An in situ hydrogel bioink induces self-aggregation of human cells for in vitro and in vivo tissue modeling

Immediate treatment of large hard-tissue defects remains a major challenge in tissue engineering, particularly because rapid tissue integration and vascularization are difficult to achieve using conventional 3D-printed scaffolds alone. Although stem cell-based therapies offer considerable regenerative potential, effective strategies for the immediate transplantation and retention of high-density stem cells within volumetric defects remain limited. In this study, we developed a 3D scaffold system that enables the direct implantation of dental stem cells using an injectable and in situ-forming carboxymethyl chitosan (CMCTS)/oxidized hyaluronic acid (oHA) hydrogel. Stem cells from the apical papilla (SCAP) were incorporated at high density into the self-crosslinking CMCTS/oHA hydrogel and directly injected into a 3D-printed poly(methyl methacrylate) (PMMA) scaffold, allowing immediate implantation without prior in vitro tissue maturation.

The injectable hydrogel exhibited favorable flowability, cytocompatibility, and scaffold-filling capacity while providing a temporary 3D microenvironment for cell retention and organization. Silver sulfadiazine (AgSD) was additionally incorporated into the hydrogel to provide antibacterial activity, with 0.1% AgSD supporting cell proliferation while exhibiting antimicrobial effects against S. mutans and E. faecalis. Following implantation, the CMCTS/oHA hydrogel gradually degraded while the transplanted cells formed three-dimensional tissue throughout the internal spaces of the scaffold. The newly formed tissue extended beyond the scaffold and integrated with the surrounding host tissue. In vivo, the implanted constructs demonstrated extensive tissue integration within 3 weeks, accompanied by the formation of mature blood vessels, indicating successful vascularization of the regenerated tissue.

These findings demonstrate that the combination of a mechanically supportive 3D-printed scaffold with an injectable, biodegradable, and antibacterial cell-laden hydrogel enables the immediate transplantation of dental stem cells and subsequent formation of vascularized 3D tissue in situ. This strategy may provide a practical platform for volumetric hard-tissue regeneration and other musculoskeletal tissue engineering applications requiring rapid treatment and vascularized tissue integration.

Professor Sangjin Lee obtained an Associate in Science Degree in Dental Technology from Daegu Health College, Korea, in 2010, followed by a Bachelor of Science degree in Dental Laboratory Science from Catholic University of Pusan, Korea, in 2012. He then earned a Master of Science degree in Maxillofacial Biomedical Engineering and a PhD in Dentistry from Kyung Hee University, Korea, in 2014 and 2017, respectively. Prior to joining the Faculty of Dentistry, Dr. Lee served as a postdoctoral research associate in the Department of Biomedical Engineering at the University of Illinois at Chicago from 2018 to 2022. Since 2022, he has held the position of Assistant Professor in the Faculty of Dentistry at the University of Hong Kong. Additionally, Dr. Lee started a guest faculty position at the School of Dentistry, Seoul National University, in September 2025. His research focuses on tissue engineering and regenerative medicine, specifically the creation of cell-integrated craniofacial artificial tissue complexes using various biocompatible materials and specialized processing equipment, which are then implanted to regenerate damaged or missing tissues in the body. He is also actively involved in research related to drug delivery and maxillofacial cancer treatment using biomaterials.