Formulations for microprojection/microneedle vaccine delivery: Structure, strength and release profiles

Microneedles: multifunctional devices for drug delivery, body fluid extraction, and bio-sensing

Microneedles represent a miniaturized mechanical structure with versatile applications, including transdermal drug delivery, vaccination, body-fluid extraction, and bio-sensing. Over the past two decades, microneedle-based devices have garnered considerable attention in the biomedicine field, exhibiting the potential for mitigating patient discomfort, enhancing treatment adherence, avoiding first-pass effects, and facilitating precise therapeutic interventions. As an application-oriented technology, the innovation of microneedles is generally carried out in response to a specific demand. Currently, three most common applications of microneedles are drug delivery, fluid extraction, and bio-sensing. This review focuses on the progress in the materials, fabrication techniques, and design of microneedles in recent years. On this basis, the progress and innovation of microneedles in the current research stage are introduced in terms of their three main applications.

Characterising Skin Electrical Impedance Using Tape Stripping Methods: A Bioelectrical Study of a Porcine Model

Background Recent advancements in ultra-low power electronics and wireless devices have facilitated the widespread adoption of wearable technology for fitness and health monitoring, paving the way for personalized medicine. Microneedle-based devices, comprising small epidermal patches that penetrate the skin's stratum corneum to potentially access biomarkers in the extracellular fluid of the viable epidermis, represent a promising innovation in this field. Objectives This project aimed to develop and validate a novel method to evaluate microneedle engagement in the skin in real-time. To our knowledge, there are no studies published to date that have characterized the electrical impedance of stratum corneum and epidermis using the tape stripping method to selectively remove cell layers. Additionally, no studies have been published comparing the electrical impedance of fresh to frozen-thawed porcine skin. The objective of this study was to develop and validate a novel method to evaluate microneedle engagement in skin, in real-time, that does not require processing of the tissue. Methods A tape stripping technique was employed to selectively remove the stratum corneum from fresh and frozen-thawed porcine skin samples which were then electrically characterized using an excitation frequency of 5 kHz with a peak Voltage of 1 V. Results This study demonstrated a mean impedance reduction of 97.08 ± 1.3 % for fresh porcine skin, and 98.04 ± 0.3 % for frozen-thawed porcine skin when transitioning from the surface stratum corneum to the viable epidermis. The correlation between the reduction of impedance and the number of tape strips across all 18 test sites was significant (r = 0.98, p < 0.00001). However, comparing the skin impedance of the fresh and frozen-thawed specimens showed poor equivalence, with the frozen-thawed sites approximately 5.5 times the impedance of the fresh sites before any tape stripping, and 4.19 times greater after 30 tape strips. Conclusions These findings suggest that monitoring for an interelectrode impedance decrease of greater than 95% between two projections of a microneedle device could provide a rapid and effective evaluation of skin engagement, crucial for advancing the development and clinical application of microneedle-based technologies in personalized medicine. The study also underscores the impact of the freeze-thaw process on the mechanical and electrical properties of skin, which is crucial for standardizing testing protocols.

Egg microneedles for transdermal vaccination of inactivated influenza virus

The use of dissolving microneedles (DMNs) is a drug delivery technique in which drug dissolution occurs once it is administered into the skin. The skin is a remarkable site for vaccination due to its significant immunologic properties. Compared to the traditional hypodermic intramuscular (IM) injection, vaccination via DMN does not require cold chains and allows for minimal invasive drug delivery. On account of the significance of skin vaccination, preceding studies have been conducted to elucidate the importance of the DMN technology in vaccination. Most of these studies focused on formulations that maintain the activity of the vaccine, so formulations designed to be specific to the mechanical properties of the microneedle could not be used together independently. In this study, we have developed influenza vaccine loaded egg microneedles (EMN) and characterized the specificity of layer-specific functions of EMN by distinguishing between formulations that can maintain the activity of the vaccine and have the mechanical strength. By the use of in vitro tests such as ELISA and SRID assays, we quantitively evaluated the antigen activity of the formulation candidates to be 87% and 91%, respectively. In vivo tests were also conducted as mouse groups were inoculated with the formulation constructed into egg microneedles (FLU-EMN) to determine the protective efficacy against infection. The results demonstrated that FLU-EMN with functionalized formulations successfully enabled protective immune response even with a fractional dose compared to IM injection.

The role of ion channels in the relationship between the immune system and cancer

The immune system is capable of identifying and eliminating cancer, a complicated illness marked by unchecked cellular proliferation. The significance of ion channels in the complex interaction between the immune system and cancer has been clarified by recent studies. Ion channels, which are proteins that control ion flow across cell membranes, have variety of physiological purposes, such as regulating immune cell activity and tumor development. Immune cell surfaces contain ion channels, which have been identified to control immune cell activation, motility, and effector activities. The regulation of immune responses against cancer cells has been linked to a number of ion channels, including potassium, calcium, and chloride channels. As an example, potassium channels are essential for regulating T cell activation and proliferation, which are vital for anti-tumor immunity. Calcium channels play a crucial role when immune cells produce cytotoxic chemicals in order to eliminate cancer cells. Chloride channels also affect immune cell infiltration and invasion into malignancies. Additionally, tumor cells' own expressed ion channels have an impact on their behavior and in the interaction with the immune system. The proliferation, resistance to apoptosis, and immune evasion of cancer cells may all be impacted by changes in ion channel expression and function. Ion channels may also affect the tumor microenvironment by controlling angiogenesis, inflammatory responses, and immune cell infiltration. Ion channel function in the interaction between the immune system and cancer has important implications for cancer treatment. A possible method to improve anti-tumor immune responses and stop tumor development is to target certain ion channels. Small compounds and antibodies are among the ion channel modulators under investigation as possible immunotherapeutics. The complex interaction between ion channels, the immune system, and cancer highlights the significance of these channels for tumor immunity. The development of novel therapeutic strategies for the treatment of cancer will be made possible by unraveling the processes by which ion channels control immune responses and tumor activity. Hence, the main driving idea of the present chapter is trying to understand the possible function of ion channels in the complex crosstalk between cancer and immunoresponse. To this aim, after giving a brief journey of ion channels throughout the history, a classification of the main ion channels involved in cancer disease will be discussed. Finally, the last paragraph will focus on more recently advancements in the use of biomaterials as therapeutic strategy for cancer treatment. The hope is that future research will take advantage of the promising combination of ion channels, immunomodulation and biomaterials filed to provide better solutions in the treatment of cancer disease.

Formulation and Characterization of Emulgel-Based Jelly Candy: A Preliminary Study on Nutraceutical Delivery

The development of consumer-friendly nutraceutical dosage forms is highly important for greater acceptance. In this work, such dosage forms were prepared based on structured emulsions (emulgels), where the olive oil phase was filled within the pectin-based jelly candy. The emulgel-based candies were designed as bi-modal carriers, where oil-soluble curcumin and water-soluble riboflavin were incorporated as the model nutraceuticals. Initially, emulsions were prepared by homogenizing varied concentrations (10% to 30% (w/w)) of olive oil in a 5% (w/w) pectin solution that contained sucrose and citric acid. Herein, pectin acted as a structuring agent-cum-stabilizer. Physico-chemical properties of the developed formulations were thoroughly analyzed. These studies revealed that olive oil interferes with the formation of polymer networks of pectin and the crystallization properties of sugar in candies. This was confirmed by performing FTIR spectroscopy and DSC studies. In vitro disintegration studies showed an insignificant difference in the disintegration behavior of candies, although olive oil concentration was varied. Riboflavin and curcumin were then incorporated into the jelly candy formulations to analyze whether the developed formulations could deliver both hydrophilic and hydrophobic nutraceutical agents. We found that the developed jelly candy formulations were capable of delivering both types of nutraceutical agents. The outcome of the present study may open new directions for designing and developing oral nutraceutical dosage forms.

Assessment of formulation variables of poor water soluble diacerein for its improved loading and anti-inflammatory activity

Dissolving microneedles have become a popular method for percutaneous administrationof drugs. However, loading poorly soluble drugs into water-based dissolving microneedles remains a challenge. In view of this, we aimed to improve Diacerein (DCN) solubility formulating dissolving microneedles. DCN microsuspension was created by high-speed homogenization with organic solvents or wet milling with Tween 80 as a stabilizer (LD1). They were analyzed for particle size and saturation solubility. Subsequently, the organic solvent-based microneedles were prepared under vacuum, whereas LD1 was mixed with HPMC (8% w/w) and PVP (30% w/w) matrix to concentrate the drug in acral fraction through centrifugation. DCN microsuspension in DMSO had the highest drug solubility with an average particle size of 6 µm, whereas LD1 had a particle size of 3.28 µm showing improved solubility. TD-3 had the highest drug loading and the least amount of drug migration into the blank baseplate. Within 5 min, these microneedles dissolved completely in an agarose-gel block. LD1 was likewise put in the baseplate to generate TD3-B. Within 24 h, 74.39% of the medication was released from TD3-B, with only a small amount remaining in the baseplate. TLC examination indicated the conversion of DCN to Rhein in the skin, whereas DSC and TGA studies revealed amorphous features. DCN microneedles showed no sign of skin irritancy but showed anti-inflammatory response on carrageenan-induced paw edema model. Microneedles remained stable during accelerated stability testing. Wet milling in the presence of a stabilizer can be an effective approach for enhancing DCN solubility for improved drug loading in dissolving microneedles. Improvement in solubility of Diacerein for subsequent loading in Dissolving Microneedle for percutaneous delivery.

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

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

Recent advances in biomimetic hemostatic materials

Although the past decade has witnessed unprecedented medical advances, achieving rapid and effective hemostasis remains challenging. Uncontrolled bleeding and wound infections continue to plague healthcare providers, increasing the risk of death. Various types of hemostatic materials are nowadays used during clinical practice but have many limitations, including poor biocompatibility, toxicity and biodegradability. Recently, there has been a burgeoning interest in organisms that stick to objects or produce sticky substances. Indeed, applying biological adhesion properties to hemostatic materials remains an interesting approach. This paper reviews the biological behavior, bionics, and mechanisms related to hemostasis. Furthermore, this paper covers the benefits, challenges and prospects of biomimetic hemostatic materials.

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.

A Narrative Review on Non-Invasive Drug Delivery of Teriparatide: A Ray of Hope

In the field of pharmaceutical biotechnology and formulation development, various protein and peptide-based drugs have been used for therapeutic and clinical implications. These are mainly given via parenteral routes like intravenous, subcutaneous or intramuscular delivery. Teriparatide, also known as PTH 1-34, is a U.S. Food & Drug Administartion-approved anabolic drug to treat osteoporosis is currently available in market only as subcutaneous injection. The quest for elimination of needle in case of given peptidal delivery to replace it with alternative routes like nasal, buccal, transdermal and pulmonary pathways has driven meticulous drug research. The pharmaceutical scientists are working on innovation and approaches involving new materials and methods to develop the formulations for protein and peptides by noninvasive routes. Lately, various approaches have been carried out which involve many strategies and technologies to deliver teriparatide via alternative routes. But, physicochemical instability, proteolytic degradation, low bioavailability, etc. are some obstacles to develop suitable delivery system for teriparatide. This review intends to gather the overall developments in delivery systems specific to teriparatide which meant for better convenience and avoids vulnerability of multiple subcutaneous injections. In addition, the article emphasizes on the successes to develop noninvasive technologies and devices, and new milestones for teriparatide delivery.

Current and next-generation formulation strategies for inactivated polio vaccines to lower costs, increase coverage, and facilitate polio eradication

Implementation of inactivated polio vaccines (IPV) containing Sabin strains (sIPV) will further enable global polio eradication efforts by improving vaccine safety during use and containment during manufacturing. Moreover, sIPV-containing vaccines will lower costs and expand production capacity to facilitate more widespread use in low- and middle-income countries (LMICs). This review focuses on the role of vaccine formulation in these efforts including traditional Salk IPV vaccines and new sIPV-containing dosage forms. The physicochemical properties and stability profiles of poliovirus antigens are described. Formulation approaches to lower costs include developing multidose and combination vaccine formats as well as improving storage stability. Formulation strategies for dose-sparing and enhanced mucosal immunity include employing adjuvants (e.g. aluminum-salt and newer adjuvants) and/or novel delivery systems (e.g. ID administration with microneedle patches). The potential for applying these low-cost formulation development strategies to other vaccines to further improve vaccine access and coverage in LMICs is also discussed.

The clinical and translational prospects of microneedle devices, with a focus on insulin therapy for diabetes mellitus as a case study

Microneedles have the clinical advantage of being able to deliver complex drugs across the skin in a convenient and comfortable manner yet haven't successfully transitioned to medical practice. Diabetes mellitus is a complicated disease, which is commonly treated with multiple daily insulin injections, contributing to poor treatment adherence. Firstly, this review determines the clinical prospect of microneedles, alongside considerations that ought to be addressed before microneedle technology can be translated from bench to bedside. Thereafter, we use diabetes as a case study to consider how microneedle-based-technology may be successfully harnessed. Here, publications referring to insulin microneedles were evaluated to understand whether insertion efficiency, angle of insertion, successful dose delivery, dose adjustability, material biocompatibility and therapeutic stability are being addressed in early stage research. Moreover, over 3,000 patents from 1970-2019 were reviewed with the search term '"microneedle" AND "insulin"' to understand the current status of the field. In conclusion, the reporting of early stage microneedle research demonstrated a lack of consistency relating to the translational factors addressed. Additionally, a more rational design, based on a patient-centred approach is required before microneedle-based delivery systems can be used to revolutionise the lives of people living with diabetes following regulatory approval.

A 3D-printed transepidermal microprojection array for human skin microbiome sampling

Skin microbiome sampling is currently performed with tools such as swabs and tape strips to collect microbes from the skin surface. However, these conventional approaches may be unable to detect microbes deeper in the epidermis or in epidermal invaginations. We describe a sampling tool with a depth component, a transepidermal microprojection array (MPA), which captures microbial biomass from both the epidermal surface and deeper skin layers. We leveraged the rapid customizability of 3D printing to enable systematic optimization of MPA for human skin sampling. Evaluation of sampling efficacy on human scalp revealed the optimized MPA was comparable in sensitivity to swab and superior to tape strip, especially for nonstandard skin surfaces. We observed differences in species diversity, with the MPA detecting clinically relevant fungi more often than other approaches. This work delivers a tool in the complex field of skin microbiome sampling to potentially address gaps in our understanding of its role in health and disease.

Dissolvable polymer microneedles for drug delivery and diagnostics

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

Feasibility of Enhancing Skin Permeability of Acyclovir through Sterile Topical Lyophilized Wafer on Self-Dissolving Microneedle-Treated Skin

Acyclovir is an antiviral drug that is frequently prescribed for the herpes virus. However, the drug requires frequent dosing due to limited bioavailability (10–26.7%). The rationale of the present study was to develop a self-dissolving microneedle system for local and systemic delivery of acyclovir using a topical lyophilized wafer on microneedle-treated skin to provide the drug at the site of infection. The microneedles prepared with hydroxypropyl methylcellulose (HPMC) (8% w/w) or HPMC (8% w/w)-polyvinyl pyrrolidone (PVP) (30% w/w) penetrated excised rat skin, showing sufficient mechanical strength and rapid polymer dissolution. The topical wafer was prepared with acyclovir (40% w/w; equivalent to 200 mg of drug), gelatin (10% w/w), mannitol (5% w/w), and sodium chloride (5% w/w). The uniform distribution of acyclovir within the wafer in an amorphous form was confirmed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). No polymer–drug interaction was evident in the lyophilized wafer as per Fourier transform infrared spectroscopy (FTIR) analysis. The wafer showed a sufficiently porous structure for rapid hydration as per scanning electron microscopy (SEM) analysis. During ex-vivo analysis, the skin was pre-treated with a self-dissolving microneedle array for 5 minutes, and the wafer was placed on this microporated-skin. Topical wafer provided ∼7–11 times higher skin concentration than the ID₉₉ reported with a lower lag-time. Based on in-vivo testing, ∼2.58 µg/ml of Cmax was achieved in rabbit plasma during 24 hours’ study. Our findings suggest that the self-dissolving microneedle-assisted topical wafer, proposed for the first time, would be efficacious against the infection residing in the skin layer and for systemic therapy.

Bletilla striata polysaccharide microneedle for effective transdermal administration of model protein antigen

Traditional vaccination relies on subcutaneous injection or intramuscular injection, which requires professional medical personnel and is accompanied by the risk of needle-related diseases and injuries. Therefore, to promote immunization coverage and reduce costs, it is necessary to provide a new method of vaccine administration. Dissolving microneedle (DMN) has been proposed as an alternative to hypodermic needles, providing prospects for self-inoculation and increasing immunogenicity by directly targeting skin dendritic cells. This study reported the successful preparation and characterization of Bletilla striata polysaccharide microneedles (BMNs) and investigated the potential of this natural material-based DMN as a vaccine carrier. The prepared BMNs exhibited more excellent mechanical properties and stability compared with microneedles made of hyaluronic acid and polyvinyl alcohol. BMNs had good cell compatibility, low bacterial skin permeability, slight irritation to the skin, and no infection or inflammation in the body. In addition, as shown by circular dichroism, the molecular structure of the antigen ovalbumin (OVA) loaded in BMN did not change during storage for 21 days. The Franz diffusion cell experiment showed 76.74% of OVA was released to the skin within 3 h. These encouraging findings indicate that the BMNs can be a promising tool for effective vaccine delivery.

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.

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

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

Microneedle for transdermal drug delivery: current trends and fabrication

Background

Transdermal delivery has the advantage of bypassing the first-pass effect and allowing sustained release of the drug. However, the drug delivery is limited owing to the barrier created by the stratum corneum. Microneedles are a transdermal drug delivery system that is painless, less invasive, and easy to self-administer, with a high drug bioavailability.

Area covered

The dose, delivery rate, and efficacy of the drugs can be controlled by the microneedle design and drug formulations. This review introduces the types of microneedles and their design, materials used for fabrication, and manufacturing methods. Additionally, recent biological applications and clinical trials are introduced.

Expert opinion

With advancements made in formulation technologies, the drug-loading capability of microneedles can be improved. 3D printing and digital technology contribute to the improvement of microneedle fabrication technology. However, regulations regarding the manufacture of microneedle products should be established as soon as possible to promote commercialization.

Needleless or Noninvasive Delivery Technology

Injections of drugs or vaccines have become an indispensable part of living systems. Introduction to injections begins from the vaccination regimen at the neonatal stage and continues throughout the life span of an individual. Conventionally, injections are administered using hypodermic needles and syringes. These usually inject the liquid in the muscle, thus making intramuscular injections the most common form of administration. Although hypodermic syringes have been a clinician's tool in global vaccination efforts, they also have a set of undesirable characteristics. Pathogen transmission in case of HIV and HBV is one of the deadliest disadvantages of the needle-based injection system. Generation of plastic wastes in clinics, needlestick injury, and most importantly, pain associated with needle-based injections are a few more reasons of concern. In light of these issues, developing needle-free injection systems has excited researchers across the globe since the 1950s. Significant advancement has been reported in this field and various needle-free injection systems have been developed and are in clinical practice. This article briefly describes the history of needle-free injection systems and provides a detailed account of a few well-known methods of needle-less injections available.

Microneedles Drug Delivery Systems for Treatment of Cancer: A Recent Update

Microneedles (MNs) are tiny needle like structures used in drug delivery through layers of the skin. They are non-invasive and are associated with significantly less or no pain at the site of administration to the skin. MNs are excellent in delivering both small and large molecules to the subjects in need thereof. There exist several strategies for drug delivery using MNs, wherein each strategy has its pros and cons. Research in this domain lead to product development and commercialization for clinical use. Additionally, several MN-based products are undergoing clinical trials to evaluate its safety, efficacy, and tolerability. The present review begins by providing bird's-eye view about the general characteristics of MNs followed by providing recent updates in the treatment of cancer using MNs. Particularly, we provide an overview of various aspects namely: anti-cancerous MNs that work based on sensor technology, MNs for treatment of breast cancer, skin carcinoma, prostate cancer, and MNs fabricated by additive manufacturing or 3 dimensional printing for treatment of cancer. Further, the review also provides limitations, safety concerns, and latest updates about the clinical trials on MNs for the treatment of cancer. Furthermore, we also provide a regulatory overview from the "United States Food and Drug Administration" about MNs.

Amifostine-loaded armored dissolving microneedles for long-term prevention of ionizing radiation-induced injury

Amifostine is a cytoprotective agent against the hematopoietic damage induced by ionizing radiation, although the intravenous injection of amifostine is a unique administration method with strict dosing time limitation. Hence, the fields of application of amifostine are greatly limited. Here, we developed an amifostine-loaded armored microneedle (AAMN) with long-term prevention of hematopoietic injury induced by ionizing radiation. First, amifostine-loaded hyaluronic acid microneedles (AMNs) were fabricated, and the AMNs were then dipped in an N-vinyl-2-pyrrolidone (NVP) solution followed by ultraviolet (UV) photocuring to obtain AAMNs. AAMNs were nail-shaped with much higher mechanical strength compared to the conical shape and weak strength of AMNs, which was verified by their in silico simulation. In the in vitro release experiment, more than 55% of amifostine was released from AAMNs within 10 min, and 95% was released in 60 min. Drug skin permeation of AAMNs was also high, at twice that of AMNs. AAMNs provided long-term protection of the hematopoietic system from radiation within 3-7 h pre-radiation compared to the unique amifostine injection 0.5 h pre-radiation because topical application of AAMNs led to the long-term maintenance of the in vivo effective drug concentration. More importantly, AAMNs led to the survival of all irradiated mice due to intravenous amifostine. AAMNs are a promising transdermal delivery system of amifostine for long-term protection against ionizing radiation-induced injury. STATEMENT OF SIGNIFICANCE: An amifostine-loaded dissolving armored microneedle (AAMN) patch is developed for long-term prevention of ionizing radiation-induced injury. High drug loads in microneedles (MNs) with adequate mechanical strength is a challenge. We fabricated armors on the surface of high amifostine-loaded hyaluronic acid microneedles (AMNs) by dipping the tips of AMNs in N-vinyl-2-pyrrolidone (NVP) solutions and then subjecting them to UV irradiation, and high-strength armored AMNs (AAMNs) were obtained. AAMNs show deeper skin insertion and much higher drug permeation than AMNs. The controlled drug release from AAMNs in the mouse skins provides a long-term protection of radiation-induced injury with 3-7 h administration pre-radiation compared to the merely 0.5-h point of amifostine injection.

Recent advances on microneedle arrays-mediated technology in cancer diagnosis and therapy

Regarding the increasing prevalence of cancer throughout the globe, the development of novel alternatives for conventional therapies is inevitable to circumvent limitations such as low efficacy, complications, and high cost. Recently, microneedle arrays (MNs) have been introduced as a novel, minimally invasive, and low-cost approach. MNs can delivery both small molecule and macromolecular drugs or even nanoparticles (NPs) to the tumor tissue in a safe and controlled manner. Relying on the recent promising outcomes of MNs in transdermal delivery of anticancer agents, this review is aimed to summarize constituent materials, fabrication methods, advantages, and limitations of different types of MNs used in cancer therapy applications. This review paper also presents the potential use of MNs in transdermal delivery of NPs for effective chemotherapy, gene therapy, immunotherapy, photodynamic, and photothermal therapy. Additionally, MNs are currently explored as routine point-of-care health monitoring devices for transdermal detection of cancer biomarkers or physiologically relevant analytes which will be addressed in this paper. Despite the promising potential of MNs for cancer therapy and diagnosis, several limitations have impeded their therapeutic efficacy and real-time applicability that are addressed in this paper.

Microneedle-Based Delivery: An Overview of Current Applications and Trends

Microneedle arrays (MNA) are considered as one of the most promising resources to achieve systemic effects by transdermal delivery of drugs. They are designed as a minimally invasive, painless system which can bypass the stratum corneum, overcoming the potential drawbacks of subcutaneous injections and other transdermal delivery systems such as chemical enhancers, nano and microparticles, or physical treatments. As a trendy field in pharmaceutical and biomedical research, its applications are constantly evolving, even though they are based on very well-established techniques. The number of molecules administered by MNA are also increasing, with insulin and vaccines administration being the most investigated. Furthermore, MNA are being used to deliver cells and applied in other organs and tissues like the eyes and buccal mucosae. This review intends to offer a general overview of the current state of MNA research, focusing on the strategies, applications, and types of molecules delivered recently by these systems. In addition, some information about the materials and manufacturing processes is presented and safety data is discussed.

Engineered biomaterials for cancer immunotherapy

Although cancer immunotherapy is showing tremendous promise and has progressed to the clinic, it has only achieved sporadic efficacy, with only a fraction of patients benefitting from the therapy and with undesirable side effects due to poor selectivity and high doses. Localized delivery of immunomodulators to activate anticancer immunity in situ avoids overactivation of the systemic immune system and reduces side effects. Engineered biomaterials-implantable, injectable, or transdermal-fabricated into drug delivery devices are critical components for the development of localized cancer immunotherapies. In this review, we briefly summarize progress in the application of engineered biomaterials to the localized delivery of cancer immunotherapy.

Intradermal and transdermal drug delivery using microneedles - Fabrication, performance evaluation and application to lymphatic delivery

The progress in microneedle research is evidenced by the transition from simple 'poke and patch' solid microneedles fabricated from silicon and stainless steel to the development of bioresponsive systems such as hydrogel-forming and dissolving microneedles. In this review, we provide an outline on various microneedle fabrication techniques which are currently employed. As a range of factors, including materials, geometry and design of the microneedles, affect the performance, it is important to understand the relationships between them and the resulting delivery of therapeutics. Accordingly, there is a need for appropriate methodologies and techniques for characterization and evaluation of microneedle performance, which will also be discussed. As the research expands, it has been observed that therapeutics delivered via microneedles has gained expedited access to the lymphatics, which makes them a favorable delivery method for targeting the lymphatic system. Such opportunity is valuable in the area of vaccination and treatment of lymphatic disorders, which is the final focus of the review.

Rational Design of Rapidly Separating Dissolving Microneedles for Precise Drug Delivery by Balancing the Mechanical Performance and Disintegration Rate

The precise delivery of traditional dissolving microneedles (TDMNs) is often limited by the incomplete insertion due to the skin deformation, and the topical irritation is inevitable after long application, which ultimately results in compromised therapeutic efficacy. The aim of this study is to develop a rapidly separating dissolving microneedles (RSDMNs) system to achieve precise drug delivery. Therapeutic molecules are concentrated in the needle tip, while the blank separating part allows it to counteract skin indentation and rapidly separate from the base part. For rational design of an ideal separating part, and the molecular interactions between polymer and sugar are explored to make a good balance between mechanical performance and disintegration rate. The optimal RSDMNs can rapidly disintegrate in the mimic skin within 30 s, and the generated micropores in the skin reseal quickly. The ex vivo drug permeation of RSDMNs is significantly higher than that of TDMNs due to the complete needle imbed aided by the separating part. Furthermore, RSDMNs exhibit excellent in vivo anti-inflammation effect by remarkably down regulating the expression of TNF-α, IL-1β, and IL-6. In conclusion, the RSDMNs can reach precise drug delivery in a short time, which are more reliable for the self-administration strategy in the future.

Extended delivery of vaccines to the skin improves immune responses

Vaccines prevent 2-3 million childhood deaths annually; however, low vaccine efficacy and the resulting need for booster doses create gaps in immunization coverage. In this translational study, we explore the benefits of extended release of licensed vaccine antigens into skin to increase immune responses after a single dose in order to design improved vaccine delivery systems. By administering daily intradermal injections of inactivated polio vaccine according to six different delivery profiles, zeroth-order release over 28 days resulted in neutralizing antibody titers equivalent to two bolus vaccinations administered one month apart. Vaccinations following this profile also improved immune responses to tetanus toxoid and subunit influenza vaccine but not a live-attenuated viral vaccine, measles vaccine. Finally, using subunit influenza vaccine, we demonstrated that daily vaccination by microneedle patch induced a potent, balanced humoral immunity with an increased memory response compared to bolus vaccination. We conclude that extended presentation of antigen in skin via intradermal injection or microneedle patch can enhance immune responses and reduce the number of vaccine doses, thereby enabling increased vaccination efficacy.

Recent advances of microneedles for biomedical applications: drug delivery and beyond

The microneedle (MN), a highly efficient and versatile device, has attracted extensive scientific and industrial interests in the past decades due to prominent properties including painless penetration, low cost, excellent therapeutic efficacy, and relative safety. The robust microneedle enabling transdermal delivery has a paramount potential to create advanced functional devices with superior nature for biomedical applications. In this review, a great effort has been made to summarize the advance of microneedles including their materials and latest fabrication method, such as three-dimensional printing (3DP). Importantly, a variety of representative biomedical applications of microneedles such as disease treatment, immunobiological administration, disease diagnosis and cosmetic field, are highlighted in detail. At last, conclusions and future perspectives for development of advanced microneedles in biomedical fields have been discussed systematically. Taken together, as an emerging tool, microneedles have showed profound promise for biomedical applications.

Advances in transdermal insulin delivery

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

Touch-actuated microneedle array patch for closed-loop transdermal drug delivery

To date, only approximately 20 drugs synthesized with small molecules have been approved by the FDA for use in traditional transdermal patches (TTP) owing to the extremely low permeation rate of the skin barrier for macromolecular drugs. A novel touch-actuated microneedle array patch (TMAP) was developed for transdermal delivery of liquid macromolecular drugs. TMAP is a combination of a typical TTP and a solid microneedle array (MA). High doses of liquid drug formulations, especially heat-sensitive compounds can be easily filled and stored in the drug reservoir of TMAPs. TMAP can easily penetrate the skin and automatically retract from it to create microchannels through the stratum corneum (SC) layer using touch-actuated 'press and release' actions for passive permeation of liquid drugs. Comparison of subcutaneous injection, TTP, solid MA, and dissolvable MA, indicated that insulin-loaded TMAP exhibited the best hypoglycemic effect on type 1 diabetic rats. A 'closed-loop' permeation control was also provided for on-demand insulin delivery based on feedback of blood glucose levels (BGLs). Twenty IU-insulin-loaded TMAP maintained the type 1 diabetic rats in a normoglycemic state for approximately 11.63 h, the longest therapeutic duration among all previously reported results on microneedle-based transdermal patches. TMAP possesses excellent transdermal drug delivery capabilities.

Using elongated microparticles to enhance tailorable nanoemulsion delivery in excised human skin and volunteers

This study demonstrates, for the first time, clinical testing of elongated silica microparticles (EMP) combined with tailorable nanoemulsions (TNE) to enhance topical delivery of hydrophobic drug surrogates. Likewise, this is the first report of 6-carboxyfluorescein (a model molecule for topically delivered hydrophobic drugs) AM1 & DAMP4 (novel short peptide surfactants) used in volunteers. The EMP penetrates through the epidermis and stop at the dermal-epidermal junction (DEJ). TNE are unusually stable and useful because the oil core allows high drug loading levels and the surface properties can be easily controlled. At first, we chose alginate as a crosslinking agent between EMP and TNE. We initially incorporated a fluorescent lipophilic dye, DiI, as a hydrophobic drug surrogate into TNE for visualization with microscopy. We compared four different coating approaches to combine EMP and TNE and tested these formulations in freshly excised human skin. The delivery profile characterisation was imaged by dye- free coherent anti-Stoke Raman scattering (CARS) microscopy to detect the core droplet of TNE that was packed with pharmaceutical grade lipid (glycerol) instead of DiI. These data show the EMP penetrating to the DEJ followed by controlled release of the TNE. Freeze-dried formulations with crosslinking resulted in a sustained release profile, whereas a freeze-dried formulation without crosslinking showed an immediate burst-type release profile. Finally, we tested the crosslinked TNE coated EMP formulation in volunteers using multiphoton microscopy (MPM) and fluorescence-lifetime imaging microscopy (FLIM) to document the penetration depth characteristics. These forms of microscopy have limitations in terms of image acquisition speed and imaging area coverage but can detect fluorescent drug delivery through the superficial skin in volunteers. 6-Carboxyfluorescein was selected as the fluorescent drug surrogate for the volunteer study based on the similarity of size, charge and hydrophobicity characteristics to small therapeutic drugs that are difficult to deliver through skin. The imaging data showed a 6-carboxyfluorescein signal deep in volunteer skin supporting the hypothesis that EMP can indeed enhance the delivery of TNE in human skin. There were no adverse events recorded at the time of the study or after the study, supporting the use of 6-carboxyfluorescein as a safe and detectable drug surrogate for topical drug research. In conclusion, dry formulations, with controllable release profiles can be obtained with TNE coated EMP that can effectively enhance hydrophobic payload delivery deep into the human epidermis.

Hepatitis B vaccination using a dissolvable microneedle patch is immunogenic in mice and rhesus macaques

Chronic Hepatitis B virus infection remains a major global public health problem, accounting for about 887,000 deaths in 2015. Perinatal and early childhood infections are strongly associated with developing chronic hepatitis B. Adding a birth dose of the hepatitis B vaccine (HepB BD) to routine childhood vaccination can prevent over 85% of these infections. However, HepB BD coverage remains low in many global regions, with shortages of birth attendants trained to vaccinate and limited HepB BD supply at birth. To address the challenges, we developed coated metal microneedle patches (cMNPs) and dissolvable microneedle patches (dMNPs) that deliver adjuvant‐free hepatitis B vaccine to the skin in a simple‐to‐administer manner. The dMNP contains micron‐scale, solid needles encapsulating vaccine antigen and dissolve in the skin, generating no sharps waste. We delivered HepB BD via cMNP to BALB/c mice and via dMNP to both mice and rhesus macaques. Both cMNP and dMNP were immunogenic, generating hepatitis B surface antibody levels similar to human seroprotection. Biomechanical analysis showed that at high forces the microneedles failed mechanically by yielding but microneedles partially blunted by axial compression were still able to penetrate skin. Overall, this study indicates that with further development, dMNPs could offer a method of vaccination to increase HepB BD access and reduce needle waste in developing countries.

Development of Stabilizing Formulations of a Trivalent Inactivated Poliovirus Vaccine in a Dried State for Delivery in the Nanopatch™ Microprojection Array

The worldwide switch to inactivated polio vaccines (IPVs) is a key component of the overall strategy to achieve and maintain global polio eradication. To this end, new IPV vaccine delivery systems may enhance patient convenience and compliance. In this work, we examine Nanopatch™ (a solid, polymer microprojection array) which offers potential advantages over standard needle/syringe administration including intradermal delivery and reduced antigen doses. Using trivalent IPV (tIPV) and a purpose-built evaporative dry-down system, candidate tIPV formulations were developed to stabilize tIPV during the drying process and on storage. Identifying conditions to minimize tIPV potency losses during rehydration and potency testing was a critical first step. Various classes and types of pharmaceutical excipients (∼50 total) were then evaluated to mitigate potency losses (measured through D-antigen ELISAs for IPV1, IPV2, and IPV3) during drying and storage. Various concentrations and combinations of stabilizing additives were optimized in terms of tIPV potency retention, and 2 candidate tIPV formulations containing cyclodextrin and a reducing agent (e.g., glutathione), maintained ≥80% D-antigen potency during drying and subsequent storage for 4 weeks at 4°C, and ≥60% potency for 3 weeks at room temperature with the majority of losses occurring within the first day of storage.

Bioceramic microneedle arrays are able to deliver OVA to dendritic cells in human skin

Bioceramic arrays with high-aspect-ratio microneedles were able to penetrate human ex vivo skin and deliver their cargo to dendritic cells.

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

Microneedle (MN) patches are promising for transcutaneous vaccination because they enable vaccine antigens to physically penetrate the stratum corneum via low-invasive skin puncturing, and to be effectively delivered to antigen-presenting cells in the skin. In second-generation MN patches, the dissolving MNs release the loaded vaccine antigen into the skin. To shorten skin application time for clinical practice, this study aims to develop novel faster-dissolving MNs. We designed two types of MNs made from a single thickening agent, carboxymethylcellulose (CMC) or hyaluronan (HN). Both CMC-MN and HN-MN completely dissolved in rat skin after a 5-min application. In pre-clinical studies, both MNs could demonstrably increase antigen-specific IgG levels after vaccination and prolong antigen deposition compared with conventional injections, and deliver antigens into resected human dermal tissue. In clinical research, we demonstrated that both MNs could reliably and safely puncture human skin without any significant skin irritation from transepidermal water loss measurements and ICDRG (International Contact Dermatitis Research Group) evaluation results.

Recent advances in the design of polymeric microneedles for transdermal drug delivery and biosensing

Microneedles are an efficient and minimally invasive approach to transdermal drug delivery and extraction of skin interstitial fluid. Compared to solid microneedles made of silicon, metals and ceramics, polymeric microneedles have attracted extensive attention due to their excellent biocompatibility, biodegradability and nontoxicity. They are easy to fabricate in large scale and can load drugs in high amounts. More importantly, polymers with different degradation profiles, swelling properties, and responses to biological/physical stimuli can be employed to fabricate polymeric microneedles with different mechanical properties and performance. This review provides a guideline for the selection of polymers and the corresponding fabrication methods for polymeric microneedles while summarizing their recent application in drug delivery and fluid extraction. It should be noted that although polymeric microneedles can achieve efficient transdermal delivery of drugs, their wide applications were limited by their unsatisfactory transdermal therapeutic efficiency. Delivery of nanomedicines that incorporate drugs into functional nanoparticles/capsules can address this problem and thus may be an interesting direction in the future.

Engineering Microneedle Patches for Vaccination and Drug Delivery to Skin

Microneedle patches (MNPs) contain arrays of solid needles measuring hundreds of microns in length that deliver drugs and vaccines into skin in a painless, easy-to-use manner. Optimal MNP design balances multiple interdependent parameters that determine mechanical strength, skin-insertion reliability, drug delivery efficiency, painlessness, manufacturability, and other features of MNPs that affect their performance. MNPs can be made by adapting various microfabrication technologies for delivery of small-molecule drugs, biologics, and vaccines targeted to the skin, which can have pharmacokinetic and immunologic advantages. A small number of human clinical trials, as well as a large and growing market for MNP products for cosmetics, indicate that MNPs can be used safely, efficaciously, and with strong patient acceptance. More advanced clinical trials and commercial-scale manufacturing will facilitate development of MNPs to realize their potential to dramatically increase patient access to otherwise-injectable drugs and to improve drug performance via skin delivery.

Fabrication of a Ti porous microneedle array by metal injection molding for transdermal drug delivery

Microneedle arrays (MA) have been extensively investigated in recent decades for transdermal drug delivery due to their pain-free delivery, minimal skin trauma, and reduced risk of infection. However, porous MA received relatively less attention due to their complex fabrication process and ease of fracturing. Here, we present a titanium porous microneedle array (TPMA) fabricated by modified metal injection molding (MIM) technology. The sintering process is simple and suitable for mass production. TPMA was sintered at a sintering temperature of 1250°C for 2 h. The porosity of TPMA was approximately 30.1% and its average pore diameter was about 1.3 μm. The elements distributed on the surface of TPMA were only Ti and O, which may guarantee the biocompatibility of TPMA. TPMA could easily penetrate the skin of a human forearm without fracture. TPMA could diffuse dry Rhodamine B stored in micropores into rabbit skin. The cumulative permeated flux of calcein across TPMA with punctured skin was 27 times greater than that across intact skin. Thus, TPMA can continually and efficiently deliver a liquid drug through open micropores in skin.