Biodegradable, amorphous copolyester-urethane networks having shape-memory properties
Biodegradable, amorphous copolyester-urethane networks having shape-memory properties
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DOI：
10.1002/anie.200461360
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Lendlein, A
中科院分区：
文献类型：
--
作者：
Alteheld, A;Feng, YK;Lendlein, A
1189 Angew。化学。Int。编辑。2005,44,1188-1192 www。应用。[j], [c], [c], [c]。对于生物医学应用，可以通过增加乙醇酸含量来调节网络的Tg值。在708℃，即比Tg高约208℃时，聚合物网络处于橡胶弹性状态，应力-应变试验中没有颈缩现象发生。杨氏模量E和断裂伸长率εb取决于共价网络的段长，随着前体分子量的增加，即网络链长的增加，E减小，εb增大。在708℃下进行的力学试验结果表明，从永久形状到临时形状的变形率可达470%。与在258C下测量的相同样品相比，E的值降低了60到530倍（表1）。松散交联材料NP-LG(17)-10000的εb值从708C时的470%下降到258C时的250%。当测量温度从70℃降低到258C时，断裂时的拉应力σb增加了至少一个数量级。无定形可生物降解共聚酯-氨基甲酸乙酯网络的形状记忆效应见图2。在编程步骤中，将非晶态聚氨酯网络在高温（大腿= 708C）下由其永久形状变形为其临时形状，保持其变形形状，并在Ttrans以下冷却至flow。变形的临时形状固定完成后，卸除载荷。在恢复步骤中，将网络在Ttrans到Thigh上方重新加热，恢复了原始的永久形状。这些材料的宏观形状记忆效应如图2所示。从临时形状（“SM”）到永久形状的复杂转变
1189 Angew. Chem. Int. Ed. 2005, 44, 1188–1192 www. angewandte. org 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim possible dangling chain ends or loop formation may also influence Tg. For biomedical applications the Tg value of the networks could potentially be adjusted around body temperature by increasing the glycolide content. At 708C, approximately 208C above Tg, the polymer networks are in a rubber-elastic state, and no necking occurred in the stress–strain test. Young s modulus E and elongation at break εb depend on the segment length of the covalent network: with increasing molecular weight of the precursors, in other words, increasing chain lengths of the networks, E decreases and εb increases, respectively. The results of mechanical tests at 708C showed that it was possible to realize deformations from the permanent to the temporary shape of up to 470%. The value for E decreased by a factor between 60 and 530 compared to that of identical sample measured at 258C (Table 1). The value for εb decreased from 470% at 708C to 250% at 258C for the loosely cross-linked material NP-LG (17)-10000. The tensile stress at break σb increased by at least an order of magnitude when the measurement temperature was decreased from 70 to 258C. The shape-memory effect of amorphous biodegradable copolyester-urethane networks is illustrated in Scheme 2. In the programming step, the amorphous polyurethane network was deformed from its permanent shape to its temporary shape at a high temperature (Thigh= 708C), held in its deformed shape, and cooled below Ttrans to Tlow. After fixation of the deformed temporary shape was complete, the load was removed. In the recovery step the network was reheated above Ttrans to Thigh, and the original permanent shape was recovered. The macroscopic shape-memory effect of these materials is demonstrated in Figure 2. The complex transformation from the temporary shape (“SM”) to the perma-