生物质生物预处理研究进展与展望

木质纤维素生物质分布广、产量大、可再生,用于制备生物基能源、生物基材料和生物基化学品。木质纤维素生物质组成复杂,包含纤维素、半纤维素和木质素等,木质素与半纤维素通过共价键、氢键交联形成独特的“包裹结构”,纤维素含有复杂的分子内与分子间氢键,上述因素制约着其资源化利用。生物预处理以其独特优越性成为生物质研究的重要方面。系统阐述了生物预处理过程中木质素降解和基团修饰对纤维素酶解的影响,纤维素含量及结晶区变化,半纤维素五碳糖利用,微观物理结构的改变。进一步提出了以生物预处理为核心的组合预处理、基于不同功能的多酶协同催化体系、木质纤维素组分分级利用和新型高效细菌预处理工艺是生物预处理未来发展的重要趋势。     

木质素酶及其生产菌的筛选育种

木质素酶降解木质纤维素材料中的木质素,使木质素-半纤维素-纤维素结构解体,纤维素得以暴露出来供后续步骤处理.它广泛应用于生物制浆、生物漂白、废水处理等工业过程中.由于近年利用可再生木质纤维素材料用酶法水解生产酒精成了研究热点,因而作为纤维素材料生物转化工艺预处理过程中的关键角色,木质素酶也极大地唤起人们的研究兴趣.本文介绍了木质素与白腐真菌(Phanerochaete chrysosporium)木质素降解酶系的特征以及锰过氧化物酶、木质素过氧化物酶、漆酶等3种木质素酶的催化作用机理,归纳了目前流行的木质素酶产生菌的筛选方法及近年来从自然界筛选木质素酶高产菌的种类,并对产木质素酶野生菌株的诱变育种与基因工程改造的进展进行了阐述.     

秸秆汽爆炼制木质素制备酚醛泡沫材料

以木质纤维素为原料的生物炼制不仅需要考虑到纤维素和半纤维素,同时也需要考虑到木质素的利用,以提高木质纤维素炼制的整体经济效益。利用汽爆处理的玉米秸秆为原料,通过优化碱提取的温度以及碱浓度,获得木质素得率较高,糖含量较少的提取液,同时该提取液经过浓缩后直接部分替代苯酚与甲醛反应制备酚醛泡沫。结果表明:当提取温度120℃,碱浓度1%,固液比1∶10,提取时间2 h,木质素的提取率达到79.67%。由该提取液替代苯酚制备的酚醛泡沫随着替代率的增加,其泡沫的密度逐渐增加,其压缩强度相对于纯酚醛泡沫也得到了提高。而木质素的加入并没有显著影响其热导率以及阻燃性能,同时由于其利用较为低廉的可再生资源木质素替代不可再生的苯酚原料,成本低,环保性好,具有更好的市场应用前景。采用木质素提液直接制备酚醛泡沫材料,工艺流程简单;增加了副产物木质素的经济价值,提高了整个木质纤维素炼制的经济性。     

木质纤维素资源化主要途径及半纤维素优先资源化利用策略

木质纤维生物质是地球上最丰富的可再生资源,可转化为能源、化学品和材料,开发木质纤维生物质有利于废弃物的高值化利用和缓解目前面临的环境污染等问题。木质纤维素主要包括纤维素、半纤维素和木质素,将其主要组分进行高效分离,是实现多元化、高值化生物精炼的基础。基于此,笔者简要总结了目前主要的木质纤维素资源化途径,如基于纤维素资源化、基于半纤维素资源化、基于木质素资源化、基于碳水化合物资源化以及全组分资源化的研究策略。依据半纤维素在植物细胞壁中承担的角色,结合前期的研究基础,提出半纤维素优先原位催化转化的木质纤维素生物炼制新策略,实现半纤维素的高选择性溶出和高效转化,保留结构完整的纤维素和木质素分级转化为小分子化学品和材料,最终实现资源生物量全利用,多元化产品联产的目的。     

聚乙烯醇复合水凝胶外用膜剂的制备与性能*

摘要目的：考察PVA/ 葡聚糖/ 羧甲基纤维素钠复合水凝胶外用膜剂的制备方法,并与纯PVA 水凝胶贴膜进行对比,考察本膜 剂在物理性能和药物体系的体外释放行为上所具备的优越性。方法：利用冷冻-解冻物理交联方法制备水凝胶装载胰岛素模型药 物的外用膜剂,通过万能拉力机和差示扫描量热法考察膜剂的物理性能,利用高效液色谱法考察该膜剂的体外释放行为。结果： PVA复合水凝胶外用贴膜相较于纯PVA水凝胶贴膜的韧性减小、刚性增加,体外释放变好。结论：通过将具有材料友好性的PVA 和多糖葡聚糖、羧甲基纤维素钠合并使用制备胰岛素复合水凝胶贴膜,既能保证贴膜具有良好的物理性能,又具有较好地释放行 为,优于目前文献报道的纯PVA水凝胶贴膜性能,有望继续研究优化性能。     

聚乙烯醇复合水凝胶外用膜剂的制备与性能

目的：考察PVA／葡聚糖／羧甲基纤维素钠复合水凝胶外用膜剂的制备方法,并与纯PVA水凝胶贴膜进行对比,考察本膜剂在物理性能和药物体系的体外释放行为上所具备的优越性。方法：利用冷冻-解冻物理交联方法制备水凝胶装载胰岛素模型药物的外用膜剂,通过万能拉力机和差示扫描量热法考察膜剂的物理性能,利用高效液色谱法考察该膜剂的体外释放行为。结果：PVA复合水凝胶外用贴膜相较于纯PVA水凝胶贴膜的韧性减小、刚性增加,体外释放变好。结论：通过将具有材料友好性的PVA和多糖葡聚糖、羧甲基纤维素钠合并使用制备胰岛素复合水凝胶贴膜,既能保证贴膜具有良好的物理性能,又具有较好地释放行为,优于目前文献报道的纯PVA水凝胶贴膜性能,有望继续研究优化性能。     

负载NGF的可注射壳聚糖透明质酸水凝胶材料理化性能及生物相容性研究

制备负载NGF的可注射壳聚糖透明质酸复合水凝胶,探讨其理化性能以及生物相容性。     

木质纤维素生物炼制的研究进展

木质纤维素是一种广泛存在的可再生生物质资源,主要由纤维素、半纤维素和木质素组成。如何更有效地综合利用木质纤维素是当前面临的世界性难题。本文中,笔者梳理了木质纤维素生物化学法转化生产以燃料乙醇为代表的生物基产品,特别是转化过程中关键技术环节的研究现状及难点,深入探讨了木质素的生物转化利用趋势,并综述了合成生物学在这些领域的研究趋势和最新成果。本文力图描绘出木质纤维素生物炼制研究全景,为后续研究提供潜在思路。     

γ-聚谷氨酸水凝胶研究与应用进展

主要介绍了一种集吸水性能、保水性能、环境友好性于一身的高分子材料γ-聚谷氨酸水凝胶的研究现状及发展前景,分别从γ-聚谷氨酸水凝胶、γ-聚谷氨酸与其他物质复合水凝胶的合成以及γ-聚谷氨酸类水凝胶的应用三方面进行了综述。     

木质素生物炼制研究进展

木质素为天然的芳香族聚合物,是自然界第二大丰富的可再生碳源,占木质纤维素干重的15%~30%。因木质素富含芳香族结构,故其具有极高的应用价值。生物法转化利用木质素具有专一性强和环境友好等特点,使得木质素生物炼制成为研究热点。本文根据国内外研究进展,从木质素降解酶的研究现状、芳香族化合物胞内代谢途径及木质素生物基化学品研究进展等几个方面做了综述。     

pH响应型蔗渣木质素水凝胶的制备及其对蛋白质的控释性能

该研究以蔗渣木质素和甲基丙烯酸为原料合成了pH敏感型蔗渣木质素/聚甲基丙烯酸水凝胶,对其合成条件、pH敏感性、溶胀-退溶胀性能以及对牛血清蛋白的控释等性质进行研究,并采用红外光谱、扫描电镜等对凝胶进行表征。结果表明:(1)对凝胶溶胀比影响的因素由大到小依次为甲基丙烯酸用量、交联剂用量、催化剂用量、反应的温度、木质素用量。当甲基丙烯酸单体浓度为1.75 mol·L~(-1)、木质素浓度为25 g·L~(-1)、交联剂浓度为3.25×10~(-2)mol·L~(-1)、引发剂浓度为1.25×10~(-2)mol·L~(-1)、反应温度为65℃时,所得水凝胶在模拟肠液中的溶胀比最大(28.16 g·g~(-1))。与不加木质素的聚甲基丙烯酸水凝胶相比,蔗渣木质素/聚甲基丙烯酸水凝胶的溶胀比有所下降,但其敏感pH由4~5碱移至6~8。(2)蔗渣木质素/聚甲基丙烯酸水凝胶的溶胀—退溶胀可逆性受组成的影响较大,但相对于聚甲基丙烯酸水凝胶,蔗渣木质素/聚甲基丙烯酸水凝胶对pH值的敏感响应性更强、响应速率更快,同时能在更短时间内达到溶胀平衡。(3)加入木质素可以提高水凝胶对牛血清蛋白的负载量,所试验的蔗渣木质素/聚甲基丙烯酸水凝胶样品对牛血清蛋白的最大负载量可达577 mg·g~(-1)。(4)牛血清蛋白在12 h后基本可达释放平衡;在模拟胃液中,牛血清蛋白的释放率仅10%,而在模拟肠液中释放率达92%。pH响应型蔗渣木质素/聚甲基丙烯酸水凝胶可以作为口服型蛋白类药物的潜在载体。     

明胶/海藻酸钠/沙蒿胶复合水凝胶的制备及表征

为探究明胶（G）、海藻酸钠（SA）,沙蒿胶（ASKG）对复合水凝胶的力学性能、溶胀和保湿性能的影响,采用共混-离子交联法制备海藻酸钠/明胶/沙蒿胶复合水凝胶,并对制得的水凝胶进行结构表征和溶血率测试。结果表明:当G质量分数为2.5%,SA为1.5%,ASKG为0.7%时,复合水凝胶压缩强度达到427.2 kPa,拉伸强度达到563.449 kPa,断裂伸长率为117%,溶胀率为744%,且具有较好的保湿性能。红外光谱表明,由于沙蒿胶中存在大量羟基,因此加入沙蒿胶后在3 300 cm^-1～3 600 cm^-1羟基峰形变宽。G/SA/ASKG复合水凝胶溶血率低于5%,具有较好的网络孔结构和血液相容性,为复合水凝胶在医用敷料方面的应用提供一定的参考价值。     

组织工程用纤维增强天然多糖水凝胶的进展

天然多糖水凝胶具有良好的生物相容性,然而其力学性能调节幅度小,无法满足组织工程应用巨大的需求。通过纤维增强法,不仅可显著提高天然多糖水凝胶的力学性能,还能调节复合水凝胶的降解性能、促进细胞粘附、增殖与分化行为及其组织沉积。常用的天然多糖组织工程水凝胶的纤维增强方法有物理共混法、化学作用法、静电驱动法与自组装法等。本文综述了纤维增强水凝胶的结构与功能特点,讨论了纤维增强对组织工程水凝胶的意义,以期对纤维增强组织工程水凝胶的发展起到促进作用。     

Fabrication of elastomeric silk fibers

Methods to generate fibers from hydrogels, with control over mechanical properties, fiber diameter, and crystallinity, while retaining cytocompatibility and degradability, would expand options for biomaterials. Here, we exploited features of silk fibroin protein for the formation of tunable silk hydrogel fibers. The biological, chemical, and morphological features inherent to silk were combined with elastomeric properties gained through enzymatic crosslinking of the protein. Postprocessing via methanol and autoclaving provided tunable control of fiber features. Mechanical, optical, and chemical analyses demonstrated control of fiber properties by exploiting the physical cross‐links, and generating double network hydrogels consisting of chemical and physical cross‐links. Structure and chemical analyses revealed crystallinity from 30 to 50%, modulus from 0.5 to 4 MPa, and ultimate strength 1–5 MPa depending on the processing method. Fabrication and postprocessing combined provided fibers with extensibility from 100 to 400% ultimate strain. Fibers strained to 100% exhibited fourth order birefringence, revealing macroscopic orientation driven by chain mobility. The physical cross‐links were influenced in part by the drying rate of fabricated materials, where bound water, packing density, and microstructural homogeneity influenced cross‐linking efficiency. The ability to generate robust and versatile hydrogel microfibers is desirable for bottom‐up assembly of biological tissues and for broader biomaterial applications.     

壳聚糖基温敏水凝胶的研究进展

壳聚糖是一种由甲壳素脱乙酰化得到的氨基多糖,具有生物相容性、低细胞毒性和可生物降解性等特点。壳聚糖/β-甘油磷酸钠溶液温敏水凝胶在组织工程、药物缓释等领域多有报道,其成胶性能取决于凝胶的组分和浓度。针对单纯壳聚糖水凝胶强度较低、降解较快、药物突释等缺陷,通常对壳聚糖进行改性或引入新材料共混,获得更符合实际需要的壳聚糖基温敏水凝胶。对近年来壳聚糖基水凝胶的研究进展进行综述,包括改性壳聚糖、共混体系等,概述了其在组织工程(软骨、血管、神经修复)、药物缓释(癌症药物缓释、糖尿病治疗)领域中研究和应用的新进展,以期为后续温敏水凝胶的进一步研究提供参考。     

Drug loading into and drug release from pH- and temperature-responsive cylindrical hydrogels

Hydrogels that undergo deformation upon appropriate changes in pH or temperature have considerable promise as drug delivery vehicles. Drug uptake in swelling and nonswelling cylindrical hydrogels and drug release from these into a target fluid are investigated here. A mathematical model for hydrogel-solution composite, a composite of a distributed parameter system (cylindrical hydrogel) and a lumped parameter system (surrounding solution), is developed. The polymer network displacement in a swelling/deswelling hydrogel is described by a stress diffusion coupling model. The analytical solution for network displacement is used to predict solvent intake by swelling hydrogels, solvent efflux from deswelling hydrogels, and changes in pressure, porosity, and effective drug diffusivity. These in turn influence drug uptake during and after hydrogel swelling and drug release from hydrogel during and after deswelling. Numerical results illustrate benefits of hydrogel swelling for drug loading and merits of different modes of drug release. Drug uptake and drug release by temperature-responsive hydrogels are compared with those by hydrogels not subject to deformation.     

基于天然水凝胶的生物材料在骨组织工程中的应用*

天然水凝胶是指原材料来自于天然生物材料的水凝胶。由于这种天然的聚合物含有构成生物体的天然成分,与天然组织具有生物学和化学相似性,而受到特别关注。天然水凝胶由于其与细胞外基质高度的相似性被认为是骨组织工程中优良的仿生基质材料。而针对天然水凝胶机械性能差、成骨诱导性能弱等缺陷,通常需要对天然水凝胶进行改性、引入其他材料或生物活性因子,以此来获得更适用于骨组织工程支架材料。对近年来基于天然水凝胶的生物材料在骨组织工程的应用,与其不同的应用形式(可注射水凝胶、多孔水凝胶支架、3D生物打印水凝胶支架等)进行了概述,以期对这类基于天然水凝胶的生物材料在未来骨组织工程中的应用提供参考。     

Viscoelastic properties and nanoscale structures of composite oligopeptide-polysaccharide hydrogels

Biocompatible and biodegradable peptide hydrogels are drawing increasing attention as prospective materials for human soft tissue repair and replacement. To improve the rather unfavorable mechanical properties of our pure peptide hydrogels, in this work we examined the possibility of creating a double hydrogel network. This network was created by means of the coassembly of mutually attractive, but self-repulsive oligopeptides within an already-existing fibrous network formed by the charged, biocompatible polysaccharides chitosan, alginate, and chondroitin. Using dynamic oscillatory rheology experiments, it was found that the coassembly of the peptides within the existing polysaccharide network resulted in a less stiff material as compared to the pure peptide networks (the elastic modulus G' decreased from 90 to 10 kPa). However, these composite oligopeptide-polysaccharide hydrogels were characterized by a greater resistance to deformation (the yield strain γ grew from 4 to 100%). Small-angle neutron scattering (SANS) was used to study the 2D cross-sectional shapes of the fibers, their dimensional characteristics, and the mesh sizes of the fibrous networks. Differences in material structures found with SANS experiments confirmed rheology data, showing that incorporation of the peptides dramatically changed the morphology of the polysaccharide network. The resulting fibers were structurally very similar to those forming the pure peptide networks, but formed less stiff gels because of their markedly greater mesh sizes. Together, these findings suggest an approach for the development of highly deformation-resistant biomaterials.     

Catechol-functionalized chitosan/pluronic hydrogels for tissue adhesives and hemostatic materials

Bioinspired from adhesion behaviors of mussels, injectable and thermosensitive chitosan/Pluronic composite hydrogels were synthesized for tissue adhesives and hemostatic materials. Chitosan conjugated with multiple catechol groups in the backbone was cross-linked with terminally thiolated Pluronic F-127 triblock copolymer to produce temperature-sensitive and adhesive sol-gel transition hydrogels. A blend mixture of the catechol-conjugated chitosan and the thiolated Pluronic F-127 was a viscous solution state at room temperature but became a cross-linked gel state with instantaneous solidification at the body temperature and physiological pH. The adhesive chitosan/Pluronic injectable hydrogels with remnant catechol groups showed strong adhesiveness to soft tissues and mucous layers and also demonstrated superior hemostatic properties. These chitosan/Pluronic hydrogels are expected to be usefully exploited for injectable drug delivery depots, tissue engineering hydrogels, tissue adhesives, and antibleeding materials.     

PEGDA hydrogels with patterned elasticity: Novel tools for the study of cell response to substrate rigidity

The ability of cells to migrate in response to mechanical gradients (durotaxis) and differential cell behavior in adhesion, spreading, and proliferation in response to substrate rigidity are key factors both in tissue engineering, in which materials must be selected to provide the appropriate mechanical signals, and in studies of mechanisms of diseases such as cancer and atherosclerosis, in which changes in tissue stiffness may inform cell behavior. Using poly(ethylene glycol) diacrylate hydrogels with varying polymer chain length and photolithographic patterning techniques, we are able to provide substrates with spatially patterned, tunable mechanical properties in both gradients and distinct patterns. The hydrogels can be patterned to produce anisotropic structures and exhibit patterned strain under mechanical loading. These hydrogels may be used to study cell response to substrate rigidity in both two and three dimensions and can also be used as a scaffold in tissue‐engineering applications. Biotechnol. Bioeng. 2010; 105: 636–644. © 2009 Wiley Periodicals, Inc.