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

Turbulence-enhanced microneedle immunoassay platform (TMIP) for high-precision biomarker detection from skin interstitial fluid

Conventional diagnostic methods for biomarker detection often require invasive procedures and exhibit limited reproducibility and sensitivity. In this study, the turbulence-enhanced microneedle immunoassay platform (TMIP) was designed to enhance the performance and accuracy of biomarker detection in skin interstitial fluid (ISF). TMIP combines a bullet-shaped microneedle (MN) array for minimally invasive biomarker capture, a microfluidic device for MN-mediated immunoassay process simplification, and a star-shaped magnetic stirrer tool (MST) to facilitate efficient washing. By targeting S100 calcium-binding protein B (S100B), a diagnostic biomarker for melanoma, TMIP demonstrated substantial improvements in reproducibility, reducing signal deviations by up to 55 % compared to manual operation. The application of nanoporous MNs (NPMNs) achieved a low detection limit of 20 pg/mL with a high linearity (R2 = 0.9758). Validation using a gelatin phantom mimicking human skin confirmed TMIP's ability to achieve improved reproducibility and sensitivity. Furthermore, TMIP successfully detected S100B with high reproducibility in both the phantom (R2 = 0.97523) and melanoma-expressing mice within a rapid incubation time of 1 min. TMIP enables the detection of biomarkers with remarkable reproducibility and sub-nanogram sensitivity by simplifying the analysis process and enhancing reagent washing through turbulence. These features suggest that TMIP has the potential to serve as an efficient and reliable tool for biomarker detection in skin ISF.

Bio-inspired microneedles with hierarchical microchannels for rapid interstitial fluid collection and analysis

The rapid and efficient detection of biomarkers in interstitial fluid (ISF) represents a compelling alternative to traditional invasive blood sampling for diagnostic and monitoring purposes. Here, bio-inspired microneedles (MNs) with hierarchical microchannels (HMC-MNs), emulating the liquid transport properties of Sarracenia trichomes, are presented. These MNs are fabricated using a secondary mold replication technique, ensuring cost-effectiveness and scalability. The HMC-MNs leverage capillary action to enhance ISF extraction, as validated through ex vivo and in vivo experiments demonstrating their robust ISF extraction capability. Integrated with a microneedle-based ISF sensing system (MISS), the platform enables real-time electrochemical and colorimetric detection of biomarkers, underscoring its potential for health monitoring and point-of-care applications. Furthermore, the collected ISF supports detailed off-needle analyses, expanding its diagnostic utility. By combining minimal invasiveness, rapid ISF collection, and versatile sensing capabilities, the HMC-MN system marks a significant step forward in wearable diagnostics, offering promising applications in both clinical and personal health management.

Advances in microneedle-based drug delivery system for metabolic diseases: structural considerations, design strategies, and future perspectives

As the prevalence of metabolic diseases such as diabetes and obesity continue to rise, the search for more effective and convenient treatments has become a crucial issue in medical research. Microneedles (MNs), as an innovative drug delivery system, have shown advantages in the treatment of metabolic diseases in recent years. MNs-based drug delivery system, which use MNs to deliver drugs directly to the subcutaneous tissue, improve drug bioavailability and reduce systemic side effects. This review aims to summarize the latest concepts, designs, and types of MNs, and to investigate the materials and manufacturing methods used in their construction. Subsequently, the mechanisms of drug delivery and graded release of MNs and recent research progress are further summarized. This article focuses on the application of MNs in the treatment of common metabolic diseases, with a special emphasis on the progress and optimization of diabetic and anti-obesity MNs. The main challenges and future perspectives in the production and evaluation of MNs, as well as in enhancing treatment efficacy and improving safety, are elucidated.

Morphology Design and Precision Control of Microneedles by PμSL 3D Printing

Microneedles (MNs) hold significant potential for applications in transdermal drug delivery and biosensing. However, when traditional 3D printing technology is used for their manufacture, a substantial deviation in output size occurs. The effects of various parameters on the morphology of MNs produced through microscale 3D printing remain unclear. This study investigated the relationship between the design and fabrication of acrylic resin MNs and their output forms via a projection microstereolithography (PµSL) technology system. Modifying the shape parameters and array configurations elucidates the causes of size deviation and proposes a control strategy. This is particularly significant for the prototyping and mold manufacturing of MNs in relevant fields. This study indicates that a printing layer thickness of 10 µm optimally balances efficiency and clinical conversion requirements. Additionally, an exposure intensity of 65 mW/cm2 achieves both a high fidelity and an appropriate base size. The printing angle significantly influences the morphology and mechanical properties of MNs. The diameter and aspect ratio of solid MNs correlate with their dimensional stability. Clinically, conical or quadrilateral MNs with defined parameters are recommended. A critical spacing (≥40 µm) and an optimal arrangement of the MN arrays were established. The specific exposure intensity and vertical printing angle of the hollow MNs ensure the precision of the micropore diameter and wall thickness. This approach offers theoretical insights and process parameters essential for high-precision, customizable MN engineering design.

Nanotechnology-Based Wearable Electrochemical Biosensor for Disease Diagnosis

Recently, flexible electronics have significantly transformed information and communications technology (ICT). In particular, wearable devices, via integration with attachable biosensors, have driven the development of new types of biosensors and diagnostic devices for point-of-care testing (POCT). Moreover, wearable electrochemical biosensors can be applied to diagnose diseases in real time based on the synergistic effect generated from the incorporation of the electrochemical technique. Besides, to improve the sensitivity of electrochemical biosensors while retaining their wearability, novel nanomaterials and nanotechnologies have been introduced. In this review, recent studies on nanotechnology-based wearable electrochemical biosensors for accurate disease diagnosis are discussed. First, widely used techniques for developing flexible electrodes, including nanolithography- and nano/microneedle-based patches, are presented. Next, the latest studies on developing wearable electrochemical biosensors for the diagnosis of diseases such as diabetes and dermatitis are discussed by categorizing the biosensors into nanolithography- and nano/microneedle-based categories. Finally, this review explores the latest research trends on the application of nanotechnology-enabled nanopatterning and nano/microneedle technologies to electrochemical wearable biosensors. This review suggests novel approaches and methods for developing wearable electrochemical biosensors for real-time disease diagnosis under POCT applications.

Ice-pop making inspired photothermal ultra-swelling microneedles to facilitate loading and intradermal vaccination of tumor antigen

Cancer vaccines hold great promise in the fight against cancer. Here, we report an ice-pop making inspired photothermal ultra-swelling microneedle (PUSMN) patch for facilitating and enhancing cancer vaccination. The PUSMN patch consist of an array of microneedles made from photo-crosslinked methacrylated hyaluronic acid and polydopamine, a near-infrared photothermal conversion material, connected to a customized resin handle like an ice-pop stick. Using a fabrication process similar to ice-pop making, the PUSMNs exhibit a rapid swelling ratio of over 2000 %, enabling straightforward and efficient loading of tumor antigen with just a 1-min incubation in the antigen solution, followed by 15 min of drying. The handle not only ensures convenient application but also guarantees full embedding of the PUSMNs in the skin after penetration. Under near-infrared irradiation, PUSMNs efficiently generate local heat, further promoting the activation and maturation of dendritic cells. In vivo vaccination with the model antigen ovalbumin using PUSMNs combined with near-infrared irradiation elicits robust tumor antigen-specific cellular and humoral immune responses, ultimately resulting in delayed tumor growth. Given its ease of use, efficiency, and safety features, this biocompatible PUSMN patch could greatly improve cancer vaccination.

NIR-II Fluorescent Thermophoretic Nanomotors for Superficial Tumor Photothermal Therapy

Peritumoral subcutaneous injection has been highly envisioned as an efficient yet low-risk administration of photothermal agents for superficial tumor photothermal therapy. However, obstructed by complex subcutaneous tissue, the delivery of injected photothermal agents to the specific tumor remains a critical issue. Herein, the study reports a polydopamine (PDA)-encapsulated spherical core/shell nanomotor with fluorescent indocyanine green (ICG) immobilized on its PDA shell. Upon the first near-infrared (NIR-I) irradiation, this motor can generate favorable photothermal heat, and meantime, emit a robust ICG fluorescence in the second near-infrared window (NIR-II). The heat turns the motor into an active photothermal agent able to perform thermophoretic propulsion along the irradiation direction in subcutaneous tissue, while the ICG fluorescence can direct the subcutaneous propulsion of motors toward specific tumor through real-time NIR-II imaging. These functions endow the motor with the ability of moving to tumor after being injected at peritumoral site, enabling an enhanced photothermal therapy (PTT). The results demonstrated herein suggest an integrated nanorobotic tool for the superficial PTT using peritumoral administration, highlighting an NIR-II imaging-directed subcutaneous propulsion.

Advances in adhesion of microneedles for bioengineering

Microneedles have provided promising platforms in various fields thanks to their safety, painlessness, minimal invasiveness and ease of operation. The excellent adhesion of microneedles is the key characteristic to achieve long-term and comfortable treatment. However, a complex environment, such as the roughness of skin, various bodily fluids in vivo, and the movement of the body, presents great challenges to the adhesion characteristics of microneedles. This review mainly reports the remarkable adhesion properties of microneedles based on interlocking by shape effects, chemical bonds, and suction forces. Firstly, the main mechanisms of adhesion and various types of microneedles are introduced, with an emphasis on the progress in adhesive microneedles. Combined with the preparation and application of microneedles, the challenges and future trends of adhesive microneedles are discussed.

Recent Advances in MXene-Based Electrochemical Sensors

MXene is a new family of two-dimensional nanomaterials with outstanding electrical conductivity, tunable structure, biocompatibility, and a large surface area. Thanks to these unique physicochemical properties, MXene has been used for constructing electrochemical sensors (MECSens) with excellent performance. In particular, the abundant surface termination of MXene can contribute to greatly enhancing the analytical sensitivity and selectivity of MECSens. Recently, MECSens have been widely applied in many fields including clinical diagnosis, infectious disease surveillance, and food security. However, not all MXene materials are suitable for building electrochemical sensors. In this article, we present an overview of different MECSens that have been developed so far. We begin with a short summary of the preparation and characterization of MECSens. Subsequently, the electrochemical performance, detection strategies, and application scenarios of MECSens are classified and briefly discussed. The article ends with a short conclusion and future perspectives. We hope this article will be helpful for designing and constructing MECSens with outstanding activity for electrochemical analysis.

Stepwise Lighting Up Gold(I)-Thiolate Complexes from AIE Nanoaggregates to AIEE Nanoprobes with a ZIF-8 Shell for Glucose Biosensing

Aggregation-induced emission (AIE) or aggregation-induced emission enhancement (AIEE) has endowed gold species with responsive fluorescent properties, favoring their potential applications in sensing, imaging, and therapy. However, it remains an interesting challenge to fabricate fluorophores with both AIE and AIEE effects. Herein, we presented highly luminescent Au(I) thiolate nanocomplex-based biosensors with Zn2+ induced-AIE and zeolite imidazolate framework (ZIF-8) induced-AIEE effects. The nonemissive monovalent gold-glutathione complexes (AuI-SGs) were obtained to synthesize the core-shell Zn2+/AuI-SG@ZIF-8 composites with strong luminescence via the coordination-assisted self-assembly strategy. By immobilizing GOx on the surface of Zn2+/AuI-SG@ZIF-8, Zn2+/AuI-SG@ZIF-8/GOx biosensors exhibited effective responsiveness to glucose, showing a "turn-off" detection model. The mechanism study revealed that the robust luminescence of Zn2+/AuI-SG@ZIF-8 to glucose sensing was attributed to the acid-stimulated degradation of the probe facilitated by H+ generated from the glucose oxidase (GOx)-catalyzed oxidation process. To achieve noninvasive and intelligent blood glucose detection, the Zn2+/AuI-SG@ZIF-8/GOx-loaded microneedle (MN)-patch fluorescent platform was further developed. The MN-patch-based sensing platform had promising performance for on-needle capture and in situ glucose detection. This study demonstrated a universal and feasible protocol to construct luminescent biosensors for glucose detection and their potential for the development of MN-based analytical devices.

3D printed microneedles: revamping transdermal drug delivery systems

One of the advancements of the transdermal drug delivery system (TDDS) is the development of microneedles (MNs). These micron-sized needles are used for delivering various types of drugs to address the disadvantage of other transdermal techniques as well as oral drug delivery systems. MNs have high patient acceptance due to self-administration with minimally invasive and pain compared to the parenteral drug delivery. Over the years, various methods have been adopted to evolve the MNs and make them more cost-effective, accurate, and suitable for multiple applications. One such method is the 3D printing of MNs. The development of MN platforms using 3D printing has been made possible by improved features like precision, printing resolution, and the feasibility of using low-cost raw materials. In this review, we have tried to explain various types of MNs, fabrication methods, materials used in the formulation of MNs, and the recent applications that utilize 3D-printed MNs.

Electrostatic Force-Enabled Microneedle Patches that Exploit Photoredox Catalysis for Transdermal Phototherapy

Microneedle patches for topical administration of photodynamic therapy (PDT) sensitizers are attractive owing to their safety, selectivity, and noninvasiveness. However, low-efficiency photosensitizer delivery coupled with the limitations of the hypoxic tumor microenvironment remains challenging. To overcome these issues, we developed an effective microneedle patch based on intermolecular electrostatic interactions within a photosensitizer matrix containing a zinc-containing porphyrin analogue, ZnBP (w). This design improved the mechanical strength of the microneedle patch and enhanced the photosensitizer loading efficiency in aqueous environments. A key feature of the system is efficient electron transfer between ZnBP (w) and NADH upon photoirradiation. Electrostatic interactions between ZnBP (w) and NADH were hypothesized to support initial binding and subsequent photoinduced electron transfer, disrupting NADH/NAD+ homeostasis and inducing tumor cell death. The developed microneedle patch demonstrated an antiangiogenesis effect in a vascular malformation model and an antitumor effect in a melanoma mouse model after transdermal administration. This study highlights the benefits of electrostatic interactions in designing microneedle PDT patches and their clinical potential, particularly in reducing systemic phototoxicity.

Micro-vibration assisted dual-layer spiral microneedles to rapidly extract dermal interstitial fluid for minimally invasive detection of glucose

Various hydrogels have been explored to create minimally invasive microneedles (MNs) to extract interstitial fluid (ISF). However, current methods are time-consuming and typically require 10-15 min to extract 3-5 mg of ISF. This study introduces two spiral-shaped swellable MN arrays: one made of gelatin methacryloyl (GelMA) and polyvinyl alcohol (PVA), and the other incorporating a combination of PVA, polyvinylpyrrolidone (PVP), and hyaluronic acid (HA) for fast ISF extraction. These MN arrays demonstrated a rapid swelling ratio of 560 ± 79.6% and 370 ± 34.1% in artificial ISF within 10 min, respectively. Additionally, this study proposes a novel method that combines MNs with a custom-designed Arduino-based applicator vibrating at frequency ranges (50-100 Hz) to improve skin penetration efficiency, thereby enhancing the uptake of ISF in ex vivo. This dynamic combination enables GelMA/PVA MNs to rapidly uptake 6.41 ± 1.01 mg of ISF in just 5 min, while PVA/PVP/HA MNs extract 5.38 ± 0.77 mg of ISF within the same timeframe. To validate the capability of the MNs to recover glucose as the target biomarker, a mild heating procedure is used, followed by determining glucose concentration using a D-glucose content assay kit. The efficient extraction of ISF and glucose detection capabilities of the spiral MNs suggest their potential for rapid and minimally invasive biomarker sensing.

Microneedles: multifunctional devices for drug delivery, body fluid extraction, and bio-sensing

Microneedles represent a miniaturized mechanical structure with versatile applications, including transdermal drug delivery, vaccination, body-fluid extraction, and bio-sensing. Over the past two decades, microneedle-based devices have garnered considerable attention in the biomedicine field, exhibiting the potential for mitigating patient discomfort, enhancing treatment adherence, avoiding first-pass effects, and facilitating precise therapeutic interventions. As an application-oriented technology, the innovation of microneedles is generally carried out in response to a specific demand. Currently, three most common applications of microneedles are drug delivery, fluid extraction, and bio-sensing. This review focuses on the progress in the materials, fabrication techniques, and design of microneedles in recent years. On this basis, the progress and innovation of microneedles in the current research stage are introduced in terms of their three main applications.

Hydrogel-Forming Microneedles and Applications in Interstitial Fluid Diagnostic Devices

Hydrogel-forming microneedles are constructed from or coated with polymeric, hydrophilic materials that swell upon insertion into the skin. Designed to dissolve or disintegrate postinsertion, these microneedles can deliver drugs, vaccines, or other therapeutics. Recent advancements have broadened their application scope to include the collection, transport, and extraction of dermal interstitial fluid (ISF) for medical diagnostics. This review presents a brief introduction to the characteristics of dermal ISF, methods for extraction and sampling, and critical assessment of the state-of-the-art in hydrogel-forming microneedles for ISF diagnostics. Key factors are evaluated including material composition, swelling behavior, biocompatibility, and mechanical strength necessary for effective microneedle performance and ISF collection. The review also discusses successful examples of dermal ISF assays and microneedle sensor integrations, highlighting notable achievements, identifying research opportunities, and addressing challenges with potential solutions. Despite the predominance of synthetic hydrogels in reported hydrogel-forming microneedle technologies due to their favorable swelling and gelation properties, there is a significant variety of biopolymers and composites reported in the literature. The field lacks consensus on the optimal material, composition, or fabrication methods, though emerging evidence suggests that processing and fabrication techniques are critical to the performance and utility of hydrogel-forming microneedles for ISF diagnostics.

Self-Extracting Dextran-Based Hydrogel Microneedle Arrays with an Interpenetrating Bioelectroenzymatic Sensor for Transdermal Monitoring with Matrix Protection

Continuous glucose monitors have revolutionized diabetes management, yet such devices are limited by their cost, invasiveness, and stability. Microneedle (MN) arrays could offer improved comfort compared to invasive implanted or mm-sized needle devices, but such arrays are hampered by complex fabrication processes, limited mechanical and sensor stability, and/or cytotoxicity concerns. This work demonstrates the first crosslinked hydrogel microneedle-bioelectroenzymatic sensor arrays capable of biomarker extraction and robust transdermal continuous monitoring in artificial interstitial fluid for 10 days. The fabrication process via micromolding of dextran-methacrylate (Dex-MA) and dry-state visible light crosslinking is simple and permits the robust fixation of diverse prefabricated electrodes in a single array. Dry-state crosslinking minimized material shrinkage to enable the formation of resistant Dex-MA microneedles with shape control and reproducibility. The polymer substitution level (9-62%) and mass content (10-30 wt%) affect the mechanical, swelling, and bioelectrocatalytic properties of the integrated sensors. Crosslinked Dex-MA hydrogel matrices provide beneficial cytotoxicity protection and flux-limiting membrane properties to the integrated second generation dehydrogenase-based nanostructured buckypaper biosensor and Ag/AgCl reference electrodes. Polysaccharide-based microneedle technology with encapsulated porous bioelectrodes promise to be a valuable alternative to more invasive devices for safer and longer-term biomarker monitoring.

Intradermal implantation of methotrexate-loaded puerarin-gelatin hydrogel via bubble-generating microneedles for psoriasis treatment

Methotrexate (MTX) is a primary treatment for moderate to severe psoriasis, but conventional oral or subcutaneous delivery has limitations, including poor drug targeting, side effects, and low patient compliance. This study introduces implantable hydrogel microneedles (HMNs) made from photo-cross-linked gelatin methacryloyl (GelMA) and puerarin (Pue), a traditional Chinese medicine, for intradermal and sustained MTX delivery. The ratio of Pue to GelMA significantly influenced the morphology, mechanical strength, MTX release profiles, and degradation behavior of the HMNs. After insertion into the skin, the backing layer of the microneedles, which incorporates effervescent agents (NaHCO3 and citric acid), rapidly generates gas bubbles (CO₂) upon contact with skin interstitial fluid, facilitating the immediate separation of the HMNs from the backing and their implantation into skin tissue as MTX reservoirs. HMNs with 1.5 % w/v Pue and 20 % w/v GelMA achieved a 10-day MTX release in vivo. In vivo studies demonstrate that MTX-loaded Pue/GelMA HMNs significantly enhance therapeutic outcomes in alleviating psoriasis symptoms and downregulating psoriasis-associated cytokines due to the synergistic effects of MTX and Pue, outperforming oral administration, subcutaneous injection, and GelMA HMNs containing either Pue or MTX alone. This HMN patch offers great promise for improving psoriasis treatment and patient adherence.

I-Motif DNA Based Fluorescent Ratiometric Microneedle Sensing Patch for Sensitive Response of Small pH Variations in Interstitial Fluid

Detection of slight pH changes in skin interstitial fluid (ISF) is crucial yet challenging for studying pathological processes and understanding personal health conditions. In this work, we construct an i-motif DNA based fluorescent ratiometric microneedle sensing patch (IFR-pH MN patch) strategy that enables minimally invasive, high-resolution, and sensitive transdermal monitoring of small pH variations in ISF. The IFR-pH MN patch with advanced integration of both ISF sampling and pH sensing was fabricated from the cross-linking of gelatin methacryloyl and methacrylated hyaluronic acid, wrapping with pH-sensitive hairpin-containing i-motif DNA based fluorescent ratiometric probes in the matrix. Because it is mechanically robust for skin penetration and has high swelling ability, the IFR-pH MN patch could be quickly extracted as sufficient liquid from agarose gel (∼56.4 μL in 10 min). Benefiting from conformation changes of the hairpin-containing i-motif DNA under pH variation and ratiometric fluorescence signal readout, the IFR-pH MN patch could quantitate pH over a small range between pH 6.2 and 6.9 with an accuracy of 0.2 pH units in the mimic skin model. Furthermore, in vivo testing on wound and tumor mouse models indicated the ability of the biocompatible IFR-pH MN patch to penetrate the skin for obtaining transdermal pH values, demonstrating the potential applications in monitoring and intervention of pathological states.

Active-reset protein sensors enable continuous in vivo monitoring of inflammation

Continuous measurement of proteins in vivo is important for real-time disease management and prevention. Implantable sensors for monitoring small molecules such as glucose have been available for more than a decade. However, analysis of proteins remains an unmet need because the lower physiological levels require that sensors have high affinities, which are linked to long complexation half-lives (t1/2 ~20 hours) and slow equilibration when concentrations decrease. We report active-reset sensors by use of high-frequency oscillations to accelerate dissociation, which enables regeneration of the unbound form of the sensor within 1 minute. When implemented within implanted devices, these sensors allow for real-time, in vivo monitoring of proteins within interstitial fluid. Active-reset protein sensors track biomarker levels on a physiological timescale for inflammation monitoring in living animals.

Synergistic Strategies of Biomolecular Transport Technologies in Transdermal Healthcare Systems

Transdermal healthcare systems have gained significant attention for their painless and convenient drug administration, as well as their ability to detect biomarkers promptly. However, the skin barrier limits the candidates of biomolecules that can be transported, and reliance on simple diffusion poses a bottleneck for personalized diagnosis and treatment. Consequently, recent advancements in transdermal transport technologies have evolved toward active methods based on external energy sources. Multiple combinations of these technologies have also shown promise for increasing therapeutic effectiveness and diagnostic accuracy as delivery efficiency is maximized. Furthermore, wearable healthcare platforms are being developed in diverse aspects for patient convenience, safety, and on-demand treatment. Herein, a comprehensive overview of active transdermal delivery technologies is provided, highlighting the combination-based diagnostics, therapeutics, and theragnostics, along with the latest trends in platform advancements. This offers insights into the potential applications of next-generation wearable transdermal medical devices for personalized autonomous healthcare.

Advances in novel biosensors in biomedical applications

Biosensors, devices capable of detecting biomolecules or bioactive substances, have recently become one of the important tools in the fields of bioanalysis and medical diagnostics. A biosensor is an analytical system composed of biosensitive elements and signal-processing elements used to detect various biological and chemical substances. Biomimetic elements are key to biosensor technology and are the components in a sensor that are responsible for identifying the target analyte. The construction methods and working principles of biosensors based on synthetic biomimetic elements, such as DNAzyme, molecular imprinted polymers and aptamers, and their updated applications in biomedical analysis are summarised. Finally, the technical bottlenecks and future development prospects for biomedical analysis are summarised and discussed.

Development of an electrochemical biosensor for non-invasive cholesterol monitoring via microneedle-based interstitial fluid extraction

In this study, we present the development of an innovative electrochemical biosensor integrated into a microneedle-based system for non-invasive and sensitive quantification of cholesterol levels in interstitial fluid (ISF). The biosensor employs a graphene-based electrode with a polyelectrolyte interlayer to immobilize cholesterol oxidase (ChOx), enabling selective cholesterol detection. Graphene oxide is electrochemically reduced to form a conductive layer, and PANI is chosen as the optimal polyelectrolyte for ChOx immobilization. The biosensor's performance is thoroughly evaluated, demonstrating excellent sensitivity, stability, and selectivity. Furthermore, the biosensor is successfully applied to skin-mimicking agarose gel and porcine skin, showcasing its potential for real-world interstitial fluid extraction and cholesterol monitoring. The integrated microneedle-based system offers a promising approach for non-invasive monitoring of cholesterol levels, with implications for personalized healthcare diagnostics.

Microneedles as transdermal drug delivery system for enhancing skin disease treatment

Microneedles (MNs) serve as a revolutionary paradigm in transdermal drug delivery, heralding a viable resolution to the formidable barriers presented by the cutaneous interface. This review examines MNs as an advanced approach to enhancing dermatological pathology management. It explores the complex dermis structure and highlights the limitations of traditional transdermal methods, emphasizing MNs' advantage in bypassing the stratum corneum to deliver drugs directly to the subdermal matrix. The discourse outlines the diverse typologies of MNs, including solid, coated, hollow, hydrogel, and dissolvable versions. Each type is characterized by its unique applications and benefits. The treatise details the deployment of MNs in the alleviation of cutaneous cancers, the administration of inflammatory dermatoses such as psoriasis and atopic dermatitis, and their utility in wound management. Additionally, the paper contemplates the prospects of MNs within the realm of aesthetic dermatology and the burgeoning market traction of cosmetic MN formulations. The review summarizes the scientific and commercial challenges to the clinical adoption of MN therapeutics, including dosage calibration, pharmacodynamics, biocompatibility, patient compliance, sterilization, mass production, and regulatory oversight. It emphasizes the need for ongoing research, innovation, and regulatory harmonization to overcome these obstacles and fully realize MNs' potential in treating skin diseases and improving patient welfare.

Advancements in Materials for 3D-Printed Microneedle Arrays: Enhancing Performance and Biocompatibility

The rapid advancement of 3D printing technology has revolutionized the fabrication of microneedle arrays (MNAs), which hold great promise in biomedical applications such as drug delivery, diagnostics, and therapeutic interventions. This review uniquely explores advanced materials used in the production of 3D-printed MNAs, including photopolymer resins, biocompatible materials, and composite resins, designed to improve mechanical properties, biocompatibility, and functional performance. Additionally, it introduces emerging trends such as 4D printing for programmable MNAs. By analyzing recent innovations, this review identifies critical challenges and proposes future directions to advance the field of 3D-printed MNAs. Unlike previous reviews, this paper emphasizes the integration of innovative materials with advanced 3D printing techniques to enhance both the performance and sustainability of MNAs.

Design of nanosystems for melanoma treatment

Melanoma is a prevalent and concerning form of skin cancer affecting millions of individuals worldwide. Unfortunately, traditional treatments can be invasive and painful, prompting the need for alternative therapies with improved efficacy and patient outcomes. Nanosystems offer a promising solution to these obstacles through the rational design of nanoparticles (NPs) which are structured into nanocomposite forms, offering efficient approaches to cancer treatment procedures. A range of NPs consisting of polymeric, metallic and metal oxide, carbon-based, and virus-like NPs have been studied for their potential in treating skin cancer. This review summarizes the latest developments in functional nanosystems aimed at enhancing melanoma treatment. The fundamentals of these nanosystems, including NPs and the creation of various functional nanosystem types, facilitating melanoma treatment are introduced. Then, the advances in the applications of functional nanosystems for melanoma treatment are summarized, outlining both their benefits and the challenges encountered in implementing nanosystem therapies.

3D Printed Microneedles for the Transdermal Delivery of NAD+ Precursor: Toward Personalization of Skin Delivery

3D printing of microneedles (μNDs) for transdermal therapy has the potential to enable patient personalization based on the target disease, site of application, and dosage requirements. To convert this concept to reality, it is necessary that the 3D printing technology can deliver high resolution, an affordable cost, and large print volumes. With the introduction of benchtop 4K and 8K 3D printers, it is now possible to manufacture medical devices like μNDs at sufficient resolution and low cost. In this research, we systematically optimized the 3D printing design parameters such as resin viscosity, print angle, layer height, and curing time to generate customizable μNDs. We have also developed an innovative 3D coating microtank device to optimize the coating method. We have applied this to the development of novel μNDs to deliver an established NAD+ precursor molecule, nicotinamide mononucleotide (NMN). A methacrylate-based polymer photoresin (eSun resin) was diluted with methanol to adjust the resin viscosity. The 3D print layer height of 25 μm yielded a smooth surface, thus reducing edge-ridge mismatches. Printing μNDs at 90° to the print platform yielded 84.28 ± 2.158% (n = 5) of the input height thus increasing the tip sharpness (48.52 ± 10.43 μm, n = 5). The formulation containing fluorescein (model molecule), sucrose (viscosity modifier), and Tween-20 (surface tension modifier) was coated on the μNDs using the custom designed microtank setup, and the amount deposited was determined fluorescently. The dye-coated μND arrays inserted into human skin (in vitro) showed a fluorescence signal at a depth of 150 μm (n = 3) into the skin. After optimization of the 3D printing parameters and coating protocol using fluorescein, NMN was coated onto the μNDs, and its diffusion was assessed in full-thickness human skin in vitro using a Franz diffusion setup. Approximately 189 ± 34.5 μg (5× dipped coated μNDs) of NMN permeated through the skin and 41.2 ± 7.53 μg was left in the skin after 24 h. Multiphoton microscopy imaging of NMN-coated μND treated mouse ear skin ex vivo demonstrated significantly (p < 0.05) increased free-unbound NADPH and reduced fluorescence lifetime of NADPH, both of which are indicative of cellular metabolic rates. Our study demonstrates that low-cost benchtop 3D printers can be used to print high-fidelity μNDs with the ability to rapidly coat and release NMN which consequently caused changes in intracellular NAD+ levels.

Electrical Microneedles for Wound Treatment

Electrical stimulation has been hotpot research and provoked extensive interest in a broad application such as wound closure, tissue injury repair, and nerve engineering. In particular, immense efforts have been dedicated to developing electrical microneedles, which demonstrate unique features in terms of controllable drug release, real-time monitoring, and therapy, thus greatly accelerating the process of wound healing. Here, a review of state-of-art research concerning electrical microneedles applied for wound treatment is presented. After a comprehensive analysis of the mechanisms of electrical stimulation on wound healing, the derived three types of electrical microneedles are clarified and summarized. Further, their applications in wound healing are highlighted. Finally, current perspectives and directions for the development of future electrical microneedles in improving wound healing are addressed.

Integrated Electrochemical Aptamer Biosensing and Colorimetric pH Monitoring via Hydrogel Microneedle Assays for Assessing Antibiotic Treatment

Current methods for therapeutic drug monitoring (TDM) have a long turnaround time as they involve collecting patients' blood samples followed by transferring the samples to medical laboratories where sample processing and analysis are performed. To enable real-time and minimally invasive TDM, a microneedle (MN) biosensor to monitor the levels of two important antibiotics, vancomycin (VAN) and gentamicin (GEN) is developed. The MN biosensor is composed of a hydrogel MN (HMN), and an aptamer-functionalized flexible (Flex) electrode, named HMN-Flex. The HMN extracts dermal interstitial fluid (ISF) and transfers it to the Flex electrode where sensing of the target antibiotics happens. The HMN-Flex performance is validated ex vivo using skin models as well as in vivo in live rat animal models. Data is leveraged from the HMN-Flex system to construct pharmacokinetic profiles for VAN and GEN and compare these profiles with conventional blood-based measurements. Additionally, to track pH and monitor patient's response during antibiotic treatment, an HMN is developed that employs a colorimetric method to detect changes in the pH, named HMN-pH assay, whose performance has been validated both in vitro and in vivo. Further, multiplexed antibiotic and pH detection is achieved by simultaneously employing the HMN-pH and HMN-Flex on live animals.

Silver Nanoclusters-Decorated Porous Microneedles Coupling Duplex-Specific Nuclease-Assisted Signal Amplification for Sampling and Detection of MicroRNA in Interstitial Fluid

MicroRNAs (miRNAs) in dermal interstitial fluid (ISF) have recently been recognized as clinically promising biomarkers for the diagnosis and prognosis of cancer. However, the detection poses significant challenges, primarily due to the low abundance of miRNAs and the limitations of current sampling techniques. To address this issue, we develop novel porous microneedles (PMNs) array-based sensor composed of poly(vinyl alcohol) porous hydrogel and DNA-templated silver nanoclusters (AgNCs) to facilitate the enrichment and highly sensitive detection of ISF miRNA. Leveraging the capillary action facilitated by its unique porous structure and the swelling properties of the hydrogel, the PMNs array can efficiently extract 2.7 ± 0.3 mg of ISF within 5 min. Additionally, the interconnected pores within the PMNs array contribute to an increased specific surface area, thereby offering a convenient platform for the decoration of DNA-templated AgNCs. The immobilized large amount of AgNCs effectively capture the target miRNA from the extracted ISF, resulting in miRNA-induced fluorescence quenching of AgNCs. Subsequently, the introduction of the duplex-specific nuclease leads to the cleavage of DNA in DNA-RNA heteroduplexes, which release miRNA to interact with other AgNCs. This process of target recycling triggers a further reduction in fluorescence intensity, thereby enabling sensitive detection of the low-abundant miRNA down to 1.6 pM. Both in vitro and in vivo experiments validate the efficacy of the AgNCs immobilized PMNs array for the detection of miRNA biomarkers in ISF within minutes. These results indicate that the proposed PMNs array-based sensor holds great potential for the development of noninvasive personalized diagnostic strategies.

Hyaluronic acid dissolving microneedle patch-assisted acupoint transdermal delivery of triptolide for effective rheumatoid arthritis treatment

Triptolide (TP), a major active component of the herb Tripterygium wilfordii Hook F, has been shown excellent pharmacological effects on rheumatoid arthritis. However, TP is prone to causing severe organ toxicity, which limits its clinical application. In recent years, microneedle technology has provided a new option for the treatment of arthritis due to its advantages of efficient local transdermal drug delivery. In this study, we constructed a microneedle platform to deliver TP locally to the joints, thereby enhancing TP penetration and reducing systemic toxicity. Additionally, we investigated whether acupoint drug delivery can produce a synergistic effect of needles and drugs. First, TP was loaded into microneedles using polyvinylpyrrolidone and hyaluronic acid as matrix materials. Next, we established a rat adjuvant-induced arthritis (AIA) model to evaluate the therapeutic effect of TP-loaded microneedles. The experiments showed that TP-loaded microneedles alleviated the AIA rats' inflammatory response, joint swelling, and bone erosion. However, there was no significant difference in the therapeutic effect observed in the acupoint and non-acupoint administration groups. In conclusion, TP-loaded microneedles have the advantages of safety, convenience, and high efficacy over conventional administration routes, laying a foundation for the transdermal drug delivery system-based treatment of rheumatoid arthritis.

Microneedle sensors for dermal interstitial fluid analysis

The rapid advancement in personalized healthcare has driven the development of wearable biomedical devices for real-time biomarker monitoring and diagnosis. Traditional invasive blood-based diagnostics are painful and limited to sporadic health snapshots. To address these limitations, microneedle-based sensing platforms have emerged, utilizing interstitial fluid (ISF) as an alternative biofluid for continuous health monitoring in a minimally invasive and painless manner. This review aims to provide a comprehensive overview of microneedle sensor technology, covering microneedle design, fabrication methods, and sensing strategy. Additionally, it explores the integration of monitoring electronics for continuous on-body monitoring. Representative applications of microneedle sensing platforms for both monitoring and therapeutic purposes are introduced, highlighting their potential to revolutionize personalized healthcare. Finally, the review discusses the remaining challenges and future prospects of microneedle technology.

Graphical Abstract

Multifunctional nanomaterials for smart wearable diabetic healthcare devices

Wearable diabetic healthcare devices have attracted great attention for real-time continuous glucose monitoring (CGM) using biofluids such as tears, sweat, saliva, and interstitial fluid via noninvasive ways. In response to the escalating global demand for CGM, these devices enable proactive management and intervention of diabetic patients with incorporated drug delivery systems (DDSs). In this context, multifunctional nanomaterials can trigger the development of innovative sensing and management platforms to facilitate real-time selective glucose monitoring with remarkable sensitivity, on-demand drug delivery, and wireless power and data transmission. The seamless integration into wearable devices ensures patient's compliance. This comprehensive review evaluates the multifaceted roles of these materials in wearable diabetic healthcare devices, comparing their glucose sensing capabilities with conventionally available glucometers and CGM devices, and finally outlines the merits, limitations, and prospects of these devices. This review would serve as a valuable resource, elucidating the intricate functions of nanomaterials for the successful development of advanced wearable devices in diabetes management.

Glucose detection: In-situ colorimetric analysis with double-layer hydrogel microneedle patch based on polyvinyl alcohol and carboxymethyl chitosan

Skin interstitial fluid (ISF) has emerged as a significant reservoir of biomarkers for disease diagnosis and prevention. Microneedle (MN) patches are regarded as an optimal platform for ISF extraction from the skin due to their non-invasive nature. However, challenges such as prolonged sampling durations and complex detection procedures impede timely metabolic analysis. In this investigation, we amalgamated MN technology with immobilized enzyme technology to fabricate a dual-layer MN patch integrating sampling and detection functionalities, thereby enabling in-situ colorimetric detection of hyperglycemia. The tip layer of the patch, comprising polyvinyl alcohol/carboxymethyl chitosan (PVA/CMCS) MN, was synthesized utilizing a chemical crosslinking approach for the first time, with glucose oxidase (GOx) being incorporated. The hydrophilicity of CMCS expedited the extraction process, facilitating the retrieval of approximately 10 mg of ISF within 10 min. The backing layer consisted of an immobilized polyvinyl alcohol-chitosan-horseradish peroxidase (PVA-CS-HRP) hydrogel film loaded with 3,3', 5,5'-tetramethylbenzidine (TMB). Incorporating macromolecular polymer PVA and CS for HRP immobilization addressed the issue of poor stability associated with traditional natural enzymes, thereby enhancing the sensitivity of the reaction system. The in-situ colorimetric sensor facilitated minimally invasive ISF extraction and swift conversion of glucose levels into detectable color changes.

Semi-invasive wearable clinic: Solution-processed smart microneedle electronics for next-generation integrated diagnosis and treatment

The integrated smart electronics for real-time monitoring and personalized therapy of disease-related analytes have been gradually gaining tremendous attention. However, human tissue barriers, including the skin barrier and brain-blood barrier, pose significant challenges for effective biomarker detection and drug delivery. Microneedle (MN) electronics present a promising solution to overcome these tissue barriers due to their semi-invasive structures, enabling effective drug delivery and target-analyte detection without compromising the tissue configuration. Furthermore, MNs can be fabricated through solution processing, facilitating large-scale manufacturing. This review provides a comprehensive summary of the recent three-year advancements in smart MNs development, categorized as follows. First, the solution-processed technology for MNs is introduced, with a focus on various printing technologies. Subsequently, smart MNs designed for sensing, drug delivery, and integrated systems combining diagnosis and treatment are separately summarized. Finally, the prospective and promising applications of next-generation MNs within mediated diagnosis and treatment systems are discussed.

Design of poly(vinyl pyrrolidone) and poly(ethylene glycol) microneedle arrays for delivering glycosaminoglycan, chondroitin sulfate, and hyaluronic acid

Osteoarthritis (OA) is a prevalent joint disorder characterized by cartilage and bone degradation. Medical therapies like glucosaminoglycan (GAG), chondroitin sulfate (CS), and hyaluronic acid (HA) aim to preserve joint function and reduce inflammation but may cause side effects when administered orally or via injection. Microneedle arrays (MNAs) offer a localized drug delivery method that reduces side effects. Thus, this study aims to demonstrate the feasibility of delivering GAG, CS, and HA using microneedles in vitro. An optimal needle geometry is crucial for the successful application of MNA. To address this, here we employ a multi-objective optimization framework using the non-dominated sorting genetic algorithm II (NSGA-II) to determine the ideal MNA design, focusing on preventing needle failure. Then, a three-step fabrication approach is followed to fabricate the MNAs. First, the master (male) molds are fabricated from poly(methyl methacrylate) using mechanical micromachining based on optimized needle geometry. Second, a micro-molding with Polydimethylsiloxane (PDMS) is used for the fabrication of production (female) molds. In the last step, the MNAs were fabricated by microcasting the hydrogels using the production molds. Light microscopy (LIMI) confirms the accuracy of the MNAs manufactured, and in vitro skin insertion tests demonstrate failure-free needle insertion. Subsequently, we confirmed the biocompatibility of MNAs by evaluating their impact on the L929 fibroblast cell line, human chondrocytes, and osteoblasts.

Optical blood glucose non-invasive detection and its research progress

Blood glucose concentration is an important index for the diagnosis of diabetes, its self-monitoring technology is the method for scientific diabetes management. Currently, the typical household blood glucose meters have achieved great success in diabetes management, but they are discrete detection methods, and involve invasive blood sampling procedures. Optical detection technologies, which use the physical properties of light to detect the glucose concentration in body fluids non-invasively, have shown great potential in non-invasive blood glucose detection. This article summarized and analyzed the basic principles, research status, existing problems, and application prospects of different optical glucose detection technologies. In addition, this article also discusses the problems of optical detection technology in wearable sensors and perspectives on the future of non-invasive blood glucose detection technology to improve blood glucose monitoring in diabetic patients.

A hyaluronic acid-based dissolving microneedle patch loaded with 5-aminolevulinic acid for improved oral leukoplakia treatment

INTRODUCTION

A local microneedle patch loaded with 5-aminolevulinic acid (ALA) was constructed to improve the efficiency of ALA photodynamic treatment of oral leukoplakia, reduce local photosensitivity reactions, and promote the healing of lesions.

METHODS

The microneedle patch loaded with ALA was constructed with the hyaluronic acid (HA) solution (ALA-HAMN), and its morphology, strength, mucosal penetration, and biocompatibility were tested.

RESULTS

In vivo safety and permeability tests confirmed that ALA-HAMN had good biocompatibility and could penetrate the mucosal barrier and quickly dissolve and release ALA for in situ transdermal administration. The 4-nitroquinoline oxide (NQO) rat model experiment showed that ALA-HAMN can significantly improve photodynamic therapy (PDT) efficiency and has no damage to mucosal tissue compared with the commonly used ALA cotton ball dressing.

CONCLUSIONS

The ALA-loaded microneedle patch was successfully constructed for the photodynamic treatment of oral leukoplakia, and the photodynamic efficiency and comfort of oral leukoplakia were improved, which provided an effective delivery mode to improve clinical ALA-PDT treatment of oral leukoplakia (OLK).

Remote-Controlled Sensing and Drug Delivery via 3D-Printed Hollow Microneedles

Remote health monitoring and treatment serve as critical drivers for advancing health equity, bridging geographical and socioeconomic disparities, ensuring equitable access to quality healthcare for those in underserved or remote regions. By democratizing healthcare, this approach offers timely interventions, continuous monitoring, and personalized care independent of one's location or socioeconomic status, thereby striving for an equitable distribution of health resources and outcomes. Meanwhile, microneedle arrays (MNAs), revolutionize painless and minimally invasive access to interstitial fluid for drug delivery and diagnostics. This paper introduces an integrated theranostic MNA system employing an array of colorimetric sensors to quantitatively measure -pH, glucose, and lactate, alongside a remotely-triggered system enabling on-demand drug delivery. Integration of an ultrasonic atomizer streamlines the drug delivery, facilitating rapid, pumpless, and point-of-care drug delivery, enhancing system portability while reducing complexities. An accompanying smartphone application interfaces the sensing and drug delivery components. Demonstrated capabilities include detecting pH (3 to 8), glucose (up to 16 mm), and lactate (up to 1.6 mm), showcasing on-demand drug delivery, and assessing delivery system performance via a scratch assay. This innovative approach confronts drug delivery challenges, particularly in managing chronic diseases requiring long-term treatment, while also offering avenues for non-invasive health monitoring through microneedle-based sensors.

A Versatile Cryomicroneedle Patch for Traceable Photodynamic Therapy

Photodynamic therapy (PDT) continues to encounter multifarious hurdles, stemming from the ineffectual preservation and delivery system of photosensitizers, the dearth of imaging navigation, and the antioxidant/hypoxic tumor microenvironment. Herein, a versatile cryomicroneedle patch (denoted as CMN-CCPH) is developed for traceable PDT. The therapeutic efficacy is further amplified by catalase (CAT)-induced oxygen (O2) generation and Cu2+-mediated glutathione (GSH) depletion. The CMN-CCPH is composed of cryomicroneedle (CMN) as the vehicle and CAT-biomineralized copper phosphate nanoflowers (CCP NFs) loaded with hematoporphyrin monomethyl ether (HMME) as the payload. Importantly, the bioactive function of HMME and CAT can be optimally maintained under the protection of CCPH and CMN for a duration surpassing 60 days, leading to bolstered bioavailability and notable enhancements in PDT efficacy. The in vivo visualization of HMME and oxyhemoglobin saturation (sO2) monitored by fluorescence (FL)/photoacoustic (PA) duplex real-time imaging unveils the noteworthy implications of CMN-delivered CCPH for intratumoral enrichment of HMME and O2 with reduced systemic toxicity. This versatile CMN patch demonstrates distinct effectiveness in neoplasm elimination, underscoring its promising clinical prospects.

Rapid and In-Field Sensing of Hydrogen Peroxide in Plant by Hydrogel Microneedle Patch

The rapidly changing climate is exacerbating the environmental stress that negatively impacts crop health and yield. Timely sensing of plant response to stress is beneficial to timely adjust planting conditions, promoting the healthy growth of plants, and improving plant productivity. Hydrogen peroxide (H2O2) is an important molecule of signal transduction in plants. However, the common methods for detecting H2O2  in plants are associated with certain drawbacks, such as long extraction time, cumbersome steps, dependence on large instruments, and difficulty in realizing in-field sensing. Therefore, it is urgent to establish more efficient detection methods to realize the rapid detection of H2O2 content in plants. In this research, poly (methyl vinyl ether-alt-maleic acid) (PMVE/MA) hydrogel microneedle (MN) patch for rapid extraction of leaf sap are prepared, and the extraction mechanism of PEG-crosslinked PMVE/MA hydrogel MN patch is studied. A method of rapid detection of H2O2 content in plants based on MN patch with optical detection technology is constructed. The hydrogel MN patch can be used for timely H2O2 analysis. This application enables new opportunities in plant engineering, and can be extended to the safety and health monitoring of other plants and animals.

Advances in Polysaccharide-Based Microneedle Systems for the Treatment of Ocular Diseases

The eye, a complex organ isolated from the systemic circulation, presents significant drug delivery challenges owing to its protective mechanisms, such as the blood-retinal barrier and corneal impermeability. Conventional drug administration methods often fail to sustain therapeutic levels and may compromise patient safety and compliance. Polysaccharide-based microneedles (PSMNs) have emerged as a transformative solution for ophthalmic drug delivery. However, a comprehensive review of PSMNs in ophthalmology has not been published to date. In this review, we critically examine the synergy between polysaccharide chemistry and microneedle technology for enhancing ocular drug delivery. We provide a thorough analysis of PSMNs, summarizing the design principles, fabrication processes, and challenges addressed during fabrication, including improving patient comfort and compliance. We also describe recent advances and the performance of various PSMNs in both research and clinical scenarios. Finally, we review the current regulatory frameworks and market barriers that are relevant to the clinical and commercial advancement of PSMNs and provide a final perspective on this research area.

Research Progress of Hydrogel Microneedles in Wound Management

Microneedles are a novel drug delivery system that offers advantages such as safety, painlessness, minimally invasive administration, simplicity of use, and controllable drug delivery. As a type of polymer microneedle with a three-dimensional network structure, hydrogel microneedles (HMNs) possess excellent biocompatibility and biodegradability and encapsulate various therapeutic drugs while maintaining drug activity, thus attracting significant attention. Recently, they have been widely employed to promote wound healing and have demonstrated favorable therapeutic effects. Although there are reviews about HMNs, few of them focus on wound management. Herein, we present a comprehensive overview of the design and preparation methods of HMNs, with a particular emphasis on their application status in wound healing, including acute wound healing, infected wound healing, diabetic wound healing, and scarless wound healing. Finally, we examine the advantages and limitations of HMNs in wound management and provide suggestions for future research directions.

Machine Learning Assists in the Design and Application of Microneedles

Microneedles (MNs), characterized by their micron-sized sharp tips, can painlessly penetrate the skin and have shown significant potential in disease treatment and biosensing. With the development of artificial intelligence (AI), the design and application of MNs have experienced substantial innovation aided by machine learning (ML). This review begins with a brief introduction to the concept of ML and its current stage of development. Subsequently, the design principles and fabrication methods of MNs are explored, demonstrating the critical role of ML in optimizing their design and preparation. Integration between ML and the applications of MNs in therapy and sensing were further discussed. Finally, we outline the challenges and prospects of machine learning-assisted MN technology, aiming to advance its practical application and development in the field of smart diagnosis and treatment.

Multifunctional Dopamine-Based Hydrogel Microneedle Electrode for Continuous Ketone Sensing

Diabetic ketoacidosis (DKA), a severe complication of type 1 diabetes (T1D), is triggered by production of large quantities of ketone bodies, requiring patients with T1D to constantly monitor their ketone levels. Here, a skin-compatible hydrogel microneedle (HMN)-continuous ketone monitoring (HMN-CKM) device is reported. The sensing mechanism relies on the catechol-quinone chemistry inherent to the dopamine (DA) molecules that are covalently linked to the polymer structure of the HMN patch. The DA serves the dual-purpose of acting as a redox mediator for measuring the byproduct of oxidation of 3-beta-hydroxybutyrate (β-HB), the primary ketone bodies; while, also facilitating the formation of a crosslinked HMN patch. A universal approach involving pre-oxidation and detection of the generated catechol compounds is introduced to correlate the sensor response to the β-HB concentrations. It is further shown that real-time tracking of a decrease in ketone levels of T1D rat model is possible using the HMN-CKM device, in conjunction with a data-driven machine learning model that considers potential time delays.

Wearable Aptalyzer Integrates Microneedle and Electrochemical Sensing for In Vivo Monitoring of Glucose and Lactate in Live Animals

Continuous monitoring of clinically relevant biomarkers within the interstitial fluid (ISF) using microneedle (MN)-based assays, has the potential to transform healthcare. This study introduces the Wearable Aptalyzer, an integrated system fabricated by combining biocompatible hydrogel MN arrays for ISF extraction with an electrochemical aptamer-based biosensor for in situ monitoring of blood analytes. The use of aptamers enables continuous monitoring of a wide range of analytes, beyond what is possible with enzymatic monitoring. The Wearable Aptalyzer is used for real-time and multiplexed monitoring of glucose and lactate in ISF. Validation experiments using live mice and rat models of type 1 diabetes demonstrate strong correlation between the measurements collected from the Wearable Aptalyzer in ISF and those obtained from gold-standard techniques for blood glucose and lactate, for each analyte alone and in combination. The Wearable Aptalyzer effectively addresses the limitations inherent in enzymatic detection methods as well as solid MN biosensors and the need for reliable and multiplexed bioanalytical monitoring in vivo.

Colorimetric sensing for translational applications: from colorants to mechanisms

Colorimetric sensing offers instant reporting via visible signals. Versus labor-intensive and instrument-dependent detection methods, colorimetric sensors present advantages including short acquisition time, high throughput screening, low cost, portability, and a user-friendly approach. These advantages have driven substantial growth in colorimetric sensors, particularly in point-of-care (POC) diagnostics. Rapid progress in nanotechnology, materials science, microfluidics technology, biomarker discovery, digital technology, and signal pattern analysis has led to a variety of colorimetric reagents and detection mechanisms, which are fundamental to advance colorimetric sensing applications. This review first summarizes the basic components (e.g., color reagents, recognition interactions, and sampling procedures) in the design of a colorimetric sensing system. It then presents the rationale design and typical examples of POC devices, e.g., lateral flow devices, microfluidic paper-based analytical devices, and wearable sensing devices. Two highlighted colorimetric formats are discussed: combinational and activatable systems based on the sensor-array and lock-and-key mechanisms, respectively. Case discussions in colorimetric assays are organized by the analyte identities. Finally, the review presents challenges and perspectives for the design and development of colorimetric detection schemes as well as applications. The goal of this review is to provide a foundational resource for developing colorimetric systems and underscoring the colorants and mechanisms that facilitate the continuing evolution of POC sensors.

Harnessing the role of microneedles as sensors: current status and future perspectives

In recent years, microneedles (MNs) have been transformed to serve a wide range of applications in the biomedical field. Their role as sensors in wearable devices has provided an alternative to blood-based monitoring of health and diagnostic methods. Hence, they have become a topic of research interest for several scientists working in the biomedical field. These MNs as sensors offer the continuous monitoring of biomarkers like glucose, nucleic acids, proteins, polysaccharides and electrolyte ions, which can therefore screen for and diagnose disease conditions in humans. The present review focuses on types of MN sensors and their applications. Various clinical trials and bottlenecks of MN R&D are also discussed.

Additive manufacturing of microneedles for sensing and drug delivery

INTRODUCTION

Microneedles (MNs) are miniaturized, painless, and minimally invasive platforms that have attracted significant attention over recent decades across multiple fields, such as drug delivery, disease monitoring, disease diagnosis, and cosmetics. Several manufacturing methods have been employed to create MNs; however, these approaches come with drawbacks related to complicated, costly, and time-consuming fabrication processes. In this context, employing additive manufacturing (AM) technology for MN fabrication allows for the quick production of intricate MN prototypes with exceptional precision, providing the flexibility to customize MNs according to the desired shape and dimensions. Furthermore, AM demonstrates significant promise in the fabrication of sophisticated transdermal drug delivery systems and medical devices through the integration of MNs with various technologies.

AREAS COVERED

This review offers an extensive overview of various AM technologies with great potential for the fabrication of MNs. Different types of MNs and the materials utilized in their fabrication are also discussed. Recent applications of 3D-printed MNs in the fields of transdermal drug delivery and biosensing are highlighted.

EXPERT OPINION

This review also mentions the critical obstacles, including drug loading, biocompatibility, and regulatory requirements, which must be resolved to enable the mass-scale adoption of AM methods for MN production, and future trends.

Baroreceptor-Inspired Microneedle Skin Patch for Pressure-Controlled Drug Release

Objective: We have developed a baroreceptor-inspired microneedle skin patch for pressure-controlled drug release. Impact Statement: This design is inspired by the skin baroreceptors, which are mechanosensitive elements of the peripheral nervous system. We adopt the finger touching to trigger the electric stimulation, ensuring a fast-response and user-friendly administration with potentially minimal off-target effects. Introduction: Chronic skin diseases bring about large, recurrent skin damage and often require convenient and timely transdermal treatment. Traditional methods lack spatiotemporal controllable dosage, leaving a risk of skin irritation or drug resistance issues. Methods: The patch consists of drug-containing microneedles and stretchable electrode array. The electrode array, integrated with the piezoconductive switch and flexible battery, provides a mild electric current only at the spot that is pressed. Drugs in microneedles will then flow along the current into the skin tissues. The stretchable feature also provides the mechanical robustness and electric stability of the device on large skin area. Results: This device delivers Cy3 dye in pig skin with spatiotemporally controlled dosage, showing ~8 times higher fluorescence intensity than the passive delivery. We also deliver insulin and observe the reduction of the blood glucose level in the mouse model upon pressing. Compared with passive delivery without pressing, the dosage of drugs released by the simulation is 2.83 times higher. Conclusion: This baroreceptor-inspired microneedle skin patch acts as a good example of the biomimicking microneedle device in the precise control of the drug release profile at the spatiotemporal resolution.

Advances in microneedles for transdermal diagnostics and sensing applications

Microneedles, the miniaturized needles, which can pierce the skin with minimal invasiveness open up new possibilities for constructing personalized Point-of-Care (POC) diagnostic platforms. Recent advances in microneedle-based POC diagnostic systems, especially their successful implementation with wearable technologies, enable biochemical detection and physiological recordings in a user-friendly manner. This review presents an overview of the current advances in microneedle-based sensor devices, with emphasis on the biological basis of transdermal sensing, fabrication, and application of different types of microneedles, and a summary of microneedle devices based on various sensing strategies. It concludes with the challenges and future prospects of this swiftly growing field. The aim is to present a critical and thorough analysis of the state-of-the-art development of transdermal diagnostics and sensing devices based on microneedles, and to bridge the gap between microneedle technology and pragmatic applications.