Hydrogels are crosslinked polymer chains with three-dimensional (3D) network structures, which can absorb relatively large amounts of fluid. Because of the high water content, soft structure, and porosity of hydrogels, they closely resemble living tissues. Research in recent years shows that hydrogels have been applied in various fields, such as agriculture, biomaterials, the food industry, drug delivery, tissue engineering, and regenerative medicine. Along with the underlying technology improvements of hydrogel development, hydrogels can be expected to be applied in more fields. Although not all hydrogels have good biodegradability and biocompatibility, such as synthetic hydrogels (polyvinyl alcohol, polyacrylamide, polyethylene glycol hydrogels, etc.), their biodegradability and biocompatibility can be adjusted by modification of their functional group or incorporation of natural polymers. Hence, scientists are still interested in the biomedical applications of hydrogels due to their creative adjustability for different uses. In this review, we first introduce the basic information of hydrogels, such as structure, classification, and synthesis. Then, we further describe the recent applications of hydrogels in 3D cell cultures, drug delivery, wound dressing, and tissue engineering.

Background Ischemia/reperfusion (I/R) injury causes the generation of many ROS such as H 2 O 2 and leads to vascular thrombosis, which causes tissue damage. Purpose In this investigation, poly (lactideco-glycolide) (PLGA)-based nanoparticles are used for their anticoagulant and antioxidant properties in vascular therapy. Methods Both heparin and glutathione are entrapped on PLGA-stearylamine nanoparticles by layer-by-layer interactions. Results The drug release rate is successfully controlled with only 10.3% of the heparin released after 96 hours. An H 2 O 2 -responsive platform is also developed by combining silk fibroin and horse peroxidase to detect H 2 O 2 in this drug delivery system. Besides, hyaluronic acid was decorated on the surface of nanoparticles to target the human bone marrow mesenchymal stem cells (hBMSCs) for cell therapy. The results of an in vitro study indicate that the nanoparticles could be taken up by hBMSCs within 2 hours and exocytosis occurred 6 hours after cellular uptake. Conclusion We propose that the multifunctional nanoparticles that are formed herein can be effectively delivered to the site of an I/R injury via the hBMSC homing effect. The proposed approach can potentially be used to treat vascular diseases, providing a platform for hBMSCs for the controlled delivery of a wide range of drugs.

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The effects of the stiffness of substrates on the cell behaviours of human bone marrow-derived mesenchymal stem cells (hBMSC) have been investigated, but the effects of the secondary structures of proteins in the substrates on the morphological transformation and differentiation of hBMSC have yet been elucidated. To investigate these issues, silk fibroin-poly(ε-caprolactone) SP cardiac patches of poly(ε-caprolactone; P), on which is grafted by silk fibroin (SF) with various β-sheet contents (or crystallinity) to provide various degrees of stiffness, were produced to examine the in vitro behaviours of hBMSC during proliferation, and cardiomyogenesis on the SP patches. β-sheet contents of SF from 20% to 44% (SP20 to SP44, respectively) were induced on patches, which were examined by attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, and analysed using the Fourier self-deconvolution method. The stiffness of the SP patches, quantified by their Young's moduli and elasticities, increased with the crystallinity of the SF. During 3 days of proliferation, hBMSC migrated and morphologically transformed into 3D microtissues with diameters of approximately 150-200 μm on low-stiffness SP20 and SP30 patches, whereas 2D monolayers were observed on the SP37 and SP44 patches. The 3D microtissues/patch yielded more extensive in vitro cardiomyogenesis of hBMSC than the 2D cell monolayer with significantly higher expressions of all examined cardiac-specific proteins after induction by 5-aza. Notably, in vivo subcutaneously growing 3D microtissues on SP20 patches and a 2D monolayer on SP44 patches were preliminarily demonstrated in a rat model. Morphological transformations of hBMSC from a 2D monolayer to a 3D microtissue by low-stiffness SP cardiac patches, promoting cardiomyogenesis, provide a new opportunity for cardiac tissue engineering.