Tunable mechano-responsive organogels by ring-opening copolymerizations of N-carboxyanhydrides.
Tunable mechano-responsive organogels by ring-opening copolymerizations of N-carboxyanhydrides.
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DOI：
10.1039/c3sc52504j
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发表时间：
2014-01
期刊：
影响因子：
8.4
通讯作者：
Wooley KL
中科院分区：
文献类型：
--
作者：
Fan J;Zou J;He X;Zhang F;Zhang S;Raymond JE;Wooley KL
利用N-羧基酸酐（NCA）单体的简单共聚来产生具有α-螺旋和β-折叠子结构的组合的共聚肽，所述共聚肽当从亲溶剂合成聚合物嵌段链段生长时，能够可逆地驱动机械响应性超分子溶胶-凝胶-溶胶和溶胶-凝胶-凝胶转变，这也允许基于注射的加工和自修复行为。以聚乙二醇胺（mPEG-amine）为引发剂，通过统计开环共聚法合成了一种新型多肽基有机胶凝剂--甲氧基聚乙二醇-嵌段-聚谷氨酸苄酯-甘氨酸共聚物（mPEG-b-P（BLG-co-Gly））。这些系统表现出可调的二级结构，并导致有机凝胶的超声刺激响应性，其中多肽片段的变化通过改变共聚过程中BLG NCA与Gly NCA的比例来控制。衰减全反射-傅里叶变换红外光谱（ATR-FTIR）研究表明，随着甘氨酸摩尔分数的增加，多肽链段中α-螺旋组分减少，而β-折叠含量系统性地增加。通过透射电子显微镜（TEM）表征了具有在10.4 - 14.5 nm范围内可调宽度的β-折叠纳米原纤的超分子组装体，其中BLG与Gly的比例是变化的。这些纳米结构在N，N-二甲基甲酰胺（DMF）中进一步自组装成3-D凝胶网络，发生在低临界凝胶化浓度（CGC）（最低约100 μ mol/L）下。0.6重量百分比）。增加的BLG与Gly比率导致多肽区段的二级结构中的α-螺旋组分增加，从而产生更宽和更柔性的纳米原纤维。聚合物中α-螺旋组分的存在增强了有机凝胶对超声处理的稳定性，并且观察到瞬时凝胶到凝胶转变，因为在超声处理后凝胶材料内发生网络的原位重建。与此形成鲜明对比的是，由mPEG-b-PGly制备的富含β-片层的凝胶在超声处理后表现出瞬间的凝胶至溶胶转变。这种mPEG-b-P（BLG-共-Gly）有机凝胶系统的CGC浓度和刚度可以通过在合成期间控制BLG与Gly的比率来简单地改变二级结构中α-螺旋和β-折叠的百分比来调节。通过动态力学分析（DMA）研究了这些有机凝胶的力学性能，其储能模量约为1.25。12.1 kPa（室温）。通过直接观察宏观自修复行为实验，证明了可注射性和自修复能力。
The simple copolymerization of N-carboxyanhydride (NCA) monomers is utilized to generate copolypeptides having a combination of α-helix and β-sheet sub-structures that, when grown from a solvophilic synthetic polymer block segment, are capable of driving mechano-responsive supramolecular sol-to-gel-to-sol and sol-to-gel-to-gel transitions reversibly, which allow also for injection-based processing and self-healing behaviors. A new type of polypeptide-based organogelator, methoxy poly(ethylene glycol)-block-poly(γ-benzyl-l-glutamate-co-glycine) (mPEG-b-P(BLG-co-Gly)), is facilely synthesized by statistical ring-opening copolymerizations (ROPs) of γ-benzyl-l-glutamate (BLG) and glycine (Gly) NCAs initiated by mPEG-amine. These systems exhibit tunable secondary structures and result in sonication stimulus responsiveness of the organogels with the polypeptide segment variation, controlled by varying the ratio of BLG NCA to Gly NCA during the copolymerizations. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) studies indicate the α-helical component decreases while the β-sheet content increases systematically with a higher mole fraction of Gly in the polypeptide segment. The supramolecular assembly of β-sheet nanofibrils, having a tunable width over the range of 10.4 – 14.5 nm with varied BLG to Gly ratio, are characterized by transmission electron microscopy (TEM). The further self-assembly of these nanostructures into 3-D gel networks within N,N-dimethylformamide (DMF) occurs at low critical gelation concentrations (CGC) (lowest ca. 0.6 wt %). Increased BLG to Gly ratios lead to an increase of the α-helical component in the secondary structures of the polypeptide segments, resulting in wider and more flexible nanofibrils. The presence of α-helical component in the polymers enhances the stability of the organogels against sonication, and instantaneous gel-to-gel transitions are observed as in situ reconstruction of networks occurs within the gelled materials after sonication. In marked contrast, the β-sheet-rich gel, prepared from mPEG-b-PGly, exhibits an instant gel-to-sol transition after sonication is applied. The CGC concentration and stiffness of this mPEG-b-P(BLG-co-Gly) organogel system can be tuned by simply varying the percentages of α-helix and β-sheet in the secondary structures through control of the BLG to Gly ratio during synthesis. The mechanical properties of these organogels are studied by dynamic mechanical analyses (DMA), having storage moduli of ca. 12.1 kPa at room temperature. The injectability and self-healing capabilities are demonstrated by direct observation of the macroscopic self-healing behavior experiment.