Understanding Mesoscale Structures of Nanocrystalline Domains in Silk using Sum Frequency Generation Vibrational Spectroscopy

在化学部（CHE）的化学测量和成像（CMI）计划的支持下，以及材料研究部（DMR）的生物材料计划（BMAT）的共同资助下，Penn州立大学的Seong Kim博士和他的团队正在开发一种强大的探针，用于研究生物体如何组装水溶性材料，以产生不溶性的半水溶性物质。结晶聚合物，以提供各种机械功能，如结构支撑和能量储存。他们的工作旨在推进目前对生物体如何利用结构顺序来定制晶体生物聚合物（如丝纤维中发现的那些）的机械性能的理解。该方法将利用复杂的光谱工具来定量探测天然丝绸内部的结构顺序和组装。来自代表性不足群体的学生，包括第一代大学生，将参与这些现代光谱研究，与Kim博士和他的研究生密切合作。研究动机和方法将被整合到一个研究生水平的材料表征课程。 与宾夕法尼亚州立大学弗罗斯特昆虫博物馆相关的外联活动将有助于公众熟悉节肢动物产生的材料科学。这项工作的主要表征方法是振动和频产生（SFG）光谱学-一种源于非中心对称的非线性光学过程。 虽然SFG通常被认为是一种表面敏感的工具，但它也可以区分分子的非中心对称排列与其无序的环境。虽然可能用作分散在无定形聚合物基质（例如，丝纤维中的β-折叠结构域），在多尺度三维结构分析中遇到的挑战远远超出了二维表面的复杂性。为了解决这一障碍，Kim小组正在努力：（i）建立天然丝纤维中普遍存在的β-折叠部分的SFG光谱解释;（ii）破译丝中结晶β-折叠的介观三维有序性;以及（iii）在受控湿度条件下在无应力和拉伸应变状态下对丝纤维进行操作SFG分析。从这项研究中建立的操作SFG方法和知识将可能适用于其他天然生物聚合物的研究，如甲壳素，胶原蛋白和弹性蛋白以及仿生材料，突出了这项工作的广泛科学影响的潜力。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

With support from the Chemical Measurement and Imaging (CMI) program in the Division of Chemistry (CHE), and co-funding from the Biomaterials Program (BMAT) in the Division of Materials Research (DMR), Dr. Seong Kim and his team at Penn State University are developing powerful probes of the way living organisms assemble water-soluble materials to produce insoluble semi-crystalline polymers to serve various mechanical functions such as structural support and energy storage. Their work aims to advance current understanding of how structural order is exploited by living organisms to tailor mechanical properties of crystalline biopolymers like those found in silk fibers. The approach will utilize sophisticated spectroscopic tools to quantitatively probe structural order and assembly inside natural silk. Students from underrepresented groups, including first-generation college students, will be involved in these modern spectroscopic studies, working in close collaboration with Dr. Kim and his graduate students. The research motivations and methodologies will be integrated into a graduate-level materials characterization course. Outreach activities associated with the Frost Entomological Museum at Penn State will help familiarize the general public with the science of materials produced by arthropods The main characterization method of this work is vibrational sum-frequency-generation (SFG) spectroscopy - a nonlinear optical process originating from noncentrosymmetry. While SFG is typically considered to be a surface-sensitive tool, it can also distinguish noncentrosymmetric arrangements of molecules from their disordered surroundings. While potentially useful as a probe of nano- to meso-scale order of noncentrosymmetric crystals dispersed in an amorphous polymer matrix (e.g., beta-sheet domains in silk fibers), the challenges encountered in the analysis of multi-scale three-dimensional structures are far beyond the complexity of two-dimensional surfaces. To address this obstacle, the Kim group is working to: (i) establish the SFG spectral interpretation of beta-sheet moieties prevalent in natural silk fibers; (ii) decipher mesoscale three-dimensional order of crystalline beta-sheets in silk; and (iii) conduct operando SFG analysis of silk fibers under stress-free and tensile strain states in controlled humidity conditions. The operando SFG methodology and knowledge established from this study will likely be applicable to studies of other natural biopolymers such as chitin, collagen and elastin as well as biomimetic materials, highlighting the potential for broad scientific impact of this work.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.