Stelian Vlad

Segmented biopolyurethanes for medical applications

Polyurethanes are one of the most popular groups of biomaterials applied for medical devices. Their segmented block copolymeric character endows them a wide range of versatility in terms of tailoring their physical properties, blood and tissue compatibility. Polyester- and polyether-urethanes have been modified with hydroxypropyl cellulose aiming the change of their surface and bulk characteristics to confer them biomaterial qualities. In this respect, dynamic contact angle measurements, dynamic mechanical analyses accompanied by mechanical testing have been done. Platelet adhesion test has been carried out in vitro and the use of hydroxypropyl cellulose in the polyurethane matrix reduces the platelet adhesion and therefore recommends them as candidates for biocompatible materials.

Thermal, dynamic mechanical, and dielectric analyses of some polyurethane biocomposites

Polymer biocomposites based on segmented poly(ester urethane) and extracellular matrix components have been prepared for the development of tissue engineering applications with improved biological characteristics of the materials in contact with blood and tissues for long periods. Thermal, dynamical, and dielectrical analyses were employed to study the molecular dynamics of these materials and the influence of changing the physical network morphology and hydrogen bond interactions accompanied by phase transitions, interfacial effects, and polarization or conductivity. All phenomena that concur in the tested materials are evaluated by cross-examination of the dynamic mechanical characteristic properties (storage modulus, loss modulus, and loss factor) and dielectric properties (relative permittivity, relative loss factor, and loss tangent) as a function of temperature. Comparative aspects were elucidated by calculating the apparent activation energies of multiplex experiments.

Evaluation of polyurethane based on cellulose derivative-ketoprofen biosystem for implant biomedical devices.

A polyether-urethane based on polytetrahydrofuran containing hydroxypropyl cellulose for biomedical applications was tested for its biocompatibility. Ketoprofen was incorporated (3% and 6%) in the polyurethane matrix as an anti-inflammatory drug. Dynamic vapour sorption method was employed for testing the water sorption/desorption behaviour of these materials with the determination of the surface isotherms, surface parameters and the kinetic curves of sorption/desorption processes. Cytotoxicity testing in vitro for quantifying cell proliferation was employed, and the results evidence noncytotoxicity for the studied polyurethane-drug systems. In vivo biocompatibility study was performed on 200 g weight male rats. It was found that after implantation of the polyether-urethane samples a reduced acute inflammation occurred, especially for polyurethane samples with added ketoprofen.

Characteristics of polyurethane-based sustained release membranes for drug delivery

AbstractThis paper is focused on the preparation and physicochemical characterization of two poly(ester ether urethane)s with rifampicin in their matrix and different molar concentrations of urethane groups. The polyurethanes with rifampicin were processed as asymmetrical microporous membranes by a phase inversion method and characterized by attenuated total reflection — Fourier transform infrared (ATR-FTIR) spectroscopy and differential scanning calorimetry (DSC). The influence of the surface morphology in the release of drug compounds was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle, and water uptake. The release of rifampicin depends on the molar concentration of urethane groups and also on the surface morphology of the polyurethane membranes. The antibacterial activity was evaluated with S. Epidermidis RP 62 A and P. Aeruginosa ATCC 1544. Finally, the biocompatibility of the polyurethane membranes was studied with human dermal fibroblasts (HDF) to evaluate the potential biomedical applications.

New polyurethane materials from renewable resources: synthesis and characterization

Abstract In the present study new types of polyurethane-cellulose derivative biomaterials based on urethane prepolymers functionalized with hydroxypropylcellulose are presented. The aim of the present study is to obtain materials with better haemocompatibility, biocompatibility and amphiphilic microphase-separated domain structures. The outcome of remarkable chemical versatility characteristic to polyurethane materials combined with polymers derived from nature like cellulose derivatives resulting in bulk and surface properties is evidenced by means of different techniques like DSC, TGA, FT-IR, AFM and mechanical tensile tests. The influence of various factors on the developed morphologies and the microstructural changes is investigated. Both polyester and polyether macrodiols have been used to prepare these polyurethanes. The aim of this study is to find also alternative methods for improving biostability while maintaining the excellent biocompatibility and other properties.

Polyurethane/β-cyclodextrin/ciprofloxacin composite films for possible medical coatings with antibacterial properties

Polyurethane/β-cyclodextrin/ciprofloxacin composite films have been prepared and structural and morphological behaviours reveal the progressive incorporation of the drug ciprofloxacin into polyurethane backbones. Spectral changes such as frequency shifts, band broadening and changes in the intensity are indicative of drug-polyurethane interactions. X-ray powder diffraction experiments demonstrate that ciprofloxacin retains its crystallinity in the polyurethane matrix. Electron microscopy and mercury porosimetry reveal open and interconnected macroporous pore morphology for the as-prepared polyurethane-drug films. Antimicrobial activity was evaluated by the agar disc diffusion method and the ciprofloxacin-polyurethane films demonstrate their potency as antibacterial medical systems. However, the ciprofloxacin-polyurethane films do not reveal antifungal properties.

Electrospun/electrosprayed polyurethane biomembranes with ciprofloxacin and clove oil extract for urinary devices

Polyurethane–eugenol solutions in N,N-dimethyl formamide were electrospun/electrosprayed onto polyurethane–ciprofloxacin biomembranes to obtain drug delivery systems for urinary devices. Following electrospinning/electrospraying, particle-fiber morphology was evidenced by scanning electronic microscope analysis. Contact angle determinations along with surface free energy calculations, moisture diffusion test, and diffusion coefficient determinations were done for polyurethane–ciprofloxacin biomembranes. Determination of bioactive ciprofloxacin release kinetics evidences non-Fickian/anomalous/diffusion mechanism, coupling Fickian diffusion with the relaxation of the polymeric chains within the matrix network. A slight increase in n values for electrospun/electrosprayed coated samples evidenced a behavior closer to a case II transport mechanism with zero-order kinetics. The biological activity of the electrospun/electrosprayed polyurethane membrane samples tested against Staphylococcus aureus, Sarcina lutea, Bacillus cereus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa showed comparable antibacterial activity with standard ciprofloxacin.

Thermal, mechanical and wettability properties of some branched polyetherurethane elastomers

Abstract In this study three series of polyetherurethanes (PEU) based on Terathane ® (polytetramethyleneetherglycol - PTMEG, Mn 1400) as polyol; isophorone diisocyanate (IPDI), 4,4’-methylene-bis-(cyclohexyl-isocyanate) (HMDI) and hexamethylene diisocyanate (HDI) as aliphatic diisocyanate components; 1,4- butanediol (BD) and glycerin (Gly) as chain extenders were synthesized. The glycerin as triol is responsible for the crosslinking structures. All polyether urethanes were synthesized by prepolymer method. The PTMEG was reacted with diisocyanate to realize a diisocyanate-terminated prepolymer, which in next step was extended with blend of the 1,4-butanediol (BD) and glycerin (Gly) in different proportion. The influence of the diisocyanate structure and chain extender functionality on the thermal, mechanical and wettability properties were the aim of this study. The physical, mechanical and wettability properties of these polymers were measured according to standard methods. All polymers were characterized by conventional characterization methods. Different methods of thermal analysis (TGA and DSC) were used for characterization. Wettability was estimated by determination of the dynamic contact angle. The structures were confirmed by FTIR and H-NMR analysis. The results show that the thermal stability, mechanical and wettability properties of the final products are influenced by the diisocyanate and chain extenders nature.

Chloramphenicol-based poly(ester-ether)urethane bioconjugates with antibacterial properties for biomedical applications

New chloramphenicol-based poly(ester-ether)urethane bioconjugates intended for biomedical applications are presented. Structure–property relationship in the tested biomaterials is established by cross-inspection of the ATR-FTIR investigation, DSC analysis, thermogravimetric analysis, surface morphology characterization, water sorption and/or desorption properties, and antimicrobial efficiency of the obtained polyurethane biomembranes. The estimated values of activation energy for thermal degradation under nitrogen fall between those found for poly(ether urethane)s and poly(ester urethane)s. SEM microphotographs show that the resulted morphologies of polyurethanes are different due to the diverse polyether segments which determine the supramolecular architecture of the self-assembled films. The estimated moisture diffusion coefficients, sorption capacity are dependent on polyurethane network microstructure. The monolayer sorption and average pore size values were estimated by applying BET model. The values of BET area and monolayer capacity are correlated with antibacterial activities. The synthesized biocidal polyurethanes bearing covalently attached chloramphenicol are effective at inactivation of tested bacteria: Sarcina lutea and Escherichia coli.

Poly(alkylene sebacate ether)urethane hydrogels for indomethacin delivery formulations

A series of aliphatic polyurethane hydrogels based on poly(alkylene sebacate) diols was developed by polyaddition reaction. The chemical structures of unloaded and indomethacin-loaded poly(alkylene sebacate ether)urethane hydrogels were characterized using ATR-FT-IR spectroscopy. The aim of this research was to study the influence of the long alkylene chains on the indomethacin release rate. The swelling kinetics was analyzed using power law and second-order equation and it was found that both diffusion and polymer relaxation mechanisms control the overall rate of water uptake. The release mechanism follows the same behavior as swelling, but the interaction of the drug with the hydrophobic matrix influences the release kinetics. The surface properties and the influence of the surface configuration on the indomethacin release kinetics were also investigated using contact angle measurements. The mechanical properties of the dry samples were affected by the crosslinker, while, for the swollen samples, the stress–strain curves were overlapping and the mechanical parameter values decrease. The swelling of these hydrogels was also attributed to the network porosity, which was revealed by scanning electron microscopy (SEM) on freeze-dried specimens. The results prove the importance of the polyurethane matrix structure in the development of new drug releasing systems.