【作者】 常春雨；

【导师】 张俐娜；

【作者基本信息】 武汉大学 ， 高分子化学与物理， 2011， 博士

【摘要】 水凝胶作为一类独特的“软”材料,具有高度溶胀性、力学强度、光学透明性、生物可降解性、生物相容性等优点,在农业、工业、生物医疗和生理卫生等领域有广泛的应用。聚合物水凝胶研究涉及到高分子物理、聚集态物理、材料科学、生命科学和医学等多学科交叉领域。纤维素和甲壳素是地球上最丰富的两种可再生资源,是未来的主要化工原料之一。本工作利用我们实验室研发的新溶剂(氢氧化钠/尿素水溶液)分别溶解纤维素和甲壳素,构建各种纤维素及甲壳素水凝胶,并通过液体/固体核磁共振碳谱(13CNMR)、红外光谱(FT-IR)、X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、热重分析(TGA)、示差扫描量热(DSC)、动态力学分析(DMA)、流变仪、紫外-可见光谱仪(UV)、荧光光谱仪(FL)和力学性能试验等表征水凝胶的结构和性能,并研究它们之间的构效关系,由此构建生物质基功能性水凝胶并评价它们的应用前景。本工作的主要创新点包括：在NaOH/尿素水体系中成功构筑优良性能的纤维素水凝胶及复合水凝胶并找出结构对功能影响的科学规律；通过引入亲水性大分子,制备出超吸水性纤维素基水凝胶,并阐明纤维素刚性链对大孔形成的作用；在纤维素网络结构中引入硒化镉/硫化锌纳米粒子构筑出纤维素/量子点荧光水凝胶；通过互穿聚合物网络技术以及两性生物大分子复合分别构建温度、pH和盐敏感型智能水凝胶；通过水体系低温溶解甲壳素,成功创建甲壳素及其杂化水凝胶。本论文的主要研究内容和结论包括以下十部分。首先,纤维素溶解在预冷的氢氧化钠/尿素水溶液中形成透明的溶液,以环氧氯丙烷为交联剂,得到一系列纤维素水凝胶。水凝胶的光学透明性和溶胀率随纤维素浓度增加而降低,但再溶胀和储能模量则增加。通过加热交联的纤维素水凝胶具有更好的光学透明性,高平衡溶胀率和再溶胀率。然而,经过冷冻处理的纤维素水凝胶则具有较快的再溶胀速度和较高的力学性能。因为冷冻能增加分子间氢键作用力,导致力学性能增加。基于聚乙烯醇在冷冻/解冻过程中氢键增强的特性,制备出纤维素/聚乙烯醇物理水凝胶。通过冷冻/解冻循环法构建的纤维素/聚乙二醇物理水凝胶具有紧密的结构,并表现很强的分子间相互作用导致其力学强度很高。然而,在化学水凝胶中,纤维素和聚乙烯醇原有的紧密堆积链结构明显减少,由此表现出高溶胀和高吸水率。首次将低分子量的聚乙二醇引入纤维素网络结构,制备出高强度纤维素/聚乙二醇复合水凝胶。与纯纤维素水凝胶的力学性能相比,纤维素/聚乙二醇复合水凝胶的力学强度可以提高上百倍。DMA和DSC的实验结果证明聚乙二醇有力地破坏水凝胶中纤维素的分子间氢键,同时它与纤维素分子形成新的氢键配体,明显改善材料的相容性和力学性能。SEM和TEM的结果示出了复合水凝胶内部的多孔形貌,且孔的尺寸为纳米级。这类排列紧密的小孔结构使复合水凝胶的拉伸强度和压缩强度都高达几兆帕。在氢氧化钠/尿素水体系中,通过环氧氯丙烷交联,成功制备纤维素-海藻酸大孔水凝胶。SEM、DMA和溶胀测试结果显示这类水凝胶具有均匀的大孔结构、良好的力学强度和很高的溶胀率。这种复合水凝胶中,海藻酸大分子贡献于吸收大量的水导致水凝胶孔尺寸和溶胀率明显上升。半刚性链的纤维素主要起支撑大孔孔壁的作用。本工作通过将刚性和高亲水性天然高分子结合在一起,为构建大孔径水凝胶提供了简便而有效的新途径。利用纤维素为水凝胶网络的支撑骨架,通过非共价键力引入高亲水性羧甲基纤维素制备出新型纤维素水凝胶。其平衡溶胀率可达到1000g/g,是一种超吸水性凝胶。纤维素-羧甲基纤维素水凝胶具有智能行为,它们在无机盐水溶液、生理盐水、合成尿中表现出敏感的溶胀和收缩行为。该类水凝胶具有智能溶胀、超吸水性、以及对蛋白质控制释放的能力。基于水溶性量子点的亲水性将其均匀分散在纤维素溶液中,然后交联纤维素大分子得到无机／有机杂化水凝胶。在交联过程,水溶性量子点表面配体(酰胺键)水解断裂导致聚丙烯酸和辛胺脱离量子点,从而量子点由亲水性转变为疏水性。由于疏水性量子点与纤维素骨架之间相互作用明显大于它与水之间的作用力,从而固定在纤维素基质中。纤维素骨架结构不仅固定量子点,而且保护它的结构,在紫外光下呈现出从绿到红各种荧光色彩。这种杂化水凝胶具有良好的光学和力学性能,并且在荧光免疫分析和生物标记技术等领域具有应用前景。由纤维素和聚(N-异丙基丙烯酰胺)通过互穿聚合物网络技术(IPN)成功构筑出新型温敏性双网络水凝胶。纤维素作为第一层网络结构,聚(N-异丙基丙烯酰胺)作为第二层网络结构,它们在IPN水凝胶中表现出很好的相容性以及均匀的结构和形貌。FTIR和固体13CNMR的结果证明第一层网络和第二层网络的形成是相互独立的,它们之间不存在任何化学键,但两者之间存在很强的氢键相互作用。这类IPN水凝胶表现出均匀的多孔结构、高力学强度和温度敏感性。互穿聚合物网络水凝胶中纤维素对提高水凝胶的力学强度起重要作用,而PNIPAAm的主要贡献于温度敏感性。在NaOH/尿素水介质中成功合成纤维素季铵盐,并利用它和羧甲基纤维素分别作为聚阳离子和聚阴离子通过化学交联成功制备出两性水凝胶。纤维素季铵盐/羧甲基纤维素水凝胶的平衡溶胀率依赖于纤维素季铵盐和羧甲基纤维素的化学组成,可以从8.6g/g急剧增加到498g/g。因此调节纤维素季铵盐和羧甲基纤维素的质量比可以得到不同平衡溶胀率的水凝胶。这些水凝胶展现出多重响应行为,包括pH和盐敏感性。其中,纤维素季铵盐主要贡献于水凝胶的pH敏感性,而羧甲基纤维素则主要贡献于水凝胶网络的伸展和溶胀率。此外,纤维素季铵盐/羧甲基纤维素水凝胶在氯化钠、氯化钙和氯化铁水溶液中的溶胀表现出智能行为,它们在生物材料领域很有应用前景。甲壳素通过冷冻/解冻法成功溶解在8 wt%NaOH/4 wt%尿素水溶液中,得到透明的甲壳素浓溶液。证明甲壳素在NaOH/尿素水体系低温溶解是物理过程,而且由甲壳素溶液首次制备出甲壳素水凝胶。尤其,甲壳素溶液可以迅速交联得到甲壳素化学水凝胶。这种水凝胶表现出均匀的多孔结构,可调节的溶胀率和良好力学性能。细胞试验的结果证明甲壳素水凝胶无毒、具有很好的生物相容性,这主要是由于甲壳素是节肢类动物骨骼和真菌细胞壁之中的活性成分,其本性有利于细胞生长。利用纳米羟基磷灰石分散在甲壳素水凝胶中成功的制备出甲壳素/纳米羟基磷灰石水凝胶。纳米羟基磷灰石的尺寸为10-30纳米,它们与甲壳素网络结构具有很好的相容性,并且保持羟基磷灰石的原有结构和性质。同时,甲壳素/纳米羟基磷灰石水凝胶具有均匀结构和良好的力学性能。尤其,COS-7细胞可以在甲壳素/纳米羟基磷灰石水凝胶材料上很好的黏附和生长,而且不显示毒性。纳米羟基磷灰石具有良好的骨诱导和骨传导性,该材料将在骨组织工程领域有应用前景。本论文利用我们具有自主知识产权的纤维素“绿色”新溶剂成功创建出纤维素和甲壳素水凝胶,并阐明水凝胶的结构与性能之间的关系。由此,设计出高强度水凝胶、超吸收性水凝胶、环境敏感水凝胶、发光水凝胶、甲壳素水凝胶以及无机/有机杂化水凝胶等一系列功能材料。这些基础研究结果可为环境友好的生物质水凝胶的设计、制备及应用提供重要科学依据和理论,而且可推进绿色化学进程。因此本论文具有重要的学术价值和应用前景。更多还原

【Abstract】 Hydrogels, unique "soft" materials with high swelling ratio, mechanical strength, transparency, biodegradability, and biocompatibility, have been applied widely in agriculture, industry, biomedical materials, and physical hygiene. The research on polymer hydrogels have covered large interdisciplinary area crossing polymer physics, condensed matter, material science, life science, and medicine. Cellulose and chitin are the most abundant bioresouce on the earth, and will be the main chemical resource of the future. This work focused on construction of cellulose and chitin hydrogels by using NaOH/urea aqueous solution developed in our group. The structure, properties, and structure-activity relationship of hydrogels were characterized by liquid/solid state 13CNMR,、Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), rheological measurements, dynamic mechanical analysis (DMA) thermogravimetric analysis (TGA), UV-vis spectroscopy(UV), photoluminescence spectra (PL) and mechanical testing. The correlation of structure to properties was studied, and biobased functional hydrogels were constructed to evaluate their potential applications.The innovation of this work was as follows:cellulose hydrogels and composite hydrogel with excellent properties were fabricated successfully in NaOH/urea aqueous solution. Superabsorbent hydrogels were constructed by introducing high hydrophilic polymers into hydrogel networks, and the effect of cellulose stiff chains were clarified. Cellulose/quantum dots (QDs) hydrogels were prepared by embedding CdSe/ZnS nanoparticles in cellulose matrices. By using IPN technique or cross-linking amphoteric cellulose derivatives, a series of stimuli-responsive hydrogels were fabricated. Chitin was dissolved in NaOH/urea aqueous solution, and chitin hydrogels (hybrid hydrogels) were prepared.The primary content and conclusion of this work can be divided into ten parts.Firstly, transparent hydrogels have been synthesized from cellulose in NaOH/urea aqueous solutions by using ECH as crosslinker. With the increase of the cellulose concentration, the transparency and equilibrium swelling ratio of the hydrogels decreased, while the reswelling water uptake and the storage modulus increased. Cellulose hydrogels prepared by heating displayed better light transmittance, higher equilibrium swelling ratios, higher water uptakes and relatively weaker mechanical strength. However, Cellulose hydrogels prepared by freezing method had faster swelling rate and higher mechanical strength.The cellulose/PVA hydrogels prepared by freezing/throwing method had dense structure and exhibited strong interaction between cellulose and PVA, high strength and storage modulus. However, cellulose/PVA hydrogels prepared by chemical cross-linking with ECH had good swelling ratio and high water uptake, due to cross-linking reaction destroyed the crystallization of polymer chains.Cellulose/poly(ethyl glycol) (PEG) hydrogels were fabricated by introducing low molecular weight PEG into cellulose hydrogel network. These hydrogels showed excellent mechanical properties, which was hundredfold of cellulose hydrogels. DMA and DSC results indicated that the hydrogen bonds of cellulose were destroyed by PEG and new hydrogen bonds formed between cellulose and PEG. SEM and TEM results revealed that cellulose/PEG hydrogels had nanoporous morphology, leading to the high strength of hydrogels.Macroporous hydrogels fabricated from cellulose and sodium alginate (SA) in NaOH/urea aqueous system by chemical crosslinking had high swelling ratio. SEM and DMA results indicated that hydrogels had macroporous structure and high strength. In the hydrogels, SA played an important role on increasing pore size and swelling ratio, whereas cellulose contributed to support the pore wall. This work provided a simple way to construct macroporous hydrogels by combining of natural polymers with semi-stiff chain and high hydrophilic properties.Furthermore, novel superabsorbent hydrogels were fabricated by using cellulose as support and CMC as high hydrophilic polymer, which had superabsorbent capability and high swelling ratio (more than 1000). The hydrogels were sensitive to inorganic aqueous solution, physical saline water and synthetic urine, showing smart swelling and shrinking behaviors, as well as controlled release of BSA.Cellulose/quantum dots (QDs) hydrogels were created by cross-linking cellulose chains with epichlorohydrin containing water-soluble QDs (CdSe/ZnS) when the hydrophilic-hydrophobic transition of QDs occurred by hydrolyzing ligand. The relatively hydrophobic CdSe/ZnS core-shell nanoparticles were dispersed well and embedded firmly in the cellulose matrices through electrostatic attraction and hydrophobic interactions. The cellulose-QDs hydrogels emitted strong fluorescence with different colors of green, greenish-yellow, yellow and red, depending on the size of the CdSe/ZnS nanoparticles, and exhibited relatively high fluorescence (PL) quantum yields as well as good transparence and mechanical strength, leading to great promises in applications in the fields of fluoroimmunoassay and biological labeling.Novel hydrogels composed of cellulose and poly(N-isopropylacrylamide) (PNIPAAm) were created with IPN strategy. Cellulose hydrogel was employed as the first network, and PNIPAAm was polymerized/cross-kinked in presence of cellulose hydrogel as the second network, leading to the double networks structure. The two different networks exhibited good compatibility and homogeneous morphology in the IPN hydrogels. Analyses of FT-IR and solid 13CNMR supported that the first network and the second network were formed independently, and there was no chemical reaction between them. These IPN hydrogels displayed uniform porous network, good mechanical strength and temperature-sensitive properties.A series of ampholytic hydrogels through chemical cross-linking were constructed successfully from two cellulose-based polyelectrolytes (QC and CMC). The swelling ratios of these QC/CMC hydrogels changed dramatically from 8.6 to 498 g/g, depending on the chemical composition of QC and CMC. Therefore, ampholytic hydrogels with required swelling ratio could be obtained by fine-tuning the mass ratio of QC and CMC. These hydrogels exhibited multiple responsive behaviors, including pH and salt. CMC in the hydrogels with high CMC content contributed to the expansion of the hydrogel network, and the swelling ratio changed slightly in different pH solutions.Chitin power was dissolved successfully in 8 wt% NaOH/4 wt% urea aqueous solution via a freezing/thawing method to produce a transparent solution. For the first time, it has been demonstrated that the chitin dissolution was. a physical process without showing an occurrence of any derivatives and a new class of hydrogels from chitin solution was created successfully. The gelation of the chitin solution occurred rapidly in the presence of ECH, leading to the perfect formation of hydrogels. The chitin hydrogels exhibited a uniform microporous structure, smart swelling ratio, and excellent mechanical strength. In particular, the results from 293 T cell culture indicated that chitin hydrogels had non-toxicity and good biocompatibility, due to the fact of chitin is one of the active ingredients in the exoskeleton of arthropods or in the cell walls of fungi and yeasts, and its native properties benefited the growing of cells.Chitin/nano-hydroxyapatite (nano-HA) hydrogels were prepared by introducing hydroxyapatite nanoparticles in chitin hydrogels. Nano-HA with particle size of 10-30 nm was well dispersed in the chitin hydrogel matrix. Hybrid hydrogels exhibited uniform structure and good compressive strength. Moreover, COS-7 cells were well adhered, proliferated, and grown on the hydrogel surface, showing good biocompatibility. Due to the excellent osteoinduction effect and osteoconductivity of hydroxyapatite, these hybrid hydrogels may be promising for bone tissue engineering applications.This work developed a series of cellulose and chitin based hydrogels by using our "green" solvent system, and clarified the relationships between their structure and properties of hydrogel. Moreover, a series of functional materials including high strength hydrogels, superabsorbent hydrogels, stimuli-responsive hydrogels, photoluminescent hydrogel, chitin hydrogels, and inorganic/organic hybrid hydrogels were constructed and evaluated. These basic researches provided valuable information for construction, and development of biobased hydrogels with different properties from renewable resource, and are accordance with national sustainable strategy. Therefore, this thesis is highly valuable for academic study and great potential.更多还原