Fluidic Pressure Research Articles

An optimized MOPSA algorithm for highly accurate deterministic lateral displacement microfluidic sorting chip design

Abstract Deterministic lateral displacement (DLD) sorting is a passive sorting technology. Due to the advantages of small volume and high accuracy, the DLD devices have been used in many applications. The critical diameter (Dc) value of the DLD device depends on the geometric structure of the internal post array. However, the existing empirical formula cannot match all types of post-arrays. Achieving the desired Dc value typically involves multiple iterative processes, leading to increased labor and time costs. In this paper, we propose an optimized trajectory prediction algorithm based on the original MOPSA, which considers the impact of fluidic pressure on particle trajectories. The method is to stretch the 2D physical field space into 3D, the particle expands from a 2D circle into a 3D ball on the pressure analysis. The net pressure on the particle is calculated, and the displacement of the particle is predicted by combining Newton’s second law and the displacement formula. A DLD device with Dc=10.6 μm was designed using this optimized algorithm and fabricated. It is verified by separation of 10 μm and 11 μm polystyrene particles. The test results were consistent with the simulation results. Compared with the empirical formula and the original MOPSA, this optimized algorithm can improve the prediction accuracy of particle trajectories in DLD devices.

Tactile Sensing and Grasping Through Thin‐Shell Buckling

Soft and lightweight grippers have greatly enhanced the performance of robotic manipulators in handling complex objects with varying shape, texture, and stiffness. However, the combination of universal grasping with passive sensing capabilities still presents challenges. To overcome this limitation, a fluidic soft gripper is introduced based on the buckling of soft, thin hemispherical shells. Leveraging a single fluidic pressure input, the soft gripper can grasp slippery and delicate objects while passively providing information on this physical interaction. Guided by analytical, numerical, and experimental tools, the novel grasping principle of this mechanics‐based soft gripper is explored. First, the buckling behavior of a free hemisphere is characterized as a function of its geometric parameters. Inspired by the free hemisphere's two‐lobe mode shape ideal for grasping purposes, it is demonstrated that the gripper can perform dexterous manipulation and gentle gripping of fragile objects in confined spaces and underwater environments. Last, the soft gripper's embedded capability of detecting contact, grasping, and release conditions during the interaction with an unknown object is proved. This simple buckling‐based soft gripper opens new avenues for the design of adaptive gripper morphologies with tactile sensing capabilities for applications ranging from medical and agricultural robotics to space and underwater exploration.

Fully 3D-Printed Miniature Soft Hydraulic Actuators with Shape Memory Effect for Morphing and Manipulation.

Miniature shape-morphing soft actuators driven by external stimuli and fluidic pressure hold great promise in morphing matter and small-scale soft robotics. However, it remains challenging to achieve both rich shape morphing and shape locking in a fast and controlled way due to the limitations of actuation reversibility and fabrication. Here, fully 3D-printed, sub-millimeter thin-plate-like miniature soft hydraulic actuators with shape memory effect (SME) for programable fast shape morphing and shape locking, are reported. It combines commercial high-resolution multi-material 3D printing of stiff shape memory polymers (SMPs) and soft elastomers and direct printing of microfluidic channels and 2D/3D channel networks embedded in elastomers in a single print run. Leveraging spatial patterning of hybrid compositions and expansion heterogeneity of microfluidic channel networks for versatile hydraulically actuated shape morphing, including circular, wavy, helical, saddle, and warping shapes with various curvatures, are demonstrated. The morphed shapes can be temporarily locked and recover to their original planar forms repeatedly by activating SME of the SMPs. Utilizing the fast shape morphing and locking in the miniature actuators, their potential applications in non-invasive manipulation of small-scale objects and fragile living organisms, multimodal entanglement grasping, and energy-saving manipulators, are demonstrated.

Controlling the fold: proprioceptive feedback in a soft origami robot.

We demonstrate proprioceptive feedback control of a one degree of freedom soft, pneumatically actuated origami robot and an assembly of two robots into a two degree of freedom system. The base unit of the robot is a 41 mm long, 3-D printed Kresling-inspired structure with six sets of sidewall folds and one degree of freedom. Pneumatic actuation, provided by negative fluidic pressure, causes the robot to contract. Capacitive sensors patterned onto the robot provide position estimation and serve as input to a feedback controller. Using a finite element approach, the electrode shapes are optimized for sensitivity at larger (more obtuse) fold angles to improve control across the actuation range. We demonstrate stable position control through discrete-time proportional-integral-derivative (PID) control on a single unit Kresling robot via a series of static set points to 17 mm, dynamic set point stepping, and sinusoidal signal following, with error under 3 mm up to 10 mm contraction. We also demonstrate a two-unit Kresling robot with two degree of freedom extension and rotation control, which has error of 1.7 mm and 6.1°. This work contributes optimized capacitive electrode design and the demonstration of closed-loop feedback position control without visual tracking as an input. This approach to capacitance sensing and modeling constitutes a major step towards proprioceptive state estimation and feedback control in soft origami robotics.

Biomimetic Curved Artificial Compound Eyes: A Review

Natural compound eyes (NCEs) are the most abundant and successful eye designs in the animal kingdom. An NCE consists of a number of ommatidia, which are distributed along a curved surface to receive light. This curved feature is critical to the functions of NCE, and it ensures that different ommatidia point to slightly different directions and thus enables panoramic vision, depth perception, and efficient motion tracking while minimizing aberration. Consequently, biomimetic curved artificial compound eyes (BCACEs) have garnered substantial research attention in replicating the anatomical configuration of their natural counterparts by distributing ommatidia across a curved surface. The reported BCACEs could be briefly categorized into 2 groups: fixed focal lengths and tunable focal lengths. The former could be further subcategorized into simplified BCACEs, BCACEs with photodetector arrays within curved surfaces, and BCACEs with light guides. The latter encompasses other tuning techniques such as fluidic pressure modulation, thermal effects, and pH adjustments. This work starts with a simple classification of NCEs and then provides a comprehensive review of main parameters, operational mechanisms, recent advancements, fabrication methodologies, and potential applications of BCACEs. Finally, discussions are provided on future research and development. Compared with other available review articles on artificial compound eyes, our work is distinctive since we focus especially on the “curved” ones, which are difficult to fabricate but closely resemble the architecture and functions of NCEs, and could potentially revolutionize the imaging systems in surveillance, machine vision, and unmanned vehicles.

Frequency-constrained topology optimization in incompressible multi-material systems under design-dependent loads

In the realm of engineering design, structures grappling with fluidic pressure loads within precise frequency constraints necessitate innovative approaches. This study introduces a method to address the intricacies of design-dependent load-based structures, focusing on three key aspects: (i) managing structures constrained by frequency under fluidic pressure loads dependent on the design, (ii) integrating the use of multiple materials, and (iii) dealing with nearly incompressible materials. The proposed approach, detailed in this paper, employs polytopal composite finite elements (PCEs) to overcome the inherent volumetric locking phenomenon in incompressible materials. By incorporating Darcy’s law and a drainage term alongside the representative-solid phase, this approach ensures consistent treatment of fluidic pressure loads, dynamically adjusting their direction and location during the multi-material design process. The porosity of each element, intricately linked to its density variable through a Heaviside function, facilitates a smooth transition between solid and void phases. The application of Darcy’s law establishes a specific pressure field, solved using PCEs, enabling the computation of consistent nodal loads. This method simplifies the assessment of load sensitivities through the adjoint-variable technique. The method’s effectiveness and reliability are validated through numerical examples, demonstrating its capability to optimize compliance within specific volume constraints for frequency-limited structures subjected to design-dependent pressure loading and considering a diverse range of materials from compressible to nearly incompressible.

Attogram-level light-induced antigen-antibody binding confined in microflow

The analysis of trace amounts of proteins based on immunoassays and other methods is essential for the early diagnosis of various diseases such as cancer, dementia, and microbial infections. Here, we propose a light-induced acceleration of antigen-antibody reaction of attogram-level proteins at the solid-liquid interface by tuning the laser irradiation area comparable to the microscale confinement geometry for enhancing the collisional probability of target molecules and probe particles with optical force and fluidic pressure. This principle was applied to achieve a 102-fold higher sensitivity and ultrafast specific detection in comparison with conventional protein detection methods (a few hours) by omitting any pretreatment procedures; 47–750 ag of target proteins were detected in 300 nL of sample after 3 minutes of laser irradiation. Our findings can promote the development of proteomics and innovative platforms for high-throughput bio-analyses under the control of a variety of biochemical reactions.

Targeted Depletion of Hyaluronic Acid Mitigates Murine Breast Cancer Growth.

Simple SummaryBreast cancer often contains excessive stromal matrix components that serve as a barrier to therapy. One such component is hyaluronic acid (HA), which also plays important roles in tumor progression and spread. In this study, we engineered an attenuated Salmonella typhimurium secreting a bacterial hyaluronidase (YS-HAse) and show that it degrades HA within murine breast tumors, resulting in enhanced tumor permeability and growth control. YS-HAse represents a promising new therapeutic approach that could also be used alongside current treatments to improve their delivery and effectiveness.Hyaluronic acid (HA) is highly elevated in breast cancers compared to normal breast tissue and is associated with increased tumor aggressiveness and poor prognosis. HA interacts with cell-trafficking CD44 receptors to promote tumor cell migration and proliferation and regulates both pro- and anti-inflammatory cytokine production through tumor-associated macrophages. The highly negative charge of HA enables its uptake of vast amounts of water that greatly increases the tumor interstitial fluidic pressure, which, combined with the presence of other extracellular matrix components such as collagen, results in tumor stroma with abnormal vasculature, hypoxia, and increased drug resistance. Thus, the degradation of HA in breast cancer may attenuate growth and improve permeability to anticancer agents. Previous methods to deplete tumor HA have resulted in significant off-tumor effects due to the systemic use of mammalian hyaluronidases. To overcome this, we developed a hyaluronidase-secreting Salmonella typhimurium (YS-HAse) that specifically and preferentially colonizes tumors to deplete HA. We show that the systemic administration of YS-HAse in immunocompetent murine models of breast cancer enhances tumor perfusion, controls tumor growth, and restructures the tumor immune contexture. These studies highlight the utility of YS-HAse as a novel microbial-based therapeutic that may also be combined with existing therapeutic approaches.

Microfluidics-Assisted Selective Depolarization of Axonal Mitochondria.

Mitochondria are the primary suppliers of ATP (adenosine triphosphate) in neurons. Mitochondrial dysfunction is a common phenotype in many neurodegenerative diseases. Given some axons' elaborate architecture and extreme length, it is not surprising that mitochondria in axons can experience different environments compared to their cell body counterparts. Interestingly, dysfunction of axonal mitochondria often precedes effects on the cell body. To model axonal mitochondrial dysfunction in vitro, microfluidic devices allow treatment of axonal mitochondria without affecting the somal mitochondria. The fluidic pressure gradient in these chambers prevents diffusion of molecules against the gradient, thus allowing for analysis of mitochondrial properties in response to local pharmacological challenges within axons. The current protocol describes the seeding of dissociated hippocampal neurons in microfluidic devices, staining with a membrane-potential sensitive dye, treatment with a mitochondrial toxin, and the subsequent microscopic analysis. This versatile method to study axonal biology can be applied to many pharmacological perturbations and imaging readouts, and is suitable for several neuronal subtypes.

Piston-Driven Pneumatically-Actuated Soft Robots: Modeling and Backstepping Control

Actuators’ dynamics have been so far mostly neglected when devising feedback controllers for continuum soft robots since the problem under the direct actuation hypothesis is already quite hard to solve. Directly considering actuation would have made the challenge too complex. However, these effects are, in practice, far from being negligible. The present work focuses on model-based control of piston-driven pneumatically-actuated soft robots. We propose a model of the relationship between the robot’s state, the acting fluidic pressure, and the piston dynamics, which is agnostic to the chosen model for the soft system dynamics. We show that backstepping is applicable even if the feedback coupling of the outer on the inner subsystem is not linear. Thus, we introduce a general model-based control strategy based on backstepping for soft robots actuated by fluidic drive. As an example, we derive a specialized version for a robot with piecewise constant curvature.

Microfluidic acoustic sawtooth metasurfaces for patterning and separation using traveling surface acoustic waves.

We demonstrate a sawtooth-based metasurface approach for flexibly orienting acoustic fields in a microfluidic device driven by surface acoustic waves (SAW), where sub-wavelength channel features can be used to arbitrarily steer acoustic fringes in a microchannel. Compared to other acoustofluidic methods, only a single travelling wave is used, the fluidic pressure field is decoupled from the fluid domain's shape, and steerable pressure fields are a function of a simply constructed polydimethylsiloxane (PDMS) metasurface shape. Our results are relevant to microfluidic applications including the patterning, concentration, focusing, and separation of microparticles and cells.

Modeling of Soft Robotic Grippers Integrated With Fluidic Prestressed Composite Actuators

Abstract Soft robotic grippers can gently grasp and maneuver objects. However, they are difficult to model and control due to their highly deformable fingers and complex integration with robotic systems. This paper investigates the design requirements as well as the grasping capabilities and performance of a soft gripper system based on fluidic prestressed composite (FPC) fingers. An analytical model is constructed as follows: each finger is modeled using the chained composite model (CCM); strain energy and work done by pressure and loads are computed using polynomials with unknown coefficients; net energy is minimized using the Rayleigh–Ritz method to calculate the deflected equilibrium shapes of the finger as a function of pressure and loads; and coordinate transformation and gripper geometries are combined to analyze the grasping performance. The effects of prestrain, integration angle, and finger overlap on the grasping performance are examined through a parametric study. We also analyze gripping performance for cuboidal and spherical objects and show how the grasping force can be controlled by varying fluidic pressure. The quasi-static responses of fabricated actuators are measured under pressures and loads. It is shown that the actuators’ modeled responses agree with the experimental results. This work provides a framework for the theoretical analysis of soft robotic grippers and the methods presented can be extended to model grippers with different types of actuation.

Axial forces at disk surfaces in a cylindrical nanopore

Understanding the physics of object translocation in nanopores is critical for using nanopores as sensors of molecular properties and as object size and shape sensors. Based on Poisson-Nernst-Planck and Navier-Stokes simulations we dissect three axial pressures and forces at disk edges (upper, lower and rim) - Coulomb, dielectric and fluidic. Axial Coulomb and dielectric rim forces are small and cancel each other. Upper and lower axial forces are largely controlled by the external axial electric field and interestingly by the pore wall charges that determine the amplitude and direction of axial combined force. Axial total Coulomb force (sum of its upper and lower edge components) makes the greatest contribution, but the axial total dielectric force (calculated using Maxwell stress tensor), which opposes it is surprisingly large. External ion concentration alters Coulomb and axial dielectric forces but influences only their amplitude. Axial total fluidic force is near zero (its upper and lower disk edge components are significant but cancel each other) regardless of external electric field, but pore wall charges and external fluidic pressure can alter it. Modest changes of external electric field or concentration produce axial forces comparable to those produced by large external fluidic pressures. Axial forces depend little on disk's axial position. Finally, mean axial pressures (calculated to compare forces acting on disks of different radius) are greater for larger disks.

A dynamic electrically driven soft valve for control of soft hydraulic actuators

Regulation systems for fluid-driven soft robots predominantly consist of inflexible and bulky components. These rigid structures considerably limit the adaptability and mobility of these robots. Soft valves in various forms for fluidic actuators have been developed, primarily fluidically or electrically driven. However, fluidic soft valves require external pressure sources that limit robot locomotion. State-of-the-art electrostatic valves are unable to modulate pressure beyond 3.5 kPa with a sufficient flow rate (>6 mL⋅min-1). In this work, we present an electrically powered soft valve for hydraulic actuators with mesoscale channels based on a different class of ultrahigh-power density dynamic dielectric elastomer actuators. The dynamic dielectric elastomer actuators (DEAs) are actuated at 500 Hz or above. These DEAs generate 300% higher blocked force compared with the dynamic DEAs in previous works and their loaded power density reaches 290 W⋅kg-1 at operating conditions. The soft valves are developed with compact (7 mm tall) and lightweight (0.35 g) dynamic DEAs, and they allow effective control of up to 51 kPa of pressure and a 40 mL⋅min-1 flow rate with a response time less than 0.1 s. The valves can also tune flow rates based on their driving voltages. Using the DEA soft valves, we demonstrate control of hydraulic actuators of different volumes and achieve independent control of multiple actuators powered by a single pressure source. This compact and lightweight DEA valve is capable of unprecedented electrical control of hydraulic actuators, showing the potential for future onboard motion control of soft fluid-driven robots.

A pneumatically controlled microfluidic rectifier enabling zero backflow under pulsatile flow regime

A pulsatile microfluidic pump transports discrete volume to specific target locations. However, backflow in the pulsatile microfluidic pump often decreases the pumping efficiency and causes unwanted sample mixing due to unsteady boundaries. Employing the concept of a transistor, we developed a pneumatically controlled microfluidic rectifier (PCMR) that prevents backflow in the pulsatile flow regime. This PCMR was interconnected with a microfluidic pulsatile pumping system to characterize the functions of PCMR under continuous pumping sequences (CPS) and discrete pumping sequences (DPS) with various gate pressures on the PCMR. In the passive mode (zero gate pressure), 1.07% backflow for a DPS and 0.12% for a CPS were achieved. However, by adjusting the gate pressure on PCMR actively, we were able to achieve zero backflow for both pumping sequences at the cost of pumping efficiency. Interestingly, when the flow passes through the PCMR under the controlled gate-pressure, a fluidic oscillation was observed due to the force balance between the fluidic pressure and the gate-pressure. This microfluidic system successfully demonstrated half-rectification from various pulsatile flow profiles. By incorporating multiple three-microvalve systems in parallel with frequency modulation, a fully rectified flow pattern can be realized to enable steady laminar flow from pulsatile micropumps.

A simple, low cost and reusable microfluidic gradient strategy and its application in modeling cancer invasion

Microfluidic chemical gradient generators enable precise spatiotemporal control of chemotactic signals to study cellular behavior with high resolution and reliability. However, time and cost consuming preparation steps for cell adhesion in microchannels as well as requirement of pumping facilities usually complicate the application of the microfluidic assays. Here, we introduce a simple strategy for preparation of a reusable and stand-alone microfluidic gradient generator to study cellular behavior. Polydimethylsiloxane (PDMS) is directly mounted on the commercial polystyrene-based cell culture surfaces by manipulating the PDMS curing time to optimize bonding strength. The stand-alone strategy not only offers pumpless application of this microfluidic device but also ensures minimal fluidic pressure and consequently a leakage-free system. Elimination of any surface treatment or coating significantly facilitates the preparation of the microfluidic assay and offers a detachable PDMS microchip which can be reused following to a simple cleaning and sterilization step. The chemotactic signal in our microchip is further characterized using numerical and experimental evaluations and it is demonstrated that the device can generate both linear and polynomial signals. Finally, the feasibility of the strategy in deciphering cellular behavior is demonstrated by exploring cancer cell migration and invasion in response to chemical stimuli. The introduced strategy can significantly decrease the complexity of the microfluidic chemotaxis assays and increase their throughput for various cellular and molecular studies.

Multistable inflatable origami structures at the metre scale.

From stadium covers to solar sails, we rely on deployability for the design of large-scale structures that can quickly compress to a fraction of their size1-4. Historically, two main strategies have been used to design deployable systems. The first and most frequently used approach involves mechanisms comprising interconnected bar elements, which can synchronously expand and retract5-7, occasionally locking in place through bistable elements8,9. The second strategy makes use of inflatable membranes that morph into target shapes by means of a single pressure input10-12. Neither strategy, however, can be readily used to provide an enclosed domain that is able to lock in place after deployment: the integration of a protective covering in linkage-based constructions is challenging and pneumatic systems require a constant applied pressure to keep their expanded shape13-15. Here we draw inspiration from origami-the Japanese art of paper folding-to design rigid-walled deployable structures that are multistable and inflatable. Guided by geometric analyses and experiments, we create a library of bistable origami shapes that can be deployed through a single fluidic pressure input. We then combine these units to build functional structures at the metre scale, such as arches and emergency shelters, providing a direct route for building large-scale inflatable systems that lock in place after deployment and offer a robust enclosure through their stiff faces.

Establishment of a heart-on-a-chip microdevice based on human iPS cells for the evaluation of human heart tissue function

Human iPS cell (iPSC)-derived cardiomyocytes (CMs) hold promise for drug discovery for heart diseases and cardiac toxicity tests. To utilize human iPSC-derived CMs, the establishment of three-dimensional (3D) heart tissues from iPSC-derived CMs and other heart cells, and a sensitive bioassay system to depict physiological heart function are anticipated. We have developed a heart-on-a-chip microdevice (HMD) as a novel system consisting of dynamic culture-based 3D cardiac microtissues derived from human iPSCs and microelectromechanical system (MEMS)-based microfluidic chips. The HMDs could visualize the kinetics of cardiac microtissue pulsations by monitoring particle displacement, which enabled us to quantify the physiological parameters, including fluidic output, pressure, and force. The HMDs demonstrated a strong correlation between particle displacement and the frequency of external electrical stimulation. The transition patterns were validated by a previously reported versatile video-based system to evaluate contractile function. The patterns are also consistent with oscillations of intracellular calcium ion concentration of CMs, which is a fundamental biological component of CM contraction. The HMDs showed a pharmacological response to isoproterenol, a β-adrenoceptor agonist, that resulted in a strong correlation between beating rate and particle displacement. Thus, we have validated the basic performance of HMDs as a resource for human iPSC-based pharmacological investigations.

Inkjet Printing of Complex Soft Machines with Densely Integrated Electrostatic Actuators

A multimaterial inkjet printing method for integrated soft multifunctional machines is reported, combining dense arrays of electrostatic actuators, multilayer electrical routing, and complex networks of microfluidic channels in one printing process. Most additive manufacturing methods for soft robots are developed for devices driven by external fluidic pressure sources and are not suited to fabricate soft electrically driven actuators. To integrate electrostatic zipping actuators and microfluidics in stretchable soft machines without any rigid components, inks for sacrificial layers, dielectric elastomers, and compliant electrodes are developed herein, along with a unified printing process to print multilayer structures. Printed 2.5D stacks are transformed into fully functional 3D soft machines by inflating thin elastomer channels. Two demonstrators are reported, each consisting of seven printed layers: a flexible peristaltic pump and a compliant slug drive, inspired by the locomotion of slugs. The peristaltic pump has six integrated actuators, whereas the slug drive has 28 integrated actuators, generating a travelling wave used to transport objects. These soft devices demonstrate how inkjet printing produces densely packed high‐voltage actuators, including vias for electrical routing. Sensors and logic may be printed in the future to produce more complex autonomous soft machines.

Active microvalve driven by electro-conjugate fluid jet flow with a hydraulic power source on a chip

Powered microvalves are necessary for a variety of microfluidic applications such as on-demand droplet generators and droplet capture systems. Currently, a central challenge for these microvalve systems is the miniaturization of bulky power sources and control components, for example, air compressors, hydraulic pumps, solenoid valves, and regulators. In this paper, we propose a polydimethylsiloxane (PDMS)-based microvalve integrated with an on-chip power source, an electro-conjugate fluid (ECF) micropump. The assembled PDMS membrane of the device deforms and then blockades the port in the microchannel via fluidic pressure generated by the ECF micropump with the application of high DC voltage. Following finite element method simulations, we utilized 15 electrode pairs for the on-chip ECF micropump. By combining a MEMS process and the bonding process, we successfully realized the designed device and proceeded to evaluation of its performance characteristics. First, we evaluated the performance of the ECF micropump, which showed a maximum output pressure and a flow rate of 49.7 kPa, 87.3 mm3 s−1, respectively, at an applied voltage of 2.0 kV. Second, we found that the minimum sealing pressure of the microvalve was 10 kPa without any load condition. Third, we investigated the cracking pressures, which were 20 kPa and 50 kPa at the applied voltages of 1.5 kV and 2.0 kV to the ECF micropump, respectively. This study experimentally demonstrated the feasibility of the proposed microvalve device and its potential to be integrated into other microfluidic devices for precision control of liquid volumes.