Silicone based polyurethane materials: a promising biocompatible elastomeric formulation for cardiovascular applications

The biocompatibility of a new material for cardiovascular applications constituted by a poly(ether)urethane (PEtU) and a silicone [polydimethylsiloxane (PDMS)] was evaluated. The achieved material shows properties similar to both polyurethanes and silicones. The material was transformed into porous membranes by a spray-deposition technique. Since any material preparation and manufacturing procedure may introduce some toxicity, in vitro cytotoxicity screening tests were carried out. Human umbilical vein endothelial cells (HUVECs) and a mouse fibroblasts cell line (L929) were cultivated with extracts obtained from materials containing 10, 40 and 100% (w/w) of PDMS. The commercially available Estane 5714-F1 and Cardiothane 51 were used as controls. Extracts were incubated up to 72 hours with HUVECs and L929 cells. The cytotoxic effect was evaluated by light microscopy, cell viability (MTT reduction and neutral red uptake) and proliferation (5-bromo-2'-deoxyuridine incorporation) tests. In vivo studies were carried out using materials containing the same PDMS percentages as for in vitro experiments. The same commercial controls were used. Results obtained with cell culture studies agreed with those obtained in the in vivo experiments and showed that the material preparation and manufacturing procedure do not introduce any toxicity in the products at each PDMS concentration investigated.     

Novel photonic recursive signal processor with reduced phase-induced intensity noise

A new technique to reduce the dominant phase-induced intensity noise (PIIN) in active high-Q recursive photonic signal processors is presented. This is based on using cross-gain-modulation effects in a semiconductor optical amplifier in the recursive loop of the processor. Two different laser sources are used, and no recombination of the optical power from the same laser source occurs in the optical domain, hence, PIIN generation is suppressed. The processor structure also features the advantage that it does not require an incoherent light source. Hence, the free spectral range of the processor is not limited by the coherence of the laser source, as in existing incoherent approaches. Experimental results for the new processor demonstrate a more-than-30-dB reduction in PIIN level for a high-Q bandpass filter, compared to the conventional approach for the same filtering parameters.     

Utilization of solar earth-water stills for desalination of groundwater

Three solar earth-water stills of single-sloped type, designed for producing drinking water in remote areas, have been investigated. These stills were installed over an insulated hole, a hole with insulated base, and a hole with insulated walls. Multiple linear regression equations, relating to ambient air temperature, wind speed, and solar radiation, were developed to estimate the productivity of these stills. The study showed that condensation process inside these stills is achieved during the period between sunset and sunrise. Results showed also that the average wall's contribution in supplying fresh water is about 56%, whereas base contribution is about 31%. It is concluded, therefore, that setting many stills on a number of separated holes will give higher output rather than setting a single still on one large hole of the same volume.     

Optimization of wavelength tuning of erbium-doped fiber ring lasers

The dynamics of erbium-doped fiber ring lasers undergoing wavelength tuning is examined. The relaxation oscillations and mode build-up time are characterized. An all-optical damping technique which is capable of complete elimination of relaxation oscillations is analyzed, and measurements on a tunable erbium-doped fiber lasers are reported. An analytical solution is derived for the mode build-up time of tunable fiber lasers. Limiting parameters for the design of a high-speed tunable fiber laser are identified. An equalization technique for obtaining uniform switching speed is described     

Theoretical Study of the Depolymerization of Starch under the Combined Action of Protons and Gamma Radiation

A theoretical study of the depolymerization of starch under the combined action of protons and gamma radiation is proposed. It allows prediction of the variations of the average degree of polymerization and the mass of water-soluble products of the sample as a function of the parameters of the treatment and the characteristics of the starch; the main interest of this combined treatment is to allow independent variations of these two values.     

Light microscopy evaluation of polyurethane vascular grafts porosity by Sudan Black B staining

In small‐diameter vascular grafts, the porosity of the internal surface plays an important role because it affects initial thrombus deposition and therefore the graft’s patency. As well as many other studies reported in the literature we have carried out a study of the relationship between porosity and the manufacturing parameters of polyurethane (PU) grafts by standard scanning electron microscopy (SEM) analysis. However, SEM was not completely satisfactory for evaluating the ‘sponge‐like’ uptake of water by the graft due to the unavoidable water loss and metal coating during preparation. In fact this preparation produces artefacts of the three‐dimensional porous structure. To avoid this problem we investigated the possibility of observing the graft’s internal surface through a stereomicroscope after it had absorbed water. We looked into a simple staining procedure which preferentially colours the PU graft fibres with respect to the void areas. After testing different kinds of stains, we eventually found that Sudan Black B, which usually stains for all kinds of lipid, turned out to be an excellent stain for the water‐loaded PU grafts when diluted with ethanol. This staining procedure, coupled with a computerized image analysis system, allowed us to evaluate the degree of void and average void size of the graft internal surface and to correlate these data with graft density and manufacturing parameters.     

Biomechanical pathology of the upper limb: a new epidemic?

Work-related upper limb disorders are one leading occupational diseases in many industrialized countries. The paper reviews the evidence of work-relatedness of the most common upper limb disorders (namely carpal tunnel syndrome, hand-wrist and shoulder tendinitis, trapezius myalgia, hand hammer syndrome). Attention is drawn to the difference in the number of reported cases in Italy and other countries, assuming, as an underlying cause, underreporting of such conditions in Italy.     

Opportunistic infections occurring during highly active antiretroviral treatment

OBJECTIVE: To analyse the characteristics of opportunistic infections in patients receiving highly active antiretroviral treatment (HAART). DESIGN AND METHODS: A retrospective study performed in seven hospitals, included all patients starting treatment by ritonavir or indinavir between 26 March and 31 December 1996. Patients were evaluated for the development of AIDS-defining events. Clinical evaluation, plasma HIV-1 RNA quantification, CD4 cell count were recorded at baseline and at the onset of the event. RESULTS: Four hundred and eighty-six patients were included: 44.2% had a CD4 cell count below 50 x 10(6) cells/l. Fifty clinical events were recorded in 46 patients with a mean follow-up of 6.1 months, of which 34 events (68%) were observed during the first 2 months of HAART. Eighteen of these occurred despite a reduction of viral load by at least 1.5 log10) and a 100% increase of the CD4 cell count compared with that at the onset of the event, corresponding to 11 cytomegalovirus infections, five mycobacterial infections, one case of cryptococcosis, and one case of Varicella-Zoster virus-related acute retinal necrosis. Among the 16 events observed after the second month, six occurred despite a marked biological improvement, corresponding to a recurrence in five of six patients who had stopped their maintenance therapy. Events were one cytomegalovirus infection, two mycobacterial infections, one episode of oesophageal candidiasis and one cryptococcal meningitis. CONCLUSION: In patients at high risk of developing an opportunistic infection prior to the institution of a HAART regimen, prophylaxis should not be discontinued during the first 2 months of treatment, and maintenance therapy should be carried on despite a significant increase in the CD4 cell count.     

Analysis of intermodulation distortion in GaAs m.e.s.f.e.t. amplifiers

Intermodulation distortion generated in a m.e.s.f.e.t. amplifier is analysed using a Volterra series representation. The transistor model used enables direct analytical determination of the nonlinear elements from small signal measurements. Experimental verification comparing predicted and measured second-and third-order intermodulation products in the amplifer is presented.