Engineering Microneedle Patches for Vaccination and Drug Delivery to Skin

Dissolving Microneedle Delivery of a Prophylactic HPV Vaccine

Prophylactic vaccines capable of preventing human papillomavirus (HPV) infections are still inaccessible to a vast majority of the global population due to their high cost and challenges related to multiple administrations performed in a medical setting. In an effort to improve distribution and administration, we have developed dissolvable microneedles loaded with a thermally stable HPV vaccine candidate consisting of Qβ virus-like particles (VLPs) displaying a highly conserved epitope from the L2 protein of HPV (Qβ-HPV). Polymeric microneedle delivery of Qβ-HPV produces similar amounts of anti-HPV16 L2 IgG antibodies compared to traditional subcutaneous injection while delivering a much smaller amount of intradermal dose. However, a dose sparing effect was found. Furthermore, immunization yielded neutralizing antibody responses in a HPV pseudovirus assay. The vaccine candidate was confirmed to be stable at room temperature after storage for several months, potentially mitigating many of the challenges associated with cold-chain distribution. The ease of self-administration and minimal invasiveness of such microneedle patch vaccines may enable wide-scale distribution of the HPV vaccine and lead to higher patient compliance. The Qβ VLP and its delivery technology is a plug-and-play system that could serve as a universal platform with a broad range of applications. Qβ VLPs may be stockpiled for conjugation to a wide range of epitopes, which are then packaged and delivered directly to the patient via noninvasive microneedle patches. Such a system paves the way for rapid distribution and self-administration of vaccines.

Design and fabrication of r-hirudin loaded dissolving microneedle patch for minimally invasive and long-term treatment of thromboembolic disease

Cardiovascular disease is the leading cause of global mortality, with anticoagulant therapy being the main prevention and treatment strategy. Recombinant hirudin (r-hirudin) is a direct thrombin inhibitor that can potentially prevent thrombosis via subcutaneous (SC) and intravenous (IV) administration, but there is a risk of haemorrhage via SC and IV. Thus, microneedle (MN) provides painless and sanitary alternatives to syringes and oral administration. However, the current technological process for the micro mould is complicated and expensive. The micro mould obtained via three-dimensional (3D) printing is expected to save time and cost, as well as provide a diverse range of MNs. Therefore, we explored a method for MNs array model production based on 3D printing and translate it to micro mould that can be used for fabrication of dissolving MNs patch. The results show that r-hirudin-loaded and hyaluronic acid (HA)-based MNs can achieve transdermal drug delivery and exhibit significant potential in the prevention of thromboembolic disease without bleeding in animal models. These results indicate that based on 3D printing technology, MNs combined with r-hirudin are expected to achieve diverse customizable MNs and thus realize personalized transdermal anticoagulant delivery for minimally invasive and long-term treatment of thrombotic disease.

Microneedle-Mediated Transdermal Delivery of Drug-Carrying Nanoparticles

Drug-carrying nanoparticles have obtained great attention for disease treatments due to the fact that they can improve drug solubility, provide drug protection and prolong release duration, thus enhancing drug bioavailability and increasing therapeutic efficacy. Although nanoparticles containing drugs can be administered via different routes such as oral, intravenous and ocular, transdermal delivery of nanoparticles mediated by microneedles has attracted considerable interest due to the capability of circumventing enzymatic degradation caused by gastrointestinal track, and increasing patient compliance by reducing pain associated with hypodermic injection. In this review, we first introduce four types of nanoparticles that were used for drug delivery, and then summarize strategies that have been employed to facilitate delivery of drug-loaded nanoparticles via microneedles. Finally, we give a conclusion and provide our perspectives on the potential clinical translation of microneedle-facilitated nanoparticles delivery.

Immunomodulatory Microneedle Patch for Periodontal Tissue Regeneration

Periodontal diseases are caused by microbial infection and the recruitment of destructive immune cells. Current therapies mainly deal with bacteria elimination, but the regeneration of periodontal tissues remains a challenge. Here we developed a modular microneedle (MN) patch that delivered both antibiotic and cytokines into the local gingival tissue to achieve immunomodulation and tissue regeneration. This MN patch included a quickly dissolvable gelatin membrane for an immediate release of tetracycline and biodegradable GelMA MNs that contained tetracycline-loaded poly(lactic-co-glycolic acid) nanoparticles and cytokine-loaded silica microparticles for a sustained release. Antibiotic release completely inhibited bacteria growth, and the release of IL-4 and TGF-β induced the repolarization of anti-inflammatory macrophages and the formation of regulatory T cells in vitro. In vivo delivery of MN patch into periodontal tissues suppressed proinflammatory factors and promoted pro-regenerative signals and tissue healing, which demonstrated the therapeutic potential of local immunomodulation for tissue regeneration.

Micro/nanofluidic devices for drug delivery

Micro/nanofluidic drug delivery systems have attracted significant attention as they offer unique advantages in targeted and controlled drug delivery. Based on the desired application, these systems can be categorized into three different groups: in vitro, in situ and in vivo microfluidic drug delivery platforms. In vitro microfluidic drug delivery platforms are closely linked with the emerging concept of lab-on-a-chip for cell culture studies. These systems can be used to administer drugs or therapeutic agents, mostly at the cellular or tissue level, to find the therapeutic index and can potentially be used for personalized medicine. In situ and in vivo microfluidic drug delivery platforms are still at the developmental stage and can be used for drug delivery at tissue or organ levels. A famous example of these systems are microneedles that can be used for painless and controllable delivery of drugs or vaccines through human skin. This chapter presents the cutting edge advances in the design and fabrication of in vitro microfluidic drug delivery systems that can be used for both cellular and tissue drug delivery. It also briefly discusses the in situ drug delivery platforms using microneedles.

Bioengineering Strategies for Developing Vaccines against Respiratory Viral Diseases

Respiratory viral pathogens like influenza and coronaviruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have caused outbreaks leading to millions of deaths. Vaccinations are, to date, the best and most economical way to control such outbreaks and have been highly successful for several pathogens. Currently used vaccines for respiratory viral pathogens are primarily live attenuated or inactivated and can risk reversion to virulence or confer inadequate immunity. The recent trend of using potent biomolecules like DNA, RNA, and protein antigenic components to synthesize vaccines for diseases has shown promising results. Still, it remains challenging to translate due to their high susceptibility to degradation during storage and after delivery. Advances in bioengineering technology for vaccine design have made it possible to control the physicochemical properties of the vaccines for rapid synthesis, heightened antigen presentation, safer formulations, and more robust immunogenicity. Bioengineering techniques and materials have been used to synthesize several potent vaccines, approved or in trials, against coronavirus disease 2019 (COVID-19) and are being explored for influenza, SARS, and Middle East respiratory syndrome (MERS) vaccines as well. Here, we review bioengineering strategies such as the use of polymeric particles, liposomes, and virus-like particles in vaccine development against influenza and coronaviruses and the feasibility of adopting these technologies for clinical use.

A novel dermal delivery system using natural spicules for cosmetics and therapeutics

BACKGROUND

Dermal delivery is versatile in therapeutics as well as cosmetics in pursuit of enhancing safety/efficacy and alleviating pain/fear to alternate oral/injective administrations. Natural siliceous spicules offer a potential approach via simple topical medications to circumvent poor penetrations through the skin barrier by loading, carrying and releasing the active ingredients in a highly efficient and controlled manner.

AIMS

The delivery of ingredients loaded on spicules is assessed to improve the dermal efficacy compared to simple topical treatments.

METHODS

First, needle-like spicules were isolated from natural freshwater sponges. Then, the active ingredient was loaded via liposome formations. Finally, the dermal efficiency was evaluated.

RESULTS

Natural siliceous spicules were purified, sorted, and fully characterized to appear 250 μm of length and 12 μm of diameter on average. A model ingredient, pectolinarin, was efficiently loaded onto the internal space of spicules via lecithin-based liposome formations. The penetration was visualized using a porcine skin sample with a fluorescent dye and assessed quantitatively by a Franz diffusion cell system. Dermal absorption rate was measured 73.4%, while the percutaneous penetration rate was 2.2%. The release pattern turned out a simple diffusion analyzed by Fick's law and Higuchi model. The liposomes loaded onto spicules were further stabilized by a hydrophobic capsulation, which may benefit the overall efficacy of the ingredient.

CONCLUSION

A novel dermal delivery system is beneficial to improve the topical efficacy of biologically active ingredients. The outcomes shed a light upon developing skin-protective/improving cosmetics and therapeutics with enhanced performance.

Role of drug delivery technologies in the success of COVID-19 vaccines: a perspective

The triumphant success of mRNA vaccines is a testimony to the important role drug delivery technologies have played in protecting billions of people against SARS-CoV-2 (or the Corona Virus Disease 2019; COVID-19). Several lipid nanoparticle (LNP) mRNA vaccines were developed and have been instrumental in preventing the disease by boosting the immune system against the pathogen, SARS-CoV-2. These vaccines have been built on decades of scientific research in drug delivery of mRNA, vaccines, and other biologicals. In this manuscript, several leading and emerging scientists in the field of drug delivery share their perspective on the role of drug delivery technologies in developing safe and efficacious vaccines, in a roundtable discussion. The authors also discussed their viewpoint on the current challenges, and the key research questions that should drive this important area of research.

The effects of molecular weight of hyaluronic acid on transdermal delivery efficiencies of dissolving microneedles

Hyaluronic acid (HA) is widely adopted to fabricate dissolving microneedles for transdermal drug delivery applications, yet the structure-activity relationship between molecular weight of HA and transdermal delivery efficiency of microneedles (HA-MNs) has not been fully explored, particularly in the transdermal delivery of small molecule drugs. Herein, we report the fabrication of three types of HA-MNs of various molecular weights (10k, 74k and 290k Da), which incorporate rhodamine B as the model drug. We assess the influence of molecular weight of HA on the mechanical properties of HA-MNs and transdermal delivery of rhodamine B in vitro and in vivo. The mechanical strength of all types of HA-MNs exceeds the minimal force requirement for skin penetration, with the highest values of compression force found in 10k-HA-MN. Interestingly, 74k-HA-MN that owns a medium mechanical strength, exhibits the highest efficiency in transdermal delivery of rhodamine B in a porcine skin and a Franz cell transdermal model. Further in vivo fluorescence imaging of HA-MN-treated mice reveals a tunable transdermal delivery of rhodamine B, which is controllable according to the molecular weight of HA. Importantly, 74k-HA-MN treatment demonstrates the highest initial delivering amount and longest retention time of rhodamine B in mice. In addition, histological examinations of puncture sites of the skin tissues confirm the complete recovery of skin and excellent biocompatibility of HA-MNs.

Designing spatial and temporal control of vaccine responses

Vaccines are the key technology to combat existing and emerging infectious diseases. However, increasing the potency, quality and durability of the vaccine response remains a challenge. As our knowledge of the immune system deepens, it becomes clear that vaccine components must be in the right place at the right time to orchestrate a potent and durable response. Material platforms, such as nanoparticles, hydrogels and microneedles, can be engineered to spatially and temporally control the interactions of vaccine components with immune cells. Materials-based vaccination strategies can augment the immune response by improving innate immune cell activation, creating local inflammatory niches, targeting lymph node delivery and controlling the time frame of vaccine delivery, with the goal of inducing enhanced memory immunity to protect against future infections. In this Review, we highlight the biological mechanisms underlying strong humoral and cell-mediated immune responses and explore materials design strategies to manipulate and control these mechanisms.

Non-dermal applications of microneedle drug delivery systems

Microneedles (MNs) are micron-scaled needles measuring 100 to 1000 μm that were initially explored for delivery of therapeutic agents across the skin. Considering the success in transcutaneous drug delivery, the application of microneedles has been extended to different tissues and organs. The review captures the application of microneedles to the oral mucosa, the eye, vagina, gastric mucosa, nail, scalp, and vascular tissues for delivery of vaccines, biologics, drugs, and diagnostic agents. The technology has created easy access to the poorly accessible segments of eye to facilitate delivery of monoclonal antibodies and therapeutic agents in management of neovascular disease. Microporation has been reported to drastically improve the drug delivery through the poorly permeable nail plate. Curved microneedles and spatially designed microneedle cuffs have been found to be capable of delivering stem cells and therapeutic macromolecules directly to the cardiac tissue and the vascular smooth muscle cells, respectively. Besides being minimally invasive and patient compliant, the technology has the potential to offer viable solutions to deliver drugs through impermeable barriers owing to the ability to penetrate several biological barriers. The technology has been successful to overcome the delivery hurdles and enable direct delivery of drug to the target sites, thus maximizing the efficacy thereby reducing the required dose. This review is an attempt to capture the non-dermatological applications of microneedles being explored and provides an insight on the future trends in the field of microneedle technology. Pictorial representation of different microneedle application.

A Dual-Delivery Platform for Vaccination using Antigen-loaded Nanoparticles in Dissolving Microneedles

Effective vaccines delivered via painless methods would revolutionize the way people approach vaccinations. This study focused on the development of fast-dissolving microneedles (MNs) to deliver antigen-loaded sustained release polymeric nanoparticles (NPs), achieving a dual-delivery platform for vaccination through the skin. The platform utilizes dissolving MNs (dMNs), which penetrate to the epidermal layer of the skin and rapidly dissolve, releasing the antigen-loaded NPs. In this study, seven dissolving microneedle formulations were tested based on screening of various biocompatible and biodegradable polymers and sugars. The lead dMN formulation was selected based on optimal mechanical strength and dissolution of the needles and was loaded with poly(lactic-co-glycolic) acid (PLGA) NPs encapsulating a model influenza matrix 2 (M2) protein antigen. Antigen-loading efficiency in the needles was determined by centrifugation of the lead formulation containing various concentrations of antigen nanoparticles. Next, the reproducibility and translatability of ex vivo mechanical strength and dissolvability of the lead M2 PLGA NP-loaded dMN formulation was assessed by formulating and testing two different microneedle arrays on murine and porcine skin. Finally, the lead microneedle array was loaded with fluorescent dye NPs and evaluated for pore formation and closure in vivo in a murine model. This proof-of-concept study yielded an easy-to-formulate, well-characterized, translatable antigen NP-loaded dMN platform for transdermal vaccine administration.

Facile Photolithographic Fabrication of Zwitterionic Polymer Microneedles with Protein Aggregation Inhibition for Transdermal Drug Delivery

Microneedle technology has received considerable attention in transdermal drug delivery system research owing to its minimally invasive and convenient self-administration with enhanced transdermal transport. The pre-drug loading microneedle method has been developed for several protein and chemical medicines. However, the protein activity and efficacy are severely affected owing to protein aggregation. Herein, we aim to develop non-degradable hydrogel photocross-linkable microneedles for suppressing protein aggregation. Four-point star-shaped microneedles are fabricated via a photolithography process, and sulfobetaine (SPB) monomer is combined with dextran-glycidyl methacrylate/acrylic acid to form the hydrogel network. Incorporating zwitterionic poly-sulfobetaine (poly-SPB) in the microneedles enables the protection of proteins from denaturation even under external stress, releases the proteins in their native state (without activity loss), and exhibits sufficient mechanical strength to penetrate porcine skin. The microneedles exhibit a high drug loading capacity along with an efficient drug release rate. The rhodamine B drug loading and release model shows that the microneedles can load 8 μg of drugs on one microneedle patch of 41 needles and release nearly 80% of its load within 1 h. We anticipate that this pre-drug loading platform and the advanced features of the microneedles can provide an effective option for administering therapeutic drugs.

Nanovaccine Delivery Approaches and Advanced Delivery Systems for the Prevention of Viral Infections: From Development to Clinical Application

Viral infections causing pandemics and chronic diseases are the main culprits implicated in devastating global clinical and socioeconomic impacts, as clearly manifested during the current COVID-19 pandemic. Immunoprophylaxis via mass immunisation with vaccines has been shown to be an efficient strategy to control such viral infections, with the successful and recently accelerated development of different types of vaccines, thanks to the advanced biotechnological techniques involved in the upstream and downstream processing of these products. However, there is still much work to be done for the improvement of efficacy and safety when it comes to the choice of delivery systems, formulations, dosage form and route of administration, which are not only crucial for immunisation effectiveness, but also for vaccine stability, dose frequency, patient convenience and logistics for mass immunisation. In this review, we discuss the main vaccine delivery systems and associated challenges, as well as the recent success in developing nanomaterials-based and advanced delivery systems to tackle these challenges. Manufacturing and regulatory requirements for the development of these systems for successful clinical and marketing authorisation were also considered. Here, we comprehensively review nanovaccines from development to clinical application, which will be relevant to vaccine developers, regulators, and clinicians.

Human-centred design of a new microneedle-based hormonal contraceptive delivery system

Background: It is estimated that 225 million women worldwide have an unmet need for family planning, and more than half live in low- and middle-income countries. Increasing the choice of contraceptive methods available can reduce this unmet need. Microneedle drug delivery systems represent a new technology for minimally invasive self-administration of contraceptives. We explored stakeholders’ views on different aspects of a proposed microneedle-based hormonal contraceptive delivery system. The feedback was used to iteratively develop this delivery system.

Methods: Focus group discussions and semi-structured interviews were conducted with potential stakeholders (women and trans males of childbearing age, their partners, and health professionals and organisations that provide family planning advice and contraception services) in Uganda, The Gambia, Malawi, and the UK, exploring concept acceptability and gathering feedback on different aspects of design and usability of the proposed delivery system.

Results: Participants viewed the concept of a new, microneedle-based contraceptive favourably. In Uganda, participants were presented with 7 different prototype applicators and identified desirable features of a preferred delivery device; their input reducing the number of prototypes that were subsequently evaluated by stakeholders in The Gambia and the UK. Participants in these countries helped to identify and/or confirm the most desirable characteristics of the applicator, resulting in design consolidation into a refined concept applicator. The final, optimised applicator prototype was validated during user research in Malawi. This human-centred design approach was also used to iteratively develop an information leaflet for the device. During these user studies, other preferred aspects of a contraceptive delivery system were also evaluated, such as anatomical site of application, duration of action, and return to fertility.

Conclusions: A new microneedle-based contraceptive delivery system was iteratively developed using a human-centred design approach and was favourably received by potential stakeholders. The product is now being refined for testing in pre-clinical studies.

Electrical aspects of skin as a pathway to engineering skin devices

Skin is one of the indispensable organs for life. The epidermis at the outermost surface provides a permeability barrier to infectious agents, chemicals, and excessive loss of water, while the dermis and subcutaneous tissue mechanically support the structure of the skin and appendages, including hairs and secretory glands. The integrity of the integumentary system is a key for general health, and many techniques have been developed to measure and control this protective function. In contrast, the effective skin barrier is the major obstacle for transdermal delivery and detection. Changes in the electrical properties of skin, such as impedance and ionic activity, is a practical indicator that reflects the structures and functions of the skin. For example, the impedance that reflects the hydration of the skin is measured for quantitative assessment in skincare, and the current generated across a wound is used for the evaluation and control of wound healing. Furthermore, the electrically charged structure of the skin enables transdermal drug delivery and chemical extraction. This paper provides an overview of the electrical aspects of the skin and summarizes current advances in the development of devices based on these features.

Microneedle-Mediated Vaccination: Innovation and Translation

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

Toward closed-loop drug delivery: Integrating wearable technologies with transdermal drug delivery systems

The recent advancement and prevalence of wearable technologies and their ability to make digital measurements of vital signs and wellness parameters have triggered a new paradigm in the management of diseases. Drug delivery as a function of stimuli or response from wearable, closed-loop systems can offer real-time on-demand or preprogrammed drug delivery capability and offer total management of disease states. Here we review the key opportunities in this space for development of closed-loop systems, given the advent of digital wearable technologies. Particular considerations and focus are given to closed-loop systems combined with transdermal drug delivery technologies.

Microneedle patch designs to increase dose administered to human subjects

Microneedle (MN) patches are being developed for many different kinds of drugs, but are often limited to delivering sub-milligram doses. This is because larger patches can be more difficult to apply to the skin, and acceptability of larger MN patches by human subjects has received limited study. Here, we fabricated 18 different large MN patch designs by laser microfabrication with different MN length (800-1500 μm), number of MNs (225 to 900 MNs per patch), space between MNs (600-1100 μm), and MN base diameter (200-250 μm). After manual application of these patches to human participants, we assessed dose delivery efficiency, total dose delivered, dose delivered per MN, depth of MN penetration and whole-MN delivery efficiency. We found that all of these parameters generally increased with decreased MN length, increased number of MNs (among those ≤1000 μm in length) and increased MN-MN spacing. All MN patch designs caused less pain than a pin prick sensation and were generally considered acceptable by the study participants. The MN patches induced mild, or sometimes moderate, transient erythema on skin. Study participants showed higher preference for MN patches for long-acting contraception compared with conventional options, indicating strong interest and acceptability of MN patches in this study.

Microneedles in Drug Delivery: Progress and Challenges

In recent years, an innovative transdermal delivery technology has attracted great interest for its ability to distribute therapeutics and cosmeceuticals for several applications, including vaccines, drugs, and biomolecules for skin-related problems. The advantages of microneedle patch technology have been extensively evaluated in the latest literature; hence, the academic publications in this area are rising exponentially. Like all new technologies, the microneedle patch application has great potential but is not without limitations. In this review, we will discuss the possible limitations by highlighting the areas where a great deal of improvements are required. Emphasising these concerns early on should help scientists and technologists to address the matters in a timely fashion and to use their resources wisely.

Application of armodafinil-loaded microneedle patches against the negative influence induced by sleep deprivation

Cognition maintenance is essential for healthy and safe life if sleep deprivation happens. Armodafinil is a wake-promoting agent against sleep deprivation related disorders. However, only the tablet formulation is available, which may limit its potential in some circumstances. Here, we report the synthesis of a new formulation of armodafinil, microneedle patches, which can be conveniently used by any individual and removed in time if not wanted. To produce the needles of higher mechanical strength and higher drug loading, polyvinylpyrrolidone (PVP) K90 was used to fabricate armodafinil-loaded microneedles by applying the mold casting method after dissolving in methanol and drying. The higher mechanical strength was validated by COMSOL Multiphysics® software stimulation and universal mechanical testing machines. The obtained armodafinil microneedles can withstand a force of 70 N and penetrate the skin to a depth of 230 μm, and quickly released the drug within 1.5 h in vitro. The pharmacokinetic analysis showed that microneedle administration can maintain a more lasting and stable blood concentration as compared to oral administration. After the treatment of sleep deprived mice with microneedles, the in vivo pharmacodynamics study clearly demonstrated that armodafinil microneedles could eliminate the effects of sleep deprivation and improve the cognitive functions of sleep-deprived mice. A self-administered, high drug-loaded microneedle patch were prepared successfully, which appeared to be highly promising in preserving cognition by transdermal administration.

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.

Microneedle arrays integrated with living organisms for smart biomedical applications

Various living organisms have proven to influence human health significantly, either in a commensal or pathogenic manner. Harnessing the creatures may remarkably improve human healthcare and cure the intractable illness that is challenged using traditional drugs or surgical approaches. However, issues including limited biocompatibility, poor biosafety, inconvenience for personal handling, and low patient compliance greatly hinder the biomedical and clinical applications of living organisms when adopting them for disease treatment. Microneedle arrays (MNAs), emerging as a promising candidate of biomedical devices with the functional diversity and minimal invasion, have exhibited great potential in the treatment of a broad spectrum of diseases, which is expected to improve organism-based therapies. In this review, we systemically summarize the technologies employed for the integration of MNAs with specific living organisms including diverse viruses, bacteria, mammal cells and so on. Moreover, their applications such as vaccination, anti-infection, tumor therapy and tissue repairing are well illustrated. Challenges faced by current strategies, and the perspectives of integrating more living organisms, adopting smarter materials, and developing more advanced technologies in MNAs for future personalized and point-of-care medicine, are also discussed. It is believed that the combination of living organisms with functional MNAs would hold great promise in the near future due to the advantages of both biological and artificial species.

Microneedle-based insulin transdermal delivery system: current status and translation challenges

Diabetes mellitus is a metabolic disease manifested by hyperglycemia. For patients with type 1 and advanced type 2 diabetes mellitus, insulin therapy is essential. Subcutaneous injection remains the most common administration method. Non-invasive insulin delivery technologies are pursued because of their benefits of decreasing patients' pain, anxiety, and stress. Transdermal delivery systems have gained extensive attention due to the ease of administration and absence of hepatic first-pass metabolism. Microneedle (MN) technology is one of the most promising tactics, which can effectively deliver insulin through skin stratum corneum in a minimally invasive and painless way. This article will review the research progress of MNs in insulin transdermal delivery, including hollow MNs, dissolving MNs, hydrogel MNs, and glucose-responsive MN patches, in which insulin dosage can be strictly controlled. The clinical studies about insulin delivery with MN devices have also been summarized and grouped based on the study phase. There are still several challenges to achieve successful translation of MNs-based insulin therapy. In this review, we also discussed these challenges including safety, efficacy, patient/prescriber acceptability, manufacturing and scale-up, and regulatory authority acceptability.

Microscale engineering of hollow microneedle tips: design, manufacturing, optimization and validation

Transdermal and intradermal drug delivery utilizing microneedles is an emerging front in painless therapeutics. Drug delivery using hollow microneedles is the most preferred method for delivering generic transdermal drugs in the clinical setup. The needle tip must be extremely short as the drug is administered to sub-millimeter depths. Also, they need to be sharp enough to pierce through the skin with minimal skin flexing. There are multiple challenges in engineering a tip profile that is short and sharp at the same time. Stainless steel (SS) hypodermic needles with the lancet tip profile are ubiquitous in subcutaneous and intramuscular injections. They have long bevel lengths that make them inappropriate as microneedles. Thus, designing a unique tip profile and developing the manufacturing technology for microneedle applications are necessary. This article presents the design and optimization of microneedle tip profiles through analytical models. Further, manufacturing strategies for reliably obtaining designed profiles are discussed. The article concludes with experimental validation of improved piercing performance of the optimized tip profile compared to other tip profiles. The article discusses about tip geometries of stainless steel needles for microneedle applications, where depth of delivery is less than 1 mm. Through series of analyses, the optimum needle tip geometry evolved from single plane bevel (SPB) to hex plane bevel (HPB) progressively improving piercing performance.

Manufacturing readiness assessment for evaluation of the microneedle array patch industry: an exploration of barriers to full-scale manufacturing

Microneedle array patch (MAP) technology is a promising new delivery technology for vaccines and pharmaceuticals, yet due to several differing and novel production methods, barriers to full-scale manufacturing exist. PATH conducted a manufacturing readiness assessment and follow-up interviews to identify both the current manufacturing readiness of the industry as well as how readiness varies by developer type and MAP type. Follow-up interviews identified barriers the industry faces in reaching full manufacturing readiness, including the perceived regulatory and investment risk of manufacturing MAPs at scale due to quality requirements and control methods, uncertain sterility requirements, lack of standard production methods (especially around dissolvable MAP drying methods), and the lack of available contract manufacturing organizations with MAP manufacturing capabilities. A Regulatory Working Group has been established to identify and address critical quality issues specific to MAP manufacturing with the aim of providing developers insight into what will be expected for MAP product approvals. Standardizing MAP production equipment and automatic, visual quality control could reduce the overall investment risk to developers and contract manufacturing organizations in pursuing pilot-scale manufacturing capabilities and ultimately lower barriers to the scale-up of full medical MAP product lines.

Thermostability of Measles and Rubella Vaccines in a Microneedle Patch

Measles and rubella vaccinations are highly effective at reducing disease prevalence; however, logistic issues related to subcutaneous administration and vaccine wastage limit the extent of vaccination coverage. Microneedle (MN) patches can increase coverage by easing logistics through simplified administration and improved stability. This study demonstrates the thermostability of a bivalent measles and rubella vaccine MN patch. Rubella vaccine stability required pH buffering during drying; potassium phosphate buffer at neutral pH was optimal for both vaccines. Screening 43 excipients for their ability to retain potency during drying and storage yielded sucrose-threonine-potassium phosphate buffer formulation at pH 7.5 as an optimal formulation. MN patches made with this formulation had no significant loss of vaccine titer after one month and remained within a one log10 titer loss cutoff after 3 - 4 months at 5°C, 25°C and 40°C. Finally, these patches were shown to be immunogenic in juvenile rhesus macaques. This work demonstrates the potential for MN patches for measles and rubella vaccination to be removed from the cold chain, which is expected to decrease vaccine cost and wastage, and increase vaccination coverage.

Micro array patch (MAP) for the delivery of thermostable vaccines in Australia: A cost/benefit analysis

BACKGROUND

It is anticipated that transforming the vaccine supply chain from syringe-and-needle to thermostable vaccines enabled by Micro Array Patch (MAP) will result in reduced supply chain costs as well as reduced wastes (environmental impact) and improved safety. This paper provides a thorough cost comparison of the conventional syringe-and-needle vaccine supply chain versus the MAP vaccine supply chain for influenza vaccine delivery in Australia.

OBJECTIVE

To determine the potential cost implications and general benefits of replacing syringe-and-needle flu vaccine with MAP-enabled thermostable flu vaccine in Australia.

METHODS

We first provide a snapshot of the existing flu vaccine supply chain in Australia including its limitations and opportunities for improvement. Data/information is collected through interviewing the key stakeholders across vaccine supply chain including vaccine manufacturers, logistics providers, clinics, hospitals, and pharmacies. A cost/benefit analysis of the anticipated supply chain of the MAP-enabled vaccine will reveal the opportunities and challenges of supply chain transformation for flu vaccine delivery in Australia.

FINDINGS

Our high-level practice-informed cost/benefit analysis identifies cold chain removal as an important source of cost saving, but administrative cost savings appear to be even more significant (e.g., time saving for nurses and those involved in cold chain management). Our analysis also identifies the key benefits and limitations of vaccine supply chain transformation in Australia.

CONCLUSION

We conclude that the benefits of moving from syringe-and-needle vaccines to thermostable MAP-delivered vaccines are beyond transportation and storage cost saving. Potential benefits through cost saving, waste reduction, and service level improvement are discussed along with various safety and wellbeing consequences as well as directions for future research in this area.

Transforming the vaccine supply chain in Australia: Opportunities and challenges

BACKGROUND

Analyzing potential benefits of thermostable vaccines delivered through Micro Array Patch (MAP) has received great attention in low and middle-income countries. The experience may or may not be the same in developed countries where the infrastructure is more developed. It is anticipated that transforming the vaccine supply chain from syringe-and-needle to thermostable MAP-delivered vaccines will result in reduced supply chain costs - including manufacturing/supply, logistics/distribution, and administration costs - as well as reduced wastes and improved safety. This paper provides an end-to-end supply chain analysis comparing the key aspects (cost, safety and environmental aspects) of the conventional syringe-and-needle vaccine supply chain with those of the MAP vaccine supply chain for influenza vaccine delivery in Australia. Directions for future research in this area will be provided.

OBJECTIVE

To determine the potential supply chain impacts of replacing syringe-and-needle flu vaccine with MAP-enabled thermostable flu vaccine in Australia.

METHODS

We analyze the current flu vaccine supply chain in Australia to identify practical limitations and opportunities for improvement. Data/information is collected through interviewing the key stakeholders across vaccine supply chain including vaccine manufacturers, logistics providers, clinics, hospitals, and pharmacies.

FINDINGS

A detailed practice-informed analysis is completed on the key operations of the flu vaccine supply chain. Barriers and limitations of the conventional flu vaccine are discussed, along with potential improvements that can be achieved through the implementation of MAP-enabled flu vaccine delivery. We discuss how technology-driven innovations can help advance vaccine supply chains, improve vaccine visibility, reduce wastes, and enable informed decision-making.

CONCLUSION

We find that the benefits of moving from syringe-and-needle vaccines to thermostable MAP-delivered vaccines are beyond transportation and storage cost saving. Potential benefits through cost saving, waste reduction, and service level improvement are discussed along with various safety and wellbeing consequences followed by directions for future research in this area.

Development of a thermostable oxytocin microneedle patch

Oxytocin is a nonapeptide hormone used in labor to initiate uterine contractions and to prevent and treat postpartum hemorrhage. Oxytocin is currently administered by injection and requires refrigerated transport and storage, which limits access, especially during home birth in developing countries. Here, we propose a thermostable, simple-to-administer microneedle (MN) patch for rapid delivery of oxytocin suitable for use by healthcare workers with limited training, like traditional birth attendants. Oxytocin (10 IU, 16.8 μg) coated onto stainless steel MN arrays was released into skin within 1-5 min after manual insertion. Among tested excipients, polyacrylic acid was best at stabilizing oxytocin stored at 75% relative humidity, with no significant loss for up to 2 months at 40 °C. Under desiccated conditions, MNs coated with formulations containing trehalose in a mixture of citrate buffer and ethanol retained 75% oxytocin potency at 40 °C for 12 months; the commercial oxytocin product Pitocin® was reduced to 35% potency under these conditions. These findings support development of MN patches for oxytocin administration with improved ease of use, extended thermostability and simplified logistics to enable greater access to this life-saving medicine.

Immediate detachment of microneedles by interfacial fracture for sustained delivery of a contraceptive hormone in the skin

Despite their high efficacy and safety, long-acting contraceptive methods are underutilized among women in some settings because they usually require injection or implantation by healthcare personnel. Here, we report a self-administrable microneedle (MN) patch for the rapid administration of a sustained-release contraceptive hormone delivery system into the skin that increases the simplicity and reliability of the MN delivery. We developed an immediate microneedle detachment system using a porous patch backing that has sufficient strength during MN insertion into skin under compression, but enables immediate detachment (< 1 s) of the MNs due to fracture at the MN - backing interface upon patch removal under tension from the skin surface. After patch application, the removed patch produced no biohazardous sharps waste, and was designed to achieve long-acting contraception by formulating poly(lactic-co-glycolic acid) MNs to slowly release the contraceptive hormone levonorgestrel for up to 1 month. Our combined strategy using immediate MN detachment in the skin and sustained drug delivery from the MNs could facilitate greater access to long-acting contraception by providing a simple and convenient option for self-administered, long-acting contraception.

Fabrication of pure-drug microneedles for delivery of montelukast sodium

Dissolving microneedle (MN) patches are usually formulated with a blend of drug and excipients added for mechanical strength and drug stabilization. In this study, we developed MNs made of pure drug to maximize drug loading capacity. MN patches were fabricated for transdermal delivery of montelukast sodium (MS) which is used to treat asthma and allergic rhinitis. We developed three different fabrication methods - solvent casting, melt casting, and solvent washing - and determined that filling molds with MS powder followed by a solvent washing method enabled MS to be loaded selectively to the MNs. Drug localization was confirmed with Raman imaging. MNs were able to penetrate in vitro and ex vivo skin models, and maintained strong mechanical properties during 6 months' storage at 22 °C. MS was also stable and compatible with the formulation used for the patch backing layer after 3 months' storage at 40 °C. MS delivery efficiency into skin was 55%, which enabled delivery of 3.2 mg MS into porcine skin ex vivo, which is in the range of MS doses in human clinical use. We conclude that the solvent washing method can be used to prepare MNs containing pure drug, such as MS at milligram doses in a ~ 1 cm² MN patch.

Nanotechnologies for the delivery of biologicals: Historical perspective and current landscape

Biological macromolecule-based therapeutics irrupted in the pharmaceutical scene generating a great hope due to their outstanding specificity and potency. However, given their susceptibility to degradation and limited capacity to overcome biological barriers new delivery technologies had to be developed for them to reach their targets. This review aims at analyzing the historical seminal advances that shaped the development of the protein/peptide delivery field, along with the emerging technologies on the lead of the current landscape. Particularly, focus is made on technologies with a potential for transmucosal systemic delivery of protein/peptide drugs, followed by approaches for the delivery of antigens as new vaccination strategies, and formulations of biological drugs in oncology, with special emphasis on mAbs. Finally, a discussion of the key challenges the field is facing, along with an overview of prospective advances are provided.

Administration of pilocarpine by microneedle patch as a novel method for cystic fibrosis sweat testing

The sweat test is the gold standard for the diagnosis of cystic fibrosis (CF). The test utilizes iontophoresis to administer pilocarpine to the skin to induce sweating for measurement of chloride concentration in sweat. However, the sweat test procedure needs to be conducted in an accredited lab with dedicated instrumentation, and it can lead to inadequate sweat samples being collected in newborn babies and young children due to variable sweat production with pilocarpine iontophoresis. We tested the feasibility of using microneedle (MN) patches as an alternative to iontophoresis to administer pilocarpine to induce sweating. Pilocarpine-loaded MN patches were developed. Both MN patches and iontophoresis were applied on horses to induce sweating. The sweat was collected to compare the sweat volume and chloride concentration. The patches contained an array of 100 MNs measuring 600 μm long that were made of water-soluble materials encapsulating pilocarpine nitrate. When manually pressed to the skin, the MN patches delivered >0.5 mg/cm2 pilocarpine, which was double that administered by iontophoresis. When administered to horses, MN patches generated the same volume of sweat when normalized to drug dose and more sweat when normalized to skin area compared to iontophoresis using a commercial device. Moreover, both MN patches and iontophoresis generated sweat with comparable chloride concentration. These results suggest that administration of pilocarpine by MN patches may provide a simpler and more-accessible alternative to iontophoresis for performing a sweat test for the diagnosis of CF.

Human-centred design of a new microneedle-based hormonal contraceptive delivery system

Background: It is estimated that 225 million women worldwide have an unmet need for family planning, and more than half live in low- and middle-income countries. Increasing the choice of contraceptive methods available can reduce this unmet need. Microneedle drug delivery systems represent a new technology for minimally invasive self-administration of contraceptives. We explored stakeholders’ views on different aspects of a proposed microneedle-based hormonal contraceptive delivery system. The feedback was used to iteratively develop this delivery system. Methods: Focus group discussions and semi-structured interviews were conducted with potential stakeholders (women and trans males of childbearing age, their partners, and health professionals and organisations that provide family planning advice and contraception services) in Uganda, The Gambia, Malawi, and the UK, exploring concept acceptability and gathering feedback on different aspects of design and usability of the proposed delivery system. Results: Participants viewed the concept of a new, microneedle-based contraceptive favourably. In Uganda, participants were presented with 7 different prototype applicators and identified desirable features of a preferred delivery device; their input reducing the number of prototypes that were subsequently evaluated by stakeholders in The Gambia and the UK. Participants in these countries helped to identify and/or confirm the most desirable characteristics of the applicator, resulting in design consolidation into a refined concept applicator. The final, optimised applicator prototype was validated during user research in Malawi. This human-centred design approach was also used to iteratively develop an information leaflet for the device. During these user studies, other preferred aspects of a contraceptive delivery system were also evaluated, such as anatomical site of application, duration of action, and return to fertility. Conclusions: A new microneedle-based contraceptive delivery system was iteratively developed using a human-centred design approach and was favourably received by potential stakeholders. The product is now being refined for testing in pre-clinical studies.

Translation of Polymeric Microneedles for Treatment of Human Diseases: Recent Trends, Progress, and Challenges

The ongoing search for biodegradable and biocompatible microneedles (MNs) that are strong enough to penetrate skin barriers, easy to prepare, and can be translated for clinical use continues. As such, this review paper is focused upon discussing the key points (e.g., choice polymeric MNs) for the translation of MNs from laboratory to clinical practice. The review reveals that polymers are most appropriately used for dissolvable and swellable MNs due to their wide range of tunable properties and that natural polymers are an ideal material choice as they structurally mimic native cellular environments. It has also been concluded that natural and synthetic polymer combinations are useful as polymers usually lack mechanical strength, stability, or other desired properties for the fabrication and insertion of MNs. This review evaluates fabrication methods and materials choice, disease and health conditions, clinical challenges, and the future of MNs in public healthcare services, focusing on literature from the last decade.

Immunologic mechanisms of seasonal influenza vaccination administered by microneedle patch from a randomized phase I trial

In a phase 1 randomized, single-center clinical trial, inactivated influenza virus vaccine delivered through dissolvable microneedle patches (MNPs) was found to be safe and immunogenic. Here, we compare the humoral and cellular immunologic responses in a subset of participants receiving influenza vaccination by MNP to the intramuscular (IM) route of administration. We collected serum, plasma, and peripheral blood mononuclear cells in 22 participants up to 180 days post-vaccination. Hemagglutination inhibition (HAI) titers and antibody avidity were similar after MNP and IM vaccination, even though MNP vaccination used a lower antigen dose. MNPs generated higher neuraminidase inhibition (NAI) titers for all three influenza virus vaccine strains tested and triggered a larger percentage of circulating T follicular helper cells (CD4 + CXCR5 + CXCR3 + ICOS + PD-1+) compared to the IM route. Our study indicates that inactivated influenza virus vaccination by MNP produces humoral and cellular immune response that are similar or greater than IM vaccination.

Enhanced extraction of skin interstitial fluid using a 3D printed device enabling tilted microneedle penetration

Interstitial fluid (ISF) is a body fluid that fills, surrounds cells and contains various biomarkers, but it has been challenging to extract ISF in a reliable and sufficient amount with high speed. To address the issues, we developed the tilted microneedle ISF collecting system (TMICS) fabricated by 3D printing. In this system, the microneedle (MN) was inserted at 66° to the skin by TMICS so that the MN length could be extended within a safe range of skin penetration. Moreover, TMICS incorporating three MN patches created reliable ISF collecting conditions by penetrating the skin at consistent angle and force, 4.9 N. Due to the MN length increase and the patch number expansion, the surface area of the penetrated tissue was increased, thereby confirming that ISF extraction efficiency was improved. Skin ISF was collected into the paper reservoir on the patch, and the absorbed area was converted into a volume. ISF extraction from the rat skin in vivo by TMICS was well tolerated, and the 2.9 μL of ISF was obtained within 30 s. Therefore, TMICS is promising to apply in the diagnosis of multiple biomarkers in ISF with high speed and stability.

3D printed hollow microneedles array using stereolithography for efficient transdermal delivery of rifampicin

A 3D printed assembly of hollow microneedles (HMNs) array, conjoined with a reservoir void, was designed and additively manufactured using stereolithography (SLA) technology utilizing a proprietary class-I resin. The HMNs array was utilized for transdermal delivery of high molecular weight antibiotics, i.e., rifampicin (M_w 822.94 g/mol), which suffers from gastric chemical instability, low bioavailability, and severe hepatotoxicity. HMNs morphology was designed with sub-apical holes present in a quarter of the needle tip to improve its mechanical strength and integrity of the HMNs array. The HMNs array was characterized by optical microscopy and electron microscopy to ascertain the print quality and uniformity across the array. The system was also subjected to mechanical characterization for failure and penetration analyses. The ex vivo permeation and consequent transport of rifampicin across porcine skin were systematically evaluated. Finally, in vivo examinations of rifampicin administration through the microneedle reservoir system in SD rats revealed efficient penetration and desired bioavailability.

Development of Polylactic Acid and Bovine Serum Albumin-layered-coated Chitosan Microneedles Using Novel Bees Wax Mould

Objectives

This work illustrates a novel method of fabrication of polymeric microneedle (MN) construct using bees wax as mould and development of coated polymeric MNs for drug delivery.

Materials and Methods

A novel method of MN fabrication using bees wax as mould was established. The porous chitosan MN arrays were fabricated and coated with polylactic acid (PLA). The optimized MN arrays were coated with bovine serum albumin (BSA). The MNs were subjected to physiochemical and tensile strength characterization, followed by drug release study. The skin penetration and irritation study were performed in vivo in Wistar Albino rats.

Results

The constructed MN arrays contain MNs with 0.9 mm length, 600 μm width at the base, 30-60 μm diameter at the tip, and 1.5 mm distance between 2 needles. These MNs patch was having good mechanical strength (0.72 N/needle) and tensile strength 15.23 Mpa. The MN array patch had 6.26% swelling index and 98.5% drug release was observed on the 50th hr. Good penetration and no skin irritation was observed for optimized MN batch.

Conclusion

Polymeric MN arrays were successfully developed using bees wax mould and were successfully coated with PLA to deliver the BSA through skin epidermis layer.

Human-centred design of a new microneedle-based hormonal contraceptive delivery system

Background: It is estimated that 225 million women worldwide have an unmet need for family planning, and more than half live in low- and middle-income countries. Increasing the choice of contraceptive methods available can reduce this unmet need. Microneedle drug delivery systems represent a new technology for minimally invasive self-administration of contraceptives. We explored stakeholders’ views on different aspects of a proposed microneedle-based hormonal contraceptive delivery system. The feedback was used to iteratively develop this delivery system. Methods: Focus group discussions and semi-structured interviews were conducted with potential stakeholders (women and trans males of childbearing age, their partners, and health professionals and organisations that provide family planning advice and contraception services) in Uganda, The Gambia, Malawi, and the UK, exploring concept acceptability and gathering feedback on different aspects of design and usability of the proposed delivery system. Results: Participants viewed the concept of a new, microneedle-based contraceptive favourably. In Uganda, participants were presented with 7 different prototype applicators and identified desirable features of a preferred delivery device; their input reducing the number of prototypes that were subsequently evaluated by stakeholders in The Gambia and the UK. Participants in these countries helped to identify and/or confirm the most desirable characteristics of the applicator, resulting in design consolidation into a refined concept applicator. The final, optimised applicator prototype was validated during user research in Malawi. This human-centred design approach was also used to iteratively develop an information leaflet for the device. During these user studies, other preferred aspects of a contraceptive delivery system were also evaluated, such as anatomical site of application, duration of action, and return to fertility. Conclusions: A new microneedle-based contraceptive delivery system was iteratively developed using a human-centred design approach and was favourably received by potential stakeholders. The product is now being refined for testing in pre-clinical studies.

Wound healing applications of creams and "smart" hydrogels

Although superficial wounds are often easy to treat for healthy individuals, there are some more severe types of wounds (burns, ulcers, diabetic wounds, etc.) that are a challenge for clinicians. A good therapeutic result is based on the delivery of a treatment at the right time, for the right patient. Our goal was to sum up useful knowledge regarding wound healing and wound treatments, based on creams and hydrogels with various active ingredients. We concluded that both preparations have application in preventing infections and promoting healing, but their efficacy is clearly conditioned by the type, depth, severity of the wound and patient profile. However, due to their superior versatility and capability of maintaining the integrity and functionality of the active ingredient, as well as it is controlled release at site, hydrogels are more suited for incorporating different active ingredients. New wound healing devices can combine smart hydrogel dressings with physical therapies to deliver a more efficient treatment to patients if the indications are appropriate.

Transdermal Delivery of Lidocaine-Loaded Elastic Nano-Liposomes with Microneedle Array Pretreatment

This study aimed to improve the transdermal delivery of lidocaine hydrochloride (LidH) using elastic nano-liposomes (ENLs) and microneedle (MN) array pretreatment. LidH-containing ENLs were prepared using soybean phosphatidylcholine and cholesterol, with Span 80 or Tween 80, using a reverse-phase evaporation method. The ENL particle size, stability, and encapsulation efficiency (EE) were characterized and optimized based on the component ratio, pH, and type of surfactant used. In vitro transdermal diffusion study was performed on MN-pretreated mouse skin using Franz diffusion cells. The anesthetic effects of LidH in various formulations after dermal application were evaluated in vivo in rats by measuring the tail withdrawal latency after photothermic stimulation. Stable LidH-loaded Tween 80 or Span 80 ENLs were obtained with particle sizes of 115.8 and 146.6 nm and EEs of 27% and 20%, respectively. The formulations did not exert any cytotoxicity in HaCaT cells. Tween 80 and Span 80 ENL formulations showed enhanced LidH delivery on pretreated mice skin in vitro and prolonged the anesthetic effect in vivo compared to that by LidH application alone. LidH-loaded ENLs applied to MN-pretreated skin can shorten the onset time and prolong the anesthetic effect safely, which merits their further optimization and practical application.

Design of Dissolvable Microneedles for Delivery of a Pfs47-Based Malaria Transmission-Blocking Vaccine

The development of effective malaria vaccines remains a global health priority. In addition to an effective vaccine, there is urgent demand for effective delivery technologies that can be easily deployed. The need for effective vaccine delivery tools is particularly pertinent in resource-poor settings where access to healthcare is limited. Microneedles are micron-scale structures that offer distinct advantages for vaccine delivery by efficiently targeting skin-resident immune cells, eliminating injection-associated pain, and improving patient compliance. Here, we developed and characterized a candidate malaria vaccine loaded and deployed using dissolvable microneedle arrays. Of note, a newly indicated human-relevant antigen was employed, Plasmodium falciparum surface protein P47. P47 and a potent toll-like receptor (TLR9) agonist vaccine adjuvant, CpG, were fabricated into microneedles using a gelatin polymer. Protein binding, ELISA, and fluorescence analysis confirmed the molecular structure, and the function of the P47 antigen and CpG was maintained after fabrication, storage, and release from microneedles. In cell culture, the cargo released from the microneedle arrays triggered TLR9 signaling and activated primary dendritic cells at levels similar to native, unincorporated vaccine components. Together, these studies demonstrate the potential of microneedles as an easily deployable strategy for a P47-based malaria vaccine.

Dissolvable Microneedle Patches to Enable Increased Access to Vaccines against SARS-CoV-2 and Future Pandemic Outbreaks

Vaccines are an essential component of pandemic preparedness but can be limited due to challenges in production and logistical implementation. While vaccine candidates were rapidly developed against severe acute respiratory syndrome coronavirus 2 (SARS-COV-2), immunization campaigns remain an obstacle to achieving herd immunity. Dissolvable microneedle patches are advantageous for many possible reasons: improved immunogenicity; dose-sparing effects; expected low manufacturing cost; elimination of sharps; reduction of vaccine wastage; no need for reconstitution; simplified supply chain, with reduction of cold chain supply through increased thermostability; ease of use, reducing the need for healthcare providers; and greater acceptability compared to traditional hypodermic injections. When applied to coronavirus disease 2019 (COVID-19) and future pandemic outbreaks, microneedle patches have great potential to improve vaccination globally and save many lives.

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.

Ethnobotany and the Role of Plant Natural Products in Antibiotic Drug Discovery

The crisis of antibiotic resistance necessitates creative and innovative approaches, from chemical identification and analysis to the assessment of bioactivity. Plant natural products (NPs) represent a promising source of antibacterial lead compounds that could help fill the drug discovery pipeline in response to the growing antibiotic resistance crisis. The major strength of plant NPs lies in their rich and unique chemodiversity, their worldwide distribution and ease of access, their various antibacterial modes of action, and the proven clinical effectiveness of plant extracts from which they are isolated. While many studies have tried to summarize NPs with antibacterial activities, a comprehensive review with rigorous selection criteria has never been performed. In this work, the literature from 2012 to 2019 was systematically reviewed to highlight plant-derived compounds with antibacterial activity by focusing on their growth inhibitory activity. A total of 459 compounds are included in this Review, of which 50.8% are phenolic derivatives, 26.6% are terpenoids, 5.7% are alkaloids, and 17% are classified as other metabolites. A selection of 183 compounds is further discussed regarding their antibacterial activity, biosynthesis, structure-activity relationship, mechanism of action, and potential as antibiotics. Emerging trends in the field of antibacterial drug discovery from plants are also discussed. This Review brings to the forefront key findings on the antibacterial potential of plant NPs for consideration in future antibiotic discovery and development efforts.

Early immune responses in skin and lymph node after skin delivery of Toll-like receptor agonists in neonatal and adult pigs

The skin is potentially an important vaccine delivery route facilitated by a high number of resident antigen presenting cells (APCs), which are known to be stimulated by different Toll-like receptor agonists (TLRa). In this study, neonatal and adult pigs were vaccinated in the skin using dissolving microneedle patches to investigate the immuno-stimulatory potential of different TLRa and possible age-dependent differences early after vaccination. These patches contained TLR1/2a (Pam3Cys), TLR7/8a (R848) or TLR9a (CpG ODN) combined with inactivated porcine reproductive and respiratory syndrome virus (PRRSV) or with an oil-in-water stable emulsion. Vaccinated skin and draining lymph nodes were analysed for immune response genes using microfluidic high-throughput qPCR to evaluate the early immune response and activation of APCs. Skin pathology and immunohistochemistry were used to evaluate the local immune responses and APCs in the vaccinated skin, respectively. In both neonatal and adult pigs, skin vaccination with TLR7/8a induced the most prominent early inflammatory and immune cell responses, particularly in the skin. Skin histopathology and immunohistochemistry of APCs showed comparable results for neonatal and adult pigs after vaccination with the different TLRa vaccines. However, in vaccinated neonatal pigs in the skin and draining lymph node more immune response related genes were upregulated compared to adult pigs. We showed that both neonatal and adult skin could be stimulated to develop an immune response, particularly after TLR7/8a vaccination, with age-dependent differences in regulation of immune genes. Therefore, age-dependent differences in local early immune responses should be considered when developing skin vaccines.