Antibacterial coatings on haemodialysis catheters by photochemical deposition of silver nanoparticles.

Antibacterial coatings on catheters for acute dialysis were obtained by an innovative and patented silver deposition technique based on the photo-reduction of the silver solution on the surface of catheter, with consequent formation of antibacterial silver nanoparticles. Aim of this work is the structural and morphological characterization of these medical devices in order to analyze the distribution and the size of clusters on the polymeric surface, and to verify the antibacterial capability of the devices treated by this technique against bacterial proliferation. The structure and morphology of the silver nanoparticles were investigated by using scanning and transmission electron microscopy. The antimicrobial capability of the catheters after silver deposition was confirmed by antibacterial tests with Escherichia coli. Both scanning electron microscopy analysis and antibacterial tests were performed also after washing catheters for 30 days in deionized water at 37°C, relating these data to thermogravimetric analysis and to energy dispersive spectroscopy, in order to check the resistance of coating and its antimicrobial capability after the maximum time of life of these devices.

Characterization of antibacterial silver coated yarns.

Surface treatments of textile fibers and fabrics significantly increase their performances for specific biomedical applications. Nowadays, silver is the most used antibacterial agent with a number of advantages. Among them, it is worth to note the high degree of biocompatibility, an excellent resistance to sterilization conditions, antibacterial properties with respect to different bacteria associated with a long-term of antibacterial efficiency. However, there are only a few antibacterial fibres available, mainly synthetic with high production cost and limited effectiveness. Cotton yarns with antimicrobial properties are most suitable for wound healing applications and other medical treatments thanks to their excellent moisture absorbance while synthetic based fibres are most suitable for industrial applications such as automotive tapestry and air filters. The silver-coated fibers were developed applying an innovative and low cost silver deposition technique for natural and synthetic fibers or yarns. The structure and morphology of the silver nanoclusters on the fibers was observed by scanning electron microscopy (SEM), atomic force microscopy analysis (AFM) and XRD analysis, and quantitatively confirmed by thermogravimetric analysis (TGA) measurements. Good silver coating stability has been confirmed performing several industrial washing. Antimicrobial tests with Escherichia coli were performed.

Collagen- and gelatine-based films sealing vascular prostheses: evaluation of the degree of crosslinking for optimal blood impermeability.

The stiffness as well as the biodegradation rate of collagen and gelatine products can be modulated by performing a number of crosslinking treatments. In many biomedical applications, an optimal degree of crosslinking seems to exist, depending on the mechanical and/or biosynthesis properties of the host site. The aim of this study was to evaluate the optimal degree of crosslinking of collagen and gelatine films, to be used as sealants for vascular prostheses. Various crosslinking treatments, including exposure to aldehydes, dehydrothemal treatment, carbodiimide crosslinking and combinations of them, were performed on collagen and gelatine films, and the resulting increases in stiffness, degree of crosslinking and denaturation temperature were evaluated. Analogue crosslinking treatments were also performed on sealed prostheses, which were then tested for blood leakage. The experimental results showed that a good blood impermeability of both collagen and gelatine films was obtained for crosslinking density of about 1.2-1.3 x 10(-5) mol/cm(3), which could be yielded by a dehydrothermal crosslinking treatment (DHT). In particular, dehydrothermally treated gelatine-coated prostheses were found to perform better than analogue collagen-coated ones. The presence of glycerol in crosslinked collagen films was found to have plasticizing effects, which are likely to facilitate blood impermeability, and to increase the thermal stability of collagen.

Use of steel fibres recovered from waste tyres as reinforcement in concrete: pull-out behaviour, compressive and flexural strength.

The increasing amount of waste tyres worldwide makes the disposition of tyres a relevant problem to be solved. In the last years over three million tons of waste tyres were generated in the EU states [ETRA, 2006. Tyre Technology International - Trends in Tyre Recycling. http://www.etra-eu.org]; most of them were disposed into landfills. Since the European Union Landfill Directive (EU Landfill, 1999) aims to significantly reduce the landfill disposal of waste tyres, the development of new markets for the tyres becomes fundamental. Recently some research has been devoted to the use of granulated rubber and steel fibres recovered from waste tyres in concrete. In particular, the concrete obtained by adding recycled steel fibres evidenced a satisfactory improvement of the fragile matrix, mostly in terms of toughness and post-cracking behaviour. As a consequence RSFRC (recycled steel fibres reinforced concrete) appears a promising candidate for both structural and non-structural applications. Within this context a research project was undertaken at the University of Salento (Italy) aiming to investigate the mechanical behaviour of concrete reinforced with RSF (recycled steel fibres) recovered from waste tyres by a mechanical process. In the present paper results obtained by the experimental work performed up to now are reported. In order to evaluate the concrete-fibres bond characteristics and to determine the critical fibre length, pull-out tests were initially carried out. Furthermore compressive strength of concrete was evaluated for different volume ratios of added RSF and flexural tests were performed to analyze the post-cracking behaviour of RSFRC. For comparison purposes, samples reinforced with industrial steel fibres (ISF) were also considered. Satisfactory results were obtained regarding the bond between recycled steel fibres and concrete; on the other hand compressive strength of concrete seems unaffected by the presence of fibres despite their irregular geometric properties. Finally, flexural tests furnished in some cases results comparable to those obtained when using ISF as concerns the post-cracking behaviour.

Modeling spiking activity of in vitro neuronal networks through non linear methods.

Neuroscience research is even more exploiting technologies developed for electronic engineering use: this is the case of Micro-Electrode Array (MEA) technology, an instrumentation which is able to acquire in vitro neuron spiking activity from a finite number of channels. In this work we present three models of synaptic neuronal network connections, called 'Full-Connected', 'Hierarchical' and 'Closed-Path'. Related to each one we implemented an index giving quantitative measures of similarity and of statistical dependence among neuron activities recorded in different MEA channels. They are based on Information Theory techniques as Mutual and Multi Information: the last one extending the pair-wise information to higher-order connections on the entire MEA neuronal network. We calculated indexes for each model in order to test the presence of self-synchronization among neurons evolving in time, in response to external stimuli such as the application of chemical neuron-inhibitors. The availability of such different models helps us to investigate also how much the synaptic connections are spatially sparse or hierarchically structured and finally how much of the information exchanged on the neuronal network is regulated by higher-order correlations.

Non linear methods estimating neural network behavior on Micro-Electrode Array technology.

In the recent years Neuroscience research is exploiting technologies initially developed only for electronic engineering use: this is the case of Micro-Electrode Array (MEA) technology, where a finite number of channels acquires in vitro neural spiking activity. In this work we present a new method to process time data series from MEA trough an ad-hoc software-framework. Our aim is to build a classifier giving quantitative measures of similarity and statistical dependence among neurons activities recorded in different MEA channels. Methods applied to extract specific information about neuronal behavior are Mutual Information and Dynamic Time Warping. In order to extend the pair-wise information so obtained to the entire neuronal networks on MEA, we have chosen to implement a sub-optimal criterion thanks to Genetic Algorithms (GA): this technique support us to sort MEA channels based on dependent activity, thus providing a global index. We applied it to test the presence of self-synchronization among neurons, which can evolve in time and adapt their self in response to specific external stimuli, such as those of the chemical neuron-inhibitors here analyzed.

Synthesis and characterization of macroporous poly(ethylene glycol)-based hydrogels for tissue engineering application.

Peptide activated poly(ethylene glycol) (PEG)-based hydrogels have received wide attention as material for tissue engineering application. However, the close structure of these materials may pose severe barriers to tissue invasion and nutrient transport. The aim of this work was to synthesize highly interconnected macroporous PEG hydrogels, suitable for use as tissue engineering scaffolds, by combining the photocrosslinking reaction with a foaming process. In particular, various porous samples, differing for both the polymer molecular weight and concentration in the starting precursor solution, have been prepared and characterized by means of scanning electron microscopy and mercury porosimetry. Moreover, water swelling properties have been evaluated and compared with those of the conventional nonporous ones, by performing both equilibrium and kinetic swelling measurements in distilled water. Results indicated that foamed hydrogels display a well-interconnected porous network, suitable for tissue invasion and free molecular trafficking within them. Pores dimension as well as swelling rate can be modulated by polymer concentrations and bubbling agent composition in the precursor solution.

Polymeric meshes for internal sutures with differentiated adhesion on the two sides.

The aim of this work is to investigate the effects of different plasma treatments on ePTFE abdominal prostheses with the final goal of obtaining a new prosthesis, made of a single strand of ePTFE, with clearly differentiated adhesion properties on the two sides, which should be able to promote tissue ingrowth on one side and prevent post surgical visceral adhesions on the other. Samples obtained from ePTFE Bard Dulex Meshes have been treated sequentially with three different gases (N(2), O(2) and NH(3)) in order to choose the optimal treatment conditions to improve ePTFE wettability. In particular, no modification was induced by N(2) treatment, while the full treatment after the final ammonia gas resulted in the best suitable candidate. As demonstrated by scanning electron microscopy, AFM analyses and contact angle measurements, ammonia plasma treatment increases ePTFE surface roughness and renders it more hydrophilic, thus promoting adhesion without any alteration of the material's bulk properties. The reported results also evidence the possibility to obtain the maximum wettability with a cheap treatment by optimizing plasma exposure time. As a preliminary cell adhesion study, Swiss 3T3 fibroblasts (mouse, embryo) have been seeded on the treated and untreated materials in order to assess whether there was any difference in terms of cell attachment and spreading. Cells seeded on the ammonia plasma treated material showed a better adhesion and spreading when compared to the untreated material.

Cellulose derivative-hyaluronic acid-based microporous hydrogels cross-linked through divinyl sulfone (DVS) to modulate equilibrium sorption capacity and network stability.

The aim of this work is to obtain a chemically cross-linked hydrogel from hyaluronic acid and cellulose derivatives that exhibits sensitivity to variation of the composition of the external absorbing medium and an equilibrium sorption capacity higher than a common hyaluronic acid-based hydrogel, in view of its potential use in prevention of postsurgical soft tissue adhesion. This has been achieved by chemical stabilization of hyaluronic acid (HA) and cellulose derivatives, hydroxyethylcellulose (HEC) and carboxymethylcellulose (CMCNa) through the difunctional cross-linker divinyl sulfone. Significant increase in sorption capacity, both in water and in water solutions at different ionic strength, has been observed for these samples in comparison with hydrogels obtained through chemical stabilization of hyaluronic acid. Moreover, different dehydration procedures adopted for the xerogel synthesis have been used, which resulted in a modulation of the equilibrium sorption capacity. Hyaluronic acid stability has been confirmed by means of NMR analysis.

Characterization of the kinetic behavior of resin modified glass-ionomer cements by DSC, TMA and ultrasonic wave propagation.

In this study the isothermal kinetic behavior of two resin modified glass ionomer cements (RMGIC) and a dental composite have been compared by differential scanning calorimetry (DSC) and thermo-mechanical analysis (TMA). The simultaneous evolution of the multiple reactions occurring in RMGIC has been analyzed not only by DSC and TMA but also by ultrasonic wave propagation using the pulse-echo technique. The propagation of ultrasonic waves, acting as a dynamic mechanical deformation at high frequencies, is proportional to the longitudinal bulk moduli of the material and may be used to measure the changes of mechanical properties induced by a chemical reaction as occurs in RMGIC. TMA and ultrasonic analysis have been used to monitor the acid-base reaction of RMGIC in dark conditions. Moreover an RMGIC presenting a double reactive mechanism in dark conditions, a thermally activated radical polymerization and an acid-base reaction are studied using these experimental techniques. Finally DSC and TMA results obtained during photopolymerization of an RMGIC and of a dental composite have been compared.

In-situ polymerization behaviour of bone cements.

The polymerization behaviour of bone cements during total hip replacements is characterized by a fast and highly non-isothermal bulk reaction. In the first part of this paper the reaction kinetics are analysed by calorimetric analysis in order to determine the rates of polymerization in isothermal and non-isothermal conditions. A phenomenological kinetic model, accounting for the effects of autoacceleration and vitrification, is presented. This model, integrated with an energy balance, is capable of predicting the temperature across the prosthesis, the cement and the bone and the degree of reaction in the cement, during in situ polymerization. The temperature and the degree of reaction profiles are calculated, as a function of the setting time, taking into account the system geometry, the thermal diffusivity of bone, prosthesis and cement, and the heat rate generated by the reaction according to the kinetic model. Material properties, boundary and initial conditions are the input data of the heat transfer model. Kinetic and heat transfer models are coupled and a numerical solution method is used. The model is applied in order to study the effects of different application procedures on temperature and degree of reaction profiles across the bone-cement-prosthesis system.

Photopolymerization of dental composite matrices.

The kinetic behaviour of dental composite is traditionally studied, considering only the isothermal behaviour, whereas a fast and highly non-isothermal bulk polymerization is expected as a consequence of the significant heat developed due to the exothermic nature of the polymerization reaction. In this paper the photopolymerization kinetics of a commercial dental composite activated by visible light are analysed by differential scanning calorimetry. This technique is applied to determine the degree of reaction and the glass transition temperature of thin layers of the composite matrix, at different isothermal cure temperatures. A phenomenological kinetic model is then integrated with an energy balance in order to analyse the cure behaviour of thicker composite layers. The full model results indicate that non-isothermal cure conditions may be achieved, obtaining higher values for the glass transition temperature and the degree of reaction.