Fabric-based exosuits, for VR body haptics or to generate muscular assistance, require compliant, efficient, fast, lightweight yet high-force actuators. Much prior work has focused on pneumatic principles, an effective solution, but that needs an external pump or compressor. I will present several electrically-driven fiber-format flexible actuators developed in my lab. Making actuators shaped like fibers is key to their integration in active textiles. Our devices operate on electrostatic principles, which offers high energy density and high efficiency. I report fiber-format pumps, 2 mm in diameter and several meters in length, that generate fluid flow with no moving parts, and can be woven into fabrics, allowing both thermal management and shape change. I also report fiber-shaped electrostatic sliding stepper motors, 4 mm in diameter, that serve as long thin muscles to power gloves for VR and back-support exoskeletons. I will discuss open challenges and opportunities in making active wearables.

Recent developments in materials engineering and device architectures form the foundations for rapidly emerging classes of sensors and energy devices with mechanical characteristics that allow for conformal interfaces with the soft, curvilinear surfaces of the human body. Despite these advances, major challenges in these fields exist: wearable chemical sensors typically require complex, battery-powered electronics while the vast majority of demonstrated tissue-mounted energy storage and energy harvesting systems rely on toxic components that substantially diminish their attractiveness in bio-related applications. In this presentation I will discuss non-traditional approaches to address some of these grand challenges. I will demonstrate how seamless integration of advances in electrochemistry, soft materials, fluid mechanics, wireless electronics, and design engineering are crucial for realizing such advanced systems. Examples will include wearable sweat sensors, wound monitors, wearable and implantable biodegradable batteries.

In this presentation, we discuss point-of-use applications for motor skills characterization. There is no objective metric for evaluating motor skill training progress, and current assessments rely on qualitative surveys. We have fabricated an instrumented glove with pressure and motion sensors for motor characterization. This glove is useful for characterizing motor skills of people suffering from hypertonicity, a neuromuscular disorder that causes muscle stiffness/resistance and jerky movement. Analyses of force versus velocity show movement-dependent muscle resistance in a patient with hypertonicity. Through the flexible sensor systems, the shift from subjective scores to objective measurement will promote better diagnosis and dramatically improve the accuracy in tracking patient response to therapy.

The isolation of graphene in 2004 also unveiled a diverse range of graphene-like 2D materials with exceptional mechanical, thermal, and electrical properties. 2D material-based textiles have shown promise for next-generation wearable electronic textiles (e-textiles) and sustainable composite applications due to their excellent mechanical, electrical, and other performance properties. However, the realization of robust and reliable smart textiles at a mass scale remains hugely challenging due to limitations in material performance and sustainability, complex and time-consuming fabrications, poor comfortability, and durability. We have developed a highly scalable and cost-effective way of manufacturing 2D material-based textiles at commercial production rates of ∼150 m/min for fabrics and (∼1000 kg/h) for textile yarns. The graphene textiles thus produced are washable, flexible, and bendable. We then demonstrate the potential uses of such textiles for multifunctional and high-performance wearable electronics and sustainable composites applications, which will be covered in this talk.

My current research focuses on flexible and stretchable biocompatible electronics in the forms of wearable and implantable platforms. Conventional rigid systems have limitations in forming tissue interfaces due to a Young’s modulus mismatch, resulting in poor device capabilities and noise. To overcome these limitations, we have been developing flexible and stretchable electronics with a low modulus to establish intimate contact with the skin, enabling the acquisition of high-quality signals and tissue actuation. Among the various soft bio-integrated electronics that we are developing, in this talk, I will primarily introduce recent advances on soft neural interfaces for unconventional brain-machine interfaces. Specifically, I will discuss our efforts on (1) 3D neural interfaces, (2) mri compatible neural interfaces, (3) space unrestricted optogenetics, and (4) bioresorbable hybrid neural interfaces for diverse applications, including the diagnosis and treatment of disorders, paving the way for the next generation of neuroscience and medical science.

The rise in significance of wearable actuators can be attributed to their capability to offer real-time tactile feedback, multi-functionality, and above all, optimal comfort to users. While various actuator types like motor-driven tendons, pneumatics, and electromagnetics have been utilized in wearable applications, they often entail the addition of a cumbersome rigid system to the wearer, potentially leading to discomfort. Shape memory alloys (SMAs), which alter their physical form and rigidity based on temperature variance, present a viable option for wearable actuators, particularly when processed into fabric form using SMA wires. In this study, we developed an SMA-based fabric type actuator by intricately knotting SMA wires and subsequently expanding them into 2D textile form. Further, the auxetic meta-design is introduced, enhancing its adaptability to the 3D contours of human body. This auxetic-architectured SMA fabric was effectively employed as a wearable haptic device, conveying spatiotemporal feedbacks to users.

Wearable sweat biosensors have the potential to provide non-invasive molecular analysis toward predictive analytics and treatment. In this talk, I will introduce our efforts in developing wearable biosensors for non-invasive molecular analysis. Such wearables can autonomously access body fluids (e.g., human sweat) across the activities and continuously measure a broad spectrum of analytes including metabolites, nutrients, hormones, and proteins. Laser engraving and inkjet printing are used to manufacture high-performance nanobiosensors at large scale and low cost. The clinical value of our wearable systems is evaluated through various human trials toward precision nutrition, stress/mental health assessment, and chronic disease management.

Wearable sweat sensors have the potential to provide valuable information related to the health and disease states of individuals. Existing sweat sensors mainly rely on biomacromolecules, such as enzymes and antibodies, as biorecognition elements to achieve specific quantification of metabolites and hormones. However, these biomacromolecules tend to degrade over time, limiting the sensors’ shelf life and compromising the sensor performance upon environmental changes, such as varying temperature and humidity. Here, we introduce a wearable plasmonic paper-based microfluidic system to continuously and simultaneously quantify sweat loss, sweat rate, and biochemicals in sweat. Plasmonic sensors based on surface-enhanced Raman spectroscopy (SERS) are label-free and can identify the analytes of interest via the chemical “fingerprint” information. We show that simple and low-cost plasmonic papers allow for detecting and quantifying biochemicals in sweat. The well-defined flow kinetics of paper microfluidic devices enable accurate quantification of sweat loss and sweat rate in real time.

There are two basic types of dispersal mechanisms in natural seeds: (1) Parachute-like seeds, such as dandelions, employ parachute-like structures equipped with fine, filamentous appendages that create air resistance; and (2) Maple seeds can autorotate in the air, utilizing mechanisms reminiscent of helicopters to generate lift, thus prolonging their airborne time. Our research demonstrates the feasibility of engineering passive flying soft robots through the combination of smart materials (liquid crystalline elastomers) with tailored aerodynamic designs. We have created two wind-assisted fliers, parachute-like flier and spinning one, inspired by dandelion seed and maple rotary seed, respectively. We report the fine-tune of the soft fliers’ structure by change of external stimuli, i.e., light and humidity, light control of the take-off and landing. We also demonstrate possibility to integrate onboard materials sensors for remote sensing (optical reflection, humidity, pH, etc).

Bio-inspired electro-ionic artificial muscles are considered suitable for biomimetic soft robotic applications. However, their slow response time, low blocking force, and limited durability have prevented their application in soft robotics. Here, we report soft electro-ionic artificial muscles based on 3D dendritic nickel cobalt sulfide nanorods grown on graphene electrodes. Importantly, both the phase transition from nickel-cobalt oxide to nickel-cobalt sulfide and the use of a graphene template influence the tuning of the electrical and electrochemical properties of the composite electrodes. The ionic artificial muscles with the electrodes exhibit significantly improved bending displacement and durable response to both AC and DC input signals without phase delay or distortion. These significant enhancements in the performance of artificial muscles have allowed us to demonstrate bioinspired soft locomotive robots. Therefore, these artificial muscles have the potential to expand the soft electronics industry in next-generation human-machine interfaces

This research delves into an innovative approach to layer jamming, where the jamming structure serves a dual purpose: jamming and pressure sensing. The tunable stiffness technique empowers soft grippers to manage both their grip strength and rigidity. To bolster stiffness control, a piezoresistive sensor is integrated, monitoring changes in resistance during gripping operations. This is achieved by stacking multiple thin layers of MWCNT-polyurethane acrylate material within an elastomer envelope, forming the gripper's jamming structure and pressure sensor. The sensor fabrication combines Direct Ink Writing and Digital Light Projection printing methods, while the gripper itself is crafted from Polydimethylsiloxane and Ecoflex. Utilizing resistance value shifts from the sensor, we optimize gripping performance. Experimental validations confirm the efficacy of the sensing and layer jamming approaches. Precise gripper stiffness control is achieved through data gleaned from the sensor's force measurements. Furthermore, this study illuminates potential applications in healthcare and the wearable technology industry.

Functional carbon materials are the key to a clean, safe, and sustainable working environment and advanced energy-related devices because they can be reused, recycled, and repurposed. However, effort is necessary to make them ideal candidates for such applications. In this study, we introduce a novel approach by designing covalent-organic frameworks (COFs) and metal-organic frameworks (MOFs) with contrasting electrical and electrochemical properties, aiming to achieve highly desirable electrochemical soft actuators. A careful structural investigation is carried out to determine the structure–property relationship, while the fascinating properties of them are validated by real-field demonstrations. The proposed functional carbon materials exhibit exceptional actuation properties, thereby representing a significant advancement for complex robotic interactions.

Researchers are developing a master glove with haptic feedback to control robot hands for precise object manipulation. This technology ensures the robot applies the right amount of force when grasping objects, preventing damage or insufficient grip. A 3D-printed robot hand with DYNAMIXEL motors was used, and reinforcement learning determined the optimal grip force through grasping experiments with haptic feedback. The results demonstrate the successful and stable grasping of various objects, especially soft ones, by the robot hand using this method.

Currently, many technology innovations have advanced piezoelectric materials and composites toward a broad range of biomedical applications. In this talk, I introduce our most recent development of piezoelectric materials and composites that are particularly designed for implantable nanogenerator applications. First, I present our wafer-scale approach to creating piezoelectric biomaterial thin films based on γ glycine crystals. The self-assembled sandwich film structure enabled both strong piezoelectricity and largely improved flexibility. Then, new ferroelectric composites are presented as a new material used in 3D printing for directly manufacturing of piezoelectric architectures with tunable piezoelectric and mechanical properties. Toward the end, development of implantable nanogenerator devices are introduced, including biocompatibility, degradability and packaging. This type of devices enables new capability of in vivo charging and electrostimulations, which revolutionaries the design and implementation of many biomedical therapeutics.

Tribomaterials are important not only for improving the output performance of energy harvesting devices but also for extending their applications. In general, the static surface charges are created by the contact electrification, in which the driving force is possibly related to the difference of the surface chemical potential. However, as limited by the surface potential difference, the charge density generally cannot reach an ultimate high level to approach, commonly ~ tens of uC/m2. Here, we present facile strategies to maximize the charge density via sophisticated materials design as well as the potential applications such as filters for polluted air, microbial disinfection, and energy harvesting devices.

In the field of energy harvesting and sensing technologies, triboelectric nanogenerators (TENGs) have emerged as a promising platform for self-powered sensors. However, user convenience is often overlooked during the material and design selection process. User-friendliness relies not only on material flexibility but also on the sensitivity of the force-to-signal relationship in TENG applications. This study aims to address this gap by tailoring material properties to enhance user experience specifically. We investigated the electrical and mechanical properties of various filler materials, utilizing styrene-ethylene-butylene-styrene (SEBS) as a stretchable polymer base. The resulting self-standing membranes were evaluated for comfort, durability, and adaptability, while maintaining functional effectiveness under low external force. These findings lay the groundwork for designing user-centric, self-powered sensing systems based on TENGs.

Bioresorbable bioelectronics, with their natural degradation properties, hold significant potential to eliminate the need for surgical removal. Despite notable achievements, two major challenges hinder their practical application in medical settings. Firstly, they necessitate sustainable energy solutions with biodegradable components via biosafe powering mechanisms. More importantly, reliability in their function is undermined by unpredictable device lifetimes due to the complex polymer degradation kinetics. Here, we propose an on-demand bioresorbable neurostimulator to address these issues, thus allowing for clinical operations to be manipulated using biosafe ultrasound sources. Our ultrasound-mediated transient mechanism enables i) electrical stimulation through transcutaneous ultrasound-driven triboelectricity and ii) rapid device elimination using high-intensity ultrasound without adverse health effects. Furthermore, we perform neurophysiological analyses to show that our neurostimulator provides therapeutic benefits for both compression peripheral nerve injury and hereditary peripheral neuropathy.

Electrospun polymeric piezoelectric fibers have considerable potential for shape-adaptive mechanical energy harvesting and self-powered sensing in biomedical, wearable, and industrial applications. However, their unsatisfactory piezoelectric performance remains an issue to be overcome. While strategies for increasing the crystallinity of electroactive β phases have thus far been the central focus in realizing enhanced piezoelectric performance, controlling the fiber surface morphology and yarn structuring can also be promising alternatives. Here, we summarize a collection of advances that push the boundaries to achieve a drastic enhancement of self-powered sensing and multifunctional biomedical wound healing performance by tailoring both material and structural properties of electrospun piezoelectric polymer fibers and yarns at multi-scales.

Electrical stimulation has emerged as a therapeutic approach for accelerating the healing of wound. Piezoelectric materials, characterized by their ability to generate electrical potential differences when applied to mechanical stress, have shown great potential in this regard. Poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE), an important engineering piezoelectric polymer, exhibits biocompatibility, high piezoelectric properties, and chemical stability. Electrospinning is a promising way for fabricating P(VDF-TrFE) fibers with enhanced electroactive β-phase contents of P(VDF-TrFE) through in-situ poling effects and mechanical stretching.In this work, we tailor P(VDF-TrFE) fiber porous structures to mimic the structure of extracellular matrix (ECM) and furthermore, enhance electrical stimulation for accelerating wound healing. Moreover, the wound healing process is often hindered by bacterial infections. To address this concern, our strategy is to incorporate antibacterial zinc oxide (ZnO) nanoparticles into PVDF-TrFE electrospun fibers. We conduct in vitro wound healing assays and evaluate the antibacterial properties of our multifunctional piezoelectric fibers..

Our study emphasizes tailoring ceramic suspensions for optimizing the 3D printability of Digital Light Processing (DLP) 3D printing. Barium titanate (BTO) has emerged as an eco-friendly piezoelectric ceramic alternative to lead titanates. Utilizing DLP, an advanced 3D printing method, we can fabricate complex 3D-printed ceramic architectures. In contrast to pure resin suspension, one of the most significant issues in ceramic DLP printing is the poor layer-by-layer adhesion owing to reduced photocuring. In this work, we control BTO ceramic particle sizes and additives for optimal ceramic suspension, leading to improved rheological properties, increased packing density, and reduced light scattering. Furthermore, the final ceramics exhibit enhanced dielectric and ferroelectric properties after heat-treating the 3D-printed green bodies using specifically designed profiles for de-binding and sintering. These optimized 3D-printed BTO architectures show potential for self-powered sensing, energy harvesting, and ultrasound transducers applications.

Dysphagia, prevalent among Parkinson's and stroke patients, hinders proper eating, impacting their quality of life and potentially leading to fatal outcomes if untreated. Currently, Videofluoroscopic Swallowing Study (VFSS) is the gold standard for diagnosis but requires specialized facilities and trained staff. While many wearable devices have been developed to ease these burdens, none could reliably detect specific dysfunctions like silent aspiration without VFSS. We present a multimodal wearable swallowing monitor incorporating machine learning for automatic dysfunction assessment and silent aspiration diagnosis. The device, featuring a kirigami pattern, is directly mounted on the neck for continuous, high-fidelity monitoring of electromyograms and swallowing sounds. The built-in machine learning algorithm classifies various swallowing patterns, including silent aspiration. Clinical trials with stroke patients underscored the device's significance, matching the VFSS in detecting swallowing disorders. This wearable technology holds promise for advancing dysphagia healthcare and post-stroke rehabilitation therapy.

Nanocellulose has aroused extensive interests in materials engineering and design owing to its great potential in fabricating robust architectures for diverse applications and functionalities. On the other hand, the sensitivity of cellulose to water results in the deterioration of strength, durability, and functionality thus unsuitable for advanced applications. To address this challenge, we present an efficient, sustainable and scalable strategy to convert cellulose into an advanced biomaterial by integration with a green hydrogen bonded slurry. The resultant cellulose hybrid slurry was cast and cured to fabricate strong and tough biofilms. The hydrogen bonded slurry was revealed to promote tight rapping of the nanofibers resulting to a compact structure with an enhanced performance. The dry and wet tensile characteristics of the cellulose hybrid biofilms (375.1 MPa and 160.0 MPa) were much improved compared to the neat cellulose film. The hybrid biofilms also possess excellent UV shielding characteristics, hydrophobicity and a unique antioxidant activity. Of particular interest, the hybrid biofilms can be readily recycled or biodegraded at end of life, hence promoting a circular

The convergence of wearable technology and healthcare monitoring has revolutionized personalized health monitoring through real-time data acquisition and analysis. To fully unleash the potential of wearable sensors, developing a soft, disposable, and flexible platform that can easily interface with the epidermis is required. Leveraging printing technologies in flexible sensor fabrication offers a platform that is easily customizable, highly scalable, and disposable, all while possessing notable attributes such as speed, high throughput, and cost-effectiveness. Printed organic electrochemical transistors (OECTs) are one of the prominent candidates for flexible and wearable sweat sensing due to their inherent properties, including signal amplification and the ability to mitigate challenges in miniaturization, and complexities in interfacing with electronic readout due to their high input impedance. Here, we present an epidermal wearable chemical sensing patch for sweat ions analysis fabricated using inkjet printing and direct 3D writing. This real-time monitoring of sweat analytes will ensure timely medication and enhance the experience of personalized healthcare monitoring.

Personalized healthcare is undergoing a revolution with wearable sensors that continuously monitor biomarkers, notably sweat-based ones. However, powering these devices sustainably has been challenging. We introduce a solution using a flexible perovskite solar cell (FPSC) for autonomous sweat sensors. Our FPSC wearable efficiently harvests ambient light energy, ensuring continuous monitoring even in low activity. A standout feature is its 31% power conversion efficiency in indoor light, achieved by incorporating α-methylbenzylamine (MBA) into the perovskite. Additionally, the FPSC endures bending, enhancing its suitability for wearables. Tested in real-world scenarios, our device consistently analyzed sweat biomarkers, highlighting the potential of solar-driven sensors in advancing personalized healthcare.

Global climate change is increasing the frequency of cold events, which can threaten health and increase the demand for energy. Having sun as the heat and body radiation as warmth preservation source, the need to save energy is mitigated through personal thermal management (PTM). Herein, we report a self-powered woven Kevlar fiber (WKF)-based flexible PTM device with a porous Ag@MoxFe1-xSe nanostructure (NS) between a substrate of WKF and Ti3C2 MXene film dispersed in polydimethylsiloxane (PDMS).

Electronics that can seamlessly integrate with soft organs could have significant impact in medical diagnostic, therapeutics. However, seamless integration is a grand challenge because of the distinct nature between electronics and human body. Conventional electronics are rigid and planar, made out of rigid materials. Human body are soft, deformable, comprised of biological materials, organs and tissues. This talk will introduce our solution to address the challenge through the recent development rubbery electronics, which is constructed all based on elastic rubber electronic materials of semiconductors, conductors and dielectrics, which possesses tissue-like softness and mechanical stretchability to allow seamless integration with soft deformable tissues and organs. Rubbery electronic materials (semiconductors, conductors, dielectrics) and device innovations set the foundation. This presentation will describe the development the recent advances of rubbery electronics and rubbery bioelectronics. As a platform technology, rubbery electronics could address many challenges in biomedical research and clinical studies.

Herein, we synthesized four sensing materials namely N-MWCNT, N-MWCNT/CMC, N-MWCNT/PANI, and N-MWCNT/PPy, and characterized them using FTIR, XRD, XPS, SEM, and TEM. Then, we studied the effect of polymers such as CMC, PANI, and PPy on the N-MWCNT for the detection of DMMP with a concentration ranging from 2–10 ppm. The results showed that N-MWCNT alone possesses the lowest sensitivity towards 10 ppm DMMP molecules. When the polymers were added to the N-MWCNT, the results showed enhancement in the sensitivity towards the DMMP molecules. The order of highest sensitivity is N-MWCNT/CMC > N-MWCNT/PANI > N-MWCNT/PPy > N-MWCNT.

The practical wearable electronics applications of stretchable conductive nanocomposites have been hindered by mechanical and electrical irreversibility. Here we report a resistive-type nanocomposite strain sensor, demonstrating excellent reversibility (30% strain, 3000 cycles). The sensor element consists of flower-shaped silver nanoparticles (AgNFs) embedded in a stretchable polyurethane (PU) matrix. The thin petals of AgNFs construct efficient percolation network with neighboring AgNFs. The nanocomposite sensor shows high sensitivity (gauge factor 32.08) and impressive mechanical and electrical reversibility. The recent progress in our lab will also be introduced. Reference: [1] Compos. Sci. and Tech., 221, 109305 (2022).

This study was conducted to explore the impact of bending angle, radius, and number of bending cycles on the performance of solid polymer electrolyte (SPE) capacitors. The bending angle, radius, and cycles were carefully controlled. The results showed that the bending angle had the greatest impact on the capacitors’ performance, with higher bending angles leading to a decrease in specific capacitance. This finding shows that when designing flexible electronic devices with SPE based capacitors, the bending parameters should be carefully considered to ensure optimal performance and longer lifespan.