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At least 721 records · Page 40Linked to original sources

PubMed2007

Synthesis, characterization, and in vitro activity of antibiotic releasing polyurethanes to prevent bacterial resistance.

Central venous catheters are a major cause of nosocomial bloodstream infections. Different attempts have been made to incorporate antimicrobial agents into catheters, particularly directed at the surface-coating of devices. To facilitate the antimicrobial adsorption, various cationic surfactants, which however showed several problems, have been used. On the other hand, impregnated catheters with only antimicrobials have demonstrated a short-term duration due to the difficulties to deliver the drug slowly. Thus, in order to obtain high antimicrobial-polymer affinity we synthesized or modified polyurethanes to introduce different functional groups. Polymers were loaded with two antibiotics, cefamandole nafate and rifampin (RIF), chosen for both their functional groups and their action spectrum. The in vitro release behavior showed that the elution of drugs depended on the matrix hydrophilicity and on the antibiotic-polymer and antibiotic-antibiotic interactions. To increase the amount of drug released, polyethylene glycol (PEG) used as a pore forming agent at different molecular weights was incorporated in the polymer bulk with antibiotics. As for the in vitro antimicrobial activity of matrices, assessed by Kirby-Bauer test, it was seen that antibiotics released from various formulations inhibited the bacterial growth and exerted a synergistic effect when both were present. In particular, PEG10000-containing polymer was active against the RIF-resistant S. aureus strain up to 23 days. These results suggest that the combined entrapping of antibiotics and pore formers in these novel polymer systems could be promising to prevent the bacterial colonization and to control the emergence of bacterial resistance.

Anti-Bacterial Agents↗

PubMed2003

Electrospun nanofibrous polyurethane membrane as wound dressing.

Produced via electrospinning, polyurethane membrane, which has a unique property, has been of interest in medical fields. Electrospinning is a process by which nanofibers can be produced by an electrostatically driven jet of polymer solution. Electrospun fibers are collected in the form of membranes. The porous structured electrospun membrane is particularly important for its favorable properties: it exudates fluid from the wound, does not build up under the covering, and does not cause wound desiccation. The electrospun nanofibrous membrane shows controlled evaporative water loss, excellent oxygen permeability, and promoted fluid drainage ability, but still it can inhibit exogenous microorganism invasion because its pores are ultra-fine. Histological examination indicates that the rate of epithelialization is increased and the dermis becomes well organized if wounds are covered with electrospun nanofibrous membrane. This electrospun membrane has potential applications for wound dressing based upon its unique properties.

Animals↗

PubMed2006

Structural features and mechanical properties of in situ-bonded meshes of segmented polyurethane electrospun from mixed solvents.

The relationships between the structural features and mechanical properties of electrospun segmented polyurethane (SPU) meshes and electrospinning parameters such as formulation (e.g., polymer concentration and solvent mixing ratio) and operation parameters (e.g., applied voltage, air gap, and flow rate) were studied with the use of a mixed-solvent system of tetrahydrofuran (THF) and N,N-dimethylacrylamide (DMF). After the relationships between the structure of electrospun SPU and the operation parameters under a fixed SPU concentration of single THF solution were established, SPU was electrospun from the mixed solvent of THF and DMF with different mixing ratios [DMF content: 5, 10, and 30% (v/v)]. Scanning electron microscopy showed that an increase in DMF ratio significantly enhances the degree of bonding between SPU fibers at contact sites and decreases the diameter of fibers formed. The porosimetric characterization showed the following: (1) The porosity of the electrospun SPU meshes decreased with an increase of DMF ratio. (2) The pore size distribution exhibited three representative peaks of different void sizes (i.e., approximately 5, 20, and 70 microm). (3) The proportion of the 20-microm void markedly decreased with an increase in DMF ratio. A tensile test on the meshes showed that an increase in DMF ratio induces an increase in elasticity of the mesh. Such a regulation of the structural features and mechanical properties of electrospun SPU meshes using a mixed-solvent system with low- and high-boiling-point solvents may be useful in the engineering of SPU-fiber based matrices or scaffolds.

Acrylamides↗

PubMed2006

Fabrication of microporous thermoplastic polyurethane for use as small-diameter vascular graft material. I. Phase-inversion method.

Fabrication conditions of microporous thermoplastic polyurethane to be used in small-diameter vascular grafts are studied. Porosity variations due to various factors such as concentration of PU solution, composition of coagulation bath, effect of coagulant temperature, and effect of dissolved air in PU solution are discussed. The liquid-liquid phase-inversion process used for preparation of PU films and the mechanism for the formation of microporous films are discussed. Surface and cross-section morphologies of PU films are studied with the use of scanning electron microscopy (SEM), and porosity value and mechanical strength of PU films are also determined. SEM photomicrographs show that PU films prepared in an alcoholic coagulant have uniform porous structure compared to films prepared in water coagulant. Increasing the polymer concentration and coagulant temperature (>23 degrees C) decreases the macrovoid formation, as seen in cross sections of PU films. This enhances the tensile modulus of PU films. By using this process adjustment may be made on the morphology and compliance, as they are important factors in design and fabrication of small-diameter vascular grafts.

Blood Vessel Prosthesis↗

PubMed2006

Improving the elasticity and cytophilicity of biodegradable polyurethane by changing chain extender.

Two types of biodegradable polyurethanes (PUs) were synthesized from methylene di-p-phenyl-diisocyanate (MDI), polycaprolactone diol (PCL-diol), and chain extenders of either butanediol (BD) or 2,2'-(methylimino)diethanol (MIDE). The effects of two types of chain extenders on the degradation, mechanical properties, hydrophilicity, and cytophilicity of PUs were evaluated. In vitro degradation studies showed that PU containing MIDE has a higher degradation rate than PU synthesized using BD as a chain extender. Mechanical testing on dry and wet samples demonstrated that PU containing MIDE has a much higher elongation in the elastic region than PU containing BD. PU containing MIDE is more hydrophilic and retains more liquid during in vitro culture. Furthermore, preliminary cytocompatibility studies showed that both types of degradable PU are nontoxic, and fibroblasts adhere better and proliferate faster on MIDE containing PU than BD containing PU. To compare the cytocompatibility and degradation behaviors of the synthesized PU with existing FDA approved biocompatible material, polylactide (PLA), with a similar degradation rate, was used as negative control. Two types of PU were shown to have similar cytocompatibility and degradation behaviors as those of the PLA material. To verify the effectiveness of the cytotoxicity assay, latex was used as a positive control. Latex samples showed toxicity to cultured cells as expected. In conclusion, by changing the type of chain extender used during the synthesis of degradable PUs, the degradation rate, mechanical properties, hydrophilicity, and cytophilicity can be adjusted for different tissue engineering applications.

Absorbable Implants↗

PubMed2004

Changes in macrophage function and morphology due to biomedical polyurethane surfaces undergoing biodegradation.

Monocytes are recruited to the material surface of an implanted biomedical device recognizing it as a foreign body. Differentiation into macrophages subsequently occurs followed by fusion to form foreign body giant cells (FBGCs). Consequently, implants can become degraded, cause chronic inflammation or become isolated by fibrous encapsulation. In this study, a relationship between material surface chemistry and the FBGC response was demonstrated by seeding mature monocyte-derived macrophages (MDMs) on polycarbonate-based polyurethanes that differed in their chemical structures (synthesized with poly(1,6-hexyl 1,2-ethyl carbonate) diol, and either (14)C-hexane diisocyanate and butanediol (BD) (referred to as HDI) or 4,4'-methylene bisphenyl diisocyanate and (14)C-BD (referred to as MDI)) and material degradation assessed. At 48 h of cell-material interaction, the FBGC attached to HDI were more multinucleated (73%) compared to MDI or the polystyrene (PS) control (21 and 36%, respectively). There was a fivefold increase in the synthesis and secretion of a protein with an approximate molecular weight of 48 kDa and a pI of 6.1 (determined by two-dimensional gel electrophoresis) only from cells seeded on HDI. Immunoprecipitation confirmed that MSE and CE were synthesized and secreted de novo. Immunoblotting also showed an increase in secreted monocyte-specific esterase (MSE) and cholesterol esterase (CE) from cells seeded on HDI relative to PS and MDI. Significantly more radiolabel ((14)C) release and esterase activity were elicited by MDMs on HDI than MDI (P < 0.05). The material that was more degradable (HDI), elicited greater protein synthesis and esterase secretion as well as more multinucleated MDMs than MDI, suggesting that the material surface chemistry modulates the function of MDM at the site of an inflammatory response to an implanted device.

Absorbable Implants↗

PubMed2006

New polyurethane-based material for vascular corrosion casting with improved physical and imaging characteristics.

Vascular corrosion casting has been established as a method to reconstruct the three-dimensional (3D) structure of blood vessels of organs and tissues. After replacing the blood volume with a low viscosity resin, the surrounding tissue is removed to replicate the vascular architecture, typically using scanning electron microscopy (SEM). To date available casting resins have had significant limitations such as lack of viscosity, leading to insufficient perfusion of smallest capillaries in organs and tissues of smaller species, interaction with surrounding tissue or fragility of resulting casts. We have reported here about a new polyurethane-based casting resin (PU4ii) with superior physical and imaging characteristics. Low viscosity, timely polymerization, and minimal shrinking of PU4ii produces high quality casts, including the finest capillaries. These casts are highly elastic while retaining their original structure to facilitate postcasting tissue dissection and pruning of casts. SEM images illustrate the high reproduction quality, including endothelial cell imprints, features that allow one to discern arterial and veinal vessels. For quantitative analysis, casts from PU4ii can be imaged using micro-computed tomography to produce digital 3D reconstructions. The inherent fluorescence of PU4ii is sufficient to reproduce casts with or without tissue using confocal microscopy (CM). Because of the simplified casting procedure, the high reproducibility and the superior reproduction quality, a combination of vascular corrosion casting using PU4ii with advanced imaging technologies has great potential to support the description of vascular defects and drug effects in disease models using mutant mice.

Animals↗

PubMed2006

Comparative analysis of dental enamel polyvinylsiloxane impression and polyurethane casting methods for SEM research.

Dental casting is a very common procedure for making high-quality replicas of paleo-anthropological remains. Replicas are frequently used, instead of original remains, to study both fossil and extant Primate teeth in morphological and metrical analyses. Several commercial products can be used in molds. This study analyzed SEM image resolution and enamel surface feature definition of tooth molds at various magnification levels and obtained, with both Coltène and 3M low-viscosity body polyvinylsiloxane impression, materials and polyurethane casts. Results, through comparison with the original teeth, show that both the negative molds and the positive casts are highly reliable in replicating enamel surfaces. However, positive cast quality is optimal for SEM observation only till the fourth consecutive replica from the original mold, especially at high SEM magnification levels.

Dental Enamel↗

PubMed2006

Immobilization of gene vectors on polyurethane surfaces using a monoclonal antibody for localized gene delivery.

BACKGROUND: Conventional strategies of gene therapy using viral vectors result in suboptimal localization and potentially dangerous distal spread of vector. We hypothesized that localized delivery of adenoviral gene vectors could be achieved from a polyurethane (PU) film through a mechanism involving anti-viral antibody tethering. METHODS: PU films were formulated with a collagen coating. Anti-adenoviral monoclonal antibodies were covalently bound to the collagen surface. These antibodies enabled tethering of replication-defective adenoviruses [Ad-GFP (encoding green fluorescent protein)] through highly specific antigen-antibody affinity. The binding stability and in vitro delivery of virus bound on PU films were investigated. Cell culture studies with rat arterial smooth muscle cells (A10) assessed transduction on or near the PU matrix. In vivo experiments with collagen-coated PU films investigated atrial epicardial implant and subdermal implant models in Yorkshire swine. RESULTS: We report for the first time successful PU film-based gene delivery using antibody-tethered adenovirus encoding the green fluorescent protein (GFP), demonstrating efficient and highly localized gene delivery to arterial smooth muscle cells in cell culture and pig implant. In comparison, direct injections of viral vectors into subcutaneous sites gave sparse, needle-track-oriented GFP expression patterns. CONCLUSION: We conclude that PU film is a suitable platform for a localizable viral vector delivery system that also prevents systemic spread of vector. Gene delivery using PU film-based anti-viral antibody tethering of vectors should be suitable for a wide array of single or multiple therapeutic gene strategies, and for further device-based gene delivery therapeutic strategies.

Adenoviridae↗

PubMed1975

Correlation of kinetic parameters and thermal behavior of segmented polyurethane elastomers with biological responses.

Kinetic studies of thermal degradation of 16 segmented polyether polyurethane samples, containing various amounts of 3,4-diaminotoluene and dibutyltin diacetate as additives, were carried out by thermogravimetry. From a single dynamic thermogravimetric experiment, the temperatures of initiation of degradation, 10, 25, and 50% (w/w) of degradation, as well as the activation energies for degradation, were determined. The activation energies were computed from the thermogravimetric curves using Broido's graphical approximation method, which applies to first-order decomposition kinetics. The results of stepwise multiple linear regression analysis indicate that the biological responses to elastomar samples, such as tissue culture, hemolysis, intramuscular implant, intradermal irritation, systemic toxicity, and histopathological rating, and the cumulative biological response index are highly correlated with thermal stability and kinetic measurements of the materials.

Animals↗

PubMed1981

Mass transport properties of co(polyether)polyurethane membranes I: Preparation and characterization.

A series of polyurethane copolymers containing polyethylene glycol 600, 1000, or 1540 was synthesized, purified by reprecipitation, and cast into clear, tough, flexible membranes using the solution method. The weight average molecular weight of each polymer was estimated by gel permeation chromatography. The ability of the various polymers to absorb water was measured and increased with the increasing molecular weight of the polyethylene-glycol. The ability of the copolymer membranes to hold a pH gradient decreased with increasing polyethylene glycol molecular weight.

Hydrogen-Ion Concentration↗

PubMed1981

Mass transport properties of co(polyether)polyurethane membranes II: permeability and sorption characteristics.

A series of co(polyether)polyurethane polymers containing polyethylene glycol 600, 1000, or 1540 was synthesized, purified by reprecipitation, and cast into clear, tough, flexible membranes using the solution method. Hydration and membrane swelling increased with increasing polyethylene glycol molecular weight. Paroxypropione, 5-nitrosalicylic acid, sulfaguanidine, and phenylbutazone were used as penetrants of a 1 mM donor concentration. Transport rates through the 1540 and 1000 copolymer membranes were in decreasing order: paroxypropione greater than 5-nitrosalicylic acid greater than sulfaguanidine greater than phenylbutazone; however, through the 600 copolymer membrane the rates were paroxypropione greater than 5-nitrosalicylic acid approximately sulfaguanidine. Phenylbutazone did not penetrate during the experiment. Good agreement was obtained between apparent diffusion coefficients calculated by both the time lag and nonsteady-state methods. Boundary layer effects were examined by variations in stirring speeds. Evidence that diffusion may occur primarily through the aqueous region of the hydrated membranes is presented.

Adsorption↗

PubMed2005

Surface-imprinted polyurethane having affinity sites for ampicillin.

Affinity sites for an antibacterial drug, ampicillin, were created on the surface of polyurethane using the technique of non-covalent molecular imprinting. This was achieved by polymerizing aminophenylboronic acid in the presence of the ampicillin as a template. The extent of adsorption of the drug by the imprinted surface is nearly five times higher than the non-imprinted surface. The in vitro release studies have shown that the drug is retained for a prolonged period on the imprinted surface while it is rapidly released from the non-imprinted surface. These modified materials were subjected to interactions with two bacterial strains, E. Coli and S. aureus. These species could not adhere to the imprinted surface, further showing the ability of the surface to retain the drug for a prolonged period of time. The non-imprinted surface retained the bacterial strains, reflecting the lack of the drug on the surface. This novel approach seems to be useful for creating surfaces capable of retaining components of interest through non-covalent interactions to impart specific features, such as improved blood compatibility and antibacterial properties. [diagram in text].

Ampicillin↗

PubMed2005

In-vitro hemocompatibility evaluation of a thermoplastic polyurethane membrane with surface-immobilized water-soluble chitosan and heparin.

The surface of a thermoplastic polyurethane (TPU) membrane was treated with low temperature plasma (LTP) and was then grafted with poly(acrylic acid) (PAA), followed by the grafting of water-soluble chitosan (WSC) and heparin (HEP). The surface was characterized with static contact-angle and X-ray photoelectron spectroscopy (XPS). The results showed that the surface densities of peroxides and PAA reached a maximum when treated with LTP for 90 s. A higher pH of the reacting solution led to higher graft densities of WSC and HEP. After WSC and HEP grafting, the hydrophilicity of the TPU membrane was increased. The adsorption of proteins on HEP-grafted TPU membranes was effectively curtailed. In addition, HEP grafting also reduced platelet adhesion, elevated thrombin inactivation, and prolonged the blood coagulation time. According to the L929 fibroblast cell growth inhibition index, the HEP-grafted TPU membranes exhibited non-cytotoxicity. Overall results demonstrated that the HEP immobilization could not only improve the hydrophilicity but also the hemocompatibility of the TPU membrane, while maintaining the ascendant biocompatibility.

Animals↗

PubMed1983

Evaluation of the patency rate of fibrous microvascular polyurethane prostheses after implantation in the rat aorta.

Two types of fibrous polyurethane prostheses with different compliances were implanted into the rat aorta with interrupted sutures and a running suture line. Excluding two technical failures, one unexplained death, and three infected prostheses, both groups (n = 21) showed a patency rate of 100%, up to 6 months after implantation. Rapid reendothelialisation occurred, and a stable neo-intima was formed. Compliance of the prostheses, as well as the suture technique used, has proven to be an unimportant factor in the rat aorta model, probably due to the low magnitude of the pulsations of the rat aorta. The experience of the surgeon with microsurgical techniques seems to be an underestimated factor in determining patency rates of microvascular prostheses.

Animals↗

PubMed1991

Failure to obtain long-term patency after implantation of fibrous polyurethane prostheses in the carotid arteries of rabbits.

Fibrous polyurethane prostheses were implanted in the carotid arteries and aortae of New Zealand white (NZW) and Chinchilla (CHIN) rabbits. No immediate post-implantation patency was obtained after implantation in the carotid arteries in NZW rabbits. In CHIN rabbits patency up to 1 week was obtained after carotid implantation. Attempts to increase patency rates by administration of 20 mg/kg body weight/day of both dipyridamol (DIP) and acetyl-salicylic acid (ASA) p.o., starting the week before implantation, had an adverse effect; prostheses became occluded within a few hours after implantation. Coagulation tests (Lee and White, Am J Med Sci 145:495-503, 1913) carried out with blood drawn from CHIN rabbits revealed hypercoaguability after administration of either 10 or 20 mg/kg body weight/day of both DIP and ASA compared to pre-medication values. Prostheses implanted in the aortae of both strains remained patent without anti-platelet-aggregation therapy for a 3-month observation period. It is concluded that in the NZW rabbit carotid implantation was not successful due to severe spasmic reactions and that in CHIN rabbits only very short-term patency could be obtained both with and without administration of 10 or 20 mg/kg body weight/day medication DIP and ASA.

Animals↗

PubMed1999

Evaluation of a hybrid artificial liver using a polyurethane foam packed-Bed culture system in dogs.

BACKGROUND AND AIMS: We developed a polyurethane foam packed-bed culture system of hepatocyte spheroids as a hybrid artificial liver (PUF-HAL), which was effective for recovery from liver failure in rat experiments. In this report, the design of a scaled-up PUF-HAL for dogs is described and evaluated using a dog acute liver failure model. METHODS: Warm ischemic liver failure was induced with a portocaval shunt in each dog. The dogs were divided into two groups: (1) a control group (N = 4), in which each dog was attached to a PUF-HAL without hepatocytes for 9 h, and (2) a HAL group (N = 5), in which each dog was attached to a PUF-HAL with hepatocytes. Blood pressure, blood ammonia, blood glucose, serum creatinine, and other parameters related to liver function were compared between the two groups. RESULTS: In the HAL group, blood ammonia and serum creatinine levels were significantly lower, and blood pressure and blood glucose levels significantly higher, than those in the control group. CONCLUSIONS: The scaled-up PUF-HAL developed for large animals is useful as a liver support system in the dog acute liver failure model.

Ammonia↗

PubMed1990

Anchorage-dependent mammalian cell culture using polyurethane foam as a new substratum for cell attachment.

Anchorage-dependent mammalian cells were cultivated at high cell density in a novel culture system using polyurethane foam (PUF) as a substratum for cell attachment. PUF has a macroporous structure giving a high surface area to volume ratio. Monkey kidney cells (Vero) and Chinese hamster ovary cells (CHO-K1) attached to the internal surface of PUF and grew to a high cell density (1.04 X 10(8) cells/cm3 PUF and 3.5 X 10(7) cells/cm3 PUF, respectively) in PUF stationary cultures. In addition, we have designed a PUF-particle packed-bed culture system for high density mass cell culture. A maximum cell density of 2.4 X 10(7) cells/cm3 culture vessel volume was obtained in a packed-bed culture of Vero cells.

Animals↗