Silk Polymer Models for Structure-Function Relationships

智能优点-丝蛋白是一种有用的模型系统，用于研究疏水聚合物在水体系中衍生的新功能特性。绢丝纤维令人印象深刻的机械性能在于对家蚕和蜘蛛腺体结构发育的不同寻常的控制，所有这些都是通过控制水分含量和适当的顺序化学来实现的。其目的是通过控制丝素溶液中的水分含量，了解丝蛋白组装的机理基础，以此作为获得新的和改进的疏水聚合物加工选择的途径。这一见解对：(A)从丝绸中进行新材料工程，以及(B)模拟丝绸的新聚合物化学/序列具有重大意义，因为设计(化学序列)必须考虑加工环境和功能结果。系统地研究了通过渗透胁迫获得的含有高浓度蛋白质的丝素凝胶的形成和结构特征，以及通过化学和机械因素诱导的后续转变和结构和形态特征。具体地说，将追求以下目标：(A)通过系统地控制水分含量来比较水体系中的结构发展，包括比较来自蚕腺的天然凝胶和重组蚕丝；以及(B)研究特定环境因素(例如，pH、二价阳离子、温度)在不同水分含量下对结构和形态发展的速率和性质的作用。为了解决这些问题，将使用光谱技术(傅立叶变换红外光谱，FTIR；拉曼光谱)、散射技术(广角和小角X射线散射，WAXS/SAXS；小角光散射，SALS)和成像技术(原子力显微镜，AFM；扫描电子显微镜，扫描电子显微镜；光学椭偏测量法；差分干涉对比显微镜，DIC)来表征模型材料，以评估不同长度尺度的形貌和结构。这些评估将允许制定静态丝素凝胶的相图。然后，为了接近纤维形成的步骤，将研究应力(使用拉伸变形和剪切)对重组丝绸结构演变和相应的力学性能的影响。计划中的研究建立在实验室关于丝蛋白的溶解行为和控制这种行为的最新发现的基础上。更广泛的影响--拟议的实验代表了一种跨学科的方法来研究这种独特的聚合物，包括一名生物化学家(David Kaplan)和一名物理学家(Peggy Cebe)。参与研究的研究生和本科生将在他们的研究过程中从这两个角度获得直接的见解，同时也为聚合物科学和工程的新方向做出贡献。研究方法和成果将以多种方式输出到课堂环境中，供更广泛的学生使用，包括本科生和研究生课程的讲座模块，为本科生提供的研究实验室经验窗口，以及为聋人和听力障碍学生提供的具体方案。

Intellectual Merit - Silk proteins are a useful model system for the study of novel functional properties derived from hydrophobic polymers in aqueous systems. The impressive mechanical properties of spun silk fibers rest with the unusual control of structure development in glands in silkworms and spiders, all achieved through control of water content in combination with appropriate sequence chemistry. The objective is to understand the mechanistic basis for silk protein assembly, through control of water content in silk solutions, as a route to new and improved processing options for hydrophobic polymers in general. This insight has strong implications for: (a) new materials engineering from silks, and (b) for new polymer chemistries/sequences that mimic silk in that the designs (chemical sequences) must consider processing environments as well as functional outcomes. A systematic investigation will be undertaken into the formation and structural features of silk gels containing high concentrations of protein achieved via osmotic stress, and subsequent transitions and structural and morphological features induced through chemical and mechanical factors. Specifically, the following aims will be pursued: (a) to compare structure development in aqueous systems by systematic control of water content, including comparisons between native gels from silkworm glands and reconstituted silkworm silk; and, (b) to study the role of specific environmental factors (e.g., pH, divalent cations, temperature) on rates and nature of structure and morphology development at different water contents. To address these questions, model materials will be characterized using spectroscopic techniques (Fourier Transform infrared, FTIR; Raman), scattering techniques (wide and small angle X-ray scattering, WAXS/SAXS; small angle light scattering, SALS), and imaging techniques (atomic force microscopy, AFM; scanning electron microscopy, SEM; optical ellipsometry; differential interference contrast microscopy, DIC) to assess morphologies and structures at a variety of length scales. These assessments will permit the formulation of phase diagrams for quiescent silk gels. Then, to approximate the step of fiber formation, the effects of stress (using tensile deformation and shear) on structure evolution and the corresponding mechanical properties of reconstituted silks will be studied. The planned studies build off the recent discoveries from the lab on the solution behavior of silk proteins and control of this behavior. %%%Broader Impact - The proposed experiments represent an interdisciplinary approach to the study of this unique polymer, including a biochemist (David Kaplan) and a physicist (Peggy Cebe). The graduate and undergraduate students involved will gain direct insight from both perspectives during their research, while also contributing to new directions in polymer science and engineering. The research approaches and outcomes will be exported into classroom settings in a number of ways for a broader audience of students including lecture modules in both undergraduate and graduate courses, windows on research laboratory experiences for undergraduate students, and specific programs for deaf and hearing impaired students.