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PubMed2006

In vivo biostability of shore 55D polyether polyurethanes with and without fluoropolymer surface modifying endgroups.

Polyether polyurethanes are subject to autooxidation and environmental stress cracking (ESC) because of interactions with lysosomal oxygen-free radicals. Oxidation can also be catalyzed by and caused by direct (redox) reaction with transition metal ions (metal ion oxidation, MIO). The source of the ions is corrosion of metallic parts within an implanted device. A previous study on a Shore 80A polyether polyurethane modified with fluoropolymer surface modifying end groups demonstrated improved biostability over unmodified controls. We predicted that this could be extrapolated to the inherently more biostable Shore 55D version (E55DF). While it is difficult to demonstrate significant biodegradation in the harder polymers within a reasonable time frame, we did see excellent biologic autooxidation and ESC resistance for both E55DF and its unmodified Shore 55D (P55D) control. E55DF was slightly, but significantly more resistant to MIO than P55D. This was particularly evident in molecular weight distributions with P55D exhibiting a large decrease in number average molecular weight compared to no change for E55DF. Both were markedly superior to the softer Shore 80A control. It does appear that one can extrapolate accelerated in vivo biostability results with the softer polymers to their harder analogues.

Animals↗

PubMed2006

Chromotropic acid-functionalized polyurethane foam: A new sorbent for on-line preconcentration and determination of cobalt and nickel in lettuce samples.

A chromotropic acid-functionalized polyurethane foam has been developed for use in an on-line preconcentration system for cobalt and nickel determination. The packing material was prepared by covalent coupling of chromotropic acid with the polyurethane foam through an azo group. Co and Ni ions were sorbed in the mini-column, from which they could be eluted directly to the nebulizer-burner system of a flame atomic absorption spectrometer. Elution of cobalt and nickel from the mini-column can be accomplished with 0.50 and 0.75 M HCl solutions, respectively. The enrichment factors obtained were 22 (Co) and 27 (Ni), for 60 s preconcentration time, and 57 (Co) and 59 (Ni), if a preconcentration time of 180 s was used. Under the optimum conditions, the proposed procedure allowed the determination of metals with detection limits of 0.43 (cobalt) and 0.52 microg/L (nickel), respectively, on using preconcentration periods of 180 s. The accuracy of the developed procedure was evaluated by analysis of the certified reference materials NIST 1515 Apple Leaves and NIST 1570a Spinach Leaves. The method was applied to the analysis of lettuce samples. The contents of cobalt in the samples analyzed varied from 0.75 to 0.98 microg/g. Nickel was not detected in the lettuce samples.

Cobalt↗

PubMed1985

Three years experience with experimental implantation of fibrous polyurethane microvascular prostheses in the rat aorta.

The results of a 3-year study in which a series of 355 implantations of 1-cm-long fibrous polyurethane microvascular prostheses into the infrarenal aorta of the rat (group A) were evaluated with respect to patency and formation, structure, and fate of the neo-intima. Rats were sacrificed at various intervals from 1 day to 2 years in order to obtain a time-related impression of the re-endothelialization and stability of the neo-intima. A second series of 51 implants was done with prostheses 10 cm in length, placed in a 1.5-cm loop in the abdominal aorta (group B). An overall patency rate of 92.7% was achieved in group A. Initially, eight technical failures caused early thrombosis of the prostheses. Sixteen prostheses became infected and subsequently occluded. The overall patency in group B was 52.9%, due to kinking from adhesion formation and normal growth of the rat. In both the long and short prostheses, a continuous multilayered neo-intima developed, growing from the aortic stumps into the prosthesis from both sides. According to the growth rate of 0.3 mm/day, a 1-cm prosthesis was re-endothelialized after +/- 20 days and a 10-cm prosthesis after +/- 9 months. Once developed, the neo-intima, consisting of myofibroblasts and smooth muscle cells covered with a flat endothelium, remained stable and continuous, throughout the observation period. The neo-intima was firmly anchored onto the prosthetic wall by means of cellular protrusions extending between the polyurethane fibres. The significance of rapid healing of an implanted prosthesis is emphasized with respect to preventing (late) hematogenous, endogenous infection of the prosthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Production of gluconic acid by Aspergillus niger immobilized on polyurethane foam.

Production of gluconic acid by cells of Aspergillus niger immobilized on polyurethane foam was studied in repeated-batch shake-flask and bubble-column fermentations. For passive immobilization, various amounts of polyurethane foam and spore suspension were tested in order to obtain a suitable combination for optimal concentration of immobilized biomass. Immobilized cells were successfully reused with higher levels of product formation being maintained for longer period (65-70 h) than free cells. The highest gluconic acid concentration of about 143 g l-1 was reached on hydrol-based production medium with 0.3-cm3 foam cubes in the bubble column, where the effect of more suitable aeration and particle volume: medium volume ratio scheme was also investigated.

Aspergillus niger↗

PubMed1976

[Development and application of a new polyurethane plastics support bandage (author's transl)].

Experiences with a newly developed plastics support bandage on 1007 patients are reported. A polyurethane hard foam composition developed specially for medical purposes was used, which is created by blending the two components A (polyol) and B (isocyanate). The principle of our support bandage lies in the fact that after being mixed in a 1:1 ratio, the two highly viscous components are packed into a cotton stocking having a high transverse elasticity. After being rolled out to the desired thickness, the stocking is wrapped around the extremity which it is to support, where it hardens out into a polyurethane hard foam composition. By reason of the moisture content of the scoured cotton stocking, a 1 to 2 mm thick layer of foam forms in the contact region and renders any further padding unnecessary. Correspondingly, by using a double chamber stocking, circular bandages have been produced which can be removed, by means of incorporated zip and interengaging hook fasteners. Reclining shells, abduction bandages and body corsets can be made in the same way. The physical properties of the support bandage are illustrated: apart from its low weight, the bandage is particularly advantageous by reason of its high strength, insensitivity to water and ideal permeability to X-rays. The support bandages are easily made up and entail negligible cost.

Braces↗

PubMed1990

Long-term results of polyurethane-covered prostheses.

Forty two of 63 cases of bilateral augmentation mammaplasty are surveyed in which the so-called Ashley "Natural-Y" polyurethane-covered prosthesis was used. The cases were evaluated 15-17 years after the primary operation. These cases were compared with breasts augmented with other devices with respect to capsular contracture. The extreme difficulty of removing these implants because of the deterioration of the polyurethane cover leads the author to conclude that any further use of these implants is unjustifiable.

Breast↗

PubMed1994

Extraction of uranium from acidic solutions by TBP impregnated polyurethane foam.

Polyurethane foams can be used as a selective absorbent for a number of substances from dilute aqueous solutions. Absorption of uranium (VI) has been investigated using an open-cell polyurethane foam impregnated with tri-butyl phosphate (TBP). The extraction efficiency was observed to depend on the pH of the uranium solution and the concentration of uranyl ions. Also, the effects of TBP concentration, temperature, and squeezing time on the extraction of uranium were examined.

Adsorption↗

PubMed2001

Copper removal from aqueous solution using Aspergillus niger mycelia in free and polyurethane-bound form.

This study assesses the ability of mycelia of Aspergillus niger B-77 (both free and immobilized on polyurethane foam) to remove copper from single-ion solution. All experiments were conducted using 0.5 mM solutions of CuSO4.5H2O. Mycelia immobilized on polyurethane foam cells showed a three-fold increase in uptake, compared with that of free cells. The efficiency of copper removal (mg Cu2+ removed/mg Cu2+ added) in a column system reached more than 99% before the break-through point was attained.

Aspergillus niger↗

PubMedDate not supplied

Evaluation of polyurethane nasolacrimal duct stents: in vivo studies in New Zealand rabbits.

The purpose of this study was to evaluate the radiographic and biological effects of different polyurethane nasolacrimal duct stents in an animal model. Fifteen polyurethane nasolacrimal duct stents (n = 5 mushroom-type stents, n = 5 newly designed S-shaped TearLeader stents without hydrophilic coating, and n = 5 S-shaped TearLeader stents with hydrophilic coating) were implanted in the nasolacrimal ducts of eight unaffected New Zealand rabbits. One nasolacrimal system served as control. Clinical and radiographic follow-up was performed at 1-, 2-, and 4-week intervals, then after a 3-month interval, after which the animals were euthanized. All stents were implanted without major periprocedural complications. The stents proved to be patent by the end of the procedure. During follow-up, all mushroom-type stents were occluded at 4 weeks. None of these stents opened to forced irrigation. Clinically, all rabbits demonstrated severe dacryocystitis. Three out of five TearLeader stents without hydrophilic coating were blocked at 4 weeks; one out of five was open to irrigation. Best results were observed in the stent group with hydrophilic coating. Follow-up dacryocystography demonstrated patent stents in nasolacrimal ducts of all animals after 4 weeks. In only one of five cases, the coated stent became partially occluded after 2 months. These animals were free of clinical symptoms. After 3 months, at least three out of five stents still opened to forced irrigation and only one stent was completely blocked. Dislocation of the stents was not observed. Refinement of the stent surface and stent design improves the results of nasolacrimal duct stenting in this animal model. Implantation of hydrophilic-coated S-shaped stents is highly superior to conventional mushroom-type stents and noncoated stent types. Hydrophilic coating seems to prevent foreign-body reactions, resulting in maximized stent patency.

Animals↗

PubMedDate not supplied

Treatment of complete and partial obstruction of the nasolacrimal system with polyurethane stents: initial experience.

PURPOSE: To present our experience in the treatment of nasolacrimal occlusion by means of polyurethane stents. METHODS: Forty polyurethane stents were placed under fluoroscopic guidance in 35 consecutive patients with epiphora due to total or partial obstruction of the nasolacrimal system. The set designed by Song was used in all patients. The procedure was performed by introducing a guidewire through the superior punctum into the canaliculus and advancing it across the obstruction into the inferior meatus of the nasal cavity. After pulling out the guidewire, the stent was advanced in retrograde fashion and released into the sac and the nasolacrimal duct. RESULTS: The technical success rate was 100%. The average time for the procedure was 25 min (range 10-60 min). Immediate complications were: mild pain (n = 5), severe pain (n = 1), minimal epistaxis (n = 7), and moderate epistaxis (n = 1). No major complications occurred. The last clinical control revealed complete resolution of epiphora in 35 eyes and partial resolution in four; one patient did not improve. CONCLUSION: This technique for treatment of obstruction of the nasolacrimal system is simple and safe, and may obviate the use of more invasive procedures.

Adult↗

PubMed2000

[Site of a polyurethane stent in dacryocystography. Is postoperative success hereby predictable?].

BACKGROUND: Despite new methods for treating complete stenosis of the nasolacrimal duct dacryocystorhinostomy remains the standard operation. Implanting a nasolacrimal polyurethane stent through the nasolacrimal duct to preserve the natural lacrimal pathway seems to offer alternative procedure with similar success rate and without skin incision and general anesthesia. We examined whether an anatomically correct position increases its success rates. METHODS: This prospective study included 40 patients (mean age 57 years). The polyurethane stent was implanted during dacryocystography, and its position was checked at follow-up visits after 6 months. In the event of an additional canalicular stenosis a 45-mm-long stent was implanted, in the other patients a 35-mm-long stent. RESULTS: A dacryocystographically correct position was found in only 21 of 40 patients; in the other 19 the stent did not enter the nose under the inferior concha. However, there was no correlation between correct position under the inferior concha and success rate. In 8 of the 40 patients the stent was not patent. CONCLUSION: The postoperative success rate cannot be predicted by the radiographic position along the ductus nasolacrimalis.

Adult↗

PubMed2005

Polyurethane stents for lacrimal duct stenoses: 5-year results.

PURPOSE: To present 5-year results of polyurethane stent implantation for treatment of postsaccal lacrimal duct stenoses. METHODS: Ninety-two consecutive patients admitted to our hospital for stent implantation between 1997 and 2001 were retrospectively analysed. The patients who were not re-treated in our clinic were asked by questionnaire about their satisfaction and complaints. RESULTS: In 5 patients (5.4%) the implantation was not completed, 38 patients (41.3%) were re-treated due to relapsing epiphora during follow-up, and 11 stents (12.0%) were removed by dacryocystorhinostomy (DCR). Five stents (5.4%) were extracted transnasally. Four stents (4.3%) were removed in another hospital. Eighteen patients (19.6%) had relapsing epiphora but have not been re-treated so far. Forty-nine of 92 patients (53.3%) were not re-treated in our clinic and were interrogated by means of a questionnaire. Twenty-seven answered (55.1%), 8 did not answer (16.3%) and 14 patients (28.6%) did not receive the letter because they had moved away or died. Only 12 of the patients who answered the questionnaire had no or slight complaints (44.4%, or 18.5% of all treated patients). CONCLUSIONS: The long-term success rate of polyurethane stent implantation is very low (18.5%).

Adult↗

PubMed2000

The polyurethane nasolacrimal duct stent for lower tear duct obstruction: long-term success rate and complications.

BACKGROUND: The polyurethane nasolacrimal duct stent is used as an alternative to conventional techniques for treatment of lower tear duct obstruction. The aim of this study was to evaluate the clinical success rate after a follow-up of 2 years. METHODS: Nasolacrimal duct stent implantation was attempted in 19 patients with nasolacrimal duct obstruction proven by digital substraction dacryocystography. The median age of the patients was 50 years, and the minimum duration of symptoms was 3 months. Patients were followed up 1 week, 6 months, 1 year and 2 years after the procedure. RESULTS: Eighteen stents were implanted in 17 patients without surgical complications. All stents were proven to be patent at the end of the procedure. Success rate, defined as proportion of patients free of symptoms, was 66.6%, 55.5% and 50% after 1 week, 6 months and I year, respectively, and remained unchanged thereafter. Three stents had to be removed between 6 months and 2 years after implantation. Histological examination showed granulation tissue growing into the opening and obstructing the stent in one case. CONCLUSION: Implantation of a polyurethane nasolacrimal duct stent is an alternative to conventional techniques in lower tear duct obstruction. Its overall success rate is lower than that reported after conventional dacryocystorhinostomy, but the procedure is fast, safe and reversible. Refinement of the surface and stent design may improve results in the future.

Adult↗

PubMed2006

Biological monitoring of workers exposed to 4,4'-methylenediphenyl diisocyanate (MDI) in 19 French polyurethane industries.

OBJECTIVES: To study the range of urinary levels of 4,4'-methylenedianiline (MDA), a metabolite of methylenediphenyl diisocyanate (MDI), across factories in the polyurethane industries and to evaluate the validity of this biomarker to assess MDI occupational exposure. METHODS: Workers exposed to MDI, as well as non-occupationally exposed subjects, were studied and pre- and post-shift urine samples were collected from 169 workers of 19 French factories and 120 controls. Details on work activities and practices were collected by a questionnaire and workers were classified into three job categories. The identification and quantification of the total urinary MDA were performed by high-performance liquid chromatography with electrochemical detection (HPLC/EC). RESULTS: For all the factories, MDA was detectable in 73% of the post-shift urine samples. These post-shift values, in the range of <0.10 (detection limit)-23.60 microg/l, were significantly higher than those of the pre-shift samples. Urinary MDA levels in the control group were in the range of < 0.10-0.80 microg/l. The degree of automation of the mixing operation (polyols and MDI) appears as a determinant in the extent of exposure levels. The highest amounts of MDA in urine were found in the spraying or hot processes. The excretion levels of the workers directly exposed to the hardener containing the MDI monomer were significantly higher than those of the other workers. In addition, skin exposure to MDI monomer or to polyurethane resin during the curing step were always associated with significant MDA levels in urine. CONCLUSIONS: Total MDA in post-shift urine samples is a reliable biomarker to assess occupational exposure to MDI in various industrial applications and to help factories to improve their manufacturing processes and working practices. A biological guiding value not exceeding 7 microg/l (5 microg/g creatinine) could be proposed in France.

Environmental Monitoring↗

PubMed2005

Polyurethanes as potential substrates for sub-retinal retinal pigment epithelial cell transplantation.

Transplantation of cultured retinal pigment epithelial (RPE) cells under the failing macular is a potential treatment for age related macular degeneration. An important step in the development of this procedure is the identification of a suitable membrane on which to grow and transplant the cells. This paper evaluates the potential of using polyurethanes in this application since they possess several of the required properties, such as, flexibility, robustness, biostability and good biocompatiblilty although their hydrophobicity can limit cell adhesion. Three commercially available polyether urethanes (Pellethane, Tecoflex and Zytar) were evaluated in terms of their wettability using dynamic contact angle analysis and their ability to support a monolayer of functioning RPE cells (ARPE-19) . Furthermore Pellethane and Tecoflex were treated with a simple air plasma treatment and analysed as above. In the "as received condition" only a few RPE cells attached to the Pellethane and Tecoflex and remained clumped. RPE cells grew to confluence on the Zytar substrate by 7 days without further surface modification. Air gas plasma treatment of both Pellethane and Tecoflex increased the wettability of the surfaces and this resulted in the growth of a monolayer of well-spread RPE cells on both materials. Morphologically these cells grew with a normal 'cobblestone' phenotype. These results demonstrate the potential of these polyurethanes for this application.

Cell Line↗

PubMed1984

The elastic properties of a polyurethane arterial prosthesis.

The relationship between the mechanical properties of a fibrous polyurethane arterial prosthesis and the graft manufacturing process variables was studied from uniaxial tensile tests. A non-linear model was used to characterize the cylindrical elastic properties. Experiments on cylindrical segments were carried out to determine the constitutive constants and to assess the applicability of the model to the polyurethane graft. The compliance of 4 mm internal diameter grafts with various wall-thicknesses was predicted. The results were used to produce grafts with compliance matched to that of the carotid and femoral arteries.

Biomechanical Phenomena↗

PubMed1991

Stress distribution on the cusps of a polyurethane trileaflet heart valve prosthesis in the closed position.

In this paper, a finite element analysis of the stress distribution on the cusps of a polyurethane trileaflet heart valve prosthesis in the closed position is presented. The geometry of the valve was modified from a relationship proposed by Ghista and Reul (J. Biomechanics 10, 313-324, 1977). The effects of variations in stent height, leaflet thickness and coaptation area on the stress distribution were also analyzed. Analyses were performed with both rigid and flexible stents for the trileaflet valve in order to delineate the effect of stent flexibility on the leaflet stress distribution. The results showed that regions of stress concentration were present near the commissural attachment similar to those predicted with the bioprostheses. The stresses on the leaflets were reduced by increasing the stent height with both rigid and flexible stents. Selectively increasing the leaflet thickness near the commissures and also increasing the coaptation area did not prove to reduce the leaflet stresses when the stent flexibility was taken into account. The possible effect of high stresses on the structural integrity of polyurethane leaflets and its relationship with calcification is yet to be investigated.

Heart Valve Prosthesis↗

PubMed1990

Production of acid proteinases by Humicola lutea mycelium immobilized in polyurethane sponge.

Humicola lutea 120-5 spores were entrapped in polyurethane sponge cubes and were cultivated inside the carrier to form an immobilized mycelium further used for production of acid proteinases in batch mode. A carrier--spore suspension ratio of 10:0.5 (wt) should be used to obtain optimal results. The polyurethane sponge-immobilized mycelium could be applied repeatedly, the enzyme activity secreted during the first 10 cycles being about the same as that produced by free cells. The advantages of immobilizing fungal cells by germinating conidia entrapped inside the supporting material are discussed.

Aspartic Acid Endopeptidases↗