Influence of skin model on in vitro performance of drug-loaded soluble microneedle arrays

A plethora of studies have described the in vitro assessment of dissolving microneedle (MN) arrays for enhanced transdermal drug delivery, utilising a wide variety of model membranes as a representation of the skin barrier. However, to date, no discussion has taken place with regard to the choice of model skin membrane and the impact this may have on the evaluation of MN performance. In this study, we have, for the first time, critically assessed the most common types of in vitro skin permeation models - a synthetic hydrophobic membrane (Silescol(®) of 75 µm) and neonatal porcine skin of definable thickness (300-350 µm and 700-750 µm) - for evaluating the performance of drug loaded dissolving poly (methyl vinyl ether co maleic acid) (PMVE/MA) MN arrays. It was found that the choice of in vitro skin model had a significant effect on the permeation of a wide range of small hydrophilic molecules released from dissolving MNs. For example, when Silescol(®) was used as the model membrane, the cumulative percentage permeation of methylene blue 24h after the application of dissolvable MNs was found to be only approximately 3.7% of the total methylene blue loaded into the MN device. In comparison, when dermatomed and full thickness neonatal porcine skin were used as a skin model, approximately 67.4% and 47.5% of methylene blue loaded into the MN device was delivered across the skin 24h after the application of MN arrays, respectively. The application of methylene blue loaded MN arrays in a rat model in vivo revealed that the extent of MN-mediated percutaneous delivery achieved was most similar to that predicted from the in vitro investigations employing dermatomed neonatal porcine skin (300-350 µm) as the model skin membrane. On the basis of these results, a wider discussion within the MN community will be necessary to standardise the experimental protocols used for the evaluation and comparison of MN devices.

Design, optimization and characterisation of polymeric microneedle arrays prepared by a novel laser-based micromoulding technique

Design and evaluation of a novel laser-based method for micromoulding of microneedle arrays from polymeric materials under ambient conditions. The aim of this study was to optimise polymeric composition and assess the performance of microneedle devices that possess different geometries.

Comparison of frequency-selective screen-based linear to circular split-ring polarisation convertors

This study presents the use of periodic arrays of freestanding slot frequency-selective screens (FSS) as a means for generating circularly polarised signals from an incident linearly polarised signal at normal incidence to the structure. Measured and simulated results for crossed, linear and various ring slot element shapes in single and double-layer polarisation convertor structures are presented for 10 GHz operation. It is shown that 3 dB axial ratio (AR) bandwidths of 21% can be achieved with the one-layer perforated screen design and that the rate of change is lower than the double-layer structures. An insertion loss of 0.34 dB can be achieved for the split circular ring double-layer periodic array, and of the three topologies presented the hexagonal split-ring polarisation convertor gives the lowest variation of AR with angle of incidence 1.8 dB/45° and 3.6 dB/45° for the single and double-screen FSS, respectively. In addition, their tolerance to angle of incidence variation is presented. The capability of the surfaces reported here as twist polariser or spatial isolator components has been demonstrated with up to -30 dB isolation between incident and re-reflected signals for the double-layer designs being measured. © 2010 The Institution of Engineering and Technology.

Skin Dendritic Cell Targeting via Microneedle Arrays Laden with Antigen-Encapsulated Poly-D, L-lactide-co-Glycolide Nanoparticles Induces Efficient Antitumor and Antiviral Immune Responses

The efficacious delivery of antigens to antigen-presenting cells (APCs), in particular, to dendritic cells (DCs), and their subsequent activation remains a significant challenge in the development of effective vaccines. This study highlights the potential of dissolving microneedle (MN) arrays laden with nanoencapsulated antigen to increase vaccine immunogenicity by targeting antigen specifically to contiguous DC networks within the skin. Following in situ uptake, skin-resident DCs were able to deliver antigen-encapsulated poly-d,l-lactide-co-glycolide (PGLA) nanoparticles to cutaneous draining lymph nodes where they subsequently induced significant expansion of antigen-specific T cells. Moreover, we show that antigen-encapsulated nanoparticle vaccination via microneedles generated robust antigen-specific cellular immune responses in mice. This approach provided complete protection in vivo against both the development of antigen-expressing B16 melanoma tumors and a murine model of para-influenza, through the activation of antigen-specific cytotoxic CD8(+) T cells that resulted in efficient clearance of tumors and virus, respectively. In addition, we show promising findings that nanoencapsulation facilitates antigen retention into skin layers and provides antigen stability in microneedles. Therefore, the use of biodegradable polymeric nanoparticles for selective targeting of antigen to skin DC subsets through dissolvable MNs provides a promising technology for improved vaccination efficacy, compliance, and coverage.

An integrated wideband multifunctional antenna using a microstrip patch with two U-slots

In this paper a multifunctional microstrip antenna is designed, fabricated and experimentally verified for operation in AWS, GSM, WiMAX and WLAN bands. This microstrip patch antenna has two U-shaped slots to achieve the dual wideband operation required to meet these specifications. The dimensions and locations of the U-slots are designed appropriately. The thick substrate used here helps in integrating the antenna with the existing aircraft panel material while achieving wide bandwidths. Experimental results of this single feed antenna indicate that it meets all current requirements for in-cabin wireless communication needs.

A wideband antenna array for DVB-T based passive bistatic radar applications

A Digital Video Broadcast Terrestrial (DVB-T) based passive radar requires the development of an antenna array that performs satisfactorily over the entire DVB-T band. The array should require no mechanical adjustments to inter-element spacing to correspond to the DVB-T carrier frequency used for any particular measurement. This paper will describe the challenges involved in designing an antenna array with a bandwidth of 450 MHz. It will discuss the design procedure and demonstrate a number of simulated array configurations. The final configuration of the array will be shown as well as simulations of the expected performance over the desired frequency span.

Evaluation of the performance of a multi-band antenna for On-Board applications

The performance of a multi-band antenna consisting of a microstrip patch with two U-slots is designed and tested for use in aircraft cabin wireless access points. The objective of this paper is to evaluate this antenna that covers most of the current wireless bands from 1.7GHz to 5.85GHz.A specially designed wideband probe antenna is used for characterization
of field radiated from this antenna. This measurement setup gives room for future development like human presence in the cabin, the fading effects, and the path loss between transmitter and receiver.

Design of a wideband conformal array antenna system with beamforming and null steering, for application in a DVB-T based passive radar

The use of radars in detecting low flying, small targets is being explored for several decades now. However radar with counter-stealth abilities namely the passive, multistatic, low frequency radars are in the focus recently. Passive radar that uses Digital Video Broadcast Terrestrial (DVB-T) signals as illuminator of opportunity is a major contender in this area. A DVB-T based passive radar requires the development of an antenna array that performs satisfactorily over the entire DVB-T band. At Fraunhofer FHR, there is currently a need for an array antenna to be designed for operation over the 450-900 MHz range with wideband beamforming and null steering capabilities. This would add to the ability of the passive radar in detecting covert targets and would improve the performance of the system. The array should require no mechanical adjustments to inter-element spacing to correspond to the DVB-T carrier frequency used for any particular measurement. Such an array would have an increased flexibility of operation in different environment or locations.

The design of such an array antenna and the applied techniques for wideband beamforming and null steering are presented in the thesis. The interaction between the inter-element spacing, the grating lobes and the mutual couplings had to be carefully studied and an optimal solution was to be reached at that meets all the specifications of the antenna array for wideband applications. Directional beams, nulls along interference directions, low sidelobe levels, polarization aspects and operation along a wide bandwidth of 450-900 MHz were some of the key considerations.

Small aperture evanescent-mode waveguide antenna matched using distributed coupled resonators

Presented is a design methodology which permits the application of distributed coupled resonator bandpass filter principles to form wideband small-aperture evanescent-mode waveguide antenna designs. This approach permits matching of the complex antenna aperture admittance of an evanescent-mode open-ended waveguide to a real impedance generator, and thereby to a coaxial feed probe. A simulated reflection coefficient of < - 10 dB was obtained over a bandwidth of 20%, from 2.0-2.45 GHz, in a 2.58 GHz cutoff waveguide. Dielectric-filled propagating waveguide and air-filled evanescent-mode waveguide sections are used to form the resonators/coupling elements of the antenna's coupled resonator matching sections. Simulated realised gain variation from 3.4-5.0 dBi is observed across the bandwidth. The antenna's maximum aperture dimension is < 0.47 wavelength at the upper operating frequency and so it is suitable for use in a wide angle scanning phased array.

Phenomenology of Resonance Reflectance by Intertwined Spiral Arrays

The physical mechanisms underlying the dramatic reduction of the unit cell electrical size along with broadening fractional bandwidths provided by intertwined spiral arrays are discussed. Based upon this insight, a multi-strip transmission line (MTL) model is developed to analytically estimate the equivalent capacitance and inductance of intertwined spiral array elements in terms of their geometrical parameters. The proposed MTL model enables an accurate prediction of the fundamental resonance characteristics and provides a valuable tool for design of the arrays with the specified frequency response.

Entwined spiral arrays on ferrite substrates

The properties of metasurfaces formed by the entwined spiral arrays on normally magnetised fer-rite substrates have been explored. It is shown that the coupling between the array fundamental topological resonance and the ferromagnetic resonance of the ferrite substrate leads to significant increase of the fractional bandwidth (FBW). The features of resonance transmittance assisted by the volume spin waves excited by the entwined spirals in the ferrite substrate are discussed.