A proposed model membrane and test method for microneedle insertion studies

A commercial polymeric film (Parafilm M (R), a blend of a hydrocarbon wax and a polyolefin) was evaluated as a model membrane for microneedle (MN) insertion studies. Polymeric MN arrays were inserted into Parafilm M (R) (PF) and also into excised neonatal porcine skin. Parafilm M (R) was folded before the insertions to closely approximate thickness of the excised skin. Insertion depths were evaluated using optical coherence tomography (OCT) using either a force applied by a Texture Analyser or by a group of human volunteers. The obtained insertion depths were, in general, slightly lower, especially for higher forces, for PF than for skin. However, this difference was not a large, being less than the 10% of the needle length. Therefore, all these data indicate that this model membrane could be a good alternative to biological tissue for MN insertion studies. As an alternative method to OCT, light microscopy was used to evaluate the insertion depths of MN in the model membrane. This provided a rapid, simple method to compare different MN formulations. The use of Parafilm M (R), in conjunction with a standardised force/time profile applied by a Texture Analyser, could provide the basis for a rapid MN quality control test suitable for in-process use. It could also be used as a comparative test of insertion efficiency between candidate MN formulations. 

Membrane fission is promoted by insertion of amphipathic helices and is restricted by crescent BAR domains

Shallow hydrophobic insertions and crescent-shaped BAR scaffolds promote membrane curvature. Here, we investigate membrane fission by shallow hydrophobic insertions quantitatively and mechanistically. We provide evidence that membrane insertion of the ENTH domain of epsin leads to liposome vesiculation, and that epsin is required for clathrin-coated vesicle budding in cells. We also show that BAR-domain scaffolds from endophilin, amphiphysin, GRAF, and β2-centaurin limit membrane fission driven by hydrophobic insertions. A quantitative assay for vesiculation reveals an antagonistic relationship between amphipathic helices and scaffolds of N-BAR domains in fission. The extent of vesiculation by these proteins and vesicle size depend on the number and length of amphipathic helices per BAR domain, in accord with theoretical considerations. This fission mechanism gives a new framework for understanding membrane scission in the absence of mechanoenzymes such as dynamin and suggests how Arf and Sar proteins work in vesicle scission.

Toward A Reliable Quality Control Test For Microneedle Insertion

Microneedles (MNs) are emerging devices that can be used for the delivery of drugs at specific locations1. Their performance is primarily judged by different features and the penetration through tissue is one of the most important aspects to evaluate. For detailed studies of MN performance different kind of in-vitro, exvivo and in-vivo tests should be performed. The main limitation of some of these tests is that biological tissue is too heterogeneous, unstable and difficult to obtain. In addition the use of biological materials sometimes present legal issues. There are many studies dealing with artificial membranes for drug diffusion2, but studies of artificial membranes for Microneedle mechanical characterization are scarce3. In order to overcome these limitations we have developed tests using synthetic polymeric membranes instead of biological tissue. The selected artificial membrane is homogeneous, stable, and readily available. This material is mainly composed of a roughly equal blend of a hydrocarbon wax and a polyolefin and it is commercially available under the brand name Parafilm®. The insertion of different kind of MN arrays prepared from crosslinked polymers were performed using this membrane and correlated with the insertion of the MN arrays in ex-vivo neonatal porcine skin. The insertion depth of the MNs was evaluated using Optical coherence tomography (OCT). The implementation of MN transdermal patches in the market can be improved by make this product user-friendly and easy to use. Therefore, manual insertion is preferred to other kind of procedures. Consequently, the insertion studies were performed in neonatal porcine skin and the artificial membrane using a manual insertion force applied by human volunteers. The insertion studies using manual forces correlated very well with the same studies performed with a Texture Analyzer equipment. These synthetic membranes seem to mimic closely the mechanical properties of the skin for the insertion of MNs using different methods of insertion. In conclusion, this artificial membrane substrate offers a valid alternative to biological tissue for the testing of MN insertion and can be a good candidate for developing a reliable quality control MN insertion test.

Controlled release of a model antibacterial drug from a novel self-lubricating silicone biomaterial

Abstract There is considerable interest in developing medical devices that provide controlled delivery of biologically active agents, for example, to reduce the incidence of device-related infection. Silicone elastomers are one of the commonest biomaterials used in medical device production. However, they have a relatively high coefficient of friction and the resulting lack of lubricity can cause pain and tissue damage on device insertion and removal. Novel silicone cross-linking agents have recently been reported that produce inherently ‘self-lubricating’ silicone elastomers with very low coefficients of friction. In this study, the model antibacterial drug metronidazole has been incorporated into these self-lubricating silicone elastomers to produce a novel bioactive biomaterial. The in vitro release characteristics of the bioactive component were evaluated as a function of cross-linker composition and drug loading. Although conventional matrix-type release kinetics were observed for metronidazole from the silicone systems, it was also observed that increasing the concentration of the cross-linking agent responsible for the lubricious character (tetra(oleyloxy)silane) relative to that of the standard non-lubricious cross-linking agent (tetrapropoxysilane) produced an increase in the metronidazole flux rate by up to 65% for a specified drug loading. The results highlight the potential for developing lubricious silicone medical devices with enhanced drug release characteristics.

Self-lubricating silicone elastomer biomaterials

Silicone has a relatively high coefficient of friction and silicone medical devices therefore lack inherent lubricity, leading to pain on device insertion and potential tissue trauma. In this study, higher molecular weight tetra(alkoxy) silanes, particularly tetra(oleyloxy) silane, have been used as crosslinkers in the condensation cure of a hydroxy end-functionalised linear poly(dimethylsiloxane). The resulting elastomers displayed a persistent lubricous surface of oleyl alcohol, and coefficients of friction (static and dynamic) approaching zero. Chemical structures of the synthesised silanes and surface alcohol exudate were confirmed by nuclear magnetic resonance spectroscopy. Mechanical properties of the elastomers, which were chemically identical to conventionally cured systems, suggested that an 80/20 mixture of tetra(oleyloxy) silane and tetra(propoxysilane) gave the best compromise between desirable mechanical and frictional properties.

Is there an association between angiotensin-converting enzyme gene variants and chronic nonproductive cough?

Background: It is unclear why some patients develop a chronic nonproductive cough. Angiotensin-converting enzyme (ACE) inactivates tussive peptides in the airways such as bradykinin and tachykinins. An insertion/deletion polymorphism in the ACE gene accounts for variation in ACE levels, and patients with the II genotype have lowest serum ACE levels compared with ID and DD genotypes. We hypothesized that the II genotype would be associated with increased risk of developing a chronic cough.

Materials and methods: We recruited 47 patients (33 women), referred for evaluation of cough (median cough duration, 24 months; range, 2 to 240 months). Cough patients were evaluated using a comprehensive diagnostic protocol, and cough reflex sensitivity was measured using a capsaicin inhalation challenge. ACE genotyping was performed on DNA samples from patients using the polymerase chain reaction followed by agarose gel electrophoresis. ACE genotypes in patients with chronic cough were compared with those in 199 healthy control subjects. Serum ACE levels were determined using a colorimetric assay.

Results: Genotype frequencies for the ACE gene were similar between patients and control subjects. There was no correlation between capsaicin sensitivity and ACE genotypes or serum ACE levels.

Conclusion: Susceptibility to develop chronic cough is not associated with ACE genotype.

Polyploid measles virus with hexameric genome length

Particles of most virus species accurately package a single genome, but there are indications that the pleomorphic particles of parainfluenza viruses incorporate multiple genomes. We characterized a stable measles virus mutant that efficiently packages at least two genomes. The first genome is recombinant and codes for a defective attachment protein with an appended domain interfering with fusion-support function. The second has one adenosine insertion in a purine run that interrupts translation of the appended domain and restores function. In that genome, a one base deletion in a different purine run abolishes polymerase synthesis, but restores hexameric genome length, thus ensuring accurate RNA encapsidation, which is necessary for efficient replication. Thus, the two genomes are complementary. The infection kinetics of this mutant indicate that packaging of multiple genomes does not negatively affect growth. We also show that polyploid particles are produced in standard infections at no expense to infectivity. Our results illustrate how the particles of parainfluenza viruses efficiently accommodate cargoes of different volume, and suggest a mechanism by which segmented genomes may have evolved.

Spatial Demultiplexing in the sub-millimeter wave band using multlayer free-standing frequency selective surfaces

In this paper, we show that a multilayer freestanding slot array can be designed to give an insertion loss which is significantly lower than the value obtainable from a conventional dielectric backed printed frequency selective surface (FSS). This increase in filter efficiency is highlighted by comparing the performance of two structures designed to provide frequency selective beamsplitting in the quasioptical feed train of a submillimeter wave space borne radiometer. A two layer substrateless FSS providing more than 20 dB of isolation between the bands 316.5â??325.5 GHz and 349.5â??358.5 GHz, gives an insertion loss of 0.6 dB when the filter is orientated at 45 incidence in the TM plane, whereas the loss exhibited by a conventional printed FSS is in excess of 2 dB. A similar frequency response can be obtained in the TE plane, but here a triple screen structure is required and the conductor loss is shown to be comparable to the absorption loss of a dielectric backed FSS. Experimental devices have been fabricated using a precision micromachining technique. Transmission measurements performed in the range 250â??360 GHz are in good agreement with the simulated spectral performance of the individual periodic screens and the two multilayer freestanding FSS structures.

Micromachined 300GHz high Q resonant slot frequency selective surface filter

The design of a low loss quasi-optical beam splitter which is required to provide efficient diplexing of the bands 316.5-325.5 GHz and 349.5-358.5 GHz is presented. To minimise the filter insertion loss, the chosen architecture is a three-layer freestanding array of dipole slot elements. Floquet modal analysis and finite element method computer models are used to establish the geometry of the periodic structure and to predict its spectral response. Two different micromachining approaches have been employed to fabricate close packed arrays of 460 mm long elements in the screens that form the basic building block of the 30mm diameter multilayer frequency selective surface. Comparisons between simulated and measured transmission coefficients for the individual dichroic surfaces are used to determine the accuracy of the computer models and to confirm the suitability of the fabrication methods.

Detection of the icaADBC gene cluster and biofilm formation in Staphylococcus epidermidis isolates from catheter-related urinary tract infections.

Cho SH, Naber K, Hacker J, Ziebuhr W. Institut für Molekulare Infektionsbiologie, Röntgenring 11, D-97070 Würzburg, Germany. Biofilm production in Staphylococcus epidermidis is an important virulence factor that is mediated by the expression of the icaADBC operon. In this study 41 S. epidermidis isolates obtained from catheter-related urinary tract infections were analyzed for the presence of the icaADBC operon and biofilm formation. Eighteen of 41 isolates (44%) were shown to carry ica-specific DNA, but only 11 isolates (27%) produced biofilms spontaneously under normal growth conditions. Upon induction by external stress or antibiotics, biofilm formation could be stimulated in five of seven ica-positive, biofilm-negative isolates, indicating that the icaADBC expression was down-regulated in these strains. Genetic analyses of the ica gene clusters of the remaining two ica-positive, biofilm-negative strains revealed a spontaneous ICAC::IS256 insertion in one strain. Insertion of the element caused a target site duplication of seven base pairs and a biofilm-negative phenotype. After repeated passages the insertion mutant was able to revert to a biofilm-forming phenotype which was due to the precise excision of IS256 from the icaC gene. The data show that icaC::IS256 integrations occur during S. epidermidis polymer-related infections and the results highlight the biological relevance of the IS256-mediated phase variation of biofilm production in S. epidermidis during an infection.

Polarisation independent bandpass FSS

The spectral transmittance of a frequency selective surface (FSS), which consists of two free-standing arrays of short-circuited nested annular slots, is presented. The FSS was designed to provide a minimum of 20 dB isolation between the frequency bands 316.5-325.5 and 349.5-358.5 GHz when the filter operates in the TE and TM planes at 45 degrees incidence. Experimental results, which are in close agreement with the computed transmission coefficients, show that the maximum insertion loss is 0.9 dB, and the minimum cross-polar discrimination is at least 21 dB in the passbands. The FSS yields virtually identical spectral responses in the two polarisation planes over the frequency range 315-359 GHz.

Liquid crystal tunable mm wave frequency selective surface

A frequency selective surface (FSS) which exploits the dielectric anisotropy of liquid crystals to generate an electronically tunable bandpass filter response at D Band (110-170 GHz) is presented. The device consists of two printed arrays of slot elements which are separated by a 130-mu m thick layer of liquid crystals. A 3% shift in the filter passband occurs when the substrate permittivity is increased by applying a control signal of 10 V. Measured results show that the insertion loss increases from -3.7 dB to -10.4 dB at resonance (134 GHz), thus demonstrating the potential to create a FSS which can be switched between a transmitting and a reflecting structure.

Single sideband FSS with high image rejection

The design of a quasi-optical single sideband filter, which provides more than 30 dB of isolation between the frequency bands 294-305.5 and 329.5-341.5 GHz in the TM plane at 45 degrees incidence, is described. The structure, which consists of three free-standing arrays of dipole slot elements, generates a bandpass spectral response with an insertion loss below 0.5 dB at resonance. Simulated and measured transmission coefficients in the range 250-400 GHz are shown to be in good agreement.