. In order to operationalize the concept of an in vivo bioprinting system, we used a modified printing system that enables direct printing on the desired anatomical location through the use of cell-laden structures that result in differentiation niches based on printing parameters such as stiffness of the bioink and topographical and biochemical cues. To show the feasibility of the in situ bioprinting system, we used collagen bioink laden with human adipose-derived stem cells (hASCs) and human umbilical vein endothelial cells (HUVECs) and assessed the myogenic and angiogenic differentiation under optimal printing conditions combined with a simultaneous crosslinking process. Furthermore, the cellsladen bioinks processed with the in situ printing showed outstanding myogenesis through the implantation in the temporalis muscle flap of rats. To extend the technology, two bioinks-a decellularized extracellular matrix derived from porcine tendon and collagen/beta-TCP-were accommodated, and the fabricated cell-laden structures processed with the bioprinting system were well differentiated into the designed tenogenic or osteogenic linages without using any additional in vitro experiments. Based on these results, we believe that the modified bioprinting process offers several important keys for achieving in situ bioprinting and provides valuable insights into the current directions of 3D bioprinting.