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Flexible polyurethane foams are mainly used for their particular mechanical properties such as hardness and resilience. The correlation of the foam properties with the material structure is believed to be important but it has always been difficult to identify the individual contributions of the cellular structure and of the polymer to the foam physical properties.
The biocompatibility of polyurethane resin-implants derived from castor bean (Ricinus communis) was analyzed in the rat dental alveolus. Histometric evaluation of trial areas adjacent to the implants showed, by week 1, the polymer granules encircled by a conspicuous capsule and surrounded by immature connective tissue. By weeks 2 and 3, the implants were surrounded by less prominent fibrous capsules and most of the tested area was occupied by mature trabecular bone. By week 6, the fibrous capsule was thinner and the tested area was almost totally covered with bone, which in several places was in close contact with the implants. The results suggest that the material is compatible, as it was progressively integrated into alveolar bone in the wound-healing process.
In modern medicine, infection is one of the most serious complications of implanted plastic devices. The host is not able to overcome this special type of opportunistic infection despite having a normal immune response and a low virulence of most of the bacteria involved. Antimicrobial therapy alone generally cannot cure the infection and the removal of catheters often remains the only choice of therapy. Bacterial adhesion to the polymer surface of the catheter, be it luminal or external, is an important step in the pathogenesis of catheter-associated infections. In this report, we describe new approaches to the prevention of infections by impregnation of polyurethane and silicone with silver by two different methods. The antimicrobial activity of these silver-impregnated catheters is more than 10 fold higher for coagulase-negative staphylococci (CNS) compared to catheters without silver. Similar results are obtained with other microbial organisms like Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Candida albicans. The new polymers show no cytotoxic or thrombogenic side effects in vitro.
Following promising results in animals, implantation of polyurethane vascular prostheses for femoral reconstruction was performed in 15 patients over a 10-month period. This prospective study was carried out to evaluate the patency, limb salvage and complications associated with this type of small diameter conduit for arterial occlusive diseases. The indications for surgery included acute and chronic ischaemia, non-healing ulceration or gangrene. There were five early occlusions, which resulted in a 1-month primary patency rate of 66% and a secondary patency rate of 80%. The mean limb salvage rate at 1 month was 80% and is 66% at the present time. Infection occurred in one patient following multiple attempts at graft thrombectomy. There were no statistically significant differences in patency rates between proximal and distal popliteal graft anastomoses. Two critical phases of healing were identified where the graft was prone to flow deterioration; at 4-6 weeks and at 4-6 months. It is concluded that although this type of graft has many interesting features, e.g. the presence of endothelial cells under poor haemodynamic conditions, excellent graft-host healing and good resistance at the suture site, further investigations on protein absorption and complement activation as well as intensive structural testing are required before further recommendations can be made.
A cell culture line was established from enzymatically-derived canine jugular endothelial cells and further cultured. Whenever sufficient cells were present, fibrous polyurethane vascular prostheses, impregnated with gelatin and coated with fibronectin, were seeded with 4.8 x 10(5)/cm2 cells, sufficient to establish a confluent monolayer, and implanted in the femoral arteries of 16 dogs. A non-seeded prosthesis on the contralateral side served as control. Eight dogs received antiplatelet aggregation medication: 250 mg aspirin together with 25 mg dipyridamole, orally three times daily, starting 2 weeks prior to the implantation operation and continued for the duration of the experiment. Results show that in the non-medicated dogs all control prostheses become occluded within 3 weeks after implantation, whereas five out of eight seeded prostheses remained patent. In the medicated group, two out of eight control prostheses occluded and all seeded prostheses remained patent. Scanning and light microscopy revealed that seeded prostheses were completely lined with endothelial cells (Factor VIII positive stain) week 3 (n = 3) and 12 (n = 3) after implantation, while endothelialisation in control prostheses had advanced only 5 mm into the prostheses in 12 weeks. Two dogs of each group were included in long-term patency studies. We conclude that prostheses seeded with a confluent monolayer of endothelial cells result in superior patency rates for both medicated and non-medicated dogs. No immunological reaction against the (allogeneic) seeded endothelial cells were noted.
The cytocompatibility of polyurethane membranes was tested following ultraviolet or gamma irradiation as well as treatment with hydrogen peroxide or glutaraldehyde containing solutions. Despite the fact that all of the methods had been recommended for antimicrobial treatment of glucose biosensors, the treatments investigated significantly influenced cytocompatibility characteristics. Cytotoxicity of membrane eluates was not observed following irradiation treatments. This was also the case when the membranes were repeatedly washed following chemical treatment. Cell growth upon the membranes was stimulated to a different extent after gamma and UV irradiation as well as following hydrogen peroxide treatments. Residues of an urea-based hydrogen peroxide inclusion compound caused a restriction in cell growth upon the membranes as was similarly observed with 2 and 4% glutaraldehyde solutions acting over 2 and 4 h, respectively. It is concluded that cytocompatibility in vitro reflecting the host response against a biomaterial in vivo does not only depend upon the material itself but also upon antimicrobial treatments which could have consequences for its bioperformance characteristics.
Chemical microsensors based on ion-selective field effect transistor (ISFET) transducers with ion-selective and enzymatic membranes have been fabricated. In this case, photolithographically patterned membranes based on acrylated urethanes have been developed and applied onto the gate area of ISFET chips. Aliphatic urethane diacrylate has been used for K+ and NH+4 membranes, while a photocurable hydrogel formulation based on other type of acrylated urethane has been optimized for urea-FET sensors. Resulting potassium and ammonium sensors show similar performances to those found when PVC membranes are employed. An integrated packaging process for ISFET-based sensors has been developed giving the possibility of carrying out most of the encapsulation on wafer level. For this purpose, a photocurable polyurethane encapsulant formulation has been optimized to be microstructured by photolithography. Finally, a preliminary study of biocompatibility of photosensitive formulations containing urethane oligomers has been performed in order to examine future applications in biomedical and clinical analysis.
Polyurethane (PU) films were prepared by solution-casting after co-polymerization of liquefied woods (LWs) and polymeric methylene diphenylene diisocyanate (PMDI). The resulting PU films had various [NCO]/[OH] ratios ranging from 0.6 to 1.4 and contained 5.0-16.8% dissolved woody components at the [NCO]/[OH] ratio of 1.0. The crosslink densities of the films with [NCO]/[OH] ratios of 0.6-1.4 increased remarkably with increasing [NCO]/[OH] ratio. Similarly, there were large increases in glass transition temperatures (Tg). These characteristics could be attributed to effective incorporation of PMDI into the LW. The crosslink densities and Tg of the PU films prepared at the [NCO]/[OH] ratio of 1.0 increased because the amounts of dissolved woody components in the films increased. It is concluded that the dissolved woody components acted as crosslinking points in PU network formations. The thermal degradation of the PU films at an [NCO]/[OH] ratio of more than 0.8 or with more than 10.6% dissolved wood started above 262 degrees C under an N2 atmosphere. The thermostability was lost at low crosslink density or with large amount of co-polymerized glycerol structures in the PU networks.
The purpose of this trial was to prepare for a large randomized trial comparing Arglaes film dressing, a recent innovation containing silver ions, against Tegaderm, a transparent polyurethane dressing. Thirty-one patients admitted to the intensive care unit and requiring the insertion of an arterial line or central venous catheter were recruited into the study. Skin swabs were taken from the insertion sites prior to catheterization and on removal of the intravascular device to measure skin colonization rate between the two dressings. The catheter tips were also cultured on removal to establish if there was a difference between the two groups. No statistical differences were found in bacterial growth between the two dressings.
RATIONALE AND OBJECTIVES: We describe a self-expanding metallic biliary Gianturco-Rösch stent coated with polymeric material. The coating was designed to prevent the growth of neoplastic and reactive tissue within the biliary ducts. METHODS: The stents were coated with a solvent-casting technique, which consists of dissolving polyurethane (polyether urethane or polycarbonate urethane) pellets in a solvent (dimethylacetamide), dipping the stent in the solution, and completely evaporating the solvent. In vitro mechanical characterization of the stent was performed to determine the adhesion of the coating to the metallic cage, the best introducer caliber for implantation of the device, and the relationship between the stent's diameter and radial stress. RESULTS: Reports in the literature on the biostability of polycarbonate urethane compared with polyether urethane prompted us to use the former material to coat the stents. The solvent technique gives a smooth internal surface of the stent wall, leaving in relief the coated structure of the stent on the external surface. The functional tests demonstrated that the coating did not compromise the original characteristics of the stent in terms of self-expandability, axial flexibility, and increased radial rigidity of the device. CONCLUSION: Functional tests verified coating stability and device handling, which are the first steps toward in vivo experimentation.
OBJECTIVES: Compliance mismatch between graft and native artery, and failure of the graft to develop an endothelial lining are the two main factors in graft failure. The objective of this study was to assess a new compliant graft for effective cell attachment and cell retention at physiological levels of pulsatile shear stress over a 6-hour period of physiological pulsatile flow. DESIGN: Laboratory haemodynamic study. MATERIALS AND METHODS: Human umbilical vein endothelial cells labelled with 111In-oxine were seeded on compliant polyurethane (CPU) and polytetrafluoroethylene (PTFE) vascular grafts. These were then exposed to varying shear stresses of up to 13.8 +/- 0.6 dyn/cm2 using a pulsatile flow model. Dynamic scintigraphy images were acquired using a gamma camera linked to an on-line computer during 6 h of perfusion and data presented as mean +/- standard error of mean. RESULTS: Mean seeding efficiencies were significantly different at 4,316 +/- 505 and 825 +/- 504 CPM/cm2 on the CPU and PTFE grafts, respectively (p = 0.018). The flow experiment showed a higher percentage of cells retained on the CPU graft after exposure to shear stress caused by pulsatile flow compared to PTFE with respect to time. After 6 h pulsatile perfusion there was a significantly higher proportion of initial cells attached to CPU graft compared to PTFE graft (73 +/- 8% vs 42 +/- 8%, p = 0.018). The areas under the time activity curves over the 6-hour period were 280 +/- 26.4 for CPU and 176.0 +/- 30.0 for PTFE, confirming a significant greater total cell loss from PTFE compared with CPU grafts (51 +/- 7.0% vs 23 +/- 8.3%, p = 0.018, Wilcoxon matched-pairs signed-ranks test). CONCLUSIONS: This flow model provides an effective method of assessing cell retention on graft materials under physiological conditions over a 6-hour period; CPU combines both excellent compliance and endothelial cell attachment rates after 6 h exposure to shear stress.
We studied rates of peripheral intravenous (IV) catheter tip and insertion site colonization after randomly assigning patients to transparent polyurethane (TP) dressings (N = 316) or dry gauze (DG) dressings (N = 421). The study was conducted during both summer and fall seasons, in a facility which lacked air conditioning. All patients had a teflon plastic catheter inserted, maintained and cultured by a member of the IV therapy team; no antibiotic or antiseptic ointments were used. Colonization rates were higher in the summer than in the fall for both catheter tips (9.0% vs 3.5%, p = 0.005) and sites (21.6% vs 7.0%, p = 0.001). During the summer season, the rate of catheter tip colonization with TP dressings was nearly twice that of DG dressings (12.4% vs 6.8%, p = 0.04). Logistic regression analysis indicated that catheter tip colonization was associated with the summer season (odds ratio = 3.0, 95% CI 1.4-6.2) and TP dressings (odds ratio = 1.8, 95% CI 1.1-3.2), and that site colonization was associated with both summer (odds ratio = 4.0, 95% CI 2.2-7.1) and receipt of antibiotics (odds ratio = 1.9, 95% CI 1.1-3.2). Coagulase-negative staphylococci were isolated from 55.5% of the colonized catheter tips and insertion sites. The data suggest that bacterial colonization of peripheral IV catheters is increased in summer, and that use of TP dressings may increase both tip colonization and cost nearly twofold.
Glass cartridges containing 6-10 g of Tenax-GC or 15 g of XAD-2 resin packed between two slices of polyurethane foam (PUF) were used in a General Metal Works PS-1 high-volume sampler to collect chlorobenzenes (CBs) containing three to six chlorine atoms, hexachlorocyclohexanes (HCHs), and two-ring aromatic hydrocarbons from 35-385 m3 of air. Laboratory experiments were run by vaporizing known quantities of analytes into a clean airstream for sampling by the PS-1 system at 20 degrees C. Collection efficiencies, determined from mass balance of the quantities introduced and recovered, ranged from 70 to 120% for individual compounds and averaged 93% overall. Penetration of analytes to backup adsorbent traps showed an inverse correlation to vapor pressure. The method was used to collect the above compounds from urban and rural air.
The susceptibility of segmented polyurethanes (SPUs) to in vivo oxidative cleavage and hydrolysis constitutes a drawback in the use of these materials in the fabrication of implantable devices. The introduction of poly(dimethylsiloxane) (PDMS) groups into the polymer main chain has been previously reported to enhance the stability of SPUs. Herein, we evaluated the use of BioSpan-S, a silicone-modified SPU, in the design of membranes for cation-selective electrodes. The resulting electrodes exhibited good potentiometric response with all of the tested ionophores (valinomycin, sodium ionophore X, and nonactin). The obtained selectivity coefficients meet the selectivity requirements for the determination of sodium and potassium in blood. Moreover, as reflected by SEM studies, membranes prepared with BioSpan-S showed less adhesion of platelets than membranes prepared with conventional poly(vinyl chloride) (PVC). These results lead to the conclusion that BioSpan-S would be an appropriate candidate for the fabrication of implantable ion-selective electrodes.
A new method for the sampling and off-site analysis of hemoglobin variants by mass spectrometry is reported. This technique uses a nonporous polyurethane membrane as the collection device and transportation medium of a blood sample for analysis. The same membrane is then used as the MALDI-TOF MS sample support for mass spectrometric analysis. Minimal invasive sample collection is afforded by collecting less than 1 microL of blood using a common lancet device. MALDI-TOF MS is performed directly on the membrane, after washing off the interfering plasma components, followed by the addition of matrix. This reduces the time of analysis and prevents sample loss. Enzymatic digestion can be performed directly on the membrane, using in this case trypsin, allowing for further characterization of the sample. The method is much less invasive compared to drawing blood with a syringe. The sample may be transported to the laboratory by regular mail, and thus the method can serve remote locations. We demonstrate the procedure by characterizing the Hb Shepherds Bush hemoglobin variant, b74-(E18)Gly-->Asp.
Peptides containing the RGD sequence were covalently attached to an isocyanate-containing polyurethane prepolymer and the biological properties of the complexes were evaluated. For the pentapeptide H2N-Tyr-Arg-Gly-Asp-Ser-OH (single-letter code, YRGDS), polymer conjugation lead to an increased half-life in the blood circulation of mice to > 10 h. The effect of covalent attachment of polymer on biological activity was examined in a related peptide, H2N-Gly-Arg-Gly-Asp-Ser-Pro-Ala-Cys- OH (GRGDSPAC). Inhibition of B16-F10 melanoma cell attachment and spreading on plates coated with fibronectin by an RGD-containing peptide and polymer-conjugated GRGDSPAC was observed to occur at similar concentrations. We conclude that the conjugation of peptides containing the Arg-Gly-Asp motif to this polymer resolves previous problems of their rapid loss from the circulation, while still allowing retention of full biological inhibitory activity.
Lipophilic polymer membranes incorporating binding sites are widely used in various potentiometric, amperometric, and optical sensors. Here, we report on the biofunctional modification of the surface of a Ca(2+)-selective membrane. A photoactivatable biotin derivative was synthesized and covalently immobilized on a soft polyurethane membrane. The modified polymer was characterized by X-ray photoelectron spectroscopy (XPS) as well as by potentiometric measurements. The selective binding of streptavidin by the photo-cross-linked biotin derivative was demonstrated. The surface coverage obtained with different experimental protocols was analyzed by autoradiography using [(35)S]-streptavidin. The new approach may significantly extend the scope of applicability of potentiometric sensors.
The synthesis of polyurethane polymers in the presence of diisopropylfluorophosphatase (DFPase) has enabled the irreversible attachment of the enzyme to the polymeric matrix. The resulting bioplastic hydrolyzes diisopropylfluorophosphate (DFP) in buffered media up to 67% of the rate for the same amount of soluble enzyme. Above a DFPase concentration of approximately 0.1 mg/gfoam, the rate of the reaction catalyzed by the enzyme-containing polymer was controlled by internal mass transfer. Increasing foam hydrophilicity, via the use of nonionic surfactants during polymerization, significantly affected the structural properties of matrix, thereby enhancing the intrinsic and apparent efficiency of modified DFPase. The resulting reduction in internal mass transfer limitations was explained morphologically with electron microscopy.