Department of Materials Science and Engineering, Monash Institute of Medical Engineering, Monash University, Wellington Road, Clayton, VIC 3800, Australia.
Biomacromolecules. 2020 Dec 14;21(12):5323-5335. doi: 10.1021/acs.biomac.0c01408. Epub 2020 Nov 25.
Microgels are emerging as an outstanding platform for tissue regeneration because they overcome issues associated with conventional bulk/macroscopic hydrogels such as limited cell-cell contact and cell communication and low diffusion rates. Owing to the enhanced mass transfer and injectability via a minimally invasive procedure, these microgels are becoming a promising approach for bone regeneration applications. Nevertheless, there still remains a huge gap between the understanding of how the hydrogel matrix composition can influence cell response and overall tissue formation when switching from bulk formats to microgel format, which is often neglected or rarely studied. Here, we fabricated polyethylene glycol-based microgels and bulk hydrogels incorporating gelatin and hyaluronic acid (HA), either individually or together, and assessed the impact of both hydrogel composition and format upon the osteogenic differentiation of encapsulated human bone marrow-derived mesenchymal stem cells (hBMSCs). Osteogenesis was significantly greater in microgels than bulk hydrogels for both gelatin alone (Gel) and gelatin HA composite (Gel:HA) hydrogels, as determined by the expression of Runt-related transcription factor (Runx2) and alkaline phosphatase (ALP) genes and mineral deposition. Interestingly, Gel and Gel:HA hydrogels behaved differently between bulk and microgel format. In bulk format, overall osteogenic outcomes were better in Gel:HA hydrogels, but in microgel format, while the level of osteogenic gene expression was equivalent between both compositions, the degree of mineralization was reduced in Gel:HA microgels. Investigation into the affinity of hydroxyapatite for the different matrix compositions indicated that the decreased mineralization of Gel:HA microgels was likely due to a low affinity of hydroxyapatite to bind to HA and support mineral deposition, which has a greater impact on microgels than bulk hydrogels. Together, these findings suggest that both hydrogel composition and format can determine the success of tissue formation and that there is a complex interplay of these two factors on both cell behavior and matrix deposition. This has important implications for tissue engineering, showing that hydrogel composition and geometry must be evaluated together when optimizing conditions for cell differentiation and tissue formation.
微凝胶作为组织再生的杰出平台正在兴起，因为它们克服了传统的块状/宏观水凝胶的相关问题，例如有限的细胞-细胞接触和细胞通讯以及低扩散率。由于通过微创程序提高了传质和可注射性，这些微凝胶正在成为骨再生应用的一种有前途的方法。然而，当从块状格式切换到微凝胶格式时，水凝胶基质组成如何影响细胞反应和整体组织形成的理解仍然存在巨大差距，这通常被忽视或很少研究。在这里，我们制备了基于聚乙二醇的微凝胶和包含明胶和透明质酸（HA）的块状水凝胶，单独或一起，评估了水凝胶组成和格式对包封的人骨髓间充质干细胞（hBMSC）成骨分化的影响。通过 Runx2 和碱性磷酸酶（ALP）基因的表达和矿物质沉积，发现明胶单独（Gel）和明胶 HA 复合材料（Gel:HA）水凝胶的微凝胶中的成骨作用明显大于块状水凝胶。有趣的是，Gel 和 Gel:HA 水凝胶在块状和微凝胶格式之间表现不同。在块状格式中，Gel:HA 水凝胶的整体成骨效果更好，但在微凝胶格式中，尽管两种成分的成骨基因表达水平相当，但 Gel:HA 微凝胶中的矿化程度降低。对不同基质组成的羟基磷灰石亲和力的研究表明，Gel:HA 微凝胶中矿物质减少的原因可能是羟基磷灰石与 HA 的亲和力低，不利于矿物质沉积，这对微凝胶的影响大于块状水凝胶。总的来说，这些发现表明水凝胶组成和格式都可以决定组织形成的成功，并且这两个因素对细胞行为和基质沉积都有复杂的相互作用。这对组织工程具有重要意义，表明在优化细胞分化和组织形成的条件时，必须一起评估水凝胶组成和几何形状。
