Yan Huixian, Jin Bo
School of Aerospace Engineering and Applied Mechanics, Tongji University, 200092 Shanghai, China.
Eur Phys J E Soft Matter. 2012 May;35(5):36. doi: 10.1140/epje/i2012-12036-7. Epub 2012 May 25.
Amphoteric hydrogels contain both ionizable acidic and basic groups attached on the polymer chains, which can change their volume in response to the slight alteration of the surrounding environmental p H. In this paper, a theory of equilibrium swelling of amphoteric p H-sensitive hydrogels which is an extension of the formalism proposed by Marcombe et al. and a new hybrid free-energy density function of amphoteric hydrogels composed of the Edwards-Vilgis slip-link model and the Flory-Huggins solution theory as well as the contributions of mixing the mobile ions with the solvent, and dissociating the acidic and basic groups are presented for the prediction of the influence of environmental solution p H, microstructural parameters and geometric constraints on mechanical behavior. The calculations were modeled on chitosan-genipin gels, and the results were compared to experimental data. Numerical calculations show that the model is able to predict the dependence of swelling on p H and crosslinker qualitatively well and quantitatively close to the experimental data. Each gel shows minimal swelling at low p H but an increase in swelling until a maximum was reached; for most of the p H range, a good fit was achieved except for where the maximum swelling occurs; for experimental data, the maximum swelling appears at about pH = 4 , but for modeled data the maximum swelling appears between pH = 4 and pH = 6 ; each gel swell decreasing with increasing crosslinker concentration was also successfully predicted. The calculated results also show that microstructural parameters and geometric constraints have a significant impact on the mechanical behavior of the amphoteric hydrogels; the gel swells less when the network is more densely entangled and the maximum swelling ratio of the gels under biaxial constraint is only about one-third of the maximum when the gels swell freely. The theory developed here is valuable for the design and optimization of a drug delivery system.
两性水凝胶在聚合物链上同时含有可电离的酸性和碱性基团，这些基团可根据周围环境pH值的微小变化改变其体积。本文提出了一种两性pH敏感水凝胶的平衡溶胀理论，该理论是对马尔科姆等人提出的形式主义的扩展，以及一种由爱德华兹-维尔吉斯滑动链模型、弗洛里-哈金斯溶液理论以及移动离子与溶剂混合和解离酸性和碱性基团的贡献组成的两性水凝胶新的混合自由能密度函数，用于预测环境溶液pH值、微观结构参数和几何约束对力学行为的影响。计算以壳聚糖-京尼平凝胶为模型，并将结果与实验数据进行比较。数值计算表明，该模型能够定性地很好预测溶胀对pH值和交联剂的依赖性，并且在定量上接近实验数据。每种凝胶在低pH值下溶胀最小，但溶胀会增加，直到达到最大值；在大多数pH范围内，除了出现最大溶胀的地方外，都能很好地拟合；对于实验数据，最大溶胀出现在约pH = 4处，但对于模型数据，最大溶胀出现在pH = 4和pH = 6之间；还成功预测了每种凝胶随着交联剂浓度增加溶胀减小。计算结果还表明，微观结构参数和几何约束对两性水凝胶的力学行为有显著影响；当网络缠结更紧密时，凝胶溶胀较小，并且在双轴约束下凝胶的最大溶胀率仅为自由溶胀时最大溶胀率的三分之一左右。这里开发的理论对于药物递送系统的设计和优化具有重要价值。
