Buskohl Philip R, Vaia Richard A
Functional Materials Division, Materials and Manufacturing Directorate, Air Force Research Laboratory, 2179 12th Street, Wright-Patterson Air Force Base, OH 45433, USA.
Sci Adv. 2016 Sep 23;2(9):e1600813. doi: 10.1126/sciadv.1600813. eCollection 2016 Sep.
Belousov-Zhabotinsky (BZ) autonomic hydrogel composites contain active nodes of immobilized catalyst (Ru) encased within a nonactive matrix. Designing functional hierarchies of chemical and mechanical communication between these nodes enables applications ranging from encryption, sensors, and mechanochemical actuators to artificial skin. However, robust design rules and verification of computational models are challenged by insufficient understanding of the relative importance of local (molecular) heterogeneities, active node shape, and embedment geometry on transient and steady-state behavior. We demonstrate the predominance of asymmetric embedment and node shape in low-strain, BZ-gelatin composites and correlate behavior with gradients in BZ reactants. Asymmetric embedment of square and rectangular nodes results in directional steady-state waves that initiate at the embedded edge and propagate toward the free edge. In contrast, symmetric embedment does not produce preferential wave propagation because of a lack of diffusion gradient across the catalyzed region. The initiation at the embedded edge is correlated with bromide absorption by the inactive matrix, which locally elevates the bromate concentration required for catalyst oxidation. The competition between embedment asymmetry and node geometry was used to demonstrate a repeatable switch in wave direction that functions as a signal delay. Furthermore, signal propagation in or out of the composite was demonstrated via embedment asymmetry and relative dimensions of a T-shaped active network node. Overall, structural asymmetry provides a robust approach to controlling initiation and orientation of chemical-mechanical communication within composite BZ gels.
别洛索夫-扎博京斯基（BZ）自主水凝胶复合材料包含固定在非活性基质中的催化剂（钌）活性节点。设计这些节点之间化学和机械通信的功能层次结构，可实现从加密、传感器、机械化学致动器到人造皮肤等各种应用。然而，由于对局部（分子）不均匀性、活性节点形状和嵌入几何形状对瞬态和稳态行为的相对重要性理解不足，稳健的设计规则和计算模型的验证面临挑战。我们证明了在低应变的BZ-明胶复合材料中不对称嵌入和节点形状的主导作用，并将行为与BZ反应物中的梯度相关联。方形和矩形节点的不对称嵌入会产生定向稳态波，这些波从嵌入边缘开始并向自由边缘传播。相比之下，对称嵌入不会产生优先波传播，因为在催化区域缺乏扩散梯度。嵌入边缘的起始与非活性基质对溴化物的吸收相关，这会局部提高催化剂氧化所需的溴酸盐浓度。利用嵌入不对称性和节点几何形状之间的竞争，证明了作为信号延迟的波方向上的可重复切换。此外，通过T形活性网络节点的嵌入不对称性和相对尺寸，证明了信号在复合材料中的传入或传出。总体而言，结构不对称性为控制复合BZ凝胶内化学-机械通信的起始和方向提供了一种稳健的方法。
