Postdoc The University of Hong Kong; Center for Neuromusculoskeletal Restorative Medicine, Hong Kong
Abstract: 3D bioprinting of cell-laden hydrogels enables the fabrication of complex structures and delivery of stem cells in situ for bone tissue engineering. However, certain bone defects such as those in cranial bone, possess inherent curvature, which makes it challenging for 3D bioprinted hydrogels to perfectly match the structure. Therefore, developing 4D bioprinted hydrogels with shape-morphing capacities to conform to the native structure of cranial bone defects is essential. In the current study, we prepared a photocrosslinkable bioink consisting of gelatin methacryloyl (GelMA), oxidized alginate (OAlg), magnesium-doped hydroxyapatite (MgHAp), and bone marrow-derived mesenchymal stem cells (BMSCs). Methacryloxyethyl thiocarbamoyl rhodamine (RhB), an effective UV absorber, was employed to create a graded crosslinking density in the hydrogel and thus realize its shape morphing behavior. The printing inks exhibited excellent printability, and that the printed hydrogels displayed high fidelity. Subsequently, a comprehensive study was conducted to evaluate the effects of various parameters, including UV crosslinking time, photoinitiator concentration, RhB concentration, the thickness and length-to-width ratio of printed hydrogels, and medium types, on the shape morphing behavior of hydrogels. Notably, our simulation results corroborated the significant influence of these parameters and mirrored the experimental observations. Furthermore, BMSCs showed a significant survival rate (> 90%) in 4D printed hydrogels and exhibited expanded morphology due to the dynamic network formed by GelMA and OAlg. The 4D printed hydrogels could sustainably release Ca2+ and Mg2+, which promoted the osteogenic differentiation of BMSCs by enhancing the expression of osteogenic-related genes and proteins. In vivo rabbit skull bone defect models indicated that 4D bioprinted hydrogels perfectly matched the native curvature of cranial bone defects and significantly facilitated the regeneration of the defects. As a result, the current study presents a novel and versatile approach to overcoming the hurdle of achieving shape changes in cell-laden hydrogels to match the native curvature of specific bone tissues, demonstrating significant promise in bone tissue engineering.
