Improved influenza vaccination in the skin using vaccine coated microneedles

Current Status of Microneedle Array Technology for Therapeutic Delivery: From Bench to Clinic

In recent years, microneedle (MN) patches have emerged as an alternative technology for transdermal delivery of various drugs, therapeutics proteins, and vaccines. Therefore, there is an urgent need to understand the status of MN-based therapeutics. The article aims to illustrate the current status of microneedle array technology for therapeutic delivery through a comprehensive review. However, the PubMed search was performed to understand the MN's therapeutics delivery status. At the same time, the search shows the number no of publications on MN is increasing (63). The search was performed with the keywords "Coated microneedle," "Hollow microneedle," "Dissolvable microneedle," and "Hydrogel microneedle," which also shows increasing trend. Similarly, the article highlighted the application of different microneedle arrays for treating different diseases. The article also illustrated the current status of different phases of MN-based therapeutics clinical trials. It discusses the delivery of different therapeutic molecules, such as drug molecule delivery, using microneedle array technology. The approach mainly discusses the delivery of different therapeutic molecules. The leading pharmaceutical companies that produce the microneedle array for therapeutic purposes have also been discussed. Finally, we discussed the limitations and future prospects of this technology.

Advanced Formulation Approaches for Proteins

Proteins and peptides are highly desirable as therapeutic agents, being highly potent and specific. However, there are myriad challenges with processing them into patient-friendly formulations: they are often unstable and have a tendency to aggregate or degrade upon storage. As a result, the vast majority of protein actives are delivered parenterally as solutions, which has a number of disadvantages in terms of cost, accessibility, and patient experience. Much work has been undertaken to develop new delivery systems for biologics, but to date this has led to relatively few products on the market. In this chapter, we review the challenges faced when developing biologic formulations, discuss the technologies that have been explored to try to overcome these, and consider the different delivery routes that can be applied. We further present an overview of the currently marketed products and assess the likely direction of travel in the next decade.

Three Dimensional Printing and Its Applications Focusing on Microneedles for Drug Delivery

Microneedles (MNs) are considered to be a novel smart injection system that causes significantly low skin invasion upon puncturing, due to the micron-sized dimensions that pierce into the skin painlessly. This allows transdermal delivery of numerous therapeutic molecules, such as insulin and vaccines. The fabrication of MNs is carried out through conventional old methods such as molding, as well as through newer and more sophisticated technologies, such as three-dimensional (3D) printing, which is considered to be a superior, more accurate, and more time- and production-efficient method than conventional methods. Three-dimensional printing is becoming an innovative method that is used in education through building intricate models, as well as being employed in the synthesis of fabrics, medical devices, medical implants, and orthoses/prostheses. Moreover, it has revolutionary applications in the pharmaceutical, cosmeceutical, and medical fields. Having the capacity to design patient-tailored devices according to their dimensions, along with specified dosage forms, has allowed 3D printing to stand out in the medical field. The different techniques of 3D printing allow for the production of many types of needles with different materials, such as hollow MNs and solid MNs. This review covers the benefits and drawbacks of 3D printing, methods used in 3D printing, types of 3D-printed MNs, characterization of 3D-printed MNs, general applications of 3D printing, and transdermal delivery using 3D-printed MNs.

Engineering of tetanus toxoid-loaded polymeric microneedle patches

This study is aimed to fabricate tetanus toxoid laden microneedle patches by using a polymeric blend comprising of polyvinyl pyrrolidone and sodium carboxymethyl cellulose as base materials and sorbitol as a plasticizer. The tetanus toxoid was mixed with polymeric blend and patches were prepared by using vacuum micromolding technique. Microneedle patches were evaluated for physical attributes such as uniformity of thickness, folding endurance, and swelling profile. Morphological features were assessed by optical and scanning electron microscopy. In vitro performance of fabricated patches was studied by using bicinchoninic acid assay (BCA). Insertion ability of microstructures was studied in vitro on model skin parafilm and in vivo in albino rat. In vivo immunogenic activity of the formulation was assessed by recording immunoglobulin G (IgG) levels, interferon gamma (IFN-γ) levels, and T-cell (CD4⁺ and CD8⁺) count following the application of dosage forms. Prepared patches, displaying sharp-tipped and smooth-surfaced microstructures, remained intact after 350 ± 36 foldings. Optimized microneedle patch formulation showed ~ 74% swelling and ~ 85.6% vaccine release within an hour. The microneedles successfully pierced parafilm. Histological examination of microneedle-treated rat skin confirmed disruption of epidermis without damaging the underneath vasculature. A significant increase in IgG levels (~ 21%), IFN-γ levels (~ 30%), CD4⁺ (~ 41.5%), and CD8⁺ (~ 48.5%) cell count was observed in tetanus vaccine-loaded microneedle patches treated albino rats with respect to control (untreated) group at 42nd day of immunization. In conclusion, tetanus toxoid-loaded microneedle patches can be considered as an efficient choice for transdermal delivery of vaccine without inducing pain commonly experienced with hypodermic needles.

Microarray patches: scratching the surface of vaccine delivery

INTRODUCTION

Microneedles are emerging as a promising technology for vaccine delivery, with numerous advantages over traditional needle and syringe methods. Preclinical studies have demonstrated the effectiveness of MAPs in inducing robust immune responses over traditional needle and syringe methods, with extensive studies using vaccines targeted against different pathogens in various animal models. Critically, the clinical trials have demonstrated safety, immunogenicity, and patient acceptance for MAP-based vaccines against influenza, measles, rubella, and SARS-CoV-2.

AREAS COVERED

This review provides a comprehensive overview of the different types of microarray patches (MAPs) and analyses of their applications in preclinical and clinical vaccine delivery settings. This review also covers additional considerations for microneedle-based vaccination, including adjuvants that are compatible with MAPs, patient safety and factors for global vaccination campaigns.

EXPERT OPINION

MAP vaccine delivery can potentially be a game-changer for vaccine distribution and coverage in both high-income and low- and middle-income countries. For MAPs to reach this full potential, many critical hurdles must be overcome, such as large-scale production, regulatory compliance, and adoption by global health authorities. However, given the considerable strides made in recent years by MAP developers, it may be possible to see the first MAP-based vaccines in use within the next 5 years.

Polymeric Biomaterials for Topical Drug Delivery in the Oral Cavity: Advances on Devices and Manufacturing Technologies

There are several routes of drug administration, and each one has advantages and limitations. In the case of the topical application in the oral cavity, comprising the buccal, sublingual, palatal, and gingival regions, the advantage is that it is painless, non-invasive, allows easy application of the formulation, and it is capable of avoiding the need of drug swallowing by the patient, a matter of relevance for children and the elderly. Another advantage is the high permeability of the oral mucosa, which may deliver very high amounts of medication rapidly to the bloodstream without significant damage to the stomach. This route also allows the local treatment of lesions that affect the oral cavity, as an alternative to systemic approaches involving injection-based methods and oral medications that require drug swallowing. Thus, this drug delivery route has been arousing great interest in the pharmaceutical industry. This review aims to condense information on the types of biomaterials and polymers used for this functionality, as well as on production methods and market perspectives of this topical drug delivery route.

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.

Microneedles enable the development of skin-targeted vaccines against coronaviruses and influenza viruses

Throughout the COVID-19 pandemic, many have seriously worried that the plus burden of seasonal influenza that might create a destructive scenario, resulting in overwhelmed healthcare capacities and onwards loss of life. Many efforts to develop a safe and efficacious vaccine to prevent infection by coronavirus and influenza, highlight the importance of vaccination to combat infectious pathogens. While vaccines are traditionally given as injections into the muscle, microneedle (MN) patches designed to precisely deliver cargos into the cutaneous microenvironment, rich in immune cells, provide a noninvasive and self-applicable vaccination approach, reducing overall costs and improving access to vaccines in places with limited supply. The current review aimed to highlight advances in research on the development of MNs-mediated cutaneous vaccine delivery. Concluding remarks and challenges on MNs-based skin immunization are also provided to contribute to the rational development of safe and effective MN-delivered vaccines against these emerging infectious diseases.

3D Printing-A "Touch-Button" Approach to Manufacture Microneedles for Transdermal Drug Delivery

Microneedles (MNs) represent the concept of attractive, minimally invasive puncture devices of micron-sized dimensions that penetrate the skin painlessly and thus facilitate the transdermal administration of a wide range of active substances. MNs have been manufactured by a variety of production technologies, from a range of materials, but most of these manufacturing methods are time-consuming and expensive for screening new designs and making any modifications. Additive manufacturing (AM) has become one of the most revolutionary tools in the pharmaceutical field, with its unique ability to manufacture personalized dosage forms and patient-specific medical devices such as MNs. This review aims to summarize various 3D printing technologies that can produce MNs from digital models in a single step, including a survey on their benefits and drawbacks. In addition, this paper highlights current research in the field of 3D printed MN-assisted transdermal drug delivery systems and analyzes parameters affecting the mechanical properties of 3D printed MNs. The current regulatory framework associated with 3D printed MNs as well as different methods for the analysis and evaluation of 3D printed MN properties are outlined.

Transdermal drug delivery systems for fighting common viral infectious diseases

Transdermal drug delivery systems (TDDS) have many advantages and represent an excellent alternative to oral delivery and hypodermic injections. TDDS are more convenient and less invasive tools for disease and viral infection treatment, prevention, detection, and surveillance. The emerging development of microneedles for TDDS has facilitated improved skin barrier penetration for the delivery of macromolecules or hydrophilic drugs. Microneedle TDDS patches can be fabricated to deliver virus vaccines and potentially provide a viable alternative vaccine modality that offers improved immunogenicity, thermostability, simplicity, safety, and compliance as well as sharp-waste reduction, increased cost-effectiveness, and the capacity for self-administration, which could improve vaccine distribution. These advantages make TDDS-based vaccine delivery an especially well-suited option for treatment of widespread viral infectious diseases including pandemics. Because microneedle-based bioassays employ transdermal extraction of interstitial fluid or blood, they can be used as a minimally invasive approach for surveying disease markers and providing point-of-care (POC) diagnostics. For cutaneous viral infections, TDDS can provide localized treatment with high specificity and less systemic toxicity. In summary, TDDS, especially those that employ microneedles, possess special attributes that can be leveraged to reduce morbidity and mortality from viral infectious diseases. In this regard, they may have considerable positive impact as a modality for improving global health. In this article, we introduce the possible role and summarize the current literature regarding TDDS applications for fighting common cutaneous or systemic viral infectious diseases, including herpes simplex, varicella or herpes zoster, warts, influenza, measles, and COVID-19.

Next-Generation Vaccines: Nanoparticle-Mediated DNA and mRNA Delivery

Nucleic acid vaccines are a method of immunization aiming to elicit immune responses akin to live attenuated vaccines. In this method, DNA or messenger RNA (mRNA) sequences are delivered to the body to generate proteins, which mimic disease antigens to stimulate the immune response. Advantages of nucleic acid vaccines include stimulation of both cell-mediated and humoral immunity, ease of design, rapid adaptability to changing pathogen strains, and customizable multiantigen vaccines. To combat the SARS-CoV-2 pandemic, and many other diseases, nucleic acid vaccines appear to be a promising method. However, aid is needed in delivering the fragile DNA/mRNA payload. Many delivery strategies have been developed to elicit effective immune stimulation, yet no nucleic acid vaccine has been FDA-approved for human use. Nanoparticles (NPs) are one of the top candidates to mediate successful DNA/mRNA vaccine delivery due to their unique properties, including unlimited possibilities for formulations, protective capacity, simultaneous loading, and delivery potential of multiple DNA/mRNA vaccines. This review will summarize the many varieties of novel NP formulations for DNA and mRNA vaccine delivery as well as give the reader a brief synopsis of NP vaccine clinical trials. Finally, the future perspectives and challenges for NP-mediated nucleic acid vaccines will be explored.

Microneedles in Smart Drug Delivery

Significance: In biomedical setup, at large, and drug delivery, in particular, transdermal patches, hypodermal needles, and/or dermatological creams with the topical appliance are among the most widely practiced routes for transdermal drug delivery. Owing to the stratum corneum layer of the skin, traditional drug delivery methods are inefficient, and the effect of the administered therapeutic cues is limited. Recent Advances: The current advancement at the microlevel and nanolevel has revolutionized the drug delivery sector. Particularly, various types of microneedles (MNs) are becoming popular for drug delivery applications because of safety, patient compliance, and smart action. Critical Issues: Herein, we reviewed state-of-the-art MNs as a smart and sophisticated drug delivery approach. Following a brief introduction, the drug delivery mechanism of MNs is discussed. Different types of MNs, that is, solid, hollow, coated, dissolving, and hydrogel forming, are discussed with suitable examples. The latter half of the work is focused on the applied perspective and clinical translation of MNs. Furthermore, a detailed overview of clinical applications and future perspectives is also included in this review. Future Directions: Regardless of ongoing technological and clinical advancement, the focus should be diverted to enhance the efficacy and strength of MNs. Besides, the possible immune response or interference should also be avoided for successful clinical translation of MNs as an efficient drug delivery system.

Microarray patches enable the development of skin-targeted vaccines against COVID-19

The COVID-19 pandemic is a serious threat to global health and the global economy. The ongoing race to develop a safe and efficacious vaccine to prevent infection by SARS-CoV-2, the causative agent for COVID-19, highlights the importance of vaccination to combat infectious pathogens. The highly accessible cutaneous microenvironment is an ideal target for vaccination since the skin harbors a high density of antigen-presenting cells and immune accessory cells with broad innate immune functions. Microarray patches (MAPs) are an attractive intracutaneous biocargo delivery system that enables safe, reproducible, and controlled administration of vaccine components (antigens, with or without adjuvants) to defined skin microenvironments. This review describes the structure of the SARS-CoV-2 virus and relevant antigenic targets for vaccination, summarizes key concepts of skin immunobiology in the context of prophylactic immunization, and presents an overview of MAP-mediated cutaneous vaccine delivery. Concluding remarks on MAP-based skin immunization are provided to contribute to the rational development of safe and effective MAP-delivered vaccines against emerging infectious diseases, including COVID-19.

Microneedles: Characteristics, Materials, Production Methods and Commercial Development

Although transdermal drug delivery systems (DDS) offer numerous benefits for patients, including the avoidance of both gastric irritation and first-pass metabolism effect, as well as improved patient compliance, only a limited number of active pharmaceutical ingredients (APIs) can be delivered accordingly. Microneedles (MNs) represent one of the most promising concepts for effective transdermal drug delivery that penetrate the protective skin barrier in a minimally invasive and painless manner. The first MNs were produced in the 90s, and since then, this field has been continually evolving. Therefore, different manufacturing methods, not only for MNs but also MN molds, are introduced, which allows for the cost-effective production of MNs for drug and vaccine delivery and even diagnostic/monitoring purposes. The focus of this review is to give a brief overview of MN characteristics, material composition, as well as the production and commercial development of MN-based systems.

Progress in microneedle array patch (MAP) for vaccine delivery

A microneedle array patch (MAP) has been developed as a new delivery system for vaccines. Preclinical and clinical trials with a vaccine MAP showed improved stability, safety, and immunological efficacy compared to conventional vaccine administration. Various vaccines can be delivered with a MAP. Currently, microneedle manufacturers can mass-produce pharmaceutical MAP and cosmetic MAP and this mass-production system can be adapted to produce a vaccine MAP. Clinical trials with a vaccine MAP have shown comparable efficacy with conventional administration, and discussions about regulations for a vaccine MAP are underway. However, there are concerns of reasonable cost, mass production, efficacy, and safety standards that meet FDA approval, as well as the need for feedback regarding the best method of administration. Currently, microneedles have been studied for the delivery of many kinds of vaccines, and preclinical and clinical studies of vaccine microneedles are in progress. For the foreseeable future, some vaccines will continue to be administered with syringes and needles while the use of a vaccine MAP continues to be improved because of the advantages of less pain, self-administration, improved stability, convenience, and safety.

Measles and rubella microarray array patches to increase vaccination coverage and achieve measles and rubella elimination in Africa

The African Region is committed to measles elimination by 2020 but coverage with the first dose of measles-containing vaccine was only 70% in 2017. Several obstacles to achieving high coverage with measles and rubella vaccines exist, some of which could be overcome with new vaccine delivery technologies. Microarray array patches (MAPs) are single-dose devices used for transcutaneous administration of molecules, including inactivated or attenuated vaccines, that penetrate the outer stratum corneum of the skin, delivering antigens to the epidermis or dermis. MAPs to deliver measles and rubella vaccines have the potential to be a transformative technology to achieve elimination goals in the African Region. MAPs for measles and rubella vaccination have been shown to be safe, immunogenic and thermostable in preclinical studies but results of clinical studies in humans have not yet been published. This review summarizes the current state of knowledge of measles and rubella MAPs, their potential advantages for immunization programs in the African Region, and some of the challenges that must be overcome before measles and rubella MAPs are available for widespread use.

Topical delivery of 5-fluorouracil-loaded carboxymethyl chitosan nanoparticles using microneedles for keloid treatment

Keloids are induced by skin injuries such as surgeries, skin piercings, burns, and trauma. The intra-lesional injection of 5-fluorouracil (5-FU) is a promising therapy to treat keloid. However, local 5-FU injections have caused several side effects such as pain at administration and hyperpigmentation. This study suggests a safer and more effective 5-FU delivery system. We used microneedles to treat keloid because this method has the feasibility of self-administration without pain. In this study, 5-FU-loaded carboxymethyl chitosan (CMC) nanoparticles were prepared and characterized by various analytical methods and then coated on stainless solid microneedles. The blank CMC nanoparticles caused an increase in cell viability on human normal fibroblasts to 150%. In particular, the 5-FU-loaded CMC nanoparticles showed a significant inhibitory effect on the human keloid fibroblast to 16%. The intercellular uptake of the 5-FU-loaded CMC nanoparticles was observed on both human normal and keloid fibroblasts by using a confocal microscope. In addition, it was found that the nanoparticles showed an inhibition of TGF-β1 by ELISA. For topical drug delivery, it was confirmed that the nanoparticles coated onto the microneedles were dissolved and diffused at the administration site in the porcine dorsal skin model. According to these results, the suggested microneedle-mediated drug delivery system not only inhibits the human keloid fibroblasts by delivering drugs effectively into the keloids but also has the feasibility to self-administer without pain. Therefore, this new system including 5-FU-loaded CMC nanoparticles and microneedles has the potential to treat keloid scars. Graphical abstract.

Materials for Immunotherapy

Breakthroughs in materials engineering have accelerated the progress of immunotherapy in preclinical studies. The interplay of chemistry and materials has resulted in improved loading, targeting, and release of immunomodulatory agents. An overview of the materials that are used to enable or improve the success of immunotherapies in preclinical studies is presented, from immunosuppressive to proinflammatory strategies, with particular emphasis on technologies poised for clinical translation. The materials are organized based on their characteristic length scale, whereby the enabling feature of each technology is organized by the structure of that material. For example, the mechanisms by which i) nanoscale materials can improve targeting and infiltration of immunomodulatory payloads into tissues and cells, ii) microscale materials can facilitate cell-mediated transport and serve as artificial antigen-presenting cells, and iii) macroscale materials can form the basis of artificial microenvironments to promote cell infiltration and reprogramming are discussed. As a step toward establishing a set of design rules for future immunotherapies, materials that intrinsically activate or suppress the immune system are reviewed. Finally, a brief outlook on the trajectory of these systems and how they may be improved to address unsolved challenges in cancer, infectious diseases, and autoimmunity is presented.

The potential role of using vaccine patches to induce immunity: platform and pathways to innovation and commercialization

Introduction: In the last two decades, the evidence related to using vaccine patches with multiple short projections (≤1 mm) to deliver vaccines through the skin increased significantly and demonstrated their potential as an innovative delivery platform.Areas covered: We review the vaccine patch literature published in English as of 1 March 2019, as well as available information from key stakeholders related to vaccine patches as a platform. We identify key research topics related to basic and translational science on skin physical properties and immunobiology, patch development, and vaccine manufacturing.Expert opinion: Currently, vaccine patch developers continue to address some basic science and other platform issues in the context of developing a potential vaccine patch presentation for an existing or new vaccine. Additional clinical data and manufacturing experience could shift the balance toward incentivizing existing vaccine manufactures to further explore the use of vaccine patches to deliver their products. Incentives for innovation of vaccine patches differ for developed and developing countries, which will necessitate different strategies (e.g. public-private partnerships, push, or pull mechanisms) to support the basic and applied research needed to ensure a strong evidence base and to overcome translational barriers for vaccine patches as a delivery platform.

Dissolving undercut microneedle arrays for multicomponent cutaneous vaccination

The skin is an attractive tissue target for vaccination, as it is readily accessible and contains a dense population of antigen-presenting and immune-accessory cells. Microneedle arrays (MNAs) are emerging as an effective tool for in situ engineering of the cutaneous microenvironment to enable diverse immunization strategies. Here, we present novel dissolving undercut MNAs and demonstrate their application for effective multicomponent cutaneous vaccination. The MNAs are composed of micron-scale needles featuring pyramidal heads supported by undercut stem regions with filleted bases to ensure successful skin penetration and retention during application. Prior efforts to fabricate dissolving undercut microstructures were limited and required complex and lengthy processing and assembly steps. In the current study, we strategically combine three-dimensional (3D) laser lithography, an emerging micro-additive manufacturing method with unique geometric capabilities and nanoscale resolution, and micromolding with favorable materials. This approach enables reproducible production of dissolving MNAs with undercut microneedles that can be tip-loaded with multiple biocargos, such as antigen (ovalbumin) and adjuvant (Poly(I:C)). The resulting MNAs fulfill the geometric (sharp tips and smooth edges) and mechanical-strength requirements for failure-free penetration of human and murine skin to simultaneously deliver multicomponent (antigen plus adjuvant) vaccines to the same cutaneous microenvironment. Cutaneous vaccination of mice using these MNAs induces more potent antigen-specific cellular and humoral immune responses than those elicited by traditional intramuscular injection. Together, the unique geometric features of these undercut MNAs and the associated manufacturing strategy, which is compatible with diverse drugs and biologics, could enable a broad range of non-cutaneous and cutaneous drug delivery applications, including multicomponent vaccination.

Non-transdermal microneedles for advanced drug delivery

Microneedles (MNs) have been used to deliver drugs for over two decades. These platforms have been proven to increase transdermal drug delivery efficiency dramatically by penetrating restrictive tissue barriers in a minimally invasive manner. While much of the early development of MNs focused on transdermal drug delivery, this technology can be applied to a variety of other non-transdermal biomedical applications. Several variations, such as multi-layer or hollow MNs, have been developed to cater to the needs of specific applications. The heterogeneity in the design of MNs has demanded similar variety in their fabrication methods; the most common methods include micromolding and drawing lithography. Numerous materials have been explored for MN fabrication which range from biocompatible ceramics and metals to natural and synthetic biodegradable polymers. Recent advances in MN engineering have diversified MNs to include unique shapes, materials, and mechanical properties that can be tailored for organ-specific applications. In this review, we discuss the design and creation of modern MNs that aim to surpass the biological barriers of non-transdermal drug delivery in ocular, vascular, oral, and mucosal tissue.

Microneedle Coating Methods: A Review with a Perspective

A coated microneedle array comprises sharp micrometer-sized needle shafts attached to a base substrate and coated with a drug on their surfaces. Coated microneedles are under investigation for drug delivery into the skin and other tissues, and a broad assortment of active materials, including small molecules, peptides, proteins, deoxyribonucleic acids, and viruses, have been coated onto microneedles. To coat the microneedles, different methods have been developed. Some coating methods achieve selective coating of just the microneedle shafts, whereas other methods coat not only microneedle shafts but also the array base substrate. Selective coating of just the microneedle shafts is more desirable since it provides control over drug dosage, prevents drug waste, and offers high delivery efficiency. Different excipients are added to the coating liquid to modulate its viscosity and surface tension in order to achieve uniform coatings on microneedles. Coated microneedles have been used in a broad range of biomedical applications. To highlight these different applications, a table summarizing the different active materials and the amounts coated on microneedles is provided. We also discuss factors that should be considered when deciding suitability of coated microneedles for new-drug delivery applications. In recent years, many coated microneedles have been investigated in human clinical trials, and there is now a strong effort to bring the first coated microneedle-based product to market.

Novel approaches for the design, delivery and administration of vaccine technologies

It is easy to argue that vaccine development represents humankind's most important and successful endeavour, such is the impact that vaccination has had on human morbidity and mortality over the last 200 years. During this time the original method of Jenner and Pasteur, i.e. that of injecting live-attenuated or inactivated pathogens, has been developed and supplemented with a wide range of alternative approaches which are now in clinical use or under development. These next-generation technologies have been designed to produce a vaccine that has the effectiveness of the original live-attenuated and inactivated vaccines, but without the associated risks and limitations. Indeed, the method of development has undoubtedly moved away from Pasteur's three Is paradigm (isolate, inactivate, inject) towards an approach of rational design, made possible by improved knowledge of the pathogen-host interaction and the mechanisms of the immune system. These novel vaccines have explored methods for targeted delivery of antigenic material, as well as for the control of release profiles, so that dosing regimens can be matched to the time-lines of immune system stimulation and the realities of health-care delivery in dispersed populations. The methods by which vaccines are administered are also the subject of intense research in the hope that needle and syringe dosing, with all its associated issues regarding risk of injury, cross-infection and patient compliance, can be replaced. This review provides a detailed overview of new vaccine vectors as well as information pertaining to the novel delivery platforms under development.

A low inflammatory, Langerhans cell-targeted microprojection patch to deliver ovalbumin to the epidermis of mouse skin

In a low inflammatory skin environment, Langerhans cells (LCs) - but not dermal dendritic cells (dDCs) - contribute to the pivotal process of tolerance induction. Thus LCs are a target for specific-tolerance therapies. LCs reside just below the stratum corneum, within the skin's viable epidermis. One way to precisely deliver immunotherapies to LCs while remaining minimally invasive is with a skin delivery device such as a microprojection arrays (MPA). Today's MPAs currently achieve rapid delivery (e.g. within minutes of application), but are focussed primarily at delivery of therapeutics to the dermis, deeper within the skin. Indeed, no MPA currently delivers specifically to the epidermal LCs of mouse skin. Without any convenient, pre-clinical device available, advancement of LC-targeted therapies has been limited. In this study, we designed and tested a novel MPA that delivers ovalbumin to the mouse epidermis (eMPA) while maintaining a low, local inflammatory response (as defined by low erythema after 24 h). In comparison to available dermal-targeted MPAs (dMPA), only eMPAs with larger projection tip surface areas achieved shallow epidermal penetration at a low application energy. The eMPA characterised here induced significantly less erythema after 24 h (p = 0.0004), less epidermal swelling after 72 h (p < 0.0001) and 52% less epidermal cell death than the dMPA. Despite these differences in skin inflammation, the eMPA and dMPA promoted similar levels of LC migration out of the skin. However, only the eMPA promoted LCs to migrate with a low MHC II expression and in the absence of dDC migration. Implementing this more mouse-appropriate and low-inflammatory eMPA device to deliver potential immunotherapeutics could improve the practicality and cell-specific targeting of such therapeutics in the pre-clinical stage. Leading to more opportunities for LC-targeted therapeutics such as for allergy immunotherapy and asthma.

Three-Step Thermal Drawing for Rapid Prototyping of Highly Customizable Microneedles for Vascular Tissue Insertion

Microneedles (MNs) have been extensively developed over the last two decades, and highly efficient drug delivery was demonstrated with their minimal invasiveness via a transdermal route. Recently, MNs have not only been applied to the skin but also to other tissues such as blood vessels, scleral tissue, and corneal tissue. In addition, the objective of the MN application has been diversified, ranging from drug delivery to wound closure and biosensing. However, since most MN fabrication methods are expensive and time-consuming, they are inappropriate to prototype MNs for various tissues that have different and complex anatomies. Although several drawing-based techniques have been introduced for rapid MN production, they fabricated MNs with limited shapes, such as thin MNs with wide bases. In this study, we propose a three-step thermal drawing for rapid, prototyping MNs that can have a variety of shapes and can be fabricated on curved surfaces. Based on the temperature control of polymer bridge formation during thermal drawing, the body profile and aspect ratios of MNs were conveniently controlled, and the effect of temperature control on the body profile of MNs was explained. Thermally drawn MNs with different shapes were fabricated both on flat and curved surfaces, and they were characterized in terms of their mechanical properties and insertion into vascular tissue to find an optimal shape for vascular tissue insertion.

Insulin delivery systems combined with microneedle technology

Diabetes, a metabolic disorder of glucose, is a serious chronic disease and an important public health problem. Insulin is one of the hormones for modulating blood glucose level and the products of which is indispensable for most diabetes patients. Introducing microneedles (MNs) to insulin delivery is promising to pave the way for modulating glucose level noninvasively of diabetes patients, as which born to be painless, easy to handle and no need of any power supply. In this work, we review the process of insulin delivery systems (IDSs) based on MN technology in terms of two categories: drug free MNs and drug loaded MNs. Drug free MNs include solid MNs ("poke and patch"), hollow MNs ("poke and flow") and reservoir-based swelling MNs ("poke and swell R-type"), and drug loaded MNs include coated MNs ("coat and poke"), dissolving MNs ("poke and release") and insulin incorporated swelling MNs ("poke and swell I-type"). Majority researches of MN-based IDSs have been conducted by using hollow MNs or dissolving MNs, and almost all clinical trials for MN-based IDSs have employed hollow MNs. "Poke and patch" approach dramatically increase skin permeability compared to traditional transdermal patch, but MNs fabricated from silicon or metal may leave sharp waste in the skin and cause a safety issue. "Poke and flow" approach, similar to transitional subcutaneous (SC) injection, is capable of producing faster insulin absorption and action than SC injection but may associate with blockage, leakage and low flow rate. Coated MNs are able of retaining the activity of drug, which loaded in a solid phase, for a long time, however have been relatively less studied for insulin application as the low drug dosing. "Poke and release" approach leaves no biohazardous sharp medical waste and is capable of rapid drug release. "Poke and swell R-type" can be seen as a combination of "poke and flow" and "poke and patch" approach, while "poke and swell I-type" is an approach between "coat and poke" and "poke and release" approach. Insulin MNs are promising for painless diabetes therapeutics, and additional efforts for addressing fundamental issues including the drug loading, the PK/PD profile, the storage and the safety of insulin MNs will accelerate the clinical transformation.

Transdermal immunomodulation: Principles, advances and perspectives

Immunomodulation, manipulation of the immune responses towards an antigen, is a promising strategy to treat cancer, infectious diseases, allergies, and autoimmune diseases, among others. Unique features of the skin including the presence of tissue-resident immune cells, ease of access and connectivity to other organs makes it a unique target organ for immunomodulation. In this review, we summarize advances in transdermal delivery of agents for modulating the immune responses for vaccination as well as tolerization. The biological foundation of skin-based immunomodulation and challenges in its implementation are described. Technological approaches aimed at enhancing the delivery of immunomodulatory therapeutics into skin are also discussed in this review. Progress made in the treatment of several specific diseases including cancer, infections and allergy are discussed. Finally, this review discusses some practical considerations and offers some recommendations for future studies in the field of transdermal immunomodulation.

Polymeric microneedles for transdermal protein delivery

The intrinsic properties of therapeutic proteins generally present a major impediment for transdermal delivery, including their relatively large molecule size and susceptibility to degradation. One solution is to utilize microneedles (MNs), which are capable of painlessly traversing the stratum corneum and directly translocating protein drugs into the systematic circulation. MNs can be designed to incorporate appropriate structural materials as well as therapeutics or formulations with tailored physicochemical properties. This platform technique has been applied to deliver drugs both locally and systemically in applications ranging from vaccination to diabetes and cancer therapy. This review surveys the current design and use of polymeric MNs for transdermal protein delivery. The clinical potential and future translation of MNs are also discussed.

Microneedles containing cross-linked hyaluronic acid particulates for control of degradation and swelling behaviour after administration into skin

Microneedles (MN) containing cross-linked hyaluronic acid (X-linked HA) particulates were prepared to control the degradation and swelling behaviour after transdermal drug delivery. The X-linked HA particulates were prepared by cross-linking HA chains and then passing the particulates through a sieve. Then, microneedles were prepared by micromolding method. The rheological properties of X-linked HA were studied. The penetration success rate, mechanical failure and dissolution rate of microneedles containing only hyaluronic acid (HA MN) and microneedles containing X-linked HA were compared. The delivery of fluorescein into the skin with X-linked HA MN was also observed using a confocal microscope. The size of the pulverised particulates in water ranged between 29 and 82 μm in diameter. The HA MN and X-linked HA MN were 270 μm in length. X-linked HA MN with fluorescein was inserted to a depth of 90% of the microneedle length successfully. There was no decrease in the penetration success rate for MN with up to 20% content of X-linked HA particulates. X-linked HA MN with up to 20% of particulate content did not change the dissolution time. Delay in degradation of HA, sustained drug release, and swelling behaviour of the skin layer can be obtained by X-linked HA MN.

Cationic Niosomes for Enhanced Skin Immunization of Plasmid DNA-Encoding Ovalbumin via Hollow Microneedles

The purpose of the present study was to evaluate the use of cationic niosomes composed of Span20:cholesterol:cationic lipid (N ¹,N ¹-dimyristeroyloxyethyl-spermine) at the molar ratio of 2.5:2.5:0.5 mM combined with hollow microneedle (MN) devices for in vivo skin immunization of plasmid DNA-encoding ovalbumin (pOVA). The results revealed that using hollow MNs with cationic niosomes for pOVA penetration successfully induced both humoral and cell-mediated immune responses including immunoglobulin G (IgG) antibody responses, interleukin-4 (IL-4), and interferon gamma (IFN-γ) cytokine secretion. When using hollow MNs with cationic niosome/pOVA complexes, the immune response was superior to naked pOVA, which testifies the increased amount of IgG antibody responses and cytokine secretion. In comparison with conventional subcutaneous (SC) injections, using hollow MNs with cationic niosome/pOVA complexes induced a higher level of both IgG immune response and cytokine release. Moreover, a group of mice immunized with hollow MNs did not show infection or bleeding on the skin. Consequently, targeted delivery of pOVA using cationic niosomes combined with hollow MNs might prove a promising vaccination method for skin vaccination.

Development of the novel coating formulations for skin vaccination using stainless steel microneedle

This study focused on the development of novel coating formulations for stainless steel microneedles against influenza A virus. With in vitro studies, various viscosity enhancers and stabilizers were screened based on the hemagglutination activity of the vaccine, which was coated and dried onto a stainless steel chip at room temperature for 1 day. Following the long-term storage test, the hemagglutination activity and particle size of the vaccine, which was formulated with conventional or methylcellulose or hydroxyethyl cellulose and dried onto the microneedle, were monitored. Next, to evaluate the in vivo immunogenicity and protection effect of each dried vaccine formulation, mice were immunized by the antigen-coated microneedle, which had either the conventional or the proposed formulation. Two novel formulations were chosen in the preliminary screening, and in further evaluations, they exhibited a 20 % higher HA activity during storage for 3 months, and no aggregation was observed during storage after drying. In a mouse model, the microneedle with the novel formulation elicited a higher level of IgG and IgG2a was more prevalent in the IgG isotype profile. In addition, mice immunized with the HEC-coated microneedle survived with small weight loss (>90 %) against lethal challenge infection. Overall, the novel formulation hydroxyethyl cellulose preserved significantly higher HA activity during the production and storage of the microneedle as well as improved the in vivo immunogenicity of the vaccine.

Effect of zymosan and poly (I:C) adjuvants on responses to microneedle immunization coated with whole inactivated influenza vaccine

Microneedles are the micrometer size devices used for the delivery of vaccines and biotherapeutics. In order to increase the vaccine efficacy and reduce the antigen dose, there is a significant need to find some adjuvants for the microneedle vaccination. In this study, zymosan, which is the cell wall preparation of Saccharomyces cerevisiae, or poly (I:C) was coated on a microneedle with inactivated influenza virus, and then immunized into BALB/c mouse to determine the immunogenicity, protection and synergetic effect between two adjuvants. As a result, the group administered with zymosan and vaccine antigen showed significantly stronger IgG response, HI titer and IgG subtypes without any adverse effects, compared to the group immunized with the vaccine antigen alone. Also, there were enhanced cellular immune responses in the group received adjuvant with vaccine antigen. In addition, they showed superior protection and lung viral reduction against lethal viral challenge. Taken together, this study confirms that zymosan can be used as an immunostimulant for microneedle vaccination.

Acceptability of microneedle-patch vaccines: A qualitative analysis of the opinions of parents

INTRODUCTION

Vaccines incorporated into microneedle-based patch platforms offer advantages over conventional hypodermic injections. However, the success and clinical utility of these platforms will depend on its acceptance among stakeholders. Minimal focus has been placed on determining parents' acceptability of microneedle-patch vaccines intended for paediatric use. This qualitative study probes the perceived acceptability of microneedle technology for paediatric vaccination in a parent population.

RESEARCH DESIGN AND METHODOLOGY

Focus groups (n=6) were convened through purposive sampling of Cork city primary schools. Discussions were audio-recorded, transcribed verbatim, anonymised, independently verified and analysed by thematic analysis, with constant comparison method applied throughout.

RESULTS

The opinions of 32 parents were included. All participants declared that their children were fully vaccinated. Five core themes were identified and defined as: (i) concern, (ii) suitability for paediatric use, (iii) potential for parental administration, (iv) the role of the healthcare professional and (v) special populations. Drivers for acceptance include; concerns with current vaccines and vaccination programmes; attributes of microneedle-patch (reduced pain, bleeding, fear and increased convenience) and endorsement by a healthcare professional. Barriers to acceptance include; lack of familiarity, concerns regarding feasibility and suitability in paediatrics, allergic potential, inability to confirm delivery and potential reduction in vaccine coverage.

CONCLUSION

This is the first study to explore parental acceptance of microneedle-patch vaccines. Capturing the opinions of parents, the ultimate decision makers in paediatric vaccination, is crucial in the understanding of the eventual uptake of microneedle technology and therefore adds to literature currently available. This study has revealed that even "vaccine-acceptors"; parents who agree with, or do not question vaccination, will question the safety and efficacy of this novel method. Participants in this study remained tentative. However, the study has also revealed that endorsement by healthcare professionals could reduce this tentativeness, thereby identifying the role of healthcare professionals in disseminating information and providing support to parents. An increased awareness of developments in microneedle technology is needed to permit informed decision-making by parents.

Nano-patterning of a stainless steel microneedle surface to improve the dip-coating efficiency of a DNA vaccine and its immune response

DNA vaccination with microneedles (MNs) into the skin represents a potential therapeutic approach for the clinical treatment of viral diseases as well as for intradermal genetic immunization. In this study, we investigated a DNA vaccination against the severe fever with thrombocytopenia syndrome virus (SFTSV) delivered by nano-patterned microneedles (nMNs) to improve the efficiency compared to a conventional MN vaccination. Because DNA vaccinations delivered by coated MNs have major disadvantages such as a poor coating efficiency and immunogenicity, additional excipients are necessary. Therefore, we developed nMNs to improve the affinity of stainless steel for plasmid DNA vaccinations. The results show that the nMNs have an improved DNA vaccine loading capacity because their surfaces have an increased hydrophilicity from the high surface/volume ratio. The cytocompatibility analysis also showed a higher cell proliferation when using the nMNs. Finally, the in vivo experiments with balb/c mice vaccinated with the SFTSV DNA vaccine-coated nMNs generated a higher level of cellular immune responses than that of the unmodified MNs.

The success of microneedle-mediated vaccine delivery into skin

Microneedles (MNs) are designed to specifically target the outermost, skin barrier layer, the stratum corneum, creating transient pathways for minimally invasive transcutaneous delivery. It is reported that MNs can facilitate delivery without stimulating the pain receptors or damaging blood vessels that lie beneath, thus being perceived as painless and associated with reduced bleeding. This immunocompetence of the skin, coupled with its ease of access, makes this organ an attractive vaccination site. The purpose of this review was to collate primary scientific literature pertaining to MN-mediated in vivo vaccination programmes. A total of 62 original research articles are presented, compiling vaccination strategies in 6 different models (mouse, rat, guinea pig, rabbit, pig, macaque and human). Vaccines tested span a wide range of viral, bacterial and protozoan pathogens and includes 7 of the 13 vaccine-preventable diseases, as defined by the WHO. This review highlights the paucity of available clinical trial data. MN-delivered vaccines have demonstrated safety and immunogenicity in pre-clinical models and boast desirable attributes such as painless administration, thermostability, dose-sparing capacity and the potential for self-administration. These advantages should contribute to enhanced global vaccine access.