Fabrication of coated polymer microneedles for transdermal drug delivery

Tailoring Design of Microneedles for Drug Delivery and Biosensing

Microneedles (MNs) are emerging as versatile tools for both therapeutic drug delivery and diagnostic monitoring. Unlike hypodermic needles, MNs achieve these applications with minimal or no pain and customizable designs, making them suitable for personalized medicine. Understanding the key design parameters and the challenges during contact with biofluids is crucial to optimizing their use across applications. This review summarizes the current fabrication techniques and design considerations tailored to meet the distinct requirements for drug delivery and biosensing applications. We further underscore the current state of theranostic MNs that integrate drug delivery and biosensing and propose future directions for advancing MNs toward clinical use.

Seeing through the skin: Optical methods for visualizing transdermal drug delivery with microneedles

Optical methods play a pivotal role in advancing transdermal drug delivery research, particularly with the emergence of microneedle technology. This review presents a comprehensive analysis of optical methods used in studying transdermal drug delivery facilitated by microneedle technology. Beginning with an introduction to microneedle technology and skin anatomy and optical properties, the review explores the integration of optical methods for enhanced visualization. Optical imaging offers key advantages including real-time drug distribution visualization, non-invasive skin response monitoring, and quantitative drug penetration analysis. A spectrum of optical imaging modalities ranging from conventional dermoscopy and stereomicroscopy to advance techniques as fluorescence microscopy, laser scanning microscopy, in vivo imaging system, two-photon microscopy, fluorescence lifetime imaging microscopy, optical coherence tomography, Raman microspectroscopy, laser speckle contrast imaging, and photoacoustic microscopy is discussed. Challenges such as resolution and depth penetration limitations are addressed alongside potential breakthroughs and future directions in optical techniques development. The review underscores the importance of bridging the gap between preclinical and clinical studies, explores opportunities for integrating optical imaging and chemical sensing methods with drug delivery systems, and highlight the importance of non-invasive "optical biopsy" as a valuable alternative to conventional histology. Overall, this review provides insight into the role of optical methods in understanding transdermal drug delivery mechanisms with microneedles.

A systematic review of microneedles technology in drug delivery through a bibliometric and patent overview

The transdermal drug delivery (TDD) route has gathered considerable attention for its potential to improve therapeutic efficacy while minimizing systemic side effects. Among transdermal technologies, microneedle (MN) devices have proven to be a promising approach that combines the advantages of traditional needle injections and non-invasive topical applications. This review provides a comprehensive analysis of progress in transdermal drug delivery systems (TDDS) via MN from 2000 to 2023, integrating bibliometric analysis and patent landscape to present a multi-faceted perspective on the evolution of this technology. The study identifies key trends, challenges, and opportunities in the research, implementation, and commercialization of MN tools through a systematic examination of scientific literature and an extensive investigation of global patent databases. The study of bibliometric trends reveals the leading experts, organizations, companies, and countries contributing to this field, collaboration networks, and the thematic evolution of research topics. The patent analysis offers insights into innovative trajectories, key players, and geographical distribution of intellectual property. This review resumes the latest advancements in MN devices and provides a strategic outlook that can guide future research directions, promote partnerships, and inform stakeholders involved in the development of TDDS.

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.

Self-Assembly of Microstructured Protein Coatings with Programmable Functionality for Fluorescent Biosensors

Proteins, as genetically programmable functional macromolecules, hold immense potential as biocompatible self-assembling building blocks, owing to their versatility in building coating materials and programming their functionality genetically. In this study, we demonstrate a modular self-assembly of protein coatings that are genetically programmable for a biosensor application. We designed and produced recombinant fusion protein building blocks to form microstructured coatings on diverse substrates, such as glass or polymers, through thermally triggered liquid-liquid phase separation and an orthogonal high-affinity coiled-coil interaction. We incorporated fluorescence proteins into coatings and controlled the protein density to enable fluorescence imaging and quantification in a low-resource setting. Then, we created a coating for a calcium biosensor using a genetically engineered calcium indicator protein. This protein coating served as the foundation for our smartphone-based fluorescent biosensor, which successfully measured free calcium concentrations in the millimolar range at which extracellular calcium homeostasis is maintained. Using this fluorescent biosensor, we were able to detect abnormal physiological conditions, such as mild or moderate hypercalcemia. We envision that this modular and genetically programmable functional protein coating platform could be extended to the development of highly accessible, low-cost fluorescent biosensors for a variety of targets.

Optimizing CNC milling parameters for manufacturing of ultra-sharp tip microneedle with various tip angles

Microneedle technology has emerged as an advanced method for transdermal drug delivery, which focuses on diverse fabrication techniques to develop microneedles with various models and geometries. This study explores the application of Computer Numerical Control (CNC) milling technology to create microneedle master molds with extremely sharp tips. We examined the effects of two key machining parameters, feed rate and ramp angle, on the tip sharpness of the microneedles. Our results showed that increasing both the feed rate and ramp angle could significantly reduce machining time. However, a higher feed rate also led to larger tip diameters and notable tip defects. Conversely, changes in the ramp angle at a constant feed rate had minimal impact on tip size. We identified an optimal condition balancing cutting time and tip sharpness at a feed rate of 100 mm/min and a ramp angle of 1.5°. Additionally, we assessed the CNC's capability to produce needles with different tip angles. The findings confirm that needles with varying tip angles maintained tip diameters below 10 μm, with needles having a 50° tip angle exhibiting the sharpest tips at approximately 3.3 μm. Further compression, insertion and diffusion tests were conducted to evaluate the performance of needles with different geometries.

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.

Panoramic review on polymeric microneedle arrays for clinical applications

Transdermal drug delivery (TDD) has significantly advanced medical practice in recent years due to its ability to prevent the degradation of substances in the gastrointestinal tract and avoid hepatic metabolism. Among different available approaches, microneedle arrays (MNAs) technology represents a fascinating delivery tool for enhancing TDD by penetrating the stratum corneum painless and minimally invasive for delivering antibacterial, antifungal, and antiviral medications. Polymeric MNAs are extensively utilized among many available materials due to their biodegradability, biocompatibility, and low toxicity. Therefore, this review provides a comprehensive discussion of polymeric MNAs, starting with understanding stratum corneum and developing MNA technology. Furthermore, the engineering concepts, fundamental considerations, challenges, and future perspectives of polymeric MNAs in clinical applications are properly outlined, offering a comprehensive and unique overview of polymeric MNAs and their potential for a broad spectrum of clinical applications.

Emerging Trends in Dissolving-Microneedle Technology for Antimicrobial Skin-Infection Therapies

Skin and soft-tissue infections require significant consideration because of their prolonged treatment duration and propensity to rapidly progress, resulting in severe complications. The primary challenge in their treatment stems from the involvement of drug-resistant microorganisms that can form impermeable biofilms, as well as the possibility of infection extending deep into tissues, thereby complicating drug delivery. Dissolving microneedle patches are an innovative transdermal drug-delivery system that effectively enhances drug penetration through the stratum corneum barrier, thereby increasing drug concentration at the site of infection. They offer highly efficient, safe, and patient-friendly alternatives to conventional topical formulations. This comprehensive review focuses on recent advances and emerging trends in dissolving-microneedle technology for antimicrobial skin-infection therapy. Conventional antibiotic microneedles are compared with those based on emerging antimicrobial agents, such as quorum-sensing inhibitors, antimicrobial peptides, and antimicrobial-matrix materials. The review also highlights the potential of innovative microneedles incorporating chemodynamic, nanoenzyme antimicrobial, photodynamic, and photothermal antibacterial therapies. This review explores the advantages of various antimicrobial therapies and emphasizes the potential of their combined application to improve the efficacy of microneedles. Finally, this review analyzes the druggability of different antimicrobial microneedles and discusses possible future developments.

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).

Microneedle system for tissue engineering and regenerative medicines: a smart and efficient therapeutic approach

The global demand for an enhanced quality of life and extended lifespan has driven significant advancements in tissue engineering and regenerative medicine. These fields utilize a range of interdisciplinary theories and techniques to repair structurally impaired or damaged tissues and organs, as well as restore their normal functions. Nevertheless, the clinical efficacy of medications, materials, and potent cells used at the laboratory level is always constrained by technological limitations. A novel platform known as adaptable microneedles has been developed to address the abovementioned issues. These microneedles offer a solution for the localized distribution of various cargos while minimizing invasiveness. Microneedles provide favorable patient compliance in clinical settings due to their effective administration and ability to provide a painless and convenient process. In this review article, we summarized the most recent development of microneedles, and we started by classifying various microneedle systems, advantages, and fundamental properties. Subsequently, it provides a comprehensive overview of different types of microneedles, the material used to fabricate microneedles, the fundamental properties of ideal microneedles, and their applications in tissue engineering and regenerative medicine, primarily focusing on preserving and restoring impaired tissues and organs. The limitations and perspectives have been discussed by concluding their future therapeutic applications in tissue engineering and regenerative medicines.

Biomaterial-Based Sustained-Release Drug Formulations for Localized Cancer Immunotherapy

Cancer immunotherapy has revolutionized clinical cancer treatments by taking advantage of the immune system to selectively and effectively target and kill cancer cells. However, clinical cancer immunotherapy treatments often have limited efficacy and/or present severe adverse effects associated primarily with their systemic administration. Localized immunotherapy has emerged to overcome these limitations by directly targeting accessible tumors via local administration, reducing potential systemic drug distribution that hampers drug efficacy and safety. Sustained-release formulations can prolong drug activity at target sites, which maximizes the benefits of localized immunotherapy to increase the therapeutic window using smaller dosages than those used for systemic injection, avoiding complications of frequent dosing. The performance of sustained-release formulations for localized cancer immunotherapy has been validated preclinically using various implantable and injectable scaffold platforms. This review introduces the sustained-release formulations developed for localized cancer immunotherapy and highlights their biomaterial-based platforms for representative classes, including inorganic scaffolds, natural hydrogels, synthetic hydrogels, and microneedle patches. The design rationale and other considerations are summarized for further development of biomaterials for the construction of optimal sustained-release formulations.

Microneedle-mediated drug delivery for neurological diseases

Neurological disorders, including brain injury, brain tumors, and neurodegenerative diseases, rank as the second leading cause of death worldwide. Exploring effective new treatments for neurological disorders has long been a hot research issue in clinical practice. Recently, microneedles (MNs) have attracted much attention due to their designation as a "painless and non-invasive" novel transdermal delivery method, characterized by their biocompatibility and sustainability. The advantages of MNs open an avenue for potential therapeutic interventions targeting neurological disorders. This review presents a concise overview of progress in the field of MNs, with highlights on the application in the treatment of neurological disorders. Notably, trends in the development of MNs and future challenges are also discussed.

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.

On-demand drug delivery bioelectronics through a water-processable low dimensional highly conductive MXene layer

On-demand drug delivery holds great promise to optimize pharmaceutical efficacy while minimizing the side effects. However, existing on-demand drug delivery systems often require complicated manufacturing processes that preclude their wide implementation of a broad range of drugs. In this work, we demonstrate the introduction of MXene-coated microneedles (MNs) into bioelectronics for digitally controllable gate-valve drug delivery. MXenes, featuring high electronic conductivity, excellent biocompatibility, and solution processibility, enable low-cost scalability for printable bioelectronics. In an electrolytic state (e.g., body fluid), the coated MXene is oxidized and desorbed due to redox reactions caused by electrical bias, allowing the underlying drug to be controllably released. The MXene-incorporated drug delivery system not only demonstrates excellent biocompatibility and operational stability, but also features low-cost construction and sustainable usage. Besides, these MXene-coated MNs allow both on-demand transformation and local-region customization, further increasing the structural versatility and capability of multidrug delivery systems.

Advances in novel biomaterials combined with traditional Chinese medicine rehabilitation technology in treatment of peripheral nerve injury

Peripheral nerve injuries (PNI) represent one of the primary neuropathies leading to lifelong disability. Nerve regeneration and targeted muscle atrophy stand as the two most crucial factors influencing functional rehabilitation post peripheral nerve injury. Over time, traditional Chinese medicine (TCM) rehabilitation approaches such as acupuncture, Tuina, and microneedles serve as pivot means to activate the regeneration of injured nerve Schwann cells. By promoting axon regeneration, these approaches can accomplish nerve repair, reconstruction, and functional rehabilitation. Although TCM rehabilitation approaches have clinically demonstrated effectiveness in promoting the repair and regeneration of PNI, the related molecular mechanisms remain unclear. This significantly hampers the application and promotion of TCM rehabilitation in PNI recovery. Therefore, deeply delving into the cellular and molecular mechanisms of TCM rehabilitation technologies to foster nerve regeneration stands as the most pressing issue. On the other hand, in recent years, novel biomaterials represented by hydrogels, microfluidic platforms, and new chitosan scaffolds have showed their unique roles in treating various degrees of nerve injury. These methods exhibit immense potential in conducting high-throughput cell and organoid culture in vitro and synthesizing diverse tissue engineering scaffolds and drug carriers. We believe that the combination of TCM rehabilitation technology and novel biomaterials can more effectively address precise treatment issues such as identification of treatment target and dosage control. Therefore, this paper not only summarizes the molecular mechanisms of TCM rehabilitation technology and novel biomaterials in treating peripheral nerve injury individually, but also explores the research direction of precise treatment by integrating the two at both macro and micro levels. Such integration may facilitate the exploration of cellular and molecular mechanisms related to neurodegeneration and regeneration, providing a scientific and theoretical foundation for the precise functional rehabilitation of PNI in the future.

Spiderweb-Shaped Iron-Coordinated Polymeric Network as the Novel Coating on Microneedles for Transdermal Drug Delivery Against Infectious Wounds

Coated microneedles (CMNs) are a minimally invasive platform for immediate-release transdermal drug delivery. However, the practical applications of CMNs have been significantly hindered by the challenges associated with complex formulations, single function, and limited drug loading capacity. This study has developed a spiderweb-shaped iron-coordinated polymeric nanowire network (Fe-IDA NWs). The resulting Fe-IDA NWs are endowed with a certain viscosity due to the synergy of multiple supramolecular interactions. This allows them to replace traditional polymeric thickeners as microneedle coatings. The Fe-IDA NWs-coated microneedles (Fe-IDA MNs) display rapid disintegration in the skin model, which also enables the swift diffusion of Fe-IDA NWs and their payloads into the deeper skin layers. Additionally, Fe-IDA MNs exhibit desirable enzymatic activity and potential antibacterial ability. Thus, Fe-IDA MNs can enhance the therapeutic efficacy against wound infection through synergistic effects, and avoid the overly complicated formulation and the release of nontherapeutic molecules of conventional CMNs. As a proof-of-concept, Fe-IDA MNs loaded with chlorin e6 showed a synergistic chemodynamic-photodynamic antibacterial effect in a methicillin-resistant Staphylococcus aureus-infected wound model in mice. Collectively, this work has significant implications for the future of CMNs-based transdermal drug delivery systems and expands the application fields of metal coordination polymer (MCP) materials.

Fabrication and mechanical modelling of dissolvable PVA/PVP composite microneedles with biocompatibility for efficient transdermal delivery of ibuprofen

Microneedles offer minimally invasive, user-friendly, and subcutaneously accessible transdermal drug delivery and have been widely investigated as an effective transdermal delivery system. Ibuprofen is a common anti-inflammatory drug to treat chronic inflammation. It is crucial to develop microneedle patches capable of efficiently delivering ibuprofen through the skin for the effective treatment of arthritis patients requiring repeated medication. In this study, the mechanical properties of a new type of polymer microneedle were studied by finite element analysis, and the experimental results showed that the microneedle could effectively deliver drugs through the skin. In addition, a high ibuprofen-loaded microneedle patch was successfully prepared by micromolding and subjected to evaluation of its infrared spectrum morphology and dissolve degree. The morphology of microneedles was characterized by scanning electron microscopy, and the mechanical properties were assessed using a built linear stretching system. In the in-vitro diffusion cell drug release test, the microneedle released 85.2 ± 1.52% (210 ± 3.7 μg) ibuprofen in the modified Franz diffusion within 4 h, exhibiting a higher drug release compared to other drug delivery methods. This study provides a portable, safe and efficient treatment approach for arthritis patients requiring daily repeated medication.

Unravelling the role of microneedles in drug delivery: Principle, perspectives, and practices

In recent year, the research of transdermal drug delivery systems has got substantial attention towards the development of microneedles (MNs). This shift has occurred due to multifaceted advantages of MNs as they can be utilized to deliver the drug deeper to the skin with minimal invasion, offer successful delivery of drugs and biomolecules that are susceptible to degradation in gastrointestinal tract (GIT), act as biosensors, and help in monitoring the level of biomarkers in the body. These can be fabricated into different types based on their applications as well as material for fabrication. Some of their types include solid MNs, hollow MNs, coated MNs, hydrogel forming MNs, and dissolving MNs. These MNs deliver the therapeutics via microchannels deeper into the skin. The coated and hollow MNs have been found successful. However, they suffer from poor drug loading and blocking of pores. In contrast, dissolving MNs offer high drug loading. These MNs have also been utilized to deliver vaccines and biologicals. They have also been used in cosmetics. The current review covers the different types of MNs, materials used in their fabrication, properties of MNs, and various case studies related to their role in delivering therapeutics, monitoring level of biomarkers/hormones in body such as insulin. Various patents and clinical trials related to MNs are also covered. Covered are the major bottlenecks associated with their clinical translation and potential future perspectives.

Coated Microneedle System for Delivery of Clotrimazole in Deep-Skin Mycoses

Mycoses of the skin are infectious diseases caused by fungal microorganisms that are generally treated with topical agents. However, such therapy is often ineffective and has to be supported by oral use of active substances, which, in turn, can cause many side effects. A good alternative for the treatment of deep-skin mycoses seems to be microneedles (MNs). The aim of this research was to fabricate and evaluate the properties of innovative MNs coated with a hydrogel as potential carriers for clotrimazole (CLO) in the treatment of deep fungal skin infections. A 3D printing technique using a photo-curable resin was employed to produce MNs, which were coated with hydrogels using a dip-coating method. Hydrogels were prepared with carbopol EZ-3 Polymer (Lubrizol) in addition to glycerol and triisopropanolamine. Clotrimazole was introduced into the gel as the solution in ethanol or was suspended. In the first step of the investigation, a texture analysis of hydrogels was prepared with a texture analyzer, and the drug release studies were conducted with the use of automatic Franz diffusion cells. Next, the release profiles of CLO for coated MNs were checked. The last part of the investigation was the evaluation of the antifungal activity of the prepared systems, and the inhibition of the growth of Candida albicans was checked with the diffusion and suspended-plate methods. The texture profile analysis (TPA) for the tested hydrogels showed that the addition of ethanol significantly affects the following studied parameters: hardness, adhesiveness and gumminess, causing a decrease in their values. On the other hand, for the gels with suspended CLO, better spreadability was seen compared to gels with dissolved CLO. The presence of the active substance did not significantly affect the values of the tested parameters. In the dissolution study, the results showed that higher amounts of CLO were released for MNs coated with a hydrogel containing dissolved CLO. Also, microbiological tests proved its efficacy against fungal cultures. Qualitative tests carried out using the diffusion method showed that circular zones of inhibition of fungal growth on the plate were obtained, confirming the hypothesis of effectiveness. The suspension-plate technique confirmed the inhibitory effect of applied CLO on the growth of Candida albicans. From the analysis of the data, the MNs coated with CLO dissolved in hydrogel showed better antifungal activity. All received results seem to be helpful in developing further studies for MNs as carriers of antifungal substances.

Applications and prospects of microneedles in tumor drug delivery

As drug delivery devices, microneedles are used widely in the local administration of various drugs. Such drug-loaded microneedles are minimally invasive, almost painless, and have high drug delivery efficiency. In recent decades, with advancements in microneedle technology, an increasing number of adaptive, engineered, and intelligent microneedles have been designed to meet increasing clinical needs. This article summarizes the types, preparation materials, and preparation methods of microneedles, as well as the latest research progress in the application of microneedles in tumor drug delivery. This article also discusses the current challenges and improvement strategies in the use of microneedles for tumor drug delivery.

A Hollow Microneedle Equipped with a Micropillar for Improved Needle Insertion and Injection of Drug Solution

PURPOSE

Hollow-type microneedles (hMNs) are a promising device for the effective administration of drugs into intradermal sites. Complete insertion of the needle into the skin and administration of the drug solution without leakage must be achieved to obtain bioavailability or a constant effect. In the present study, several types of hMN with or without a rounded blunt tip micropillar, which suppresses skin deformation, around a hollow needle, and the effect on successful needle insertion and administration of a drug solution was investigated. Six different types of hMNs with needle lengths of 1000, 1300, and 1500 µm with or without a micropillar were used.

METHODS

Needle insertion and the disposition of a drug in rat skin were investigated. In addition, the displacement-force profile during application of hMNs was also investigated using a texture analyzer with an artificial membrane to examine needle factors affecting successful insertion and administration of a drug solution by comparing with in vivo results.

RESULTS

According to the results with the drug distribution of iodine, hMN1300 with a micropillar was able to successfully inject drug solution into an intradermal site with a high success rate. In addition, the results of displacement-force profiles with an artificial membrane showed that a micropillar can be effective for depth control of the injected solution as well as the prevention of contact between the hMN pedestal and the deformed membrane.

CONCLUSION

In the present study, hMN1300S showed effective solution delivery into an intradermal site. In particular, a micropillar can be effective for depth control of the injected solution as well as preventing contact between the hMN pedestal and the deformed membrane. The obtained results will help in the design and development of hMNs that ensure successful injection of an administered drug.

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.

Recent progress on the development of bioinspired surfaces with high aspect ratio microarray structures: From fabrication to applications

Surfaces with high aspect ratio microarray structures can implement sophisticated assignment in typical fields including microfluidics, sensor, biomedicine, et al. via regulating their deformation or the material properties. Inspired by natural materials and systems, for example sea cockroaches, water spiders, cacti, lotus leaves, rice leaves, and cedar leaves, many researchers have focused on microneedle functional surface studies. When the surface with high aspect ratio microarray structures is stimulated by the external fields, such as optical, electric, thermal, magnetic, the high aspect ratio microarray structures can undergo hydrophilic and hydrophobic switching or shape change, which may be gifted the surfaces with the ability to perform complex task, including directional liquid/air transport, targeted drug delivery, microfluidic chip sensing. In this review, the fabrication principles of various surfaces with high aspect ratio microarray structures are classified and summarized. Mechanisms of liquid manipulation on hydrophilic/hydrophobic surfaces with high aspect ratio microarray structures are clarified based on Wenzel model, Cassie model, Laplace pressure theories and so on. Then the intelligent control strategies have been demonstrated. The applications in microfluidic, drug delivery, patch sensors have been discussed. Finally, current challenges and new insights of future prospects for dynamic manipulation of liquid/air based on biomimetic surface with high aspect ratio microarray structures are also addressed.

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.

Aggregation-induced emission photosensitizer microneedles for enhanced melanoma photodynamic therapy

The incidence and mortality rates of skin melanoma have been increasing annually. Photodynamic therapy (PDT) enables effective destruction of tumor cells while minimizing harm to normal cells. However, traditional photosensitizers (PSs) suffer from photobleaching, photodegradation and the aggregation-caused quenching (ACQ) effect, and it is challenging for light to reach the deep layers of the skin to maximize the efficacy of PSs. Herein, we developed dissolving microneedles (MNs) loaded with PSs of TPE-EPy@CB[7] through supramolecular assembly. The PSs effectively enhanced the type-I reactive oxygen species (ROS) generation capacity, with a concentration of 2 μM possessing nearly half of the tumor cell-killing ability under 10 min white light irradiation. The MNs were successfully pierced into the targeted site for precise drug delivery. Additionally, the conical structure of the MNs, as well as the lens-like structure after dissolution, facilitated the transmission of light in the subcutaneous tissue, achieving significant inhibition of tumor growth with a tumor suppression rate of 97.8% and no systemic toxicity or side effects in melanoma mice. The results demonstrated the potent melanoma inhibition and biosafety of this treatment approach, exhibiting a new and promising strategy to conquer malignant melanoma.

Fabrication Technology of Self-Dissolving Sodium Hyaluronate Gels Ultrafine Microneedles for Medical Applications with UV-Curing Gas-Permeable Mold

Microneedles are of great interest in diverse fields, including cosmetics, drug delivery systems, chromatography, and biological sensing for disease diagnosis. Self-dissolving ultrafine microneedles of pure sodium hyaluronate hydrogels were fabricated using a UV-curing TiO2-SiO2 gas-permeable mold polymerized by sol-gel hydrolysis reactions in nanoimprint lithography processes under refrigeration at 5 °C, where thermal decomposition of microneedle components can be avoided. The moldability, strength, and dissolution behavior of sodium hyaluronate hydrogels with different molecular weights were compared to evaluate the suitability of ultrafine microneedles with a bottom diameter of 40 μm and a height of 80 μm. The appropriate molecular weight range and formulation of pure sodium hyaluronate hydrogels were found to control the dissolution behavior of self-dissolving ultrafine microneedles while maintaining the moldability and strength of the microneedles. This fabrication technology of ultrafine microneedles expands their possibilities as a next-generation technique for bioactive gels for controlling the blood levels of drugs and avoiding pain during administration.

Microneedles: A Versatile Drug Delivery Carrier for Phytobioactive Compounds as a Therapeutic Modulator for Targeting Mitochondrial Dysfunction in the Management of Neurodegenerative Diseases

Neurodegenerative disease (ND) is the fourth leading cause of death worldwide, with limited symptomatic therapies. Mitochondrial dysfunction is a major risk factor in the progression of ND, and it-increases the generation of reactive oxygen species (ROS). Overexposure to these ROS induces apoptotic changes leading to neuronal cell death. Many studies have shown the prominent effect of phytobioactive compounds in managing mitochondrial dysfunctions associated with ND, mainly due to their antioxidant properties. The drug delivery to the brain is limited due to the presence of the blood-brain barrier (BBB), but effective drug concentration needs to reach the brain for the therapeutic action. Therefore, developing safe and effective strategies to enhance drug entry in the brain is required to establish ND's treatment. The microneedle-based drug delivery system is one of the effective non-invasive techniques for drug delivery through the transdermal route. Microneedles are micronsized drug delivery needles that are self-administrable. It can penetrate through the stratum corneum skin layer without hitting pain receptors, allowing the phytobioactive compounds to be released directly into systemic circulation in a controlled manner. With all of the principles mentioned above, this review discusses microneedles as a versatile drug delivery carrier for the phytoactive compounds as a therapeutic potentiating agent for targeting mitochondrial dysfunction for the management of ND.

Fabrication and characterization of coated microneedle patches based on PEGDA for transdermal administration of metformin

Type 2 diabetes is one of the major challenges that the world is facing today. However, metformin (MET) as most type 2 diabetics' first-line oral hypoglycemic drug may cause serious side effects such as gastrointestinal irritation and nausea which reduce the patients' medication compliance. Therefore, the aim of the study was to design a safe and effective self-treatment device for the delivery of MET. Here, a kind of coated microneedle (MN) patches based on poly(ethylene glycol)diacrylate (PEGDA) were prepared by a two-step casting method and photopolymerization process for transdermal administration of MET. The needles wrapped with drug-loaded hyaluronic acid (HA) coating showed promising mechanical properties and drug delivery ability that allowed them to penetrate the skin barrier for rapid drug delivery, and they had no skin irritancy. The in vivo experiment of type 2 diabetic rats showed a satisfying hypoglycemic effect of the coated MN patches. The study shows that the prepared MN patches will be a potential method for the treatment of type 2 diabetes in the future.

Drug Delivery Systems based on Microneedles for Dermatological Diseases and Aesthetic Enhancement

Microneedle (MN) devices comprise of micron-sized structures that circumvent biological barriers in a minimally invasive manner. MN research continues to grow and evolve; the technology was recently identified as one of the top ten overall emerging technologies of 2020. There is a growing interest in using such devices in cosmetology and dermatological conditions where the MNs mechanically disrupt the outer skin barrier layer, creating transient pathways that allow the passage of materials to underlying skin layers. This review aims to appraise the application of microneedle technologies in skin science, provide information on potential clinical benefits, as well as indicate possible dermatological conditions that can benefit from this technology, including autoimmunemediated inflammatory skin diseases, skin aging, hyperpigmentation, and skin tumors. A literature review was carried out to select studies that evaluated the use of microneedles to enhance drug delivery for dermatologic purposes. MN patches create temporary pathways that allow the passage of therapeutic material to deeper layers of the skin. Given their demonstrable promise in therapeutic applications it will be essential for healthcare professionals to engage with these new delivery systems as they transition to the clinic.

Metallic elements combine with herbal compounds upload in microneedles to promote wound healing: a review

Wound healing is a dynamic and complex restorative process, and traditional dressings reduce their therapeutic effectiveness due to the accumulation of drugs in the cuticle. As a novel drug delivery system, microneedles (MNs) can overcome the defect and deliver drugs to the deeper layers of the skin. As the core of the microneedle system, loaded drugs exert a significant influence on the therapeutic efficacy of MNs. Metallic elements and herbal compounds have been widely used in wound treatment for their ability to accelerate the healing process. Metallic elements primarily serve as antimicrobial agents and facilitate the enhancement of cell proliferation. Whereas various herbal compounds act on different targets in the inflammatory, proliferative, and remodeling phases of wound healing. The interaction between the two drugs forms nanoparticles (NPs) and metal-organic frameworks (MOFs), reducing the toxicity of the metallic elements and increasing the therapeutic effect. This article summarizes recent trends in the development of MNs made of metallic elements and herbal compounds for wound healing, describes their advantages in wound treatment, and provides a reference for the development of future MNs.

Transdermal drug delivery via microneedles for musculoskeletal systems

As the population is ageing and lifestyle is changing, the prevalence of musculoskeletal (MSK) disorders is gradually increasing with each passing year, posing a serious threat to the health and quality of the public, especially the elderly. However, currently prevalent treatments for MSK disorders, mainly administered orally and by injection, are not targeted to the specific lesion, resulting in low efficacy along with a series of local and systemic adverse effects. Microneedle (MN) patches loaded with micron-sized needle array, combining the advantages of oral administration and local injection, have become a potentially novel strategy for the administration and treatment of MSK diseases. In this review, we briefly introduce the basics of MNs and focus on the main characteristics of the MSK systems and various types of MN-based transdermal drug delivery (TDD) systems. We emphasize the progress and broad applications of MN-based transdermal drug delivery (TDD) for MSK systems, including osteoporosis, nutritional rickets and some other typical types of arthritis and muscular damage, and in closing summarize the future prospects and challenges of MNs application.

Progress in the preparation and evaluation of glucose-sensitive microneedle systems and their blood glucose regulation

Glucose-sensitive microneedle systems (GSMSs) as an intelligent strategy for treating diabetes can well solve the problems of puncture pain, hypoglycemia, skin damage, and complications caused by the subcutaneous injection of insulin. According to the various functions of each component, herein, therapeutic GSMSs are reviewed based on three parts (glucose-sensitive models, diabetes medications, and microneedle body). Moreover, the characteristics, benefits, and drawbacks of three types of typical glucose-sensitive models (phenylboronic acid based polymer, glucose oxidase, and concanavalin A) and their drug delivery models are reviewed. In particular, phenylboronic acid-based GSMSs can provide a long-acting drug dose and controlled release rate for the treatment of diabetes. Moreover, their painless, minimally invasive puncture also greatly improves patient compliance, treatment safety, and potential application prospects.

Exosome-loaded microneedle patches: Promising factor delivery route

During the past decades, the advent of different microneedle patch (MNPs) systems paves the way for the targeted and efficient delivery of several growth factors into the injured sites. MNPs consist of several micro-sized (25-1500 μm) needle rows for painless delivery of incorporated therapeutics and increase of regenerative outcomes. Recent data have indicated the multifunctional potential of varied MNP types for clinical applications. Advances in the application of materials and fabrication processes enable researchers and clinicians to apply several MNP types for different purposes such as inflammatory conditions, ischemic disease, metabolic disorders, vaccination, etc. Exosomes (Exos) are one of the most interesting biological bioshuttles that participate in cell-to-cell paracrine interaction with the transfer of signaling biomolecules. These nano-sized particles, ranging from 50 to 150 nm, can exploit several mechanisms to enter the target cells and deliver their cargo into the cytosol. In recent years, both intact and engineered Exos have been increasingly used to accelerate the healing process and restore the function of injured organs. Considering the numerous benefits provided by MNPs, it is logical to hypothesize that the development of MNPs loaded with Exos provides an efficient therapeutic platform for the alleviation of several pathologies. In this review article, the authors collected recent advances in the application of MNP-loaded Exos for therapeutic purposes.

Design, analysis and fabrication of solid polymer microneedle patch using CO2 laser and polymer molding

Microneedle-based transdermal drug delivery into the skin has gained attraction for the past few years. An affordable and effective fabrication methodology is required for the development of micron size needle. Manufacturing cost-effective microneedle patches in batch production is a challenging process. In this work, we proposed a cleanroom-free technique for fabrication of conical and pyramidal geometry of microneedle array for transdermal drug delivery. Using the COMSOL Multiphysics tool, the mechanical strength of the designed microneedle array under axial, bending, and buckling loads for the geometries during skin insertion was investigated. A CO2 laser and polymer molding technique are used to fabricate 10 × 10 designed microneedle array structure. On an acrylic sheet, a designed pattern is engraved to produce a 20 mm × 20 mm sharp conical and pyramidal shape master mold. We successfully created a biocompatible polydimethylsiloxane (PDMS) microneedle patch with an average height of 1200 µm, base diameter of 650 µm, and a tip diameter of 50 µm using acrylic master mold. According to structural simulation analysis, the microneedle array will experience resultant stress that is within a safe range. The mechanical stability of the fabricated microneedle patch was investigated using hardness test and universal testing machine. The depth of penetration studies were performed in an in vitro Parafilm® M model by manual compression tests and its detailed insertion depth was reported. The developed master mold is efficient to replicate several polydimethylsiloxane microneedle patches. The proposed combined method of laser processing and molding mechanism is simple and low-cost for rapid prototyping of microneedle array.

Fabrication of polyvinyl pyrrolidone-K90/Eudragit RL100-based dissolving microneedle patches loaded with alpha-arbutin and resveratrol for skin depigmentation

Alpha-arbutin (AA) and resveratrol (Res) are widely used in skin-lightening products. However, current topical formulations have minimal skin-lightening effects due to the low absorption and poor solubility of these active compounds. This study investigated the efficacy and safety of using dissolving microneedle (DMN) patches to improve the delivery of AA and Res for skin depigmentation. The DMN patches (F0-F3) fabricated from polyvinyl pyrrolidone-K90 (PVP-K90)/Eudragit RL100 blends successfully penetrated excised porcine skin and showed sufficient mechanical strength to resist compression forces. Loading DMNs with 10% AA and 2% Res at a ratio of 5 : 1 (F3) resulted in a synergistic interaction between the drugs with desirable dissolving ability, drug loading, and stability. Furthermore, both in vitro and in vivo studies revealed that the use of F3 DMN patches successfully enhanced the intradermal delivery of AA and Res over a 24 h period, with the delivered amount being higher (∼2.6 times) than that provided by a cream formulation (P < 0.05). After removing the DMN patches, the mice's skin was spontaneously and completely resealed within 12 h. In clinical studies, F3 DMN patches slightly decreased the melanin index of the participants without causing skin irritation or erythema at any time during the 24 h period when the patches were applied (P < 0.05). Moreover, application of the patches for 24 h was not found to affect skin hydration, transepidermal water loss, or skin elasticity. Therefore, AA/Res-loaded DMN patches could offer a promising approach for the effective local delivery of cosmetic agents for skin depigmentation.

Transdermal on-demand drug delivery based on an iontophoretic hollow microneedle array system

Transdermal drug delivery has emerged as an alternative administration route for therapeutic drugs, overcoming current issues in oral and parenteral administration. However, this technology is hindered by the low permeability of the stratum corneum of the skin. In this work, we develop a synergic combination of two enhancing technologies to contribute to an improved and on-demand drug delivery through an iontophoretic system coupled with hollow microneedles (HMNs). For the first time, a polymeric HMN array coupled with integrated iontophoresis for the delivery of charged molecules and macromolecules (e.g. proteins) is devised. To prove the concept, methylene blue, fluorescein sodium, lidocaine hydrochloride, and bovine serum albumin-fluorescein isothiocyanate conjugate (BSA-FITC) were first tested in an in vitro setup using 1.5% agarose gel model. Subsequently, the ex vivo drug permeation study using a Franz diffusion cell was conducted, exhibiting a 61-fold, 43-fold, 54-fold, and 17-fold increment of the permeation of methylene blue, fluorescein sodium, lidocaine hydrochloride, and BSA-FITC, respectively, during the application of 1 mA cm^-2 current for 6 h. Moreover, the total amount of drug delivered (i.e. in the skin and receptor compartment) was analysed to untangle the different delivery profiles according to the types of molecule. Finally, the integration of the anode and cathode into an iontophoretic hollow microneedle array system (IHMAS) offers the full miniaturisation of the concept. Overall, the IHMAS device provides a versatile wearable technology for transdermal on-demand drug delivery that can improve the administration of personalised doses, and potentially enhance precision medicine.

Microneedles: An Emerging Vaccine Delivery Tool and a Prospective Solution to the Challenges of SARS-CoV-2 Mass Vaccination

Vaccination is an effective measure to prevent infectious diseases. Protective immunity is induced when the immune system is exposed to a vaccine formulation with appropriate immunogenicity. However, traditional injection vaccination is always accompanied by fear and severe pain. As an emerging vaccine delivery tool, microneedles overcome the problems associated with routine needle vaccination, which can effectively deliver vaccines rich in antigen-presenting cells (APCs) to the epidermis and dermis painlessly, inducing a strong immune response. In addition, microneedles have the advantages of avoiding cold chain storage and have the flexibility of self-operation, which can solve the logistics and delivery obstacles of vaccines, covering the vaccination of the special population more easily and conveniently. Examples include people in rural areas with restricted vaccine storage facilities and medical professionals, elderly and disabled people with limited mobility, infants and young children afraid of pain. Currently, in the late stage of fighting against COVID-19, the main task is to increase the coverage of vaccines, especially for special populations. To address this challenge, microneedle-based vaccines have great potential to increase global vaccination rates and save many lives. This review describes the current progress of microneedles as a vaccine delivery system and its prospects in achieving mass vaccination against SARS-CoV-2.

Recent Advancement of Medical Patch for Transdermal Drug Delivery

Transdermal patches are a non-invasive method of drug administration. It is an adhesive patch designed to deliver a specific dose of medication through the skin and into the bloodstream throughout the body. Transdermal drug delivery has several advantages over other routes of administration, for instance, it is less invasive, patient-friendly, and has the ability to bypass first-pass metabolism and the destructive acidic environment of the stomach that occurs upon the oral ingestion of drugs. For decades, transdermal patches have attracted attention and were used to deliver drugs such as nicotine, fentanyl, nitroglycerin, and clonidine to treat various diseases or conditions. Recently, this method is also being explored as a means of delivering biologics in various applications. Here, we review the existing literatures on the design and usage of medical patches in transdermal drug delivery, with a focus on the recent advances in innovation and technology that led to the emergence of smart, dissolvable/biodegradable, and high-loading/release, as well as 3D-printed patches.

Transdermal drug delivery via microneedles to mediate wound microenvironment

Cutaneous wound healing is a complex process, while modulating the wound microenvironment has become an essential therapeutic goal. In clinics, advanced dressings or dermal templates can promote wound healing but their ability in mediating wound microenvironment is limited. In the last decade, microneedle (MN) array patches have emerged as a new class of wound dressings. These dressings enable non-invasive transdermal and precise medication delivery. Combined with smart materials, MN additionally allows real-time monitoring of wound site markers such as inflammatory factors, oxygen levels, vascularization, pH and temperature, etc., while releasing therapeutic molecules responsively to the wound site. In this review, the MN-based strategies were reviewed for modulating wound microenvironment via introducing the main characteristics of the wound microenvironment and various types of MN-based delivery systems. Additionally, the progress and future trends in the application of MNs in mediating wound microenvironments are also discussed.

Microneedle arrays integrated with microfluidic systems: Emerging applications and fluid flow modeling

Microneedle arrays are patches of needles at micro- and nano-scale, which are competent and versatile technologies that have been merged with microfluidic systems to construct more capable devices for biomedical applications, such as drug delivery, wound healing, biosensing, and sampling body fluids. In this paper, several designs and applications are reviewed. In addition, modeling approaches used in microneedle designs for fluid flow and mass transfer are discussed, and the challenges are highlighted.

3D Printed Hollow Microneedles for Treating Skin Wrinkles Using Different Anti-Wrinkle Agents: A Possible Futuristic Approach

Skin wrinkles are an inevitable phenomenon that is brought about by aging due to the degradation of scleroprotein fibers and significant collagen reduction, which is the fundamental basis of anti-wrinkle technology in use today. Conventional treatments such as lasering and Botulinum toxin have some drawbacks including allergic skin reactions, cumbersome treatment procedures, and inefficient penetration of the anti-wrinkle products into the skin due to the high resistance of stratum corneum. Bearing this in mind, the cosmetic industry has exploited the patient-compliant technology of microneedles (MNs) to treat skin wrinkles, developing several products based on solid and dissolvable MNs incorporated with antiwrinkle formulations. However, drug administration via these MNs is limited by the high molecular weight of the drugs. Hollow MNs (HMNs) can deliver a wider array of active agents, but that is a relatively unexplored area in the context of antiwrinkle technology. To address this gap, we discuss the possibility of bioinspired 3D printed HMNs in treating skin wrinkles in this paper. We compare the previous and current anti-wrinkling treatment options, as well as the techniques and challenges involved with its manufacture and commercialization.

Microneedle-based interstitial fluid extraction for drug analysis: Advances, challenges, and prospects

Similar to blood, interstitial fluid (ISF) contains exogenous drugs and biomarkers and may therefore substitute blood in drug analysis. However, current ISF extraction techniques require bulky instruments and are both time-consuming and complicated, which has inspired the development of viable alternatives such as those relying on skin or tissue puncturing with microneedles. Currently, microneedles are widely employed for transdermal drug delivery and have been successfully used for ISF extraction by different mechanisms to facilitate subsequent analysis. The integration of microneedles with sensors enables in situ ISF analysis and specific compound monitoring, while the integration of monitoring and delivery functions in wearable devices allows real-time dose modification. Herein, we review the progress in drug analysis based on microneedle-assisted ISF extraction and discuss the related future opportunities and challenges.

Betamethasone-loaded dissolvable microneedle patch for oral ulcer treatment

Oral inflammatory disease (OID) is among the most common oral lesions, affecting people's quality of life and even leading to oral cancer. Oral ulcers are the most common OID. However, the pain and fear caused by the localized injection of hormones hinder the clinical treatment of oral ulcers. To address this problem, soluble hyaluronic acid (HA) microneedle patches (BSP-BDP@HAMN) containing betamethasone 21-phosphate sodium (BSP) and betamethasone 17,21-dipropionate (BDP) were fabricated for potential application in oral ulcers. BSP-BDP@HAMNs had the sufficient mechanical strength to penetrate the rat tongue abdomen mucosa with an insertion depth of approximately 207 ± 3 µm. The rapidly solubilized HA microneedle carrier released BSP and BDP into the ulcer base within 3 min of entering the mucosa. Cellular assays have shown that BDP@HAMNs have wound healing-promoting and anti-inflammatory effects. Compared with topical injections and creams, BSP-BDP@HAMNs not only penetrated the ulcer surface painlessly but also worked deep in the ulcer for a long time. In conclusion, the proposed BSP-BDP@HAMN patch can improve the comfort and efficacy of oral ulcer treatment, thus providing a new prospect for oral ulcer treatment.

Microneedle system for tissue engineering and regenerative medicine

Global increasing demand for high life quality and length facilitates the development of tissue engineering and regenerative medicine, which apply multidisciplinary theories and techniques to achieve the structural reconstruction and functional recovery of disordered or damaged tissues and organs. However, the clinical performances of adopted drugs, materials, and powerful cells in the laboratory are inescapably limited by the currently available technologies. To tackle the problems, versatile microneedles are developed as the new platform for local delivery of diverse cargos with minimal invasion. The efficient delivery, as well as painless and convenient procedure endow microneedles with good patient compliance in clinic. In this review, we first categorize different microneedle systems and delivery models, and then summarize their applications in tissue engineering and regenerative medicine mainly involving maintenance and rehabilitation of damaged tissues and organs. In the end, we discuss the advantages, challenges, and prospects of microneedles in depth for future clinical translations.

Deferasirox Nanosuspension Loaded Dissolving Microneedles for Intradermal Delivery

Microneedles are minimally invasive systems that can deliver drugs intradermally without pain and bleeding and can advantageously replace the hypodermal needles and oral routes of delivery. Deferasirox (DFS) is an iron chelator employed in several ailments where iron overload plays an important role in disease manifestation. In this study, DFS was formulated into a nanosuspension (NSs) through wet media milling employing PVA as a stabilizer and successfully loaded in polymeric dissolving microneedles (DMNs). The release studies for DFS-NS clearly showed a threefold increased dissolution rate compared to pure DFS. The mechanical characterization of DFS-NS-DMNs revealed that the system was sufficiently strong for efficacious skin penetration. Optical coherence tomography images confirmed an insertion of up to 378 µm into full-thickness porcine skin layers. The skin deposition studies showed 60% drug deposition from NS-DMN, which was much higher than from the DFS-NS transdermal patch (DFS-NS-TP) (without needles) or pure DFS-DMNs. Moreover, DFS-NS without DMNs did not deposit well inside the skin, indicating that DMNs played an important role in effectively delivering drugs inside the skin. Therefore, it is evident from the findings that loading DFS-NS into novel DMN devices can effectively deliver DFS transdermally.

Subcutaneous Implantable Microneedle System for the Treatment of Alzheimer's Disease by Delivering Donepezil

To alleviate the dilemma of drug administration in Alzheimer's disease (AD) patients, it is of great significance to develop a new drug delivery system. In this study, a subcutaneously implanted microneedle (MN) device with a swellable gelatin methacryloyl (GelMA) needle body and a dissolvable polyvinyl alcohol (PVA) backing layer was designed. The backing layer quickly dissolved once the MN was introduced into the subcutaneous, and the hydrogel needles were implanted in the subcutaneous to enable prolonged drug release. Compared with oral administration, the MN system offers the benefits of a high administration rate, a fast onset of effect, and a longer duration of action. By detecting the concentration of acetylcholine (ACH) and Aβ 1-42, it was found that MN administration exhibited a stronger therapeutic effect. The biological safety of the MN system was also assessed, and no obvious signs of hemolysis, cytotoxicity, and inflammatory reaction were observed. Together, these findings suggested that the MN system is a convenient, efficient, and safe method of delivering donepezil hydrochloride (DPH) and may provide AD patients with a novel medicine administration option.

Manufacturing of a Transdermal Patch in 3D Printing

Diabetes mellitus is an endocrine disorder that affects glucose metabolism, making the body unable to effectively use the insulin it produces. Transdermal drug delivery (TDD) has attracted strong interest from researchers, as it allows minimally invasive and painless insulin administration, showing advantages over conventional delivery methods. Systems composed of microneedles (MNs) assembled in a transdermal patch provide a unique route of administration, which is innovative with promising results. This paper presents the design of a transdermal patch composed of 25 microneedles manufactured with 3D printing by stereolithography with a class 1 biocompatible resin and a printing angle of 0°. Finite element analysis with ANSYS software is used to obtain the mechanical behavior of the microneedle (MN). The values obtained through the analysis were: a Von Misses stress of 18.057 MPa, a maximum deformation of 2.179×10-3, and a safety factor of 4. Following this, through a flow simulation, we find that a pressure of 1.084 Pa and a fluid velocity of 4.800 ms were necessary to ensure a volumetric flow magnitude of 4.447×10-5cm3s. Furthermore, the parameters found in this work are of great importance for the future implementation of a transdermal drug delivery device.