Microneedles in Drug Delivery: Progress and Challenges

Microneedle technology for potential SARS-CoV-2 vaccine delivery

INTRODUCTION

Microneedle fabrication was conceptualised in the 1970s as devices for painless transdermal drug delivery. The last two decades have seen considerable research and financial investment in this area with SARS-CoV-2 and other vaccines catalysing their application to in vivo intradermal vaccine delivery. Microneedle arrays have been fabricated in different shapes, geometries, formats, and out of different materials.

AREAS COVERED

The recent pandemic has offered microneedle platforms the opportunity to be employed as a vehicle for SARS-CoV-2 vaccine administration. The various modes of vaccination delivery and the potential of microneedle arrays-based vaccines will be presented, with a specific focus placed on recent SARS-CoV-2 research. The advantages of microneedle-based vaccine administration, in addition to the major hurdles to their en masse implementation, will be examined.

EXPERT OPINION

Considering the widely acknowledged disadvantages of current vaccine delivery, such as anxiety, pain, and the requirement for professional administration, a large shift in this research sphere is imminent. The SARS-CoV-2 pandemic has catalysed the development of alternate vaccination platforms, working to avoid the requirement for mass vaccination centres. As microneedle vaccine patches are transitioning through clinical study phases, research will be required to ready this technology for a more mass production environment.

Buccal mucosal application of dissolvable microneedle patch containing photosensitizer provides effective localized delivery and phototherapy against oral carcinoma

The effectiveness of phototherapy using photosensitizers is limited by the challenges in their delivery at the site of irradiation. Here, we demonstrate the localized application of a photosensitizer-loaded microneedle patch for effective photodynamic and photothermal therapy in oral carcinoma. Indocyanine green (ICG) was studied as a photosensitizer for its effect on oral carcinoma, FaDu cells. Different parameters including concentration, near-infrared (NIR) laser irradiation intensity and irradiation time were optimized while measuring temperature increase and reactive oxygen species (ROS) generation in FaDu cells. A dissolvable microneedle (DMN) patch made of sodium carboxymethyl cellulose and sodium alginate was fabricated by the micromolding technique. DMN showed sufficient mechanical strength for insertion in the excised porcine buccal mucosa. DMN dissolved within 30 s in phosphate buffer and 30 min in the excised buccal mucosa. Confocal microscopy studies revealed DMN penetration up to a depth of 300 µm within the buccal mucosa. ICG-DMN applied on the back of the rat was found to be localized at the application site before and after irradiation using an 808 nm NIR laser. ICG-DMN was applied on the FaDu xenografted tumor model in athymic nude mice. The localized temperature increase and ROS generation significantly (P<0.05) decreased the tumor volume after ICG-DMN application compared with the control group. In conclusion, DMN can be developed for the localized administration of photosensitizers for phototherapy in oral carcinoma.

Enhanced Skin Permeation and Controlled Release of β-Sitosterol Using Cubosomes Encrusted with Dissolving Microneedles for the Management of Alopecia

The use of synthetic medication for treating alopecia is restricted because of systemic exposure and related negative effects. Beta-sitosterol (β-ST), a natural chemical, has lately been studied for its potential to promote hair development. The cubosomes with dissolving microneedles (CUBs-MN_D) created in this study may be a useful starting point for the creation of a sophisticated dermal delivery system for β-ST. Cubosomes (CUBs) were prepared by the emulsification method, using glyceryl monooleate (GMO) as a lipid polymer. CUBs were loaded with dissolving microneedles (MN_D) fabricated with HA and a PVP-K90 matrix. An ex vivo skin permeation study and an in vivo hair growth efficacy test of β-ST were performed with both CUB and CUB-MN_D. The average particle size of the CUBs was determined to be 173.67 ± 0.52 nm, with a low polydispersity index (0.3) and a high zeta potential value that prevents the aggregate formation of dispersed particles. When compared to CUBs alone, CUBs-MN_D displayed higher permeating levels of β-ST at all-time points. In the animals from the CUB-MN_D group, significant hair development was observed. According to the results of the current investigation, CUBs that integrate dissolving microneedles of β-ST are superior in terms of transdermal skin penetration and activity for the treatment of alopecia.

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.

Enhanced skin drug delivery using dissolving microneedles: a potential approach for the management of skin disorders

INTRODUCTION

For decades, finding effective long-term or disease-modifying treatments for skin disorders has been a major focus of scientists. The conventional drug delivery systems showed poor efficacy with high doses and are associated with side effects, which lead to challenges in adherence to therapy. Therefore, to overcome the limitations of conventional drug delivery systems, drug delivery research has focused on topical, transdermal, and intradermal drug delivery systems. Among all, the dissolving microneedles have gained attention with a new range of advantages of drug delivery in skin disorders such as breaching skin barriers with minimal discomfort and its simplicity of application to the skin, which allows patients to administer it themselves.

AREAS COVERED

This review highlighted the insights into dissolving microneedles for different skin disorders in detail. Additionally, it also provides evidence for its effective utilization in the treatment of various skin disorders. The clinical trial status and patents for dissolving microneedles for the management of skin disorders are also covered.

EXPERT OPINION

The current review on dissolving microneedles for skin drug delivery is accentuating the breakthroughs achieved so far in the management of skin disorders. The output of the discussed case studies anticipated that dissolving microneedles can be a novel drug delivery strategy for the long-term treatment of skin disorders.

Rapidly Dissolving Microneedles for the Delivery of Steroid-Loaded Nanoparticles Intended for the Treatment of Inflammatory Skin Diseases

Drug delivery through the skin has immense advantages compared to other routes of administration and offers an optimal way to treat inflammatory skin diseases, where corticosteroids are the cornerstone of topical therapy. Still, their therapeutic efficiency is limited due to inadequate skin permeability, potential side effects, and reduced patient compliance. To overcome these drawbacks, we propose a drug delivery system consisting of dexamethasone (DEX)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) incorporated in sodium alginate (SA) microneedles (MNs) as a minimally invasive dosage form for controlled drug release. Drug-loaded PLGA NPs were prepared by a nanoprecipitation method with a high encapsulation yield. They exhibited a controlled release pattern over 120 h. A modified vacuum-deposition micromolding method was used to load the obtained DEX-NPs into the tips of dissolving MNs. The NP-MNs showed improved insertion capabilities into the skin-simulant parafilm model and enhanced mechanical strength when tested against different static forces compared to their counterparts (SA-MNs). The results of an MN dissolution study following application to ex vivo chicken skin and agarose gel indicate that the NP-loaded segments of MNs dissolve within 15 s, in which the NPs are released into the skin. Taken together, the incorporation of DEX-NPs into SA-MNs could be a promising approach to bypass the limitations of conventional topical treatment of skin diseases, allowing for self-administration, increased patient compliance, and controlled drug release.

Stem cell-derived exosomes in the treatment of melasma and its percutaneous penetration

BACKGROUND AND OBJECTIVES

Melasma is a refractory skin disease due to its complex pathogenesis and difficult treatment. Studies have found that human umbilical cord mesenchymal stem cell-derived exosomes (hUCMSC-Exos) could serve as a novel cell-free therapeutic strategy in regenerative and esthetic medicine. It could potentially treat melasma, but the skin barrier is a challenge. In this study, we aim to explore the safety and efficacy of hUCMSC-Exos in the treatment of melasma and the means to promote its percutaneous penetration.

MATERIALS AND METHODS

In the animal study about the effect of penetration, percutaneous penetration of PKH67-labeled hUCMSC-Exos was studied under microneedles, 1565 nm nonablative fractional laser (NAFL), and a plasma named Peninsula Blue Aurora Shumin Master (PBASM) treatments, observed by confocal laser scanning microscopy. In the clinical application study, 60 patients with melasma treated in our department were divided into four groups. NAFL combined with normal saline treatment was used for Group A. Microneedles, NAFL, and PBASM combined with hUCMSC-Exos treatments were used for Groups B, C, and D, respectively. Each patient received four treatments at 1-month intervals. Assessments were done using the degree of pain posttreatment, melasma area and severity score, improvement rate, physician global assessment score, satisfaction, and complications.

RESULTS

In the animal study about the effect of penetration, hUCMSC-Exos can penetrate the deep dermis under microneedles, NAFL, and PBASM treatments. In the clinical application study, compared with Group A, Groups B, C, and D showed significantly improved therapeutic effect and patient satisfaction (p < 0.05), and there was no significant difference among Groups B, C, and D.(p > 0.05). Patients in Group B reported higher pain levels than those in the other three groups (p < 0.05); the treatment experience of patients in Group D was better.

CONCLUSION

hUCMSC-Exos can improve the symptoms of melasma safely and effectively. Compared with microneedles, NAFL and PBASM can also achieve a good effect toward promoting penetration. These findings are worthy of exploration and clinical application.

Improved transdermal delivery of valsartan using combinatorial approach of polymeric transdermal hydrogels and solid microneedles: an ex vivo proof of concept investigation

Valsartan (VAL) is used as a first-line agent to treat hypertension. However, VAL exhibits poor absorption and low bioavailability when administrated orally. To overcome these issues, VAL transdermal gel was developed in this study, where Carbopol was used as the gel matrices. Additionally, solid microneedles (Dermaroller^®) with various needle lengths were combined with transdermal gel to improve its permeation across the stratum corneum as a skin barrier. Developed formulations were further evaluated for various parameters, including pH, viscosity, spreadability, extrudability, gel strength, drug content, ex vivo permeation, in vitro release, occlusivity, and hemolysis. The results showed that all formulations exhibited desired physical characteristics without any potential to cause toxicity. Moreover, this approach showed that using microneedles could significantly enhance the permeation of VAL up to 3 folds compared to untreated skin. The use of microneedles 1.5 mm was found to be the optimum combination to improve VA permeation without affecting skin integrity. As much as 1.69 ± 0.004 mg of VAL permeated after 8 h. Finally, it could be concluded that this work had successfully developed a new approach for VALS drug delivery and could potentially show a significant impact on the treatment of hypertension. Further in vivo work should be considered.

Silk Fibroin Microneedles for Transdermal Drug Delivery: Where Do We Stand and How Far Can We Proceed?

Microneedles are a patient-friendly technique for delivering drugs to the site of action in place of traditional oral and injectable administration. Silk fibroin represents an interesting polymeric biomaterial because of its mechanical properties, thermal stability, biocompatibility and possibility of control via genetic engineering. This review focuses on the critical research progress of silk fibroin microneedles since their inception, analyzes in detail the structure and properties of silk fibroin, the types of silk fibroin microneedles, drug delivery applications and clinical trials, and summarizes the future development trend in this field. It also proposes the future research direction of silk fibroin microneedles, including increasing drug loading doses and enriching drug loading types as well as exploring silk fibroin microneedles with stimulation-responsive drug release functions. The safety and effectiveness of silk fibroin microneedles should be further verified in clinical trials at different stages.

Silk Nanocarrier with Tunable Size to Improve Transdermal Capacity for Hydrophilic and Hydrophobic Drugs

Transdermal drug delivery is an attractive option for multiple disease therapies as it reduces adverse reactions and improves patient compliance. Water-dispersible β-sheet rich silk nanofiber carriers have hydrophobic properties that benefit transdermal delivery but still show inferior transdermal capacities. Thus, hydrophobic silk nanofibers were fabricated to fine-tune their size and endow them with desirable transdermal delivery capacities. Silk nanocarrier length was shortened from 2000 nm to approximately 40 nm after ultrasonic treatment. In vitro human skin and in vivo animal studies revealed different transdermal behaviors for silk nanocarriers at different nanosizes. Silk nanocarriers passed slowly through the corneum without destroying the corneum structure. Improved transdermal capacity was achieved for smaller size carriers. Both hydrophilic and hydrophobic drugs could be loaded onto silk nanocarriers, suggesting a promising future for different disease therapies. No cytotoxicity and skin irritation were identified for silk nanocarriers, which strengthened their superiority as transdermal carriers. Therefore, silk nanocarriers <100 nm may promote the percutaneous absorption of active cargos for disease therapy and cosmetic applications.

Microneedle-Mediated Transdermal Delivery of Biopharmaceuticals

Transdermal delivery provides numerous benefits over conventional routes of administration. However, this strategy is generally limited to a few molecules with specific physicochemical properties (low molecular weight, high potency, and moderate lipophilicity) due to the barrier function of the stratum corneum layer. Researchers have developed several physical enhancement techniques to expand the applications of the transdermal field; among these, microneedle technology has recently emerged as a promising platform to deliver therapeutic agents of any size into and across the skin. Typically, hydrophilic biomolecules cannot penetrate the skin by passive diffusion. Microneedle insertion disrupts skin integrity and compromises its protective function, thus creating pathways (microchannels) for enhanced permeation of macromolecules. Microneedles not only improve stability but also enhance skin delivery of various biomolecules. Academic institutions and industrial companies have invested substantial resources in the development of microneedle systems for biopharmaceutical delivery. This review article summarizes the most recent research to provide a comprehensive discussion about microneedle-mediated delivery of macromolecules, covering various topics from the introduction of the skin, transdermal delivery, microneedles, and biopharmaceuticals (current status, conventional administration, and stability issues), to different microneedle types, clinical trials, safety and acceptability of microneedles, manufacturing and regulatory issues, and the future of microneedle technology.

Porous Microneedles for Therapy and Diagnosis: Fabrication and Challenges

The use of microneedles (MNs), an innovative transdermal technology, enables efficient, convenient, painless, and controlled-release drug delivery. Porous microneedles (pMNs), special MNs with abundant interconnected pores that can produce capillary action, are gaining increasing attention as a novel MNs technology. pMNs can actively adsorb bioactive ingredients from solutions of drugs or vaccines for in vivo delivery or from interstitial skin fluids (ISFs) for wearable and point-of-care testing (POCT) products. Different pore sizes and porosities of pMNs can be achieved with different materials and preparation processes, which makes the application of pMNs adaptable to multiple scenarios. In addition, easier and faster detection will be accomplished by the smart combination of pMNs with other detection technologies. This paper aims to summarize the recent research progress of pMNs, focusing on the influence of various materials and their corresponding preparation methods on its structure and function display, discussing the key issues and looking forward to the future development.

Development of an Automated Design Tool for FEM-Based Characterization of Solid and Hollow Microneedles

Microneedle design for biomedical applications, such as transdermal drug delivery, vaccination and transdermal biosensing, has lately become a rapidly growing research field. In this sense, finite element analysis has been extendedly used by microneedle designers to determine the most suitable structural parameters for their prototypes, and also to predict their mechanical response and efficiency during the insertion process. Although many proposals include computer-aided tools to build geometrical models for mechanical analysis, there is a lack of software utilities intended to automate the design process encompassing geometrical modeling, simulation setup and postprocessing of results. This work proposes a novel MATLAB-based design tool for microneedle arrays that permits personalized selection of the basic characteristics of a mechanical model. The tool automatically exports the selected options to an ANSYS batch file, including instructions to run a static and a linear buckling analysis. Later, the subsequent simulation results can be retrieved for on-screen display and potential postprocessing. In addition, this work reviews recent proposals (2018-2022) about finite element model characterization of microneedles to establish the minimum set of features that any tool intended for automating a design process should provide.

Mechanistic modeling-guided optimization of microneedle-based skin patch for rapid transdermal delivery of naloxone for opioid overdose treatment

Naloxone, an FDA-approved opioid inhibitor, used to reverse opioid overdose complications has up till date faced challenges associated with its delivery. Limitations include the use of invasive delivery forms and the need for frequent redosing due to its short half-life. The goal of the current study was to design a transdermal rapidly dissolving polymeric microneedle (MN) patch with delivery and pharmacokinetic properties comparable to that seen with the commercially available NAL products, eliminating their delivery limitations. Patches of varying dimensions (500 µm; 100 array,800 µm; 100array, and 600 µm; 225 array) were fabricated to evaluate the effect of increasing MN length, and density (no. of needles/unit area) on drug release. Drug dose in each of these patches was 17.89 ± 0.23 mg, 17.2 ± 0.77 mg, and 17.8 ± 1.01 mg, respectively. Furthermore, the insertion efficiency of each of the MN patches was 94 ± 4.8%, 90.6 ± 1.69%, and 96 ± 1.29%, respectively. Compared to passive permeation, a reduced lag time of about 5-15 min was observed with a significant drug flux of 15.09 ± 7.68 g[Formula: see text]/cm²/h seen in the first 1 h (p < 0.05) with the array of 100 needles (500 µm long). Over 24 h, a four and ten-fold increase in permeation was seen with the longer length and larger density MN patch, respectively, when compared to the 500 µm (100 array) patch. Model simulations and analyses revealed the significance of needle base diameter and needle count in improving systemic pharmacokinetics of NAL.

Pharmacokinetic improvement provided by microneedle patch in delivering bee venom, a case study in combating scopolamine-induced neurodegeneration in mouse model

Much research has shown Bee venom to be an effective neuroprotective agent. However, the usual transdermal injection of bee venom poses many pharmacokinetic disadvantages. Here, we compared the administration of bee venom via subcutaneous injection (SC) and via Microneedle patch (MN). Both administrated routes produce significant recovery effects, however: the MN significantly prolongs the bio-significant-and-yet-lower concentration of bee venom in mice bodies. In contrast, SC could produce only a short period of much higher bee venom levels in the blood and brain. We also see that due to the concentration-response-curve of bee venom (represented by melittin): mice bodies do not require much higher bee venom concentration (seen in the SC group) to produce a much more significant neuroprotective effect (than seen in those treated with the MN method). Therefore, a MN could maintain bee venom levels in mice bodies at lower-yet-more-efficient concentrations. This is important, as bee venom can cause more adverse effects and pain sensations, at higher concentrations. For the first time, we confirmed that the pharmacokinetic advantages of MN delivered bee venom also guarantee a holistic neuroprotection effect (which was shown by SC delivered bee venom in previous research). This was proven via the results of the water maze experiments for long-term learning memory assessment and protein analysis of key neuronal regulatory proteins: BDNF, p-CREB, iNOS, and mArhR 1. In conclusion, for situations where we ought to administrate drugs at a more downward amount, such as bee venom, MN can keep the therapeutic concentrations at a lower, yet interestingly, more-efficient level.

A Review of 3D-Printing of Microneedles

Microneedles are micron-sized devices that are used for the transdermal administration of a wide range of active pharmaceutics substances with minimally invasive pain. In the past decade, various additive manufacturing technologies have been used for the fabrication of microneedles; however, they have limitations due to material compatibility and bioavailability and are time-consuming and expensive processes. Additive manufacturing (AM), which is popularly known as 3D-printing, is an innovative technology that builds three-dimensional solid objects (3D). This article provides a comprehensive review of the different 3D-printing technologies that have the potential to revolutionize the manufacturing of microneedles. The application of 3D-printed microneedles in various fields, such as drug delivery, vaccine delivery, cosmetics, therapy, tissue engineering, and diagnostics, are presented. This review also enumerates the challenges that are posed by the 3D-printing technologies, including the manufacturing cost, which limits its viability for large-scale production, the compatibility of the microneedle-based materials with human cells, and concerns around the efficient administration of large dosages of loaded microneedles. Furthermore, the optimization of microneedle design parameters and features for the best printing outcomes is of paramount interest. The Food and Drug Administration (FDA) regulatory guidelines relating to the safe use of microneedle devices are outlined. Finally, this review delineates the implementation of futuristic technologies, such as artificial intelligence algorithms, for 3D-printed microneedles and 4D-printing capabilities.

Imaging-Guided Micromachines: Towards Intelligent Systems

Micromachines with controllable motion, deformation, and collective behaviors provide advanced methods for performing tasks that traditional machines have difficulty completing thanks to the development of small-scale robotics, nanotechnology, biocompatible materials, and imaging techniques [...].

Lasered Graphene Microheaters Modified with Phase-Change Composites: New Approach to Smart Patch Drug Delivery

The combination of paraffin wax and O,O'-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol was used as a phase-change material (PCM) for the controlled delivery of curcumin. The PCM was combined with a graphene-based heater derived from the laser scribing of polyimide film. This assembly provides a new approach to a smart patch through which release can be electronically controlled, allowing repetitive dosing. Rather than relying on passive diffusion, delivery is induced and terminated through the controlled heating of the PCM with transfer only occurring when the PCM transitions from solid to liquid. The material properties of the device and release characteristics of the strategy under repetitive dosing are critically assessed. The delivery yield of curcumin was found to be 3.5 µg (4.5 µg/cm2) per 3 min thermal cycle.

Microneedle-Based Vaccine Delivery: Review of an Emerging Technology

Vaccination has produced a great improvement to the global health by decreasing/eradicating many infectious diseases responsible for significant morbidity and mortality. Thanks to vaccines, many infections affecting childhood have been greatly decreased or even eradicated (smallpox, measles, and polio). That is why great efforts are made to achieve mass vaccination against COVID-19. However, developed vaccines face many challenges with regard to their safety and stability. Moreover, needle phobia could prevent a significant proportion of the population from receiving vaccines. In this context, microneedles (MNs) could potentially present a solution to address these challenges. MNs represent single dose administration systems that do not need reconstitution or cold-chain storage. Being self-administered, pain-free, and capable of producing superior immunogenicity makes them a more attractive alternative. This review explores microneedles’ types, safety, and efficacy in vaccine delivery. Preclinical and clinical studies for microneedle-based vaccines are discussed and patent examples are included.

Microneedle-Based Natural Polysaccharide for Drug Delivery Systems (DDS): Progress and Challenges

In this focused progress review, the most widely accepted methods of transdermal drug delivery are hypodermic needles, transdermal patches and topical creams. However, microneedles (MNs) (or microneedle arrays) are low-invasive 3D biomedical constructs that bypass the skin barrier and produce systemic and localized pharmacological effects. In the past, biomaterials such as carbohydrates, due to their physicochemical properties, have been extensively used to manufacture microneedles (MNs). Due to their wide range of functional groups, carbohydrates enable the design and development of tunable properties and functionalities. In recent years, numerous microneedle products have emerged on the market, although much research needs to be undertaken to overcome the various challenges before the successful introduction of microneedles into the market. As a result, carbohydrate-based microarrays have a high potential to achieve a future step in sensing, drug delivery, and biologics restitution. In this review, a comprehensive overview of carbohydrates such as hyaluronic acid, chitin, chitosan, chondroitin sulfate, cellulose and starch is discussed systematically. It also discusses the various drug delivery strategies and mechanical properties of biomaterial-based MNs, the progress made so far in the clinical translation of carbohydrate-based MNs, and the promotional opportunities for their commercialization. In conclusion, the article summarizes the future perspectives of carbohydrate-based MNs, which are considered as the new class of topical drug delivery systems.

Application of microneedle patches for drug delivery; doorstep to novel therapies

In the past decade, microneedle-based drug delivery systems showed promising approaches to become suitable and alternative for hypodermic injections and can control agent delivery without side effects compared to conventional approaches. Despite these advantages, the procedure of microfabrication is facing some difficulties. For instance, drug loading method, stability of drugs, and retention time are subjects of debate. Besides, the application of novel refining fabrication methods, types of materials, and instruments are other issues that need further attention. Herein, we tried to summarize recent achievements in controllable drug delivery systems (microneedle patches) in vitro and in vivo settings. In addition, we discussed the influence of delivered drugs on the cellular mechanism and immunization molecular signaling pathways through the intradermal delivery route. Understanding the putative efficiency of microneedle patches in human medicine can help us develop and design sophisticated therapeutic modalities.