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PubMed1999

Polyurethanes based on dihydroxamic acids. Synthesis, chemical characterization, and biological activity.

A series of segmented polyurethanes based on polyethylene oxide/polycaprolactone diol, isophorone diisocyanate, and dihydroxamic acids were synthesized and characterized. Biocompatibility and antitumoral activity were in vivo tested on Wistar male rats and Wistar rats affected with Walker 256 carcinosarcoma, respectively. The effect of dihydroxamic acid structure on the biological properties was determined. A better antitumoral response of the polyurethanes containing aliphatic dihydroxamic segment compared with those which resulted using terephthaloyl dihydroxamic acid was evidenced. With increasing polymer chain polyethylene oxide content the antitumoral activity was also enhanced. Some attempts on the in vitro biodegradation of above polyurethanes were also performed.

Animals↗

PubMedDate not supplied

Stability studies on colloidal suspensions of polyurethane nanocapsules.

Generally nanocapsules suspensions are a colloidal system in a metastable state, there is aggregation due to attraction and repulsion forces between particles. The objective of this work was to bring the role of the polymeric membrane in the protection of the active drug against damaging caused by external agents and to select the monomer which leads to obtain stable formulation with the highest possible payload of the active drug. The stability testing involving visual aspect, particle size measurement, transmission electron microscopy (TEM) examination, and drug loss was conduced after 6 months of storage at different temperatures (4, 25, and 45 degrees C). The colloidal suspensions of nanocapsules were obtained using the combined interfacial polycondensation and spontaneous emulsification, the technique was used to encapsulate alpha-tocopherol using polyurethanes polymers. It is a one step procedure: An organic phase composed of a water miscible solvent (acetone), lipophilic monomer (Isophorone diisocyanate IPDI), oil, and a lipophilic surfactant, is injected in an aqueous phase containing hydrophilic monomer (diol with various molecular weight: 1,2-ethanediol (ED), 1,4-butanediol (BD), and 1,6-hexanediol (HD)) and hydrophilic emulsifying agent. The water miscible solvent diffuses to the aqueous phase, the oil precipitates as nano-droplets, and the two monomers react at the interface, forming a membrane around the nanoemulsion leading to nanocapsules. A good physical stability of suspensions corresponds to absence of symptoms such as sedimentation or agglomeration, significant size change and alpha-tocopherol degradation due to external agents such as oxygen, temperature, and ultraviolet (UV) irradiation. The size of nanocapsules before storage was about 232 +/- 3, 258 +/- 29, and 312 +/- 4 nm for ED, BD, and HD, respectively. After 6 months of storage, polyurethanes nanocapsules possess good stability against aggregation at 4 and 25 degrees C. Comparing results obtained using different monomers, it reveals that the polyurethane based on HD offers good protection of alpha-tocopherol against damaging caused by the temperature and UV irradiation.

Antioxidants↗

PubMed2003

Polyurethane grafts: a viable alternative for dialysis arteriovenous access?

Polyurethane grafts, promoted for their self-sealing properties and low complication rates, were recently introduced for hemodialysis access. We review our experience with this graft material to determine its complication and patency rates. Between January 1995 and December 1999, 118 patients, 75 female and 43 male, with a mean age of 51 years, had a total of 163 polyurethane arteriovenous grafts inserted. The grafts were mostly 6 mm in diameter (69.3%), placed in a loop configuration (91.4%) in the forearm (49.7%). The median follow-up period was 12 months. The grafts were first cannulated for hemodialysis at a median time of 19 days after implantation, with 12% used within 3 days. Thrombosis and infection were the most common complications at rates of 32.7% and 30.0%, respectively. Infection was the most common cause of graft loss (61.5%). These complications were amenable to salvage intervention. The 1-year primary and secondary patency rates were 73% and 86%, respectively; the 3-year secondary patency rate, 72%. The 1-year serviceability rate was 64%. With satisfactory patency rates and the advantage of its self-sealing properties permitting early cannulation, polyurethane grafts provide a viable alternative for hemodialysis access. Early recognition and appropriate management of complications can prolong graft survival.

Adult↗

PubMed2002

Endothelial cell seeding of a 4-mm I.D. polyurethane vascular graft.

We evaluated the extent (luminal coverage) of the endothelial cell (EC) lining/neointimal development and the thromboresistance of electrostatically EC seeded small diameter ChronoFlex-polyurethane vascular grafts. The evaluation consisted of harvesting autologous, canine jugular vein ECs, electrostatically seeding the polyurethane grafts (4-mm I.D., length = 6 cm) with the harvested ECs, implanting the grafts in a canine femoral artery model for four to six weeks, and excising the grafts for histological and scanning electron microscopy evaluations. Results of the histological evaluation (mid-graft region only) indicated that electrostatic EC seeding led to neointimal development and to minimal to no thrombus formation within the EC seeded grafts. The unseeded control grafts resulted in no neointimal development and substantial thrombus formation on the graft luminal surfaces. Scanning electron microscopy examination demonstrated a mature, confluent endothelium with a "cobblestone" appearance on the EC seeded graft luminal surface after six weeks. We conclude that electrostatic EC seeding enhanced the development of a neointima and reduced the incidence of thrombosis in polyurethane grafts implanted in a canine femoral artery model.

Animals↗

PubMed1987

Autooxidative degradation of implanted polyether polyurethane devices.

While certain polyether polyurethanes have been shown to be biostable, undesirable interactions between polymer, the body environment and device can occur. For example, the corrosion products of metallic parts can cause relatively rapid autooxidation of polyether soft segments. This phenomenon was first demonstrated in our laboratories by immersing polyurethane test specimens in metal ion solutions of different oxidation potentials. Subsequently, the mechanism was reasonably duplicated by immersing Pellethane 2363-80A insulated cardiac pacing leads in 3%, 37 degrees C hydrogen peroxide. In vivo studies after 1 year show that corrosion products from pure Co and Fe produce the most rapid degradation of the polyurethane.

Animals↗

PubMed1987

Chemical modification of polyurethanes by radiation-induced grafting.

Basic methods of radiation-induced modification of polyurethanes for biomedical applications and of their characterization are briefly described. The most important works found in literature on radiation grafting of polyurethanes are discussed. The radiation grafting of polyetherurethane films and tubings by the preswelling method using various monomers and their physico-chemical characterization are discussed in detail with respect to the antithrombogenic properties of the materials. Novel applications for radiation-modified polyurethanes as drug delivery systems or antiinfectious materials are briefly mentioned.

Biocompatible Materials↗

PubMed1988

Biomedical applications of polyurethanes: implications of failure mechanisms.

Three mechanisms have been described which explain various observed interactions between polyurethane chemistry and body chemistry. These include calcification, environmental stress cracking, and chain scission. Each may result in implant device failure, and each appears to involve metal ion complexation as a key parameter. Continued expansion of polyurethane into implantable product applications will require further clarification of the effect of each of these interactions on long-term product performance. It is believed that design considerations and polymer modifications will help control the effects of each of the interactions and will result in new and improved polyurethane implant products.

Biocompatible Materials↗

PubMed1997

Blood compatible phospholipid-containing polyurethanes: synthesis characterization and blood compatibility evaluation.

A new diol, bis[2-(2-hydroxyethyldimethylammonio)ethyl] butylenediphosphate, that contains two phosphatidylcholine analogous moieties in one diol molecule, was synthesized and characterized. The diol together with 1,4-butanediol as chain extender was further incorporated into the propolymer of poly(ethylene oxide) (Mn = 1000, 2000, 6000) and 4,4'-methylenediphenyl diisocyanate. The resulting phospholipid poly(ether urethane)s show viscosity behavior of common polyelectrolytes. The bulk and surface characteristics of the new phospholipid poly(ether urethane)s were investigated by IR, GPC, ATR-FTIR, ESCA and contact angle measurements. The new polymers possessed relatively hydrophilic surface revealed by contact angle measurements. The blood compatibilities of the polyurethanes were evaluated by platelet rich plasma contacting studies and scanning electron microscopy observation using medical grade PVC as the reference. No platelet adhesion was observed for all new phospholipid polyurethane casting films. This new type of phospholipid polyurethane is expected to have potential biomedical applications.

Animals↗

PubMedDate not supplied

Nasolacrimal polyurethane stent placement: preliminary results.

PURPOSE: To present our initial results in the treatment of nasolacrimal obstruction by placing a polyurethane stent. METHODS: 74 nasolacrimal stents were implanted under fluoroscopic guidance in obstructed nasolacrimal systems of 64 patients. Dacryocystography and CT were used to verify the position and patency of the stents. Mean follow-up was 15 months. Clinical examinations were done at the first week, first month, third month and sixth month after stent placement. RESULTS: Polyurethane stents were successfully inserted and permeable in 59 patients (92.1%), but could not be inserted in 5 patients (7.8%). Epiphora was solved and permeable in 53 cases (82.8%), it was not permeable but asymptomatic in 2 cases (3.1%), and was not permeable but symptomatic in 4 (6.2%). In 5 cases (7.8%) stents remained permeable although patients complained of epiphora. CONCLUSIONS: Polyurethane stent placement is a non-invasive technique that can replace dacryocystorhinostomy, giving better results and tolerance.

Adolescent↗

PubMed2004

Polyurethanes loaded with antibiotics: influence of polymer-antibiotic interactions on in vitro activity against Staphylococcus epidermidis.

Acidic or basic polyurethanes were loaded with antibiotics to develop materials to prevent medical device-related infections. A correlation between polymer-antibiotic interactions and amount of drug absorbed by polymers and released over time was found. Since the employed antibiotics, i.e. amoxicillin, cefamandole nafate, rifampin and vancomycin, possessed at least an acidic group in their structural formula, the introduction of basic tertiary amines in the polyurethane side-chain resulted in an increased polymer ability to adsorb antibiotics. However, a stronger ionic interaction between this polymer and the antibiotics caused a release of lower amount of drug over time. Antibiotics released from polymers inhibited Staphylococcus epidermidis growth on agar. Antibiotic-loaded polyurethanes kept in water for increasing times were still able to show inhibition zones of bacterial growth. The antibacterial activity lasted up to 3 hours for amoxicillin, 24 hours for vancomycin, 8 days for cefamandole nafate and 8 months for rifampin.

Amoxicillin↗

PubMed2005

Risk evaluation of occupational exposure to methylene dianiline and toluene diamine in polyurethane foam.

Methylene diphenylisocyanate (MDI) and toluene diisocyanate (TDI) are widely used in industry to produce polyurethane foam products. Small amounts of methylenedianiline (MDA) and toluene diamine (TDA) are released during MDI and TDI polymerization and may be present in newly finished polyurethane foam parts. MDA and TDA concentrations in foam decline exponentially within several hours of demolding. MDA and the 2,4-isomer of TDA are known animal carcinogens and, in addition, have significant non-carcinogenic health effects. Our goal was to determine whether worker exposure to MDA or TDA in freshly produced polyurethane foams was associated with unacceptable health risks. Sampling and analysis of the fresh foam indicated that MDA and TDA concentrations varied considerably among products, but concentrations in all materials evaluated declined rapidly over time. We found that, under a worst-case exposure scenario, cancer risks from TDA exposure were approximately 5 x 10(-6), whereas cancer risks from MDA exposure resulted in a tumorigenic margin of exposure (MOE) of 85 000. Non-cancer chronic hazard indices were well below 1.0. Therefore, the potential cancer and non-cancer health risks from MDA or TDA exposure to newly manufactured foam parts appear to fall well within acceptable health risk criteria.

Aniline Compounds↗

PubMed1996

The influence of open leaflet geometry on the haemodynamic flow characteristics of polyurethane trileaflet artificial heart valves.

In vitro velocity data were obtained downstream of two versions of the Leeds polyurethane trileaflet heart valve in a simulated pulsatile flow regime using laser Doppler velocimetry. The main difference between the two valves studied was the manufacturing method used to create the valves. The film-fabricated valve was constructed from solvent-cast sheets of polyurethane, thermally formed into the correct leaflet geometry. The dip-cast valve used a stainless steel mould which was dipped into a polyurethane solution to produce the valve leaflets. Significant differences were visible between the fully open leaflet shape of each valve. The distribution of mean axial velocity and Reynolds normal stress (RNS) was shown to be dependent on the shape of the fully open valve orifice. For the film-fabricated valves, flow recirculation and high values of RNS were present downstream of the frame posts. The maximum value of RNS obtained downstream of the film-fabricated valve at peak systole was 147 N/m2. Results for the dip-cast valve showed a more uniform distribution of mean axial velocity and RNS resulting from the more circular central orifice produced by the dip-cast leaflets. The maximum value of RNS obtained downstream of the dip-cast valve at peak systole was 109 N/m2. These results demonstrate the effect of the open valve geometry on the flow characteristics downstream of trileaflet valves and that minor changes to the open leaflet geometry can significantly affect the flow characteristics and the possibility of flow-related blood damage occurring in vivo.

Aortic Valve↗

PubMedDate not supplied

[Polyurethane or silicone as long-term implant substance--a critical evaluation].

Long-term implants made from thermoplastic elastomers have a long history of clinical use. Among other rubber materials, such as polyolefin rubber, much of the demand for rubber-like biomaterials is met by silicone and polyurethane elastomers. The last two elastomers both have sufficient biocompatibility for long-term applications, but differ in terms of biodegradability. Inadequate resistance to degradation almost always leads to implant function loss, which may even threaten the patient's life. Long-term implantation studies in the rat show different mechanisms of biodegradation for polyurethane and silicone. Polyurethane shown deep fissures in the surface, compared with erosion of silicone surfaces. Mechanical and electrical parameters determined to evaluate degradation, additionally show differences in the extent of damage occurring.

Animals↗

PubMed2002

Treatment of nasolacrimal duct obstruction with polyurethane stent placement: long-term results.

OBJECTIVE: The purpose of this study was to evaluate the long-term efficacy of polyurethane stent placement in adults with nasolacrimal duct obstruction. SUBJECTS AND METHODS: Polyurethane stents were placed under fluoroscopic guidance in 52 eyes of 49 patients (mean age, 43 years) with severe epiphora due to idiopathic nasolacrimal duct obstruction. The obstruction was complete in 44 eyes and partial in eight. Clinical success was defined as complete resolution of or great improvement in the symptoms of epiphora and the patency of the lacrimal system to irrigation. Mean follow-up was 23 months (range, 14-44 months). RESULTS: Stent placement was technically successful in 50 eyes (96%). The mean fluoroscopy screening time was 2.2 min (range, 0.2-5.8 min). Two patients were lost to follow-up. Clinical success was obtained in 33 (69%) of 48 eyes. Lacrimal symptoms developed in 23 (70%) of these 33 eyes at least once during the follow-up, but these patients responded well to topical drug treatment and lacrimal irrigation. External dacryocystorhinostomy was performed in 13 eyes after failure of the stents. At surgery, lacrimal sacs were shrunken, hyperemic, and fragile in all eyes, making it difficult to anastomose with nasal mucosa. Histologic examination showed granulation tissue and chronic inflammation of the sac epithelium. CONCLUSION: The success rate of the nasolacrimal stent decreases as follow-up lengthens. After stent treatment, lacrimal symptoms frequently develop, even if the stent remains patent, and require multiple office visits and therapy. The polyurethane stent may induce a chronic inflammatory response in the lacrimal sac, which can interfere with subsequent dacryocystorhinostomy.

Adult↗

PubMedDate not supplied

A novel microporous polyurethane blood conduit: biocompatibility assessment of the UTA arterial prosthesis by an organo-typic culture technique.

An organotypic culture assay has been used to assess the biocompatibility and cytotoxicity of an arterial prosthesis developed at the University of Texas-Arlington (the UTA graft) from a structurally modified polyurethane (PU) elastomer (Tecoflex). The cell culture test was applied to the UTA graft after sterilization by ethylene oxide and by gamma radiation in two separate series. First, small specimens of the prosthesis were incubated for 7 days on a semisolid nutrient medium with their luminal surface in direct contact with endothelium explanted from the aorta of chick embryos. Second, the possibility of cytotoxic contaminants being leached from the polyurethane was assessed by immersing the biomaterial in the liquid culture medium for 5 days at 37 degrees C prior to conducting the organo-typic culture assay on a standard control surface. The structure of the UTA polyurethane prosthesis is porous, but the graft wall is impervious because it contains closed (i.e., noncommunicating) pores. In addition, four other vascular prostheses were included in the study for comparison. They were the Hydrophilic Mitrathane PU graft with a similar impervious, closed pore structure, an experimental Hydrophobic Mitrathane PU graft with a fibrous, open pore structure, and the commercial Impra and Reinforced Goretex expanded PTFE grafts. Following 7 days of cell culture, the biocompatibility and cytotoxicity of the various biomaterials were measured in terms of the area of migrating cells, the density of cells surrounding the explants, and the level of cell adhesion. Comparison of the results against control cultures demonstrated that the UTA graft, along with the other four prostheses, does not release cytotoxic extractables. Microscopic observations of its cultured surface indicated that the UTA graft promotes a high density of cell growth over a limited area, similar to the Hydrophilic Mitrathane graft. This level of biocompatibility is considered inferior to that of the two PTFE and the Hydrophobic Mitrathane prostheses, which promote more extensive cell migration, greater cell adhesion, and cell growth in a continuous single layer.

Animals↗

PubMedDate not supplied

A novel microporous polyurethane vascular graft: in vivo evaluation of the UTA prosthesis implanted as infra-renal aortic substitute in dogs.

A novel microporous polyurethane blood conduit developed at the University of Texas at Arlington was implanted as an infra-renal substitute in dogs. The prosthesis was fabricated by precipitating a solution of the polymer with dry nitrogen onto a rotating mandrel. The grafts were sterilized either by gamma radiation (series I) or ethylene oxide (series II); they were implanted for the following prescheduled periods: 4, 24, 48 hours, and 1 week (short-term) and 2, 4 weeks, 3 and 6 months (medium-term). The thrombohematological characteristics of each animal were evaluated prior to implantation and confirmed that the index of blood coagulability was normal. In the short-term group, five out of eight grafts were patent and three were partially occluded; four grafts in the medium-term group were patent; one was partially occluded; and three were thrombosed at retrieval. One week after implantation, the prostheses were surrounded by an external capsule, which was present mainly at the two anastomoses. The external capsule covered the entire graft at 3 months. No kinking of the grafts was observed and the presence of a mild yellow stain related to bilirubin uptake was detected at 2 weeks, 1, 3, and 6 months. Histological studies have revealed the formation of a thin internal capsule at both anastomoses, 2 weeks postimplantation, which was not anchored to the graft wall. In the medium-term group, the thrombosed grafts failed to develop an internal capsule, whereas the patent graft exhibited a thick internal capsule made of neocollagenous tissue over the entire graft. This new microporous polyurethane prosthesis did not perform satisfactorily as an infra-renal substitute in dogs and its in vivo stability requires further assessment. Thus, the concept of a polyurethane with closed pores does not achieve what was anticipated.

Animals↗

PubMedDate not supplied

Evaluation of the biodurability of polyurethane-covered stent using a flow phantom.

OBJECTIVE: To evaluate the biodurability of the covering material in retrievable metallic stents covered with polycarbonate polyurethane. MATERIALS AND METHODS: Using a peristaltic pump at a constant rate of 1 ml/min, bile was recirculated from a reservoir through a long tube containing four stents. Each of these was removed from the system every two weeks and a radial tensile strength test and scanning electron microscopy (SEM) were performed. Each stent, removed at 2, 4, 6 and 8 weeks, was compared with a control stent not exposed to bile juice. RESULTS: Gross examination showed that stents were intact at 2 weeks, but at 4, 6 and 8 weeks cracks were observed. The size of these increased gradually in accordance with the duration of exposure, and at 8 weeks several large holes in the polyurethane membrane were evident. With regard to radial tensile strength, extension and peak load at break were 84.47% and 10.030 N/mm, 54.90% and 6.769 N/mm, 16.55% and 2.452 N/mm, 11.21% and 1.373 N/mm at 0, 2, 4 and 6 weeks, respectively. Scanning electron microscopy at 2 weeks revealed intermittent pitting and cracking, and examination at 4, 6 and 8 weeks showed that the size of these defects was gradually increasing. CONCLUSION: When the polyurethane membrane was exposed to bile, biodegradation was first observed at week two and increased gradually according to the duration of exposure.

Bile Acids and Salts↗

PubMed1999

Male polyurethane condoms do not enhance brief HIV-STD risk reduction interventions for heterosexually active men: results from a randomized test of concept.

The current study examined the effects of a brief HIV risk reduction intervention for men. Participants were recruited (n = 108) from an urban public health clinic and randomly assigned to one of 3 experimental intervention conditions: (1) 3 h HIV-STD risk reduction behavioural skills building latex condom intervention; (2) the same 3 h skills workshop but focused on male polyurethane condoms; or (3) a 3 h HIV education workshop. Results showed all 3 interventions increased AIDS knowledge and positively influenced attitudes, but men who received the polyurethane condom skills intervention were more likely to request condoms at follow ups. In addition, men who received either of the 2 skills interventions evidenced increased condom use at the one-month follow up, with no differences at 3-month follow up. This study is among the first to test a brief HIV risk reduction intervention for men and is the first to test whether polyurethane male condoms enhance HIV risk reduction efforts.

Acquired Immunodeficiency Syndrome↗