Bucciarelli Alessio, Greco Gabriele, Corridori Ilaria, Pugno Nicola M, Motta Antonella
Microsystem Technology Group, Center for Materials and Microsystems, Fondazione Bruno Kessler, Via Sommarive 9, Trento 38123, Italy.
Laboratory of Bio-inspired, Bionic, Nano, Meta Materials and Mechanics, Department of Civil, Environmental and Mechanical Engineering, University of Trento, Via Mesiano 77, Trento 38123, Italy.
ACS Biomater Sci Eng. 2021 Apr 12;7(4):1374-1393. doi: 10.1021/acsbiomaterials.0c01657. Epub 2021 Feb 17.
Silk fibroin is a protein with a unique combination of properties and is widely studied for biomedical applications. The extraction of fibroin (degumming) from the silk filament impacts the properties of the outcoming material. The degumming can be conducted with different procedures. Among them, the most used and studied procedure in the research field is the alkali degumming with sodium carbonate (NaCO). In this study, by the use of a statistical method, namely, design of experiment (DOE), we characterized the NaCO degumming, taking into consideration the main process factors involved and changing them within a selected range of values. We considered the process temperature and time, the salt concentration, and the number of baths used, testing the impact of these variables on the fibroin properties by building empirical models. These models not only took into consideration the direct effect of the process factors but also their combined effect, which are not conventionally detectable with other methods. The weight loss and the amount of sericin removed in the process were determined and used as a measure of the effectiveness of the process. The secondary structure, the molecular weight, the diameter of fibers, and their morphology and mechanical properties were studied with the intent to correlate the macroscopical properties with the structural changes. We report, for the first time, the possibility to effectively remove all sericin from the silk fibroin using NaCO, using a process that requires less salt, water, and energy, in comparison with the standard alkali protocol, making this technique overall more environmentally sustainable; in addition, we have demonstrated the possibility to tune the material properties by varying the degumming conditions and even to optimize them with empirical statistically based equations that allow one to directly set the optimal process parameters. The major effect on the macroscopical properties (such as the ultimate strength and Young's modulus) has been proved to be correlated with the removal of sericin instead of the microstructural variations. Finally, a ready-to-use table with a set of optimized degumming procedures to maximize or minimize the studied properties was provided.
丝素蛋白是一种具有独特性能组合的蛋白质，在生物医学应用方面受到广泛研究。从丝纤维中提取丝素蛋白（脱胶）会影响所得材料的性能。脱胶可以通过不同的程序进行。其中，研究领域中最常用和研究最多的程序是用碳酸钠（Na₂CO₃）进行碱脱胶。在本研究中，我们使用一种统计方法，即实验设计（DOE），对Na₂CO₃脱胶进行了表征，考虑了主要的工艺因素，并在选定的值范围内改变这些因素。我们考虑了工艺温度和时间、盐浓度以及使用的浴数，通过建立经验模型来测试这些变量对丝素蛋白性能的影响。这些模型不仅考虑了工艺因素的直接影响，还考虑了它们的综合影响，而这是其他方法通常无法检测到的。测定了该过程中的失重和丝胶去除量，并将其用作该过程有效性的度量。研究了二级结构、分子量、纤维直径及其形态和力学性能，旨在将宏观性能与结构变化联系起来。我们首次报道了使用Na₂CO₃从丝素蛋白中有效去除所有丝胶的可能性，与标准碱法相比，该方法所需的盐、水和能源更少，使该技术总体上更具环境可持续性；此外，我们还证明了通过改变脱胶条件来调整材料性能的可能性，甚至可以使用基于经验统计的方程对其进行优化，这些方程允许直接设置最佳工艺参数。已证明对宏观性能（如极限强度和杨氏模量）的主要影响与丝胶的去除有关，而不是与微观结构变化有关。最后，提供了一个现成的表格，其中包含一组优化的脱胶程序，可最大化或最小化所研究的性能。
