State-of-the-art strategies to enhance the mechanical properties of microneedles

Microneedles (MNs) have gained increasing attention in the biomedical field, owing to their notable advantages over injectable and transdermal preparations. The mechanical properties of MNs are the key to determine whether MNs can puncture the skin for efficient drug delivery and therapeutic purposes. However, there is still lacking of a systemic summary on how to improve the mechanical properties of MNs. Herein, this review mainly analyzes the key factors affecting the mechanical properties of MNs from the theoretical point of view and puts forward improvement approaches. First, we analyzed the major stresses exerted on the MNs during skin puncture and described general methods to evaluate the mechanical properties of MNs. We then provided detail examples to elucidate how the physicochemical properties of single polymer, formulation compositions, and geometric parameters affected the mechanical properties of MNs. Overall, the mechanical strength of MNs can be enhanced by tuning the crosslinking density, crystallinity degree, and molecular weight of single polymer, introducing polysaccharides and nano-microparticles as reinforcers to form complex with polymer, and optimizing the geometric parameters of MNs. Therefore, this review will provide critical guidance on how to fabricate MNs with robust mechanical strength for successful transdermal drug delivery.

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.

Fabrication and Characterization of Dissolving Microneedles Containing Oryza sativa L. Extract Complex for Enhancement of Transfollicular Delivery

Dissolving microneedles are extensively applied in drug delivery systems to enhance penetration into the skin. In this study, dissolving microneedles fabricated from polyvinylpyrrolidone K90 (PVP-K90) and hydroxypropylmethyl cellulose (HPMC) E50 in different ratios were characterized. The selected formulations incorporated Oryza sativa L. extract complex and its characteristics, transfollicular penetration, and safety were observed. The microneedles, fabricated from PVP K90: HPMC E50 in a ratio of 25:5 (P25H5) and 20:10 (P20H10), revealed excellent morphological structure, proper mechanical strength, and excellent skin insertion. P25H5 microneedles exhibited faster dissolution than P20H10 microneedles. Microneedles containing Oryza sativa L. extract complex showed excellent morphological structure via scanning electron microscopy but decreased mechanical strength. P25H5-O, which exhibited an effective ability to enter skin, was selected for further investigation. This microneedle formulation had a high percentage of drug-loading content, enhanced skin penetration via the transfollicular route, and was safe for keratinocytes. As a result, the dissolving microneedle containing Oryza sativa L. extract complex can be used to enhance transfollicular delivery through the skin with safety.

Fabrication, evaluation, and enhanced penetration of vinyl and cellulose-engineered transdermal patch of nifedipine using essential oil as penetration enhancer

The aim of this study was to develop and evaluate the transdermal patch formulations of nifedipine. The patch formulations containing nifedipine were prepared and optimized with different ratios of vinyl and cellulose-derived polymers, drug contents, and permeation enhancers. Among the various formulations, the patch formulation containing a 1:5 ratio of ethyl cellulose and polyvinyl pyrrolidone was selected for ex vivo pharmacokinetic study based on in vitro permeation studies using stratum corneum of the pig's skin. The cumulative percentage release after the transdermal administration of the optimized patch formulation was 71.43%, and the plasma concentration of nifedipine was maintained for 16 hrs. The physicochemical evaluation study including flatness, thickness, moisture content and uptake, drug content in vitro release, and ex vivo permeation indicated satisfactory results. The formulation batch with clove oil as a penetration enhancer has shown better ex vivo permeation as compared to the formulations without enhancers and another synthetic enhancer. These results suggest that the optimized patch formulation Q3 could be further developed for clinical applications, providing the therapeutic plasma level of nifedipine over an extended period. Hence analyzing the results of the evaluation tests, in vitro and ex vivo data on the preparation and optimization of nifedipine-loaded transdermal patch, it can be concluded that the formulation shows its feasibility as an effective transdermal delivery system for nifedipine.

Cyclosporin A-loaded dissolving microneedles for dermatitis therapy: Development, characterisation and efficacy in a delayed-type hypersensitivity in vivo model

Several drugs can be used for treating inflammatory skin pathologies like dermatitis and psoriasis. However, for the management of chronic and long-term cases, topical administration is preferred over oral delivery since it prevents certain issues due to systemic side effects from occurring. Cyclosporin A (CsA) has been used for this purpose; however, its high molecular weight (1202 Da) restricts the diffusion through the skin structure. Here, we developed a nano-in-micro device combining lipid vesicles (LVs) and dissolving microneedle array patches (DMAPs) for targeted skin delivery. CsA-LVs allowed the effective incorporation of CsA in the hydrophilic DMAP matrix despite the hydrophobicity of the drug. Polymeric matrix composed of poly (vinyl alcohol) (5% w/v), poly (vinyl pyrrolidine) (15% w/v) and CsA-LV dispersion (10% v/v) led to the formation of CsA-LVs@DMAPs with adequate mechanical properties to penetrate the stratum corneum barrier. The safety and biocompatibility were ensured in an in vitro viability test using HaCaT keratinocytes and L929 fibroblast cell lines. Ex vivo permeability studies in a Franz-diffusion cell setup showed effective drug retention in the skin structure. Finally, CsA-LVs@DMAPs were challenged in an in vivo murine model of delayed-type hypersensitivity to corroborate their potential to ameliorate skin inflammatory conditions. Different findings like photon emission reduction in bioluminescence study, normalisation of histological damage and decrease of inflammatory cytokines point out the effectivity of CsA-LVs@DMAPs to treat these conditions. Overall, our study demonstrates that CsA-LVs@DMAPs can downregulate the skin inflammatory environment which paves the way for their clinical translation and their use as an alternative to corticosteroid-based therapies.

Fabrication of dissolving microneedles for transdermal delivery of protein and peptide drugs: polymer materials and solvent casting micromoulding method

Proteins and peptides are rapidly developing pharmaceutical products and are expected to continue growing in the future. However, due to their nature, their delivery is often limited to injection, with drawbacks such as pain and needle waste. To overcome these limitations, microneedles technology is developed to deliver protein and peptide drugs through the skin. One type of microneedles, known as dissolving microneedles, has been extensively studied for delivering various proteins and peptides, including ovalbumin, insulin, bovine serum albumin, polymyxin B, vancomycin, and bevacizumab. This article discusses polymer materials used for fabricating dissolving microneedles, which are poly(vinylpyrrolidone), hyaluronic acid, poly(vinyl alcohol), carboxymethylcellulose, GantrezTM, as well as other biopolymers like pullulan and ulvan. The paper is focused solely on solvent casting micromoulding method for fabricating dissolving microneedles containing proteins and peptides, which will be divided into one-step and two-step casting micromoulding. Additionally, future considerations in the market plan for dissolving microneedles are discussed in this article.

Bibliometric analysis and visualization of transdermal drug delivery research in the last decade: global research trends and hotspots

Background: Transdermal delivery has become a crucial field in pharmaceutical research. There has been a proliferation of innovative methods for transdermal drug delivery. In recent years, the number of publications regarding transdermal drug delivery has been rising rapidly. To investigate the current research trends and hotspots in transdermal drug delivery, a comprehensive bibliometric analysis was performed. Methods: An extensive literature review was conducted to gather information on transdermal drug delivery that had been published between 2003 and 2022. The articles were obtained from the Web of Science (WOS) and the National Center for Biotechnology Information (NCBI) databases. Subsequently, the collected data underwent analysis and visualization using a variety of software tools. This approach enables a deeper exploration of the hotspots and emerging trends within this particular research domain. Results: The results showed that the number of articles published on transdermal delivery has increased steadily over the years, with a total of 2,555 articles being analyzed. The most frequently cited articles were related to the optimization of drug delivery and the use of nanotechnology in transdermal drug delivery. The most active countries in the field of transdermal delivery research were the China, United States, and India. Furthermore, the hotspots over the past 2 decades were identified (e.g., drug therapy, drug delivery, and pharmaceutical preparations and drug design). The shift in research focus reflects an increasing emphasis on drug delivery and control release, rather than simply absorption and penetration, and suggests a growing interest in engineering approaches to transdermal drug delivery. Conclusion: This study provided a comprehensive overview of transdermal delivery research. The research indicated that transdermal delivery would be a rapidly evolving field with many opportunities for future research and development. Moreover, this bibliometric analysis will help researchers gain insights into transdermal drug delivery research's hotspots and trends accurately and quickly.

Hofmeister effect-based soaking strategy for gelatin hydrogels with adjustable gelation temperature, mechanical properties, and ionic conductivity

As a natural polymer with good biocompatibility, gelatin hydrogel has been widely used in the field of biomedical science for a long time. However, the lack of suitable gelation temperature and mechanical properties often limit the clinical applicability in diverse and complex environments. Here, we proposed a strategy based on the Hofmeister effect that gelatin hydrogels were soaked in the appropriate concentration of sodium sulfate solution, and the change in molecular chain interactions mainly guided by kosmotropic ions resulted in a comprehensive adjustment of multiple properties. A series of gelatin hydrogels treated with different concentrations of the salt solution gave rise to microstructural changes, which brought a decrease in the number and size of pores, a wide range of gelation temperature from 32 °C to 46 °C, a stress enhancement of about 40 times stronger to 0.8345 MPa, a strain increase of about 7 times higher to 238.05 %, and a certain degree of electrical conductivity to be utilized for versatile applications. In this regard, for example, we prepared microneedles and obtained a remarkable compression (punctuation) strength of 0.661 N/needle, which was 55 times greater than those of untreated ones. Overall, by integrating various characterizations and suggesting the corresponding mechanism behind the phenomenon, this method provides a simpler and more convenient performance control procedure. This allowed us to easily modulate the properties of the hydrogel as per the intended purpose, revealing its vast potential applications such as smart sensors, electronic skin, and drug delivery.

Development and Evaluation of an Innovative Approach Using Niosomes Based Polymeric Microneedles to Deliver Dual Antioxidant Drugs

Ascorbic acid (AA) and caffeine (CAFF) work to protect cells from ultraviolet (UV) radiation and slow down the photoaging process of the skin. However, cosmetic application of AA and CAFF is limited due to poor penetration across the skin and rapid oxidation of AA. The aim of this study was to design and evaluate the dermal delivery of dual antioxidants utilizing microneedles (MNs) loaded with AA and CAFF niosomes. The niosomal nanovesicles were prepared using the thin film method and had particle sizes ranging from 130.6-411.2 nm and a negative Zeta potential of around -35 mV. The niosomal formulation was then combined with polyvinylpyrrolidone (PVP) and polyethylene glycol 400 (PEG 400) to create an aqueous polymer solution. The best skin deposition of AA and CAFF was achieved with the formulation containing 5% PEG 400 (M3) and PVP. Furthermore, the role of AA and CAFF as antioxidants in preventing cancer formation has been well-established. Here we validated the antioxidant properties of ascorbic acid (AA) and caffeine (CAFF) in a novel niosomal formulation referred to as M3 by testing its ability to prevent H₂O₂-indued cell damage and apoptosis in MCF-7 breast cancer cells. Results showed that M3 was able to shield MCF-7 cells from H₂O₂ induced damage at concentrations below 2.1 µg/mL for AA and 1.05 µg/mL for CAFF, and also exhibited anticancer effects at higher concentrations of 210 µg/mL for AA and 105 µg/mL. The formulations were stable for two months at room temperature in terms of moisture and drug content. The use of MNs and niosomal carriers could be a promising approach for dermal delivery of hydrophilic drugs like AA and CAFF.

Characterization of silk fibroin-based microneedles and in vitro study of stromal cell-derived factor-1-loaded microneedles on adipose stem cell recruitment

Silk fibroin (SF) has good biocompatibility, degradability and mechanical properties. In this study, SF-based microneedle (MN) patches were fabricated as stromal cell-derived factor-1 (SDF-1) carriers that may be used for adipose stem cell (ASC) recruitment. Therefore, SF was chosen as the main MN material to achieve sustained drug release. In addition, the variations in SF-based MN crystallinity after water annealing treatment were also determined. The results indicated that SF-based MN patches were successfully fabricated with a 3M™ commercial template and Polydimethylsiloxane mold. Through optical coherence tomography, it was found that all of the SF-based MN patches prepared in this study had sufficient strength to penetrate the skin to a depth of approximately 400 μm. Sustained release of the model drug-dextran from the SF-based MNs was demonstrated. Although SF-based MNs release SDF-1 in a sustained manner, the quantity released can be regulated and improved. Subsequently, dual-layer SDF-1-loaded MNs fabricated with a gelatin tip and SF body were prepared to enhance SDF-1 release for ASC recruitment. SF-based MNs can show good penetration ability and provide good sustained release while dual-layer MNs can regulate the amount of drug released, which could present an alternative for stem cell therapy.

Quantification methods comparing in vitro and in vivo percutaneous permeation by microneedles and passive diffusion

Microneedles (MNs) are needles with a tip diameter ranging from 10 to 100 um and a length ranging up to 1 mm. The first patent for drug delivery device for percutaneous administration filed by Alza corporation dates back to 1976 (Gerstel and Place, 1976), and in between 1989 and 2021 the filed patents for MNs are more than 4500 (Banks et al., 2010). These devices can potential overcome some drawbacks of traditional needles, such as the pain generated during insertion, requirement for trained personnel to manipulate syringes, and difficulty of performing injections in elderly and obese patients. MNs and MNs arrays are emerging as a convenient method to deliver compounds and extract blood without causing any pain. A promising application is the use of MNs as alternative solution to topical creams (TC) and transdermal patches (TP) for transdermal drug delivery. The external layer of human skin, the epidermis, offers a major barrier to transdermal drug delivery, thanks to the stratum corneum (SC). Exposed to the external environment, SC ultimately protects the human body from UV light radiation, heat, water loss, bacteria, fungi and viruses, and it is the barrier that controls diffusion rate for almost all compounds. TC and TP applications are limited by the skin permeability to lipophilic compounds and small molecules, and by the slow delivery rate of some compounds. MNs have been around for more than 35 year now, and it is a general opinion that MN increase delivery compared to passive diffusion, thanks to the feature of penetrating the SC and reaching the dermis. This review recollects the existing studies that compare MNs delivery of drugs with passive diffusion of the same drugs in alive organisms, giving an overview of what are the type of MNs, the chemical delivered and the methods employed to quantify drug delivery into skin and/or in the bloodstream. The final aim is to quantify the enhancement factor of MNs with respect to passive diffusion, and establish a possible standard on how tests can be performed in order to compare different data.

Design and Evaluation of Dissolvable Microneedles for Treating Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease caused predominantly by immune dysregulation. The global impact of AD continues to increase, making it not only a significant public health issue but also a risk factor for progression into other allergic phenotype disorders. Treatment of moderate-to-severe symptomatic AD involves general skin care, restoration of the skin barrier function, and local anti-inflammatory drug combinations, and may also require systemic therapy, which is often associated with severe adverse effects and is occasionally unsuitable for long-term use. The main objective of this study was to develop a new delivery system for AD treatment based on dissolvable microneedles containing dexamethasone incorporated in a dissolvable polyvinyl alcohol/polyvinylpyrrolidone matrix. SEM imaging of the microneedles showed well-structured arrays comprising pyramidal needles, fast drug release in vitro in Franz diffusion cells, an appropriate mechanical strength recorded with a texture analyzer, and low cytotoxicity. Significant clinical improvements, including in the dermatitis score, spleen weights, and clinical scores, were observed in an AD in vivo model using BALB/c nude mice. Taken together, our results support the hypothesis that microneedle devices loaded with dexamethasone have great potential as a treatment for AD and possibly for other skin conditions as well.

Enhancing Intradermal Delivery of Lidocaine by Dissolving Microneedles: Comparison between Hyaluronic Acid and Poly(Vinyl Pyrrolidone) Backbone Polymers

Lidocaine hydrochloride (LiH), an amide-type local anesthetic agent, is commonly used in dermatological procedures. LiH is categorized as a BCS (biopharmaceutics classification system) class III group, which has high solubility and poor permeability. It should be noted that, in this context, LiH is intended as a local anesthetic, so the level of LiH in systemic circulation should be minimized to avoid toxicity and unwanted side effects such as hypotension and bradycardia. This study aimed to formulate and evaluate LiH-loaded dissolving microneedles (DMNs) with different polymer bases. Moreover, an in vitro permeation study using Franz diffusion cells and in vivo study were also performed. LiH-loaded DMNs were prepared using polymer groups of poly(vinyl pyrrolidone) (PVP-K30) and hyaluronic acid (HA). DMNs were created using the micro-molding method with centrifugation. The formulations selected based on the evaluation were F3 (HA 10%) and F5 (PVP-K30 25%). Based on the in vitro permeation study, the amount of drug permeated and deposited in the skin at F3 (HA 10%) was 247.1 ± 41.85 and 98.35 ± 12.86 μg, respectively. On the other hand, the amount of drug permeated and deposited in the skin at F5 (PVP-K30 25%) was 277.7 ± 55.88 and 59.46 ± 9.25 μg, respectively. Our in vivo drug-permeation study showed that only one rat from the PVP-K30 polymer group-with a concentration of 150.32 ng/mL-was detected on rat plasma. Therefore, LiH can be formulated into a DMN and can be deposited in the skin with a safe concentration of the drug permeating into systemic circulation.

Dissolving Microneedles Loaded with Gestodene: Fabrication and Characterization In Vitro and In Vivo

Background

Gestodene (GEST) is widely used in female contraception. It is currently being used as an oral contraceptive. However, unfortunately, oral contraceptives are often associated with several bothersome side effects and poor compliance. Therefore, a sustained delivery system for GEST to overcome these shortcomings is highly desirable.

Objectives

The present study successfully developed a kind of novel dissolving microneedles (DMNs) with a potential for sustained release and a minimally invasive intradermal treatment of GEST.

Methods

The dissolving microneedles containing GEST were fabricated using polyvinylpyrrolidone as the base material. The characteristics in vitro and pharmacokinetics in vivo of GEST-loaded DMNs were investigated.

Results

The results showed that the microneedle could pierce the porcine skin and release the drug at an average dose of 20µg/cm2 daily for seven days. The pharmacokinetic experiment of the microneedles indicated that the plasma level of GEST in rats increased with increasing drug dosage, and the plasma drug concentration-time curves were much flatter compared with subcutaneous injection and oral administration. In addition, no cutaneous irritation was observed.

Conclusions

GEST-loaded DMNs may be a promising intradermal sustained delivery system for contraceptive use.

A Comprehensive Review of the Evolution of Insulin Development and Its Delivery Method

The year 2021 marks the 100th anniversary of the momentous discovery of insulin. Through years of research and discovery, insulin has evolved from poorly defined crude extracts of animal pancreas to recombinant human insulin and analogues that can be prescribed and administered with high accuracy and efficacy. However, there are still many challenges ahead in clinical settings, particularly with respect to maintaining optimal glycemic control whilst minimizing the treatment-related side effects of hypoglycemia and weight gain. In this review, the chronology of the development of rapid-acting, short-acting, intermediate-acting, and long-acting insulin analogues, as well as mixtures and concentrated formulations that offer the potential to meet this challenge, are summarized. In addition, we also summarize the latest advancements in insulin delivery methods, along with advancement to clinical trials. This review provides insights on the development of insulin treatment for diabetes mellitus that may be useful for clinicians in meeting the needs of their individual patients. However, it is important to note that as of now, none of the new technologies mentioned have superseded the existing method of subcutaneous administration of insulin.

Dissolvable polymer microneedles for drug delivery and diagnostics

Dissolvable transdermal microneedles (μND) are promising micro-devices used to transport a wide selection of active compounds into the skin. To provide an effective therapeutic outcome, μNDs must pierce the human stratum corneum (~10 to 20 μm), without rupturing or bending during penetration, then release their cargo at the predetermined area and time. The ability of dissolvable μND arrays/patches to sufficiently pierce the skin is a crucial requirement, which depends on the material composition, μND geometry and fabrication techniques. This comprehensive review not only provides contemporary knowledge on the μND design approaches, but also the materials science facilitating these delivery systems and the opportunities these advanced materials can provide to enhance clinical outcomes.

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.

Emergence of microneedles as a potential therapeutics in diabetes mellitus

Diabetes mellitus is a severe condition in which the pancreas produces inadequate insulin or the insulin generated is ineffective for utilisation by the body; as a result, insulin therapy is required for control blood sugar levels in patients having type 1 diabetes and is widely recommended in advanced type 2 diabetes patients with uncontrolled diabetes despite dual oral therapy, while subcutaneous insulin administration using hypodermic injection or pump-mediated infusion is the traditional route of insulin delivery and causes discomfort, needle phobia, reduced adherence, and risk of infection. Therefore, transdermal insulin delivery has been extensively explored as an appealing alternative to subcutaneous approaches for diabetes management which not only is non-invasive and easy, but also avoids first-pass metabolism and prevents gastrointestinal degradation. Microneedles have been commonly investigated in human subjects for transdermal insulin administration because they are minimally invasive and painless. The different types of microneedles developed for the transdermal delivery of anti-diabetic drugs are discussed in this review, including solid, dissolving, hydrogel, coated, and hollow microneedles. Numerous microneedle products have entered the market in recent years. But, before the microneedles can be effectively launched into the market, a significant amount of investigation is required to address the numerous challenges. In conclusion, the use of microneedles in the transdermal system is an area worth investigating because of its significant benefits over the oral route in the delivery of anti-diabetic medications and biosensing of blood sugar levels to assure improved clinical outcomes in diabetes management.

Efficient Drug Delivery into Skin Using a Biphasic Dissolvable Microneedle Patch with Water-Insoluble Backing

Dissolvable microneedle patches (MNPs) enable simplified delivery of therapeutics via the skin. However, most dissolvable MNPs do not deliver their full drug loading to the skin because only some of the drug is localized in the microneedles (MNs), and the rest remains adhered to the patch backing after removal from the skin. In this work, biphasic dissolvable MNPs are developed by mounting water-soluble MNs on a water-insoluble backing layer. These MNPs enable the drug to be contained in the MNs without migrating into the patch backing due to the inability of the drugs to partition into the hydrophobic backing materials during MNP fabrication. In addition, the insoluble backing is poorly wetted upon MN dissolution in the skin, which significantly reduces drug residue on the MNP backing surface after application. These effects enable a drug delivery efficiency of >90% from the MNPs into the skin 5 min after application. This study shows that the biphasic dissolvable MNPs can facilitate efficient drug delivery to the skin, which can improve the accuracy of drug dosing and reduce drug wastage.

Diagnostic and drug release systems based on microneedle arrays in breast cancer therapy

Microneedle arrays have recently received much attention as cancer detection and treatment platforms, because invasive injections and detection of the biopsy are not needed, and drug metabolism by the liver, as well as adverse effects of systemic drug administration, are diminished. Microneedles have been used for diagnosis, vaccination, and in targeted drug delivery of breast cancer. In this review, we summarize the recent progress in diagnosis and targeted drug delivery for breast cancer treatment, using microneedle arrays to deliver active molecules through the skin. The results not only suggest that health and well-being of patients are improved, but also that microneedle arrays can deliver anticancer compounds in a relatively noninvasive manner, based on body weight, breast tumor size, and circulation time of the drug. Moreover, microneedles could allow simultaneous loading of multiple drugs and enable controlled release, thus effectively optimizing or preventing drug-drug interactions. This review is designed to encourage the use of microneedles for diagnosis and treatment of breast cancer, by describing general properties of microneedles, materials used for construction, mechanism of action, and principal benefits. Ongoing challenges and future perspectives for the application of microneedle array systems in breast cancer detection and treatment are highlighted.

Engineering of an automated nano-droplet dispensing system for fabrication of antigen-loaded dissolving microneedle arrays

Dissolving microneedle arrays (dMNAs) are promising devices for intradermal vaccine delivery. The aim of this study was to develop a reproducible fabrication method for dMNAs based on an automated nano-droplet dispensing system that minimizes antigen waste. First, a polymer formulation was selected to dispense sufficiently small droplets (<18 nL) that can enter the microneedle cavities (base diameter 330 µm). Besides, three linear stages were assembled to align the dispenser with the cavities, and a vacuum chamber was designed to fill the cavities with dispensed droplets without entrapped air. Lastly, the dispenser and stages were incorporated to build a fully automated system. To examine the function of dMNAs as a vaccine carrier, ovalbumin was loaded in dMNAs by dispensing a mixture of ovalbumin and polymer formulation, followed by determining the ovalbumin loading and release into the skin. The results demonstrate that functional dMNAs which can deliver antigen into the skin were successfully fabricated via the automatic fabrication system, and hardly any antigen waste was encountered. Compared to the method that centrifuges the mould, it resulted in a 98.5% volume reduction of antigen/polymer solution and a day shorter production time. This system has potential for scale-up of manufacturing to an industrial scale.

Antibiofilm Effects of Macrolide Loaded Microneedle Patches: Prospects in Healing Infected Wounds

AIM

The aim of this study was to fabricate polymeric microneedles, loaded with macrolides (erythromycin, azithromycin), using hyaluronic acid and polyvinyl pyrollidone.

METHODS

These microneedles were fabricated using a vacuum micromolding technique. The integrity of the microneedle patches was studied by recording their morphologic features, folding endurance, swelling and micro-piercing. Physicochemical characteristics were studied by differential scanning calorimetry, thermogravimetric analysis and fourier transform infrared spectroscopy. In-vitro drug release, antibiofilm and effect of microneedle patch on wound healing were also studied to confirm the efficacy of the formulations.

RESULTS

Formulated patches displayed acceptable folding endurance (>100) and uniform distribution of microneedles (10 × 10) that can penetrate parafilm. Differential scanning calorimetry results depict a decrease in the crystallinity of macrolides following their incorporation in to a polymer matrix. Percentage release of azithromycin and erythromycin from the polymeric patch formulations (over 30 min) was 90% and 63% respectively. Broadly, the zone of bacterial growth inhibition follows the same order for Staphylococcus aureus, Escherichia coli and Salmonella enterica. After 5 days of treatment with azithromycin patches, the wound healing was complete and skin structure (e.g. hair follicles and dermis) was regenerated.

CONCLUSION

It was concluded that azithromycin loaded microneedle patches can be used to treat biofilms in the infected wounds.

Active delivery of multi-layer drug-loaded microneedle patches using magnetically driven capsule

In this paper, we propose the active delivery of multi-layer drug-loaded microneedle (MN) patches using a capsule that can be driven by an external magnetic field. Firstly, the multi-layer drug-loaded MN patches consist of three delivered MN patches which are composed of a drug-loaded MN patch and polydimethylsiloxane layer. The drug-loaded MN patch is made of a 10% gelatin solution and a drug. The multi-layer MN patches are attached to a permanent magnet in a magnetically driven capsule. Under an external magnetic field generated by an electromagnetic actuation system, the capsule with the multi-layer MN patches can reach the target lesions, and each MN patch can be delivered to the target lesions for medical treatment. The active delivery of the multi-layer MN patches using the proposed magnetically driven capsule was confirmed via phantom experiments. Accordingly, the adhesion of the three separated faces of the multi-layer MN patches and the adhesion between the porcine small intestine and the MN patch were measured using a load cell. We demonstrate the feasibility of the active delivery of the multi-layer MN patches to the target lesions on a porcine small intestine. Consequently, we expect that the active delivery of the multi-layer drug-loaded MN patches using the magnetically driven capsule presented in this study can be a useful method for drug delivery to lesions at various locations in the gastrointestinal tract.

Study on the fabrication and characterization of tip-loaded dissolving microneedles for transdermal drug delivery

In order to increase the utilization rate of drug carried by microneedles and reduce waste, a two-step casting method was proposed to fabricate tip-loaded dissolving microneedles in this paper. The tip-loaded dissolving microneedles, also named layered microneedles, was consisted of two layers. The tip layer of the microneedles carried model drug, while the backing layer was fabricated with pure dissolving material. Polyvinyl alcohol, polyvinylpyrrolidone and hyaluronic acid were used as the base materials to fabricate the dissolving layers of the microneedle patches. Rhodamine B was chosen as the model drug to show the layered structure of tip-loaded microneedles. The material formulation and fabricating conditions of the tip-loaded dissolving microneedles and their transdermal insulin delivery efficiency were systematically studied. Nanoindentation testing showed that the tips of all three kinds of dissolving microneedles can bear the maximum loading of 50 mN with no damages, indicated sufficient mechanical strength for smooth skin puncturing as the minimum pressure required was 10 mN only. Moreover, our fabricated tip-loaded dissolving microneedles can greatly reduce the drug waste cause by unused backing layer in normal microneedles and realize a 30% enhancement of drug delivery efficiency after puncture treatment.

Effective Dispensing Methods for Loading Drugs Only to the Tip of DNA Microneedles

Here, we propose a novel and simple method to efficiently capture the diffusion of fluorescein isothiocyanate (FITC)-dextran from a biocompatible substance and load the drug only to the tip of DNA microneedles. A dispensing and suction method was chosen to fabricate the designed microneedles with efficient amounts of FITC as the drug model. Importantly, the vacuum process, which could influence the capturing of FITC diffusion from the tip, was evaluated during the manufacturing process. In addition, the simulations were consistent with the experimental results and showed apparent diffusion. Moreover, dextrans of different molecular weights labeled with FITC were chosen to fabricate the tip of microneedles for demonstrating their applicability. Finally, a micro-jetting system with a micro-nozzle (diameter: 80 μm) was developed to achieve the accurate and rapid loading of small amounts of FITC using the anti-diffusion and micro-jetting methods. Our method not only uses a simple and fast manufacturing process, but also fabricates the tips of microneedles more efficiently with FITC compared with the existing methods. We believe that the proposed method is essential for the clinical applications of the microneedle drug delivery platform.

Solid Composite Material for Delivering Viable Cells into Skin Tissues via Detachable Dissolvable Microneedles

Delivering cells to desired locations in the body is needed for disease treatments, tissue repairs, and various scientific investigations such as animal models for drug development. Here, we report the solid composite material that when embedded with viable cells, can temporarily keep cells alive. Using the material, we also show the fabrication of detachable dissolvable microneedles (DMNs) that can instantly deliver viable cells into skin tissue. B16-F10-murine-melanoma (B16-F10) and human-embryonic-kidney-293T (HEK293T) cells embedded in the solid matrix of the hyaluronic/polyvinylpyrolidone/maltose (HA/PVP/maltose) mixture show 50.6 ± 12.0 and 71.0 ± 5.96% survivals, respectively, when kept at 4 °C for 24 h. Detachable DMNs made of the HA/PVP/maltose mixture and loaded with B16-F10-cells were constructed, and the obtained DMN patches could detach the cell-loaded needles into the skin within 1 min of patch application. In vivo intradermal tumorgrafting mice with the DMNs containing 800 cells of B16-F10 developed tumors 10 times bigger in volume than tumors induced by hypodermic needle injection of suspension containing 100,000 cells. We anticipate this work to be a starting point for viable cell encapsulation in the solid matrix and viable cell delivery via DMNs.

Polymeric nanoparticles based on carboxymethyl chitosan in combination with painless microneedle therapy systems for enhancing transdermal insulin delivery

Biodegradable nanoparticles (NPs) have been frequently used as insulin transdermal delivery vehicles due to their grand bioavailability, better encapsulation, controlled release and less toxic properties. However, the skin's barrier properties prevent insulin-loaded NP permeation at useful levels. Nowadays, microneedles have been spotlighted as novel transdermal delivery systems due to their advantages such as painlessness, efficient penetration and no hazardous residues. Herein, we introduce polymeric nanocarriers based on carboxymethyl chitosan (CMCS) for insulin delivery, combining with microneedle therapy systems, which can rapidly deliver insulin (INS) into the skin. The resulting CMCS-based nanocarriers are spherical nanoparticles with a mean size around 200 nm, which could generate supramolecular micelles to effectively encapsulate insulin (EE% = 83.78 ± 3.73%). A nanocrystalline microneedle array (6 × 6, 75/150 μm) was used to penetrate the stratum corneum (SC) for enhancing transdermal insulin delivery, while minimizing the pain sensation caused by intravenous injection. Compared with the transdermal rate of passive diffusion [2.77 ± 0.64 μg (cm-2 h-1)], the transdermal rate of the insulin-loaded NP combined with microneedle penetration shows a 4.2-fold increase [10.24 ± 1.06 μg (cm-2 h-1)] from permeation experiment in vitro. In vivo hypoglycemic experiments demonstrate the potential of using nanocarrier combination with microneedle arrays for painless insulin delivery through the skin in a clinical setting. Thus, the developed combination scheme of nanoparticles and microneedle arrays offers an effective, user-friendly, and low-toxicity option for diabetes patients requiring long-term and multiple treatments.

Fabrication of Tip-Hollow and Tip-Dissolvable Microneedle Arrays for Transdermal Drug Delivery

We developed a modified micromolding method for the mass production of a novel tip-hollow microneedle array (MA). The tip-hollow MA was fabricated by tuning of the vacuum degree at -80 kPa for 60 s during the micromolding process. Subsequently, a tip-dissolvable MA encapsulated with drugs in the microcraters was fabricated from tip-hollow MA using repeated dipping and the freeze-drying process. Both the tip-hollow and tip-dissolvable MAs could easily penetrate in the rabbit skin without breakage, while the tip-hollow MA can just create a shallow loop hole in the skin. The drug-loaded tip-dissolvable MA can rapidly dissolve, releasing and diffusing the drug in the skin. The tip-dissolvable MA exhibited the best drug permeation ability in that the corresponding flux through the punctured skin using tip-dissolvable MA loaded with Rhodamine B is about 1.7- and 5.8-fold of that through the punctured skin using solid MA and the intact skin, respectively. The tip-dissolvable MA loaded with 5 IU insulin was fabricated to in vivo treat the type 1 diabetic SD rats. The tip-dissolvable MA had a good hypoglycemic effect and exhibited longer normoglycemic period in comparison with subcutaneous injection (5 IU). Therefore, our tip-dissolve MA is a promising medical device for transdermal drug delivery.

Smartphone-powered iontophoresis-microneedle array patch for controlled transdermal delivery

The incidence rate of diabetes has been increasing every year in nearly all nations and regions. The traditional control of diabetes using transdermal insulin delivery by metal needles is generally associated with pain and potential infections. While microneedle arrays (MAs) have emerged as painless delivery techniques, the integration of MA systems with electronic devices to precisely control drug delivery has rarely been realized. In this study, we developed an iontophoresis-microneedle array patch (IMAP) powered by a portable smartphone for the active and controllable transdermal delivery of insulin. The IMAP in situ integrates iontophoresis and charged nanovesicles into one patch, achieving a one-step drug administration strategy of "penetration, diffusion and iontophoresis". The MA of the IMAP is first pressed on the skin to create microholes and then is retracted, followed by the iontophoresis delivery of insulin-loaded nanovesicles through these microholes in an electrically controlled manner. This method has synergistically and remarkably enhanced controlled insulin delivery. The amount of insulin can be effectively regulated by the IMAP by applying different current intensities. This in vivo study has demonstrated that the IMAP effectively delivers insulin and produces robust hypoglycemic effects in a type-1 diabetic rat model, with more advanced controllability and efficiency than delivery by a pristine microneedle or iontophoresis. The IMAP system shows high potential for diabetes therapy and the capacity to provide active as well as long-term glycemic regulation without medical staff care.

Transdermal Microneedles-A Materials Perspective

Transdermal drug delivery is an emerging field in the pharmaceutical remit compared with conventional methods (oral and parenteral). Microneedle (MN)-based devices have gained significant interest as a strategy to overcome the skin's formidable barrier: the stratum corneum. This approach provides a less invasive, more efficient, patient friendly method of drug delivery with the ability to incorporate various therapeutic agents including macromolecules (proteins and peptides), anti-cancer agents and other hydrophilic and hydrophobic compounds. This short review attempts to assess the various materials involved in the fabrication of MNs as well as incorporation of other excipients to improve drug delivery for novel medical devices. The focus will be on polymers, metals and other inorganic materials utilised for MN drug delivery, as well as their application, limitations and future work to be carried out.

Advances in transdermal insulin delivery

Insulin therapy is necessary to regulate blood glucose levels for people with type 1 diabetes and commonly used in advanced type 2 diabetes. Although subcutaneous insulin administration via hypodermic injection or pump-mediated infusion is the standard route of insulin delivery, it may be associated with pain, needle phobia, and decreased adherence, as well as the risk of infection. Therefore, transdermal insulin delivery has been widely investigated as an attractive alternative to subcutaneous approaches for diabetes management in recent years. Transdermal systems designed to prevent insulin degradation and offer controlled, sustained release of insulin may be desirable for patients and lead to increased adherence and glycemic outcomes. A challenge for transdermal insulin delivery is the inefficient passive insulin absorption through the skin due to the large molecular weight of the protein drug. In this review, we focus on the different transdermal insulin delivery techniques and their respective advantages and limitations, including chemical enhancers-promoted, electrically enhanced, mechanical force-triggered, and microneedle-assisted methods.

Preparation, properties and challenges of the microneedles-based insulin delivery system

Microneedle technology relates to pharmacy, polymer chemistry and micromachining. Microneedle can effectively deliver insulin into systemic circulation across the skin. This process does not affect the activity of insulin. Compared to subcutaneous injection, microneedles cause less pain for their special structure. This review thoroughly discusses the preparation technologies of the microneedles-based insulin delivery system including solid, hollow, dissolving, phase transition, glucose-responsive microneedle patches. In the meantime, the properties, challenges and clinical/commercial status of the microneedles-based insulin delivery system are also discussed in this review.

Tip-loaded fast-dissolving microneedle patches for photodynamic therapy of subcutaneous tumor

5-Aminolevulinic acid (ALA) based photodynamic therapy (PDT) is a modality for the treatment of cancers. However, due to its hydrophilicity and zwitterionic nature, the transdermal delivery of ALA is limited for the PDT of subcutaneous tumor. To address this problem, tip-loaded fast-dissolving microneedles made of sodium hyaluronate (HA) were fabricated by two casting method. 122 μg of ALA was loaded per microneedle patch and mainly distributed in the tips, which could improve the utilization of drug and avoid the waste of drug residue in the base of microneedle patch after use. The HA microneedles could pierce stratum corneum with insertion depth about 200 μm in isolated skin. After insertion, HA microneedles were rapidly dissolved to release the encapsulated drug to improve patients' convenience and compliance. Importantly, in a subcutaneous mouse tumor model established in BALB/c nude mice, the PDT efficacy of ALA-loaded HA microneedle group was much better than ALA injection group in spite of a relatively lower ALA dose with HA microneedles. The tumor inhibition rate of ALA-loaded HA microneedle group (containing 0.61 mg of ALA) was up to 97%, while the tumor inhibition rate of ALA injection group (containing 1.65 mg of ALA) was just 66%. In addition, microchannels created by microneedle patch were quickly recovered within 3 h after insertion. Overall, the tip-loaded fast-dissolving HA microneedle patch with ALA as drug was promising and might improve topical PDT efficacy of subcutaneous tumor in an efficient and safe manner.