Assessment of epidermal cell viability by near infrared multi-photon microscopy following ballistic delivery of gold micro-particles

Advances and challenges in nintedanib drug delivery

INTRODUCTION

Nintedanib (N.T.B) is an orally administered tyrosine kinase inhibitor that has been approved recently by U.S.F.D.A for idiopathic pulmonary fibrosis (I.P.F) and systemic sclerosis-associated interstitial lung disease (S.Sc-I.L.D). N.T.B is also prescribed in COVID-19 patients associated with I.P.F. However, it has an extremely low bioavailability of around 4.7%, and hence, researchers are attempting to address this drawback by different approaches.

AREAS COVERED

This review article focuses on enlisting all the formulation attempts explored by researchers to increase the bioavailability of N.T.B while also providing meaningful insight into the unexplored areas in formulation development, such as targeting of the lymphatic system and transdermal delivery. All the patents on the formulation development of N.T.B have also been summarized.

EXPERT OPINION

N.T.B has the potential to act on multiple diseases that are still being discovered, but its extremely low bioavailability is a challenge that is to be dealt with for obtaining the full benefit. Few studies have been performed aiming at improving the bioavailability, but there are unexplored areas that can be used, a few of which are explained in this article. However, the ability to reproduce laboratory results when scaling up to the industry level is the only factor to be taken into consideration.

Microprojection arrays applied to skin generate mechanical stress, induce an inflammatory transcriptome and cell death, and improve vaccine-induced immune responses

Chemical adjuvants are typically used to improve immune responses induced by immunisation with protein antigens. Here we demonstrate an approach to enhance immune responses that does not require chemical adjuvants. We applied microprojection arrays to the skin, producing a range of controlled mechanical energy to invoke localised inflammation, while administering influenza split virus protein antigen. We used validated computational modelling methods to identify links between mechanical stress and energy generated within the skin strata and resultant cell death. We compared induced immune responses to those induced by needle-based intradermal antigen delivery and used a systems biology approach to examine the nature of the induced inflammatory response, and correlated this with markers of cell stress and death. Increasing the microprojection array application energy and the addition of QS-21 adjuvant were each associated with enhanced antibody response to delivered antigen and with induction of gene transcriptions associated with TNF and NF-κB signalling pathways. We concluded that microprojection intradermal antigen delivery inducing controlled local cell death could potentially replace chemical adjuvants to enhance the immune response to protein antigen.

Adjuvants play an essential function in vaccine formulations by boosting immune responses to the delivered antigen. Mark A. F. Kendall and colleagues investigate the efficacy of vaccine delivered intradermally via Nanopatch^TM—a 16 mm² ultra-high-density array of 100 micron needles. Systems analysis comparisons demonstrate that depending on the force applied, the Nanopatch^TM triggers skin transcriptomic changes similar to that elicited by the adjuvant QS-21, including evidence of localised cell death and inflammatory gene expression. Flu vaccine delivered by Nanopatch^TM elicits anti-hemagglutinin titers equivalent to that observed with conventional intradermal syringe delivery of vaccine plus adjuvant. Sterile mechanical stress elicited by the application of microneedles might therefore be a viable replacement to the use of conventional needles.

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

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

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Analysis of the effect of promoter type and skin pretreatment on antigen expression and antibody response after gene gun-based immunization

Monoclonal antibodies (mAbs) have enabled numerous basic research discoveries and therapeutic approaches for many protein classes. However, there still exist a number of target classes, such as multi-pass membrane proteins, for which antibody discovery is difficult, due in part to lack of high quality, recombinant protein. Here we describe the impact of several parameters on antigen expression and the development of mAbs against human claudin 4 (CLDN4), a potential multi-indication cancer target. Using gene gun-based DNA delivery and bioluminescence imaging, we optimize promoter type by comparing expression profiles of four robust in vivo promoters. In addition, we observe that most vectors rapidly lose expression, ultimately reaching almost background levels by three days post-delivery. Recognizing this limitation, we next explored skin pretreatment strategies as an orthogonal method to further boost the efficiency of mAb generation. We show that SDS pretreatment can boost antigen expression, but fails to significantly increase mAb discovery efficiency. In contrast, we find that sandpaper pretreatment yields 5-fold more FACS⁺ anti-CLDN4 hybridomas, without impacting antigen expression. Our findings coupled with other strategies to improve DNA immunizations should improve the success of mAb discovery against other challenging targets and enable the generation of critical research tools and therapeutic candidates.

Three-dimensional wet-electrospun poly(lactic acid)/multi-wall carbon nanotubes scaffold induces differentiation of human menstrual blood-derived stem cells into germ-like cells

Infertility caused by the disruption or absence of germ cells is a major and largely incurable medical problem. Germ cells (i.e., sperm or egg) play a key role in the transmission of genetic and epigenetic information across generations. Generation of gametes derived in vitro from stem cells hold promising prospects which could potentially help infertile men and women. Menstrual blood-derived stem cells are a unique stem cell source. Evidence suggests that menstrual blood-derived stem cells exhibit a multi-lineage potential and have attracted extensive attention in regenerative medicine. To maintain the three-dimensional structure of natural extra cellular matrices in vitro, scaffolds can do this favor and mimic a microenvironment for cell proliferation and differentiation. According to previous studies, poly(lactic acid) and multi-wall carbon nanotubes have been introduced as novel and promising biomaterials for the proliferation and differentiation of stem cells. Some cell types have been successfully grown on a matrix containing carbon nanotubes in tissue engineering but there is no report for this material to support stem cells differentiation into germ cells lineage. This study designed a 3D wet-electrospun poly(lactic acid) and poly(lactic acid)/multi-wall carbon nanotubes composite scaffold to compare infiltration, proliferation, and differentiation potential of menstrual blood-derived stem cells toward germ cell lineage with 2D culture. Our primary data revealed that the fabricated scaffold has mechanical and biological suitable qualities for supporting and attachments of stem cells. The differentiated menstrual blood-derived stem cells tracking in scaffolds using scanning electron microscopy confirmed cell attachment, aggregation, and distribution on the porous scaffold. Based on the differentiation assay by RT-PCR analysis, stem cells and germ-like cells markers were expressed in 3D groups as well as 2D one. It seems that poly(lactic acid)/multi-wall carbon nanotubes scaffold-seeded menstrual blood-derived stem cells could be viewed as a novel, safe, and accessible construct for these cells, as they enhance germ-like generation from menstrual blood-derived stem cells.

Topical and cutaneous delivery using nanosystems

The goal of topical and cutaneous delivery is to deliver therapeutic and other substances to a desired target site in the skin at appropriate doses to achieve a safe and efficacious outcome. Normally, however, when the stratum corneum is intact and the skin barrier is uncompromised, this is limited to molecules that are relatively lipophilic, small and uncharged, thereby excluding many potentially useful therapeutic peptides, proteins, vaccines, gene fragments or drug-carrying particles. In this review we will describe how nanosystems are being increasingly exploited for topical and cutaneous delivery, particularly for these previously difficult substances. This is also being driven by the development of novel technologies, which include minimally invasive delivery systems and more precise fabrication techniques. While there is a vast array of nanosystems under development and many undergoing advanced clinical trials, relatively few have achieved full translation to clinical practice. This slow uptake may be due, in part, to the need for a rigorous demonstration of safety in these new nanotechnologies. Some of the safety aspects associated with nanosystems will be considered in this review.

Influenza nucleoprotein DNA vaccination by a skin targeted, dry coated, densely packed microprojection array (Nanopatch) induces potent antibody and CD8(+) T cell responses

DNA vaccines have many advantages such as thermostability and the ease and rapidity of manufacture; for example, in an influenza pandemic situation where rapid production of vaccine is essential. However, immunogenicity of DNA vaccines was shown to be poor in humans unless large doses of DNA are used. If a highly efficacious DNA vaccine delivery system could be identified, then DNA vaccines have the potential to displace protein vaccines. In this study, we show in a C57BL/6 mouse model, that the Nanopatch, a microprojection array of high density (>21,000 projections/cm(2)), could be used to deliver influenza nucleoprotein DNA vaccine to skin, to generate enhanced antigen specific antibody and CD8(+) T cell responses compared to the conventional intramuscular (IM) delivery by the needle and syringe. Antigen specific antibody was measured using ELISA assays of mice vaccinated with a DNA plasmid containing the nucleoprotein gene of influenza type A/WSN/33 (H1N1). Antigen specific CD8(+) T cell responses were measured ex-vivo in splenocytes of mice using IFN-γ ELISPOT assays. These results and our previous antibody and CD4(+) T cell results using the Nanopatch delivered HSV DNA vaccine indicate that the Nanopatch is an effective delivery system of general utility that could potentially be used in humans to increase the potency of the DNA vaccines.

The changing shape of vaccination: improving immune responses through geometrical variations of a microdevice for immunization

Micro-device use for vaccination has grown in the past decade, with the promise of ease-of-use, painless application, stable solid formulations and greater immune response generation. However, the designs of the highly immunogenic devices (e.g. the gene gun, Nanopatch or laser adjuvantation) require significant energy to enter the skin (30-90 mJ). Within this study, we explore a way to more effectively use energy for skin penetration and vaccination. These modifications change the Nanopatch projections from cylindrical/conical shapes with a density of 20,000 per cm(2) to flat-shaped protrusions at 8,000 per cm(2), whilst maintaining the surface area and volume that is placed within the skin. We show that this design results in more efficient surface crack initiations, allowing the energy to be more efficiently be deployed through the projections into the skin, with a significant overall increase in penetration depth (50%). Furthermore, we measured a significant increase in localized skin cell death (>2 fold), and resultant infiltrate of cells (monocytes and neutrophils). Using a commercial seasonal trivalent human influenza vaccine (Fluvax 2014), our new patch design resulted in an immune response equivalent to intramuscular injection with approximately 1000 fold less dose, while also being a practical device conceptually suited to widespread vaccination.

Colocalization of cell death with antigen deposition in skin enhances vaccine immunogenicity

Vaccines delivered to the skin by microneedles – with and without adjuvants – have increased immunogenicity with lower doses than standard vaccine delivery techniques such as intramuscular (i.m.) or intradermal (i.d.) injection. However, the mechanisms behind this skin-mediated ‘adjuvant’ effect are not clear. Here, we show that the dynamic application of a microprojection array (the Nanopatch) to skin generates localized transient stresses invoking cell death around each projection. Nanopatch application caused significantly higher levels (~65-fold) of cell death in murine ear skin than i.d. injection using a hypodermic needle. Measured skin cell death is associated with modeled stresses ~1–10 MPa. Nanopatch-immunized groups also yielded consistently higher anti-IgG endpoint titers (up to 50-fold higher) than i.d. groups after delivery of a split virion influenza vaccine. Importantly, co-localization of cell death with nearby live skin cells and delivered antigen was necessary for immunogenicity enhancement. These results suggest a correlation between cell death caused by the Nanopatch with increased immunogenicity. We propose that the localized cell death serves as a ‘physical immune enhancer’ for the adjacent viable skin cells, which also receive antigen from the projections. This natural immune enhancer effect has the potential to mitigate or replace chemical-based adjuvants in vaccines.

Potential of microneedle-assisted micro-particle delivery by gene guns: a review

CONTEXT

Gene guns have been used to deliver deoxyribonucleic acid (DNA) loaded micro-particle and breach the muscle tissue to target cells of interest to achieve gene transfection.

OBJECTIVE

This article aims to discuss the potential of microneedle (MN) assisted micro-particle delivery from gene guns, with a view to reducing tissue damage.

METHODS

Using a range of sources, the main gene guns for micro-particle delivery are reviewed along with the primary features of their technology, e.g. their design configurations, the material selection of the micro-particle, the driving gas type and pressure. Depending on the gene gun system, the achieved penetration depths in the skin are discussed as a function of the gas pressure, the type of the gene gun system and particle size, velocity and density. The concept of MN-assisted micro-particles delivery which consists of three stages (namely, acceleration, separation and decoration stage) is discussed. In this method, solid MNs are inserted into the skin to penetrate the epidermis/dermis layer and create holes for particle injection. Several designs of MN array are discussed and the insertion mechanism is explored, as it determines the feasibility of the MN-based system for particle transfer.

RESULTS

This review suggests that one of the problems of gene guns is that they need high operating pressures, which may result in direct or indirect tissue/cells damage. MNs seem to be a promising method which if combined with the gene guns may reduce the operating pressures for these devices and reduce tissue/cell damages.

CONCLUSIONS

There is sufficient potential for MN-assisted particle delivery systems.

Improved biolistic transfection of hair cells

Transient transfection of hair cells has proven challenging. Here we describe modifications to the Bio-Rad Helios Gene Gun that, along with an optimized protocol, improve transfection of bullfrog, chick, and mouse hair cells. The increased penetrating power afforded by our method allowed us to transfect mouse hair cells from the basal side, through the basilar membrane; this configuration protects hair bundles from damage during the procedure. We characterized the efficiency of transfection of mouse hair cells with fluorescently-tagged actin fusion protein using both the optimized procedure and a published procedure; while the efficiency of the two methods was similar, the morphology of transfected hair cells was improved with the new procedure. In addition, using the improved method, we were able to transfect hair cells in the bullfrog sacculus and chick cochlea for the first time. We used fluorescent-protein fusions of harmonin b (USH1C) and PMCA2 (ATP2B2; plasma-membrane Ca²⁺-ATPase isoform 2) to examine protein distribution in hair cells. While PMCA2-EGFP localization was similar to endogenous PMCA2 detected with antibodies, high levels of harmonin-EGFP were found at stereocilia tapers in bullfrog and chick, but not mouse; by contrast, harmonin-EGFP was concentrated in stereocilia tips in mouse hair cells.

Nanopatch targeted delivery of both antigen and adjuvant to skin synergistically drives enhanced antibody responses

Many vaccines make use of an adjuvant to achieve stronger immune responses. Alternatively, potent immune responses have also been generated by replacing the standard needle and syringe (which places vaccine into muscle) with devices that deliver vaccine antigen to the skin's abundant immune cell population. However it is not known if the co-delivery of antigen plus adjuvant directly to thousands of skin immune cells generates a synergistic improvement of immune responses. In this paper, we investigate this idea, by testing if Nanopatch delivery of vaccine - both the antigen and the adjuvant - enhances immunogenicity, compared to intramuscular injection. As a test-case, we selected a commercial influenza vaccine as the antigen (Fluvax 2008®) and the saponin Quil-A as the adjuvant. We found, after vaccinating mice, that anti-influenza IgG antibody and haemagglutinin inhibition assay titre response induced by the Nanopatch (with delivered dose of 6.5ng of vaccine and 1.4μg of Quil-A) were equivalent to that of the conventional intramuscular injection using needle and syringe (6000ng of vaccine injected without adjuvant). Furthermore, a similar level of antigen dose sparing (up to 900 fold) - with equivalent haemagglutinin inhibition assay titre responses - was also achieved by delivering both antigen and adjuvant (1.4μg of Quil-A) to skin (using Nanopatches) instead of muscle (intramuscular injection). Collectively, the unprecedented 900 fold antigen dose sparing demonstrates the synergistic improvement to vaccines by co-delivery of both antigen and adjuvant directly to skin immune cells. Successfully extending these findings to humans with a practical delivery device - like the Nanopatch - could have a huge impact on improving vaccines.

Improving the reach of vaccines to low-resource regions, with a needle-free vaccine delivery device and long-term thermostabilization

Dry-coated microprojections can deliver vaccine to abundant antigen-presenting cells in the skin and induce efficient immune responses and the dry-coated vaccines are expected to be thermostable at elevated temperatures. In this paper, we show that we have dramatically improved our previously reported gas-jet drying coating method and greatly increased the delivery efficiency of coating from patch to skin to from 6.5% to 32.5%, by both varying the coating parameters and removing the patch edge. Combined with our previous dose sparing report of influenza vaccine delivery in a mouse model, the results show that we now achieve equivalent protective immune responses as intramuscular injection (with the needle and syringe), but with only 1/30th of the actual dose. We also show that influenza vaccine coated microprojection patches are stable for at least 6 months at 23°C, inducing comparable immunogenicity with freshly coated patches. The dry-coated microprojection patches thus have key and unique attributes in ultimately meeting the medical need in certain low-resource regions with low vaccine affordability and difficulty in maintaining "cold-chain" for vaccine storage and transport.

Improved DNA vaccination by skin-targeted delivery using dry-coated densely-packed microprojection arrays

HSV-2-gD2 DNA vaccine was precisely delivered to immunologically sensitive regions of the skin epithelia using dry-coated microprojection arrays. These arrays delivered a vaccine payload to the epidermis and the upper dermis of mouse skin. Immunomicroscopy results showed that, in 43 ± 5% of microprojection delivery sites, the DNA vaccine was delivered to contact with professional antigen presenting cells in the epidermal layer. Associated with this efficient delivery of the vaccine into the vicinity of the professional antigen presenting cells, we achieved superior antibody responses and statistically equal protection rate against an HSV-2 virus challenge, when compared with the mice immunized with intramuscular injection using needle and syringe, but with less than 1/10th of the delivered antigen.

DNA vaccine delivery by densely-packed and short microprojection arrays to skin protects against vaginal HSV-2 challenge

There is an unmet medical need for a prophylactic vaccine against herpes simplex virus (HSV). DNA vaccines and cutaneous vaccination have been tried for many applications, but few reports combine this vaccine composition and administration route. We compared DNA administration using the Nanopatch™, a solid microprojection device coated with vaccine comprised of thousands of short (110 μm) densly-packed projections (70 μm spacing), to standard intramuscular DNA vaccination in a mouse model of vaginal HSV-2 infection. A dose-response relationship was established for immunogenicity and survival in both vaccination routes. Appropriate doses administered by Nanopatch™ were highly immunogenic and enabled mouse survival. Vaginal HSV-2 DNA copy number day 1 post challenge correlated with survival, indicating that vaccine-elicited acquired immune responses can act quickly and locally. Solid, short, densely-packed arrays of microprojections applied to the skin are thus a promising route of administration for DNA vaccines.

Needle-free vaccine injection

Millions of people die each year from infectious disease, with a main stumbling block being our limited ability to deliver vaccines to optimal sites in the body. Specifically, effective methods to deliver vaccines into outer skin and mucosal layers--sites with immunological, physical and practical advantages that cannot be targeted via traditional delivery methods--are lacking. This chapter investigates the challenge for physical delivery approaches that are primarily needle-free. We examine the skin's structural and immunogenic properties in the context of the physical cell targeting requirements of the viable epidermis, and we review selected current physical cell targeting technologies engineered to meet these needs: needle and syringe, diffusion patches, liquid jet injectors, and microneedle arrays/patches. We then focus on biolistic particle delivery: we first analyze engineering these systems to meet demanding clinical needs, we then examine the interaction of biolistic devices with the skin, focusing on the mechanical interactions of ballistic impact and cell death, and finally we discuss the current clinical outcomes of one key application of engineered delivery devices--DNA vaccines.

Micro-scale devices for transdermal drug delivery

Skin makes an excellent site for drug and vaccine delivery due to easy accessibility, immuno-surveillance functions, avoidance of macromolecular degradation in the gastrointestinal tract and possibility of self-administration. However, macromolecular drug delivery across the skin is primarily accomplished using hypodermic needles, which have several disadvantages including accidental needle-sticks, pain and needle phobia. These limitations have led to extensive research and development of alternative methods for drug and vaccine delivery across the skin. This review focuses on the recent trends and developments in this field of micro-scale devices for transdermal macromolecular delivery. These include liquid jet injectors, powder injectors, microneedles and thermal microablation. The historical perspective, mechanisms of action, important design parameters, applications and challenges are discussed for each method.

The mechanical properties of the skin epidermis in relation to targeted gene and drug delivery

A challenge in combating many major diseases is breaching the skin's tough outer layer (the stratum corneum (SC)) and delivering drugs and genes into the underlying abundant immunologically sensitive viable epidermal cells with safe, practical physical technologies. To achieve this effectively and accurately, design information is needed on key skin mechanical properties when pushing into and through epidermal skin cells. We measure these important mechanical properties by penetrating through the intact SC and viable epidermis (VE) of freshly excised murine skin with a NANO-indenter, using custom tungsten probes fabricated with nominally 5 and 2 microm diameters (with nanoscale tips). We show the skin Young's modulus, storage modulus and stress all dramatically decreased through the SC. Also, for a given penetration depth, decreasing the probe size significantly increases the storage modulus. Biological variation in penetrating the skin was shown. These collective findings advance the rational design of physical approaches for delivering genes and drugs within key cells of the VE.

Characteristics of a micro-biolistic system for murine immunological studies

With an advanced computational fluid dynamics (CFD) technique, we have numerically developed and examined a micro-biolistic system for delivering particles to murine target sites. The micro-particles are accelerated by a high speed flow initiated by a traveling shock wave, so that they can attain a sufficient momentum to penetrate in to the cells of interest within murine skin (or mucosa). In immunization application, powdered vaccines are directly delivered into the antigen presenting cells (APCs) within the epidermis/dermis of the murine skin with a narrow and highly controllable velocity range (e.g., 699+/-5.6 m/s for 1.8 microm modeled gold particles) and a uniform spatial distribution over a diameter of approximately 4 mm target area. Key features of gas dynamics and gas-particle interaction are presented. Importantly, the particle impact velocity conditions are quantified as a function of: stand-off distance (2-15 mm), driver gas species (air/helium mixtures), particle density (1,050 kg/m3 and 19,320 kg/m3) and particle size (1-5 microm for gold particles and 10-50 microm for less dense particles, respectively). The influential parameters--representative of immunotherapeutic (e.g., DNA vaccination) and protein (e.g., lidocaine) biolistic applications--are studied in detail.

Numerical analysis of gas and micro-particle interactions in a hand-held shock-tube device

A unique hand-held gene gun is employed for ballistically delivering biomolecules to key cells in the skin and mucosa in the treatment of the major diseases. One of these types of devices, called the Contoured Shock Tube (CST), delivers powdered micro-particles to the skin with a narrow and highly controllable velocity distribution and a nominally uniform spatial distribution. In this paper, we apply a numerical approach to gain new insights in to the behavior of the CST prototype device. The drag correlations proposed by Henderson (1976), Igra and Takayama (1993) and Kurian and Das (1997) were applied to predict the micro-particle transport in a numerically simulated gas flow. Simulated pressure histories agree well with the corresponding static and Pitot pressure measurements, validating the CFD approach. The calculated velocity distributions show a good agreement, with the best prediction from Igra & Takayama correlation (maximum discrepancy of 5%). Key features of the gas dynamics and gas-particle interaction are discussed. Statistic analyses show a tight free-jet particle velocity distribution is achieved (570 +/- 14.7 m/s) for polystyrene particles (39 +/- 1 microm), representative of a drug payload.

Engineering of needle-free physical methods to target epidermal cells for DNA vaccination

A challenge in epidermal DNA vaccination is the efficient and targeted delivery of polynucleotides to immunologically sensitive Langerhans cells. This paper investigates this particular challenge for physical delivery approaches. The skin immunology and material properties are examined in the context of the physical cell targeting requirements of the viable epidermis. Selected current physical cell targeting technologies engineered to meet these needs are examined: needle and syringe; diffusion patches; liquid jet injectors; microneedle arrays/patches; and biolistic particle injection. The operating methods and relative performance of these approaches are discussed, with a comment on potential future developments and technologies.