Yucel Tuna, Cebe Peggy, Kaplan David L
Department of Biomedical Engineering, Tufts University, Medford, Massachusetts, USA.
Biophys J. 2009 Oct 7;97(7):2044-50. doi: 10.1016/j.bpj.2009.07.028.
A novel, to our knowledge, technique was developed to control the rate of beta-sheet formation and resulting hydrogelation kinetics of aqueous, native silk solutions. Circular dichroism spectroscopy indicated that vortexing aqueous solutions of silkworm silk lead to a transition from an overall protein structure that is initially rich in random coil to one that is rich in beta-sheet content. Dynamic oscillatory rheology experiments collected under the same assembly conditions as the circular dichroism experiments indicated that the increase in beta-sheet content due to intramolecular conformational changes and intermolecular self-assembly of the silk fibroin was directly correlated with the subsequent changes in viscoelastic properties due to hydrogelation. Vortexing low-viscosity silk solutions lead to orders-of-magnitude increase in the complex shear modulus, G*, and formation of rigid hydrogels (G* approximately 70 kPa for 5.2 wt % protein concentration). Vortex-induced, beta-sheet-rich silk hydrogels consisted of permanent, physical, intermolecular crosslinks. The hydrogelation kinetics could be controlled easily (from minutes to hours) by changing the vortex time, assembly temperature and/or protein concentration, providing a useful timeframe for cell encapsulation. The stiffness of preformed hydrogels recovered quickly, immediately after injection through a needle, enabling the potential use of these systems for injectable cell delivery scaffolds.
据我们所知，我们开发了一种新的技术来控制β-折叠的形成速率以及天然蚕丝水溶液的水凝胶化动力学。圆二色光谱表明，对家蚕丝水溶液进行涡旋处理会导致蛋白质整体结构从最初富含无规卷曲转变为富含β-折叠结构。在与圆二色性实验相同的组装条件下进行的动态振荡流变学实验表明，丝素蛋白分子内构象变化和分子间自组装导致的β-折叠含量增加与随后水凝胶化引起的粘弹性性质变化直接相关。对低粘度蚕丝溶液进行涡旋处理会使复数剪切模量G增加几个数量级，并形成刚性水凝胶（对于5.2 wt%的蛋白质浓度，G约为70 kPa）。涡旋诱导的富含β-折叠的蚕丝水凝胶由永久性的物理分子间交联组成。通过改变涡旋时间、组装温度和/或蛋白质浓度，可以轻松控制水凝胶化动力学（从几分钟到几小时），这为细胞封装提供了有用的时间范围。预成型水凝胶在通过针头注射后能迅速恢复其刚度，这使得这些系统有可能用于可注射细胞递送支架。
