Skin Interstitial Fluid Research Articles

Gelatin Methacryloyl Microneedle Patches for Minimally Invasive Extraction of Skin Interstitial Fluid.

The extraction of interstitial fluid (ISF) from skin using microneedles (MNs) has attracted growing interest in recent years due to its potential for minimally invasive diagnostics and biosensors. ISF collection by absorption into a hydrogel MN patch is a promising way that requires the materials to have outstanding swelling ability. Here, a gelatin methacryloyl (GelMA) patch is developed with an 11 × 11 array of MNs for minimally invasive sampling of ISF. The properties of the patch can be tuned by altering the concentration of the GelMA prepolymer and the crosslinking time; patches are created with swelling ratios between 293% and 423% and compressive moduli between 3.34 MPa and 7.23 MPa. The optimized GelMA MN patch demonstrates efficient extraction of ISF. Furthermore, it efficiently and quantitatively detects glucose and vancomycin in ISF in an in vivo study. This minimally invasive approach of extracting ISF with a GelMA MN patch has the potential to complement blood sampling for the monitoring of target molecules from patients.

Advances in the Formulations of Microneedles for Manifold Biomedical Applications

AbstractTransdermal delivery systems have recently attracted a great interest due to its minimal invasiveness and convenience. One latest technology in this field is the microneedle technology, which is a single or array of miniaturized needles on the micrometer scale. They pierce the stratum corneum and create transient microchannels for drug diffusion or extraction of skin interstitial fluid. The latest developments of the microneedles are reviewed here by focusing on the materials and fabrication techniques. They are categorized into nonpolymeric and polymeric ones that are made through a wide range of technologies such as lithography, micromolding, droplet‐born air blowing. Powered by the unique structures and functional materials, these microneedle platforms can provide solutions for skin diseases, diabetes, obesity, ocular diseases, as well as point‐of‐care diagnosis.

A Hydrogel Microneedle Patch for Point-of-Care Testing Based on Skin Interstitial Fluid.

Skin interstitial fluid (ISF) holds great potential as a highly desirable sample resource for point-of-care testing (POCT), where the key is to effectively collect target biomarkers from ISF. Hydrogel microneedle patch has great promise for ISF extraction. However, it is challenging to recover target biomarkers from the extracted skin ISF in hydrogel microneedle patches in an easy-administrated, fast, and bulky instrument-free manner. Herein, a hydrogel microneedle patch made of polyvinyl alcohol (PVA) and chitosan (CS) for POCT based on the ISF is developed. The phase transition property of PVA/CS hydrogel makes the microneedles stiff when dry, which is beneficial to easily penetrate into skin. Meanwhile, the highly porous microstructure of hydrogel offers good swelling ability for extraction of ISF and the thermal degradation property of PVA makes it convenient to quickly and efficiently recover target biomarkers from microneedle patch. The capability of this platform for POCT applications is further demonstrated by successful detections of typical biomarkers collected from the mimetic skin and monitoring the glucose level in rabbit skins during a day. The developed hydrogel microneedle patch holds the advantages of extraction of skin ISF and recovery of biomarkers, thus presenting as a powerful platform for skin ISF-based POCT applications.

Encoded Microneedles: Encoded Microneedle Arrays for Detection of Skin Interstitial Fluid Biomarkers (Adv. Mater. 37/2019)

In article number 1902825, Yuanjin Zhao and co-workers present encoded microneedle arrays (MNs) integrating photonic crystal (PhC) barcodes for multiplex specific detection of skin interstitial fluid biomarkers. In the skin interstitial fluid, where various biomarkers disperse, only specific biomarkers are attracted and enriched by the encoded microneedles. These biomarkers can be distinguished by reflection peaks of the barcodes and their relative content can be read out through the fluorescence intensity. The specificity, multiplicity, efficiency, and biosafety make the encoded microneedles ideal in many biomedical areas.

Hydrogel-Coated Microneedle Arrays for Minimally Invasive Sampling and Sensing of Specific Circulating Nucleic Acids from Skin Interstitial Fluid.

Minimally invasive technologies that can sample and detect cell-free nucleic acid biomarkers from liquid biopsies have recently emerged as clinically useful for early diagnosis of a broad range of pathologies, including cancer. Although blood has so far been the most commonly interrogated bodily fluid, skin interstitial fluid has been mostly overlooked despite containing the same broad variety of molecular biomarkers originating from cells and surrounding blood capillaries. Emerging technologies to sample this fluid in a pain-free and minimally-invasivemanneroften take the form of microneedle patches. Herein, we developed microneedles that are coated with an alginate-peptide nucleic acid hybrid material for sequence-specific sampling, isolation, and detection of nucleic acid biomarkers from skin interstitial fluid. Characterized by fast sampling kinetics and large sampling capacity (∼6.5 μL in 2 min), this platform technology also enables the detection of specific nucleic acid biomarkers either on the patch itself or in solution after light-triggered release from the hydrogel. Considering the emergence of cell-free nucleic acids in bodily fluids as clinically informative biomarkers, platform technologies that can detect them in an automated and minimally invasive fashion have great potential for personalized diagnosis and longitudinal monitoring of patient-specific disease progression.

British Society for Gene and Cell Therapy Annual Conference Wednesday 19th June – Friday 21st June 2019 University of Sheffield, Sheffield, UK www.bsgct.org

British Society for Gene and Cell Therapy Annual Conference Wednesday 19th June – Friday 21st June 2019 University of Sheffield, Sheffield, UK www.bsgct.org

Encoded Microneedle Arrays for Detection of Skin Interstitial Fluid Biomarkers.

Skin interstitial fluid (ISF) is considered as an emerging source of biomarkers with physiological and medical significance. Microneedle arrays (MNs) provide a promising means for painless, noninvasive detection of these biomarkers. Here, novel MNs integrated with photonic crystal (PhC) barcodes are presented, and multiplex specific detection of ISF biomarkers is realized for the first time. The PhC barcodes-loaded flexible MNs are simply fabricated by replicating dynamic ferrofluid-cast micromoldings. When the prepared MNs are inserted into skin, they can enrich specific biomarkers to their probes-decorated PhC barcodes. Thus, by adding corresponding fluorescent probes to form sandwich immunocomplexes, the relative content of the biomarkers can be read out through the fluorescence intensity of the barcodes; meanwhile, the species of these biomarkers can be clearly distinguished by the reflection peaks of the PhC barcodes. Based on the encoded MNs, their sensitivity, flexibility, and versatility of capturing and detecting three inflammatory cytokines are demonstrated in a sepsis mice model. Compared with existing MNs for ISF detection, the encoded MNs not only possess equivalent detection effects with less post-processing and simplified procedures, but can also detect multiple biomarkers simultaneously, which makes them ideal in many clinical and biomedical detection areas.

Contact-Lens Biosensors.

Rapid diagnosis and screening of diseases have become increasingly important in predictive and preventive medicine as they improve patient treatment strategies and reduce cost as well as burden on our healthcare system. In this regard, wearable devices are emerging as effective and reliable point-of-care diagnostics that can allow users to monitor their health at home. These wrist-worn, head-mounted, smart-textile, or smart-patches devices can offer valuable information on the conditions of patients as a non-invasive form of monitoring. However, they are significantly limited in monitoring physiological signals and biomechanics, and, mostly, rely on the physical attributes. Recently, developed wearable devices utilize body fluids, such as sweat, saliva, or skin interstitial fluid, and electrochemical interactions to allow continuous physiological condition and disease monitoring for users. Among them, tear fluid has been widely utilized in the investigation of ocular diseases, diabetes, and even cancers, because of its easy accessibility, lower complexity, and minimal invasiveness. By determining the concentration change of analytes within the tear fluid, it would be possible to identify disease progression and allow patient-oriented therapies. Considering the emerging trend of tear-based biosensing technology, this review article aims to focus on an overview of the tear fluid as a detection medium for certain diseases, such as ocular disorders, diabetes, and cancer. In addition, the rise and application of minimally invasive detection and monitoring via integrated contact lens biosensors will also be addressed, in regards to their practicality and current developmental progress.

Modeling In Vivo Interstitial Hydration-Pressure Relationships in Skin and Skeletal Muscle

A theoretical understanding of hydrostatic pressure-fluid volume relationships, or equations of state, of interstitial fluid in skin and skeletal muscle through mathematical/physical modeling is lacking. Here, we investigate at the microscopic level forces that seem to underlie and determine the movements of fluid and solid tissue elements on the microscopic as well as on the macroscopic level. Effects that occur during variation of hydration due to interaction between expanding glycosaminoglycans (GAGs) and the collagen interstitial matrix of tissue seem to be of major importance. We focus on these interactions that let effects from spherical GAGs expand and contract relative to collagen on the microscopic level as hydration changes and thereby generate a hydration-dependent electrostatic pressure on the extracellular matrix on the microscopic level. This pressure spreads to macroscopic levels and become a key factor for setting up equations of state for skin and skeletal muscle interstitia. The modeling for a combined skeletal muscle and skin tissue is one dimensional, i.e., a flat box that may mimic central transverse parts of tissue with more complex geometry. Incorporating values of GAG and collagen densities and fluid contents of skin and muscle tissues that are of an order of magnitude found in literature into the model gives interstitial hydrostatic pressure- fluid volume relationships for these tissues that agree well with experimental results.

Wearable Electrochemical Alcohol Biosensors.

The rapid development of wearable sensing platforms in recent years has led to an array of viable monitoring applications for various target analytes. As a significant biomarker with high impact in diverse areas, the reliable on-body detection and continuous monitoring of alcohol has become a focus of many such systems. Currently, several commercial sensing platforms are available that are capable of transdermal monitoring of alcohol consumption using insensible sweat. Drawbacks of existing alcohol sensing platforms that apply this sensing strategy have led to efforts in developing wearable biosensors capable of real-time alcohol detection in sampled biofluids such as sensible sweat and skin interstitial fluid. This review discusses the current trends in wearable electrochemical alcohol biosensing and highlights recent advances in such systems toward continuous, real-time monitoring of alcohol consumption. Our perspective on this important field is given with an outlook on the future of wearable electrochemical alcohol biosensors.

Validation and discovery of mechanisms that promote vitiligo pathogenesis using single-cell RNA-sequencing of cells isolated from skin interstitial fluid

Abstract Vitiligo is an autoimmune disease in which CD8+ T cells destroy melanocytes, leading to patchy, depigmented lesions of the skin. To investigate possible immune processes in the skin that could explain the patchy appearance of vitiligo inflammation, we performed single-cell RNA-sequencing on cells isolated from the skin using a modified suction blistering technique. We compared the transcriptomes of cells isolated from lesional and non-lesional skin of six vitiligo subjects with active, spreading lesions as well as normal skin from six healthy subjects. Using differential gene analysis to cluster more than 18,000 cell transcriptomes in an unbiased fashion, we were able to identify the cellular components of the skin: melanocytes, keratinocytes, and Langerhans cells, as well as subgroups of immune cells. Consistent with previous findings by our group and others, this approach revealed an IFNγ signature in vitiligo lesions. This method identified 87 ligand-receptor pairs that may promote vitiligo pathogenesis, including CXCR6 and CXCL16 that were just recently implicated in vitiligo. The data set also revealed that Langerhans cells actively express many genes which have known risk alleles for vitiligo, highlighting a potential pivotal role in the development of vitiligo. Overall, single-cell RNA-sequencing of the skin infiltrate in vitiligo lesions is providing robust data that confirms many previous findings, but adds additional layers of nuance missed by conventional studies of bulk material. This level of resolution will yield powerful insight into the identification of novel drug targets in previously unknown signaling pathways in vitiligo and other diseases of the skin.

Wearable physiological systems and technologies for metabolic monitoring.

Wearable sensors allow continuous monitoring of metabolites for diabetes, sports medicine, exercise science, and physiology research. These sensors can continuously detect target analytes in skin interstitial fluid (ISF), tears, saliva, and sweat. In this review, we will summarize developments on wearable devices and their potential applications in research, clinical practice, and recreational and sporting activities. Sampling skin ISF can require insertion of a needle into the skin, whereas sweat, tears, and saliva can be sampled by devices worn outside the body. The most widely sampled metabolite from a wearable device is glucose in skin ISF for monitoring diabetes patients. Continuous ISF glucose monitoring allows estimation of the glucose concentration in blood without the pain, inconvenience, and blood waste of fingerstick capillary blood glucose testing. This tool is currently used by diabetes patients to provide information for dosing insulin and determining a diet and exercise plan. Similar technologies for measuring concentrations of other analytes in skin ISF could be used to monitor athletes, emergency responders, warfighters, and others in states of extreme physiological stress. Sweat is a potentially useful substrate for sampling analytes for metabolic monitoring during exercise. Lactate, sodium, potassium, and hydrogen ions can be measured in sweat. Tools for converting the concentrations of these analytes sampled from sweat, tears, and saliva into blood concentrations are being developed. As an understanding of the relationships between the concentrations of analytes in blood and easily sampled body fluid increases, then the benefits of new wearable devices for metabolic monitoring will also increase.

Phase-transition microneedle patch for efficient transdermal delivery of bio-medicines

We describe, for the first time, quantification of in-skin swelling and fluid uptake by hydrogel-forming microneedle (MN) arrays and skin barrier recovery in human volunteers. Such MN arrays, prepared from aqueous blends of hydrolyzed poly(methylvinylether/maleic anhydride) (15%, w/w) and the cross-linker poly(ethyleneglycol) 10,000 Da (7.5%, w/w), were inserted into the skin of human volunteers (n = 15) to depths of approximately 300 μm by gentle hand pressure. The MN arrays swelled in skin, taking up skin interstitial fluid, such that their mass had increased by approximately 30% after 6 h in skin. Importantly, however, skin barrier function recovered within 24 h after MN removal, regardless of how long the MN had been in skin or how much their volume had increased with swelling. Further research on closure of MN-induced micropores is required because transepidermal water loss measurements suggested micropore closure, whereas optical coherence tomography indicated that MN-induced micropores had not closed over, even 24 h after MN had been removed. There were no complaints of skin reactions, adverse events, or strong views against MN use by any of the volunteers. Only some minor erythema was noted after patch removal, although this always resolved within 48 h, and no adverse events were present on follow-up. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

A Swellable Microneedle Patch to Rapidly Extract Skin Interstitial Fluid for Timely Metabolic Analysis.

Skin interstitial fluid (ISF) is an emerging source of biomarkers for disease diagnosis and prognosis. Microneedle (MN) patch has been identified as an ideal platform to extract ISF from the skin due to its pain-free and easy-to-administrated properties. However, long sampling time is still a serious problem which impedes timely metabolic analysis. In this study, a swellable MN patch that can rapidly extract ISF is developed. The MN patch is made of methacrylated hyaluronic acid (MeHA) and further crosslinked through UV irradiation. Owing to the supreme water affinity of MeHA, this MN patch can extract sufficient ISF in a short time without the assistance of extra devices, which remarkably facilitates timely metabolic analysis. Due to covalent crosslinked network, the MN patch maintains the structure integrity in the swelling hydrated state without leaving residues in skin after usage. More importantly, the extracted ISF metabolites can be efficiently recovered from MN patch by centrifugation for the subsequent offline analysis of metabolites such as glucose and cholesterol. Given the recent trend of easy-to-use point-of-care devices for personal healthcare monitoring, this study opens a new avenue for the development of MN-based microdevices for sampling ISF and minimally invasive metabolic detection.

Iron Oxide Nanoparticle-Powered Micro-Optical Coherence Tomography for in Situ Imaging the Penetration and Swelling of Polymeric Microneedles in the Skin.

In recent years, polymeric microneedles (MNs) have attracted keen interests among researchers because of their applicability in transdermal drug delivery and interstitial skin fluid (ISF) extraction. When designing and characterizing such devices, it is critical to monitor their real-time in vitro and in vivo performances to optimize the desired effects, yet most of the existing methods are incapable of such functions. To address this unmet need, we develop a real-time noninvasive imaging methodology by integrating iron oxide (Fe3O4) nanoparticles into polymeric MNs to enhance image contrast for micro-optical coherence tomography (μOCT) imaging. Using the Fe3O4-integrated polystyrene-block-poly(acrylic acid) (PS-b-PAA) MNs as an example, we evaluate the influences of Fe3O4 concentrations on contrast enhancement in μOCT imaging and visualize the real-time swelling process of polymeric MNs in biological samples for the first time. Our results show that a concentration of ∼4-5 wt % Fe3O4 nanoparticles not only helps achieve the best contrast-to-noise ratio in μOCT imaging, which is 10 times higher than that without Fe3O4 nanoparticles in air and hydrogel, but also enables the real-time changes in the profile of MNs to be observed clearly in their swelling process in skin tissues. On the basis of such findings, we utilize the optimized concentration of Fe3O4 nanoparticles to further quantitatively study the swelling kinetics of PS-b-PAA MNs in agarose hydrogel and fresh skin tissues, which lasts ∼20 and ∼30-35 s, respectively. The suitability of such a methodology for enhancing μOCT imaging would greatly facilitate the development and clinical translation of MN-based medical technologies.

Suction blistering of vitiligo lesional skin provides insights into the pathophysiology of organ specific autoimmunity

Abstract Vitiligo is an autoimmune disease of the skin in which CD8+ T cells destroy the pigment producing cells of the skin: melanocytes. To study the immune infiltrate that propagates vitiligo directly in human skin, we employed a novel suction blistering technique to study skin interstitial fluid by ELISA and flow cytometry. Consistent with previous publications demonstrating IFNγ signatures in vitiligo, CD8+ T cell number and CXCL9 protein concentration were elevated in vitiligo lesional skin compared to normal control skin. Receiver operator characteristic analysis revealed that these measurements may be used to distinguish active from stable disease. Phenotypic analysis of T cells in the skin interstitial fluid showed that the majority of CD4+ T cells in vitiligo skin express CXCR3, the receptor for CXCL9, whereas only 47% of CD4+ T cells expressing CXCR3 in the skin of healthy subjects. The frequency of CD8+ T cells expressing CXCR3 was high in both vitiligo patients and healthy donors. Higher CXCR3+ T cell recruitment via elevated CXCL9 expression may contribute to an observed increase in CD8+ T cell to Treg ratio observed active vitiligo skin (4.1 to 2.5 non-lesional). Additionally, all T cells in the skin microenvironment highly express PD-1. These results support the hypothesis that vitiligo is driven by IFNγ dependent signaling, and targeting components downstream of IFNγ may be useful in treating vitiligo. Moreover, suction blistering human skin is a powerful tool that can be used to aid the study of other inflammatory skin diseases.

IR-spectroscopy of skin in vivo: Optimal skin sites and properties for non-invasive glucose measurement by photoacoustic and photothermal spectroscopy.

We have reported two methods to analyze glucose in the interstitial fluid of skin based on mid-infrared excitation with a tunable quantum cascade laser and photoacoustic or photothermal detection. These methods were evaluated for optimum skin locations to obtain reproducible glucose information. The lower part of the arm, the hypothenar, the tips of the index finger and the thumb were tested. The thumb appears to be the optimal skin location, followed by the index finger. Basic requirements for an optimum site are good capillary blood perfusion, low Stratum corneum thickness and the absence of fat layers. To obtain a correlation on such a site, spectra were recorded on volunteers continuously after blood glucose manipulation. However, continuous measurements on an in vivo sample such as the skin have to cope with physiological alterations such as the formation of sweat. We have used both detection schemes to investigate the acid mantle reformation after washing during time scales similar to continuous measurements for calibration spectra. We found that reconstitution of the acid mantle of skin may be seen in less than one hour. Precleaning of the measurement site may thus be useful for intermittent, but not for long term continuous measurements.

Suction blistering the lesional skin of vitiligo patients reveals useful biomarkers of disease activity

Vitiligo is an autoimmune disease of the skin with limited treatment options; there is an urgent need to identify and validate biomarkers of disease activity to support vitiligo clinical studies. To investigate potential biomarkers of disease activity directly in the skin of vitiligo subjects and healthy subjects. Patient skin was sampled via a modified suction-blister technique, allowing for minimally invasive, objective assessment of cytokines and T-cell infiltrates in the interstitial skin fluid. Potential biomarkers were first defined and later validated in separate study groups. In screening and validation, CD8+ T-cell number and C-X-C motif chemokine ligand (CXCL) 9 protein concentration were significantly elevated in active lesional compared to nonlesional skin. CXCL9 protein concentration achieved greater sensitivity and specificity by receiver operating characteristic analysis. Suction blistering also allowed for phenotyping of the T-cell infiltrate, which overwhelmingly expresses C-X-C motif chemokine receptor 3. A small number of patients were enrolled for the study, and only a single patient was used to define the treatment response. Measuring CXCL9 directly in the skin might be effective in clinical trials as an early marker of treatment response. Additionally, use of the modified suction-blister technique supports investigation of inflammatory skin diseases using powerful tools like flow cytometry and protein quantification.

High-Salt Diet Causes Osmotic Gradients and Hyperosmolality in Skin Without Affecting Interstitial Fluid and Lymph.

The common notion is that the body Na+ is maintained within narrow limits for fluid and blood pressure homeostasis. Several studies have, however, shown that considerable amounts of Na+ can be retained or removed from the body without commensurate water loss and that the skin can serve as a major salt reservoir. Our own data from rats have suggested that the skin is hypertonic compared with plasma on salt storage and that this also applies to skin interstitial fluid. Even small electrolyte gradients between plasma and interstitial fluid would represent strong edema-generating forces. Because the water accumulation has been shown to be modest, we decided to reexamine with alternative methods in rats whether interstitial fluid is hypertonic during salt accumulation induced by high-salt diet (8% NaCl and 1% saline to drink) or deoxycorticosterone pellet implantation. These treatments resulted both in increased systemic blood pressure, skin salt, and water accumulation and in skin hyperosmolality. Interstitial fluid isolated from implanted wicks and lymph draining the skin was, however, isosmotic, and Na+ concentration in fluid isolated by centrifugation and in lymph was not different from plasma. Interestingly, by eluting layers of the skin, we could show that there was an osmolality and urea gradient from epidermis to dermis. Collectively, our data suggest that fluid leaving the skin as lymph is isosmotic to plasma but also that the skin can differentially control its own electrolyte microenvironment by creating local gradients that may be functionally important.

Transcending epithelial and intracellular biological barriers; a prototype DNA delivery device

Microneedle technology provides the opportunity for the delivery of DNA therapeutics by a non-invasive, patient acceptable route. To deliver DNA successfully requires consideration of both extra and intracellular biological barriers. In this study we present a novel two tier platform; i) a peptide delivery system, termed RALA, that is able to wrap the DNA into nanoparticles, protect the DNA from degradation, enter cells, disrupt endosomes and deliver the DNA to the nucleus of cells ii) a microneedle (MN) patch that will house the nanoparticles within the polymer matrix, breach the skin's stratum corneum barrier and dissolve upon contact with skin interstitial fluid thus releasing the nanoparticles into the skin. Our data demonstrates that the RALA is essential for preventing DNA degradation within the poly(vinylpyrrolidone) (PVP) polymer matrix. In fact the RALA/DNA nanoparticles (NPs) retained functionality when in the MN arrays after 28days and over a range of temperatures. Furthermore the physical strength and structure of the MNs was not compromised when loaded with the NPs. Finally we demonstrated the effectiveness of our MN-NP platform in vitro and in vivo, with systemic gene expression in highly vascularised regions. Taken together this ‘smart-system’ technology could be applied to a wide range of genetic therapies.