Silicone cryogel skeletons enhance the survival and mechanical integrity of hydrogel-encapsulated cell therapies

The transplantation of engineered cells that secrete therapeutic proteins presents a promising method for addressing a range of chronic diseases. However, hydrogels used to encase and protect non-autologous cells from immune rejection often suffer from poor mechanical properties, insufficient oxygenation, and fibrotic encapsulation. Here, we introduce a composite encapsulation system comprising an oxygen-permeable silicone cryogel skeleton, a hydrogel matrix, and a fibrosis-resistant polymer coating. Cryogel skeletons enhance the fracture toughness of conventional alginate hydrogels by 23-fold and oxygen diffusion by 2.8-fold, effectively mitigating both implant fracture and hypoxia of encapsulated cells. Composite implants containing xenogeneic cells engineered to secrete erythropoietin significantly outperform unsupported alginate implants in therapeutic delivery over 8 weeks in immunocompetent mice. By improving mechanical resiliency and sustaining denser cell populations, silicone cryogel skeletons enable more durable and miniaturized therapeutic implants.

Wireless, Battery-Free Implants for Electrochemical Catecholamine Sensing and Optogenetic Stimulation

Neurotransmitters and neuromodulators mediate communication between neurons and other cell types; knowledge of release dynamics is critical to understanding their physiological role in normal and pathological brain function. Investigation into transient neurotransmitter dynamics has largely been hindered due to electrical and material requirements for electrochemical stimulation and recording. Current systems require complex electronics for biasing and amplification and rely on materials that offer limited sensor selectivity and sensitivity. These restrictions result in bulky, tethered, or battery-powered systems impacting behavior and that require constant care of subjects. To overcome these challenges, we demonstrate a fully implantable, wireless, and battery-free platform that enables optogenetic stimulation and electrochemical recording of catecholamine dynamics in real time. The device is nearly 1/10th the size of previously reported examples and includes a probe that relies on a multilayer electrode architecture featuring a microscale light emitting diode (μ-LED) and a carbon nanotube (CNT)-based sensor with sensitivities among the highest recorded in the literature (1264.1 nA μM-1 cm-2). High sensitivity of the probe combined with a center tapped antenna design enables the realization of miniaturized, low power circuits suitable for subdermal implantation even in small animal models such as mice. A series of in vitro and in vivo experiments highlight the sensitivity and selectivity of the platform and demonstrate its capabilities in freely moving, untethered subjects. Specifically, a demonstration of changes in dopamine concentration after optogenetic stimulation of the nucleus accumbens and real-time readout of dopamine levels after opioid and naloxone exposure in freely behaving subjects highlight the experimental paradigms enabled by the platform.

Aspiration-mediated hydrogel micropatterning using rail-based open microfluidic devices for high-throughput 3D cell culture

Microfluidics offers promising methods for aligning cells in physiologically relevant configurations to recapitulate human organ functionality. Specifically, microstructures within microfluidic devices facilitate 3D cell culture by guiding hydrogel precursors containing cells. Conventional approaches utilize capillary forces of hydrogel precursors to guide fluid flow into desired areas of high wettability. These methods, however, require complicated fabrication processes and subtle loading protocols, thus limiting device throughput and experimental yield. Here, we present a swift and robust hydrogel patterning technique for 3D cell culture, where preloaded hydrogel solution in a microfluidic device is aspirated while only leaving a portion of the solution in desired channels. The device is designed such that differing critical capillary pressure conditions are established over the interfaces of the loaded hydrogel solution, which leads to controlled removal of the solution during aspiration. A proposed theoretical model of capillary pressure conditions provides physical insights to inform generalized design rules for device structures. We demonstrate formation of multiple, discontinuous hollow channels with a single aspiration. Then we test vasculogenic capacity of various cell types using a microfluidic device obtained by our technique to illustrate its capabilities as a viable micro-manufacturing scheme for high-throughput cellular co-culture.

Soft, skin-interfaced sweat stickers for cystic fibrosis diagnosis and management

The concentration of chloride in sweat remains the most robust biomarker for confirmatory diagnosis of cystic fibrosis (CF), a common life-shortening genetic disorder. Early diagnosis via quantitative assessment of sweat chloride allows prompt initiation of care and is critically important to extend life expectancy and improve quality of life. The collection and analysis of sweat using conventional wrist-strapped devices and iontophoresis can be cumbersome, particularly for infants with fragile skin, who often have insufficient sweat production. Here, we introduce a soft, epidermal microfluidic device ("sweat sticker") designed for the simple and rapid collection and analysis of sweat. Intimate, conformal coupling with the skin supports nearly perfect efficiency in sweat collection without leakage. Real-time image analysis of chloride reagents allows for quantitative assessment of chloride concentrations using a smartphone camera, without requiring extraction of sweat or external analysis. Clinical validation studies involving patients with CF and healthy subjects, across a spectrum of age groups, support clinical equivalence compared to existing device platforms in terms of accuracy and demonstrate meaningful reductions in rates of leakage. The wearable microfluidic technologies and smartphone-based analytics reported here establish the foundation for diagnosis of CF outside of clinical settings.

Soft, Skin-Interfaced Microfluidic Systems with Passive Galvanic Stopwatches for Precise Chronometric Sampling of Sweat

Comprehensive analysis of sweat chemistry provides noninvasive health monitoring capabilities that complement established biophysical measurements such as heart rate, blood oxygenation, and body temperature. Recent developments in skin-integrated soft microfluidic systems address many challenges associated with standard technologies in sweat collection and analysis. However, recording of time-dependent variations in sweat composition requires bulky electronic systems and power sources, thereby constraining form factor, cost, and modes of use. Here, presented are unconventional design concepts, materials, and device operation principles that address this challenge. Flexible galvanic cells embedded within skin-interfaced microfluidics with passive valves serve as sweat-activated "stopwatches" that record temporal information associated with collection of discrete microliter volumes of sweat. The result allows for precise measurements of dynamic sweat composition fluctuations using in situ or ex situ analytical techniques. Integrated electronics based on near-field communication (NFC) protocols or docking stations equipped with standard electronic measurement tools provide means for extracting digital timing results from the stopwatches. Human subject studies of time-stamped sweat samples by in situ colorimetric methods and ex situ techniques based on inductively coupled plasma mass spectroscopy (ICP-MS) and chlorodimetry illustrate the ability to quantitatively capture time-dynamic sweat chemistry in scenarios compatible with field use.

Wearable Sensors for Biochemical Sweat Analysis

Sweat is a largely unexplored biofluid that contains many important biomarkers ranging from electrolytes and metabolites to proteins, cytokines, antigens, and exogenous drugs. The eccrine and apocrine glands produce and excrete sweat through microscale pores on the epidermal surface, offering a noninvasive means for capturing and probing biomarkers that reflect hydration state, fatigue, nutrition, and physiological changes. Recent advances in skin-interfaced wearable sensors capable of real-time in situ sweat collection and analytics provide capabilities for continuous biochemical monitoring in an ambulatory mode of operation. This review presents a broad overview of sweat-based biochemical sensor technologies with an emphasis on enabling materials, designs, and target analytes of interest. The article concludes with a summary of challenges and opportunities for researchers and clinicians in this swiftly growing field.

Battery-free, skin-interfaced microfluidic/electronic systems for simultaneous electrochemical, colorimetric, and volumetric analysis of sweat

Wearable sweat sensors rely either on electronics for electrochemical detection or on colorimetry for visual readout. Non-ideal form factors represent disadvantages of the former, while semiquantitative operation and narrow scope of measurable biomarkers characterize the latter. Here, we introduce a battery-free, wireless electronic sensing platform inspired by biofuel cells that integrates chronometric microfluidic platforms with embedded colorimetric assays. The resulting sensors combine advantages of electronic and microfluidic functionality in a platform that is significantly lighter, cheaper, and smaller than alternatives. A demonstration device simultaneously monitors sweat rate/loss, pH, lactate, glucose, and chloride. Systematic studies of the electronics, microfluidics, and integration schemes establish the key design considerations and performance attributes. Two-day human trials that compare concentrations of glucose and lactate in sweat and blood suggest a potential basis for noninvasive, semi-quantitative tracking of physiological status.