Sun Guoming, Zhang Xian-Zheng, Chu Chih-Chang
Fiber and Polymer Science Program, Department of Textiles and Apparel & Biomedical Engineering Program, Cornell University, Ithaca, NY 14853-4401, USA.
J Mater Sci Mater Med. 2007 Aug;18(8):1563-77. doi: 10.1007/s10856-007-3030-9. Epub 2007 May 5.
Chitosan-based hydrogel films having both temperature and pH sensitivity were prepared by blending chitosan with temperature sensitive poly (N-isopropylacrylamide) (PNIPAAm) and polyethylene glycol (PEG, Mw 2000). PEG was added to enhance film properties, such as thermal, mechanical and swelling properties. Differential scanning calorimetry (DSC) study indicated that the physically blended films exhibited a lower critical solution temperature (LCST) identical to that of pure PNIPAAm (around 32 degrees C). FT-IR data indicated that the temperature sensitivity is due to the PNIPAAm component in the film. The thermal analysis showed that chitosan and PNIPAAm were compatible and the blended films are apt to crystallize. The X-ray diffraction study further showed that the blended films had a higher crystallinity level than chitosan or PNIPAAm alone. The newly formed crystalline domains acted as physical crosslinkers and greatly increased the crosslinking level of the blended films, which, in turn, affected the swelling behavior and mechanical property of the blended films. Scanning electron microscopy (SEM) revealed that the blended swollen films exhibited a more porous structure at 37 degrees C (>LCST) than at room temperature (<LCST), though their swelling ratios were reduced as temperature increased from room temperature to 37 degrees C because of the dehydration nature of PNIPAAm at temperatures above its LCST. The results demonstrated that physically blended temperature sensitive films could be formulated, which are capable of producing more pores upon heating. The blended films were also found to be pH sensitive due to the fact that chitosan, one of the film components, has many pendant amino groups.
通过将壳聚糖与温度敏感型聚（N-异丙基丙烯酰胺）（PNIPAAm）和聚乙二醇（PEG，分子量2000）共混，制备了具有温度和pH敏感性的壳聚糖基水凝胶薄膜。添加PEG以改善薄膜性能，如热性能、机械性能和溶胀性能。差示扫描量热法（DSC）研究表明，物理共混薄膜表现出与纯PNIPAAm相同的较低临界溶液温度（LCST）（约32℃）。傅里叶变换红外光谱（FT-IR）数据表明，温度敏感性归因于薄膜中的PNIPAAm组分。热分析表明壳聚糖和PNIPAAm具有相容性，共混薄膜易于结晶。X射线衍射研究进一步表明，共混薄膜的结晶度水平高于单独的壳聚糖或PNIPAAm。新形成的晶域充当物理交联剂，大大提高了共混薄膜的交联水平，进而影响了共混薄膜的溶胀行为和机械性能。扫描电子显微镜（SEM）显示，共混溶胀薄膜在37℃（>LCST）时比在室温（<LCST）时表现出更多孔的结构，尽管由于PNIPAAm在高于其LCST的温度下具有脱水性质，当温度从室温升高到37℃时其溶胀率降低。结果表明，可以制备物理共混的温度敏感薄膜，其在加热时能够产生更多的孔。还发现共混薄膜对pH敏感，因为薄膜组分之一壳聚糖具有许多侧链氨基。
