Department of Biomedical Engineering, Department of Chemistry, and Chemistry of Life Processes Institute, Northwestern University, Evanston, Illinois, USA.
Biomater Sci. 2018 May 1;6(5):1048-1058. doi: 10.1039/c8bm00135a.
When engineering nanomaterials for application in biological systems, it is important to understand how multivalent ions, such as calcium, affect the structural and chemical properties of polymer-modified nanoconstructs. In this work, a recently developed molecular theory was employed to study the effect of surface curvature on the calcium-induced collapse of end-tethered weak polyelectrolytes. In particular, we focused on cylindrical and spherical nanoparticles coated with poly(acrylic acid) in the presence of different amounts of Ca2+ ions. We describe the structural changes that grafted polyelectrolytes undergo as a function of calcium concentration, surface curvature, and morphology. The polymer layers collapse in aqueous solutions that contain sufficient amounts of Ca2+ ions. This collapse, due to the formation of calcium bridges, is not only controlled by the calcium ion concentration but also strongly influenced by the curvature of the tethering surface. The transition from a swollen to a collapsed layer as a function of calcium concentration broadens and shifts to lower amounts of calcium ions as a function of the radius of cylindrical and spherical nanoparticles. The results show how the interplay between calcium binding and surface curvature governs the structural and functional properties of the polymer molecules. This would directly impact the fate of weak polyelectrolyte-coated nanoparticles in biological environments, in which calcium levels are tightly regulated. Understanding such interplay would also contribute to the rational design and optimization of smart interfaces with applications in, e.g., salt-sensitive and ion-responsive materials and devices.
当工程纳米材料应用于生物系统时，了解多价离子（如钙）如何影响聚合物修饰纳米结构的结构和化学性质非常重要。在这项工作中，我们采用了最近开发的分子理论来研究表面曲率对末端接枝弱聚电解质的钙诱导坍塌的影响。特别是，我们关注的是在存在不同量的 Ca2+离子的情况下，涂覆有聚（丙烯酸）的圆柱形和球形纳米颗粒。我们描述了接枝聚合物作为钙浓度、表面曲率和形态的函数所经历的结构变化。在含有足够量 Ca2+离子的水溶液中，聚合物层会发生坍塌。这种坍塌是由于钙桥的形成，不仅受钙离子浓度的控制，而且还受到束缚表面曲率的强烈影响。随着钙浓度的增加，从溶胀层到坍塌层的转变变宽，并随着圆柱形和球形纳米颗粒半径的增加向更低的钙离子浓度移动。结果表明，钙结合与表面曲率之间的相互作用如何控制聚合物分子的结构和功能特性。这将直接影响弱聚电解质涂层纳米颗粒在生物环境中的命运，其中钙水平受到严格调节。理解这种相互作用也将有助于合理设计和优化具有智能界面的应用，例如盐敏和离子响应材料和器件。
