Immobilization of cationic rifampicin-loaded liposomes on polystyrene for drug-delivery applications.

Polymer-associated infections are a major problem in implanted or intravascular devices. Among others, microorganisms of the staphylococcal family have been identified as the most important culprit. Prevention of bacterial adhesion and colonization of polymeric surfaces by release of antimicrobial agents incorporated into the polymers itself are currently under study. We have developed a novel method for the functionalization of a polymeric surface which is based on the deposition of covalently coupled lipid structures from antibiotic loaded vesicles. We have found that such process significantly reduces the bacterial growth on polystyrene material. In this work, lipid coverage obtained from multilamellar (MLVs) and extruded unilamellar (LUVs) vesicles were analyzed with respect to their adhesion efficiency on three types of polystyrene (PS) well-plates. Two methods of lipid deposition were characterized and compared in terms of surface lipid density and time stability: deposition of cationic vesicles on negatively charged surfaces and formation of covalent linkages between functionalized lipids and amines enriched surfaces. In order to study the antibiotic encapsulation efficiency we measured how the rifampicin (RIF) loading was affected by changes of liposome charge upon introduction of various amounts of stearylamine (SA), distearoyl-trimethylammonium propane (DSTAP) or dioleoyloxypropyl-trimethylammonium chloride (DOTAP) into the liposomal formulation. RIF-coated polymeric surfaces were also tested against a Staphylococcus epidermidis strain to evaluate their efficacy in vitro, showing that only approximately 2% of such bacteria inoculated on MLV-treated PS substrate were able to proliferate. Covalently immobilized lipid films showed about a tenfold increase in time stability compared to electrostatically bonded lipid films. Furthermore, substrates covalently modified with RIF-loaded MLVs retained an antibacterial activity for up to 12 days when aged in buffer at 37 degrees C. Such antimicrobial polymer coatings show promise for their use as antibacterial barrier for the prevention of catheter-related infections.

Covalent interaction and semiempirical modeling of small molecules.

The use of sophisticated methods for modeling complex systems is gaining ever more importance recently because they allow the design of material with properties tailored to specific applications. However, problems may arise from conflicts between different reaction pathways inherent in the wide variety of chemical elements used. This is reflected by the impossibility of exactly solving the Schroedinger equation or of exactly describing the exchange interaction in density functional theory when the system complexity increases. An alternative is offered by the application of semiempirical methods because they strongly reduce system complexity. Normally, this is accomplished by increasing the degree of the approximations to the detriment of the formalism generality. This work is aimed to improve the semiempirical electronegativity equalization method. This is accomplished by modifying the point charge Madelung potential with the introduction of covalent interaction to better describe the chemical bonds.

Production and characterization of thin a-C:(H) films for gas permeation barrier functionality against He, CO(2), N(2), O(2) and H(2)O.

This work reports on (i) the gas barrier properties of a-C:H films rf-sputtered in Ar-H(2) plasmas from a graphite target on polyethylene terephthalate (PET) and (ii) the influence of the film chemical structure and defect properties on the gas permeability. The intrinsic permeabilities of the films to He, CO(2), O(2), N(2) gases and H(2)O vapour were determined and found to be orders of magnitude lower than that of the bare PET. Indirect evidence was given to a solubility-diffusion process as the more probable permeation mechanism, over a gas flow through microdefects or gas transport through nanodefects by a Knudsen diffusion mechanism. The barrier capability of the films was found to scale as the gas molecular diameter within the He, CO(2), O(2) and N(2) series, and inversely with the gas critical temperature for the CO(2), O(2), N(2) and H(2)O series. A correlation between the film Urbach energy, E(u), and the gas permeability was established, except for H(2)O. Such findings further favour a bulk diffusion contributing mechanism to permeation over the gas state transport. Conversely, this E(u)-permeability relation shed more light on the origin of the valence band tailing of the amorphous carbon electron structure.

Role of chemical interactions in bacterial adhesion to polymer surfaces.

Development of biomaterial-related infections is attracting an increasing interest due to the significant percentage of implant failure in the hospital care. Recent literature puts in evidence the dependence of the infection risk on the different biomaterials used, because of the different interactions between material surface and micro-organisms. Despite this, the mechanisms underlying the adhesion of bacteria to the biomaterial surface are still unclear. Aim of this work is to study the initial events of the processes responsible for the bacterial adhesion on polymers in order to prevent the development of bacterial infections and the consequent failure and replacement of biomedical devices. Electrostatic and Lifshitz-van der Waals forces are usually considered responsible for the interactions at the biomaterial interface. A new term that involves Lewis acid-base interactions is here introduced to better describe the bacterial adhesion to the polymer surface. Two requirements are needed to test this hypothesis: the development of an ideal polymeric surface in terms of chemical and morphological properties and the choice of a specific bacterial strain to be utilized as "probe". Experiments were worked out using an Escherichia coli (Gram-) strain that represent one of the principal isolates from infected biomaterial implants and its adhesion was investigated on polymers having different acid/basic character. The findings indicate that the bacterial adhesion is influenced by the chemical properties of the polymeric surface. These results may be interpreted taking into account a mechanism in which the acid/base (Lewis) interaction plays an important role.

A double-blind, placebo-controlled study of acetylsalicylic acid (ASA) in trained runners.

Acetylsalicylic acid (ASA) is a short-acting oral inhibitor of the cyclooxygenase enzyme. Ingestion of ASA is associated with a decrease in prostaglandins, including those of the E2 series, as well as prostacyclin, and thromboxane. Consumption of therapeutic doses is associated with decreased pain and inflammation and is therefore used in a variety of inflammatory conditions. Platelet aggregation is also inhibited. Because of these observations, and the fact that platelet aggregation has been noted to be altered during exercise, the effects of ASA on exercise tolerance was of interest. We studied 17 healthy male volunteers who regularly ran as a source of exercise. During the study they ingested either 650 mg of ASA or placebo 30 min before running 2 miles (3.2 km). Outcome of the double-blind crossover study was measured by the time required to run a 2-mile distance. No differences between ASA or placebo were noted in the subjects. These data suggest that 650 mg of ASA as a premedication has little effect on exercise performance in normal endurance runners. However, whether ASA may affect pain after exercise or whether other dosage intervals would be more beneficial needs further study.

Deep venous thrombosis in intravenous cocaine abuse mimicking septic arthritis of the shoulder.

We describe two patients with deep venous thrombosis of the upper extremity who initially were thought to have septic arthritis of the shoulder. These patients had a history of recent intravenous cocaine abuse. The diagnosis of deep venous thrombosis should be considered when a patient with a swollen shoulder has an appropriate history.