Understanding the deformation behavior of biopolymer hydrogels would aid in the design of artificial hydrogels and nanoparticle-based drug delivery systems, which have been extensively used in the fields of biomedicine. Here, we develop a mechanistically motivated constitutive model to elucidate the structural evolution of biopolymer hydrogels. A free energy function includingconfigurational entropy of biopolymer nanofibers, potential energy of physical crosslinks, and mixing energy of water molecules is formulated. Both the micro/nanostructures and dynamic features of nanofibrous network under stretching are captured investigating the evolution of physical crosslinks and water hydration. In addition, a quantitative relationship correlating the pore size in the nanofibrous network with mechanical stretching is proposed. Different from chemically crosslinked hydrogels, the pore size of physically crosslinked hydrogels could continuously increase under stretching, which is attributed to the straightening and bundling of biopolymer nanofibers. We further find that a low strain rate or a high swelling ratio promotes the structural evolution of biopolymer hydrogels and increases the pore size of the network. The model predictions are in good agreement with the experimental results. This work could shed light on the deformation mechanisms of physically crosslinked biopolymer hydrogels, thus providing guidelines for the design of drug delivery systems translocating within biopolymer hydrogels.

了解生物聚合物水凝胶的变形行为将有助于设计人造水凝胶和基于纳米颗粒的药物输送系统，这些系统已广泛应用于生物医学领域。在这里，我们开发了一个机械驱动的本构模型来阐明生物聚合物水凝胶的结构演变。制定了包括生物聚合物纳米纤维的构型熵、物理交联势能和水分子混合能的自由能函数。捕获拉伸下纳米​​纤维网络的微/纳米结构和动态特征，研究物理交联和水合作用的演变。此外，提出了将纳米纤维网络中的孔径与机械拉伸相关联的定量关系。与化学交联的水凝胶不同，物理交联的水凝胶的孔径在拉伸下会不断增加，这归因于生物聚合物纳米纤维的拉直和集束。我们进一步发现低应变率或高溶胀比促进生物聚合物水凝胶的结构演变并增加网络的孔径。模型预测与实验结果吻合较好。这项工作可以阐明物理交联的生物聚合物水凝胶的变形机制，从而为在生物聚合物水凝胶内易位的药物输送系统的设计提供指导。这归因于生物聚合物纳米纤维的拉直和集束。我们进一步发现低应变率或高溶胀比促进生物聚合物水凝胶的结构演变并增加网络的孔径。模型预测与实验结果吻合较好。这项工作可以阐明物理交联的生物聚合物水凝胶的变形机制，从而为在生物聚合物水凝胶内易位的药物输送系统的设计提供指导。这归因于生物聚合物纳米纤维的拉直和集束。我们进一步发现低应变率或高溶胀比促进生物聚合物水凝胶的结构演变并增加网络的孔径。模型预测与实验结果吻合较好。这项工作可以阐明物理交联的生物聚合物水凝胶的变形机制，从而为在生物聚合物水凝胶内易位的药物输送系统的设计提供指导。