Calcified cartilage regeneration plays an important role in successful osteochondral repair, since it provides a biological and mechanical transition from the unmineralized cartilage at the articulating surface to the underlying mineralized bone. To biomimic native calcified cartilage in engineered constructs, here we test the hypothesis that hydroxyapatite (HAP) stimulates chondrocytes to secrete the characteristic matrix of calcified cartilage. Sodium citrate (SC) was added as a dispersant of HAP within alginate (ALG), and homogeneous dispersal of HAP within ALG hydrogel was confirmed using sedimentation tests, electron microscopy, and energy dispersive spectroscopy. To examine the biological performance of ALG/HAP composites, chondrocyte survival and proliferation, extracellular matrix production, and mineralization potential were evaluated in the presence or absence of the HAP phase. Chondrocytes in ALG/HAP constructs survived well and proliferated, but also expressed higher levels of calcified cartilage markers compared to controls, including Collagen type X secretion, alkaline phosphatase (ALP) activity, and mineral deposition. Compared to controls, ALG/HAP constructs also showed an elevated level of mineralized matrix in vivo when implanted subcutaneously in mice. The printability of ALG/HAP composite hydrogel precursors was verified by 3D printing of ALG/HAP hydrogel scaffolds with a porous structure. In summary, these results confirm the hypothesis that HAP in ALG hydrogel stimulates chondrocytes to secrete calcified matrix in vitro and in vivo and reveal that ALG/HAP composites have the potential for 3D bioprinting and osteochondral regeneration.

中文翻译：

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均质羟基磷灰石/藻酸盐复合水凝胶促进钙化软骨基质沉积，具有进行三维生物打印的潜力。

钙化软骨再生在成功的骨软骨修复中起着重要作用，因为它提供了从关节表面未矿化的软骨到下层矿化骨的生物学和机械过渡。为了仿效工程构造中的天然钙化软骨，在这里我们测试了羟基磷灰石（HAP）刺激软骨细胞分泌钙化软骨特征基质的假设。加入柠檬酸钠（SC）作为海藻酸钠（ALG）内HAP的分散剂，并通过沉降测试，电子显微镜和能量色散光谱法确认了HAP在ALG水凝胶中的均匀分散。为了检查ALG / HAP复合材料的生物学性能，软骨细胞的存活和增殖，细胞外基质的产生，在存在或不存在HAP相的情况下评估了矿物的矿化度和矿化潜力。与对照组相比，ALG / HAP构建体中的软骨细胞可以很好地存活和增殖，但也表达更高水平的钙化软骨标志物，包括X型胶原分泌，碱性磷酸酶（ALP）活性和矿物质沉积。与对照相比，ALG / HAP构建体在皮下植入小鼠体内时，体内矿化基质水平也升高。通过3D打印具有多孔结构的ALG / HAP水凝胶支架，可以验证ALG / HAP复合水凝胶前体的可印刷性。综上所述，