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.

Split-Ring FSS Spiral Phase Plate

This letter gives the first report of a planar phase plate structure based on frequency selective surface (FSS) technology for the generation of helical far-field radiation patterns with circular polarization properties.The unit cell of the structure comprises two orthogonal split-ring resonators designed to ensure 180$^{\circ}$ phase shift between orthogonal transmission coefficients. This property is exploited to obtain progressive rotational phase shift within the structure and thus synthesize 360$^{\circ}$ spiral phase profile. Measured far-field radiation patterns demonstrate spiral phase front generation for 10-GHz circularly polarized waves transmitted through the structure.

Molecular similarity between myelodysplastic form of chronic myelomonocytic leukemia and refractory anemia with ring sideroblasts

Chronic myelomonocytic leukemia is similar to but a separate entity from both myeloproliferative neoplasms and myelodysplastic syndromes, and shows either myeloproliferative or myelodysplastic features. We ask whether this distinction may have a molecular basis. We established the gene expression profiles of 39 samples of chronic myelomonocytic leukemia (including 12 CD34-positive) and 32 CD34-positive samples of myelodysplastic syndromes by using Affymetrix microarrays, and studied the status of 18 genes by Sanger sequencing and array-comparative genomic hybridization in 53 samples. Analysis of 12 mRNAS from chronic myelomonocytic leukemia established a gene expression signature of 122 probe sets differentially expressed between proliferative and dysplastic cases of chronic myelomonocytic leukemia. As compared to proliferative cases, dysplastic cases over-expressed genes involved in red blood cell biology. When applied to 32 myelodysplastic syndromes, this gene expression signature was able to discriminate refractory anemias with ring sideroblasts from refractory anemias with excess of blasts. By comparing mRNAS from these two forms of myelodysplastic syndromes we derived a second gene expression signature. This signature separated the myelodysplastic and myeloproliferative forms of chronic myelomonocytic leukemias. These results were validated using two independent gene expression data sets. We found that myelodysplastic chronic myelomonocytic leukemias are characterized by mutations in transcription/epigenetic regulators (ASXL1, RUNX1, TET2) and splicing genes (SRSF2) and the absence of mutations in signaling genes. Myelodysplastic chronic myelomonocytic leukemias and refractory anemias with ring sideroblasts share a common expression program suggesting they are part of a continuum, which is not totally explained by their similar but not, however, identical mutation spectrum. © 2013 Ferrata Storti Foundation.

Polarisation independent split ring frequency selective surface

A frequency selective surface (FSS) is described which exhibits coincident spectral responses for TE and TM polarisation when the FSS operates at 45 degrees incidence. The structure consists of two closely spaced arrays of ring elements with the conductor split at one or two locations to provide independent control of the resonances for the vertical and horizontal field directions. The FSS is designed to diplex two channels separated by an edge of a band ratio of 1.7:1 and yield a common - 10 dB reflection bandwidth of 10.2%. Measured and numerical results are shown to be in good agreement over the frequency range 9-12 GHz.

Design of an intravaginal ring for the controlled delivery of 17b-estradiol as its 3-acetate ester

Suitable ester prodrugs of 17b-estradiol are identified, thus permitting effective sustained and controlled estrogen replacement therapy (ERT) from an elastomeric, silicone intravaginal ring (IVR). IVR devices of reservoir design were prepared by blending silicone elastomer base with n-propylorthosilicate (cross-linker) and 10% w/w of 17b-estradiol or an ester prodrug, the mix being activated with 0.5% w/w stannous octoate and cured at 808C for 2 min. A rate-controlling membrane was similarly prepared, without the active agent. IVR devices were of cross-sectional diameter 9 mm, outer diameter 54 mm, with core cross-sectional diameter of 2 mm and core length varied as required. Sink conditions were evident for the 17b-estradiol esters in 1.0% aqueous benzalkonium chloride solution. The low release rates into 0.9% w/v saline of the lipophilic valerate and benzoate esters were due to their intrinsically low aqueous solubilities. In vivo, these esters failed to raise plasma estradiol above baseline levels in postmenopausal human volunteers, despite good in vitro release characteristics under sink conditions. The best release rates under sink conditions, in combination with substantial aqueous solubilities as indicated by the release rates into saline, were observed for the acetate and propionate esters. A
combination of drug release characteristics, short plasma half-life and a toxicologically acceptable hydrolysis product indicated that 17b-estradiol-3-acetate was the prodrug of choice for IVR delivery of ERT. In vivo, an IVR device releasing
100 mg/day of estradiol as its 3-acetate ester maintained over 84 days a circulating plasma concentration in the region of 300 pmol l , within the clinically desirable range for ERT.

Assessment of the effectiveness of the guard ring in obtaining a uni-directional flow in an in situ water permeability test

The non-destructive evaluation of the water permeability of concrete structures is a long standing challenge, principally due to the difficulty of achieving a uni-direction flow for computing the water permeability coefficient. The use of a guard ring (GR) was originally proposed for the in situ sorptivity test, but little information can be found for the water permeability test. In this study, the effect of a GR was carefully examined through the flow simulation, which was verified by carrying out experiments. It was observed that the GR can confine the flow near the surface, but cannot achieve a uni-directional flow across the whole depth of flow. To achieve a better performance, it is essential to consider the effects of the size of the inner seal and the GR and the significant interaction between these two. The analysis of the experimental data has indicated that the GR influences the flow for porous concretes, but there is no significant effect for dense concretes. Further investigation, validated using the flow-net theory, has shown a strong correlation between the water permeability coefficients obtained with the GR (K w-GR) and without it (K w-No GR), suggesting that one dimensional flow is not essential for interpreting data for site tests. Another practical issue was that more than 30 % of the tests with GR failed due to the difficulty of achieving a good seal between the inner and the outer chambers. Based on the work reported in this paper, a new water permeability test is proposed.

pH-Sensitive brush polymer-drug conjugates by ring-opening metathesis copolymerization

Representing a new category of polymer-drug conjugates, brush polymer-drug conjugates were prepared by ring-opening metathesis copolymerization. Following judicious structural design, these conjugates exhibited well-shielded drug moieties, significant water solubility, well-defined nanostructures, and acid-triggered drug release.

Pre-clinical development of a combination microbicide vaginal ring containing dapivirine and darunavir

Objectives: Combination microbicide vaginal rings may be more effective than single microbicide rings at reducing/preventing sexual transmission of HIV. Here, we report the preclinical development and macaque pharmacokinetics of matrix-type silicone elastomer vaginal rings containing dapivirine and darunavir.

Methods: Macaque rings containing 25 mg dapivirine, 300 mg darunavir and 100 mg dapivirine, and 300 mg darunavir were manufactured and characterised by differential scanning calorimetry. In vitro release was assessed into isopropanol/water and simulated vaginal fluid. Macaque vaginal fluid and blood serum concentrations for both antiretrovirals were measured during 28-day ring use. Tissue levels were measured on day 28. Ex vivo challenge studies were performed on vaginal fluid samples and IC50 values calculated.

Results: Darunavir caused a concentration-dependent reduction in the dapivirine melting temperature in both solid drug mixes and in the combination ring. In vitro release from rings was dependent on drug loading, the number of drugs present, and the release medium. In macaques, serum concentrations of both microbicides were maintained between 101–102 pg/mL. Vaginal fluid levels ranged between 103–104 ng/g and 104–105 ng/g for dapivirine and darunavir, respectively. Tissue concentrations ranges for each drug were: vagina (1.8×103–3.8×103 ng/g) > cervix (9.4×101–3.9×102 ng/g) > uterus (0–108 ng/g) > rectum (0–40 ng/g). Measured IC50 values were > 2 ng/mL for both compounds.

Conclusions: Based on these results, and in light of recent clinical progress of the 25mg dapivirine ring, a combination vaginal ring containing dapivirine and darunavir is a viable second-generation HIV microbicide candidate.

Electrical conductivity and glass formation in nitrile-functionalized pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids: chain length and odd–even effects of the alkyl spacer between the pyrrolidinium ring and the nitrile group

The electrical conductivity of a series of pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids, functionalized with a nitrile (cyano) group at the end of an alkyl chain attached to the cation, was studied in the temperature range between 173 K and 393 K. The glass formation of the ionic liquids is influenced by the length of the alkyl spacer separating the nitrile function from the pyrrolidinium ring. The electrical conductivity and the viscosity do not show a monotonic dependence on the alkyl spacer length, but rather an odd-even effect. An explanation for this behavior is given, including the potential energy landscape picture for the glass transition.

Development of a Temperature-Recording Vaginal Ring for Monitoring User Adherence

Background: Vaginal ring devices are being actively developed for controlled delivery of HIV microbicides and as multi-purpose prevention technology (MPT) products combining hormonal contraception with prevention of HIV and other sexually transmitted diseases. Presently, there is no reliable method for monitoring user adherence in HIV vaginal ring trials; previous acceptability studies have included some type of participant self-reporting mechanism, which have often been unreliable. More objective, quantitative and accurate methods for assessing adherence are needed.
Methods: A silicone elastomer vaginal ring containing an encapsulated miniature temperature recording device has been developed that can capture and store real-time temperature data during the period of designated use. Devices were tested in both simulated vaginal environments and following vaginal placement in cynomolgus macaques. Various use protocols and data sampling rates were tested to simulate typical patient usage scenarios. Results: The temperature logging devices accurately recorded vaginal temperature in macaques, clearly showing the regular diurnal temperature cycle. When environmental temperature and vaginal temperature was significantly different, the device was able to accurately pinpoint the insertion and removal times. Based on the data collected it was possible to infer removal periods as short as 5 min when the external environmental temperature was 25 °C. Accuracy increased with data sampling rate. Conclusions: This work provides proof-of-concept for monitoring adherence using a vaginal ring device containing an encapsulated temperature logger. The addition of one or more active agents into the ring body is not anticipated to affect the temperature monitoring function. A clinical study to compare self- reported user adherence data with that obtained by the device would be highly informative.

A Combination Vaginal Ring Releasing Dapivirine and Darunavir

Background: Combination microbicide vaginal rings, containing two or more antiretrovirals targeting different steps in the HIV replicative process, may be more effective than single microbicide products at preventing sexual transmission of HIV. Here, we report the preclinical development, including in vitro release and macaque pharmacokinetics, of matrix-type silicone elastomer rings containing dapivirine (DPV; an experimental non-nucleoside reverse transcriptase inhibitor) and darunavir (DRV; a marketed protease inhibitor). Methods: Macaque rings containing 25 mg DPV, 300 mg DRV and 100 mg DPV, and 300 mg DRV were manufactured and characterised by differential scanning calorimetry. In vitro release was assessed into isopropanol/water and simulated vaginal fluid. Macaque vaginal fluid and blood serum concentrations for both antiretrovirals were measured during 28-day ring use. Tissue levels were measured on day 28. Ex vivo challenge studies were performed on vaginal fluid samples and IC50 values calculated.
Results: DRV caused a concentration-dependent reduction in the DPV melting temperature in both solid drug mixes and in the combination ring. In vitro release from rings was dependent on drug loading, the number of drugs present, and the release medium. In macaques, serum concentrations of both
microbicides were maintained between 101-102 pg/mL. Vaginal fluid levels
ranged between 103-104 ng/g and 104-105 ng/g for DPV and DRV, respectively. Vaginal tissue concentrations decreased in rank order: vagina
(1.8×103-3.8×103 ng/g) > cervix (9.4×101-3.9×102 ng/g) > uterus (0-108 ng/g) > rectum (0-40 ng/g). Measured IC50 values (HIV-1 BaL) determined from macaque vaginal fluid samples were < 2 ng/mL for both compounds. Conclusions: Based on these results, and in light of the ongoing clinical progress of the 25mg DPV ring, a combination vaginal ring containing DPV and DRV is a viable second-generation HIV microbicide candidate.