Structure and morphology of freeze/thawed PVA hydrogels
Structure and morphology of freeze/thawed PVA hydrogels
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DOI：
10.1021/ma9907587
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发表时间：
2000-04-04
期刊：
影响因子：
5.5
通讯作者：
Peppas, NA
中科院分区：
文献类型：
--
作者：
Hassan, CM;Peppas, NA
研究了在-20℃冷冻8 h和+25℃解冻4 h制备的聚乙烯醇（PVA）凝胶的结构和形态。在37℃的水中膨胀6个月，观察凝胶的长期形态变化。通过改变冻融循环次数、水溶液浓度、聚乙烯醇分子量等参数，考察了制备条件。从含水量、PVA溶解分数、结晶度和晶粒尺寸分布等方面考察了其整体结构和稳定性。增加冻结和解冻循环的次数有助于加强结构内现有的晶体。PVA水溶液初始浓度的增加导致水凝胶初始结晶度较高，膨胀后稳定性增加，PVA分子量的增加导致晶体片层厚度增加，由于PVA链长增加，晶体尺寸分布变宽。对于交联较松散的样品，二次结晶更为明显。网络中自由体积和流动性的增加允许在膨胀过程中进行额外的结晶。总的来说，中等分子量(（M) / bar(n) = 64 000）的冷冻/解冻PVA凝胶，增加了冷冻和解冻循环次数，在37℃下膨胀6个月的时间内，稳定性得到增强，证明了它们适合长期的生物医学应用。
The structure and morphology of poly(vinyl alcohol) (PVA) gels prepared by repeated cycles of 8 h freezing at -20 degrees C and 4 h thawing at +25 degrees C were examined. Long-term morphological changes of such gels were determined upon swelling in water at 37 degrees C for 6 months. The preparation conditions were examined by varying such parameters as the number of freezing and thawing cycles, the concentration of aqueous solution, and the PVA molecular weight. The overall structure and stability were examined in terms of water content, fractional PVA dissolution, degree of crystallinity, and crystal size distribution. An increase in the number of freezing and thawing cycles served to reinforce existing crystals within the structure. Increased initial concentrations of aqueous PVA solutions resulted in hydrogels that contained initially higher crystallinity and added stability upon swelling, an increase in the PVA molecular weight resulted in crystals of higher lamellar thickness and a broadening of the crystal size distribution due to an increase in PVA chain length. Secondary crystallization was more pronounced for more loosely cross-linked samples. An increase in the free volume and mobility within the network allowed for additional crystallization to proceed during swelling. Overall, freeze/thawed PVA gels of intermediate molecular weight ((M) over bar(n) = 64 000) and increased number of freezing and thawing cycles showed enhanced stability during swelling at 37 degrees C for a 6-month period of time demonstrating their appropriateness for long-term biomedical applications.