Uncovering Fundamental Transport Principles in Novel, Ultraclean Lignin-Based Hydrogels for Bioseparations

生物制品，如蛋白质和核酸，通常必须从溶液中分离出来，作为工业纯化过程的一部分。这种分离的一种方法是使含有生物制品的液体通过由水凝胶制成的膜。水凝胶是一种由聚合链组成的三维网络，旨在吸收水基溶液。木质素是一种基于植物的聚合物，可以加入到水凝胶网络中，以增强膜从溶液中捕获生物分子的能力。然而，关于向水凝胶中添加木质素如何改变所得到的复合膜的三维结构的信息相对较少。此外，从植物材料中回收木质素的传统方法导致木质素纯度低，化学结构不可预测。在水凝胶膜的生产中使用非均相木质素将导致复合材料具有不明确的网络结构，这使得设计用于实际应用的膜变得困难。该项目的目标是阐明将木质素引入水凝胶如何影响所得结构。该项目将利用一种新的木质素净化工艺来获得分子结构可控的超净木质素。通过系统地改变木质素的聚合物水凝胶结构，揭示了膜结构、分子相互作用和蛋白质通过膜运输之间的基本关系。该项目的预期结果通过为新型复合水凝胶的预测材料设计建立参数，有可能对下一代材料制造策略产生重大影响。复合水凝胶膜被广泛应用于生物分子分离、组织工程、蛋白质输送等领域。研究工作与教育推广计划密切相关，旨在通过开发与生物分离和水净化相关的“膜模块”，吸引和激励下一代工程师和科学家。该研究的目的是揭示一种新型木质素基水凝胶的蛋白质分离和固定化性能的基本运输原理和关键网络结构-性质关系。这一目标将通过利用低分散性和控制分子量的分馏木质素来系统地改变复合水凝胶的网络结构（即网孔大小）来实现。通过调整木质素的化学功能和分子量，可以阐明结构和分子尺度相互作用对膜性能的作用。木质素组分将被官能团修饰，使它们能够参与形成水凝胶网络结构的交联反应。各种生物大分子从复合膜上的分离/结合效率将通过原位渗透实验和长期的“结合-释放”实验相结合来研究。复合膜的水输运和水合力学性能将使用基于力学的技术——孔隙弹性松弛压痕来表征。利用达西定律框架，可以确定水化网络结构的平均孔（孔）大小。利用小角中子散射对水合膜的结构进行独立表征，并将结果与压痕实验结果进行比较。此外，生物大分子和复合水凝胶之间的分子水平相互作用，以及膜内的蛋白质动力学，将分别使用红外光谱和准弹性中子散射来捕获。这些发现有可能影响其他几种膜基分离工艺中新材料的设计，例如用于水净化和海水淡化的材料。最后，本提案的研究部分与基于stem的外展目标密切相关，该目标旨在将本研究的发现和材料整合到与生物分离和水净化相关的部门外展工作中。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Biological products, such as proteins and nucleic acids, must often be separated from a solution as part of an industrial purification process. One approach to this separation is to pass the fluid containing the biological product through a membrane made of hydrogels. Hydrogels are a three-dimensional network of polymeric chains that are designed to absorb water-based solutions. Lignin, a plant-based polymer, can be incorporated into the hydrogel network to enhance the membrane's ability to capture biological molecules from the solution. However, there is relatively little information on how adding lignin to the hydrogel changes the three-dimensional structure of the resulting composite membrane. Additionally, conventional methods used to recover lignin from plant material results in low-purity lignin with unpredictable chemical structure. Using heterogeneous lignin in the production of hydrogel membranes will result in composite materials with ill-defined network structures, making it difficult to design membranes for real applications. The goal of this project is to clarify how introducing lignin into hydrogels influences the resulting structure. The project will make use of a new lignin purification process to obtain ultraclean lignin with controlled molecular architecture. By systematically varying the polymeric hydrogel structure with lignin, fundamental relationships between membrane structure, molecular interactions, and protein transport through the membrane will be uncovered. The anticipated outcomes of this project have the potential substantially impact next-generation materials fabrication strategies by establishing parameters for predictive materials design of novel, composite hydrogels. Composite hydrogel membranes are finding use in applications ranging from biological molecule separation, tissue engineering, to protein delivery. The research efforts are closely tied to educational outreach initiatives that aim to engage and inspire the next generation of engineers and scientists through the development of a 'membrane module' related to bioseparations and water purification. The aim of the proposed research is to uncover the fundamental transport principles and key network structure-property relationships underlying the protein separation and immobilization performance of an emerging class of novel, lignin-based hydrogels. This aim will be achieved by leveraging fractionated lignins of low dispersity and controlled molecular weights to systematically vary the network structure (i.e., mesh size) of the composite hydrogels. By tuning both the chemical functionality and the molecular weight of the lignins, the role of both structure and molecular-scale interactions on membrane performance can be elucidated. The lignin fractions will be modified with functional groups that allow them to participate in the crosslinking reaction that forms the network structure of the hydrogel. The separation/binding efficiency of various biomacromolecules from the composite membranes will be investigated using a combination of in situ permeation experiments with longer-term, 'bind-and-release' experiments. The water transport and hydrated mechanical properties of composite membranes will be characterized using a mechanics-based technique, poroelastic relaxation indentation. Using a Darcy's law framework, the average mesh (pore) size of the hydrated network structure can be determined. The structure of the hydrated membranes will be independently characterized using small-angle neutron scattering, and the results will be compared to those obtained from indentation experiments. Additionally, molecular-level interactions between the biomacromolecules and the composite hydrogels, as well as protein dynamics within the membrane, will be captured using infrared spectroscopy and quasi-elastic neutron scattering, respectively. These findings have the potential to impact the design of new materials in several other membrane-based separations processes, such as materials for water purification and desalination. Finally, the research component of this proposal is closely tied to STEM-based outreach objectives that seek to integrate findings and materials from this research into departmental outreach efforts related to bioseparations and water purification.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.