Abstract：
Polymer-peptide hydrogels are being designed as implantable materials that deliver human mesenchymal stem cells (hMSCs) to treat wounds. Most wounds can progress through the healing process without intervention. During the normal healing process, cytokines are released from the wound to create a concentration gradient, which causes directed cell migration from the native niche to the wound site. Our work takes inspiration from this process and uniformly tethers cytokines into the scaffold to measure changes in cell-mediated degradation and motility. This is the first step in designing cytokine concentration gradients into the material to direct cell migration. We measure changes in rheological properties, encapsulated cell-mediated pericellular degradation and migration in a hydrogel scaffold with covalently tethered cytokines, either tumor necrosis factor-α (TNF-α) or transforming growth factor-β (TGF-β). TNF-α is expressed in early stages of wound healing causing an inflammatory response. TGF-β is released in later stages of wound healing causing an anti-inflammatory response in the surrounding tissue. Both cytokines cause directed cell migration. We measure no statistically significant difference in modulus or the critical relaxation exponent when tethering either cytokine in the polymeric network without encapsulated hMSCs. This indicates that the scaffold structure and rheology is unchanged by the addition of tethered cytokines. Increases in hMSC motility, morphology and cell-mediated degradation are measured using a combination of multiple particle tracking microrheology (MPT) and live-cell imaging in hydrogels with tethered cytokines. We measure that tethering TNF-α into the hydrogel increases cellular remodeling on earlier days postencapsulation and tethering TGF-β into the scaffold increases cellular remodeling on later days. We measure tethering either TGF-β or TNF-α enhances cell stretching and, subsequently, migration. This work provides rheological characterization that can be used to design new materials that present chemical cues in the pericellular region to direct cell migration.
摘要：
聚合物-肽水凝胶被设计为可植入材料,其递送人间充质干细胞(hMSC)以治疗伤口。大多数伤口可以在没有干预的情况下通过愈合过程进展。在正常的愈合过程中，细胞因子从伤口释放以产生浓度梯度，这导致细胞从天然小生境向伤口部位的定向迁移。我们的工作从这个过程中获得灵感，并将细胞因子均匀地束缚到支架中，以测量细胞介导的降解和运动的变化。这是设计进入材料的细胞因子浓度梯度以指导细胞迁移的第一步。我们测量流变特性的变化，在含有共价连接的细胞因子的水凝胶支架中封装的细胞介导的细胞周降解和迁移，肿瘤坏死因子-α（TNF-α）或转化生长因子-β（TGF-β）。TNF-α在引起炎症反应的伤口愈合的早期阶段表达。TGF-β在伤口愈合的后期释放,引起周围组织中的抗炎应答。两种细胞因子均引起定向细胞迁移。当在没有包封的hMSC的情况下将任一细胞因子束缚在聚合物网络中时，我们没有测量模量或临界松弛指数的统计学显着差异。这表明通过添加束缚的细胞因子,支架结构和流变学没有改变。hMSC运动性增加，形态和细胞介导的降解使用多颗粒跟踪微流变学(MPT)和在具有束缚细胞因子的水凝胶中的活细胞成像的组合来测量。我们测量到将TNF-α束缚到水凝胶中在封装后的较早的日子增加了细胞重塑,并且将TGF-β束缚到支架中在较晚的日子增加了细胞重塑。我们测量连接TGF-β或TNF-α增强细胞伸展，随后,迁移。这项工作提供了流变学表征，可用于设计在细胞周围区域呈现化学线索以指导细胞迁移的新材料。
