Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea.
Bioinspir Biomim. 2012 Dec;7(4):046013. doi: 10.1088/1748-3182/7/4/046013. Epub 2012 Oct 23.
Stereocilia are the basic sensory units of nature's inertial sensors and are highly sensitive over broad dynamic ranges, which is a major challenge in the design of conventional engineering sensors. The high sensitivity that is maintained by stereocilia was hypothesized to exist due to a combination of adaptation and negative stiffness mechanisms, which shift the region of highest sensitivity toward the active operation range of the stereocilia bundle. To examine the adaptation hypothesis in terms of its potential applicability to future applications regarding the design of inertial sensors, we developed a mechanical mimicry of the interplay between negative stiffness and the adaptation of the stereocilia that produces spontaneous oscillation of the hair bundle. The mechanical model consists of an inverted pendulum and a fixed T-bar that mimic the interaction of two adjacent stereocilia. To focus on the interaction of one gating spring and the corresponding adaptation motor without the effect of coupling from the other gating springs attached to the neighboring stereocilia, we fixed one bar that contains the adaptation motor. To emulate the negative resistance of the tip-link due to the transient stiffness softening by the gating ion channel, a magnet pair was attached to the top of the inverted pendulum and the fixed T-bar. Readjustment of the tip-link tension by the 'slipping down and climbing up' motion of the adaptation molecular motors was demonstrated by the side-to-side movement of the magnet by a step motor. The negative stiffness region was observed near the equilibrium position and shifted with the activation of the adaptation motor. The temporal demonstration of the stiffness shift was measured as a spontaneous oscillation. The results showed that the interplay between the negative stiffness and the adaptation mechanism was mechanically produced by the combination of a repulsive force and its continuous readjustment and is better understood through a parameter study of a biomimetic mechanical system.
静纤毛是自然界惯性传感器的基本感觉单位，其在宽动态范围内具有高度敏感性，这对传统工程传感器的设计是一个重大挑战。静纤毛保持的高灵敏度被假设是由于适应和负刚度机制的结合，这种机制将最高灵敏度区域移向静纤毛束的主动工作范围。为了根据适应假说研究其在设计惯性传感器方面的潜在适用性，我们开发了一种机械模拟，模拟负刚度和静纤毛适应之间的相互作用，从而产生毛束的自发振荡。该机械模型由一个倒立摆和一个固定的 T 形臂组成，模拟两个相邻静纤毛的相互作用。为了专注于一个门控弹簧的相互作用和相应的适应马达，而不受附着在相邻静纤毛上的其他门控弹簧的耦合影响，我们固定了一个包含适应马达的杆。为了模拟由于门控离子通道的暂态刚度软化而导致的尖端连接的负电阻，一对磁铁被附着在倒立摆和固定 T 形臂的顶部。通过步进电机使磁铁侧向移动，展示了适应分子马达的“向下滑动和向上攀爬”运动对尖端连接张力的重新调整。负刚度区域出现在平衡位置附近，并随适应马达的激活而移动。通过对生物仿生机械系统的参数研究，测量了刚度变化的时间演示，作为自发振荡。结果表明，负刚度和适应机制之间的相互作用是通过排斥力及其连续调整的组合来实现的，这通过对生物仿生机械系统的参数研究可以更好地理解。
