Due to the unique properties of biopolymer gels, they are extensively used in the food industry and biomedical applications such as drug delivery. Different from rubber-like materials, the constituting chains in many biopolymer gels randomly interlock with neighbouring chains by means of physical rather than covalent cross-linking. Such polymer networks are characterized by two principal regions: the disordered zone containing coiled chains and the ordered zone in the form of ion-mediated aggregation of macromolecules and/or helical structures. The ordered regions serve as junction zones between the disordered chains, and the size of these zones may alter as a result of zipping/unzipping phenomena. The entire polymer network can be envisaged as a collection of coil–rod structures serving as the building blocks, where the coil and rod are representative of the disordered and ordered zones, respectively. The present work aims to provide a rigorous formulation of coil–rod structure that can predict its mechanical behaviour including zipping/unzipping characteristics. The coil–rod structure is modelled by a rod attached to a freely jointed chain, where the length of the rod and the number of segments in the freely jointed chain are adjustable input parameters. The relationship between the force and end-to-end distance of the coil–rod structure is derived based on statistical mechanics. The formulation is extended to incorporate the zipping/unzipping mechanism with the aid of Boltzmann averaging. As an example of its applications, the model is implemented into the eight-chain model to describe the macroscopic mechanical response of the network. Another example is demonstrated where the zipping/unzipping mechanism is shown to be able to capture the unwinding of a double-stranded DNA under a tensile force. The formulation presented in this work paves the way for future studies that model biopolymer gel networks with potentially complex chain interactions.

由于生物聚合物凝胶的独特性能，它们广泛用于食品工业和药物输送等生物医学应用。与橡胶类材料不同，许多生物聚合物凝胶中的组成链通过物理交联而非共价交联与相邻链随机互锁。这种聚合物网络的特征在于两个主要区域：包含卷曲链的无序区和以离子介导的大分子和/或螺旋结构聚集形式存在的有序区。有序区域充当无序链之间的连接区，这些区域的大小可能会因压缩/解压缩现象而改变。整个聚合物网络可以设想为作为构建块的卷棒结构的集合，其中线圈和棒分别代表无序和有序区域。目前的工作旨在提供一个严格的卷杆结构公式，可以预测其机械行为，包括压缩/解压缩特性。线圈-杆结构由连接到自由连接链的杆建模，其中杆的长度和自由连接链中的段数是可调输入参数。基于统计力学推导了线圈-杆结构的力与端到端距离之间的关系。在玻尔兹曼平均的帮助下，该公式被扩展为包含压缩/解压缩机制。作为其应用的一个例子，该模型被实现为八链模型来描述网络的宏观力学响应。演示了另一个示例，其中显示压缩/解压缩机制能够捕获双链 DNA 在张力下的解旋。这项工作中提出的配方为未来的研究铺平了道路，这些研究模拟具有潜在复杂链相互作用的生物聚合物凝胶网络。