Needle-free vaccine injection

Effects of Extracorporeal Shock Wave-Mediated Transdermal Local Anesthetic Drug Delivery on Rat Caudal Nerves

Cavitation plays a substantial role in the clinical effects of extracorporeal shock wave therapy (ESWT). It is also generally accepted as a major mechanism in sonophoresis. To identify the enhancing effect of extracorporeal shock wave-mediated transdermal drug delivery, 24 Wistar rats were randomly assigned to four groups: (i) topical application of a eutectic mixture of local anesthetics (EMLA); (ii) 1-MHz ultrasound; (iii) ESWT pre-treatment combined with EMLA application; (iv) ESWT concurrent with EMLA application on rat tails. The degree of anesthesia was assessed using the amplitude and latency of sensory nerve action potentials within 5 min after a 60-min EMLA application. The results indicated that ESWT pre-treatment and concurrent ESWT accelerated the anesthetic effects of the EMLA cream on the tail nerve (p < 0.05). This finding might indicate that shock wave-mediated transdermal drug delivery is possible during the ESWT period.

Allometric scaling of skin thickness, elasticity, viscoelasticity to mass for micro-medical device translation: from mice, rats, rabbits, pigs to humans

Emerging micro-scale medical devices are showing promise, whether in delivering drugs or extracting diagnostic biomarkers from skin. In progressing these devices through animal models towards clinical products, understanding the mechanical properties and skin tissue structure with which they interact will be important. Here, through measurement and analytical modelling, we advanced knowledge of these properties for commonly used laboratory animals and humans (~30 g to ~150 kg). We hypothesised that skin's stiffness is a function of the thickness of its layers through allometric scaling, which could be estimated from knowing a species' body mass. Results suggest that skin layer thicknesses are proportional to body mass with similar composition ratios, inter- and intra-species. Experimental trends showed elastic moduli increased with body mass, except for human skin. To interpret the relationship between species, we developed a simple analytical model for the bulk elastic moduli of skin, which correlated well with experimental data. Our model suggest that layer thicknesses may be a key driver of structural stiffness, as the skin layer constituents are physically and therefore mechanically similar between species. Our findings help advance the knowledge of mammalian skin mechanical properties, providing a route towards streamlined micro-device research and development onto clinical use.

New Horizons in the Development of Novel Needle-Free Immunization Strategies to Increase Vaccination Efficacy

The young twenty-first century has already brought several medical advances, such as a functional artificial human liver created from stem cells, improved antiviral (e.g., against HIV) and cancer (e.g., against breast cancer) therapies, interventions controlling cardiovascular diseases, and development of new and optimized vaccines (e.g., HPV vaccine). However, despite this substantial progress and the achievements of the last century, humans still suffer considerably from diseases, especially from infectious diseases. Thus, almost one-fourth of all deaths worldwide are caused directly or indirectly by infectious agents. Although vaccination has led to the control of many diseases, including smallpox, diphtheria, and tetanus, emerging diseases are still not completely contained. Furthermore, pathogens such as Bordetella pertussis undergo alterations making adaptation of the respective vaccine necessary. Moreover, insufficient implementation of vaccination campaigns leads to re-emergence of diseases which were believed to be already under control (e.g., poliomyelitis). Therefore, novel vaccination strategies need to be developed in order to meet the current challenges including lack of compliance, safety issues, and logistic constraints. In this context, mucosal and transdermal approaches constitute promising noninvasive vaccination strategies able to match these demands.

Efficacy, Safety and Targets in Topical and Transdermal Active and Excipient Delivery

A key requirement for topical and transdermal active delivery is the effective delivery of an active to a desired target site, to achieve both safe and efficacious outcomes. This chapter seeks to explore the importance of the pharmacological, toxicological and therapeutic properties of actives and excipients, as well as the site of action as complementary components in percutaneous absorption. This is crucial for optimized topical and transdermal product design.

Tetanus vaccination with a dissolving microneedle patch confers protective immune responses in pregnancy

Maternal and neonatal tetanus claim tens of thousands lives every year in developing countries, but could be prevented by hygienic practices and improved immunization of pregnant women. This study tested the hypothesis that skin vaccination can overcome the immunologically transformed state of pregnancy and enhance protective immunity to tetanus in mothers and their newborns. To achieve this goal, we developed microneedle patches (MNPs) that efficiently delivered unadjuvanted tetanus toxoid to skin of pregnant mice and demonstrated that this route induced superior immune responses in female mice conferring 100% survival to tetanus toxin challenge when compared to intramuscular vaccination. Mice born to MNP-vaccinated mothers showed detectable tetanus-specific IgG antibodies up to 12weeks of age and complete protection to tetanus toxin challenge up at 6weeks of age. In contrast, none of the 6-week old mice born to intramuscularly vaccinated mothers survived challenge. Although pregnant mice vaccinated with unadjuvanted tetanus toxoid had 30% lower IgG and IgG1 titers than mice vaccinated intramuscularly with Alum®-adjuvanted tetanus toxoid vaccine, IgG2a titers and antibody affinity maturation were similar between these groups. We conclude that skin immunization with MNPs containing unadjuvanted tetanus toxoid can confer potent protective efficacy to mothers and their offspring using a delivery method well suited for expanding vaccination coverage in developing countries.

CFD MODELING OF HIGH SPEED LIQUID JETS FROM AN AIR-POWERED NEEDLE-FREE INJECTION SYSTEM

A liquid jet injector is a biomedical device intended for drug delivery. Medication is delivered through a fluid stream that penetrates the skin. This small diameter liquid stream is created by a piston forcing a fluid column through a nozzle. These devices can be powered by springs or compressed gas. In this study, a CFD simulation is carried out to investigate the fluid mechanics and performance of needle free injectors powered specifically by compressed air. The motion of the internal mechanisms of the injector which propels a liquid jet through an orifice is simulated by the moving boundary method and the fluid dynamics is modeled using LES/VOF techniques. In this paper, numerical results are discussed by comparing the fluid stagnation pressures of the liquid jet with previously published experimental measurements obtained using a custom-built prototype of the air-powered needle free liquid injector. Performance plots as a function of various injector parameters are presented and explained.

Needle-free jet injection of hyaluronic acid improves skin remodeling in a mouse model

PURPOSE

The purpose of this study was to improve methods of jet injection using a mouse model. We investigated the mechanism of action, efficacy, and safety of the pneumatic device using injection of hyaluronic acid (HA) solution into a mouse model.

METHODS

We evaluated the efficacy and safety of an INNOJECTOR™ pneumatic device that pneumatically accelerates a jet of HA solution under high pressure into the dermis of mouse skin. We examined the treatment effects using skin hybrid model jet dispersion experiments, photographic images, microscopy, and histological analyses.

RESULTS

Use of the INNOJECTOR™ successfully increased dermal thickness and collagen synthesis in our mouse model. Jet dispersion experiments were performed using agarose gels and a polyacrylamide gel model to understand the dependence of jet penetration on jet power. The mechanisms by which pneumatic injection using HA solution exerts its effects may involve increased dermal thickening, triggering of a wound healing process, and activation of vimentin and collagen synthesis.

CONCLUSIONS

Collagen synthesis and increased dermal thickening were successfully achieved in our mouse model using the INNOJECTOR™. Pneumatic injection of HA under high pressure provides a safe and effective method for improving the appearance of mouse skin. Our findings indicate that use of the INNOJECTOR™ may induce efficient collagen remodeling with subsequent marked dermal layer thickening by targeting vimentin.

Optimization of drug viscosity used in gas-powered liquid jet injectors

This paper describes the effect of drug viscosity on the performance of gas powered liquid jet injectors. The analysis is accomplished utilizing a Computational Fluid Dynamics (CFD) model that obtains the stagnation pressure at the nozzle outlet. The technique is based on previous work used to predict gas power driven injector piston velocity with time. The results depict the variation in average and peak injector stagnation pressure for three different driven pressures; driving injections which vary from 0.2 cP to 87 cP in viscosity. Furthermore, a numerical representation of jet shape is also obtained to verify the effect of viscosity on jet geometry. These results demonstrate that increasing viscosity by 10 times that of water produces only a slight decrease in injector stagnation pressure and produces jets with greater confinement, which will display better characteristics for puncturing the skin.

Intradermal vaccination using the novel microneedle device MicronJet600: Past, present, and future

Intradermal immunization has become a forefront of vaccine improvement, both scientifically and commercially. Newer technologies are being developed to address the need to reduce the dose required for vaccination and to improve the reliability and ease of injection, which have been major hurdles in expanding the number of approved vaccines using this route of administration. In this review, 7 y of clinical experience with a novel intradermal delivery device, the MicronJet600, which is a registered hollow microneedle that simplifies the delivery of liquid vaccines, are summarized. This device has demonstrated both significant dose-sparing and superior immunogenicity in various vaccine categories, as well as in diverse subject populations and age groups. These studies have shown that intradermal delivery using this device is safe, effective, and preferred by the subjects. Comparison with other intradermal devices and potential new applications for intradermal delivery that could be pursued in the future are also discussed.

Micro-fractional epidermal powder delivery for improved skin vaccination

Skin vaccination has gained increasing attention in the last two decades due to its improved potency compared to intramuscular vaccination. Yet, the technical difficulty and frequent local reactions hamper its broad application in the clinic. In the current study, micro-fractional epidermal powder delivery (EPD) is developed to facilitate skin vaccination and minimize local adverse effects. EPD is based on ablative fractional laser or microneedle treatment of the skin to generate microchannel (MC) arrays in the epidermis followed by topical application of powder drug/vaccine-coated array patches to deliver drug/vaccine into the skin. The novel EPD delivered more than 80% sulforhodamine b (SRB) and model antigen ovalbumin (OVA) into murine, swine, and human skin within 1h. EPD of OVA induced anti-OVA antibody titer at a level comparable to intradermal (ID) injection and was much more efficient than tape stripping in both delivery efficiency and immune responses. Strikingly, the micro-fractional delivery significantly reduced local side effects of LPS/CpG adjuvant and BCG vaccine, leading to complete skin recovery. In contrast, ID injection induced severe local reactions that persisted for weeks. While reducing local reactogenicity, EPD of OVA/LPS/CpG and BCG vaccine generated a comparable humoral immune response to ID injection. EPD of vaccinia virus encoding OVA induced significantly higher and long-lasting interferon γ-secreting CD8+ T cells than ID injection. In conclusion, EPD represents a promising technology for needle-free, painless skin vaccination with reduced local reactogenicity and at least sustained immunogenicity.

Towards clinical use of a laser-induced microjet system aimed at reliable and safe drug delivery

An Er:YAG laser with 2940-nm wavelength and 250-μs pulse duration is used to generate a microjet that is ejected at ∼50 m/s in air. The strength of the microjet depends on the bubble dynamics from the beam-water interaction within the driving chamber as well as the discharging of the drug solution underneath the elastic membrane that separates the drug from the driving liquid. The jet characteristics, such as velocity, volume, and level of atomization, are obtained by high-speed camera images taken at 42,000 fps. The enhancements in jet volume (dosage) and repeated jet generation, which are aimed at making the injector suitable for general clinical applications, are achieved. The generation of repeated microjets is achieved with the help of a stepping motor that provides a uniform pressure within the drug reservoir before an ejection occurs through a micro nozzle. Also, two types of human growth hormones are used for monitoring any potential thermal damage to the drug solution due to a repeated laser ablation when driving the microjet. We provide strong evidence to support that the drugs, as they are injected to porcine skins, are free of the damage associated with the present delivery method.

Needle-free injection into skin and soft matter with highly focused microjets

The development of needle-free drug injection systems is of great importance to global healthcare. However, in spite of its great potential and research history over many decades, these systems are not commonly used. One of the main problems is that existing methods use diffusive jets, which result in scattered penetration and severe deceleration of the jets, causing frequent pain and insufficient penetration. Another long-standing challenge is the development of accurate small volume injections. In this paper we employ a novel method of needle-free drug injection, using highly-focused high speed microjets, which aims to solve these challenges. We experimentally demonstrate that these unique jets are able to penetrate human skin: the focused nature of these microjets creates an injection spot smaller than a mosquito's proboscis and guarantees a high percentage of the liquid being injected. The liquid substances can be delivered to a much larger depth than conventional methods, and create a well-controlled dispersion pattern. Thanks to the excellent controllability of the microjet, small volume injections become feasible. Furthermore, the penetration dynamics is studied through experiments performed on gelatin mixtures (human soft tissue equivalent) and human skin, agreeing well with a viscous stress model which we develop. This model predicts the depth of the penetration into both human skin and soft tissue. The results presented here take needle-free injections a step closer to widespread use.

Experimental analysis of the performance of an air-powered needle-free liquid jet injector

An experimental study was performed using a custom-built air-powered needle-free injector to investigate the various injector parameters governing the dynamics of jet injection. A parametric study using five different nozzle sizes at driver pressure ranging from 4 to 8 bar was carried out. The fluid stagnation pressure of the liquid jet was determined using a Honeywell force sensor. Performance plots as a function of various parameters were constructed. It was determined that as the driver pressure increased both the peak and average stagnation pressure increased almost linearly within the operating range considered. Varying the injection nozzle diameter, whilst keeping the driver pressure constant did not have any significant impact on the peak or average stagnation pressure. The chamber length was also varied and no significant influence was found on peak or average stagnation pressure.

Transdermal insulin application system with dissolving microneedles

BACKGROUND

The aim of this report was to develop a dissolving microneedle (DM) application system, where 225-300 insulin-loaded DMs were formed on a chip. After the heat-sealed sheet is removed, the system covered with the press-through package layer is put on the skin. By pressing with the hand, insulin DMs were inserted into the skin.

MATERIALS AND METHODS

Factors affecting the penetration depth of DM were studied using applicator in vitro and in vivo experiments. The penetration depth was determined for rat and human skin. Two-layered DM array chips were prepared to obtain complete absorption of insulin and administered to the rat abdominal skin. Plasma glucose levels were measured for 6 h. By comparing the hypoglycemic effect with that obtained after subcutaneous injection, relative pharmacological availability (RPA) was determined.

RESULTS

The penetration depth increased from 21 ± 3 μm to 63 ± 2 μm in proportion to application speed to isolated rat skin, at 0.8-2.2 m/s. Human skin showed similar results in the penetration depth. The in vivo penetration depth was dependent on the force (0.5-2.5 N) and duration (1-10 min), as the secondary application force. The penetration depth was 211 ± 3 μm with a duration of 3 min in the in vivo rat experiment. DM array chips having an insulin-loaded space of 181.2 ± 4.2 and 209 ± 3.9 μm were evaluated in the rat. RPA values of insulin from DMs were 98.1 ± 0.8% and 98.1 ± 3.1%, respectively.

CONCLUSIONS

These results suggest the usefulness of the two-layered DM application system for the transdermal delivery of insulin.

Induction of potent CD8⁺ T cell responses through the delivery of subunit protein vaccines to skin antigen-presenting cells using densely packed microprojection arrays

The generation of both antibody and CD8⁺ T cell responses against pathogens is considered important for many advanced vaccines for diseases including tuberculosis, HIV and malaria. However, most current vaccines are delivered into muscle by the needle and syringe method and induce protection via humoral (antibody) immune responses. In this paper, we test the hypothesis that delivering a model subunit protein antigen (ovalbumin) to the skin's abundant immune cell population using a densely packed microprojection array (Nanopatch) enhances CD8⁺ T cell responses. We found that the Nanopatch significantly enhanced the CD8⁺ T cell responses when compared to intramuscular delivery of both antigen-only and adjuvanted cases (Quil-A and CpG; separately). To our knowledge, this is the first published study demonstrating significantly improved CD8⁺ T cell responses achieved by delivering subunit vaccines to the skin's abundant immune cell population. Successfully replicating these findings in humans could significantly advance the reach of vaccines.

Harnessing immune responses against Plasmodium for rational vaccine design

In recent years, groundbreaking advances have been made in understanding the biology of and immune mechanisms against the Plasmodium spp. parasite, the causative agent of malaria. Novel features of the Plasmodium life cycle have been unravelled and immune mechanisms, which take place during both infection and immunization, have been dissected. We have undoubtedly enhanced our knowledge, but the question now is how to use this information to manipulate immune responses against Plasmodium and to develop an efficacious malaria vaccine. In this review, we discuss the latest developments in the field and speculate on how immune responses against Plasmodium could be harnessed for rational vaccine design and application.