Flexible and Stretchable Microneedle Patches with Integrated Rigid Stainless Steel Microneedles for Transdermal Biointerfacing

Sliding Microneedle - Lateral flow immunoassay strip device for highly sensitive biomarker detection in interstitial fluid

Diabetes is a chronic disease with significant complications, necessitating regular treatment and checkups, which can be costly and time-consuming for patients. To address this, we developed the Sliding Microneedle (MN)-Lateral flow immunoassay strip (LFIAs) device that combines the advantages of MNs and LFIAs to detect IL-6, an independent biomarker for diabetes complications. This device offers rapid and highly sensitive detection of IL-6 by extracting interstitial fluid (ISF) through MNs and transferring it to LFIAs. The stainless MN, embedded in the 3D-printed Sliding MN-LFIAs device, was inserted into the skin at a 20° angle, minimizing blood contamination risk. With a filter paper attached to the MN surface, the device collected 4.65 ± 0.05 μL of ISF containing IL-6 within 90 s. The ISF was then transferred to the LFIAs using a running buffer. After a 15-min reaction, silver enhancement (SE) treatment was applied, allowing for the highly sensitive and specific detection of IL-6 at 102 pg/mL concentrations. The Sliding MN-LFIAs device successfully distinguished between normal and diabetic rat models, demonstrating its potential as an effective tool for detecting diabetes complications quickly and affordably.

Microneedle Patches-Integrated Transdermal Bioelectronics for Minimally Invasive Disease Theranostics

Wearable epidermal electronics with non- or minimally-invasive characteristics can collect, transduce, communicate, and interact with accessible physicochemical health indicators on the skin. However, due to the stratum corneum layer, rich information about body health is buried under the skin stratum corneum layer, for example, in the skin interstitial fluid. Microneedle patches are typically designed with arrays of special microsized needles of length within 1000 µm. Such characteristics potentially enable the access and sample of biomolecules under the skin or give therapeutical treatment painlessly and transdermally. Integrating microneedle patches with various electronics allows highly efficient transdermal bioelectronics, showing their great promise for biomedical and healthcare applications. This comprehensive review summarizes and highlights the recent progress on integrated transdermal bioelectronics based on microneedle patches. The design criteria and state-of-the-art fabrication techniques for such devices are initially discussed. Next, devices with different functions, including but not limited to health monitoring, drug delivery, and therapeutical treatment, are highlighted in detail. Finally, key issues associated with current technologies and future opportunities are elaborated to sort out the state of recent research, point out potential bottlenecks, and provide future research directions.

Advancements in transdermal drug delivery: A comprehensive review of physical penetration enhancement techniques

Transdermal drug administration has grown in popularity in the pharmaceutical research community due to its potential to improve drug bioavailability, compliance among patients, and therapeutic effectiveness. To overcome the substantial barrier posed by the stratum corneum (SC) and promote drug absorption within the skin, various physical penetration augmentation approaches have been devised. This review article delves into popular physical penetration augmentation techniques, which include sonophoresis, iontophoresis, magnetophoresis, thermophoresis, needle-free injection, and microneedles (MNs) Sonophoresis is a technique that uses low-frequency ultrasonic waves to break the skin's barrier characteristics, therefore improving drug transport and distribution. In contrast, iontophoresis uses an applied electric current to push charged molecules of drugs inside the skin, effectively enhancing medication absorption. Magnetophoresis uses magnetic fields to drive drug carriers into the dermis, a technology that has shown promise in aiding targeted medication delivery. Thermophoresis is the regulated heating of the skin in order to improve drug absorption, particularly with thermally sensitive drug carriers. Needle-free injection technologies, such as jet injectors (JIs) and microprojection arrays, offer another option by producing temporary small pore sizes in the skin, facilitating painless and effective drug delivery. MNs are a painless, minimally invasive method, easy to self-administration, as well as high drug bioavailability. This study focuses on the underlying processes, current breakthroughs, and limitations connected with all of these approaches, with an emphasis on their applicability in diverse therapeutic areas. Finally, a thorough knowledge of these physical enhancement approaches and their incorporation into pharmaceutical research has the potential to revolutionize drug delivery, providing more efficient and secure treatment choices for a wide range of health-related diseases.

Leveraging novel innovative thermoresponsive polymers in microneedles for targeted intradermal deposition

Microneedles have garnered considerable attention over the years as a versatile pharmaceutical platform that could be leveraged to deliver drugs into and across the skin. In the current work, poly (N-isopropylacrylamide) (PNIPAm) is synthesized and characterized as a novel material for the development of a physiologically responsive microneedle-based drug delivery system. Typically, this polymer transitions reversibly between a swell state at lower temperatures and a more hydrophobic state at higher temperatures, enabling precise drug release. This study demonstrates that dissolving microneedles patches made from PNIPAm, incorporating BIS-PNIPAm, a crosslinked polymer variant, exhibit enhanced mechanical properties, evident from a smaller height reduction in microneedle (∼10 %). Although microneedles using PNIPAm alone were achievable, it displayed poor mechanical strength, requiring the inclusion of additional polymeric excipients like PVA to enhance mechanical properties. In addition, the incorporation of a thermoresponsive polymer did not have a significant (p > 0.05) impact on the insertion properties of the needles as all formulations inserted to a similar depth of 500 µm into ex vivo skin. Furthering this, the needles were loaded with a model payload, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine perchlorate (DID) and the deposition of the cargo was monitored via multiphoton microscopy that showed that a deposit is formed at a depth of ≈200 µm. Also, it was revealed that crosslinked-PNIPAm (Bis-PNIPAm) formulations exhibited notable skin accumulationof the dye only after 4 h, independent of the excipient matrix used. This phenomenon was absent in non-crosslinked PNIPAm formulations, indicating a deposit formation in Bis-PNIPAm microneedle formulation. Collectively, this proof-of-concept study has advanced our understanding on the possibility to use PNIPAm for dissolving microneedle fabrication which could be harnessed for the deposition of nanoparticles into the dermis, for extended drug release within the skin.

Advancements in Skin-Mediated Drug Delivery: Mechanisms, Techniques, and Applications

Skin-mediated drug delivery methods currently are receiving significant attention as a promising approach for the enhanced delivery of drugs through the skin. Skin-mediated drug delivery offers the potential to overcome the limitations of traditional drug delivery methods, including oral administration and intravenous injection. The challenges associated with drug permeation through layers of skin, which act as a major barrier, are explored, and strategies to overcome these limitations are discussed in detail. This review categorizes skin-mediated drug delivery methods based on the means of increasing drug permeation, and it provides a comprehensive overview of the mechanisms and techniques associated with these methods. In addition, recent advancements in the application of skin-mediated drug delivery are presented. The review also outlines the limitations of ongoing research and suggests future perspectives of studies regarding the skin-mediated delivery of drugs.

Integration of polysaccharide electrospun nanofibers with microneedle arrays promotes wound regeneration: A review

Utilizing electrospun nanofibers and microneedle arrays in wound regeneration has been practiced for several years. Researchers have recently asserted that using multiple methods concurrently might enhance efficiency, despite the inherent strengths and weaknesses of each individual approach. The combination of microneedle arrays with electrospun nanofibers has the potential to create a drug delivery system and wound healing method that offer improved efficiency and accuracy in targeting. The use of microneedles with nanofibers allows for precise administration of pharmaceuticals due to the microneedles' capacity to pierce the skin and the nanofibers' role as a drug reservoir, resulting in a progressive release of drugs over a certain period of time. Electrospun nanofibers have the ability to imitate the extracellular matrix and provide a framework for cellular growth and tissue rejuvenation, while microneedle arrays show potential for enhancing tissue regeneration and enhancing the efficacy of wound healing. The integration of electrospun nanofibers with microneedle arrays may be customized to effectively tackle particular obstacles in the fields of wound healing and drug delivery. However, some issues must be addressed before this paradigm may be fully integrated into clinical settings, including but not limited to ensuring the safety and sterilization of these products for transdermal use, optimizing manufacturing methods and characterization of developed products, larger-scale production, optimizing storage conditions, and evaluating the inclusion of multiple therapeutic and antimicrobial agents to increase the synergistic effects in the wound healing process. This research examines the combination of microneedle arrays with electrospun nanofibers to enhance the delivery of drugs and promote wound healing. It explores various kinds of microneedle arrays, the materials and processes used, and current developments in their integration with electrospun nanofibers.

Advances in biomedical systems based on microneedles: design, fabrication, and application

Wearable devices have become prevalent in biomedical studies due to their convenient portability and potential utility in biomarker monitoring for healthcare. Accessing interstitial fluid (ISF) across the skin barrier, microneedle (MN) is a promising minimally invasive wearable technology for transdermal sensing and drug delivery. MN has the potential to overcome the limitations of conventional transdermal drug administration, making it another prospective mode of drug delivery after oral and injectable. Subsequently, combining MN with multiple sensing approaches has led to its extensive application to detect biomarkers in ISF. In this context, employing MN platforms and control schemes to merge diagnostic and therapeutic capabilities into theranostic systems will facilitate on-demand therapy and point-of-care diagnostics, paving the way for future MN technologies. A comprehensive analysis of the growing advances of microneedles in biomedical systems is presented in this review to summarize the latest studies for academics in the field and to offer for reference the issues that need to be addressed in MN application for healthcare. Covering an array of novel studies, we discuss the following main topics: classification of microneedles in the biomedical field, considerations of MN design, current applications of microneedles in diagnosis and therapy, and the regulatory landscape and prospects of microneedles for biomedical applications. This review sheds light on the significance of microneedle-based innovations, presenting an analysis of their potential implications and contributions to the community of wearable healthcare technologies. The review provides a comprehensive understanding of the field's current state and potential, making it a valuable resource for academics and clinicians seeking to harness the full potential of MN applications.

Skin preparation-free, stretchable microneedle adhesive patches for reliable electrophysiological sensing and exoskeleton robot control

High-fidelity and comfortable recording of electrophysiological (EP) signals with on-the-fly setup is essential for health care and human-machine interfaces (HMIs). Microneedle electrodes allow direct access to the epidermis and eliminate time-consuming skin preparation. However, existing microneedle electrodes lack elasticity and reliability required for robust skin interfacing, thereby making long-term, high-quality EP sensing challenging during body movement. Here, we introduce a stretchable microneedle adhesive patch (SNAP) providing excellent skin penetrability and a robust electromechanical skin interface for prolonged and reliable EP monitoring under varying skin conditions. Results demonstrate that the SNAP can substantially reduce skin contact impedance under skin contamination and enhance wearing comfort during motion, outperforming gel and flexible microneedle electrodes. Our wireless SNAP demonstration for exoskeleton robot control shows its potential for highly reliable HMIs, even under time-dynamic skin conditions. We envision that the SNAP will open new opportunities for wearable EP sensing and its real-world applications in HMIs.

Reverse iontophoresis generated by porous microneedles produces an electroosmotic flow for glucose determination

Blood glucose level is a key indicator of a patient's health, notably the symptoms associated with diabetes. Painless and continuously monitored interstitial glucose is highly preferable for diabetes management. Microneedle arrays can be used as an effective but minimally invasive technique to break the skin barrier. Simultaneous reverse iontophoresis enables non-invasive interstitial fluid extraction from the intercellular matrix ≤25 mm under the skin's surface. Here, we describe an ion-conductive porous microneedle (PMN)-based glucose sensing device combined with reverse ion electroosmosis, in which glucose extraction can be significantly enhanced. Four novel benefits of ionophoresis are concurrently brought about by the charged PMN: (1) decreased transdermal resistance with the low invasive penetration of highly resistant stratum corneum; (2) a reduction of transdermal resistance through interconnectivity; (3) the movement of larger molecules through linked micropores; and (4) the production of an electroosmotic flow (EOF). The EOF generated by PMN is effectively extracted from the skin interstitial fluid for glucose concentration measurement. And this will likely contribute to the long-term home management of chronic diseases.

Microneedle-based cell delivery and cell sampling for biomedical applications

Cell-based therapeutics are novel therapeutic strategies that can potentially treat many presently incurable diseases through novel mechanisms of action. Cell therapies may benefit from the ease, safety, and efficacy of administering therapeutic cells. Despite considerable recent technological and biological advances, several barriers remain to the clinical translation and commercialization of cell-based therapies, including low patient compliance, personal handling inconvenience, poor biosafety, and limited biocompatibility. Microneedles (MNs) are emerging as a promising biomedical device option for improved cell delivery with little invasion, pain-free administration, and simplicity of disposal. MNs have shown considerable promise in treating a wide range of diseases and present the potential to improve cell-based therapies. In this review, we first summarized the latest advances in the various types of MNs developed for cell delivery and cell sampling. Emphasis was given to the design and fabrication of various types of MNs based on their structures and materials. Then we focus on the recent biomedical applications status of MNs-mediated cell delivery and sampling, including tissue repair (wound healing, heart repair, and endothelial repair), cancer treatment, diabetes therapy, cell sampling, and other applications. Finally, the current status of clinical application, potential perspectives, and the challenges for clinical translation are also highlighted.

The use of cellulose, chitosan and hyaluronic acid in transdermal therapeutic management of obesity: A review

Obesity is a clinical condition with rising popularity and detrimental impacts on human health. According to the World Health Organization, obesity is the sixth most common cause of death worldwide. It is challenging to combat obesity because medications that are successful in the clinical investigation have harmful side effects when administered orally. The conventional approaches for treating obesity primarily entail synthetic compounds and surgical techniques but possess severe adverse effects and recurrences. As a result, a safe and effective strategy to combat obesity must be initiated. Recent studies have shown that biological macromolecules of the carbohydrate class, such as cellulose, hyaluronic acid, and chitosan, can enhance the release and efficacy of medications for obesity but due to their short biological half-lives and poor oral bioavailability, their distribution rate is affected. This helps to comprehend the need for an effective therapeutic approach via a transdermal drug delivery system. This review focuses on the transdermal administration, utilizing cellulose, chitosan, and hyaluronic acid via microneedles, as it offers a promising solution to overcome existing therapy limitations in managing obesity and it also highlights how microneedles can effectively deliver therapeutic substances through the skin's outer layer, bypassing pain receptors and specifically targeting adipose tissue.

Microneedle electrochemical aptamer-based sensing: Real-time small molecule measurements using sensor-embedded, commercially-available stainless steel microneedles

Microneedle sensors could enable minimally-invasive, continuous molecular monitoring - informing on disease status and treatment in real-time. Wearable sensors for pharmaceuticals, for example, would create opportunities for treatments personalized to individual pharmacokinetics. Here, we demonstrate a commercial-off-the-shelf (COTS) approach for microneedle sensing using an electrochemical aptamer-based sensor that detects the high-toxicity antibiotic, vancomycin. Wearable monitoring of vancomycin could improve patient care by allowing targeted drug dosing within its narrow clinical window of safety and efficacy. To produce sensors, we miniaturize the electrochemical aptamer-based sensors to a microelectrode format, and embed them within stainless steel microneedles (sourced from commercial insulin pen needles). The microneedle sensors achieve quantitative measurements in body-temperature undiluted blood. Further, the sensors effectively maintain electrochemical signal within porcine skin. This COTS approach requires no cleanroom fabrication or specialized equipment, and produces individually-addressable, sterilizable microneedle sensors capable of easily penetrating the skin. In the future, this approach could be adapted for multiplexed detection, enabling real-time monitoring of a range of biomarkers.

Innovative Fabrication of Hollow Microneedle Arrays Enabling Blood Sampling with a Self-Powered Microfluidic Patch

Microneedles are gaining a lot of attention in the context of sampling cutaneous biofluids such as capillary blood. Their minimal invasiveness and user-friendliness make them a prominent substitute for venous puncture or finger-pricking. Although the latter is suitable for self-sampling, the impracticality of manual handling and the difficulty of obtaining enough qualitative sample is driving the search for better solutions. In this context, hollow microneedle arrays (HMNAs) are particularly interesting for completely integrating sample-to-answer solutions as they create a duct between the skin and the sampling device. However, the fabrication of sharp-tipped HMNAs with a high aspect ratio (AR) is challenging, especially since a length of ≥1500 μm is desired to reach the blood capillaries. In this paper, we first described a novel two-step fabrication protocol for HMNAs in stainless steel by percussion laser drilling and subsequent micro-milling. The HMNAs were then integrated into a self-powered microfluidic sampling patch, containing a capillary pump which was optimized to generate negative pressure differences up to 40.9 ± 1.8 kPa. The sampling patch was validated in vitro, showing the feasibility of sampling 40 μL of liquid. It is anticipated that our proof-of-concept is a starting point for more sophisticated all-in-one biofluid sampling and point-of-care testing systems.

Microneedle Patch for Painless Intradermal Collection of Interstitial Fluid Enabling Multianalyte Measurement of Small Molecules, SARS-CoV-2 Antibodies, and Protein Profiling

Blood sampling is a common practice to monitor health, but it entails a series of drawbacks for patients including pain and discomfort. Thus, there is a demand for more convenient ways to obtain samples. Modern analytical techniques enable monitoring of multiple bioanalytes in smaller samples, opening possibilities for new matrices, and microsampling technologies to be adopted. Interstitial fluid (ISF) is an attractive alternative matrix that shows good correlation with plasma concentration dynamics for several analytes and can be sampled in a minimally invasive and painless manner from the skin at the point-of-care. However, there is currently a lack of sampling devices compatible with clinical translation. Here, to tackle state-of-the-art limitations, a cost-effective and compact single-microneedle-based device designed to painlessly collect precisely 1.1 µL of dermal ISF within minutes is presented. The fluid is volume-metered, dried, and stably stored into analytical-grade paper within the microfluidic device. The obtained sample can be mailed to a laboratory, quantitatively analyzed, and provide molecular insights comparable to blood testing. In a human study, the possibility to monitor various classes of molecular analytes is demonstrated in ISF microsamples, including caffeine, hundreds of proteins, and SARS-CoV-2 antibodies, some being detected in ISF for the first time.

Single step fabrication of hollow microneedles and an experimental package for controlled drug delivery

Hollow microneedle arrays (HMNs) are an excellent choice for managing chronic diseases requiring the administration of multiple drug doses over a prolonged duration. However, HMNs have gained partial success due to limitations in their manufacturing capabilities, and cumbersome processes. In the present study, polymeric HMNs were fabricated using a novel single-step drop-casting process without needing cleanroom facilities, and sophisticated instrumentation. When drop casted on the pyramidal tip stainless steel needles, the optimized polymer solution allowed the reproducible formation of desired height HMMs on a detachable acrylic base. To enable broader applications, the base with HMNs was integrated into an experimental package built to deliver a dose of ∼ 5 µL per 30° clockwise rotation of the actuator, allowing multiple metered drug dose administrations. The fabricated HMNs were optically imaged, and tested for mechanical integrity and stability. The working and functional utility of the HMNs package in delivering metered drug doses was demonstrated by delivering vitamin B12 (ex vivo) and insulin (in vivo), respectively. The optimized process can be used for the large-scale manufacturing of HMNs and the experimental package shows the potential to be further developed into a wearable device.

Treatment Regimens and Care Models for Older Patients Living with HIV: Are We Doing Enough?

With improved access to antiretroviral therapy throughout the world, people are aging with HIV, and a large portion of the global population of people with HIV (PWH) is now age 50 or older. Older PWH experience more comorbidities, aging-related syndromes, mental health challenges, and difficulties accessing fundamental needs than the population of older adults without HIV. As a result, ensuring that older PWH are receiving comprehensive healthcare can often be overwhelming for both PWH and the providers. Although there is a growing literature addressing the needs of this population, gaps remain in care delivery and research. In this paper, we suggest seven key components to any healthcare program designed to address the needs of older people with HIV: management of HIV, comorbidity screening and treatment, primary care coordination and planning, attention to aging related-syndromes, optimization of functional status, support of behavioral health, and improved access to basic needs and services. We review many of the difficulties and controversies related to the implementation of these components, which include the absence of screening guidelines for this population and the challenges of care integration, and we suggest key next steps.

Wearable microneedle-based electrochemical aptamer biosensing for precision dosing of drugs with narrow therapeutic windows

Therapeutic drug monitoring is essential for dosing pharmaceuticals with narrow therapeutic windows. Nevertheless, standard methods are imprecise and involve invasive/resource-intensive procedures with long turnaround times. Overcoming these limitations, we present a microneedle-based electrochemical aptamer biosensing patch (μNEAB-patch) that minimally invasively probes the interstitial fluid (ISF) and renders correlated, continuous, and real-time measurements of the circulating drugs' pharmacokinetics. The μNEAB-patch is created following an introduced low-cost fabrication scheme, which transforms a shortened clinical-grade needle into a high-quality gold nanoparticle-based substrate for robust aptamer immobilization and efficient electrochemical signal retrieval. This enables the reliable in vivo detection of a wide library of ISF analytes-especially those with nonexistent natural recognition elements. Accordingly, we developed μNEABs targeting various drugs, including antibiotics with narrow therapeutic windows (tobramycin and vancomycin). Through in vivo animal studies, we demonstrated the strong correlation between the ISF/circulating drug levels and the device's potential clinical use for timely prediction of total drug exposure.

Wearable Sensors for Healthcare: Fabrication to Application

This paper presents a substantial review of the deployment of wearable sensors for healthcare applications. Wearable sensors hold a pivotal position in the microelectronics industry due to their role in monitoring physiological movements and signals. Sensors designed and developed using a wide range of fabrication techniques have been integrated with communication modules for transceiving signals. This paper highlights the entire chronology of wearable sensors in the biomedical sector, starting from their fabrication in a controlled environment to their integration with signal-conditioning circuits for application purposes. It also highlights sensing products that are currently available on the market for a comparative study of their performances. The conjugation of the sensing prototypes with the Internet of Things (IoT) for forming fully functioning sensorized systems is also shown here. Finally, some of the challenges existing within the current wearable systems are shown, along with possible remedies.

Deep Eutectic Solvent Formulations and Alginate-Based Hydrogels as a New Partnership for the Transdermal Administration of Anti-Inflammatory Drugs

The transdermal administration of nonsteroidal anti-inflammatory drugs (NSAIDs) is a valuable and safer alternative to their oral intake. However, most of these drugs display low water solubility, which makes their incorporation into hydrophilic biopolymeric drug-delivery systems difficult. To overcome this drawback, aqueous solutions of bio-based deep eutectic solvents (DES) were investigated to enhance the solubility of ibuprofen, a widely used NSAID, leading to an increase in its solubility of up to 7917-fold when compared to its water solubility. These DES solutions were shown to be non-toxic to macrophages with cell viabilities of 97.4% (at ibuprofen concentrations of 0.25 mM), while preserving the anti-inflammatory action of the drug. Their incorporation into alginate-based hydrogels resulted in materials with a regular structure and higher flexibility. These hydrogels present a sustained release of the drug, which is able, when containing the DES aqueous solution comprising ibuprofen, to deliver 93.5% of the drug after 8 h in PBS. Furthermore, these hydrogels were able to improve the drug permeation across human skin by 8.5-fold in comparison with the hydrogel counterpart containing only ibuprofen. This work highlights the possibility to remarkably improve the transdermal administration of NSAIDs by combining new drug formulations based on DES and biopolymeric drug delivery systems.

Mapping the Mechanical and Immunological Profiles of Polymeric Microneedles to Enable Vaccine and Immunotherapy Applications

Biomaterials hold great promise for vaccines and immunotherapy. One emerging biomaterials technology is microneedle (MNs) delivery. MNs are arrays of micrometer-sized needles that are painless and efficiently deliver cargo to the specialized immunological niche of the skin. MNs typically do not require cold storage and eliminate medical sharps. Nearly all materials exhibit intrinsic properties that can bias immune responses toward either pro-immune or inhibitory effects. Thus, because MNs are fabricated from degradable polymers to enable cargo loading and release, understanding the immunological profiles of these matrices is essential to enable new MN vaccines and immunotherapies. Additionally, understanding the mechanical properties is important because MNs must penetrate the skin and conform to a variety of skin or tissue geometries. Here we fabricated MNs from important polymer classes – including extracellular matrix biopolymers, naturally-derived polymers, and synthetic polymers – with both high- and low-molecular-weights (MW). We then characterized the mechanical properties and intrinsic immunological properties of these designs. The library of polymer MNs exhibited diverse mechanical properties, while causing only modest changes in innate signaling and antigen-specific T cell proliferation. These data help inform the selection of MN substrates based on the mechanical and immunological requirements needed for a specific vaccine or immunotherapy application.

Skin Patchable Sensor Surveillance for Continuous Glucose Monitoring

Diabetes mellitus is a physiological and metabolic disorder affecting millions of people worldwide, associated with global morbidity, mortality, and financial expenses. Long-term complications can be avoided by frequent, continuous self-monitoring of blood glucose. Therefore, this review summarizes the current state-of-art glycemic control regimes involving measurement approaches and basic concepts. Following an introduction to the significance of continuous glucose sensing, we have tracked the evolution of glucose monitoring devices from minimally invasive to non-invasive methods to present an overview of the spectrum of continuous glucose monitoring (CGM) technologies. The conveniences, accuracy, and cost-effectiveness of the real-time CGM systems (rt-CGMs) are the factors considered for discussion. Transdermal biosensing and drug delivery routes have recently emerged as an innovative approach to substitute hypodermal needles. This work reviews skin-patchable glucose monitoring sensors for the first time, providing specifics of all the major findings in the past 6 years. Skin patch sensors and their progressive form, i.e., microneedle (MN) array sensory and delivery systems, are elaborated, covering self-powered, enzymatic, and non-enzymatic devices. The critical aspects reviewed are material design and assembly techniques focusing on flexibility, sensitivity, selectivity, biocompatibility, and user-end comfort. The review highlights the advantages of patchable MNs' multi-sensor technology designed to maintain precise blood glucose levels and administer diabetes drugs or insulin through a "sense and act" feedback loop. Subsequently, the limitations and potential challenges encountered from the MN array as rt-CGMs are listed. Furthermore, the current statuses of working prototype glucose-responsive "closed-loop" insulin delivery systems are discussed. Finally, the expected future developments and outlooks in clinical applications are discussed.

Insights into the mechanics of solid conical microneedle array insertion into skin using the finite element method

In order to develop optimum microneedle designs, researchers must first develop robust, repeatable and adaptable test methods which are representative of in vivo conditions. However, there is a lack of experimental tools which can accurately comparatively interrogate functional microneedle penetration of tissue. In this study, we seek to develop a state of the art finite element model of microneedle insertion into and penetration of human skin. The developed model employs a 3D hyperelastic, anisotropic pre-stressed multi-layered material which more accurately reflects in vivo skin conditions, while the microneedle is modeled as an array, which can capture the influence of adjacent microneedles on the overall response. Using the developed finite element model, we highlight the importance of accurate computational modeling which can decipher the mechanics of microneedle insertion, including the influence of its position within an array and how it correlates well with experimental observations. In particular, we have concluded that, for our model microneedle array, increasing skin pretension from 0 to 10% strain reduces the penetration force by 13%, ultimate local deformation about the microneedle by 22% and the ultimate penetration efficiency by 15%. We have also concluded that the presence of a base plate limits the penetration efficiency by up to 24%, while the penetration efficiency across a 5 × 1 microneedle array may vary by 27%. This model elucidates, for the first time, the combined effects of skin tension and needle geometry on accurately predicting microneedle penetration efficiency. STATEMENT OF SIGNIFICANCE: Microneedles arrays (MNAs) are medical devices with microscale protrusions, typically designed to penetrate the outermost layer of the skin, that upon optimisation, could lead to disruptive minimally-invasive disease management. However, the mechanics of MNA insertion are complex, due in part to a 'bed of nails' effect, and difficult to elucidate experimentally. Therefore, comparisons between designs, functional assessment of production batches and ultimately the likelihood of clinical translation are challenging to predict. Here, we have develop the most sophisticated in silico model of MNA insertion into pre-tensioned human skin to predict the extent of MNA penetration and therefore the likelihood of successful therapeutic delivery. Researchers can customise this model to predict the penetration efficiency of any MNA design.

Microscale engineering of hollow microneedle tips: design, manufacturing, optimization and validation

Transdermal and intradermal drug delivery utilizing microneedles is an emerging front in painless therapeutics. Drug delivery using hollow microneedles is the most preferred method for delivering generic transdermal drugs in the clinical setup. The needle tip must be extremely short as the drug is administered to sub-millimeter depths. Also, they need to be sharp enough to pierce through the skin with minimal skin flexing. There are multiple challenges in engineering a tip profile that is short and sharp at the same time. Stainless steel (SS) hypodermic needles with the lancet tip profile are ubiquitous in subcutaneous and intramuscular injections. They have long bevel lengths that make them inappropriate as microneedles. Thus, designing a unique tip profile and developing the manufacturing technology for microneedle applications are necessary. This article presents the design and optimization of microneedle tip profiles through analytical models. Further, manufacturing strategies for reliably obtaining designed profiles are discussed. The article concludes with experimental validation of improved piercing performance of the optimized tip profile compared to other tip profiles. The article discusses about tip geometries of stainless steel needles for microneedle applications, where depth of delivery is less than 1 mm. Through series of analyses, the optimum needle tip geometry evolved from single plane bevel (SPB) to hex plane bevel (HPB) progressively improving piercing performance.

An overview of microneedle applications, materials, and fabrication methods

Microneedle-based microdevices promise to expand the scope for delivery of vaccines and therapeutic agents through the skin and withdrawing biofluids for point-of-care diagnostics - so-called theranostics. Unskilled and painless applications of microneedle patches for blood collection or drug delivery are two of the advantages of microneedle arrays over hypodermic needles. Developing the necessary microneedle fabrication processes has the potential to dramatically impact the health care delivery system by changing the landscape of fluid sampling and subcutaneous drug delivery. Microneedle designs which range from sub-micron to millimetre feature sizes are fabricated using the tools of the microelectronics industry from metals, silicon, and polymers. Various types of subtractive and additive manufacturing processes have been used to manufacture microneedles, but the development of microneedle-based systems using conventional subtractive methods has been constrained by the limitations and high cost of microfabrication technology. Additive manufacturing processes such as 3D printing and two-photon polymerization fabrication are promising transformative technologies developed in recent years. The present article provides an overview of microneedle systems applications, designs, material selection, and manufacturing methods.

Translation of Polymeric Microneedles for Treatment of Human Diseases: Recent Trends, Progress, and Challenges

The ongoing search for biodegradable and biocompatible microneedles (MNs) that are strong enough to penetrate skin barriers, easy to prepare, and can be translated for clinical use continues. As such, this review paper is focused upon discussing the key points (e.g., choice polymeric MNs) for the translation of MNs from laboratory to clinical practice. The review reveals that polymers are most appropriately used for dissolvable and swellable MNs due to their wide range of tunable properties and that natural polymers are an ideal material choice as they structurally mimic native cellular environments. It has also been concluded that natural and synthetic polymer combinations are useful as polymers usually lack mechanical strength, stability, or other desired properties for the fabrication and insertion of MNs. This review evaluates fabrication methods and materials choice, disease and health conditions, clinical challenges, and the future of MNs in public healthcare services, focusing on literature from the last decade.

Recent Studies on Dispersion of Graphene-Polymer Composites

Graphene is an excellent 2D material that has extraordinary properties such as high surface area, electron mobility, conductivity, and high light transmission. Polymer composites are used in many applications in place of polymers. In recent years, the development of stable graphene dispersions with high graphene concentrations has attracted great attention due to their applications in energy, bio-fields, and so forth. Thus, this review essentially discusses the preparation of stable graphene-polymer composites/dispersions. Discussion on existing methods of preparing graphene is included with their merits and demerits. Among existing methods, mechanical exfoliation is widely used for the preparation of stable graphene dispersion, the theoretical background of this method is discussed briefly. Solvents, surfactants, and polymers that are used for dispersing graphene and the factors to be considered while preparing stable graphene dispersions are discussed in detail. Further, the direct applications of stable graphene dispersions are discussed briefly. Finally, a summary and prospects for the development of stable graphene dispersions are proposed.

3D-Printed Hydrogel-Filled Microneedle Arrays

Microneedle arrays (MNAs) have been used for decades to deliver drugs transdermally and avoid the obstacles of other delivery routes. Hydrogels are another popular method for delivering therapeutics because they provide tunable, controlled release of their encapsulated payload. However, hydrogels are not strong or stiff, and cannot be formed into constructs that penetrate the skin. Accordingly, it has so far been impossible to combine the transdermal delivery route provided by MNAs with the therapeutic encapsulation potential of hydrogels. To address this challenge, a low cost and simple, but robust, strategy employing MNAs is developed. These MNAs are formed from a rigid outer layer, 3D printed onto a conformal backing, and filled with drug-eluting hydrogels. Microneedles of different lengths are fabricated on a single patch, facilitating the delivery of various agents to different tissue depths. In addition to spatial distribution, temporal release kinetics can be controlled by changing the hydrogel composition or the needles' geometry. As a proof-of-concept, MNAs are used for the delivery of vascular endothelial growth factor (VEGF). Application of the rigid, resin-based outer layer allows the use of hydrogels regardless of their mechanical properties and makes these multicomponent MNAs suitable for a range of drug delivery applications.

Emerging Functional Biomaterials as Medical Patches

Medical patches have been widely explored and applied in various medical fields, especially in wound healing, tissue engineering, and other biomedical areas. Benefiting from emerging biomaterials and advanced manufacturing technologies, great achievements have been made on medical patches to evolve them into a multifunctional medical device for diverse health-care purposes, thus attracting extensive attention and research interest. Here, we provide up-to-date research concerning emerging functional biomaterials as medical patches. An overview of the various approaches to construct patches with micro- and nanoarchitecture is presented and summarized. We then focus on the applications, especially the biomedical applications, of the medical patches, including wound healing, drug delivery, and real-time health monitoring. The challenges and prospects for the future development of the medical patches are also discussed.

Microneedle-mediated transdermal drug delivery for treating diverse skin diseases

Transdermal drug delivery is an attractive route for dermatological disease therapy because it can directly target the lesion site on the skin, reduce adverse reactions associated with systemic administration, and improve patient compliance. However, the stratum corneum, as the main skin barrier, severely limits transdermal drug penetration, with compromised bioavailability. Microneedles (MNs), which are leveraged to markedly improve the penetration of therapeutic agents by piercing the stratum corneum and creating hundreds of reversible microchannels in a minimally invasive manner, have been envisioned as a milestone for effective transdermal drug delivery, especially for superficial disease therapy. Here, the emergence of versatile MNs for the transdermal delivery of various drugs is reviewed, particularly focusing on the application of MNs for the treatment of diverse skin diseases, including superficial tumors, scars, psoriasis, herpes, acne, and alopecia. Additionally, the promises and challenges of the widespread translation of MN-mediated transdermal drug delivery in the dermatology field are summarized.

Microneedles for painless transdermal immunotherapeutic applications

Immunotherapy has recently garnered plenty of attention to improve the clinical outcomes in the treatment of various diseases. However, owing to the dynamic nature of the immune system, this approach has often been challenged by concerns regarding the lack of adequate long-term responses in patients. The development of microneedles (MNs) has resulted in the improvement and expansion of immuno-reprogramming strategies due to the housing of high accumulation of dendritic cells, macrophages, lymphocytes, and mast cells in the dermis layer of the skin. In addition, MNs possess many outstanding properties, such as the ability for the painless traverse of the stratum corneum, minimal invasiveness, facile fabrication, excellent biocompatibility, convenient administration, and bypassing the first pass metabolism that allows direct translocation of therapeutics into the systematic circulation. These advantages make MNs excellent candidates for the delivery of immunological biomolecules to the dermal antigen-presenting cells in the skin with the aim of vaccinating or treating different diseases, such as cancer and autoimmune disorders, with minimal invasiveness and side effects. This review discusses the recent advances in engineered MNs and tackles limitations relevant to traditional immunotherapy of various hard-to-treat diseases.

Microneedle arrays for the treatment of chronic wounds

INTRODUCTION

Chronic wounds are seen frequently in diabetic and bedbound patients. Such skin injuries, which do not heal in a timely fashion, can lead to life-threatening conditions. In an effort to resolve the burdens of chronic wounds, numerous investigations have explored the efficacy of various therapeutics on wound healing. Therapeutics can be topically delivered to cutaneous wounds to reduce the complications associated with systemic drug delivery because the compromised skin barrier is not expected to negatively affect drug distribution. However, researchers have recently demonstrated that the complex environment of chronic wounds could lower the localized availability of the applied therapeutics. Microneedle arrays (MNAs) can be exploited to enhance delivery efficiency and consequently improved healing.

AREAS COVERED

In this review, we briefly describe the pathophysiology of chronic wounds and current treatment strategies. We further introduce methods and materials commonly used for the fabrication of MNAs. Subsequently, the studies demonstrating the benefits of MNAs in wound care are highlighted.

EXPERT OPINION

Microneedles have great potential to treat the complicated pathophysiology of chronic wounds. Challenges that will need to be addressed include development of a robust chronic wound model and MNAs that combine complex functionality with simplicity of use.

Microneedle-Based Delivery: An Overview of Current Applications and Trends

Microneedle arrays (MNA) are considered as one of the most promising resources to achieve systemic effects by transdermal delivery of drugs. They are designed as a minimally invasive, painless system which can bypass the stratum corneum, overcoming the potential drawbacks of subcutaneous injections and other transdermal delivery systems such as chemical enhancers, nano and microparticles, or physical treatments. As a trendy field in pharmaceutical and biomedical research, its applications are constantly evolving, even though they are based on very well-established techniques. The number of molecules administered by MNA are also increasing, with insulin and vaccines administration being the most investigated. Furthermore, MNA are being used to deliver cells and applied in other organs and tissues like the eyes and buccal mucosae. This review intends to offer a general overview of the current state of MNA research, focusing on the strategies, applications, and types of molecules delivered recently by these systems. In addition, some information about the materials and manufacturing processes is presented and safety data is discussed.

Geometrical optimisation of a personalised microneedle eye patch for transdermal delivery of anti-wrinkle small peptide

Acetyl-hexapeptide-3 (AHP-3) is a small peptide with good anti-wrinkle efficacy and safety profile. However, due to its hydrophilicity and high molecular weight, its skin permeation is generally poor. An innovative microneedle (MN) patch such as the curved, flexible or personalised MN patch is a viable avenue to deliver AHP-3. However, the well-researched geometrical relationship of MN on a flat MN patch cannot be assumed for these novel MN patches due to a complex mix of axial and shear forces. In this study, 3D printing was used for the fabrication of various MN patches with different MN geometries and curvatures. Both mechanical strength and skin penetration efficiency were used to determine the optimal MN geometry. The optimal MN geometry was then applied to the fabrication of a personalized MN patch (PMNP) for anti-wrinkle therapy, via 3D printing. In all, the general principles of MN geometrical effects on mechanical strength and skin penetration efficiency for a curved and a flat MN patch were similar. A MN height of 800 μm, tip diameter of 100 μm, interspacing of 800 μm and base diameter of 400 μm was observed to be the optimal MN geometry across all curvatures. In vitro skin permeation study demonstrated enhanced transdermal delivery of AHP-3 using the fabricated PMNP. Therefore, PMNP with optimized MN geometry can potentially be a novel approach to augment transdermal delivery of AHP-3 for effective wrinkle management.

Soft Bimodal Sensor Array Based on Conductive Hydrogel for Driving Status Monitoring

：Driving status monitoring is important to safety driving which could be adopted to improve driving behaviors through hand gesture detection by wearable electronics. The soft bimodal sensor array (SBSA) composed of strain sensor array based on ionic conductive hydrogels and capacitive pressure sensor array based on ionic hydrogel electrodes is designed to monitor drivers' hand gesture. SBSA is fabricated and assembled by the stretchable functional and structural materials through a sol-gel process for guaranteeing the overall softness of SBSA. The piezoresistive strain and capacitive pressure sensing abilities of SBSA are evaluated by the data acquisition system and signal analyzer with the external physical stimuli. The gauge factor (GF) of the strain sensor is 1.638 under stretched format, and -0.726 under compressed format; sensitivity of the pressure sensor is 0.267 kPa^-1 below 3.45 and 0.0757 kPa^-1 in the range of 3.45-12 kPa, which are sensitive enough to hand gesture detection and driving status monitoring. The simple recognition method for the driver's status behavior is proposed to identify the driver's behaviors with the piezoresistive properties of conductive polymers, and the turning angles are computed by the strain and pressure values from SBSA. This work demonstrates an effective approach to integrate SBSA seamlessly into an existing driving environment for driving status monitoring, expanding the applications of SBSA in wearable electronics.

Microneedle System for Transdermal Drug and Vaccine Delivery: Devices, Safety, and Prospects

Microneedle (MN) delivery system has been greatly developed to deliver drugs into the skin painlessly, noninvasively, and safety. In the past several decades, various types of MNs have been developed by the newer producing techniques. Briefly, as for the morphologically, MNs can be classified into solid, coated, dissolved, and hollow MN, based on the transdermal drug delivery methods of "poke and patch," "coat and poke," "poke and release," and "poke and flow," respectively. Microneedles also have other characteristics based on the materials and structures. In addition, various manufacturing techniques have been well-developed based on the materials. In this review, the materials, structures, morphologies, and fabricating methods of MNs are summarized. A separate part of the review is used to illustrate the application of MNs to deliver vaccine, insulin, lidocaine, aspirin, and other drugs. Finally, the review ends up with a perspective on the challenges in research and development of MNs, envisioning the future development of MNs as the next generation of drug delivery system.

A compendium of current developments on polysaccharide and protein-based microneedles

Microneedles (MNs), i.e. minimally invasive three-dimensional microstructures that penetrate the stratum corneum inducing relatively little or no pain, have been studied as appealing therapeutic vehicles for transdermal drug delivery. Over the last years, the fabrication of MNs using biopolymers, such as polysaccharides and proteins, has sparked the imagination of scientists due to their recognized biocompatibility, biodegradability, ease of fabrication and sustainable character. Owing to their wide range of functional groups, polysaccharides and proteins enable the design and preparation of materials with tunable properties and functionalities. Therefore, these biopolymer-based MNs take a revolutionary step offering great potential not only in drug administration, but also in sensing and response to physiological stimuli. In this review, a critical and comprehensive overview of the polysaccharides and proteins employed in the design and engineering of MNs will be given. The strategies adopted for their preparation, their advantages and disadvantages will be also detailed. In addition, the potential and challenges of using these matrices to deliver drugs, vaccines and other molecules will be discussed. Finally, this appraisal ends with a perspective on the possibilities and challenges in research and development of polysaccharide and protein MNs, envisioning the future advances and clinical translation of these platforms as the next generation of drug delivery systems.

Wearable All-Solid-State Potentiometric Microneedle Patch for Intradermal Potassium Detection

A new analytical all-solid-state platform for intradermal potentiometric detection of potassium in interstitial fluid is presented here. Solid microneedles are modified with different coatings and polymeric membranes to prepare both the potassium-selective electrode and reference electrode needed for the potentiometric readout. These microneedle-based electrodes are fixed in an epidermal patch suitable for insertion into the skin. The analytical performances observed for the potentiometric cell (Nernstian slope, limit of detection of 10^-4.9 potassium activity, linear range of 10^-4.2 to 10^-1.1, drift of 0.35 ± 0.28 mV h^-1), together with a fast response time, adequate selectivity, and excellent reproducibility and repeatability, are appropriate for potassium analysis in interstitial fluid within both clinical and harmful levels. The potentiometric response is maintained after several insertions into animal skin, confirming the resiliency of the microneedle-based sensor. Ex vivo tests based on the intradermal detection of potassium in chicken and porcine skin demonstrate that the microneedle patch is suitable for monitoring potassium changes inside the skin. In addition, the dimensions of the microneedles modified with the corresponding layers necessary to enhance robustness and provide sensing capabilities (1000 μm length, 45° tip angle, 15 μm thickness in the tip, and 435 μm in the base) agree with the required ranges for a painless insertion into the skin. In vitro cytotoxicity experiments showed that the patch can be used for at least 24 h without any side effect for the skin cells. Overall, the developed concept constitutes important progress in the intradermal analysis of ions related to an electrolyte imbalance in humans, which is relevant for the control of certain types of diseases.

Scanning electron microscopy examination of needle tips after different procedures of deep dry needling in humans

The aim of this study was to evaluate the tips and the surface conditions of two types of needles with different quality and their possible alterations after performing different needling on human beings. A total of 160 needles from AguPunt brand were examined. Surface conditions (lumps and scratches) and tip of the needles after needling procedures in humans were tested using a JEOL JSM-6360LV microscopy device. Additionally, a group of physiotherapists assessed the use of both types of needles in clinical practice using a self-reported questionnaire. Both types of needles, after performing different needling on human beings, kept the needle tips well preserved although the dry needle (Type B) suffered very little deformation even touching the bone of the scapula 10 times versus acupuncture needle (Type A), which were deformed slightly. The surface conditions revealed irregularities and scratches in both types of needles but the tips of Type A suffered more damage after different procedures (Odds ratio = 0.04,95% CI:0.01-0.13, p < 0.001). The cellular tissue adhered to the surface was similar in both types of needles and the questionnaire about clinical practice of both types of needles showed that Type B seemed easier than Type A when the physical therapist penetrated the skin and when the needle went out the skin.

Cationic Moieties in Polystyrene Gels Swollen with d-Limonene Improved Transdermal Delivery System

d-limonene, a terpene and natural compound, has been found to be an excellent penetration enhancer for transdermal drug delivery (TDD). It hence has been incorporated within various transdermal formulations. Herein, we report the application of polystyrene gel swollen with d-limonene and its derivatives for TDD. Poly(styrene-co-divinylbenzene) (PS gel), poly(styrene-co-divinylbenzene-co-4-vinylpyridine) (PS-4VP) gel and poly(styrene-co-divinylbenzene-co-(vinylbenzyl) trimethylammonium chloride) (PS-VBAC gel) were employed as chemical gels to improve the stability of the TDD substrates. The drug permeation properties from the PS gels swollen in limonene were examined, regarding the effect of its network density as well as their rheological properties. The lowest density of the network showed the highest steady flux of the permeation at 43.7 ± 0.3 μg/cm². FT-IR spectra were confirmed for PS-4VP and PS-VBAC, bearing cationic moieties and they could control the release of ibuprofen by the electrostatic interaction at the interface of organogel and skin. The steady state flux of skin permeation got low values from 55.2 ± 0.8 to 11.6 ± 2.0 μg/cm², when the cationic moieties were increased. Moreover, the chemical network of PS gel swollen in limonene showed high mechanical stability illustrated by elastic modulus (G') of about 98 kPa for 10% cross-linked PS gel. The developed PS gels swollen in limonene show highly promising results, suggesting their possible application in TDD.

Three-Dimensional (3D) Printed Microneedles for Microencapsulated Cell Extrusion

Cell-hydrogel based therapies offer great promise for wound healing. The specific aim of this study was to assess the viability of human hepatocellular carcinoma (HepG2) cells immobilized in atomized alginate capsules (3.5% (w/v) alginate, d = 225 µm ± 24.5 µm) post-extrusion through a three-dimensional (3D) printed methacrylate-based custom hollow microneedle assembly (circular array of 13 conical frusta) fabricated using stereolithography. With a jetting reliability of 80%, the solvent-sterilized device with a root mean square roughness of 158 nm at the extrusion nozzle tip (d = 325 μm) was operated at a flowrate of 12 mL/min. There was no significant difference between the viability of the sheared and control samples for extrusion times of 2 h (p = 0.14, α = 0.05) and 24 h (p = 0.5, α = 0.05) post-atomization. Factoring the increase in extrusion yield from 21.2% to 56.4% attributed to hydrogel bioerosion quantifiable by a loss in resilience from 5470 (J/m³) to 3250 (J/m³), there was no significant difference in percentage relative payload (p = 0.2628, α = 0.05) when extrusion occurred 24 h (12.2 ± 4.9%) when compared to 2 h (9.9 ± 2.8%) post-atomization. Results from this paper highlight the feasibility of encapsulated cell extrusion, specifically protection from shear, through a hollow microneedle assembly reported for the first time in literature.

The Influence of Microneedles on the Percutaneous Penetration of Selected Antihypertensive Agents: Diltiazem Hydrochloride and Perindopril Erbumine

BACKGROUND

It is well documented in the scientific literature that high blood pressure can lead to cardiovascular disease. Untreated hypertension has clinical consequences such as coronary artery disease, stroke or kidney failure. Diltiazem hydrochloride (DH), a calcium-channel blocker, and perindopril erbumine (PE), an inhibitor of the angiotensin converting enzyme are used for the management of hypertension.

OBJECTIVE

This project will examine the effect of microneedle rollers on the transport of DH and PE across pig ear skin. The use of the transcutaneous route of administration reduces and in sometimes eliminates the trauma and pain associated with injections. Furthermore, there is increased patient compliance. The purpose of this project was to study the effect of stainless steel microneedles on the transdermal delivery of DH and PE.

METHOD

We utilized vertical Franz diffusion cells to study in vitro transport of DH and PE across microneedle- treated pig ear skin. Confocal laser scanning microscopy (CLSM) was used to characterize microchannel depth. Transdermal flux values were determined from the slope of the linear portion of the cumulative amount versus time curve.

RESULTS

There was a 113.59-fold increase in the transdermal permeation of DH following the application of microneedle roller compared to passive diffusion.

CONCLUSION

In the case of PE, there was an 11.99-fold increase in the drug transport across pig skin following the application of microneedle rollers in comparison with passive diffusion. Student's t-test and Mann-Whitney's rank sum test were used to determine statistically significant differences between experimental and control groups.

Recent Advances in Wearable Transdermal Delivery Systems

Wearable transdermal delivery systems have recently received tremendous attention due to their noninvasive, convenient, and prolonged administration of pharmacological agents. Here, the material prospects, fabrication processes, and drug-release mechanisms of these types of therapeutic delivery systems are critically reviewed. The latest progress in the development of multifunctional wearable devices capable of closed-loop sensation and drug delivery is also discussed. This survey reveals that wearable transdermal delivery has already made an impact in diverse healthcare applications, while several grand challenges remain.

Transfer-molded wrappable microneedle meshes for perivascular drug delivery

After surgical procedures such as coronary/peripheral bypass grafting or endarterectomy for the treatment of organ ischemia derived from atherosclerosis, intimal hyperplasia (IH) which leads to restenosis or occlusion at the site of graft anastomosis frequently occurs. In order to inhibit IH caused by abnormal growth of smooth muscle cells (SMCs) in tunica media, various perivascular drug delivery devices are reported for delivery of anti-proliferation drugs into vascular tissue. However, there still remain conflicting requirements such as local and unidirectional delivery vs device porosity, and conformal tight device installation vs pulsatile expansion and constriction of blood vessels. In this study, a biodegradable microneedle (MN) array is developed on a flexible woven surgical mesh using a transfer molding method. Mechanical properties of 'wrappable' MN meshes are investigated and compared to the properties of blood vessels. Ex vivo and in vivo animal studies demonstrate enhanced drug delivery efficiency, efficacy for IH reduction, and safety of MN mesh. In particular, MN mesh showed significantly reduced neointiamal formation (11.1%) compared to other competitive groups (23.7 and 22.2%) after 4-week in vivo animal study. Additionally, wrappable MN meshes effectively suppressed side effects such as IH due to mechanical constriction, loss of toxic drug to the surroundings, and cell death that were frequently observed with other previous perivascular drug delivery devices.