Intradermal vaccination with hollow microneedles: A comparative study of various protein antigen and adjuvant encapsulated nanoparticles

Unravelling the role of microneedles in drug delivery: Principle, perspectives, and practices

In recent year, the research of transdermal drug delivery systems has got substantial attention towards the development of microneedles (MNs). This shift has occurred due to multifaceted advantages of MNs as they can be utilized to deliver the drug deeper to the skin with minimal invasion, offer successful delivery of drugs and biomolecules that are susceptible to degradation in gastrointestinal tract (GIT), act as biosensors, and help in monitoring the level of biomarkers in the body. These can be fabricated into different types based on their applications as well as material for fabrication. Some of their types include solid MNs, hollow MNs, coated MNs, hydrogel forming MNs, and dissolving MNs. These MNs deliver the therapeutics via microchannels deeper into the skin. The coated and hollow MNs have been found successful. However, they suffer from poor drug loading and blocking of pores. In contrast, dissolving MNs offer high drug loading. These MNs have also been utilized to deliver vaccines and biologicals. They have also been used in cosmetics. The current review covers the different types of MNs, materials used in their fabrication, properties of MNs, and various case studies related to their role in delivering therapeutics, monitoring level of biomarkers/hormones in body such as insulin. Various patents and clinical trials related to MNs are also covered. Covered are the major bottlenecks associated with their clinical translation and potential future perspectives.

Intrinsic immunogenicity of liposomes for tuberculosis vaccines: Effect of cationic lipid and cholesterol

Tuberculosis (TB) is still among the deadliest infectious diseases, hence there is a pressing need for more effective TB vaccines. Cationic liposome subunit vaccines are excellent vaccine candidates offering effective protection with a better safety profile than live vaccines. In this study, we aim to explore intrinsic adjuvant properties of cationic liposomes to maximize immune activation while minimizing aspecific cytotoxicity. To achieve this, we developed a rational strategy to select liposomal formulation compositions and assessed their physicochemical and immunological properties in vitro models using human monocyte-derived dendritic cells (MDDCs). A broad selection of commercially available cationic compounds was tested to prepare liposomes containing Ag85B-ESAT6-Rv2034 (AER) fusion protein antigen. 1,2-Dioleoyl-sn‑glycero-3-ethylphosphocholine (EPC)-based liposomes exhibited the most advantageous activation profile in MDDCs as assessed by cell surface activation markers, cellular uptake, antigen-specific T-cell activation, cytokine production, and cellular viability. The addition of cholesterol to 20 mol% improved the performance of the tested formulations compared to those without it; however, when its concentration was doubled there was no further benefit, resulting in reduced cell viability. This study provides new insights into the role of cationic lipids and cholesterol in liposomal subunit vaccines.

Nanotechnology of inhalable vaccines for enhancing mucosal immunity

Vaccines are the cornerstone of world health. The majority of vaccines are formulated as injectable products, facing the drawbacks of cold chain transportation, needle-stick injuries, and primary systemic immunity. Inhalable vaccines exhibited unique advantages due to their small dose, easy to use, quick effect, and simultaneous induction of mucosal and systemic responses. Facing global pandemics, especially the coronavirus disease 2019 (COVID-19), a majority of inhalable vaccines are in preclinical or clinical trials. A better understanding of advanced delivery technologies of inhalable vaccines may provide new scientific insights for developing inhalable vaccines. In this review article, detailed immune mechanisms involving mucosal, cellular, and humoral immunity were described. The preparation methods of inhalable vaccines were then introduced. Advanced nanotechnologies of inhalable vaccines containing inhalable nucleic acid vaccines, inhalable adenovirus vector vaccines, novel adjuvant-assisted inhalable vaccines, and biomaterials for inhalable vaccine delivery were emphatically discussed. Meanwhile, the latest clinical progress in inhalable vaccines for COVID-19 and tuberculosis was discussed.

Bovine serum albumin nanoparticles containing Poly (I:C) can enhance the neutralizing antibody response induced by envelope protein of Orthoflavivirus zikaense

Since the Orthoflavivirus zikaense (ZIKV) has been considered a risk for Zika congenital syndrome development, developing a safe and effective vaccine has become a high priority. Numerous research groups have developed strategies to prevent ZIKV infection and have identified the domain III of the ZIKV envelope protein (zEDIII) as a promising target. Subunit antigens are often poorly immunogenic, necessitating the use of adjuvants and/or delivery systems to induce optimal immune responses. The subject of nanotechnology has substantial expansion in recent years in terms of research and applications. Nanoparticles could be used as drug delivery systems and to increase the immunogenicity and stability of a given antigen. This work aims to characterize and validate the potential of a vaccine formulation composed of domain zEDIII and bovine serum albumin nanoparticles containing polyinosinic-polycytidylic acid (NPPI). NPPI were uptake in vitro by immature bone marrow dendritic cells and histological analysis of the skin of mice treated with NPPI showed an increase in cellularity. Immunization assay showed that mice immunized with zEDIII in the presence of NPPI produced neutralizing antibodies. Through the passive transfer of sera from immunized mice to ZIKV-infected neonatal mice, it was demonstrated that these antibodies provide protection, mitigating weight loss, clinical or neurological signs induced by infection, and significantly increased survival rates. Protection was further substantiated by the reduction in the number of viable infectious ZIKV, as well as a decrease in inflammatory cytokines and tissue alterations in the brains of infected mice. Taken together, data presented in this study shows that NPPI + zEDIII is a promising vaccine candidate for ZIKV.

Immunogenicity of Recombinant Lipid-Based Nanoparticle Vaccines: Danger Signal vs. Helping Hand

Infectious diseases are a predominant problem in human health. While the incidence of many pathogenic infections is controlled by vaccines, some pathogens still pose a challenging task for vaccine researchers. In order to face these challenges, the field of vaccine development has changed tremendously over the last few years. For non-replicating recombinant antigens, novel vaccine delivery systems that attempt to increase the immunogenicity by mimicking structural properties of pathogens are already approved for clinical applications. Lipid-based nanoparticles (LbNPs) of different natures are vesicles made of lipid layers with aqueous cavities, which may carry antigens and other biomolecules either displayed on the surface or encapsulated in the cavity. However, the efficacy profile of recombinant LbNP vaccines is not as high as that of live-attenuated ones. This review gives a compendious picture of two approaches that affect the immunogenicity of recombinant LbNP vaccines: (i) the incorporation of immunostimulatory agents and (ii) the utilization of pre-existing or promiscuous cellular immunity, which might be beneficial for the development of tailored prophylactic and therapeutic LbNP vaccine candidates.

Long-acting microneedle formulations

The minimally-invasive and painless nature of microneedle (MN) application has enabled the technology to obviate many issues with injectable drug delivery. MNs not only administer therapeutics directly into the dermal and ocular space, but they can also control the release profile of the active compound over a desired period. To enable prolonged delivery of payloads, various MN types have been proposed and evaluated, including dissolving MNs, polymeric MNs loaded or coated with nanoparticles, fast-separable MNs hollow MNs, and hydrogel MNs. These intricate yet intelligent delivery platforms provide an attractive approach to decrease side effects and administration frequency, thus offer the potential to increase patient compliance. In this review, MN formulations that are loaded with various therapeutics for long-acting delivery to address the clinical needs of a myriad of diseases are discussed. We also highlight the design aspects, such as polymer selection and MN geometry, in addition to computational and mathematical modeling of MNs that are necessary to help streamline and develop MNs with high translational value and clinical impact. Finally, up-scale manufacturing and regulatory hurdles along with potential avenues that require further research to bring MN technology to the market are carefully considered. It is hoped that this review will provide insight to formulators and clinicians that the judicious selection of materials in tandem with refined design may offer an elegant approach to achieve sustained delivery of payloads through the simple and painless application of a MN patch.

Recent progress in PLGA-based microneedle-mediated transdermal drug and vaccine delivery

Microneedles (MNs) have recently been found to have applications in drug, vitamin, protein and vaccine delivery. Polymeric MN arrays continue to attract increasing attention due to their capability to bypass the skin's stratum corneum (SC) barrier with minimal invasiveness. These carriers can achieve the targeted intradermal delivery of drugs and vaccines and improve their transdermal delivery level. As a nontoxic FDA-approved copolymer, polylactic glycolic acid (PLGA) has good biocompatibility and biodegradability. Currently, PLGA-based MNs have a noticeable tendency to be utilized as a delivery system. This study focuses on the most recent advances in PLGA-based MNs. Both PLGA nanoparticle-based MNs and PLGA matrix-based MNs, created for the delivery of vaccines, drugs, proteins and other therapeutic agents, are discussed. The paper also discusses the various types of MNs and their potential applications. Finally, the prospects and challenges of PLGA-based MNs are reviewed.

Liposome-based vaccines for minimally or noninvasive administration: an update on current advancements

INTRODUCTION

Vaccination requires innovation to provide effective protection. Traditional vaccines have several drawbacks, which can be overcome with advanced technologies and different administration routes. Over the past 10  years, a significant amount of research has focussed on the delivery of antigens into liposomes due to their dual role as antigen-carrying systems and vaccine adjuvants able to increase the immunogenicity of the carried antigen.

AREAS COVERED

This review encompasses the progress made over the last 10  years with liposome-based vaccines designed for minimally or noninvasive administration, filling the gaps in previous reviews and providing insights on composition, administration routes, results achieved, and Technology Readiness Level of the most recent formulations.

EXPERT OPINION

Liposome-based vaccines administered through minimally or noninvasive routes are expected to improve efficacy and complacency of vaccination programs. However, the translation from lab-scale production to large-scale production and collaborations with hospitals, research centers, and companies are needed to allow new products to enter the market and improve the vaccination programs in the future.

Dissolving Microneedles Loaded with Nanoparticle Formulation of Respiratory Syncytial Virus Fusion Protein Virus-like Particles (F-VLPs) Elicits Cellular and Humoral Immune Responses

Respiratory syncytial virus (RSV) is one of the leading causes of bronchiolitis and pneumonia in children ages five years and below. Recent outbreaks of the virus have proven that RSV remains a severe burden on healthcare services. Thus, a vaccine for RSV is a need of the hour. Research on novel vaccine delivery systems for infectious diseases such as RSV can pave the road to more vaccine candidates. Among many novel vaccine delivery systems, a combined system with polymeric nanoparticles loaded in dissolving microneedles holds a lot of potential. In this study, the virus-like particles of the RSV fusion protein (F-VLP) were encapsulated in poly (D, L-lactide-co-glycolide) (PLGA) nanoparticles (NPs). These NPs were then loaded into dissolving microneedles (MNs) composed of hyaluronic acid and trehalose. To test the in vivo immunogenicity of the nanoparticle-loaded microneedles, Swiss Webster mice were immunized with the F-VLP NPs, both with and without adjuvant monophosphoryl lipid A (MPL) NPs loaded in the MN. The mice immunized with the F-VLP NP + MPL NP MN showed high immunoglobulin (IgG and IgG2a) levels both in the serum and lung homogenates. A subsequent analysis of lung homogenates post-RSV challenge revealed high IgA, indicating the generation of a mucosal immune response upon intradermal immunization. A flowcytometry analysis showed high CD8+ and CD4+ expression in the lymph nodes and spleens of the F-VLP NP + MPL NP MN-immunized mice. Thus, our vaccine elicited a robust humoral and cellular immune response in vivo. Therefore, PLGA nanoparticles loaded in dissolving microneedles could be a suitable novel delivery system for RSV vaccines.

Poly(β-amino ester)s-Based Delivery Systems for Targeted Transdermal Vaccination

Nucleic acid vaccines have become a transformative technology to fight emerging infectious diseases and cancer. Delivery of such via the transdermal route could boost their efficacy given the complex immune cell reservoir present in the skin that is capable of engendering robust immune responses. We have generated a novel library of vectors derived from poly(β-amino ester)s (PBAEs) including oligopeptide-termini and a natural ligand, mannose, for targeted transfection of antigen presenting cells (APCs) such as Langerhans cells and macrophages in the dermal milieu. Our results reaffirmed terminal decoration of PBAEs with oligopeptide chains as a powerful tool to induce cell-specific transfection, identifying an outstanding candidate with a ten-fold increased transfection efficiency over commercial controls in vitro. The inclusion of mannose in the PBAE backbone rendered an additive effect and increased transfection levels, achieving superior gene expression in human monocyte-derived dendritic cells and other accessory antigen presenting cells. Moreover, top performing candidates were capable of mediating surface gene transfer when deposited as polyelectrolyte films onto transdermal devices such as microneedles, offering alternatives to conventional hypodermic administration. We predict that the use of highly efficient delivery vectors derived from PBAEs could advance clinical translation of nucleic acid vaccination over protein- and peptide-based strategies.

Iontophoresis-driven microneedle patch for the active transdermal delivery of vaccine macromolecules

COVID-19 has seriously threatened public health, and transdermal vaccination is an effective way to prevent pathogen infection. Microneedles (MNs) can damage the stratum corneum to allow passive diffusion of vaccine macromolecules, but the delivery efficiency is low, while iontophoresis can actively promote transdermal delivery but fails to transport vaccine macromolecules due to the barrier of the stratum corneum. Herein, we developed a wearable iontophoresis-driven MN patch and its iontophoresis-driven device for active and efficient transdermal vaccine macromolecule delivery. Polyacrylamide/chitosan hydrogels with good biocompatibility, excellent conductivity, high elasticity, and a large loading capacity were prepared as the key component for vaccine storage and active iontophoresis. The transdermal vaccine delivery strategy of the iontophoresis-driven MN patch is "press and poke, iontophoresis-driven delivery, and immune response". We demonstrated that the synergistic effect of MN puncture and iontophoresis significantly promoted transdermal vaccine delivery efficiency. In vitro experiments showed that the amount of ovalbumin delivered transdermally using the iontophoresis-driven MN patch could be controlled by the iontophoresis current. In vivo immunization studies in BALB/c mice demonstrated that transdermal inoculation of ovalbumin using an iontophoresis-driven MN patch induced an effective immune response that was even stronger than that of traditional intramuscular injection. Moreover, there was little concern about the biosafety of the iontophoresis-driven MN patch. This delivery system has a low cost, is user-friendly, and displays active delivery, showing great potential for vaccine self-administration at home.

Research progress of physical transdermal enhancement techniques in tumor therapy

The advancement and popularity of transdermal drug delivery (TDD) based on the physical transdermal enhancement technique (PTET) has opened a new paradigm for local tumor treatment. The drug can be directly delivered to the tumor site through the skin, thus avoiding the toxic side effects caused by the first-pass effect and achieving high patient compliance. Further development of PTETs has provided many options for antitumor drugs and laid the foundation for future applications of wearable closed-loop targeting drug delivery systems. In this highlight, the different types of PTETs and related mechanisms, and applications of PTET-related tumor detection and therapy are highlighted. According to their type and characteristics, PTETs are categorized as follows: (1) iontophoresis, (2) electroporation, (3) ultrasound, (4) thermal ablation, and (5) microneedles. PTET-related applications in the local treatment of tumors are categorized as follows: (1) melanoma, (2) breast tumor, (3) squamous cell carcinoma, (4) cervical tumor, and (5) others. The challenges and future prospects of existing PTETs are also discussed. This highlight will provide guidance for the design of PTET-based wearable closed-loop targeting drug delivery systems and personalized therapy for tumors.

Microneedle system for tissue engineering and regenerative medicine

Global increasing demand for high life quality and length facilitates the development of tissue engineering and regenerative medicine, which apply multidisciplinary theories and techniques to achieve the structural reconstruction and functional recovery of disordered or damaged tissues and organs. However, the clinical performances of adopted drugs, materials, and powerful cells in the laboratory are inescapably limited by the currently available technologies. To tackle the problems, versatile microneedles are developed as the new platform for local delivery of diverse cargos with minimal invasion. The efficient delivery, as well as painless and convenient procedure endow microneedles with good patient compliance in clinic. In this review, we first categorize different microneedle systems and delivery models, and then summarize their applications in tissue engineering and regenerative medicine mainly involving maintenance and rehabilitation of damaged tissues and organs. In the end, we discuss the advantages, challenges, and prospects of microneedles in depth for future clinical translations.

Recent advancements in single dose slow-release devices for prophylactic vaccines

Single dose slow-release vaccines herald a new era in vaccine administration. An ideal device for slow-release vaccine delivery would be minimally invasive and self-administered, making these approaches an attractive alternative for mass vaccination programs, particularly during the time of a pandemic. In this review article, we discuss the latest advances in this field, specifically for prophylactic vaccines able to prevent infectious diseases. Recent studies have found that slow-release vaccines elicit better immune responses and often do not require cold chain transportation and storage, thus drastically reducing the cost, streamlining distribution, and improving efficacy. This promise has attracted significant attention, especially when poor patient compliance of the standard multidose vaccine regimes is considered. Single dose slow-release vaccines are the next generation of vaccine tools that could overcome most of the shortcomings of present vaccination programs and be the next platform technology to combat future pandemics. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Implantable Materials and Surgical Technologies > Nanomaterials and Implants Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

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.

Flexible polymeric patch based nanotherapeutics against non-cancer therapy

Flexible polymeric patches find widespread applications in biomedicine because of their biological and tunable features including excellent patient compliance, superior biocompatibility and biodegradation, as well as high loading capability and permeability of drug. Such polymeric patches are classified into microneedles (MNs), hydrogel, microcapsule, microsphere and fiber depending on the formed morphology. The combination of nanomaterials with polymeric patches allows for improved advantages of increased curative efficacy and lowered systemic toxicity, promoting on-demand and regulated drug administration, thus providing the great potential to their clinic translation. In this review, the category of flexible polymeric patches that are utilized to integrate with nanomaterials is briefly presented and their advantages in bioapplications are further discussed. The applications of nanomaterials embedded polymeric patches in non-cancerous diseases were also systematically reviewed, including diabetes therapy, wound healing, dermatological disease therapy, bone regeneration, cardiac repair, hair repair, obesity therapy and some immune disease therapy. Alternatively, the limitations, latest challenges and future perspectives of such biomedical therapeutic devices are addressed.

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The most explored polymeric patches, such as microneedle, hydrogel, microsphere, microcapsule, and fiber are summarized.

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Polymeric patches integrated with a diversity of nanomaterials are systematically overviewed in non-cancer therapy.

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The future prospective for the development of polymeric patch based nanotherapeutics is discussed.

Recent advances in responsive hydrogels for diabetic wound healing

Poor wound healing after diabetes mellitus remains a challenging problem, and its pathophysiological mechanisms have not yet been fully elucidated. Persistent bleeding, disturbed regulation of inflammation, blocked cell proliferation, susceptible infection and impaired tissue remodeling are the main features of diabetic wound healing. Conventional wound dressings, including gauze, films and bandages, have a limited function. They generally act as physical barriers and absorbers of exudates, which fail to meet the requirements of the whol diabetic wound healing process. Wounds in diabetic patients typically heal slowly and are susceptible to infection due to hyperglycemia within the wound bed. Once bacterial cells develop into biofilms, diabetic wounds will exhibit robust drug resistance. Recently, the application of stimuli-responsive hydrogels, also known as "smart hydrogels", for diabetic wound healing has attracted particular attention. The basic feature of this system is its capacities to change mechanical properties, swelling ability, hydrophilicity, permeability of biologically active molecules, etc., in response to various stimuli, including temperature, potential of hydrogen (pH), protease and other biological factors. Smart hydrogels can improve therapeutic efficacy and limit total toxicity according to the characteristics of diabetic wounds. In this review, we summarized the mechanism and application of stimuli-responsive hydrogels for diabetic wound healing. It is hoped that this work will provide some inspiration and suggestions for research in this field.

Long-Term Vaccine Delivery and Immunological Responses Using Biodegradable Polymer-Based Carriers

Biodegradable polymers are largely employed in the biomedical field, ranging from tissue regeneration to drug/vaccine delivery. The biodegradable polymers are highly biocompatible and possess negligible toxicity. In addition, biomaterial-based vaccines possess adjuvant properties, thereby enhancing immune responses. This Review introduces the use of different biodegradable polymers and their degradation mechanism. Different kinds of vaccines, as well as the interaction between the carriers with the immune system, then are highlighted. Natural and synthetic biodegradable micro-/nanoplatforms, hydrogels, and scaffolds for local or targeted and controlled vaccine release are subsequently discussed.

Immune Enhancement of Nanoparticle-Encapsulated Ginseng Stem-Leaf Saponins on Porcine Epidemic Diarrhea Virus Vaccine in Mice

Porcine epidemic diarrhea virus (PEDV) causes severe enteric disease in pigs, particularly neonatal piglets. Current vaccines do not provide complete protection against PEDV. Ginseng stem-leaf saponins (GSLS), a promising oral adjuvant candidate, can improve intestinal immune responses in poultry and mice. However, its low stability limits further use. Poly lactic-co-glycolic acid (PLGA), a biocompatible and biodegradable nanoparticle, has been widely used in biomedicine for stable and targeted drug delivery. In this study, we developed GSLS-PLGA nanoparticles (GSLS-NPs) and evaluated the mucosal adjuvant efficacy in vitro and in vivo. GSLS-NPs significantly enhanced antigen internalization and pro-inflammatory cytokine secretion by DC2.4 cells. Mice orally administered GSLS-NPs before intramuscular inoculation generated CD11b+CD8α- and CD11b-CD103+ dendritic cells in the spleen and draining mesenteric lymph nodes, respectively, which are the types mainly responsible for antigen presentation. Additionally, enhanced neutralizing and non-neutralizing antibody responses and expanded activities of specific effector and memory CD4+ and CD8+ T cells were also observed in mice immunized with PEDV vaccines plus GSLS-NPs compared to mice receiving the vaccines alone. Furthermore, GSLS-NPs showed a good safety profile and presented great advantages over GSLS aqueous solution. Collectively, our results highlight the potential of GSLS-NPs as a mucosal adjuvant and provide an attractive vaccination strategy for combatting PEDV. Further study is required to evaluate the efficacy of this mucosal adjuvant in swine.

Microneedle-mediated drug delivery for cutaneous diseases

Microneedles have garnered significant interest as transdermal drug delivery route owing to the advantages of nonselective loading capacity, minimal invasiveness, simple operation, and good biocompatibility. A number of therapeutics can be loaded into microneedles, including hydrophilic and hydrophobic small molecular drugs, and macromolecular drugs (proteins, mRNA, peptides, vaccines) for treatment of miscellaneous diseases. Microneedles feature with special benefits for cutaneous diseases owing to the direct transdermal delivery of therapeutics to the skin. This review mainly introduces microneedles fabricated with different technologies and transdermal delivery of various therapeutics for cutaneous diseases, such as psoriasis, atopic dermatitis, skin and soft tissue infection, superficial tumors, axillary hyperhidrosis, and plantar warts.

Peptide loaded polymeric nanoparticles by non-aqueous nanoprecipitation

It is always a challenge to encapsulate water-soluble peptides in polymer nanoparticle (NP) systems. We establish and validate our newly developed non-aqueous nanoprecipitation method to encapsulate neuro-peptides drugs such as oxytocin and Luteinizing hormone-releasing hormone (LHRH) in poly(sebacic anhydride) (PSA) NPs. NPs were prepared by a solvent-antisolvent process under a strict anhydrous environment to obtain high drug loading and to avoid premature PSA degradation and drug release. Dynamic light scattering (DLS) and Scanning Electron Microscopy (SEM) reveal the size for both drug loaded PSA NPs to ∼ 300 nm. The drug loaded NPs were dispersible and spherical in shape with uniform morphology. The in vitro release profile of oxytocin from PSA NPs occurs with the burst release of ∼ 50% within the first hour in the aqueous release medium, whereas LHRH release is comparatively slow. Thus, looking into the fast degrading properties of PSA and drug release behavior, the developed NPs can be used for direct delivery of the neuropeptides to the olfactory epithelium using a refillable nasal atomizer that deposits mist onto the olfactory neuro-epithelium. We also applied our developed method to prepare NPs of poly(lactic-co-glycolic acid) (PLGA), polylactic acid (PLA), and poly(ε-caprolactone) (PCL). A Thyrotropin releasing hormone (TRH) was used as the sample neuropeptide drug to validate our non-aqueous method. The results reveal the formation of TRH loaded PLGA, PLA and PCL NPs with 100% drug loading. TEM analysis shows the formation of spherical NPs, having similar release properties as those of PSA NPs. Overall, we report that our developed method is suitable for co-encapsulating hydrophilic drugs in polymer NPs with high drug loading and release properties.

Progress in Intradermal and Transdermal Gene Therapy with Microneedles

Gene therapy is one of the most widely studied treatments and has the potential to treat a variety of intractable diseases. The skin's limited permeability, as the body's initial protective barrier, drastically inhibits the delivery effect of gene medicine. Given the potential adverse effects and physicochemical features of the medications, improving generic drug penetration into the skin barrier and achieving an effective level of target tissues remains a challenge. Microneedles have made tremendous improvements in aided gene transfer and medication delivery as a unique method. Microneedles offer the advantage of being minimally invasive and painless, as well as the ability to distribute gene medicines straight through the stratum corneum. Microneedles have been used to penetrate skin tissue with various nucleic acids and medicines in recent years, allowing for a wide range of applications in the treatment of skin ailments. This review focuses on skin-related disorders and immunity, and it primarily discusses the progress of microneedle transdermal gene therapy in recent years. It also complements the current major vectors and related microneedle gene therapy applications.

Smart combination of aluminum hydroxide and MF59 to induce strong cellular immune responses

As two of the most widely used adjuvants, aluminum hydroxide and the oil-in-water emulsion MF59 have their intrinsic limitations: classical aluminum gel induces only weak cellular immune responses while MF59 cannot be used as an antigen delivery system due to its poor physical interaction with antigen molecules. Herein, we combined these two adjuvants and constructed a novel nano-vaccine delivery system by inserting aluminum hydroxide into the surface of a modified MF59 nano-emulsion (AlNEs). A model antigen ovalbumin (OVA) and an immune potentiator CpG were adsorbed on the surface of AlNEs (hereinafter AlNEs-OVA-CpG) through a facile mixing step. After subcutaneous injection, AlNEs-OVA-CpG effectively drained to lymph nodes, delivered both cargos into lymph node-resident antigen presenting cells (APCs), and escaped from lysosomes into the cytoplasm, resulting in enhanced antigen cross-presentation. Finally, AlNEs-OVA-CpG induced potent antigen-specific humoral and cellular immune responses, which significantly inhibited tumor growth and prolonged mice survival in a EG7-OVA tumor model. In sum, our results suggested that AlNEs have a great prospect to induce CD8⁺ T cell responses for subunit antigens.

Advances in Infectious Disease Vaccine Adjuvants

Vaccines are one of the most significant medical interventions in the fight against infectious diseases. Since their discovery by Edward Jenner in 1796, vaccines have reduced the worldwide transmission to eradication levels of infectious diseases, including smallpox, diphtheria, hepatitis, malaria, and influenza. However, the complexity of developing safe and effective vaccines remains a barrier for combating many more infectious diseases. Immune stimulants (or adjuvants) are an indispensable factor in vaccine development, especially for inactivated and subunit-based vaccines due to their decreased immunogenicity compared to whole pathogen vaccines. Adjuvants are widely diverse in structure; however, their overall function in vaccine constructs is the same: to enhance and/or prolong an immunological response. The potential for adverse effects as a result of adjuvant use, though, must be acknowledged and carefully managed. Understanding the specific mechanisms of adjuvant efficacy and safety is a key prerequisite for adjuvant use in vaccination. Therefore, rigorous pre-clinical and clinical research into adjuvant development is essential. Overall, the incorporation of adjuvants allows for greater opportunities in advancing vaccine development and the importance of immune stimulants drives the emergence of novel and more effective adjuvants. This article highlights recent advances in vaccine adjuvant development and provides detailed data from pre-clinical and clinical studies specific to infectious diseases. Future perspectives into vaccine adjuvant development are also highlighted.

Rational Vaccinology: Harnessing Nanoscale Chemical Design for Cancer Immunotherapy

Cancer immunotherapy is a powerful treatment strategy that mobilizes the immune system to fight disease. Cancer vaccination is one form of cancer immunotherapy, where spatiotemporal control of the delivery of tumor-specific antigens, adjuvants, and/or cytokines has been key to successfully activating the immune system. Nanoscale materials that take advantage of chemistry to control the nanoscale structural arrangement, composition, and release of immunostimulatory components have shown significant promise in this regard. In this Outlook, we examine how the nanoscale structure, chemistry, and composition of immunostimulatory compounds can be modulated to maximize immune response and mitigate off-target effects, focusing on spherical nucleic acids as a model system. Furthermore, we emphasize how chemistry and materials science are driving the rational design and development of next-generation cancer vaccines. Finally, we identify gaps in the field that should be addressed moving forward and outline future directions to galvanize researchers from multiple disciplines to help realize the full potential of this form of cancer immunotherapy through chemistry and rational vaccinology.

Microneedle-Based Vaccine Delivery: Review of an Emerging Technology

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

Recent advances in polymer microneedles for drug transdermal delivery: Design strategies and applications

In recent years, the transdermal drug delivery based on microneedles (MNs) technology has received extensive attention, which offers a safer and painless alternative to hypodermic needle injection. They can pierce the stratum corneum and deliver drugs to the epidermis and dermis-structures of skin, showing prominent properties such as minimally invasive, bypassing first-pass metabolism, and self-administered. A range of materials have been used to fabricate MNs, such as silicon, metal, glass, and polymers. Among them, polymer MNs have gained increasing attention from pharmaceutical and cosmetic companies as one of the promising drug delivery methods. Microneedle products have recently become available on the market, and some of them are under evaluation for efficacy and safety. This paper focuses on current state of polymer MNs in the drug transdermal delivery. The materials and methods for the fabrication of polymer MNs and their drug administration are described. The recent progresses of polymer MNs for treatment of cancer, vaccine delivery, blood glucose regulation, androgenetic alopecia, obesity, tissue healing, myocardial infarction and gout are reviewed. The challenges of MNs technology are summarized and the future development trend of MNs is also prospected. This article is protected by copyright. All rights reserved.

Intradermal administration of influenza vaccine with trehalose and pullulan-based dissolving microneedle arrays

Most influenza vaccines are administered via intramuscular injection which has several disadvantages that might jeopardize the compliance of vaccinees. Intradermal administration of dissolving-microneedle-arrays (dMNAs) could serve as minimal invasive alternative to needle injections. However, during the production process of dMNAs antigens are subjected to several stresses, which may reduce their potency. Moreover, the needles need to have sufficient mechanical strength to penetrate the skin and subsequently dissolve effectively to release the incorporated antigen. Here, we investigated whether blends of trehalose and pullulan are suitable for the production of stable dMNA fulfilling these criteria. Our results demonstrate that production of trehalose/pullulan-based dMNAs rendered microneedles that were sharp and stiff enough to pierce into ex vivo human skin and subsequently dissolve within 15 min. The mechanical properties of the dMNAs were maintained well even after four weeks of storage at temperatures up to 37°C. In addition, immunization of mice with influenza antigens via both freshly prepared dMNAs and dMNAs after storage (four weeks at 4°C or 37°C) resulted in antibody titers of similar magnitude as found in intramuscularly injected mice and partially protected mice from influenza virus infection. Altogether, our results demonstrate the potential of trehalose/pullulan-based dMNAs as alternative dosage form for influenza vaccination.

Lentinan PLGA-stabilized pickering emulsion for the enhanced vaccination

Lentinan (LNT), a β-1,3-linked-d-glucan with β-1,6 glucose branches, is the main bioactive component extracted from Lentinus edodes. As a carbohydrate polymer, it has attracted increasingly attention because of immune enhancement effect. Pickering emulsion has been widely used in biomedicine due to its great stability, high loading capacity, and appreciable biocompatibility. The aim of this study is to construct an adjuvant delivery system (LNTPP/OVA) (Lentinan PLGA-stabilized Pickering emulsion loading OVA antigen) which can enhance the immune activity of LNT and can together deliver model protein antigen ovalbumin (OVA) into the organism. The characterization of the LNTPP/OVA was demonstrated that the size of LNTPP/OVA was around 1050.68 nm and was stable to store at least 28 days. Pickering emulsion was spherical shape like the raspberry with the high antigen load rate at around 82.53%. Moreover, the adjuvant effect of LNTPP/OVA formulation was detected. Compared with LNT/OVA formulation, our experimental results showed that LNTPP/OVA could promote the uptake of the OVA-antigen by macrophages in vitro. In vivo experiments, LNTPP/OVA facilitated the activation of dendritic cells (DCs) and induced strong humoral and cellular immune responses carrying a Th1 and Th2 immune responses. Therefore, LNTPP/OVA formulation have the latent capacity as a vaccine transmission system.

Immunological Assessment of Chitosan or Trimethyl Chitosan-Coated PLGA Nanospheres Containing Fusion Antigen as the Novel Vaccine Candidates Against Tuberculosis

The crucial challenge in tuberculosis (TB) as a chronic infectious disease is to present a novel vaccine candidate that improves current vaccination and provides efficient protection in individuals. The present study aimed to evaluate the immune efficacy of multi-subunit vaccines containing chitosan (CHT)- or trimethyl chitosan (TMC)-coated PLGA nanospheres to stimulate cell-mediated and mucosal responses against Mycobacterium Tuberculosis (Mtb) in an animal model. The surface-modified PLGA nanoparticles (NPs) containing tri-fusion protein from three Mtb antigens were produced by the double emulsion technique. The subcutaneously or nasally administered PLGA vaccines in the absence or presence of BCG were assessed to compare the levels of mucosal IgA, IgG1, and IgG2a production as well as secretion of IFN-γ, IL-17, IL-4, and TGF-β cytokines. According to the release profile, the tri-fusion encapsulated in modified PLGA NPs demonstrated a biphasic release profile including initial burst release on the first day and sustained release within 18 days. All designed PLGA vaccines induced a shift of Th1/Th2 balance toward Th1-dominant response. Although immunized mice through subcutaneous injection elicited higher cell-mediated responses relative to the nasal vaccination, the intranasally administered groups stimulated robust mucosal IgA immunity. The modified PLGA NPs using TMC cationic polymer were more efficient to elevate Th1 and mucosal responses in comparison with the CHT-coated PLGA nanospheres. Our findings highlighted that the tri-fusion loaded in TMC-PLGA NPs may represent an efficient prophylactic vaccine and can be considered as a novel candidate against TB.

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.

Co-assembled nanocomplexes of peptide neoantigen Adpgk and Toll-like receptor 9 agonist CpG ODN for efficient colorectal cancer immunotherapy

Cancer vaccines targeting tumor specific neoantigens derived from nonsynonymous mutations of tumor cells have emerged as an effective approach to induce antitumor T cells responses for personalized cancer immunotherapy. Despite the enormous potential of synthetic peptides as a common modality for neoantigen vaccines, their practical efficacy was limited due to their relatively low immunogenicity. Herein, we modify neoantigen peptide (Adpgk) derived from MC-38 colon carcinoma by supplementing ten consecutive positively-charged lysines (10 K-Adpgk) to obtain cationic polypeptide. And then we made them self-assemble with toll-like receptor 9 (TLR-9) agonist CpG oligodeoxynucleotides (CpG ODN) adjuvant directly forming antigen/adjuvant integrated nanocomplexes (PCNPs) through electrostatic interaction for potent tumor immunotherapy. The optimal formed PCNPs were around 175 nm with uniform size distribution and could maintain stability in physiological saline solution. CpG ODN and 10 K-Adpgk in the formed PCNPs could be effectively uptake by dendritic cells (DCs) and stimulate the maturation of DCs as well as improving the efficiency of antigen cross-presentation efficiency in vitro. Furthermore, the PCNPs vaccine could markedly improve neoantigen and adjuvant co-delivery efficiency to lymphoid organs and activate cytotoxic T cells. In addition, vaccination with PCNPs could not only offer prophylactic to protect mice from challenged MC-38 colorectal tumors, but also achieve a better anti-tumor effect in an established colorectal tumor model, and significantly prolong the survival rate of tumor-bearing mice. Therefore, this work provided a versatile but effective method for neoantigen peptide and CpG ODN co-assembly vaccine platform for efficient colorectal cancer immunotherapy.

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.

Distinct endocytosis and immune activation of poly(lactic-co-glycolic) acid nanoparticles prepared by single- and double-emulsion evaporation

Background: Poly(lactic-co-glycolic) acid (PLGA) nanoparticles can be prepared by emulsion-solvent-evaporation from o/w and w₁/o/w₂ emulsions. Aims: To elaborate similarities and differences regarding mechanical, morphological and physicochemical properties, as well as endocytosis and dose-dependent immune responses by primary human leukocytes between nanoparticles prepared by these two methods. Methods: Fluorescently labeled as well as TLR agonist (R848)-loaded PLGA nanoparticles were prepared via both single- and double-emulsion solvent evaporation. Results: Particles prepared by both methods were similar in chemical composition and surface charge but exhibited slight differences in size and morphology. Pronounced differences were found for loading, dissolution and mechanical properties. The particles were differently endocytosed by monocytes and induced qualitatively and quantitatively different immune responses. Conclusions: Variations in nanoparticle preparation can affect particle-derived immunological characteristics.

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

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

Mannosylated polylactic-co-glycolic acid (MN-PLGA) nanoparticles induce potent anti-tumor immunity in murine model of breast cancer

Nanoparticle-based cancer immunotherapy is considered a novel and promising therapeutic strategy aimed at stimulating host immune responses against tumors. To this end, in the present study, mannan-decorated polylactic-co-glycolic acid (PLGA) nanoparticles containing tumor cell lysate (TCL) and poly riboinosinic polycytidylic acid (poly I:C) were used as antigen delivery systems to immunize breast tumor-bearing Balb/c mice. PLGA nanoparticles were fabricated employing a double emulsion solvent evaporation method. The formation of spherical and uniform nanoparticles (NPs) ranging 150-250 nm was detected by field emission scanning electron microscopy (FESEM) and dynamic light scattering (DLS). Four nanoformulation were used to treat mice and vaccination-induced immunological responses. Tumor regression and overall survival rate were evaluated in four experimental groups. Tumor cell lysate and poly I:C loaded mannan-decorated nanoparticles (TCL-Poly I:C) NP-MN caused a significant decrease in tumor growth and 2- to 3-fold improvement in survival times of the treated mice. The NPs with or without mannan decoration elicited stronger responses in terms of lymphocyte proliferation, delayed-type hypersensitivity and CD107a expression. Moreover, our data indicated that the production of IFN-γ and IL-2 increased while the production of IL-4 and IL-10 decreased in splenocytes culture supernatants. In the pathological evaluations, we found that necrosis and immune cells infiltration rate in the tumor tissue of the treated mice was elevated, while tumor cellularity and lung metastases significantly decreased in particular in the group that received (TCL-Poly I:C) NP-MN. Altogether, our findings suggested that the mannan-decorated PLGA NPs antigen delivery system had significant anti-tumor effects against the murine model of breast cancer and it could be considered as a step forward to human breast cancer immunotherapy.

Recent advances in microneedles-mediated transdermal delivery of protein and peptide drugs

Proteins and peptides have become a significant therapeutic modality for various diseases because of their high potency and specificity. However, the inherent properties of these drugs, such as large molecular weight, poor stability, and conformational flexibility, make them difficult to be formulated and delivered. Injection is the primary route for clinical administration of protein and peptide drugs, which usually leads to poor patient's compliance. As a portable, minimally invasive device, microneedles (MNs) can overcome the skin barrier and generate reversible microchannels for effective macromolecule permeation. In this review, we highlighted the recent advances in MNs-mediated transdermal delivery of protein and peptide drugs. Emphasis was given to the latest development in representative MNs design and fabrication. We also summarize the current application status of MNs-mediated transdermal protein and peptide delivery, especially in the field of infectious disease, diabetes, cancer, and other disease therapy. Finally, the current status of clinical translation and a perspective on future development are also provided.

Nanotechnological Innovations Enhancing the Topical Therapeutic Efficacy of Quercetin: A Succinct Review

Nanotechnology is currently a hot topic in dermatology and nutraceutical/cosmeceutical delivery, owing to the advantages it provides in terms of enhancing the skin permeation of drugs, as well as increasing their therapeutic efficacy in the treatment of different dermatological diseases. There is also a great interest in the topical delivery of nutraceuticals; which are natural compounds with both therapeutic and cosmetic benefits, in order to overcome the side effects of topically applied chemical drugs. Quercetin is a key nutraceutical with topical antioxidant and anti-inflammatory properties which was reported to be effective in the treatment of different dermatological diseases, however, its topical therapeutic activity is hindered by its poor skin penetration. This review highlights the topical applications of quercetin, and summarizes the nanocarrier-based solutions to its percutaneous delivery challenges.

Hitchhiking on Controlled-Release Drug Delivery Systems: Opportunities and Challenges for Cancer Vaccines

Cancer vaccines represent among the most promising strategies in the battle against cancers. However, the clinical efficacy of current cancer vaccines is largely limited by the lack of optimized delivery systems to generate strong and persistent antitumor immune responses. Moreover, most cancer vaccines require multiple injections to boost the immune responses, leading to poor patient compliance. Controlled-release drug delivery systems are able to address these issues by presenting drugs in a controlled spatiotemporal manner, which allows co-delivery of multiple drugs, reduction of dosing frequency and avoidance of significant systemic toxicities. In this review, we outline the recent progress in cancer vaccines including subunit vaccines, genetic vaccines, dendritic cell-based vaccines, tumor cell-based vaccines and in situ vaccines. Furthermore, we highlight the efforts and challenges of controlled or sustained release drug delivery systems (e.g., microparticles, scaffolds, injectable gels, and microneedles) in ameliorating the safety, effectiveness and operability of cancer vaccines. Finally, we briefly discuss the correlations of vaccine release kinetics and the immune responses to enlighten the rational design of the next-generation platforms for cancer therapy.

Administration Routes of Polyethylenimine-Coated PLGA Nanoparticles Encapsulating Angelica Sinensis Polysaccharide Vaccine Delivery System Affect Immune Responses

Nanoparticle vaccine delivery systems have been emerging strategies for inducing potent immune responses to prevent and treat infectious diseases and cancers. The properties of nanoparticle vaccine delivery systems, such as nanoparticle size, surface charge, and antigen release kinetics, have been extensively studied and proven to effectively influence the efficacy of vaccine responses. However, a few types of research have focused on the influence of administration routes of nanoparticle vaccines on immune responses. Herein, to investigate how the administration routes affect the immune responses of nanoparticles vaccines, we developed a nanoparticles system (NPs), in which the ovalbumin (OVA) and Angelica sinensis polysaccharide (ASP) were incorporated into poly(lactic-co-glycolic acid) (PLGA) nanoparticles and the polyethylenimine (PEI) was coated on the surface of nanoparticles. The NPs vaccine was intramuscularly and subcutaneously injected (im and sc) into mice, and the immune responses induced by these two delivery routes were compared. The results showed that both im and sc administration of NPs vaccines elicited strong antigen-specific IgG, IgG1, and IgG2a antibody responses, with no significant difference. In contrast, NP vaccines with sc administration significantly enhanced immune responses, such as enhancing the recruitment and activation of dendritic cells (DCs) in lymph nodes (LNs), promoting the antigen transport into draining lymph nodes, increasing the secretion of cytokines, improving the ratio of CD4⁺T cells to CD8⁺ T cells, activating cytotoxic T lymphocyte response, and inducing a strong cellular immune response. These results may provide a new insight onto the development of vaccine delivery systems.

Microneedles: A New Generation Vaccine Delivery System

Transdermal vaccination route using biodegradable microneedles is a rapidly progressing field of research and applications. The fear of painful needles is one of the primary reasons most people avoid getting vaccinated. Therefore, developing an alternative pain-free method of vaccination using microneedles has been a significant research area. Microneedles comprise arrays of micron-sized needles that offer a pain-free method of delivering actives across the skin. Apart from being pain-free, microneedles provide various advantages over conventional vaccination routes such as intramuscular and subcutaneous. Microneedle vaccines induce a robust immune response as the needles ranging from 50 to 900 μm in length can efficiently deliver the vaccine to the epidermis and the dermis region, which contains many Langerhans and dendritic cells. The microneedle array looks like band-aid patches and offers the advantages of avoiding cold-chain storage and self-administration flexibility. The slow release of vaccine antigens is an important advantage of using microneedles. The vaccine antigens in the microneedles can be in solution or suspension form, encapsulated in nano or microparticles, and nucleic acid-based. The use of microneedles to deliver particle-based vaccines is gaining importance because of the combined advantages of particulate vaccine and pain-free immunization. The future of microneedle-based vaccines looks promising however, addressing some limitations such as dosing inadequacy, stability and sterility will lead to successful use of microneedles for vaccine delivery. This review illustrates the recent research in the field of microneedle-based vaccination.

Antigen Uptake After Intradermal Microinjection Depends on Antigen Nature and Formulation, but Not on Injection Depth

The skin is an attractive alternative administration route for allergy vaccination, as the skin is rich in dendritic cells (DCs) and is easily accessible. In the skin multiple subsets of DCs with distinct roles reside at different depths. In this study antigen (=allergen for allergy) formulations were injected in ex vivo human skin in a depth-controlled manner by using a hollow microneedle injection system. Biopsies were harvested at the injection site, which were then cultured for 72 h. Subsequently, the crawled-out cells were collected from the medium and analyzed with flow cytometry. Intradermal administration of ovalbumin (OVA, model antigen) solution at various depths in the skin did not affect the migration and maturation of DCs. OVA was taken up efficiently by the DCs, and this was not affected by the injection depth. In contrast, Bet v 1, the major allergen in birch pollen allergy, was barely taken up by dermal DCs (dDCs). Antigens were more efficiently taken up by CD14⁺ dDCs than CD1a⁺ dDCs, which in turn were more efficient at taken up antigen than Langerhans cells. Subsequently, both OVA and Bet v 1 were formulated in cationic and anionic liposomes, which altered antigen uptake drastically following intradermal microinjection. While OVA uptake was reduced by formulation in liposomes, Bet v 1 uptake in dDCs was increased by encapsulation in both cationic and anionic liposomes. This highlights the potential use of liposomes as adjuvant in intradermal allergy vaccine delivery. In conclusion, we observed that antigen uptake after intradermal injection was not affected by injection depth, but varied between different antigens and formulation.

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.

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

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

Hollow microneedles: A perspective in biomedical applications

Microneedles (MN) have the potential to become a highly progressive device for both drug delivery and monitoring purposes as they penetrate the skin and pierce the stratum corneum barrier, allowing the delivery of drugs in the viable skin layers and the extraction of body fluids. Despite the many years of research and the different types of MN developed, only hollow MN have reached the pharmaceutical market under the path of medical devices. Therefore, this review focuses on hollow MN, materials and methods for their fabrication as well as their application in drug delivery, vaccine delivery and monitoring purposes. Furthermore, novel approaches for the fabrication of hollow MN are included as well as prospects of microneedle-based products on the market.

Simultaneous Measurement of Temperature and Refractive Index Using High Temperature Resistant Pure Quartz Grating Based on Femtosecond Laser and HF Etching

The optical fiber temperature and refractive index sensor combined with the hollow needle structure for medical treatment can promote the standardization of traditional acupuncture techniques and improve the accuracy of body fluid analysis. A double-parameter sensor based on fiber Bragg grating (FBG) is developed in this paper. The sensor materials are selected through X-ray diffraction (XRD) analysis, and the sensor sensing principle is theoretically analyzed and simulated. Through femtosecond laser writing pure silica fiber, a high temperature resistant wavelength type FBG temperature sensor is obtained, and the FBG is corroded by hydrofluoric acid (HF) to realize a high-sensitivity intensity-type refractive index sensor. Because the light has dual characteristics of energy and wavelength, the sensor can realize simultaneous dual-parameter sensing. The light from the lead-in optical fiber is transmitted to the sensor and affected by temperature and refractive-index; then, the reflection peak is reflected back to the lead-out fiber by the FBG. The high temperature response and the refractive index response of the sensor were measured in the laboratory, and the high temperature characteristics of the sensor were verified in the accredited institute. It is demonstrated that the proposed sensor can achieve temperature sensing up to 1150 °C with the sensitivity of 0.0134 nm/°C, and refractive sensing over a refractive range of 1.333 to 1.4027 with the sensitivity of -49.044 dBm/RIU. The sensor features the advantages of two-parameter measurement, compact structure, and wide temperature range, and it exhibits great potential in acupuncture treatment.

Development and evaluation of polymeric nanoparticles as a delivery system for snake envenoming prevention

Polymer-based nanoparticles have become an appealing carrier for improving vaccine delivery efficiency. In this study, we investigated an interesting approach based on PLGA nanoparticles encapsulating Cerastes cerastes venom as an intranasal vaccine delivery system for snake envenomation prevention. Particles were synthesized by double emulsion solvent evaporation method and characterized for their size, morphology, distribution, and venom-nanoparticles interactions. An immunization trial was performed in mice by the intranasal route to evaluate the immune response, the reactogenicity, and the protective effect of this nanovaccine. The physicochemical and structural characteristics of Cc-loaded PLGA NPs revealed that the particles exhibited a spherical shape with a diameter of 370 nm, and a negatively charged surface with a zeta potential value of 19,9 mV. The immunization with Cc-PLGA NPs can induce a systemic innate and humoral immune response and confers protection against Cerastes cerastes venom (Cc) over than 6 LD50 with a cross-protection against Vipera lebetina venom (Vl) over than 5 LD50. Nano-encapsulation of Cc venom reduced its toxicity and the induced tissue alterations. Our results confirm that the nano-formulation Cc-PLGA NPs is a potent adjuvant system that improve the humoral immune response and provide protection against high lethal doses of viper venoms.