Development of Novel Faster-Dissolving Microneedle Patches for Transcutaneous Vaccine Delivery

Highly Water-Soluble Microneedle Patch for Short Wear Time and Rapid Drug Delivery

Treatment of acute medical conditions such as pain would benefit from rapid drug delivery and improved ease of administration of local anesthetics that currently have a slow onset of action by topical or oral administration and require expert administration by injection. To address this need, microneedle (MN) patches containing needlelike projections made from a polymer/drug matrix can be painlessly pressed into the skin for local or systemic drug delivery. To improve the speed and ease of drug delivery, we present a rapidly dissolving, highly water-soluble MN patch, which minimizes the wear time to 10 s to improve drug delivery in situations where rapid delivery with simplified administration is needed. MNs were made of polyvinylpyrrolidone (PVP), which is soluble in both water (enabling dissolution in the skin) and polar organic solvents (facilitating coformulation with lidocaine (L)). The addition of a highly water-soluble salt, sodium bicarbonate (NaB), to PVP/L MNs allowed for 60% faster MN dissolution in porcine skin ex vivo. Further addition of citric acid to generate effervescence upon reaction with NaB did not further decrease the MN dissolution time in the pig skin and led to poor shelf-life stability due to premature effervescence during storage. The PVP/L/NaB MNs delivered 23.8 ± 3.5 μg lidocaine to the skin ex vivo, well above the expected dose for local analgesic effect. Our highly water-soluble PVP/L/NaB MN design enables shorter wear time for faster delivery compared to the oral or topical route and easier administration compared to injection currently used for the delivery of drugs needing a rapid onset of action.

Development and optimization of a methimazole microemulsion for topical application: Formulation characteristics and transdermal permeation

BACKGROUND

Methimazole, an oral antithyroid drug, has recently gained attention for its skin-brightening effects when applied topically to treat melasma. This study aims to develop, optimize, and characterize a methimazole microemulsion as a novel, safe approach for local melasma treatment.

MATERIALS AND METHODS

We prepared microemulsion formulations containing 3% methimazole by combining appropriate amounts of surfactants (Tween 80 and Span 20), propylene glycol cosurfactant, and an oil phase (oleic acid-transcutol p at a 1:10 ratio). We then assessed droplet size, stability, viscosity, and skin permeation using rat skin models.

RESULTS

The microemulsions' droplet sizes ranged from 7.06 to 28.13 nm, with viscosities between 120 and 254 centipoises. Our analysis identified droplet size, viscosity, and membrane release as significant independent variables. We determined the permeability parameters of the optimal formulation through rat skin, including steady-state permeability rate (Jss), permeability coefficient (p), lag time (Tlag), and apparent diffusion coefficient (Dapp).

CONCLUSION

We found that the microemulsions' characteristics, physicochemical properties, and in vitro release depended on the surfactant-to-cosurfactant ratio, water content, and oil content. We developed an optimal formulation with a high surfactant-to-cosurfactant ratio and low water and oil percentages. This formulation shows potential for commercialization and manufacturing of final products.

ATP-adenosine axis regulation combined with microneedle assisted photoimmunotherapy to boost the immunotherapy efficiency

Immunogenic cell death (ICD) is associated with the release of damage-associated molecular patterns, including ATP, to promote an effective immune cycle against tumors. However, tumors have evolved an effective strategy for degrading extracellular immunostimulatory ATP via the ATP-adenosine axis, allowing the sequential action of the ectonucleotidases CD39 to degrade accumulated immunostimulatory ATP into pleiotropic immunosuppressive adenosine. Here, an ingenious dissolving microneedle patch (DMNs) is designed for the intralesional delivery of CD39 inhibitor (sodium polyoxotungstate, POM-1) and ICD inducer (IR780) co-encapsulated solid lipid nanoparticles (P/I SLNs) for antitumor therapy. Upon insertion into the tumor site, IR780 induces ICD modalities with the release of damage-associated molecular patterns from endogenous tissues, which activates the antitumor immune cycle. Simultaneously, POM-1 promotes the liberation of immunostimulatory ATP and lowers the level of immunosuppressive extracellular adenosine, which supported immune control of tumors via recruiting CD39-expressing immune cells. In vivo antitumor studies prove that this platform can effectively eliminate mice melanoma (tumor growth inhibitory rate of 96.5%) and colorectal adenocarcinoma (tumor growth inhibitory rate of 93.5%). Our results shed light on the immunological aspects of combinatorial phototherapy and ATP-adenosine regulation, which will broaden the scope of synergistic antitumor immunotherapy.

Mechanical Characterization of Dissolving Microneedles: Factors Affecting Physical Strength of Needles

Dissolving microneedles (MNs) are novel transdermal drug delivery systems that can be painlessly self-administered. This study investigated the effects of experimental conditions on the mechanical characterization of dissolving MNs for quality evaluation. Micromolding was used to fabricate polyvinyl alcohol (PVA)-based dissolving MN patches with eight different cone-shaped geometries. Axial force mechanical characterization test conditions, in terms of compression speed and the number of compression needles per test, significantly affected the needle fracture force of dissolving MNs. Characterization using selected test conditions clearly showed differences in the needle fracture force of dissolving MNs prepared under various conditions. PVA-based MNs were divided into two groups that showed buckling and unbuckling deformation, which occurred at aspect ratios (needle height/base diameter) of 2.8 and 1.8, respectively. The needle fracture force of PVA-based MNs was negatively correlated with an increase in the needle's aspect ratio. Higher residual water or higher loading of lidocaine hydrochloride significantly decreased the needle fracture force. Therefore, setting appropriate methods and parameters for characterizing the mechanical properties of dissolving MNs should contribute to the development and supply of appropriate products.

Pharmaceutical and Immunological Evaluation of Cholera Toxin A1 Subunit as an Adjuvant of Hepatitis B Vaccine Microneedles

PURPOSE

For successful delivery of a solid vaccine formulation into the skin using microneedles, the solubility of an adjuvant should be considered because the decrease in the dissolution rate by the addition of adjuvant decreases the delivery efficiency of the vaccine.

METHODS

In this study, cholera toxin A subunit 1 (CTA1) was examined as an adjuvant to Hepatitis B vaccine (HBV) microneedles because of its good water solubility, improved safety, and positive effect as shown in intramuscular administration of a liquid vaccine.

RESULTS

All solid formulations with CTA 1 dissolved in in vivo mouse skin within 30 min, and they were successfully delivered into the skin. In experiments with mice, the addition of CTA1 led to improved IgG immune response compared to the use of an aluminum hydroxide-based formulation and intramuscular administration of HBV. In addition, CTA1 induced CD8 + T cell response as much as in which the aluminum hydroxide-based formulation induced.

CONCLUSIONS

CTA1 is an adjuvant that satisfies both the delivery efficiency and the immunological characteristics required for vaccine microneedles. CTA1 will be used as a potential adjuvant through vaccine microneedles.

The promising application of hydrogel microneedles in medical application

OBJECTIVES

Hydrogel microneedles are emerging, and promising microneedles mainly composed of swelling polymers. This review is intended to summarize the preparation materials, formation mechanisms, applications and existing problems of hydrogel microneedles.

METHODS

We collected the literature on the materials, preparation and application of hydrogel microneedles in recent years, and summarized their mechanism and application in drugs delivery.

KEY FINDINGS

Hydrogel microneedles have higher safety and capabilities of controlled drug release, and have been mainly used in tumour and diabetes treatment, as well as clinical monitoring. In recent years, hydrogel microneedles have shown great potential in drug delivery, and have played the role of whitening, anti-inflammatory and promoting healing.

CONCLUSIONS

As an emerging drug delivery idea, hydrogel microneedles for drug delivery has gradually become a research hotspot. This review will provide a systematic vision for the favourable development of hydrogel microneedles and their promising application in medicine, especially drug delivery.

Responsive Microneedles as a New Platform for Precision Immunotherapy

Microneedles are a well-known transdermal or transdermal drug delivery system. Different from intramuscular injection, intravenous injection, etc., the microneedle delivery system provides unique characteristics for immunotherapy administration. Microneedles can deliver immunotherapeutic agents to the epidermis and dermis, where immune cells are abundant, unlike conventional vaccine systems. Furthermore, microneedle devices can be designed to respond to certain endogenous or exogenous stimuli including pH, reactive oxygen species (ROS), enzyme, light, temperature, or mechanical force, thereby allowing controlled release of active compounds in the epidermis and dermis. In this way, multifunctional or stimuli-responsive microneedles for immunotherapy could enhance the efficacy of immune responses to prevent or mitigate disease progression and lessen systemic adverse effects on healthy tissues and organs. Since microneedles are a promising drug delivery system for accurate delivery and controlled drug release, this review focuses on the progress of using reactive microneedles for immunotherapy, especially for tumors. Limitations of current microneedle system are summarized, and the controllable administration and targeting of reactive microneedle systems are examined.

Microneedle Transdermal Drug Delivery Systems for Allergen-Specific Immunotherapy, Skin Disease Treatment, and Vaccine Development

Transdermal drug delivery systems (TDDSs) overcome the hurdle of an intact skin barrier by penetrating the skin to allow molecules through. These systems reduce side effects associated with conventional hypodermic needles. Here, we introduce novel microneedle (MN) TDDSs that enhance drug delivery by creating micron-sized pores across the skin. Many MN TDDSs designed to deliver a diverse array of therapeutics, including allergen-specific immunotherapy, skin disease treatments, and vaccines, are under pre-clinical and clinical trials. Although epicutaneous approaches are emerging as new options for treating food allergy in many clinical trials, MN TDDSs could provide a more efficient and convenient route to deliver macromolecules. Furthermore, MN TDDSs may allow for safe vaccine delivery without permanent scars. MN TDDSs are a major emerging strategy for delivering novel vaccines and treatments for diseases, including skin diseases, allergic diseases, and so on.

An update on biomaterials as microneedle matrixes for biomedical applications

Microneedles (MNs) have been developed for various applications such as drug delivery, cosmetics, diagnosis, and biosensing. To meet the requirements of MNs used in these areas, numerous materials have been used for the fabrication of MNs. However, MNs will be exposed to skin tissues after piercing the stratum corneum barrier. Thus, it is necessary to ensure that the matrix materials of MNs have the characteristics of low toxicity, good biocompatibility, biodegradability, and sufficient mechanical properties for clinical application. In this review, the matrix materials currently used for preparing MNs are summarized and reviewed in terms of these factors. In addition, MN products used on the market and their applications are summarized in the end. This work may provide some basic information to researchers in the selection of MN matrix materials and in developing new materials.

Preparation and characterization of fast dissolving ulvan microneedles for transdermal drug delivery system

Dissolving microneedles made from natural polymers recently have gained much attention as an efficient transdermal drug delivery system (TDDS). For the first time, ulvan, a sulfated polysaccharide extracted from Ulva lactuca, was applied to fabricate dissolving microneedles through a two-step casting method. The ulvan microneedles (UMNs) made from 4% ulvan solution were in a pyramidal shape with an average height of 655 μm and an aspect ratio of 2.63. The in vitro skin insertion study showed the UMNs could totally penetrate into the porcine skin to the dermis layer and rapidly dissolved as the needle height was reduced by 90.3% after post-insertion of only 2 min. The rapid dissolution of UMNs in situ thus could release the loaded model drugs of rhodamine 6G (R6G) and bovine serum albumin-fluorescein isothiocyanate conjugate (FITC-BSA) in the skin tissue. The in vitro drug release profiles through porcine skin revealed the UMNs markedly enhanced the cumulative release of FITC-BSA. In addition, the UMNs had good biocompatibility towards normal cells of HaCaT and NIH3T3. Briefly, this study demonstrates the rapidly dissolving UMNs could effectively carry the drug into skin and thus can be developed as a potential TDDS in the pharmaceutical and cosmeceutical fields.

Analysis of immune response induction mechanisms implicating the dose-sparing effect of transcutaneous immunization using a self-dissolving microneedle patch

Transcutaneous immunization (TCI) is an effective vaccination method that is easier and less painful than the conventional injectable vaccination method. We previously developed self-dissolving microneedle patches (sdMN) and demonstrated that this TCI method has a high vaccination efficacy in mice and humans. To elucidate the mechanism of immune response induction, which is the basis for the efficacy and safety of TCI with sdMN, we examined the local reaction of the skin where sdMN was applied and the kinetics and differentiation status of immune cells in the draining lymph nodes (DLNs). We found that gene expression of the proinflammatory cytokine Il1b and the downstream transcription factor Irf7 was markedly upregulated in skin tissues after sdMN application. Moreover, activation of Langerhans cells and CD207^- dermal dendritic cells, which are subsets of antigen-presenting cells (APCs) in the skin, and their migration to the DLNs were promoted. Furthermore, the activated APC subsets promoted CD4⁺ T cell and B cell differentiation and the formation of germinal centers, which are the sites of high-affinity antibody production. These phenomena associated with sdMN application may contribute to the efficient production of antigen-specific antibodies after TCI using sdMN. These findings provide essential information regarding immune response induction mechanisms for the development and improvement of TCI preparations.

Microneedle-Mediated Vaccination: Innovation and Translation

Vaccine administration by subcutaneous or intramuscular injection is the most commonly prescribed route for inoculation, however, it is often associated with some deficiencies such as low compliance, high professionalism, and risk of infection. Therefore, the application of microneedles for vaccine delivery has gained widespread interests in the past few years due to its high compliance, minimal invasiveness, and convenience. This review focuses on recent advances in the development and application of microneedles for vaccination based on different delivery strategies, and introduces the current status of microneedle-mediated vaccination in clinical translation. The prospects for its application including opportunities and challenges are further discussed.

Recent Advances in Microneedle-Based Sensors for Sampling, Diagnosis and Monitoring of Chronic Diseases

Chronic diseases (CDs) are noncommunicable illnesses with long-term symptoms accounting for ~70% of all deaths worldwide. For the diagnosis and prognosis of CDs, accurate biomarker detection is essential. Currently, the detection of CD-associated biomarkers is employed through complex platforms with certain limitations in their applicability and performance. There is hence unmet need to present innovative strategies that are applicable to the point-of-care (PoC) settings, and also, provide the precise detection of biomarkers. On the other hand, especially at PoC settings, microneedle (MN) technology, which comprises micron-size needles arranged on a miniature patch, has risen as a revolutionary approach in biosensing strategies, opening novel horizons to improve the existing PoC devices. Various MN-based platforms have been manufactured for distinctive purposes employing several techniques and materials. The development of MN-based biosensors for real-time monitoring of CD-associated biomarkers has garnered huge attention in recent years. Herein, we summarize basic concepts of MNs, including microfabrication techniques, design parameters, and their mechanism of action as a biosensing platform for CD diagnosis. Moreover, recent advances in the use of MNs for CD diagnosis are introduced and finally relevant clinical trials carried out using MNs as biosensing devices are highlighted. This review aims to address the potential use of MNs in CD diagnosis.

Chemical imaging analysis of active pharmaceutical ingredient in dissolving microneedle arrays by Raman spectroscopy

The purpose of this study was to develop a quality evaluation method for dissolving microneedle arrays (DMNAs) and determine the spatial distribution pattern of drugs in DMNAs. Raman spectroscopy mapping was used to visualize the drug distribution in DMNAs and drug-loaded polymer films as a model. Powder X-ray diffraction (PXRD) and high-pressure liquid chromatography were also performed to characterize DMNAs. Drug-loaded polymer films and DMNAs were prepared by drying the aqueous solutions spread on the plates or casting. PXRD analysis suggested the crystallization of diclofenac sodium (DCF) in several forms depending on its amount in the sodium hyaluronate (HA)-based films. The Raman spectra of HA and DCF showed characteristic and non-overlapping peaks at 1376 and 1579 cm^-1 Raman shifts, respectively. The intensity of the characteristic peak of DCF in the DCF-loaded films increased linearly with the increasing drug content in the range of 4.8 to 16.7% (DCF, w/w). Raman imaging analysis revealed a homogenous dispersion of small DCF crystals in these films. Raman imaging indicates the distribution of DCF on the surface of the DMNA needle. This work highlights the benefit of using Raman spectroscopy mapping to reveal the spatial distribution of drugs in DMNAs.

Dissolving microneedles for transdermal delivery of huperzine A for the treatment of Alzheimer's disease

Increasingly attention has been paid to the transdermal drug delivery systems with microneedles owing to their excellent compliance, high efficiency, and controllable drug release, therefore, become promising alternative with tremendous advantages for delivering specific drugs such as huperzine A (Hup A) for treatment of Alzheimer's disease (AD) yet with low oral bioavailability. The purpose of the present study is to design, prepare, and evaluate a dissolving microneedle patch (DMNP) as a transdermal delivery system for the Hup A, investigating its in vitro drug release profiles and in vivo pharmacokinetics as well as pharmacodynamics treating of AD. Skin penetration experiments and intradermal dissolution tests showed that the blank DMNP could successfully penetrate the skin with an adequate depth and could be quickly dissolved within 5 min. In vitro transdermal release tests exhibited that more than 80% of the Hup A was accumulatively permeated from DMNP through the skin within three days, indicating a sustained release profile. In vivo pharmacokinetic analysis demonstrated that the DMNP group resulted in longer T max (twofold), longer t 1/2 (fivefold), lower C max (3:4), and larger AUC(0-∞) (twofold), compared with the oral group at the same dose of Hup A. Pharmacodynamic research showed a significant improvement in cognitive function in AD rats treated with DMNP-Hup A and Oral-Hup A, as compared to the model group without treatment. Those results demonstrated that this predesigned DMNP is a promising alternative to deliver Hup A transdermally for the treatment of AD.

Characteristic of K3 (CpG-ODN) as a Transcutaneous Vaccine Formulation Adjuvant

Transcutaneous immunization (TCI) is easy to use, minimally invasive, and has excellent efficacy in vaccines against infections. We focused on toll-like receptor (TLR) ligands as applicable adjuvants for transcutaneous formulations and characterized immune responses. TCI was performed using poke-and-patch methods, in which puncture holes are formed with a polyglycolic acid microneedle on the back skin of mice. Various TLR ligands were applied to the puncture holes and covered with an ovalbumin-loaded hydrophilic gel patch. During the screening process, K3 (CpG-oligonucleotide) successfully produced more antigen-specific antibodies than other TLR ligands and induced T helper (Th) 1-type polarization. Transcutaneously administered K3 was detected in draining lymph nodes and was found to promote B cell activation and differentiation, suggesting a direct transcutaneous adjuvant activity on B cells. Furthermore, a human safety test of K3-loaded self-dissolving microneedles (sdMN) was performed. Although a local skin reaction was observed at the sdMN application site, there was no systemic side reaction. In summary, we report a K3-induced Th1-type immune response that is a promising adjuvant for transcutaneous vaccine formulations using MN and show that K3-loaded sdMN can be safely applied to human skin.

A fast-dissolving microneedle array loaded with chitosan nanoparticles to evoke systemic immune responses in mice

Microneedle (MN) arrays offer an alternative approach to hypodermic injection via syringe needles. In this work, polyvinylpyrrolidone (PVP)-based fast dissolving MN arrays were developed in which the needle tips were loaded with chitosan nanoparticles (NPs) for coencapsulation of a model antigen, ovalbumin (OVA), and an adjuvant, CpG oligodeoxynucleotides (CpG). After insertion into the skin, these MN arrays fully dissolved within 3 min to release antigen and adjuvant co-loaded NPs rapidly in the epidermal layer. Positively charged chitosan was proven to be an excellent carrier for negatively charged OVA and CpG, which formed nanocomplexes via simple electrostatic interactions and greatly enhanced the uptake efficiency of OVA in DC2.4 dendritic cells. Vaccination studies in mice further demonstrated that chitosan NPs effectively accumulated in peripheral lymph nodes, thus inducing greatly enhanced immune responses compared to those of free OVA. The antibody dose-response curve further demonstrated that MN immunization achieved comparable levels of immune responses as compared to conventional subcutaneous injections in a more convenient and less invasive way. Overall, a PVP-based fast dissolving MN array with chitosan NPs represents a promising and robust platform system for efficient transcutaneous vaccine delivery.

Fabrication of Dissolvable Microneedle Patches Using an Innovative Laser-Cut Mould Design to Shortlist Potentially Transungual Delivery Systems: In Vitro Evaluation

There has been a great interest towards transungual delivery systems due to limited drug penetration for the treatment of nail diseases. More important, antifungal oral medicaments used may cause serious side effects including liver damage. Therefore, we propose non-oral dissolvable microneedle (MN) patch to strike the poor permeability of the nail. We report the design of MN patch mould using a laser-cutting machine and solvent casting of several hydrophilic polymers to fabricate these MN patches. Formulations were evaluated for their in vitro release and penetration properties and selected based on physical characterization for compatibility (differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD)), dimension repeatability and drug content uniformity. A 72-array of cone-shaped MN patch mould was successfully constructed on polymethylmethacrylate sheets. Interval and frequency of laser exposure were pivotal to determine the needle sharpness, attained unexpectedly at a low level of circa 30 μm. F1 platform of polyvinyl alcohol, kollicoat IR®, ethylene glycol and gelatin showed circa 74% penetration of methylhydroxy-4-benzoate (F1(A)) over 24 h, whereas F2 (same as F1-A with the addition of poloxamer 338) resulted in an almost 42% of this drug retention in the bovine hoof (24 h). Both formulations are likely to be useful for onychomycosis treatment. F1 polymers also afford enhanced permeability (almost 73.5% after 24 h) of terbinafine hydrochloride into the hoof (F1(B)). However, F3 (chitosan, gelatin and ethylene glycol) presents the prospect of developing MN patch for this drug with almost complete hoof penetration (circa 96.3% after 24 h). All medicated formulations have shown similar mechanical properties after ageing for 1 year under dry conditions.

Correction: Development of Novel Faster-Dissolving Microneedle Patches for Transcutaneous Vaccine Delivery. Pharmaceutics, 2017, 9(3), 27

The authors wish to make a change to their published paper [1].[...].