Heichel Danielle L, Burke Kelly A
Polymer Program, Institute of Materials Science, University of Connecticut, 97 North Eagleville Road Unit 3136, Storrs, Connecticut 06269-3136, United States.
Department of Chemical and Biomolecular Engineering, University of Connecticut, 191 Auditorium Road Unit 3222, Storrs, Connecticut 06269-3222, United States.
ACS Biomater Sci Eng. 2019 Jul 8;5(7):3246-3259. doi: 10.1021/acsbiomaterials.9b00786. Epub 2019 Jun 25.
Compared to conventional wound closure methods like sutures and staples, polymer-based tissue adhesives afford some distinct advantages, such as greater ease of deployment in spatially constrained surgical sites. One way to achieve aqueous adhesion is by introducing catechol functional groups that form coordinate and covalent bonds with a variety of substrates. This approach, inspired by marine organisms, has been applied to biopolymers and synthetic polymers, but one key challenge is that compositions that are soluble in water are often susceptible to high swelling ratios that can result in undesired compression of neighboring tissues. This work sought to synthesize aqueous adhesive gels that are capable of two modes of association: (1) adhesion and covalent cross-linking reactions arising from catechol oxidation and (2) noncovalent cross-linking arising from self-assembly of polymer backbones within the gelled adhesive. The network's self-assembly after gelation was envisioned to afford control over swelling and reinforce its strength. silk fibroin was selected as the backbone of the adhesive network because it can be processed into an aqueous solution yet later be rendered insoluble in water through the assembly of its hydrophobic protein core. Distinct from a previous approach to functionalize silk directly with catechol groups, this work investigated generation of catechol on silk fibroin by enzymatically modifying phenolic side chains, where it was found that this enzymatic approach led to conjugates with higher degrees of catechol functionalization and aqueous solubility. Silk fibroin was functionalized with tyramine to enrich the protein's phenolic side chains, which were subsequently oxidized into catechol groups using mushroom tyrosinase (MT). The gelation of the silk conjugates with MT was monitored by rheology, and the gels exhibited low water uptake. Phenolic enrichment increased the rate of chemical cross-linking leading to gelation but did not interrupt assembly of silk's secondary structures. Adhesion of the tyramine-silk conjugates to porcine intestine was found to be superior to fibrin sealant, and induction of β sheet secondary structures was found to further enhance adhesive strength through a second mode of cross-linking. Neither the chemical functionalization nor phenol oxidation affected the ability of intestinal epithelial cells (Caco-2) to attach and proliferate. Phenolic functionalization and oxidative cross-linking of silk fibroin was found to afford a new route to water-soluble, catechol-functionalized polymers, which were found to display excellent adhesion to mucosal tissue and whose secondary structure provides an additional mode to control strength and swelling of adhesive gels.
与缝线和吻合钉等传统伤口闭合方法相比，基于聚合物的组织粘合剂具有一些明显的优势，例如在空间受限的手术部位更易于应用。实现水性粘附的一种方法是引入儿茶酚官能团，该官能团可与多种底物形成配位键和共价键。这种受海洋生物启发的方法已应用于生物聚合物和合成聚合物，但一个关键挑战是，可溶于水的组合物往往容易出现高溶胀率，这可能导致对相邻组织产生不良压迫。这项工作旨在合成能够进行两种缔合模式的水性粘合剂凝胶：（1）由儿茶酚氧化引起的粘附和共价交联反应，以及（2）凝胶状粘合剂中聚合物主链自组装产生的非共价交联。凝胶化后网络的自组装被设想为能够控制溶胀并增强其强度。选择丝素蛋白作为粘合剂网络的主链，因为它可以加工成水溶液，但随后通过其疏水蛋白核心的组装而变得不溶于水。与先前直接用儿茶酚基团对丝进行功能化的方法不同，这项工作研究了通过酶促修饰酚侧链在丝素蛋白上生成儿茶酚，结果发现这种酶促方法导致了具有更高儿茶酚功能化程度和水溶性的共轭物。用酪胺对丝素蛋白进行功能化，以富集蛋白质的酚侧链，随后使用蘑菇酪氨酸酶（MT）将其氧化成儿茶酚基团。通过流变学监测丝共轭物与MT的凝胶化过程，凝胶表现出低吸水率。酚富集提高了导致凝胶化的化学交联速率，但没有中断丝二级结构的组装。发现酪胺 - 丝共轭物对猪肠的粘附性优于纤维蛋白密封剂，并且发现β折叠二级结构的诱导通过第二种交联模式进一步增强了粘附强度。化学功能化和酚氧化均未影响肠上皮细胞（Caco - 2）附着和增殖的能力。发现丝素蛋白的酚功能化和氧化交联提供了一条通往水溶性、儿茶酚功能化聚合物的新途径，这些聚合物被发现对粘膜组织具有优异的粘附性，并且其二级结构提供了另一种控制粘合剂凝胶强度和溶胀的模式。
