Extracellular vesicle-loaded hydrogels for tissue repair and regeneration.

Extracellular vesicles (EVs) are a collective term for nanoscale or microscale vesicles secreted by cells that play important biological roles. Mesenchymal stem cells are a class of cells with the potential for self-healing and multidirectional differentiation. In recent years, numerous studies have shown that EVs, especially those secreted by mesenchymal stem cells, can promote the repair and regeneration of various tissues and, thus, have significant potential in regenerative medicine. However, due to the rapid clearance capacity of the circulatory system, EVs are barely able to act persistently at specific sites for repair of target tissues. Hydrogels have good biocompatibility and loose and porous structural properties that allow them to serve as EV carriers, thereby prolonging the retention in certain specific areas and slowing the release of EVs. When EVs are needed to function at specific sites, the EV-loaded hydrogels can stand as an excellent approach. In this review, we first introduce the sources, roles, and extraction and characterization methods of EVs and describe their current application status. We then review the different types of hydrogels and discuss factors influencing their abilities to carry and release EVs. We summarize several strategies for loading EVs into hydrogels and characterizing EV-loaded hydrogels. Furthermore, we discuss application strategies for EV-loaded hydrogels and review their specific applications in tissue regeneration and repair. This article concludes with a summary of the current state of research on EV-loaded hydrogels and an outlook on future research directions, which we hope will provide promising ideas for researchers.

Superior stemness of a rapidly growing subgroup of isolated human auricular chondrocytes and the potential for use in cartilage regenerative therapy.

INTRODUCTION: In cartilage regenerative medicine, transplanted chondrocytes contain a mixture of populations, that complicates the regeneration of uniform cartilage tissue. Our group previously reported that chondrocytes with higher chondrogenic ability could be enriched by selection of rapidly growing cells. In this study, the detailed properties of rapidly growing chondrocytes were examined and compared to slowly growing cells. METHODS: Human auricular chondrocytes were fluorescently labeled with carboxyfluorescein succinimidyl ester (CFSE) and analyzed using flow cytometry, focusing on division rates as indicated by fluorescence intensity and cell morphology according to the forward scatter and side scatter. Rapid and slow growing cell groups were harvested on days 2 and 4 after CFSE labeling, and their ability to produce cartilage matrix in vitro was examined. To compare the chondrogenic ability in vivo, the cells were seeded on poly-l-lactic acid scaffolds and transplanted into nude mice. Gene expression differences between the rapid and slow cell groups were investigated by microarray analysis. RESULTS: On day 2 after CFSE labeling, the rapidly growing cell group showed the highest proliferation rate. The results of pellet culture showed that the rapid cell group produced more glycosaminoglycans per cell than the slow cell group. The amount of glycosaminoglycan production was highest in the rapid cell group on day 2 after CFSE labeling, indicating high chondrogenic ability. Furthermore, microarray, gene ontology, and Kyoto Encyclopedia of Genes and Genomes pathway analyses showed upregulation of genes that promote cell division such as origin recognition complex subunit 1 and downregulation of genes that inhibit cell division such as cyclin dependent kinase inhibitor 1A. Besides cell cycle-related genes, chondrocyte-related genes such as serpin family B member 2, clusterin, bone morphogenetic protein 2, and matrix metalloproteinase 3 were downregulated, while fibroblast growth factor 5 which is involved in stem cell maintenance, and coiled-coil and C2 domain containing 2A, which is required for cilia formation, were upregulated. CONCLUSION: The results showed that the rapid cell group proliferated well and had more undifferentiated properties, suggesting a higher stemness. The present findings provide a basis for the use of the rapid cell group in cartilage regeneration.

Anatomical reconstruction of the Posterolateral Corner of the knee preserving dynamic function of the popliteus tendon complex.

Almost cases of Posterolateral Corner (PLC) injuries are combined injuries involving the anterior or posterior cruciate ligament. Although numerous techniques of PLC reconstruction have been reported, it is unknown whether these techniques reconstruct PLC sufficiently. The anatomy of PLC is complex of tendon-muscle and ligament. The major structures are the fibular collateral ligament (FCL) and the Popliteus Tendon Complex. The latter comprises the popliteus tendon-muscle and the popliteo-fibular ligament (PFL). The FCL and PFL are static stabilizers, whereas the popliteus tendon-muscle is a dynamic stabilizer. The most of current PLC reconstructions statically restore all component parts, therefore not true "anatomically". We describe an operative technique to reconstruct PLC anatomically. Our technique preserves dynamic stability of the popliteus tendon-muscle and reconstructs the PFL and FCL selectively.Semitendinosus tendon is harvested, and almost used for the anterior or posterior cruciate ligament reconstruction. Gracilis tendon or contralateral semitendinosus tendon is used for PLC. Femoral bone tunnel for FCL is prepared at anatomical insertion. Fibular bone tunnel is prepared to connect PFL insertion with FCL insertion. One end of the graft is sutured to the popliteus tendon. The other end is passed though the fibular tunnel, and fixed at the femoral tunnel. The interference screws are used at each tunnel. One half of the graft composes PFL part, the other half composes FCL part. Advantages of this technique are preservation of dynamic popliteus tendon-muscle function, and simplifying preparation.

State-of-the-art review of advanced electrospun nanofiber yarn-based textiles for biomedical applications.

The pandemic of the coronavirus disease 2019 (COVID-19) has made biotextiles, including face masks and protective clothing, quite familiar in our daily lives. Biotextiles are one broad category of textile products that are beyond our imagination. Currently, biotextiles have been routinely utilized in various biomedical fields, like daily protection, wound healing, tissue regeneration, drug delivery, and sensing, to improve the health and medical conditions of individuals. However, these biotextiles are commonly manufactured with fibers with diameters on the micrometer scale (> 10 µm). Recently, nanofibrous materials have aroused extensive attention in the fields of fiber science and textile engineering because the fibers with nanoscale diameters exhibited obviously superior performances, such as size and surface/interface effects as well as optical, electrical, mechanical, and biological properties, compared to microfibers. A combination of innovative electrospinning techniques and traditional textile-forming strategies opens a new window for the generation of nanofibrous biotextiles to renew and update traditional microfibrous biotextiles. In the last two decades, the conventional electrospinning device has been widely modified to generate nanofiber yarns (NYs) with the fiber diameters less than 1000 nm. The electrospun NYs can be further employed as the primary processing unit for manufacturing a new generation of nano-textiles using various textile-forming strategies. In this review, starting from the basic information of conventional electrospinning techniques, we summarize the innovative electrospinning strategies for NY fabrication and critically discuss their advantages and limitations. This review further covers the progress in the construction of electrospun NY-based nanotextiles and their recent applications in biomedical fields, mainly including surgical sutures, various scaffolds and implants for tissue engineering, smart wearable bioelectronics, and their current and potential applications in the COVID-19 pandemic. At the end, this review highlights and identifies the future needs and opportunities of electrospun NYs and NY-based nanotextiles for clinical use.

Dental pulp stem cells response on the nanotopography of scaffold to regenerate dentin-pulp complex tissue.

The study of regenerative dentistry receives a fast growing interest. The potential ability of the dentin-pulp complex to regenerate is both promising and perplexing. To answer the challenging nature of the dental environment, scientists have developed various combinations of biomaterial scaffolds, stem cells, and incorporation of several growth factors. One of the crucial elements of this tissue engineering plan is the selection and fabrication of scaffolds. However, further findings suggest that cell behavior hugely depends on mechanical signaling. Nanotopography modifies scaffolds to alter cell migration and differentiation. However, to the best of the author's knowledge, there are very few studies addressing the correlation between nanotopography and dentin-pulp complex regeneration. Therefore, this article presents a comprehensive review of these studies and suggests a direction for future developments, particularly in the incorporation of nanotopography design for dentin-pulp complex regeneration.

Human auricular chondrocytes with high proliferation rate show high production of cartilage matrix.

Cartilage has a poor capacity for healing due to its avascular nature. Therefore, cartilage regenerative medicine including autologous chondrocyte implantation (ACI) could be a promising approach. Previous research has proposed various methods to enrich the cultured chondrocytes for ACI, yet it has been difficult to regenerate homogeneous native-like cartilage in vivo. The cell populations with an increased ability to produce cartilage matrix can show somatic stem cells-like characteristics. Stem cells, especially somatic stem cells are able to grow rapidly in vitro yet the growth rate is drastically reduced when placed in in vivo conditions [14]. Thus, in this study we investigated whether proliferation rate has an impact on in vivo regeneration of cartilage constructs by sorting human chondrocytes. The human chondrocytes were fluorescently labeled with CFSE and then cultured in vitro; once analyzed, the histogram showed a widening of fluorescence level, indicating that the cells with various division rates were included in the cell population. To compare the characteristics of the cell groups with different division rates, the chondrocytes were sorted into groups according to the fluorescence intensity (30 or 45 percent of cells plotted in the left and right sides of histogram). Then the cells of the rapid cell group and slow cell group were seeded into PLLA scaffolds respectively, and were transplanted into nude mice. Metachromatic regions stained with toluidine blue were larger in the rapid cell group compared to the slow cell group, indicating that the former had higher chondrogenic ability. We proposed a new method to enrich cell population with high matrix production, using proliferation rate alone.