Transient Polymer Hydrogels Based on Dynamic Covalent Borate Ester Bonds

Abstract

In nature, biological systems maintain their unique structures and functions by using nonequilibrium processes driven by chemical fuels. Inspired by natural systems, transient hydrogel systems based on chemical reaction networks have been developed that are in thermodynamically nonequilibrium states. The formation of dynamic covalent bonds is an effective tool for designing analogous systems. Herein, we design a transient polymer hydrogel based on fuel-mediated covalent borate ester bonds. The pH-sensitive covalent borate ester bond is formed by the reaction between polyvinyl alcohol (PVA) and boric acid (B(OH) 3 ). Sodium hydroxide (NaOH) and 1,3-propanesulfonate (PrS) are used together as the chemical fuels to temporally control the pH of the system. Meanwhile, the lifetime of the transient hydrogel can be simply controlled by adjusting the composition of the chemical fuel, and the cyclic phase transitions can also be achieved. These programmable transient hydrogels have potential applications in the fields of information transmission and fluid guidance.

Covalently Crosslinked Networks from Telechelic Polycyclooctene with Reinforced Properties

“…Compared to the permanent crosslinked networks, covalent adaptable networks defined as vitrimers have received plenty of interest in recent years, which merge the advantages in reprocessing and durability of thermoplastic and thermosetting polymers. [ 43‐55 ] Given the unique features such as free of catalyst and fast stress relaxation, the transamination of vinylogous urethane between acetoacetate groups and primary amines introduced by Winne and Du Prez et al . has been one of the most promising reversible reactions for vitrimers synthesis.…”

Transient regulation of gel properties by chemical reaction networks

“…Based on the chemical reaction between polyvinyl alcohol (PVA) and boric acid, we employed pH-sensitive borate ester bonds to design a transient hydrogel. 24 Sodium hydroxide and 1,3-propanesulfonate were used together as chemical fuels to temporally control the pH of the system. By regulating the pH, the system could achieve cyclic phase transitions, and each cycle was able to maintain the original rheological moduli and viscosity.…”

“…[20][21][22] Inspired by the nonequilibrium dynamic processes in living organisms, researchers have designed many artificial systems that exist far from equilibrium to generate gels with transient structural and functional tunability. [23][24][25][26][27][28][29][30][31][32][33][34][35] These gels are conceptually closer to biological organisms than ordinary stimuli-responsive materials. 26 The realization of most functions relies on the supply of chemical fuels to drive the formation of a transient out-of-equilibrium state at either macroscopic or microscopic levels.…”

Comprehensive Chemical Experiment of Dynamic Reconfiguration of Supramolecular Assemblies

“…化学奖 [1,2] 。这些重要成果是人类向生命体深入学习而获得的。在生物系统中，化学燃料或能量的输 入可激活结构单元，使其自组装形成瞬态结构。生命体利用这种受控于耗散热力学的非平衡超分子 组装来调整其结构和功能以实现自我调节 [3][4][5][6][7][8] 。受此启发，研究者们设计出了一系列化学燃料驱动 的、瞬态的、远离热力学平衡态的超分子体系，并将其应用于智能材料的研究和开发 [9][10][11][12][13][14][15][16] 。开发非 平衡组装体系并探究其组装机制可以加深对生命体的理解，并在设计和开发新型智能材料中发挥重 要作用。 利用非平衡组装可以制备出结构、功能、寿命可调的瞬态材料，其中以瞬态水凝胶材料最为典 型 [17] 。近年来，科学家通过模仿生命系统中的组装-解组装行为并结合化学反应网络，制备出了多种 可应用于药物控释及信息加密等领域的瞬态水凝胶材料 [9,10,15] 。与此同时，对合成体系非平衡组装机 制的深入研究同样备受关注。设计相关实验，可使学生初步接触超分子化学领域的前沿问题，激发 其学习兴趣与热情，并锻炼其综合实验技能。 在本实验中，将构建一个宏观上表现出沉淀→凝胶→沉淀转变现象的非平衡组装体系，并提出 超分子组装体动态重构机制。该实验操作简便，现象明显，适合实验教学，除基础操作外，还加入 透射电子显微镜(TEM)、荧光光谱仪、圆二色谱仪的使用，让学生在实验过程中不仅可以学习到非 平衡组装体系的构建方法及组装机制，还能满足学生学习现代科学表征技术的需求。…”