Gemeinhart R A, Chen J, Park H, Park K
Cornell University, School of Chemical Engineering, Ithaca, NY 14853-5201, USA.
J Biomater Sci Polym Ed. 2000;11(12):1371-80. doi: 10.1163/156856200744390.
Stimuli-sensitive hydrogels (or smart hydrogels) are hydrogels that swell or shrink in response to small changes in environmental conditions in which they are placed. While the extent of swelling or shrinking may be large, the kinetics of such changes is slow, since the diffusion of water into and out of the hydrogel is a slow process. To obtain fast responses, we have prepared superporous hydrogels (SPHs) that can swell or shrink extremely fast regardless of their dimensions. The swelling and shrinking are orders of magnitude faster than expected for a nonporous hydrogel of the same dimensions. Water molecules are taken up into the SPHs by capillary forces, and this makes water uptake much faster than diffusion. The swelling ratio of the poly(acrylamide-co-acrylic acid) (p(AM-co-AA)) SPHs was dependent on the pH and ionic strength of the medium. The effect of pH was most pronounced and the effect of ionic strength was observed at all pH values. SPHs made at pH around 5 showed transient maximum swelling when exposed to pH 1.2 medium due to the transient low hydrogen ion concentration inside the swelling SPHs. The p(AM-co-AA) SPHs showed repeated swelling and shrinking by alternating the medium pH between 1.2 and 7.5, and the changes in swelling ratio was quite fast occurring in a matter of a minute. This fast sensitivity may make the stimuli sensitive hydrogels useful in many applications not previously possible. These materials can be used for applications where a single-piece hydrogel is more advantageous than hydrogel microparticulates.
刺激敏感水凝胶（或智能水凝胶）是一类水凝胶，它们会根据所处环境条件的微小变化而发生溶胀或收缩。虽然溶胀或收缩的程度可能很大，但这种变化的动力学过程较慢，因为水进出水凝胶的扩散是一个缓慢的过程。为了获得快速响应，我们制备了超多孔水凝胶（SPH），无论其尺寸大小，都能极其快速地溶胀或收缩。其溶胀和收缩速度比相同尺寸的无孔水凝胶快几个数量级。水分子通过毛细作用力被吸收到超多孔水凝胶中，这使得吸水速度比扩散快得多。聚（丙烯酰胺 - 共 - 丙烯酸）（p(AM - co - AA)）超多孔水凝胶的溶胀率取决于介质的pH值和离子强度。pH值的影响最为显著，在所有pH值下都能观察到离子强度的影响。在pH约为5时制备的超多孔水凝胶，由于溶胀的超多孔水凝胶内部氢离子浓度暂时降低，当暴露于pH为1.2的介质中时会出现短暂的最大溶胀。通过在1.2和7.5之间交替改变介质pH值，p(AM - co - AA)超多孔水凝胶表现出反复的溶胀和收缩，溶胀率的变化在一分钟内就相当迅速地发生。这种快速敏感性可能使刺激敏感水凝胶在许多以前无法实现的应用中发挥作用。这些材料可用于单件水凝胶比水凝胶微粒更具优势的应用中。
