Tunable, Textile-Based Joint Impedance Module for Soft Robotic Applications.

The design of soft actuators is often focused on achieving target trajectories or delivering specific forces and torques, rather than controlling the impedance of the actuator. This article outlines a new soft, tunable pneumatic impedance module based on an antagonistic actuator setup of textile-based pneumatic actuators intended to deliver bidirectional torques about a joint. Through mechanical programming of the actuators (select tuning of geometric parameters), the baseline torque to angle relationship of the module can be tuned. A high bandwidth fluidic controller that can rapidly modulate the pressure at up to 8 Hz in each antagonistic actuator was also developed to enable tunable impedance modulation. This high bandwidth was achieved through the characterization and modeling of the proportional valves used, derivation of a fluidic model, and derivation of control equations. The resulting impedance module was capable of modulating its stiffness from 0 to 100 Nm/rad, at velocities up to 120°/s and emulating asymmetric and nonlinear stiffness profiles, typical in wearable robotic applications.

Snap-through in Graphene Nanochannels: With Application to Fluidic Control.

Recent studies on the structure and transport behaviors of water confined within lamellar graphene have attracted intense interest in filtration technology, but the mechanism of water transport in complex membrane nanostructures remains an open question. For example, similar systems but at much larger scales have indicated that the instabilities of an elastic structure, such as snap-through, play an essential role in controlling the fluid flow. Graphene sheets, which have an atomic thickness, often appear highly wrinkled in nanofluidic devices and so are vulnerable to elastic instabilities. However, it remains unclear how does the flexible wrinkled structure affect the transport of water and filtration efficiency or whether such an effect can be exploited in devices. In this work, we explore the flow-induced snap-through in graphene nanochannels by combining molecular simulations with the theoretical analysis. We further demonstrate its applications to passive control of fluid flow and to ion/molecule selection. By introducing a flexible arch embedded within a graphene nanochannel, we observe the "snap" of the arched graphene wall from one stable state to another by varying the fluid flux (i.e., velocity); the critical velocity of this snap transition is found to depend nonmonotonically on the geometric size of the channel and the arch. We also demonstrate reversible snap-through by fixing the end parts of the flexible arch. These results suggest the potential of flow-induced snap-through in graphene-based nanochannels for ion/molecule selection applications in, for example, the design of a foul-resistant, easy-to-clean, reusable filter membrane.

Multistep Fluidic Control Network toward the Automated Generation of Organ-on-a-Chip.

Organ-on-a-chip, which mimics physiological functions of organs, is a potential tool for drug development and precision medicine. This chip, accompanied by a suitable culture environment and appropriate culture procedure, allows cells to form functional tissues that can be used in drug tests. Due to difficulties in the maintenance of cells and the complex nature of the tissue development process, it is essential to develop an automated culture platform to avoid contamination and reduce operational errors during long-term tissue culture. In this study, we developed a semiautomatic culture platform that integrates with a multistep fluidic control network, which allows multiple culture steps to be controlled and meets the requirement of the air-liquid interface (ALI), while maintaining a dynamic flow onto the cells. The culture platform was assembled with a culture chip, a reservoir, a miniaturized peristaltic pump, and a fluidic control base to connect each component and to operate the multiple culture steps. To demonstrate the capability of the culture platform, we have successfully controlled the multiple cell culture steps by switching the operation modes, allowing (1) cell proliferation under a liquid-liquid interface, (2) medium change from proliferation medium to differentiation medium, (3) cell differentiation under ALI conditions, and (4) repeated mucus washing. The dynamics and ALI culture conditions can simulate a physiological environment that is capable of maintaining and enabling cell differentiation for tissue-specific functions. The results demonstrate that bronchial tissue develops in the culture chip after 4 weeks of tissue culture. A versatile combination of culture steps makes the tissue culture platform suitable as an in vitro organ-on-a-chip culture model, especially for the tissues that involve the ALI culture, such as lung and skin. This platform, with multilogic control procedures, holds promise for enabling the long-term cultivation of differentiated tissues for advanced pharmacological and toxicological applications.