Publications by authors named "Kyung-In Jang"

39 Publications

Continuous monitoring of deep-tissue haemodynamics with stretchable ultrasonic phased arrays.

Nat Biomed Eng 2021 07 16;5(7):749-758. Epub 2021 Jul 16.

Department of Nanoengineering, University of California, San Diego, La Jolla, CA, USA.

Stretchable wearable devices for the continuous monitoring of physiological signals from deep tissues are constrained by the depth of signal penetration and by difficulties in resolving signals from specific tissues. Here, we report the development and testing of a prototype skin-conformal ultrasonic phased array for the monitoring of haemodynamic signals from tissues up to 14 cm beneath the skin. The device allows for active focusing and steering of ultrasound beams over a range of incident angles so as to target regions of interest. In healthy volunteers, we show that the phased array can be used to monitor Doppler spectra from cardiac tissues, record central blood flow waveforms and estimate cerebral blood supply in real time. Stretchable and conformal skin-worn ultrasonic phased arrays may open up opportunities for wearable diagnostics.
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http://dx.doi.org/10.1038/s41551-021-00763-4DOI Listing
July 2021

Instant, multiscale dry transfer printing by atomic diffusion control at heterogeneous interfaces.

Sci Adv 2021 Jul 9;7(28). Epub 2021 Jul 9.

Department of Robotics Engineering, Daegu Gyeongbuk Institute of Science and Technology, Daegu 42988, South Korea.

Transfer printing is a technique that integrates heterogeneous materials by readily retrieving functional elements from a grown substrate and subsequently printing them onto a specific target site. These strategies are broadly exploited to construct heterogeneously integrated electronic devices. A typical wet transfer printing method exhibits limitations related to unwanted displacement and shape distortion of the device due to uncontrollable fluid movement and slow chemical diffusion. In this study, a dry transfer printing technique that allows reliable and instant release of devices by exploiting the thermal expansion mismatch between adjacent materials is demonstrated, and computational studies are conducted to investigate the fundamental mechanisms of the dry transfer printing process. Extensive exemplary demonstrations of multiscale, sequential wet-dry, circuit-level, and biological topography-based transfer printing demonstrate the potential of this technique for many other emerging applications in modern electronics that have not been achieved through conventional wet transfer printing over the past few decades.
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http://dx.doi.org/10.1126/sciadv.abh0040DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8270493PMC
July 2021

Outdoor-Useable, Wireless/Battery-Free Patch-Type Tissue Oximeter with Radiative Cooling.

Adv Sci (Weinh) 2021 05 9;8(10):2004885. Epub 2021 Mar 9.

School of Electrical Engineering and Computer Science (EECS) Gwangju Institute of Science and Technology (GIST) 123, Cheomdangwagi-ro, Bukgu Gwangju 61005 Republic of Korea.

For wearable electronics/optoelectronics, thermal management should be provided for accurate signal acquisition as well as thermal comfort. However, outdoor solar energy gain has restricted the efficiency of some wearable devices like oximeters. Herein, wireless/battery-free and thermally regulated patch-type tissue oximeter (PTO) with radiative cooling structures are presented, which can measure tissue oxygenation under sunlight in reliable manner and will benefit athlete training. To maximize the radiative cooling performance, a nano/microvoids polymer (NMVP) is introduced by combining two perforated polymers to both reduce sunlight absorption and maximize thermal radiation. The optimized NMVP exhibits sub-ambient cooling of 6 °C in daytime under various conditions such as scattered/overcast clouds, high humidity, and clear weather. The NMVP-integrated PTO enables maintaining temperature within ≈1 °C on the skin under sunlight relative to indoor measurement, whereas the normally used, black encapsulated PTO shows over 40 °C owing to solar absorption. The heated PTO exhibits an inaccurate tissue oxygen saturation (StO) value of ≈67% compared with StO in a normal state (i.e., ≈80%). However, the thermally protected PTO presents reliable StO of ≈80%. This successful demonstration provides a feasible strategy of thermal management in wearable devices for outdoor applications.
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http://dx.doi.org/10.1002/advs.202004885DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8132059PMC
May 2021

Rapidly-customizable, scalable 3D-printed wireless optogenetic probes for versatile applications in neuroscience.

Adv Funct Mater 2020 Nov 18;30(46). Epub 2020 Sep 18.

School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.

Optogenetics is an advanced neuroscience technique that enables the dissection of neural circuitry with high spatiotemporal precision. Recent advances in materials and microfabrication techniques have enabled minimally invasive and biocompatible optical neural probes, thereby facilitating optogenetic research. However, conventional fabrication techniques rely on cleanroom facilities, which are not easily accessible and are expensive to use, making the overall manufacturing process inconvenient and costly. Moreover, the inherent time-consuming nature of current fabrication procedures impede the rapid customization of neural probes in between studies. Here, we introduce a new technique stemming from 3D printing technology for the low-cost, mass production of rapidly customizable optogenetic neural probes. We detail the 3D printing production process, on-the-fly design versatility, and biocompatibility of 3D printed optogenetic probes as well as their functional capabilities for wireless optogenetics. Successful studies with 3D printed devices highlight the reliability of this easily accessible and flexible manufacturing approach that, with advances in printing technology, can foreshadow its widespread applications in low-cost bioelectronics in the future.
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http://dx.doi.org/10.1002/adfm.202004285DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7942018PMC
November 2020

Ultrasensitive and Stretchable Conductive Fibers Using Percolated Pd Nanoparticle Networks for Multisensing Wearable Electronics: Crack-Based Strain and H Sensors.

ACS Appl Mater Interfaces 2020 Oct 24;12(40):45243-45253. Epub 2020 Sep 24.

School of Electrical and Electronic Engineering, Yonsei University, Seoul 03722, Republic of Korea.

The need for wearable electronic devices continues to grow, and the research is under way for stretchable fiber-type sensors that are sensitive to the surrounding atmosphere and will provide proficient measurement capabilities. Currently, one-dimensional fiber sensors have several limitations for their extensive use because of the complex structures of the sensing mechanisms. Thus, it is essential to miniaturize these materials with durability while integrating multiple sensing capabilities. Herein, we present an ultrasensitive and stretchable conductive fiber sensor using PdNP networks embedded in elastomeric polymers for crack-based strain and H sensing. The fiber multimodal sensors show a gauge factor of ∼2040 under 70% strain and reliable mechanical deformation tolerance (10,000 stretching cycles) in the strain-sensor mode. For H sensing, the fiber multimodal sensors exhibit a wide sensing range of high sensitivity: -0.43% response at 5 ppm (0.0005%) H gas and -27.3% response at 10% H gas. For the first time, we demonstrate highly stretchable H sensors that can detect H gas under 110% strain with mechanical durability. As demonstrated, their stable performance allows them to be used in wearable applications that integrate fiber multimodal sensors into industrial safety clothing along with a microinorganic light-emitting diode for visual indication, which exhibits proper activation upon H gas exposure.
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http://dx.doi.org/10.1021/acsami.0c10460DOI Listing
October 2020

Wireless optofluidic brain probes for chronic neuropharmacology and photostimulation.

Nat Biomed Eng 2019 08 5;3(8):655-669. Epub 2019 Aug 5.

School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea.

Both in vivo neuropharmacology and optogenetic stimulation can be used to decode neural circuitry, and can provide therapeutic strategies for brain disorders. However, current neuronal interfaces hinder long-term studies in awake and freely behaving animals, as they are limited in their ability to provide simultaneous and prolonged delivery of multiple drugs, are often bulky and lack multifunctionality, and employ custom control systems with insufficiently versatile selectivity for output mode, animal selection and target brain circuits. Here, we describe smartphone-controlled, minimally invasive, soft optofluidic probes with replaceable plug-like drug cartridges for chronic in vivo pharmacology and optogenetics with selective manipulation of brain circuits. We demonstrate the use of the probes for the control of the locomotor activity of mice for over four weeks via programmable wireless drug delivery and photostimulation. Owing to their ability to deliver both drugs and photopharmacology into the brain repeatedly over long time periods, the probes may contribute to uncovering the basis of neuropsychiatric diseases.
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http://dx.doi.org/10.1038/s41551-019-0432-1DOI Listing
August 2019

Binodal, wireless epidermal electronic systems with in-sensor analytics for neonatal intensive care.

Science 2019 Mar;363(6430)

Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL 60208, USA.

Existing vital sign monitoring systems in the neonatal intensive care unit (NICU) require multiple wires connected to rigid sensors with strongly adherent interfaces to the skin. We introduce a pair of ultrathin, soft, skin-like electronic devices whose coordinated, wireless operation reproduces the functionality of these traditional technologies but bypasses their intrinsic limitations. The enabling advances in engineering science include designs that support wireless, battery-free operation; real-time, in-sensor data analytics; time-synchronized, continuous data streaming; soft mechanics and gentle adhesive interfaces to the skin; and compatibility with visual inspection and with medical imaging techniques used in the NICU. Preliminary studies on neonates admitted to operating NICUs demonstrate performance comparable to the most advanced clinical-standard monitoring systems.
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http://dx.doi.org/10.1126/science.aau0780DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6510306PMC
March 2019

The equivalent medium of cellular substrate under large stretching, with applications to stretchable electronics.

J Mech Phys Solids 2018 Nov 7;120:199-207. Epub 2017 Nov 7.

Department of Engineering Mechanics; Center for Mechanics and Materials, Tsinghua University, Beijing, 100084, China.

The concepts of open, cellular substrates for stretchable electronic systems are of interest partly due to their ability to minimize disruptions to the natural diffusive or convective flow of bio-fluids in advanced, bio-integrated implants. The overall elastic properties, and in particular the stretchability, of such systems are difficult to determine, however, because they depend strongly on the alignment and position of the serpentine interconnects relative to the openings in the cellular substrate, which is difficult to precisely control, even with the assistance of precision stages and visualization hardware. This paper establishes an analytic constitutive model for an equivalent medium for a cellular substrate under finite deformation. Results demonstrate that the elastic stretchability of a serpentine interconnect bonded to this equivalent medium represents a lower-bound estimate for the case of the actual cellular substrate, where the bonding adopts different alignments and positions. This finding provides a simple, conservative estimate of stretchability, which has general utility as an engineering design rule for platforms that exploit cellular substrates in stretchable electronics.
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http://dx.doi.org/10.1016/j.jmps.2017.11.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6101674PMC
November 2018

Three-Dimensional Silicon Electronic Systems Fabricated by Compressive Buckling Process.

ACS Nano 2018 05 17;12(5):4164-4171. Epub 2018 Apr 17.

Department of Civil and Environmental Engineering, Mechanical Engineering, and Materials Science and Engineering , Northwestern University , Evanston , Illinois 60208 , United States.

Recently developed approaches in deterministic assembly allow for controlled, geometric transformation of two-dimensional structures into complex, engineered three-dimensional layouts. Attractive features include applicability to wide ranging layout designs and dimensions along with the capacity to integrate planar thin film materials and device layouts. The work reported here establishes further capabilities for directly embedding high-performance electronic devices into the resultant 3D constructs based on silicon nanomembranes (Si NMs) as the active materials in custom devices or microscale components released from commercial wafer sources. Systematic experimental studies and theoretical analysis illustrate the key ideas through varied 3D architectures, from interconnected bridges and coils to extended chiral structures, each of which embed n-channel Si NM MOSFETs (nMOS), Si NM diodes, and p-channel silicon MOSFETs (pMOS). Examples in stretchable/deformable systems highlight additional features of these platforms. These strategies are immediately applicable to other wide-ranging classes of materials and device technologies that can be rendered in two-dimensional layouts, from systems for energy storage, to photovoltaics, optoelectronics, and others.
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http://dx.doi.org/10.1021/acsnano.8b00180DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5986289PMC
May 2018

Deterministic Integration of Biological and Soft Materials onto 3D Microscale Cellular Frameworks.

Adv Biosyst 2017 Sep 31;1(9). Epub 2017 Jul 31.

School of Chemical Sciences University of Illinois-Urbana Champaign Urbana, IL 61801, USA. Frederick Seitz Materials Research Laboratory and Department of Materials Science and Engineering University of Illinois at Urbana-Champaign Urbana, IL 61801, USA.

Complex 3D organizations of materials represent ubiquitous structural motifs found in the most sophisticated forms of matter, the most notable of which are in life-sustaining hierarchical structures found in biology, but where simpler examples also exist as dense multilayered constructs in high-performance electronics. Each class of system evinces specific enabling forms of assembly to establish their functional organization at length scales not dissimilar to tissue-level constructs. This study describes materials and means of assembly that extend and join these disparate systems-schemes for the functional integration of soft and biological materials with synthetic 3D microscale, open frameworks that can leverage the most advanced forms of multilayer electronic technologies, including device-grade semiconductors such as monocrystalline silicon. Cellular migration behaviors, temporal dependencies of their growth, and contact guidance cues provided by the nonplanarity of these frameworks illustrate design criteria useful for their functional integration with living matter (e.g., NIH 3T3 fibroblast and primary rat dorsal root ganglion cell cultures).
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http://dx.doi.org/10.1002/adbi.201700068DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5850936PMC
September 2017

Miniaturized, Battery-Free Optofluidic Systems with Potential for Wireless Pharmacology and Optogenetics.

Small 2018 01 7;14(4). Epub 2017 Dec 7.

Department of Electrical, Computer, and Energy Engineering, University of Colorado Boulder, Boulder, CO, 80309, USA.

Combination of optogenetics and pharmacology represents a unique approach to dissect neural circuitry with high specificity and versatility. However, conventional tools available to perform these experiments, such as optical fibers and metal cannula, are limited due to their tethered operation and lack of biomechanical compatibility. To address these issues, a miniaturized, battery-free, soft optofluidic system that can provide wireless drug delivery and optical stimulation for spatiotemporal control of the targeted neural circuit in freely behaving animals is reported. The device integrates microscale inorganic light-emitting diodes and microfluidic drug delivery systems with a tiny stretchable multichannel radiofrequency antenna, which not only eliminates the need for bulky batteries but also offers fully wireless, independent control of light and fluid delivery. This design enables a miniature (125 mm ), lightweight (220 mg), soft, and flexible platform, thus facilitating seamless implantation and operation in the body without causing disturbance of naturalistic behavior. The proof-of-principle experiments and analytical studies validate the feasibility and reliability of the fully implantable optofluidic systems for use in freely moving animals, demonstrating its potential for wireless in vivo pharmacology and optogenetics.
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http://dx.doi.org/10.1002/smll.201702479DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5912318PMC
January 2018

Chemical Sensing Systems that Utilize Soft Electronics on Thin Elastomeric Substrates with Open Cellular Designs.

Adv Funct Mater 2017 Mar 9;9(3). Epub 2017 Jan 9.

Center for Bio-Integrated Electronics, Departments of Materials Science and Engineering, Biomedical Engineering, Chemistry Mechanical Engineering, Electrical Engineering and Computer Science, Neurological Surgery, Simpson Querrey Institute for Bio Nanotechnology, McCormick School of Engineering and Feinberg School of Medicine, Northwestern University, Evanston, IL 60208, USA.

A collection of materials and device architectures are introduced for thin, stretchable arrays of ion sensors that mount on open cellular substrates to facilitate solution exchange for use in biointegrated electronics. The results include integration strategies and studies of fundamental characteristics in chemical sensing and mechanical response. The latter involves experimental measurements and theoretical simulations that establish important considerations in the design of low modulus, stretchable properties in cellular substrates, and in the realization of advanced capabilities in spatiotemporal mapping of chemicals' gradients. As the chemical composition of extracellular fluids contains valuable information related to biological function, the concepts introduced here have potential utility across a range of skin- and internal-organ-integrated electronics where soft mechanics, fluidic permeability, and advanced chemical sensing capabilities are key requirements.
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http://dx.doi.org/10.1002/adfm.201605476DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5630126PMC
March 2017

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition.

J Vis Exp 2017 08 29(126). Epub 2017 Aug 29.

School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology;

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.  We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.  Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.
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http://dx.doi.org/10.3791/56383DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5614389PMC
August 2017

Miniaturized Battery-Free Wireless Systems for Wearable Pulse Oximetry.

Adv Funct Mater 2017 Jan 25;27(1). Epub 2016 Nov 25.

Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

Development of unconventional technologies for wireless collection, storage and analysis of quantitative, clinically relevant information on physiological status is of growing interest. Soft, biocompatible systems are widely regarded as important because they facilitate mounting on external (e.g. skin) and internal (e.g. heart, brain) surfaces of the body. Ultra-miniaturized, lightweight and battery-free devices have the potential to establish complementary options in bio-integration, where chronic interfaces (i.e. months) are possible on hard surfaces such as the fingernails and the teeth, with negligible risk for irritation or discomfort. Here we report materials and device concepts for flexible platforms that incorporate advanced optoelectronic functionality for applications in wireless capture and transmission of photoplethysmograms, including quantitative information on blood oxygenation, heart rate and heart rate variability. Specifically, reflectance pulse oximetry in conjunction with near-field communication (NFC) capabilities enables operation in thin, miniaturized flexible devices. Studies of the material aspects associated with the body interface, together with investigations of the radio frequency characteristics, the optoelectronic data acquisition approaches and the analysis methods capture all of the relevant engineering considerations. Demonstrations of operation on various locations of the body and quantitative comparisons to clinical gold standards establish the versatility and the measurement accuracy of these systems, respectively.
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http://dx.doi.org/10.1002/adfm.201604373DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5545889PMC
January 2017

Self-assembled three dimensional network designs for soft electronics.

Nat Commun 2017 06 21;8:15894. Epub 2017 Jun 21.

Departments of Materials Science and Engineering, Biomedical Engineering, Chemistry, Mechanical Engineering, Electrical Engineering and Computer Science, Neurological Surgery, Center for Bio-Integrated Electronics, Simpson Querrey Institute for BioNanotechnology, McCormick School of Engineering and Feinberg School of Medicine, Northwestern University, Evanston, Illinois 60208, USA.

Low modulus, compliant systems of sensors, circuits and radios designed to intimately interface with the soft tissues of the human body are of growing interest, due to their emerging applications in continuous, clinical-quality health monitors and advanced, bioelectronic therapeutics. Although recent research establishes various materials and mechanics concepts for such technologies, all existing approaches involve simple, two-dimensional (2D) layouts in the constituent micro-components and interconnects. Here we introduce concepts in three-dimensional (3D) architectures that bypass important engineering constraints and performance limitations set by traditional, 2D designs. Specifically, open-mesh, 3D interconnect networks of helical microcoils formed by deterministic compressive buckling establish the basis for systems that can offer exceptional low modulus, elastic mechanics, in compact geometries, with active components and sophisticated levels of functionality. Coupled mechanical and electrical design approaches enable layout optimization, assembly processes and encapsulation schemes to yield 3D configurations that satisfy requirements in demanding, complex systems, such as wireless, skin-compatible electronic sensors.
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http://dx.doi.org/10.1038/ncomms15894DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5482057PMC
June 2017

Ferromagnetic, folded electrode composite as a soft interface to the skin for long-term electrophysiological recording.

Adv Funct Mater 2016 Oct 9;26(40):7281-7290. Epub 2016 Sep 9.

Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

This paper introduces a class of ferromagnetic, folded, soft composite material for skin-interfaced electrodes with releasable interfaces to stretchable, wireless electronic measurement systems. These electrodes establish intimate, adhesive contacts to the skin, in dimensionally stable formats compatible with multiple days of continuous operation, with several key advantages over conventional hydrogel based alternatives. The reported studies focus on aspects ranging from ferromagnetic and mechanical behavior of the materials systems, to electrical properties associated with their skin interface, to system-level integration for advanced electrophysiological monitoring applications. The work combines experimental measurement and theoretical modeling to establish the key design considerations. These concepts have potential uses across a diverse set of skin-integrated electronic technologies.
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http://dx.doi.org/10.1002/adfm.201603146DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5390688PMC
October 2016

Epidermal mechano-acoustic sensing electronics for cardiovascular diagnostics and human-machine interfaces.

Sci Adv 2016 Nov 16;2(11):e1601185. Epub 2016 Nov 16.

Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

Physiological mechano-acoustic signals, often with frequencies and intensities that are beyond those associated with the audible range, provide information of great clinical utility. Stethoscopes and digital accelerometers in conventional packages can capture some relevant data, but neither is suitable for use in a continuous, wearable mode, and both have shortcomings associated with mechanical transduction of signals through the skin. We report a soft, conformal class of device configured specifically for mechano-acoustic recording from the skin, capable of being used on nearly any part of the body, in forms that maximize detectable signals and allow for multimodal operation, such as electrophysiological recording. Experimental and computational studies highlight the key roles of low effective modulus and low areal mass density for effective operation in this type of measurement mode on the skin. Demonstrations involving seismocardiography and heart murmur detection in a series of cardiac patients illustrate utility in advanced clinical diagnostics. Monitoring of pump thrombosis in ventricular assist devices provides an example in characterization of mechanical implants. Speech recognition and human-machine interfaces represent additional demonstrated applications. These and other possibilities suggest broad-ranging uses for soft, skin-integrated digital technologies that can capture human body acoustics.
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http://dx.doi.org/10.1126/sciadv.1601185DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5262452PMC
November 2016

Preparation and implementation of optofluidic neural probes for in vivo wireless pharmacology and optogenetics.

Nat Protoc 2017 Feb 5;12(2):219-237. Epub 2017 Jan 5.

Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.

This Protocol Extension describes the fabrication and technical procedures for implementing ultrathin, flexible optofluidic neural probe systems that provide targeted, wireless delivery of fluids and light into the brains of awake, freely behaving animals. As a Protocol Extension article, this article describes an adaptation of an existing Protocol that offers additional applications. This protocol serves as an extension of an existing Nature Protocol describing optoelectronic devices for studying intact neural systems. Here, we describe additional features of fabricating self-contained platforms that involve flexible microfluidic probes, pumping systems, microscale inorganic LEDs, wireless-control electronics, and power supplies. These small, flexible probes minimize tissue damage and inflammation, making long-term implantation possible. The capabilities include wireless pharmacological and optical intervention for dissecting neural circuitry during behavior. The fabrication can be completed in 1-2 weeks, and the devices can be used for 1-2 weeks of in vivo rodent experiments. To successfully carry out the protocol, researchers should have basic skill sets in photolithography and soft lithography, as well as experience with stereotaxic surgery and behavioral neuroscience practices. These fabrication processes and implementation protocols will increase access to wireless optofluidic neural probes for advanced in vivo pharmacology and optogenetics in freely moving rodents.This protocol is an extension to: Nat. Protoc. 8, 2413-2428 (2013); doi:10.1038/nprot.2013.158; published online 07 November 2013.
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http://dx.doi.org/10.1038/nprot.2016.155DOI Listing
February 2017

Ultra-thin films with highly absorbent porous media fine-tunable for coloration and enhanced color purity.

Nanoscale 2017 Mar;9(9):2986-2991

School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology, 123 Cheomdan-gwagiro, Buk-gu, Gwangju 61005, Republic of Korea.

We demonstrate ultra-thin, fine-tunable optical coatings with enhanced color purity based on highly absorbent porous media on a metal substrate. We show that the color range provided by these ultra-thin film coatings can be extended by making the absorptive dielectric layer porous. Oblique angle deposition (OAD) of a thin (10-25 nm) germanium (Ge) film by e-beam evaporation onto a thick gold substrate yields controlled porosity. Reflectance spectra and color representations from both calculations and experiments verify the enhancement of resonance tunability and color purity in the nano-tailored coatings. Angle independent reflection properties, and the applicability of such porous Ge on various metal substrates, indicate the strength of these concepts.
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http://dx.doi.org/10.1039/c6nr08475cDOI Listing
March 2017

Stretchable multichannel antennas in soft wireless optoelectronic implants for optogenetics.

Proc Natl Acad Sci U S A 2016 12 28;113(50):E8169-E8177. Epub 2016 Nov 28.

Department of Materials Science and Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801;

Optogenetic methods to modulate cells and signaling pathways via targeted expression and activation of light-sensitive proteins have greatly accelerated the process of mapping complex neural circuits and defining their roles in physiological and pathological contexts. Recently demonstrated technologies based on injectable, microscale inorganic light-emitting diodes (μ-ILEDs) with wireless control and power delivery strategies offer important functionality in such experiments, by eliminating the external tethers associated with traditional fiber optic approaches. Existing wireless μ-ILED embodiments allow, however, illumination only at a single targeted region of the brain with a single optical wavelength and over spatial ranges of operation that are constrained by the radio frequency power transmission hardware. Here we report stretchable, multiresonance antennas and battery-free schemes for multichannel wireless operation of independently addressable, multicolor μ-ILEDs with fully implantable, miniaturized platforms. This advance, as demonstrated through in vitro and in vivo studies using thin, mechanically soft systems that separately control as many as three different μ-ILEDs, relies on specially designed stretchable antennas in which parallel capacitive coupling circuits yield several independent, well-separated operating frequencies, as verified through experimental and modeling results. When used in combination with active motion-tracking antenna arrays, these devices enable multichannel optogenetic research on complex behavioral responses in groups of animals over large areas at low levels of radio frequency power (<1 W). Studies of the regions of the brain that are involved in sleep arousal (locus coeruleus) and preference/aversion (nucleus accumbens) demonstrate the unique capabilities of these technologies.
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http://dx.doi.org/10.1073/pnas.1611769113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5167187PMC
December 2016

A soft, wearable microfluidic device for the capture, storage, and colorimetric sensing of sweat.

Sci Transl Med 2016 11;8(366):366ra165

Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

Capabilities in health monitoring enabled by capture and quantitative chemical analysis of sweat could complement, or potentially obviate the need for, approaches based on sporadic assessment of blood samples. Established sweat monitoring technologies use simple fabric swatches and are limited to basic analysis in controlled laboratory or hospital settings. We present a collection of materials and device designs for soft, flexible, and stretchable microfluidic systems, including embodiments that integrate wireless communication electronics, which can intimately and robustly bond to the surface of the skin without chemical and mechanical irritation. This integration defines access points for a small set of sweat glands such that perspiration spontaneously initiates routing of sweat through a microfluidic network and set of reservoirs. Embedded chemical analyses respond in colorimetric fashion to markers such as chloride and hydronium ions, glucose, and lactate. Wireless interfaces to digital image capture hardware serve as a means for quantitation. Human studies demonstrated the functionality of this microfluidic device during fitness cycling in a controlled environment and during long-distance bicycle racing in arid, outdoor conditions. The results include quantitative values for sweat rate, total sweat loss, pH, and concentration of chloride and lactate.
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http://dx.doi.org/10.1126/scitranslmed.aaf2593DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5429097PMC
November 2016

Epidermal radio frequency electronics for wireless power transfer.

Microsyst Nanoeng 2016 24;2:16052. Epub 2016 Oct 24.

Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

Epidermal electronic systems feature physical properties that approximate those of the skin, to enable intimate, long-lived skin interfaces for physiological measurements, human-machine interfaces and other applications that cannot be addressed by wearable hardware that is commercially available today. A primary challenge is power supply; the physical bulk, large mass and high mechanical modulus associated with conventional battery technologies can hinder efforts to achieve epidermal characteristics, and near-field power transfer schemes offer only a limited operating distance. Here we introduce an epidermal, far-field radio frequency (RF) power harvester built using a modularized collection of ultrathin antennas, rectifiers and voltage doublers. These components, separately fabricated and tested, can be integrated together via methods involving soft contact lamination. Systematic studies of the individual components and the overall performance in various dielectric environments highlight the key operational features of these systems and strategies for their optimization. The results suggest robust capabilities for battery-free RF power, with relevance to many emerging epidermal technologies.
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http://dx.doi.org/10.1038/micronano.2016.52DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6444737PMC
October 2016

Wrinkling of a stiff thin film bonded to a pre-strained, compliant substrate with finite thickness.

Proc Math Phys Eng Sci 2016 Aug;472(2192):20160339

Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL 60208, USA; Mechanical Engineering, Northwestern University, Evanston, IL 60208, USA; Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.

A stiff thin film bonded to a pre-strained, compliant substrate wrinkles into a sinusoidal form upon release of the pre-strain. Many analytical models developed for the critical pre-strain for wrinkling assume that the substrate is semi-infinite. This critical pre-strain is actually much smaller than that for a substrate with finite thickness (Ma Y 2016 (doi:10.1002/adfm.201600713)). An analytical solution of the critical pre-strain for a system of a stiff film bonded to a pre-strained, finite-thickness, compliant substrate is obtained, and it agrees well with the finite-element analysis. The finite-thickness effect is significant when the substrate tensile stiffness cannot overwhelm the film tensile stiffness.
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http://dx.doi.org/10.1098/rspa.2016.0339DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5014113PMC
August 2016

Battery-free, stretchable optoelectronic systems for wireless optical characterization of the skin.

Sci Adv 2016 08 3;2(8):e1600418. Epub 2016 Aug 3.

Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

Recent advances in materials, mechanics, and electronic device design are rapidly establishing the foundations for health monitoring technologies that have "skin-like" properties, with options in chronic (weeks) integration with the epidermis. The resulting capabilities in physiological sensing greatly exceed those possible with conventional hard electronic systems, such as those found in wrist-mounted wearables, because of the intimate skin interface. However, most examples of such emerging classes of devices require batteries and/or hard-wired connections to enable operation. The work reported here introduces active optoelectronic systems that function without batteries and in an entirely wireless mode, with examples in thin, stretchable platforms designed for multiwavelength optical characterization of the skin. Magnetic inductive coupling and near-field communication (NFC) schemes deliver power to multicolored light-emitting diodes and extract digital data from integrated photodetectors in ways that are compatible with standard NFC-enabled platforms, such as smartphones and tablet computers. Examples in the monitoring of heart rate and temporal dynamics of arterial blood flow, in quantifying tissue oxygenation and ultraviolet dosimetry, and in performing four-color spectroscopic evaluation of the skin demonstrate the versatility of these concepts. The results have potential relevance in both hospital care and at-home diagnostics.
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http://dx.doi.org/10.1126/sciadv.1600418DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4972468PMC
August 2016

Design of Strain-Limiting Substrate Materials for Stretchable and Flexible Electronics.

Adv Funct Mater 2016 Aug 23;26(29):5345-5351. Epub 2016 May 23.

Departments of Civil and Environmental Engineering, Mechanical Engineering, and Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.

Recently developed classes of electronics for biomedical applications exploit substrates that offer low elastic modulus and high stretchability, to allow intimate, mechanically biocompatible integration with soft biological tissues. A challenge is that such substrates do not generally offer protection of the electronics from high peak strains that can occur upon large-scale deformation, thereby creating a potential for device failure. The results presented here establish a simple route to compliant substrates with strain-limiting mechanics based on approaches that complement those of recently described alternatives. Here, a thin film or mesh of a high modulus material transferred onto a prestrained compliant substrate transforms into wrinkled geometry upon release of the prestrain. The structure formed by this process offers a low elastic modulus at small strain due to the small effective stiffness of the wrinkled film or mesh; it has a high tangent modulus (e.g., >1000 times the elastic modulus) at large strain, as the wrinkles disappear and the film/mesh returns to a flat geometry. This bilinear stress-strain behavior has an extremely sharp transition point, defined by the magnitude of the prestrain. A theoretical model yields analytical expressions for the elastic and tangent moduli and the transition strain of the bilinear stress-strain relation, with quantitative correspondence to finite element analysis and experiments.
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http://dx.doi.org/10.1002/adfm.201600713DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5639729PMC
August 2016

Epidermal electronics for electromyography: An application to swallowing therapy.

Med Eng Phys 2016 08 30;38(8):807-12. Epub 2016 May 30.

Institute for Reconstructive Sciences in Medicine (iRSM), Misericordia Community Hospital, Edmonton, Alberta, Canada; Department of Communication Sciences and Disorders, Faculty of Rehabilitation Medicine, University of Alberta, 8205 114St 2-70 Corbett Hall, Edmonton, Alberta, Canada.

Head and neck cancer treatment alters the anatomy and physiology of patients. Resulting swallowing difficulties can lead to serious health concerns. Surface electromyography (sEMG) is used as an adjuvant to swallowing therapy exercises. sEMG signal collected from the area under the chin provides visual biofeedback from muscle contractions and is used to help patients perform exercises correctly. However, conventional sEMG adhesive pads are relatively thick and difficult to effectively adhere to a patient's altered chin anatomy, potentially leading to poor signal acquisition in this population. Here, the emerging technology of epidermal electronics is introduced, where ultra-thin geometry allows for close contouring of the chin. The two objectives of this study were to (1) assess the potential of epidermal electronics technology for use with swallowing therapy and (2) assess the significance of the reference electrode placement. This study showed comparative signals between the new epidermal sEMG patch and the conventional adhesive patches used by clinicians. Furthermore, an integrated reference yielded optimal signal for clinical use; this configuration was more robust to head movements than when an external reference was used. Improvements for future iterations of epidermal sEMG patches specific to day-to-day clinical use are suggested.
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http://dx.doi.org/10.1016/j.medengphy.2016.04.023DOI Listing
August 2016

Soft, thin skin-mounted power management systems and their use in wireless thermography.

Proc Natl Acad Sci U S A 2016 May 16;113(22):6131-6. Epub 2016 May 16.

Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801;

Power supply represents a critical challenge in the development of body-integrated electronic technologies. Although recent research establishes an impressive variety of options in energy storage (batteries and supercapacitors) and generation (triboelectric, piezoelectric, thermoelectric, and photovoltaic devices), the modest electrical performance and/or the absence of soft, biocompatible mechanical properties limit their practical use. The results presented here form the basis of soft, skin-compatible means for efficient photovoltaic generation and high-capacity storage of electrical power using dual-junction, compound semiconductor solar cells and chip-scale, rechargeable lithium-ion batteries, respectively. Miniaturized components, deformable interconnects, optimized array layouts, and dual-composition elastomer substrates, superstrates, and encapsulation layers represent key features. Systematic studies of the materials and mechanics identify optimized designs, including unusual configurations that exploit a folded, multilayer construct to improve the functional density without adversely affecting the soft, stretchable characteristics. System-level examples exploit such technologies in fully wireless sensors for precision skin thermography, with capabilities in continuous data logging and local processing, validated through demonstrations on volunteer subjects in various realistic scenarios.
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http://dx.doi.org/10.1073/pnas.1605720113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4896718PMC
May 2016

Biological lipid membranes for on-demand, wireless drug delivery from thin, bioresorbable electronic implants.

NPG Asia Mater 2015 Nov 27;7. Epub 2015 Nov 27.

Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL, USA.

On-demand, localized release of drugs in precisely controlled, patient-specific time sequences represents an ideal scenario for pharmacological treatment of various forms of hormone imbalances, malignant cancers, osteoporosis, diabetic conditions and others. We present a wirelessly operated, implantable drug delivery system that offers such capabilities in a form that undergoes complete bioresorption after an engineered functional period, thereby obviating the need for surgical extraction. The device architecture combines thermally actuated lipid membranes embedded with multiple types of drugs, configured in spatial arrays and co-located with individually addressable, wireless elements for Joule heating. The result provides the ability for externally triggered, precision dosage of drugs with high levels of control and negligible unwanted leakage, all without the need for surgical removal. and investigations reveal all of the underlying operational and materials aspects, as well as the basic efficacy and biocompatibility of these systems.
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http://dx.doi.org/10.1038/am.2015.114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4861403PMC
November 2015

A nonlinear mechanics model of bio-inspired hierarchical lattice materials consisting of horseshoe microstructures.

J Mech Phys Solids 2016 May;90:179-202

Center for Mechanics and Materials, AML, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, P.R. China.

Development of advanced synthetic materials that can mimic the mechanical properties of non-mineralized soft biological materials has important implications in a wide range of technologies. Hierarchical lattice materials constructed with horseshoe microstructures belong to this class of bio-inspired synthetic materials, where the mechanical responses can be tailored to match the nonlinear J-shaped stress-strain curves of human skins. The underlying relations between the J-shaped stress-strain curves and their microstructure geometry are essential in designing such systems for targeted applications. Here, a theoretical model of this type of hierarchical lattice material is developed by combining a finite deformation constitutive relation of the building block (i.e., horseshoe microstructure), with the analyses of equilibrium and deformation compatibility in the periodical lattices. The nonlinear J-shaped stress-strain curves and Poisson ratios predicted by this model agree very well with results of finite element analyses (FEA) and experiment. Based on this model, analytic solutions were obtained for some key mechanical quantities, e.g., elastic modulus, Poisson ratio, peak modulus, and critical strain around which the tangent modulus increases rapidly. A negative Poisson effect is revealed in the hierarchical lattice with triangular topology, as opposed to a positive Poisson effect in hierarchical lattices with Kagome and honeycomb topologies. The lattice topology is also found to have a strong influence on the stress-strain curve. For the three isotropic lattice topologies (triangular, Kagome and honeycomb), the hierarchical triangular lattice material renders the sharpest transition in the stress-strain curve and relative high stretchability, given the same porosity and arc angle of horseshoe microstructure. Furthermore, a demonstrative example illustrates the utility of the developed model in the rapid optimization of hierarchical lattice materials for reproducing the desired stress-strain curves of human skins. This study provides theoretical guidelines for future designs of soft bio-mimetic materials with hierarchical lattice constructions.
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http://dx.doi.org/10.1016/j.jmps.2016.02.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4831080PMC
May 2016

Soft, stretchable, fully implantable miniaturized optoelectronic systems for wireless optogenetics.

Nat Biotechnol 2015 Dec 9;33(12):1280-1286. Epub 2015 Nov 9.

Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.

Optogenetics allows rapid, temporally specific control of neuronal activity by targeted expression and activation of light-sensitive proteins. Implementation typically requires remote light sources and fiber-optic delivery schemes that impose considerable physical constraints on natural behaviors. In this report we bypass these limitations using technologies that combine thin, mechanically soft neural interfaces with fully implantable, stretchable wireless radio power and control systems. The resulting devices achieve optogenetic modulation of the spinal cord and peripheral nervous system. This is demonstrated with two form factors; stretchable film appliqués that interface directly with peripheral nerves, and flexible filaments that insert into the narrow confines of the spinal epidural space. These soft, thin devices are minimally invasive, and histological tests suggest they can be used in chronic studies. We demonstrate the power of this technology by modulating peripheral and spinal pain circuitry, providing evidence for the potential widespread use of these devices in research and future clinical applications of optogenetics outside the brain.
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http://dx.doi.org/10.1038/nbt.3415DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4880021PMC
December 2015
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