Dermal Interstitial Fluid Research Articles

Optical Detection of Lithium Therapeutic Levels in Porcine Interstitial Fluid Collected Using a Hollow Microneedle.

Bipolar disorder (BD), a recurrent chronic disorder characterized by mood fluctuating between episodes of mood elevation and depression, is a leading cause of disability worldwide. Lithium is the most widely used medication for management of BD. However, despite its effectiveness in preventing and reducing mood swings and suicidality, it is a potentially hazardous drug. Lithium has a very narrow therapeutic range (0.4-1.2 mmol/L) with the upper limit being uncomfortably close to toxic levels, hence lithium levels should be monitored regularly. The current techniques of monitoring lithium levels require frequent blood tests and elaborate laboratory methods that cannot be translated into point of care devices for personal monitoring. Dermal interstitial fluid (ISF), an underutilized information-rich biofluid, can be accessed using non-invasive techniques and the lithium concentration in ISF has been found to be proportional to concentration in serum. In the current study a microneedle-based sampling method to extract ISF from porcine skin, as it is similar in anatomy to human skin, was employed. Optical determination of lithium therapeutic concentrations in porcine ISF using a colorimetric method based on the reaction between chromogenic agent Quinizarin and Li+ ion was then performed. The resulting spectra show spectral variations which are related to lithium concentrations in spiked samples of porcine ISF, hence suggesting the feasibility of utilizing ISF for real-time and minimally-invasive lithium drug monitoring.

A Wearable Aptamer Microneedle Patch for Minimally-Invasive Therapeutic Drug Monitoring

To realize personalized medicine, the right drug needs to be delivered to the right patient at the right dose. However, it is extremely challenging to dose drugs with narrow therapeutic windows (e.g., antibiotics). For these drugs, due to the small difference between ineffective and toxic concentration levels, the prescribed dosage may result in a circulating concentration outside the therapeutic window, leading to toxicity (e.g., kidney injury) and/or ineffective pharmacotherapy. To prevent such adverse events, patients under these medications are committed to therapeutic drug monitoring (TDM), which in the current clinical practice involves repeated and invasive blood draws followed by labor-intensive and high-cost lab-based analyses (e.g., chromatography, immunoassay). The turnaround times for results are prolonged, and thus, inadequate to allow for timely intervention.Wearable pharmaceutical sensing systems—capable of tracking the medication’s concentration in a continuous and non-/minimally-invasive manner—are well-suited to address these challenges encountered in current TDM practice. To establish a generalizable wearable TDM modality for a broad range of pressing clinical applications, we focus on tracking pharmaceuticals in interstitial fluid (ISF). The choice for ISF is motivated by noting that a wide panel of pharmaceuticals, particularly those with stringent personalized dosing requirements, partition into ISF with high correlation to their circulating levels. To target these analytes, microneedles emerged as promising tools, which are capable of overcoming the skin barrier to directly access ISF in a minimally-invasive manner without user intervention. By integrating sensors on microneedle substrates (e.g., on-the-tip electrochemical sensor fabrication), ISF analytes can be monitored continuously. However, currently demonstrated in-situ ISF sensors are mainly based on enzymatic sensing, which significantly limits the scope of target analytes to the ones with enzymes available.Overcoming this limitation, we devised a low-cost affinity-based biosensor-on-needle fabrication scheme, which was utilized to develop an aptamer microneedle patch (AMPatch). Our AMPatch consists of: 1) a microneedle electrode substrate based on repurposed acupuncture gold needles, leveraging the validated skin puncture performance and the high conductivity of these needles; 2) a gold nanoparticle (AuNP) coating, rendering a high-quality gold surface (comparable to standard electrodes used in electrochemistry) for strong and compact aptamer immobilization; and 3) an aptamer/signal reporter self-assembled monolayer, transducing the target binding events into measurable electrical readouts. We specifically target tobramycin, an antibiotic with a narrow therapeutic window and large intra-subject pharmacokinetic variations, which in the current clinical practice requires multiple TDM sessions to achieve an optimal dosing. Leveraging the developed AMPatch, we demonstrated real-time continuous monitoring of tobramycin ex-vivo (in a phantom gel model, mimicking the dermal ISF testing scenario) and in-vivo (via rat studies). Our results demonstrate the suitability of the AMPatch for minimally-invasive monitoring of the target drug’s pharmacokinetic profile and its potential as a viable TDM tool for personalized pharmacotherapy. Acknowledgements: This work was supported by the National Science Foundation (Award 1847729) and the UCLA Innovation Fund.

Anti-SARS-CoV-2 IgM/IgG antibodies detection using a patch sensor containing porous microneedles and a paper-based immunoassay

Infectious diseases are among the leading causes of mortality worldwide. A new coronavirus named severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) was identified in Wuhan, China in 2019, and the World Health Organization (WHO) declared its outbreak, coronavirus disease 2019 (COVID-19), as a global pandemic in 2020. COVID-19 can spread quickly from person to person. One of the most challenging issues is to identify the infected individuals and prevent potential spread of SARS-CoV-2. Recently, anti-SARS-CoV-2 immunoglobulin M (IgM) and immunoglobulin G (IgG) antibody tests using immunochromatographic methods have been used as a complement to current detection methods and have provided information of the approximate course of COVID-19 infection. However, blood sampling causes pain and poses risks of infection at the needle puncture site. In this study, a novel patch sensor integrating porous microneedles and an immunochromatographic assay (PMNIA) was developed for the rapid detection of anti-SARS-CoV-2 IgM/IgG in dermal interstitial fluid (ISF), which is a rich source of protein biomarkers, such as antibodies. Biodegradable porous microneedles (MNs) made of polylactic acid were fabricated to extract ISF from human skin by capillary effect. The extracted ISF was vertically transported and flowed into the affixed immunoassay biosensor, where specific antibodies could be detected colorimetrically on-site. Anti-SARS-CoV-2 IgM/IgG antibodies were simultaneously detected within 3 min in vitro. Moreover, the limit of detection of anti-SARS-CoV-2 IgM and IgG concentrations was as low as 3 and 7 ng/mL, respectively. The developed device integrating porous MNs and immunochromatographic biosensors is expected to enable minimally invasive, simple, and rapid anti-SARS-CoV-2 IgM/IgG antibody testing. Furthermore, the compact size of the MN and biosensor-integrated device is advantageous for its widespread use. The proposed device has great potential for rapid screening of various infectious diseases in addition to COVID-19 as an effective complementary method with other diagnostic tests.

Feasibility of Interstitial Fluid Ketone Monitoring with Microneedles.

Diabetic ketoacidosis (DKA) is one of the most dangerous and costly complications of diabetes, accounting for approximately 50% of deaths in diabetic individuals under 24 years. This results in over 130,000 hospital admissions yearly and costs the USA over USD 2.4 billion annually. Earlier diagnosis, treatment, and management of DKA are of critical importance to achieving better patient outcomes and preventing prolonged hospital admissions. Diabetic patients undergoing stress from illness or injury may not recognize early ketosis and often present advanced ketoacidosis, requiring intensive care admission. We have recently developed a microneedle-based technology to extract dermal interstitial fluid (ISF) from both animals and humans, which could enable wearable sensors to rapidly detect ketosis. Metabolite concentrations in ISF may differ in urine and blood and could likely represent local metabolic conditions in the surrounding tissue. Development of a wearable ketone detector will require an understanding of ketone concentrations and kinetics in ISF. Here, we report data that is first of its kind, with regard to the ketone concentrations present in the dermal ISF of rats, their correlation to blood, and the possible impact on the development of a wearable ISF “early warning system” to prevent morbidity from DKA. We extracted ISF, using minimally invasive microneedle arrays, from control Sprague Dawley rats and 17 h fasted rats. ISF and blood ketone levels were measured using a common glucose/ketone meter and strips. Local tissue concentrations of glucose were similar to those of blood, with an average blood to ISF glucose ratio of 0.99 ± 0.15 mg/dL. ISF ketones (0.4 ± 0.3 mM) were significantly higher (p = 4.2 × 10−9), compared with blood ketones (0.0 ± 0.0 mM). Although the fasted animals had slightly higher ISF ketones (1.3 ± 1.1 mM) compared with blood ketones (1.0 ± 1.0 mM), the difference was not significant (p = 0.3). This suggests ISF could possibly be useful as a surrogate for blood when determining ketone levels within a clinical setting.

P229 Integrated analysis of dermal blister fluid proteomics and skin biopsy transcriptomics gives new insight into pathogenesis of systemic sclerosis

Abstract Background/Aims Suction blister fluid (BF) provides a unique opportunity to analyse the dermal microenvironment of SSc. We utilised an integrated approach to analyse proteomic data from dermal interstitial fluid and genome-wide transcriptomic data from skin biopsies from early dcSSc and healthy controls (HC). Interpreting differential protein expression in the context of RNA sequencing (RNAseq) provides unique insight into potential mediators and pathways relevant to SSc. Methods The BIOPSY cohort recruited 21 early dcSSc patients with mean skin score (MRSS) of 21 (sd 11) and 16 HCs. Forearm skin BF was obtained using the dermal suction blister method and assayed using the Olink platform (www.olink.com) (1192 proteins). Simultaneous 4mm punch biopsies were taken from all subjects, for genome-wide transcriptomic profiling by RNAseq. Integrated analysis of clinical characteristics, gene and protein expression data was conducted using WGCNA and clusterProfiler in R. This method clusters individual analytes into modules sharing similar expression patterns. Each module has been arbitrarily assigned as a colour. Results WGCNA identified 6 modules in BF, and 30 modules from skin. Two BF modules and three in the skin positively correlated with each other, and all of them correlated with a diagnosis of early dcSSc. The magenta module in the skin (385 genes) and blue module (450 proteins) in BF had the strongest correlation (r = 0.74, p < 0.001 and r = 0.6, p < 0.001 respectively). Interrogating each module, key biological processes consistent with current concepts of SSc pathogenesis were identified, and skin and blister modules largely seemed to complement each other. Magenta module processes focused on angiogenesis, extracellular matrix (ECM) structure, and endothelial cell proliferation, with the highest fold change in COMP (FC = 5.06, p<0.001), COL4A4 (FC = 3.86,p<0.001), COL11A1 (FC = 3.46, p<0.001) having the highest fold change compared to HC. The red module from the skin transcriptomics consisted of genes relating to immune activation, whereas the interferon signature was predominantly seen in the genes of the pink module. Within BF proteomics, the blue module consisted of proteins centred around ECM organisation, cell adhesion, and response to TNF, with upregulation of SFRP1 (FC = 4.88, p = 0.013), TNC(FC = 4.81, p=0.0018) and KLK4 (FC = 7.17, p<0.001) in early dcSSc. Whereas metabolic processes were the centre of the turquoise module. Significant Hallmark pathways were compared between all five modules in each tissue modality. Notably, some pathways were upregulated in both skin gene expression and blister fluid modules including NFKB signalling, allograft rejection, and interferon gamma response. Significantly activated pathways in skin gene but not the blister protein modules include G2M checkpoint, p53 pathway, and xenobiotic metabolism. Conversely, protein secretion, unfolded protein response and mitotic spindle pathways were significantly increased only in the blister modules. Conclusion Simultaneous high dimensional analysis of skin gene and protein expression gives new insight into the molecular pathology of SSc. This provides a potential platform for developing a novel composite biomarker for skin. Disclosure K.E.N. Clark: None. E. Csomor: Corporate appointments; employee of GSK. C. Campochiaro: None. Y. Teo: Corporate appointments; employee of GSK. J. Freudenberg: Corporate appointments; employee of GSK. K. Nevin: Corporate appointments; employee of GSK. M.A. Morse: Corporate appointments; employee of GSK. V.H. Ong: None. E. Derrett-Smith: None. N. Wisniacki: Corporate appointments; employee of GSK. S.M. Flint: Corporate appointments; employee of GSK. C.P. Denton: None.

Optical Determination of Lithium Levels in Artificial Interstitial Fluid for Treatment Management of Bipolar Disorder.

Bipolar Disorder (BD), characterized by mood fluctuating between episodes of mood elevation and depression, is a leading cause of disability worldwide. Lithium continues to be prescribed as a first-line mood stabilizer for the management of BD. However, lithium has a very narrow therapeutic index and it is crucial to carefully monitor lithium plasma levels as concentrations greater than 1.2 mmol/L are potentially toxic and can be fatal. The current techniques of lithium monitoring are cumbersome and require frequent blood tests with the consequent discomfort which results in patients evading treatment. Dermal interstitial fluid (ISF), an underutilized information-rich biofluid, can be a proxy for direct blood sampling and allow lithium drug monitoring as its lithium concentration is proportional to the concentrations in blood. Therefore, in this study we seek to investigate the measurement of lithium therapeutic concentrations in artificial ISF. Our study employs a colorimetric method, based on the reaction between chromogenic agent Quinizarin and Li+ ion which can be detected using optical spectroscopy in the visible region (400-800 nm), to determine lithium levels in artificial ISF. The resulting spectra of our experiments show spectral variations which are related to lithium concentrations in spiked samples of artificial ISF, with a correlation coefficient (R) of 0.9. Future work will focus on investigating the feasibility of utilizing ISF for real-time and minimally-invasive lithium drug monitoring.

371 Quantitative profiling of cytokines and eicosanoids in diluted interstitial fluid samples from a pig model for wound healing

This study describes the quantification of the inflammation parameters cytokines and eicosanoids in dermal interstitial fluid (dISF) samples during the process of wound healing. The dISF samples were collected with the minimally invasive sampling method open flow microperfusion (OFM) and split skin wounds were induced in farm pigs at a depth of 0.6 mm. The cytokine and eicosanoid concentrations were monitored in six and two days old wounds and compared to fresh wounds (directly after wounding) and to control sites (non-wounded skin).

MiRNAs as Regulators of the Early Local Response to Burn Injuries.

In burn injuries, risk factors and limitations to treatment success are difficult to assess clinically. However, local cellular responses are characterized by specific gene-expression patterns. MicroRNAs (miRNAs) are single-stranded, non-coding RNAs that regulate mRNA expression on a posttranscriptional level. Secreted through exosome-like vesicles (ELV), miRNAs are intracellular signalers and epigenetic regulators. To date, their role in the regulation of the early burn response remains unclear. Here, we identified 43 miRNAs as potential regulators of the early burn response through the bioinformatics analysis of an existing dataset. We used an established human ex vivo skin model of a deep partial-thickness burn to characterize ELVs and miRNAs in dermal interstitial fluid (dISF). Moreover, we identified miR-497-5p as stably downregulated in tissue and dISF in the early phase after a burn injury. MiR-218-5p and miR-212-3p were downregulated in dISF, but not in tissue. Target genes of the miRNAs were mainly upregulated in tissue post-burn. The altered levels of miRNAs in dISF of thermally injured skin mark them as new biomarker candidates for burn injuries. To our knowledge, this is the first study to report miRNAs altered in the dISF in the early phase of deep partial-thickness burns.

Synthesis and characterization of sorbitol laced hydrogel-forming microneedles for therapeutic drug monitoring

The dermal interstitial fluid (ISF) is rich in biomarkers that are of great heuristic value for disease diagnosis and therapeutic drug monitoring. Nevertheless, the current strategies for sampling dermal ISF are both technical and invasive, limiting the potential utility of ISF for clinical medicine and research purposes. In the current work, we present, for the first time, the development, characterization, and evaluation of a novel sorbitol-laced hydrogel-forming microneedles (Sor-Hyd-MN) for sampling dermal ISF. The hydrogel system is fabricated from sorbitol and PEG 10,000 crosslinked with Gantrez® S-97 via esterification in a solvent-free manner. The sorbitol-laced hydrogel rapidly absorbs fluid when placed in aqueous media, reaching a total rise in the mass of 685% relative to the control hydrogel that only reached 436% within 15 mins. When formulated into MNs, the Sor-Hyd-MN exhibited significantly superior (p < 0.001) mechanical properties as evidenced by the minimal MN height reduction (0.9%) relative to the control-MN (3.9%) and Man-Hyd-MN (28.5%) when subjected to a compressive force of 32 N, an analog of patients' thumb pressure. The skin insertion capability of the Sor-Hyd-MN and the control-MN formulation was demonstrated using the in vitro skin simulant, Parafilm® M, and ex vivo neonatal porcine skin. When inserted into ex vivo neonatal porcine skin, the Sor-Hyd-MN showed rapid imbibement of dermal ISF within 15 mins, evidenced via the formation of swollen microchannels, which was 1.2-folds wider than the control formulation. In addition, we also demonstrated for the first time that incorporating sorbitol into Gantrez® S-97 hydrogel-forming MN improved the utility of this formulation in sampling dermal ISF. This was shown from the capability of the Sor-Hyd-MN in extracting the model compounds, isoniazid and theophylline, present within the ISF of ex vivo porcine skin. The Sor-Hyd-MN exhibited an extraction efficiency of 52.4% for isoniazid and 54.4% for theophylline which was significantly higher (p < 0.05) relative to the control formulation in a simple and straightforward manner. This work illustrates that incorporating a hyperosmolyte, such as sorbitol, can further enhance the potential utility of hydrogel-forming MN as a minimally-invasive tool for ISF sampling while providing a potential strategy to extract analytes with ease for subsequent sample analysis.

Superswelling Microneedle Arrays for Dermal Interstitial Fluid (Prote)Omics

AbstractThe noninvasive sampling of dermal interstitial fluid (ISF) for the monitoring of clinical biomarkers is a greatly appealing area of research. The identification of molecular biomarkers in biological fluids has been accelerated with ‐omics analyses but remains limited in ISF because of its time‐consuming and complex extraction process. Here, the generation of microneedle (MN) patches made of superabsorbent acrylate‐based hydrogels for the rapid sampling of dermal ISF is described to explore its proteome. In depth, iterative optimization allows the identification of novel acrylate‐based compositions with the required chemical, mechanical, and biocompatibility properties allowing proteomic analysis of the extracted ISF for the first time after sampling with swelling MNs. The generated MN arrays show no cytotoxic effect, successfully cross the stratum corneum, and can collect up to 6 µL of dermal ISF in 10 min in vivo. Proteomics lead to the detection of 176 clinically relevant biomarkers in the collected samples validating the use of ISF as a relevant bodily fluid for disease monitoring and diagnostic. Importantly, it is discovered that extraction fingerprint is strongly dependent on the MNs chemistry, and thus specific biomarkers could be selectively extracted by tuning the composition of the patch, making the system versatile and specific.

P154 High-density proteomic analysis of skin blister fluid and plasma in systemic sclerosis identifies local and systemic differences for key proteins

Abstract Background/Aims Simultaneous analysis of multiple proteins in biological fluids offers insight into the pathogenesis of SSc. Here, we report a proteomic analysis of plasma and dermal interstitial fluid in SSc compared with healthy controls (HC). Methods The prospectively collected BIOPSY cohort recruited 52 SSc patients (21 early dcSSc, 15 established dcSSc,16 lcSSc) and 16 HC. Mean baseline skin score (MRSS) for early dcSSc was 21 (sd 11.2). This analysis utilised forearm skin blister fluid obtained using the dermal suction blister method and paired simultaneous plasma samples from early dcSSc and HC at baseline. These were assayed using the Olink antibody platform(www.olink.com) and reported as normalised protein expression (NPX), corresponding to log2 (expression). T-test with FDR correction (p &amp;lt; 0.05) assessed statistical significance. Pathway analysis was conducted by STRING consortium 2020. Results 1,196 proteins were analysed in paired blister/plasma samples from 14 early dcSSc patients and 16 HC. 447 proteins were significantly different in the blister fluid of early dcSSc patients compared with HC (Table 1), whereas only 183 proteins in plasma. Of these, 130 proteins were simultaneously different in both blister fluid and plasma of early dcSSc including key cytokines associated with fibrosis and vasculopathy such as IL-6,VEGF-1, MCP-1, COL4A1, COMP, Thy1 and THBS4. No correlation was seen between these proteins and MRSS. 310 proteins were significantly elevated in blister fluid alone in early dcSSc patients compared to HC. These included cytokines (IL7,IL18, OSM), chemokines (CCL7,CCL18, CCL3), matricellular proteins (CYR61 and osteopontin). KEGG pathway analysis of the significantly elevated proteins in blister fluid in early dcSSc compared to HC highlighted pathways including cytokine-cytokine receptor interaction, cell adhesion molecules, MAPK signalling pathway and PI3K-AKT signalling pathway (FDR&amp;lt;0.01) P154 Table 1:Protein symbolRaw mean NPXFold ChangeAdjusted p valueDetails of proteinHCdcSScKLK42.69815.9260.004Kallikrein-related peptidase 4IL616.13815.1070.008Interleukin 6NT-proBNP33.60712.8570.018N-terminal pro-brain natriuretic peptideAREG12.74711.9780.017AmphiregulinLTBP24.59311.7990.015Latent-TGF beta-binding protein 2SFRP181.10710.4040.025Secreted Frizzled Related Protein 1TNC18.0128.7280.010Tenascin CCPXM12.1477.4650.002Probable carboxypeptidase X1CYR6110.4936.1060.011Cysteine-rich angiogenic inducer 61 (CCN1)PAPPA10.2675.4800.008Pregnancy-associated plasma protein AEDA2R11.4795.4070.008Ectodysplasin-A2 rceptorNOV61.6385.1190.003Nephroblastoma overexpressed protein (CCN3)GDF-1520.8074.5400.002growth/differentiation factor 15SCARF211.8684.3770.008Scavenger Receptor Class F Member 2CXCL1071.6204.1960.028interferon-γ inducible protein 10THBS4110.6824.1630.008Thrombospondin 4CXCL1324.2564.0470.011C-X-C Motif Chemokine Ligand 13MAPT1.6614.0410.015Microtubule-associated protein tauCOL4A116.7054.0090.003Collagen type IV alpha 1MCP-11128.943.6510.016Monocyte chemoattractant protein-1Top 20 most upregulated proteins in skin blister fluid for early dcSSc (n = 14) compared with healthy control (HC, n = 16). Conclusion Numerous dysregulated proteins were identified in dermal blister fluid and plasma of early dcSSc patients. Substantially more were identified in dermal blister fluid, highlighting its potential for providing detailed information on local pathologic processes. A subset of proteins were dysregulated in both plasma and blister fluid, suggesting these may reflect systemic abnormalities. Further work will utilise this cohort to integrate gene and protein expression across the full spectrum of early dcSSc, established dcSSc and lcSSc Disclosure K.E. Clark: None. C. Campochiaro: None. E. Csomor: Corporate appointments; employee of GSK. A. Taylor: Corporate appointments; employee of GSK. K. Nevin: Corporate appointments; employee of GSK. M.A. Morse: Corporate appointments; employee of GSK. V.H. Ong: None. E. Derrett-Smith: None. N. Wisniacki: Corporate appointments; employee of GSK. S. Flint: Corporate appointments; employee of GSK. C.P. Denton: Consultancies; Actelion, GlaxoSmithKline, Bayer, Sanofi, lnventiva, Boehringer Ingelheim, Roche, Bristol Myers Squibb, CSL Behring, UCB, Leadiant Biosciences, Corbus, Servier, Arxx Therapeutics.

Microneedle Arrays for Sampling and Sensing Skin Interstitial Fluid

Dermal interstitial fluid (ISF) is a novel source of biomarkers that can be considered as an alternative to blood sampling for disease diagnosis and treatment. Nevertheless, in vivo extraction and analysis of ISF are challenging. On the other hand, microneedle (MN) technology can address most of the challenges associated with dermal ISF extraction and is well suited for long-term, continuous ISF monitoring as well as in situ detection. In this review, we first briefly summarise the different dermal ISF collection methods and compare them with MN methods. Next, we elaborate on the design considerations and biocompatibility of MNs. Subsequently, the fabrication technologies of various MNs used for dermal ISF extraction, including solid MNs, hollow MNs, porous MNs, and hydrogel MNs, are thoroughly explained. In addition, different sensing mechanisms of ISF detection are discussed in detail. Subsequently, we identify the challenges and propose the possible solutions associated with ISF extraction. A detailed investigation is provided for the transport and sampling mechanism of ISF in vivo. Also, the current in vitro skin model integrated with the MN arrays is discussed. Finally, future directions to develop a point-of-care (POC) device to sample ISF are proposed.

Sampling of fluid through skin with magnetohydrodynamics for noninvasive glucose monitoring

Out of 463 million people currently with diabetes, 232 million remain undiagnosed. Diabetes is a threat to human health, which could be mitigated via continuous self-monitoring of glucose. In addition to blood, interstitial fluid is considered to be a representative sample for glucose monitoring, which makes it highly attractive for wearable on-body sensing. However, new technologies are needed for efficient and noninvasive sampling of interstitial fluid through the skin. In this report, we introduce the use of Lorentz force and magnetohydrodynamics to noninvasively extract dermal interstitial fluid. Using porcine skin as an ex-vivo model, we demonstrate that the extraction rate of magnetohydrodynamics is superior to that of reverse iontophoresis. This work seeks to provide a safe, effective, and noninvasive sampling method to unlock the potential of wearable sensors in needle-free continuous glucose monitoring devices that can benefit people living with diabetes.

Lab under the Skin: Microneedle Based Wearable Devices.

While the current smartwatches and cellphones can readily track mobility and vital signs, a new generation of wearable devices is rapidly developing to enable users to monitor their health parameters at the molecular level. Within this emerging class of wearables, microneedle-based transdermal sensors are in a prime position to play a key role in synergizing the significant advantages of dermal interstitial fluid (ISF) as a rich source of clinical indicators and painless skin pricking to allow the collection of real-time diagnostic information. While initial efforts of microneedle sensing focused on ISF extraction coupled with either on-chip analysis or off-chip instrumentation, the latest trend has been oriented toward assembling electrochemical biosensors on the tip of microneedles to allow direct continuous chemical measurements. In this context, significant advances have recently been made in exploiting microneedle-based devices for real-time monitoring of various metabolites, electrolytes, and therapeutics and toward the simultaneous multiplexed detection of key chemical markers; yet, there are several grand challenges that still exist. In this review, we outline current progress, recent trends, and new capabilities of microneedle-empowered sensors, along with the current unmet challenges and a future roadmap toward transforming the latest innovations in the field to commercial products.

Sensitive sensing of biomarkers in interstitial fluid.

A minimally invasive microneedle patch detects specific protein biomarkers in dermal interstitial fluid at high sensitivity via a needle-integrated immunoassay coupled with an ultrabright fluorescent label.

Hydrophilic and anti-adhesive modification of porous polymer microneedles for rapid dermal interstitial fluid extraction.

Porous polymer microneedles (MNs) with interconnected structures demonstrate great potential in dermal interstitial fluid (ISF) extraction. However, the fluid extraction rate and the recovery of the extracted ISF by the porous MNs are limited by the poor hydrophilicity and the adhesion of porous MNs. Herein, we present a facile and mild polydopamine (PDA) and poly(ethylene glycol) (PEG) coating strategy for hydrophilic and anti-adhesive modification of porous polymer MNs from a phase inversion method. As a proof-of-concept, taking polysulfone (PSF) as an example, PDA and PEG-coated MNs (PSF@PDA@PEG) are fabricated through the self-polymerization of dopamine and PEG anchoring. Thanks to the hydrophilicity and anti-adhesion of PEG, the resulting PSF@PDA@PEG MNs demonstrate improved hydrophilicity, fast fluid extraction speed, and low target molecular adhesion. Besides, this method can be extended to hydrophobic polymers generally used in medical fields, including polylactic acid (PLA), polyvinylidene fluoride (PVDF), etc. This investigation provides a new road for MN-based off-line analysis in point-of-care testing (POCT).

Microneedle-based skin patch for blood-free rapid diagnostic testing

Rapid diagnostic tests are one of the most commonly used tests to detect and screen for infectious diseases in the developing world. While these tests are simple, inexpensive, and readily available, they rely on finger-prick blood sampling, which requires trained medical personnel, poses risks of infection, and can complicate cooperation in young children, asymptomatic individuals, and communities with blood taboos. Here, we report a novel microneedle-based skin patch for the rapid detection of protein biomarkers in dermal interstitial fluid. Sample collection is facilitated by a hydrophilic hollow microneedle array that autonomously extracts and transports interstitial fluid to an antibody-based lateral flow test strip via surface tension for colorimetric antigen detection. We employ a simple gold enhancement treatment to enhance the detection sensitivity of this colloidal gold-based lateral flow assay and elucidate the underlying mechanism of this enhancement mechanism through experimental investigation. For proof-of-concept, this device was used to detect Plasmodium falciparum histidine-rich protein 2, a biomarker for malaria infection, which could be detected at concentrations as low as 8 ng/mL. Each test can be completed in <20 min and requires no equipment. To the best of our knowledge, this work is the first demonstration of a microneedle-based lateral flow assay for rapid protein detection in dermal interstitial fluid. In addition to its simplicity, minimally invasive nature, and low cost, this diagnostic device can be readily adapted to detect other protein biomarkers in interstitial fluid, making it a promising tool for point-of-care testing.

Minimally Invasive Electrochemical Patch-Based Sensor System for Monitoring Glucose and Lactate in the Human Body-A Survey-Based Analysis of the End-User's Perspective.

Background: Wearable electrochemical sensors that detect human biomarkers allow a comprehensive analysis of a person’s health condition. The “electronic smart patch system for wireless monitoring of molecular biomarkers for health care and well-being” (ELSAH) project aims to develop a minimally invasive sensor system that is capable of continuously monitoring glucose and lactate in the dermal interstitial fluid in real time. It is the objective of the present study to compare the intended ELSAH-patch specifications with the expectations and requirements of potential end-users at an early stage during the development phase. Methods: A questionnaire addressing different aspects of the ELSAH-patch was filled out by 383 respondents. Results: The participants stated a high general demand for such a system, and they would use the ELSAH-patch in different health care and physical fitness applications. The preferred terminal device for communication with the sensor would be the smartphone. An operating time of 24 hours would be sufficient for 55.8% of the users (95%-CI: 50.3–61.3%), while 43.5% of them (95%-CI: 38.0–48.9%) would prefer a lifetime of several days or more. The software should have a warning function, especially for critical health conditions. Since the measured personal data would be highly sensitive, the participants called for high standards for data security and privacy. Conclusion: In general, the participants’ responses on their expectations and requirements were well in line with the intended specifications of the ELSAH-patch system. However, certain technical aspects such as the lifetime, data security and accuracy require special attention during its development.

69-LB: A Wearable Microneedle Array Sensor Shows High Correlation between Dermal Glucose and Venous Blood Glucose

Objective: Current continuous glucose monitors (CGM) measure glucose in the subcutaneous interstitial fluid (ISF). Previous ex vivo research with hypodermic needles has shown that glucose in the dermal ISF is highly correlated to venous glucose with little or no lag time. However, this methodology is not viable for continuous measurement. In this study, we have developed and tested a wearable microneedle array sensor for continuous in situ measurement of glucose in the dermal ISF. A dermal CGM could be applied without an introducer needle and without pain during application. Methods: In this study the microneedle array sensor was tested against venous glucose measured every 15 minutes from a YSI analyzer in 8-hour sessions over 2 days (Phase One) and 5-7 days (Phase Two). Results: Five participants without diabetes and 10 participants with diabetes were recruited for phase One and 10 participants with diabetes were recruited for phase Two. A high degree of linear correlation (R2 ≥ 0 .90) between the microneedle array measured dermal ISF glucose and venous glucose was observed. The figure shows the linear correlation (A) and temporal profile (B) for one microneedle array sensor over 8 hours. Conclusions: A wearable microneedle array measuring dermal ISF glucose can accurately track glucose values. The study demonstrated early human feasibility of a CGM based on microneedle sensing of dermal ISF. Disclosure P.P. Samant: Employee; Self; Biolinq. M.P. Christiansen: Research Support; Self; Abbott, Ascensia Diabetes Care, Biolinq, Dexcom, Inc., Eli Lilly and Company, Lexicon Pharmaceuticals, Inc., Medtronic, Merck &amp; Co., Inc., Novo Nordisk A/S, Sanofi-Aventis, Senseonics, ViroMed Laboratories, Xeris Pharmaceuticals, Inc. S. Sattayasamitsathit: None. A. Campbell: None. T.A. Peyser: Consultant; Self; Insulet Corporation. Employee; Self; Biolinq. J.R. Windmiller: Employee; Self; Biolinq. J.R. Tangney: Board Member; Self; Biolinq. R. Lal: Consultant; Self; Abbott, Biolinq. N.C. Bhavaraju: Employee; Self; Biolinq.

Hydrogel Microfilaments toward Intradermal Health Monitoring.

SummaryDigital health promises a paradigm shift for medicine where biomarkers in individuals are continuously monitored to improve diagnosis and treatment of disease. To that end, a technology for minimally invasive quantification of endogenous analytes in bodily fluids will be required. Here, we describe a strategy for designing and fabricating hydrogel microfilaments that can penetrate the skin while allowing for optical fluorescence sensing. The polyacrylamide formulation was selected to provide high elastic modulus in the dehydrated state and optical transparency in the hydrated state. The microfilaments can be covalently tethered to a fluorescent aptamer to enable functional sensing. The microfilament array can penetrate the skin with low pain and without breaking, contact the dermal interstitial fluid, and be easily removed from the skin. In the future, hydrogel microfilaments could be integrated with a wearable fluorometer to serve as a platform for continuous, minimally invasive monitoring of intradermal biomarkers.