Considering the key roles of macrophages in tissue repair and immune therapy, designing smart biomaterials able to harness macrophage phenotypes on demand during the healing process has become a promising strategy. Here, a novel “sandwich” cell culture platform with near-infrared (NIR) responsive dynamic stiffness was fabricated to polarize bone marrow-derived macrophages (BMDMs) in situ for revealing the relationship between the macrophage phenotype and substrate stiffness dynamically. Under NIR irradiation, calcium ions (Ca2+) diffused through the middle layer of the IR780-mixed phase change material (PCM) due to the photothermal effect of IR780, resulting in an increase of hydrogel stiffness in situ by the crosslinking of the upper layer of the hyaluronic acid-sodium alginate hydrogel (MA-HA&SA). The up-regulation of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-α (TNF-α) was quantified by immunostaining and enzyme-linked immune sorbent assay (ELISA), respectively, indicating the transformation of macrophages from the anti-inflammatory to pro-inflammatory phenotype under dynamic stiffness. The nuclear Yes-associated-protein (YAP) ratio positively correlated with the shift of the macrophage phenotype. The modulation of macrophage phenotypes by stiffness-rise without the stimuli of cytokines offers an effective and noninvasive strategy to manipulate immune reactions to achieve optimized healing or therapeutic outcomes.
Here, we evaluated osteogenic differentiation in vitro and new bone formation in vivo using an alendronate-loaded chitosan/polycaprolactone scaffold (CS/PCL) in rats with a critical-sized calvarial defect. Through the action of genipin, which has a crosslinking function, alendronate (AL) was anchored throughout the CS/PCL composite scaffold (CS/ [email protected] ) to form an AL sustained release system. We demonstrated that CS/ [email protected] scaffolds significantly enhanced the osteogenic differentiation of ectomesenchymal stem cells (EMSCs) in vitro. Additionally, we explored the possible molecular mechanism of CS/ [email protected] scaffolds in the osteogenic differentiation of EMSCs. This composite scaffold exerted two positive effects on EMSC osteogenic differentiation: 1) the CS/ [email protected] scaffold enhanced EMSC osteogenic differentiation by upregulating bone morphogenetic protein 2, interleukin 10 and laminin expression; and 2) the CS/ [email protected] scaffold promoted the osteogenic differentiation of EMSCs by activating the yes-associated protein (YAP) signaling pathway. YAP and its downstream target transglutaminase are crucial mediators in the osteogenic differentiation of EMSCs. Finally, micro-computed tomography analyses and histology results suggested that the CS/ [email protected] scaffold exhibited a superior capacity to accelerate new and mature bone formation in skull bone defects in Sprague–Dawley rats. This simple and low-cost technology may represent a promising strategy to construct an efficient delivery system to repair bone defects.
The shortage of transplantable skin is the leading cause of death in patients with extensive skin defect. Addressing this challenge urgently requires the development of skin substitutes capable of wound repair and facilitating skin regeneration. In this study, a biomimetic bilayer skin tissue model consisting of collagen, gelatin/sodium alginate, fibroblasts, human umbilical vein endothelial cells, keratinocytes, melanocytes, and verteporfin was devised. Then, the skin model was fabricated using precise extrusion/inkjet bioprinters, and it reconstruction capabilities were evaluated through skin defect repair experiments. The printed skin tissue reduced the inflammatory response of the wound by 38% and inhibited the expression of TGF-β and YAP, and promoted the transformation of macrophages from M1 phenotype to M2 phenotype, thus promoting the reasonable reconstruction of fibronectin and collagen on the wound, finally promoting the wound healing, and reducing the wound contraction and scar formation. In addition, the proliferation and differentiation of human umbilical vein endothelial cells, keratinocytes, and melanocytes in printed skin increased the number of regenerated blood vessels by 123%, while promoting the reconstruction of multilayer epidermal structure and skin color. The outcomes of this investigation present a promising skin model and therapeutic strategy for skin injury, offering a potential avenue for the reconstruction of skin structure and function.
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