Multi-stimuli-responsive hydrogels are being increasingly studied due to their sensitive response to small stimuli and wide applications in biosensors and drug delivery. In this study, a multi-stimuli-responsive hydrogel, poly(hydroxyethyl methacrylate-co-N-vinyl pyrrolidone-co-methacrylic acid-co-N-isopropylacryl amide) [poly(HEMA-co-NVP-co-MAA-co-NIPA)], was synthesized by radical polymerization and characterized by Fourier transform infrared (FTIR) and ¹³C NMR spectroscopy techniques. With the aids of scanning electron microscopy (SEM) characterization, it was confirmed that the sensitive stimuli-responsive behavior of the hydrogel stemmed from its microstructure variation with those external stimulus. Rheological study showed that the hydrogel had rheological feature of typical elastomer. Compression tests revealed that the poly(hydroxyethyl methacrylate-co-N-vinyl pyrrolidone) [poly(HEMA-co-NVP)] played an important role in enhancing the compressive modulus of such hydrogel. More interestingly, the equilibrium swelling ratio (ESR) studies further confirmed that the composite hydrogel displayed response sensitively to the stimulus of temperature, pH, and ionic strength. Herein, theophylline as a drug model was adopted due to the multi-stimulus properties of hydrogels, which were a potential candidate for drug loading and delivering. Releasing drug continuously in a given period was dependent on the characteristics of solution and loading time. The mechanisms for drug release from the hydrogels were studied by Ritger–Peppas model.

中文翻译：

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多刺激响应型聚甲基丙烯酸羟乙酯-co-N-乙烯基吡咯烷酮-co-甲基丙烯酸-co-N-异丙基丙烯酰胺）水凝胶：合成，表征和在药物释放中的应用

由于对小刺激的敏感反应以及在生物传感器和药物输送中的广泛应用，对多刺激响应的水凝胶进行了越来越多的研究。在这项研究中，多刺激响应水凝胶，聚（甲基丙烯酸羟乙基共- ñ -乙烯基吡咯烷酮-共-甲基酸共- ñ -isopropylacryl酰胺）[聚（HEMA-共-NVP-共-MAA-共-NIPA）]，是通过自由基聚合反应合成的，并通过傅立叶变换红外光谱（FTIR）和¹³13 C NMR光谱技术。借助扫描电子显微镜（SEM）表征，已证实水凝胶的敏感刺激响应行为是由于其微观结构随外部刺激而发生的。流变学研究表明，水凝胶具有典型弹性体的流变特性。压缩试验表明，聚（甲基丙烯酸羟乙基共- ñ -乙烯基吡咯烷酮）[聚（HEMA-共-NVP）]在提高这种水凝胶的压缩模量中起重要作用。更有趣的是，平衡溶胀比（ESR）研究进一步证实了复合水凝胶对温度，pH和离子强度的刺激表现出敏感的响应。在此，茶碱由于其水凝胶的多刺激特性而被采用为药物模型，而水凝胶是药物装载和递送的潜在候选者。在给定的时间内连续释放药物取决于溶液的特性和上样时间。通过Ritger-Peppas模型研究了水凝胶中药物的释放机理。