Ham Trevor R, Lee Ryan T, Han Sangheon, Haque Salma, Vodovotz Yael, Gu Junnan, Burnett Luke R, Tomblyn Seth, Saul Justin M
Department of Chemical, Paper and Biomedical Engineering, Miami University , 650 East High Street, Oxford, Ohio 45056, United States.
Department of Biomedical Engineering, University of Akron , Auburn Science and Engineering Center 275, West Tower, Akron, Ohio 44325, United States.
Biomacromolecules. 2016 Jan 11;17(1):225-36. doi: 10.1021/acs.biomac.5b01328. Epub 2015 Dec 14.
Tunable erosion of polymeric materials is an important aspect of tissue engineering for reasons that include cell infiltration, controlled release of therapeutic agents, and ultimately to tissue healing. In general, the biological response to proteinaceous polymeric hydrogels is favorable (e.g., minimal inflammatory response). However, unlike synthetic polymers, achieving tunable erosion with natural materials is a challenge. Keratins are a class of intermediate filament proteins that can be obtained from several sources, including human hair, and have gained increasing levels of use in tissue engineering applications. An important characteristic of keratin proteins is the presence of a large number of cysteine residues. Two classes of keratins with different chemical properties can be obtained by varying the extraction techniques: (1) keratose by oxidative extraction and (2) kerateine by reductive extraction. Cysteine residues of keratose are "capped" by sulfonic acid and are unable to form covalent cross-links upon hydration, whereas cysteine residues of kerateine remain as sulfhydryl groups and spontaneously form covalent disulfide cross-links. Here, we describe a straightforward approach to fabricate keratin hydrogels with tunable rates of erosion by mixing keratose and kerateine. SEM imaging and mechanical testing of freeze-dried materials showed similar pore diameters and compressive moduli, respectively, for each keratose-kerateine mixture formulation (∼1200 kPa for freeze-dried materials and ∼1.5 kPa for hydrogels). However, the elastic modulus (G') determined by rheology varied in proportion with the keratose-kerateine ratios, as did the rate of hydrogel erosion and the release rate of thiol from the hydrogels. The variation in keratose-kerateine ratios also led to tunable control over release rates of recombinant human insulin-like growth factor 1.
聚合物材料的可控降解是组织工程的一个重要方面，原因包括细胞浸润、治疗剂的控释以及最终的组织愈合。一般来说，对含蛋白质的聚合物水凝胶的生物学反应是良好的（例如，炎症反应最小）。然而，与合成聚合物不同，用天然材料实现可控降解是一项挑战。角蛋白是一类中间丝蛋白，可从多种来源获得，包括人类毛发，并且在组织工程应用中的使用越来越多。角蛋白的一个重要特征是存在大量半胱氨酸残基。通过改变提取技术可以获得两类具有不同化学性质的角蛋白：（1）通过氧化提取得到的角糖和（2）通过还原提取得到的角朊。角糖的半胱氨酸残基被磺酸“封端”，在水合时不能形成共价交联，而角朊的半胱氨酸残基保留为巯基并自发形成共价二硫键交联。在这里，我们描述了一种通过混合角糖和角朊来制备具有可控降解速率的角蛋白水凝胶的简单方法。冷冻干燥材料的扫描电子显微镜成像和力学测试表明，每种角糖 - 角朊混合物配方的孔径和压缩模量分别相似（冷冻干燥材料约为1200 kPa，水凝胶约为1.5 kPa）。然而，通过流变学测定的弹性模量（G'）与角糖 - 角朊比例成比例变化，水凝胶的降解速率和水凝胶中硫醇的释放速率也是如此。角糖 - 角朊比例的变化还导致对重组人胰岛素样生长因子1释放速率的可控调节。
