Title: Valveless microliter combustion for densely packed arrays of powerful soft actuators
Existing tactile stimulation technologies powered by small actuators offer low-resolution stimuli compared to the enormous mechanoreceptor density of human skin. Arrays of soft pneumatic actuators initially show promise as small-resolution (1- to 3-mm diameter), highly conformable tactile display strategies yet ultimately fail because of their need for valves bulkier than the actuators themselves. In this paper, we demonstrate an array of individually addressable, soft fluidic actuators that operate without electromechanical valves. We achieve this by using microscale combustion and localized thermal flame quenching. Precisely, liquid metal electrodes produce sparks to ignite fuel lean methane–oxygen mixtures in a 5-mm diameter, 2-mm tall silicone cylinder. The exothermic reaction quickly pressurizes the cylinder, displacing a silicone membrane up to 6 mm in under 1 ms. This device has an estimated free-inflation instantaneous stroke power of 3 W. The maximum reported operational frequency of these cylinders is 1.2 kHz with average displacements of ∼100 µm. We demonstrate that, at these small scales, the wall-quenching flame behavior also allows operation of a 3 × 3 array of 3-mm diameter cylinders with 4-mm pitch. Though we primarily present our device as a tactile display technology, it is a platform microactuator technology with application beyond this one.
Hankiewicz, Janusz H.; Celinski, Zbigniew; Camley, Robert E.(
, Medical Physics)
AbstractPurpose
One standard method, proton resonance frequency shift, for measuring temperature using magnetic resonance imaging (MRI), in MRI‐guided surgeries, fails completely below the freezing point of water. Because of this, we have developed a new methodology for monitoring temperature with MRI below freezing. The purpose of this paper is to show that a strong temperature dependence of the nuclear relaxation timeT1in soft silicone polymers can lead to temperature‐dependent changes of MRI intensity acquired withT1weighting. We propose the use of silicone filaments inserted in tissue for measuring temperature during MRI‐guided cryoablations.
Methods
The temperature dependence ofT1in bio‐compatible soft silicone polymers was measured using nuclear magnetic resonance spectroscopy and MRI. Phantoms, made of bulk silicone materials and put in an MRI‐compatible thermal container with dry ice, allowed temperature measurements ranging from –60°C to + 20°C.T1‐weighted gradient echo images of the phantoms were acquired at spatially uniform temperatures and with a gradient in temperature to determine the efficacy of using these materials as temperature indicators in MRI. Ex vivo experiments on silicone rods, 4 mm in diameter, inserted in animal tissue were conducted to assess the practical feasibility of the method.
Results
Measurements of nuclear relaxation times of protons in soft silicone polymers show a monotonic, nearly linear, change with temperature (R2 > 0.98) and have a significant correlation with temperature (Pearson'sr > 0.99,p < 0.01). Similarly, the intensity of the MR images in these materials, taken with a gradient echo sequence, are also temperature dependent. There is again a monotonic change in MRI intensity that correlates well with the measured temperature (Pearson'sr < ‐0.98 andp < 0.01). The MRI experiments show that a temperature change of 3°C can be resolved in a distance of about 2.5 mm. Based on MRI images and external sensor calibrations for a sample with a gradient in temperature, temperature maps with 3°C isotherms are created for a bulk phantom. Experiments demonstrate that these changes in MRI intensity with temperature can also be seen in 4 mm silicone rods embedded in ex vivo animal tissue.
Conclusions
We have developed a new method for measuring temperature in MRI that potentially could be used during MRI‐guided cryoablation operations, reducing both procedure time and cost, and making these surgeries safer.
Metal-mediated cross-coupling reactions offer organic chemists a wide array of stereo- and chemically-selective reactions with broad applications in fine chemical and pharmaceutical synthesis.1 Current batch-based synthesis methods are beginning to be replaced with flow chemistry strategies to take advantage of the improved consistency and process control methods offered by continuous flow systems.2,3 Most cross-coupling chemistries still encounter several issues in flow using homogeneous catalysis, including expensive catalyst recovery and air sensitivity due to the chemical nature of the catalyst ligands.1 To mitigate some of these issues, a ligand-free heterogeneous catalysis reaction was developed using palladium (Pd) loaded into a polymeric network of a silicone elastomer, poly(hydromethylsiloxane) (PHMS), that is not air sensitive and can be used with mild reaction solvents (ethanol and water).4
In this work we present a novel method of producing soft catalytic microparticles using a multiphase flow-focusing microreactor and demonstrate their application for continuous Suzuki-Miyaura cross-coupling reactions. The catalytic microparticles are produced in a coaxial glass capillary-based 3D flow-focusing microreactor. The microreactor consists of two precursors, a cross-linking catalyst in toluene and a mixture of the PHMS polymer and a divinyl cross-linker. The dispersed phase containing the polymer, cross-linker, and cross-linking catalyst is continuously mixed and then formed into microdroplets by the continuous phase of water and surfactant (sodium dodecyl sulfate) introduced in a counter-flow configuration. Elastomeric microdroplets with a diameter ranging between 50 to 300 micron are produced at 25 to 250 Hz with a size polydispersity less than 3% in single stream production. The physicochemical properties of the elastomeric microparticles such as particle swelling/softness can be tuned using the ratio of cross-linker to polymer as well as the ratio of polymer mixture to solvent during the particle formation. Swelling in toluene can be tuned up to 400% of the initial particle volume by reducing the concentration of cross-linker in the mixture and increasing the ratio of polymer to solvent during production.5
After the particles are produced and collected, they are transferred into toluene containing palladium acetate, allowing the particles to incorporate the palladium into the polymer network and then reduce the palladium to Pd0 with the Si-H functionality present on the PHMS backbones. After the reduction, the Pd-loaded particles can be washed and dried for storage or switched into an ethanol/water solution for loading into a micro-packed bed reactor (µ-PBR) for continuous organic synthesis. The in-situ reduction of Pd within the PHMS microparticles was confirmed using energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and focused ion beam-SEM, and TEM techniques.
In the next step, we used the developed µ-PBR to conduct continuous organic synthesis of 4-phenyltoluene by Suzuki-Miyaura cross-coupling of 4-iodotoluene and phenylboronic acid using potassium carbonate as the base. Catalyst leaching was determined to only occur at sub ppm concentrations even at high solvent flow rates after 24 h of continuous run using inductively coupled plasma mass spectrometry (ICP-MS).
The developed µ-PBR using the elastomeric microparticles is an important initial step towards the development of highly-efficient and green continuous manufacturing technologies in the pharma industry. In addition, the developed elastomeric microparticle synthesis technique can be utilized for the development of a library of other chemically cross-linkable polymer/cross-linker pairs for applications in organic synthesis, targeted drug delivery, cell encapsulation, or biomedical imaging.
References
1. Ruiz-Castillo P, Buchwald SL. Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions. Chem Rev. 2016;116(19):12564-12649.
2. Adamo A, Beingessner RL, Behnam M, et al. On-demand continuous-flow production of pharmaceuticals in a compact, reconfigurable system. Science. 2016;352(6281):61 LP-67.
3. Jensen KF. Flow Chemistry — Microreaction Technology Comes of Age. 2017;63(3).
4. Stibingerova I, Voltrova S, Kocova S, Lindale M, Srogl J. Modular Approach to Heterogenous Catalysis. Manipulation of Cross-Coupling Catalyst Activity. Org Lett. 2016;18(2):312-315.
5. Bennett JA, Kristof AJ, Vasudevan V, Genzer J, Srogl J, Abolhasani M. Microfluidic synthesis of elastomeric microparticles: A case study in catalysis of palladium-mediated cross-coupling. AIChE J. 2018;0(0):1-10.
Recent progress in soft‐matter sensors has shown improved fabrication techniques, resolution, and range. However, scaling up these sensors into an information‐rich tactile skin remains largely limited by designs that require a corresponding increase in the number of wires to support each new sensing node. To address this, a soft tactile skin that can estimate force and localize contact over a continuous 15 mm2area with a single integrated circuit and four output wires is introduced. The skin is composed of silicone elastomer loaded with randomly distributed magnetic microparticles. Upon deformation, the magnetic particles change position and orientation with respect to an embedded magnetometer, resulting in a change in the net measured magnetic field. Two experiments are reported to calibrate and estimate both location and force of surface contact. The classification algorithms can localize pressure with an accuracy of >98% on both grid and circle pattern. Regression algorithms can localize pressure to a 3 mm2area on average. This proof‐of‐concept sensing skin addresses the increasing need for a simple‐to‐fabricate, quick‐to‐integrate, and information‐rich tactile surface for use in robotic manipulation, soft systems, and biomonitoring.
Xu, Siyi; Chen, Yufeng; Hyun, Nak-seung P.; Becker, Kaitlyn P.; Wood, Robert J.(
, Proceedings of the National Academy of Sciences)
null
(Ed.)
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.
Lu, Jasmine; Liu, Ziwei; Brooks, Jas; Lopes, Pedro(
, ACM Symposium on User Interface Software and Technology)
We propose a new class of haptic devices that provide haptic sensations by delivering liquid-stimulants to the user's skin; we call this chemical haptics. Upon absorbing these stimulants, which contain safe and small doses of key active ingredients, receptors in the user's skin are chemically triggered, rendering distinct haptic sensations. We identified five chemicals that can render lasting haptic sensations: tingling (sanshool), numbing (lidocaine), stinging (cinnamaldehyde), warming (capsaicin), and cooling (menthol). To enable the application of our novel approach in a variety of settings (such as VR), we engineered a self-contained wearable that can be worn anywhere on the user's skin (e.g., face, arms, legs). Implemented as a soft silicone patch, our device uses micropumps to push the liquid stimulants through channels that are open to the user's skin, enabling topical stimulants to be absorbed by the skin as they pass through. Our approach presents two unique benefits. First, it enables sensations, such as numbing, not possible with existing haptic devices. Second, our approach offers a new pathway, via the skin's chemical receptors, for achieving multiple haptic sensations using a single actuator, which would otherwise require combining multiple actuators (e.g., Peltier, vibration motors, electro-tactile stimulation). We evaluated our approach by means of two studies. In our first study, we characterized the temporal profiles of sensations elicited by each chemical. Using these insights, we designed five interactive VR experiences utilizing chemical haptics, and in our second user study, participants rated these VR experiences with chemical haptics as more immersive than without. Finally, as the first work exploring the use of chemical haptics on the skin, we offer recommendations to designers for how they may employ our approach for their interactive experiences.
Heisser, Ronald H., Aubin, Cameron A., Peretz, Ofek, Kincaid, Nicholas, An, Hyeon Seok, Fisher, Elizabeth M., Sobhani, Sadaf, Pepiot, Perrine, Gat, Amir D., and Shepherd, Robert F. Valveless microliter combustion for densely packed arrays of powerful soft actuators. Proceedings of the National Academy of Sciences 118.39 Web. doi:10.1073/pnas.2106553118.
Heisser, Ronald H., Aubin, Cameron A., Peretz, Ofek, Kincaid, Nicholas, An, Hyeon Seok, Fisher, Elizabeth M., Sobhani, Sadaf, Pepiot, Perrine, Gat, Amir D., & Shepherd, Robert F. Valveless microliter combustion for densely packed arrays of powerful soft actuators. Proceedings of the National Academy of Sciences, 118 (39). https://doi.org/10.1073/pnas.2106553118
Heisser, Ronald H., Aubin, Cameron A., Peretz, Ofek, Kincaid, Nicholas, An, Hyeon Seok, Fisher, Elizabeth M., Sobhani, Sadaf, Pepiot, Perrine, Gat, Amir D., and Shepherd, Robert F.
"Valveless microliter combustion for densely packed arrays of powerful soft actuators". Proceedings of the National Academy of Sciences 118 (39). Country unknown/Code not available: Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.2106553118.https://par.nsf.gov/biblio/10305078.
@article{osti_10305078,
place = {Country unknown/Code not available},
title = {Valveless microliter combustion for densely packed arrays of powerful soft actuators},
url = {https://par.nsf.gov/biblio/10305078},
DOI = {10.1073/pnas.2106553118},
abstractNote = {Existing tactile stimulation technologies powered by small actuators offer low-resolution stimuli compared to the enormous mechanoreceptor density of human skin. Arrays of soft pneumatic actuators initially show promise as small-resolution (1- to 3-mm diameter), highly conformable tactile display strategies yet ultimately fail because of their need for valves bulkier than the actuators themselves. In this paper, we demonstrate an array of individually addressable, soft fluidic actuators that operate without electromechanical valves. We achieve this by using microscale combustion and localized thermal flame quenching. Precisely, liquid metal electrodes produce sparks to ignite fuel lean methane–oxygen mixtures in a 5-mm diameter, 2-mm tall silicone cylinder. The exothermic reaction quickly pressurizes the cylinder, displacing a silicone membrane up to 6 mm in under 1 ms. This device has an estimated free-inflation instantaneous stroke power of 3 W. The maximum reported operational frequency of these cylinders is 1.2 kHz with average displacements of ∼100 µm. We demonstrate that, at these small scales, the wall-quenching flame behavior also allows operation of a 3 × 3 array of 3-mm diameter cylinders with 4-mm pitch. Though we primarily present our device as a tactile display technology, it is a platform microactuator technology with application beyond this one.},
journal = {Proceedings of the National Academy of Sciences},
volume = {118},
number = {39},
publisher = {Proceedings of the National Academy of Sciences},
author = {Heisser, Ronald H. and Aubin, Cameron A. and Peretz, Ofek and Kincaid, Nicholas and An, Hyeon Seok and Fisher, Elizabeth M. and Sobhani, Sadaf and Pepiot, Perrine and Gat, Amir D. and Shepherd, Robert F.},
}
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