Soft Materials Laboratory, Institute of Materials , École Polytechnique Fédérale de Lausanne , 1015 Lausanne , Switzerland.
Langmuir. 2018 Mar 20;34(11):3459-3466. doi: 10.1021/acs.langmuir.7b04163. Epub 2018 Mar 6.
Natural soft materials are often composed of proteins that self-assemble into well-defined structures and display mechanical properties that cannot be matched by manmade materials. These materials are frequently mimicked with hydrogels whose mechanical properties depend on their composition and the type and density of cross-links. Protocols to tune these parameters are well established and routinely used. The mechanical properties of hydrogels also depend on their structure; this parameter is more difficult to control. In this paper, we present a method to produce hexagonal-prismatic granular hydrogel sheets with well-defined structures and heterogeneous cross-link densities. The hydrogel sheets are made of self-assembled covalently cross-linked 40-120 μm diameter hexagonal-prismatic hydrogel particles that display a narrow size distribution. The structure and microscale surface roughness of the hydrogels sheets can be tuned with the polymerization conditions, their chemical composition with that of the individual hydrogel particles, and their mechanical properties with the cross-link density. Remarkably, the hydrogels composed of hexagonal-prismatic microparticles are significantly stiffer than unstructured counterparts. These results demonstrate that the stiffness of hydrogels can be tuned by controlling their micrometer-scale structure without altering their composition. Thereby, they open up new possibilities to design soft materials whose performance more closely resembles that of natural ones.
天然软物质通常由蛋白质组成，这些蛋白质会自组装成具有明确结构的物质，并表现出无法被人造材料所匹配的机械性能。这些物质经常被水凝胶模仿，水凝胶的机械性能取决于其组成以及交联的类型和密度。用于调整这些参数的方案已经很成熟，并且经常被使用。水凝胶的机械性能也取决于其结构，而这一参数更难控制。在本文中，我们提出了一种生产具有明确结构和不均匀交联密度的六方棱柱形颗粒水凝胶片的方法。这些水凝胶片由自组装的共价交联的 40-120μm 直径的六方棱柱形水凝胶颗粒制成，具有较窄的尺寸分布。水凝胶片的结构和微尺度表面粗糙度可以通过聚合条件来调整，其化学成分可以通过单个水凝胶颗粒的化学成分来调整，而其机械性能可以通过交联密度来调整。值得注意的是，由六方棱柱形微颗粒组成的水凝胶的硬度明显高于无定形的对应物。这些结果表明，可以通过控制水凝胶的微米级结构来调整其硬度，而无需改变其组成。因此，它们为设计性能更接近天然材料的软材料开辟了新的可能性。
