Modelling Hydrogel Mechanics

生命科学和生物医学领域的关键工程挑战之一是设计和制造用于3D细胞培养、组织工程和细胞/药物输送的定制支架，即细胞壁龛。无论是在体外用于研究细胞行为，还是在体内用于促进受损组织的再生，这些细胞利基支撑着生物技术和生物医学行业的一个巨大且不断增长的部门。为了构建这样的支架，人们已经做出了重大努力来开发新型生物材料。其中一类引起了人们极大兴趣的材料是水凝胶，因为这些柔软的、高度水合的材料可以被设计成模仿细胞的利基。理解水凝胶力学是很重要的，因为细胞的行为很大程度上取决于其力学微环境。水凝胶由交联的亲水聚合物链网络组成，当水化时，形成具有高度非线性、粘弹性机械性能的软固体。在这个项目中，我们将建立一个模型，说明这些网络结构如何影响水凝胶的宏观力学。在微观上，我们将建立一个离散模型，其中每个光纤到光纤交叉链路定义网络中的一个节点，节点的连接性通过邻接矩阵来捕获。我们将假设连接节点的光纤只抵抗一次紧绷的运动，并将调查关于其本构行为的不同假设如何影响整个网络。该项目的主要目的是了解水凝胶的微观力学性能和网络结构与其宏观力学行为之间的关系。该项目的具体目标是：-发展组成多肽基水凝胶的聚合物网络变形的微观尺度模型，在两个维度上，假设纤维的线弹性本构行为-将上述模型扩展到三维-通过将纤维建模为线粘弹性材料并在纤维之间加入二维流体流动来预测水凝胶的粘弹性行为-将粘弹性模型扩展到三维-根据现有的实验应力-应变数据测试模型的预测，使用单个纤维的力学数据作为模型的输入-根据模型的一致性或不一致性迭代模型-确定产生给定宏观应力-应变曲线所需的最佳纤维机械参数-产生使用模型设计的具有定制机械性能的新水凝胶

One of the key engineering challenges in the life science and biomedical sectors is the design and manufacturing of bespoke scaffolds for 3D cell culture, tissue engineering and cell/drug delivery, i.e. cell niches. These cell niches underpin a large and growing sector of biotech and biomed industries, whether they are used in vitro to study cell behaviour, or in vivo to promote regeneration of damaged tissues. Significant efforts have been made to develop novel biomaterials to build such scaffolds. One such class of material, which has attracted significant interest, is hydrogels, as these soft, highly hydrated materials can be engineered to mimic the cell niche. It is important to understand hydrogel mechanics, as a cell's behaviour depends strongly on its mechanical microenvironment. Hydrogels consist of networks of crosslinked, hydrophilic polymer chains, which, when hydrated, form a soft solid with highly nonlinear, viscoelastic mechanical properties. In this project, we will build a model of how the structure of these networks impacts upon the macroscale mechanics of the hydrogel. At the microscale, we will build a discrete model, whereby each fibre to fibre crosslink defines a node in the network, with the connectivity of the nodes being captured via an adjacency matrix. We will assume that the fibres connecting the nodes resist motion only once taut and will investigate how different assumptions about their constitutive behaviour impacts on the network as a whole. Finally, we will couple the microscale model to a continuum level constitutive equation to describe the macroscale mechanics.The overarching aim of the project is to understand the relationship between the microscale mechanical properties and network structure of hydrogels and their macroscale mechanical behaviour.The specific objectives of the project are to:- Develop a microscale model of the deformation of the polymer networks that make up peptide-based hydrogels, in two dimensions, assuming linear elastic constitutive behaviour for the fibres- Extend the above model to three dimensions- Predict the viscoelastic behaviour of the hydrogels by modelling the fibres as linear viscoelastic materials and incorporating fluid flow between the fibres in two dimensions- Extend the viscoelastic model to three dimensions- Test the predictions of the models against existing experimental stress-strain data, using mechanical data on individual fibres as the inputs for the models- Iterate the models based on their agreement, or lack of agreement, with the experimental data- Determine the optimal fibre mechanical parameters that are required to produce a given macroscale stress-strain curve- Produce new hydrogels with bespoke mechanical properties that have been designed using the models