Microfluidics-Based Fabrication of Cell-Laden Hydrogel Microfibers for Potential Applications in Tissue Engineering.

Fibrous hydrogel scaffolds have recently attracted increasing attention for tissue engineering applications. While a number of approaches have been proposed for fabricating microfibers, it remains difficult for current methods to produce materials that meet the essential requirements of being simple, flexible and bio-friendly. It is especially challenging to prepare cell-laden microfibers which have different structures to meet the needs of various applications using a simple device. In this study, we developed a facile two-flow microfluidic system, through which cell-laden hydrogel microfibers with various structures could be easily prepared in one step. Aiming to meet different tissue engineering needs, several types of microfibers with different structures, including single-layer, double-layer and hollow microfibers, have been prepared using an alginate-methacrylated gelatin composite hydrogel by merely changing the inner and outer fluids. Cell-laden single-layer microfibers were obtained by subsequently seeding mouse embryonic osteoblast precursor cells (MC3T3-E1) cells on the surface of the as-prepared microfibers. Cell-laden double-layer and hollow microfibers were prepared by directly encapsulating MC3T3-E1 cells or human umbilical vein endothelial cells (HUVECs) in the cores of microfibers upon their fabrication. Prominent proliferation of cells happened in all cell-laden single-layer, double-layer and hollow microfibers, implying potential applications for them in tissue engineering.

Mechanically conditioned cell sheets cultured on thermo-responsive surfaces promote bone regeneration.

Cell sheet-based scaffold-free technology holds promise for tissue engineering applications and has been extensively explored during the past decades. However, efficient harvest and handling of cell sheets remain challenging, including insufficient extracellular matrix content and poor mechanical strength. Mechanical loading has been widely used to enhance extracellular matrix production in a variety of cell types. However, currently, there are no effective ways to apply mechanical loading to cell sheets. In this study, we prepared thermo-responsive elastomer substrates by grafting poly(N-isopropyl acrylamide) (PNIPAAm) to poly(dimethylsiloxane) (PDMS) surfaces. The effect of PNIPAAm grafting yields on cell behaviours was investigated to optimize surfaces suitable for cell sheet culturing and harvesting. Subsequently, MC3T3-E1 cells were cultured on the PDMS-g-PNIPAAm substrates under mechanical stimulation by cyclically stretching the substrates. Upon maturation, the cell sheets were harvested by lowering the temperature. We found that the extracellular matrix content and thickness of cell sheet were markedly elevated upon appropriate mechanical conditioning. Reverse transcription quantitative polymerase chain reaction and Western blot analyses further confirmed that the expression of osteogenic-specific genes and major matrix components were up-regulated. After implantation into the critical-sized calvarial defects of mice, the mechanically conditioned cell sheets significantly promoted new bone formation. Findings from this study reveal that thermo-responsive elastomer, together with mechanical conditioning, can potentially be applied to prepare high-quality cell sheets for bone tissue engineering.

Biomimetic periosteum-bone substitute composed of preosteoblast-derived matrix and hydrogel for large segmental bone defect repair.

Repairing large segmental bone defects above a critical size remains challenging with high risk of delayed union or even non-union. From the perspective of bone development and clinical experience, periosteum plays an indispensable role in bone repair and reconstruction. In this study, we explored the feasibility of using preosteoblast-derived matrix (pODM) as a biomimetic periosteum. By culturing MC3T3-E1 cell sheet on poly(dimethylsiloxane) and performing decellularization, an integral cell-free sheet of pODM could be readily harvested. Bone marrow mesenchymal stem cells (BMSCs) adhered and proliferated well on pODM. In addition, pODM exhibited a chemotactic effect on BMSCs in a concentration-dependent manner and also promoted osteogenic differentiation of BMSCs. Following that, pODM was wrapped around a gelatin methacryloyl (GelMA) hydrogel to construct an engineered periosteum-bone substitute. A rabbit radius segmental bone defect model was used to examine the bone repair efficacy of pODM/GelMA. Upon implantation of pODM/GelMA construct for 12 weeks, the critical-sized bone defects completely healed with remarkable full reconstruction of medullary cavity at the radial diaphysis. Together, this work proposes a high potency of using precursor cell-derived matrix as a biomimetic periosteum, which preserves the beneficial biological factors while avoids the limitations of using exogenous cells for bone regeneration. Combining precursor cell-derived matrix with hydrogel may provide a promising periosteum-bone biomimetic substitute for bone repair. STATEMENT OF SIGNIFICANCE: Repairing large segmental bone defects above a critical size remains challenging. As the periosteum plays an essential role in bone repair, this study aimed to explore the use of preosteoblast-derived matrix (pODM), harvested from decellularized MC3T3-E1 cell sheet, as a biomimetic periosteum to facilitate bone repair. We found that in vitro, pODM exhibited considerable chemotactic effect and osteogenic induction capability to bone marrow mesenchymal stem cells (BMSCs). In vivo, implantation of pODM/gelatin methacryloyl (GelMA) constructs as engineered periosteum-bone substitutes effectively repaired the critical-sized segmental bone defects at rabbit radius. Surprisingly, remarkable full reconstruction of medullary cavity at the diaphysis was achieved. Therefore, combining pODM with hydrogel may provide a promising biomimetic substitute for bone repair.

Tissue Engineering and Regenerative Medicine: Achievements, Future, and Sustainability in Asia.

Exploring innovative solutions to improve the healthcare of the aging and diseased population continues to be a global challenge. Among a number of strategies toward this goal, tissue engineering and regenerative medicine (TERM) has gradually evolved into a promising approach to meet future needs of patients. TERM has recently received increasing attention in Asia, as evidenced by the markedly increased number of researchers, publications, clinical trials, and translational products. This review aims to give a brief overview of TERM development in Asia over the last decade by highlighting some of the important advances in this field and featuring major achievements of representative research groups. The development of novel biomaterials and enabling technologies, identification of new cell sources, and applications of TERM in various tissues are briefly introduced. Finally, the achievement of TERM in Asia, including important publications, representative discoveries, clinical trials, and examples of commercial products will be introduced. Discussion on current limitations and future directions in this hot topic will also be provided.