【作者】 张欣；

【导师】 刘俊秋；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2018， 博士

【摘要】 凝胶是具有三维空间结构的聚合物网络,它能够吸收大量的溶剂,三维空间网络可以由小分子或大分子（包括蛋白质分子）形成。尽管凝胶具有许多优异的性能,但它们的理想性能常常在宏观或微观尺寸的裂纹损坏时发生变化或甚至丧失,限制其使用寿命。为了应对这一挑战,“智能”软材料-自修复凝胶出现了,智能凝胶具有对pH、交流电（AC）、紫外光、温度、电场和磁场等外部刺激作出反应的能力。但是,由于这些强烈的外部刺激严重阻碍了它们在体内的生物医学应用。然而,水凝胶是一类特殊的凝胶,其中溶胀剂是水,其具有良好的生物相容性、水渗透性,而且通过人工合成可得到不同微观结构和性能的水凝胶材料。在水凝胶中,酶可以在温和条件下与药物,蛋白质和活细胞具有很好的生物相容性,与直接用酸或其他强烈的刺激响应调节的自修复过程相比,酶调控的自修复不仅可以显著提高水凝胶的修复效率,而且可以保持水凝胶网络的均一性和生物体的活性。此外,除了用水凝胶模拟生物体自修复功能外,生物体组织器官以及肌肉运动的模拟也是一个重要的研究领域。而蛋白质水凝胶在该领域具有突出贡献,其具有许多独特的特点和优势,内在的生物友好性和生物可降解性,可以提供人造微环境,高度模拟生物体组织器官、细胞环境的关键特征以及细胞外基质。因此,受酶和蛋白质水凝胶优良性质的启发,我们基于动态化学概念（化学相互作用与物理相互作用）构筑了几种功能性水凝胶,希望在药物递送、细胞增殖、组织工程、生物医学和生物材料领域发挥潜在的应用。1.基于柱芳烃的酶调控快速自修复水凝胶自修复,材料的令人兴奋的属性之一,经常用于修复生物和人造系统的损伤。自修复过程在生物体中非常常见,例如人体皮肤可以自动修复伤口。酶调控的自修复方法是快速高效的且具有生物相容性。在此,我们构建了一种酶调控的快速自修复水凝胶,通过柱[5]芳烃衍生物和苯甲醛修饰的PEG(DF-PEG₄₀₀₀)形成动态酰腙键交联的水凝胶,并向其中加入两种酶（葡萄糖氧化酶（GOx）和过氧化氢酶（CAT））。基于酶的协同作用,显著提高了水凝胶的修复效率与速度,该水凝胶自修复过程仅需约5分钟就可完全修复,但对于不含双酶体系的水凝胶需要超过1天时间仅部分修复。当破损的水凝胶用少量葡萄糖处理时,水凝胶中的GOx通过产生葡萄糖酸可以降低体系的pH值,这加速了动态酰腙键的重建。随后,CAT将GOx催化过程中产生的过氧化氢（H₂O₂）分解成水和氧气,从而减少H₂O₂对水凝胶机械性能的影响。同时,基于该水凝胶基元全肼柱[5]芳烃的特点,我们制备了能够均匀分散并稳定单壁碳纳米管的自修复导电水凝胶。通过将芘修饰到全肼柱[5]芳烃上,从而利用芘与单壁碳纳米管之间的π-π相互作用均匀分散了碳纳米管。本章不仅提供了一个分散碳纳米管的方法,而且提供了一个制备导电水凝胶的独特方法,该导电的自修复水凝胶有望在记忆器件、药物载体、生物传感器、超电容器、太阳能电池等领域得到广泛的应用。2.快速自修复的蛋白质水凝胶可以毫不夸张的说,生命是在水凝胶中孕育、产生和成长的,在生物体内,组织大多是由蛋白质和聚多糖组成的含有大量水的网络凝胶材料,这样保证了生物器官输送物质的高效性。良好的生物相容性、水渗透性、不同微观结构和性能的水凝胶在生物医学领域具有广泛的应用。蛋白质是维持生物体生命活动的物质之一,其具有复杂的立体结构和生物功能,蛋白质水凝胶具有内在的生物友好性和生物可降解性。这些性质可以促进药物递送、细胞增殖、组织工程、生物医学和生物材料领域的发展。在此,我们通过还原BSA蛋白质中的二硫键,使BSA蛋白质结构打开,进而在各个蛋白质分子之间二硫键发生错配形成水凝胶。该BSA蛋白质水凝胶具有高效和快速的自修复性能,断裂或破损的蛋白质水凝胶在H₂O₂刺激响应下仅需要1-2分钟左右就能完全修复。在断裂界面处滴加少量H₂O₂,H₂O₂可以加速巯基氧化,从而促进BSA蛋白质水凝胶的自修复过程。该蛋白质水凝胶具有很好的剪切变稀效果,其仅在39%左右的应变下就显示出粘性流体性能,且具有很好的恢复性,仅用针孔注射器就能将其挤出成型,该蛋白质水凝胶有望在药物递送、组织工程、可注射凝胶、3D生物打印、生物医学等领域得到广泛的应用。3.模拟肌肉生物力学行为的高伸缩性蛋白质水凝胶在生物体内,肌肉组织是由肌纤维构成,肌纤维由许多个肌节组装而成,而肌节主要由粗肌丝、细肌丝和起主要弹性功能的肌联蛋白构成。肌肉的被动运动主要由肌节来调节,在肌肉收缩和松弛过程中,这两种肌丝可以互相滑动,以实现功能,不仅依赖于将肌动蛋白作为分子弹簧的精确控制,还与钙离子诱导的蛋白质构象变化有关,这些特征的整合赋予肌肉优异的生物力学行为,即延展性,强度和弹性的独特组合。化学家们一直致力于模仿肌肉伸缩的这种过程,但是,模拟具有突出的机械性能和生物相容性的弹性肌肉仍然是一个很大的挑战。本章我们设计了一种将物理相互作用引入化学交联的蛋白质水凝胶中,大大增强了蛋白质水凝胶的拉伸性能,并结合该蛋白质水凝胶的内在和外在的特点,成功的模拟了生物体肌肉的运动。我们利用动态共价交联的BSA蛋白水凝胶与海藻酸盐链一起形成网状结构的水凝胶骨架,其中BSA和海藻酸盐链之间的动态非共价相互作用赋予水凝胶优异的拉伸性和良好的恢复性能,这是由于在拉伸过程中BSA蛋白可以沿着海藻酸盐链滑动,随着拉伸力的增加,蛋白质结构会进一步展开。值得注意的是,该水凝胶可以达到1200%的断裂应变,以及在拉伸过程中具有较大的能量耗散即具有很好的恢复性能。并且Ca²⁺调控该水凝胶的收缩恢复过程也与天然肌肉的Ca²⁺调控收缩过程高度一致。此外,该蛋白质水凝胶具有出色的生物相容性,未来有希望应用于生物医学材料和组织工程中,且有助于对肌肉运动的可视化识别。更多还原

【Abstract】 Gels,a polymer networks with three-dimensional spatial structure,can absorb a large amount of solvent and can be formed with small molecules or macromolecules（including protein molecules）.Although gels have many excellent properties,their ideal properties are often changed or even lost at macroscopic or microscopic cracks,limiting their useful life.In response to this challenge,"smart"soft materials,self-healing gels,have emerged.Smart gels have the ability to respond to external stimuli such as pH,alternating current（AC）,ultraviolet light,temperature,electric and magnetic fields.However,these strong external stimuli hinder their biomedical applications severely in vivo.Hydrogels are a special type of gel in which the swelling agent is water,which has good biocompatibility and water permeability.Hydrogels with different microstructures and properties can be obtained through artificial synthesis.Under mild conditions,enzymes have good biocompatibility with drugs,proteins,and living cells.Compared with the self-healing process that is directly regulated by the acid or other stimulus response,enzyme-controlled self-healing can not only significantly improve the hydrogel repair efficiency,but also maintain the homogeneity of the hydrogel network and the activity of the organism.In addition to simulating biological self-healing function,the simulating living tissues and organs as well as muscle movement is also an important research area.Protein hydrogels have made outstanding contributions in this field.They have many unique characteristics and advantages including inherent bio-friendliness and biodegradability,which can provide artificial micro-environment,highly simulate the key features of living tissues,cell environment,and extracellular matrix.Therefore,inspired by the excellent properties of the enzyme and protein hydrogels,we have constructed several functional hydrogels based on the dynamic chemistry concept（chemical interactions and physical interactions）.It is hoped that these hydrogels will play a potential role in drug delivery,cell proliferation,tissue engineering,biomedical and biomaterials.1.Enzyme-regulated fast self-healing of a pillararene-based hydrogel.Self-healing,one of the exciting attributes of materials,is often used to repair damage to biological and artificial systems.The self-healing process is very common in living organisms.For example,human skin can automatically repair wounds.The enzyme-regulated self-healing method is fast,efficient,and biocompatible.Here,we constructed an enzyme-controlled fast self-healing hydrogel that formed a dynamic hydrazide-linked hydrogel through amino-containing pillar[5]arene-derivant and dialdehyde-functionalized PEG(DF-PEG₄₀₀₀).Then add two enzymes（Glucose oxidase（GOx）and Catalase（CAT））to it.Based on the synergistic action of the enzymes,the hydrogel recovery efficiency and speed are significantly improved.Specifically,the double-enzyme synergistic effect allows the hydrogel to be completely repaired in only about 5 minutes,but it takes more than 1 day for the hydrogel without the dual enzyme system.When the broken hydrogel is treated with a small amount of glucose,the GOx in the hydrogel can reduce the pH of the system by producing gluconic acid,which accelerates the reconstruction of the dynamic hydrazide bond.Subsequently,CAT can decompose hydrogen peroxide（H₂O₂）produced during GOx catalysis process,reducing the effect of H₂O₂ on the mechanical properties of the hydrogel.At the same time,we modify the pyrene-1-carbaldehyde onto the amino-containing pillar[5]arene-derivant and prepare a self-healing conductive hydrogel that can uniformly disperse the single-walled carbon nanotubes（SWCNT）by theπ-πinteractions between the pyrene and the SWCNT.This not only provides a method for dispersing carbon nanotubes,but also provides a unique method of preparing a conductive hydrogel.This conductive self-healing hydrogel is expected to be widely used in memory devices,drug carriers,biosensors,ultracapacitors,solar cells and other fields.2.Injectable fast self-healing protein hydrogelIt is no exaggeration to say that life is bred,produced,and grown in hydrogels.In organisms,tissues are mostly web gel materials composed of proteins and poly-saccharides that contain large amounts of water,this ensures the efficient delivery of biological substances.Hydrogels with good biocompatibility,water permeability,and different microstructures and properties have a wide range of applications in the biomedical field.Proteins are one of the main substances that sustain the life activities of organisms,and they have complex three-dimensional structures and biological functions.Protein hydrogels are inherently bio-friendly and biodegradable.These properties can promote the development of drug delivery,cell proliferation,tissue engineering,biomedicine,and biomaterials.Here,we reduced the disulfide bonds between BSA protein molecules to form hydrogels by the mismatch of disulfide bonds.The BSA protein hydrogel has efficient and rapid self-healing properties.The broken protein hydrogel only needs 1-2 minutes to fully repair under H₂O₂stimulation response.The self-healing process of BSA protein hydrogel will be accelerated with a little H₂O₂ that is added dropwise at the fracture interface.This is because H₂O₂ can accelerate thiol oxidation.The protein hydrogel has a good shear thinning effect,exhibits fluid properties only under about 39%strain,and has excellent recovery properties.It can be extruded only with a pinhole syringe.The protein hydrogel is expected to find a wide range of applications in drug delivery,tissue engineering,injectable gels,3D bio-printing,and biomedical applications.3.Designed highly stretchable protein hydrogels to mimic the biomechanical behavior of musclesIn living organisms,muscle tissue consists of muscle fibers,which are assembled from many sarcomeres,and sarcomere is mainly composed of thick filaments,thin filaments,and titin that plays a major role in elasticity.During muscle contraction and relaxation,these two myofilaments could slide past each other to achieve functioning not only relying on the precise control of titin as molecular spring,but also related to calcium-ion-induced conformational change in the proteins.Integration of these features endows the muscles with excellent biomechanical behavior,that is,a unique combination of extensibility,strength and resilience.Chemists have been working on mimicking the process of muscle expansion,but simulating elastic muscles with outstanding mechanical properties and biocompatibility remains a big challenge.Here,we introduce physical interactions into chemically cross-linked protein hydrogels,which greatly enhances the tensile properties of protein hydrogels.In combination with the intrinsic and extrinsic characteristics of the protein hydrogels,we successfully simulated the movement of the body’s muscles.We used a dynamic covalently crosslinked BSA protein hydrogel to form a network-like hydrogel backbone with an alginate chain,where reversible non-covalent interactions between BSA and alginate chains render the hydrogel excellent stretchability and excellent recovery performance.This is due to the fact that BSA protein can slide along the alginate chain during the stretching process,and the protein structure will unfold as the stretching force increases.It is worth noting that the hydrogel can achieve a 1200%strain at break.The hydrogel has large energy dissipation during the stretching process and it determines the excellent recovery performance.And the contraction recovery process of Ca²⁺-regulated hydrogels is also highly consistent with the natural muscle contraction process.In addition,the protein hydrogel has excellent biocompatibility and is expected to be applied in biomedical materials and tissue engineering in the future,and it contributes to the visual recognition of muscle movement.更多还原