精准宏观超分子组装

Precise Macroscopic Supramolecular Assembly

宏观超分子组装是近年来超分子科学的新兴研究方向,其本质是表面修饰有大量超分子官能团的宏观构筑基元的界面组装.由于组装过程中存在较多热力学亚稳态,导致最终产生大量非精准组装体,整体结构有序度低,制约了其在高性能超分子材料方面的应用,因此,如何实现精准宏观超分子组装,构建有序超分子结构,成为了制约宏观超分子组装发展的瓶颈问题之一.本专论从宏观超分子组装的概念与组装机制出发,根据宏观超分子组装过程的特点,分析阐述了组装体中存在不同界面匹配度的热力学亚稳态的问题;继而,从能量面的角度展开分析,总结和归纳了提高组装结构有序度的精准组装策略,包括:(1)利用组装体热力学稳定性差异,设计各向异性构筑基元诱导目标组装结构的形成,发展自纠错策略提高组装界面匹配度;(2)引入宏观构筑基元的组装动力学设计,使构筑基元发生自驱动运动并通过界面长程力取向,使组装界面达到高度匹配,实现近热力学平衡态的精准组装,直接获得精准结构.进而,结合精准宏观超分子组装制备的有序结构,我们展望了其在构建组织工程支架方面的应用前景.

Macroscopic supramolecular assembly(MSA),which is mainly focused on the interfacial assembly of building blocks with a size exceeding ten micro-meter,has been a recent progress of supramolecular science.A typical MSA process resembles many interfacial phenomena such as underwater adhesion,self-healing,bioadhesion etc.;MSA is flexible in the design,fabrication and assembly of building blocks and thus is promising to prepare 3D ordered structures of various purposes such as tissue scaffolds,flexible devices and so on.To facilitate the application of MSA,much efforts have been dedicated to understanding the assembly mechanism.The intrinsic feature of MSA is an interfacial assembly event between two macroscopic building blocks modified with massive supramolecular interactive motifs.Because of increased groups and interactive area,MSA assembly normally results in a few thermodynamic metastable structures,leading to many imprecise assemblies and less ordered final structures,which is not favourable for high performance of bulk supramolecular materials and corresponding applications.Therefore,developing strategies to achieve precise MSA for the construction of ordered supramolecular structures,has remained as a challenge of further development of MSA.In this feature article,we have briefly introduced the concept of MSA by comparing the similarity and difference with supramolecular assembly of molecular level or nano-scale,which thus relies on further insight into assembly mechanism of MSA.With further analysis of the energy landscape of MSA,we have elaborated the low-precision problem of MSA towards the formation of ordered structure,which is a new issue different from molecular assembly.More than the situation of similar components leading to different assembly geometry,MSA has an extra low-precision phenomenon of meta-stable assemblies,i.e.the matching degree of even the same assembly geometry could be diverse,due to the increasing interactive area and surface groups in an MSA event.Until now,several strategies have been reported to increase the precision of MSA structures.We have summarized two general idea from the point of thermodynamic and kinetic features of MSA.(1)The thermodynamic stability of precise and imprecise assemblies differs dramatically,which provides design room for selective assembly of precise structures.For example,fabricating anisotropic building blocks could increase the selectivity of targeted assembly geometry;applying a self-correction methodology based on a dynamic assembly/disassembly principle could efficiently convert meta-stable assemblies into stable ones.(2)Assembly kinetics and pathways could be well controlled through engineering of building blocks.Self-propulsion methods could make macroscopic building blocks to locomote similar to molecules,thus providing collision and interactive chances.Long-ranged forces(e.g.curvature forces at immiscible phases)could pre-align the matching degree of macroscopic surfaces before assembly.Efficient interfacial assembly upon contact could stabilize precise assemblies by applying a‘flexible spacing coating’beneath the supramolecular groups.Finally,we envisioned potential applications of precise MSA structures in fabricating complex tissue scaffolds,which requires integration of multiple materials,diverse chemical/biological factors etc.