Poly Ether Urethane Urea Research Articles

ВЛИЯНИЕ НАПОЛНИТЕЛЕЙ НА АБРАЗИВНЫЙ ИЗНОС СЕГМЕНТИРОВАННОЙ ПОЛИУРЕТАНМОЧЕВИНЫ

As an object of research, we have chosen a well-known elastic polymer material – polyetherurethane urea SKU-PFL, which is a typical segmented block copolymer. Powdered microdispersed fillers capable to improve wear resistant such as calcium stearate and molybdenum disulfide were added to this material at the manufacturing stage in varying amounts (up to 1.5% by weight). The found level of the optimal filler concentration for the investigated elastomers in the region close to 0.5 wt% makes it possible to consider calcium stearate and molybdenum disulfide as not only effective but also economical components of promising wear-resistant polymeric materials.

Evaluation of Poly (Carbonate-Urethane) Urea (PCUU) Scaffolds for Urinary Bladder Tissue Engineering.

Although the previous success of bladder tissue engineering demonstrated the feasibility of this technology, most polyester based scaffolds used in previous studies possess inadequate mechanical properties for organs that exhibit large deformation. The present study explored the use of various biodegradable elastomers as scaffolds for bladder tissue engineering and poly (carbonate-urethane) urea (PCUU) scaffolds mimicked urinary bladder mechanics more closely than polyglycerol sebacate-polycaprolactone (PGS-PCL) and poly (ether-urethane) urea (PEUU). The PCUU scaffolds also showed cyto-compatibility as well as increased porosity with increasing stretch indicating its ability to aid in infiltration of smooth muscle cells. Moreover, a bladder outlet obstruction (BOO) rat model was used to test the safety and efficacy of the PCUU scaffolds in treating a voiding dysfunction. Bladder augmentation with PCUU scaffolds led to enhanced survival of the rats and an increase in the bladder capacity and voiding volume over a 3week period, indicating that the high-pressure bladder symptom common to BOO was alleviated. The histological analysis of the explanted scaffold demonstrated smooth muscle cell and connective tissue infiltration. The knowledge gained in the present study should contribute towards future improvement of bladder tissue engineering technology to ultimately aide in the treatment of bladder disorders.

Fabrication of porous microtent structures toward an in vitro endothelium model

This paper reports the fabrication of compliant and permeable thin films with controlled curvature preferable to serve as engineering scaffolds for the production of in vivo like vascular endothelial constructs. A simple fabrication process was developed to fabricate three-dimensional ‘tent’ like microstructures by combining electrospinning and microfabrication. In particular, the ‘microtents’ were created by electrospinning mechanically flexible poly(etherurethane)urea(PEUU) polymer on a microstructured collecting substrate. The shape of the ‘microtents’ can be tuned by adjusting the geometries of microstructures on the collecting substrate and the operational parameters of electrospinning. Mechanical characterization showed the nonlinear mechanical behavior of porous polymeric thin films is similar to those of soft tissues, indicating that these thin films may serve as scaffolds for mimicking local mechanical environment of vascular tissues. Human endothelial cells were successfully cultured on the concave side of the porous thin film, constituting an endothelium model in vitro. This work addresses the need for engineered tissue scaffolds that can mimic both morphological and mechanical environments of natural vascular endothelium. The coupled effects of mechanical, structural and biochemical factors on vascular endothelium can thus be investigated.

Behaviour of Segmented Polyether Urethane Urea in a Humid Atmosphere after Mechanical Loading

The laws governing the mechanical behaviour of plasticised polyurethane ureas in a wide range of air relative humidity are studied. It is shown that, in the presence of a plasticiser lowering the solubility of the rigid blocks in the flexible phase of the polymer, there is an increase in the stability of the mechanical characteristics of polyurethane urea on exposure to a humid atmosphere.

Activation of caspase 3 during shear stress-induced neutrophil apoptosis on biomaterials.

Within the complex environment of an implanted cardiovascular device comprised of dynamic flow and foreign materials, phagocytic neutrophils may be ineffective in combating infection due to cellular responses to shear stress. This may be explained, in part, by our recent reports of apoptosis of biomaterial-adherent leukocytes induced through exposure to shear stress. Here we utilize a rotating disk system to generate physiologically relevant shear stress levels (0-18 dynes/cm(2)) at the surface of a polyetherurethane urea (PEUU) and investigate neutrophil intracellular pathways involved in shear-induced apoptosis. In situ detection of activated caspases, the enzymatic mediators of the apoptosis cascade, showed qualitatively that these proteases participate in shear-induced apoptosis and are activated in a shear-dependent manner. The involvement of caspase 3 was confirmed through immunoprecipitation and immunoblotting of extracted neutrophil proteins. Comparative studies with neutrophils adherent under static conditions demonstrated time-dependent activation of caspases in TNF-alpha/cycloheximide-induced apoptosis, for which caspase-3 also was implicated. These findings are the first steps toward elucidation of the mechanisms behind the inappropriate induction of apoptosis by adhesion to biomaterials, which may contribute to the development and persistence of device-related infections.

BIOSTABILITY OF THORALON® LVAD BLOOD PUMPING SACS AFTER LONG TERM CLINICAL USE

The Thoratec® Ventricular Assist Device (VAD) System utilizes Thoralon® for the blood pumping sac and inflow and outflow cannulas. Thoralon is a polyetherurethaneurea (PEUU) blended with a siloxane-based surface modifying additive. The purpose of this study is to perform a physicochemical evaluation of VAD blood sacs explanted from human subjects. Four blood sacs were analyzed after 53, 171, 336 and 434 days of use and compared to unimplanted controls. Tensile strength, 300% stres and Young's modulus of explanted blood sacs showed slight increases over the controls, whereas % elongation showed slight decrease. Both number average and weight average molecular weight were higher than the unimplanted control. However, the duration of implantation had no significant effect.TableThere was no difference observed in the physical properties and molecular weight between high and low flex regions of the blood sacs. SEM and ATR FT-IR analysis did not show any signs of surface degradation. The results support the long-term biodurability of Thoralon for use in ventricular assist device clinical applications.

Shear stress-induced apoptosis of adherent neutrophils: a mechanism for persistence of cardiovascular device infections.

The mechanisms underlying problematic cardiovascular device-associated infections are not understood. Because the outcome of the acute response to infection is largely dependent on the function of neutrophils, the persistence of these infections suggests that neutrophil function may be compromised because of cellular responses to shear stress. A rotating disk system was used to generate physiologically relevant shear stress levels (0-18 dynes/cm(2); 1 dyne = 10 microN) at the surface of a polyetherurethane urea film. We demonstrate that shear stress diminishes phagocytic ability in neutrophils adherent to a cardiovascular device material, and causes morphological and biochemical alterations that are consistent with those described for apoptosis. Complete neutrophil apoptosis occurred at shear stress levels above 6 dynes/cm(2) after only 1 h. Morphologically, these cells displayed irreversible cytoplasmic and nuclear condensation while maintaining intact membranes. Analysis of neutrophil area and filamentous actin content demonstrated concomitant decreases in both cell area and actin content with increasing levels of shear stress. Neutrophil phagocytosis of adherent bacteria decreased with increasing shear stress. Biochemical alterations included membrane phosphatidylserine exposure and DNA fragmentation, as evaluated by in situ annexin V and terminal deoxynucleotidyltransferase-mediated dUTP end labeling (TUNEL) assays, respectively. The potency of the shear-stress effect was emphasized by comparative inductive studies with adherent neutrophils under static conditions. The combination of tumor necrosis factor-alpha and cycloheximide was ineffective in inducing >21% apoptosis after 3 h. These findings suggest a mechanism through which shear stress plays an important role in the development of bacterial infections at the sites of cardiovascular device implantation.

Shear stress effects on bacterial adhesion, leukocyte adhesion, and leukocyte oxidative capacity on a polyetherurethane.

Infection of implanted cardiovascular biomaterials still occurs despite inherent host defense mechanisms. Using a rotating disk system, we investigated Staphylococcus epidermidis and polymorphonuclear leukocyte (PMN) adhesion to a polyetherurethane urea (PEUU-A') under shear stress (0-17.5 dynes/cm2) for time periods up to 6 h. In addition, the superoxide (SO) release capacity of PMNs after transient exposure to PEUU-A' under shear stress was determined. Bacterial adhesion in phosphate-buffered saline (PBS) showed a linear shear dependence, decreasing with increasing shear stress. Overall adhesion in PBS decreased with time. However, bacterial adhesion in 25% human serum was similar for all time points up to 360 min. Adhesion was observed at all shear levels, displaying no shear dependence. In contrast, PMN adhesion demonstrated a strong shear dependence similarly for times up to 240 min, decreasing sharply with increasing shear stress. Although PMNs preexposed to shear stress showed a slightly diminished SO release response compared to fresh cells for all stimuli, it was not statistically significant regardless of the stimulus. We conclude that circulating leukocytes are unable to adhere in regions of high shear which may contain adherent bacteria. In addition, exposure to PEUU-A' and shear stress (in the range 0-18 dynes/cm2) is insufficient to cause a depression in the oxidative response of PMNs.

Tenacious Binding of Fibrinogen and Albumin to Pyrolite Carbon and Biomer

Adsorption of bovine fibrinogen from dilute plasma and human serum albumin (HSA) from buffered HSA solution to low-temperature isotropic (LTI) pyrolytic carbon (Pyrolite) and polyetherurethane urea (Biomer) was measured. Whereas fibrinogen adsorption to Biomer passed through a maximum at intermediate plasma dilution (a typical Vroman peak), maximal adsorption to Pyrolite occurred from undiluted plasma; i.e., there was no Vroman effect. Protein elution by sodium dodecyl sulfate (SDS) surfactant was also measured. The amount of fibrinogen eluted from both substrates by SDS was less when the protein was adsorbed from more dilute plasma or eluted after 4 days postadsorptive residence time. Under all conditions, fibrinogen retention by Pyrolite was greater than that by Biomer. Binding of a monoclonal anti-fibrinogen (against residues 402–411 of the gamma chain) to substrates preadsorbed with human plasma was measured using an ELISA. Antibody binding (normalized to the amount of fibrinogen adsorbed) to plasma preadsorbed Pyrolite was much less than that to preadsorbed Biomer. On both surfaces, normalized antibody binding was much greater when fibrinogen adsorption had occurred from more dilute plasma. Monolayer adsorption of HSA to Pyrolite was observed. HSA retention was greater when the protein was adsorbed from more dilute solution. These results demonstrate that proteins are tenaciously bound to Pyrolite compared with Biomer. Therefore, the thromboresistance of Pyrolite may be partly due to the lowered reactivity of the platelet binding domain, as well as a lessened ability of tightly bound fibrinogen to interact with platelets.

Surface modification of polyetherurethaneureas and their antithrombogenicity

Polyetherurethaneurea (PU) films were treated by oxygen plasma discharge followed by acrylic acid (AA) grafting. The carboxyl groups of the AA-grafted PU (PU-AA) surface were coupled with bovine serum albumin and heparin via water soluble carbodiimide. Surface characterization of the modified PUs was carried out by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and electron spectroscopy for chemical analysis (ESCA). The amount of immobilized albumin and heparin on the PU surface was 1.8 and 1.5 μg/cm2, respectively, as determined by the dye interaction method. Interactions between the surface-modified PUs and blood components such as plasma proteins and platelets were investigated to evaluate the blood compatibility of the samples. Plasma recalcification time (PRT) and activated partial thromboplastin time (APTT) of the albumin-immobilized PU (PU-Al) were almost the same as those of PU, while platelets were less adhered on the PU-Al than on PU. On the other hand, PRT and APTT of the PU-He were significantly longer than those of the PU, PU-AA, and PU-Al. Moreover, adhesion of platelets was effectively suppressed on the PU-He, leading to good in vitro blood compatibility.

An Investigation of the Surface Chemistry of a Polyetherurethaneurea Biomaterial Using XPS

A poly(tetramethylene oxide) [PTMO] based polyetherurethaneurea (PEUU), produced by Polymer Technology Group Inc. (Emeryville, CA) as a Primary Reference Material, was spin-cast from a 3% (w/v) DMAc solution onto a glass cover slip. The polymer coating was analyzed at ambient temperature by XPS using a 55° take-off angle. An elemental survey scan shows the presence of C, N, and O (no trace elements were detected). The C 1s spectrum shows a nearly equal concentration of ether and hydrocarbon environments, suggesting that surface localization of the PTMO soft segment is occuring. A broadened peak at higher binding energy (~289.1 eV) is indicative of the presence of both urea and urethane nitrogens. The N 1s peak location suggests that there is a greater contribution from urea groups. The dominant contributors to the O 1s spectra are ether functionalities. The urea and urethane contributions are apparent as high and low binding energy tails but are too small to be resolved accurately.

Polyetherurethaneurea reinforced poly(vinyl alcohol) dialysis membranes: studies on permeability and mechanical strength

Poly(vinyl alcohol) is a hydrogel which is extensively studied for a variety of biomedical applications. Membranes developed from crosslinked poly(vinyl alcohol) (PVA) is having excellent permeability to solutes. However its wet breaking strength is low. Polyetherurethaneurea (PEUU), having an excellent mechanical strength is blended with PVA as a reinforcement, and membranes developed are studied for its permeability and mechanical strength. The optimum membrane selected, is having permeability and wet breaking strength almost equal to the commercially available cellulose acetate membrane.

Morphological, physical and chemical evaluation of the Vascugraft® arterial prosthesis: comparison of a novel polyurethane device with other microporous structures

In this study the morphology, physical properties, surface chemical characteristics and microstructure of the Vascugraft ® arterial prosthesis have been investigated. This is a novel microporous polyurethane device, recently developed by the company Braun-Melsungen AG in Germany for use as a small calibre arterial substitute. This comparative study included two other synthetic grafts: the Mitrathane ® prosthesis, a hydrophilic prototype polyetherurethane urea graft with closed internal pores, and the commercially successful expanded polytetrafluoroethylene reinforced Goretex ® prosthesis with an open microporous structure. The Vascugraft ® prosthesis contains a network of fused microfibres of varying thickness and orientation which provide open and communicating pores similar in size to those in the Goretex ® material. In addition, they extend from one side of the graft wall to the other. As well as having superior longitudinal and radial compliance to the reinforced Goretex ® device, the Vascugraft ® prosthesis has more than adequate bursting and suture retention strengths. Through the use of contact angle measurements, electron spectroscopy for chemical analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry and molecular weight analysis by size exclusion chromatography, the surface of the Vascugraft ® prosthesis has been shown to be uniquely hydrophobic, as well as containing carbonate groups within an aliphatic polyesterurethane polymer. In addition, variations in micro-phase separation structure of hard and soft segment domains between different sizes and batches of product are marginal. Because of the interesting physical and chemical properties, it is recommended that in vitro biocompatibility and biostability studies be undertaken prior to using the prosthesis in animal or clinical trials.

Protein Adsorption - Effect of External Lubricants at the Interface

Upon exposure to blood, rapid adsorption of proteins is the initial event at the contacting surface, followed by the adhesion of platelets and other blood components. Surfaces absorbing albumin appear to possess antithrombotic character in discouraging adhesion of platelets. Therefore, for the development of a blood contacting device, the interfacial events are extremely important and need serious investigation. We have attempted to observe the variations in competitive adsorption of fibrinogen and albumin onto the polyetherurethane urea (PEUU) surface in the presence of external lubricant, such as calcium stearate and silicone fluid coating. It seems, in the presence of such mediators, that fibrinogen adsorption is increased relatively with reduction in albumin at the surface.

Cyclical strain effects on production of vasoactive materials in cultured endothelial cells.

Mechanical forces due to fluid flow and cyclical strain can alter endothelial cell morphology and function, including the release of vasoactive materials endothelin, prostacyclin (PGI2), and tissue plasminogen activator (t-PA). In this study, effects of cyclical strain were modeled by culturing bovine aortic endothelial cells on fibronectin-coated elastic membranes of silicone rubber (Silastic) or poly-etherurethane urea (Mitrathane). After growing to confluence under static conditions of 37 degrees C in humidified air with 5% CO2, cells were strained cyclically at membrane elongations of 5% or 10% for 24 hours at 1 Hz. Controls were maintained under static conditions or were exposed to fluid motions similar to the strained cells but without stretching. Secretion rates were constant throughout experiments in the strain chamber with no initial burst in metabolism associated with the initiation of strain. Secretion rates were not altered by choice of elastic membrane. At a physiological level of 10% cyclical strain, prostacyclin and endothelian secretion rates were increased by 2.5-fold and 1.7-fold, respectively, above stationary controls. Endothelin production demonstrated a dose-dependent response with cyclical strain, while PGI2 appeared to require a threshold strain before an increase in secretion occurred. No significant differences in t-PA levels were seen in cyclically strained cells compared with controls. These results indicate that endothelial cells respond metabolically to cyclical strain and suggest that mechanical strain may modulate secretion of selective vasoactive materials by vascular endothelial cells.

Effect of Fabrication, Sterilization and Mediators - Blood Compatibility of Polyurethanes

The possible changes in the surface and physical properties of polyether urethane urea (PEUU) implants, including their interaction with blood, due to the different preparation methods, sterilization techniques and long term storage in different environmental conditions have been investigated by conducting the studies of mechanical properties, contact angle, platelet adhesion and protein adsorption. Considerable variations in the mechanical properties have been observed for the PEUU grafts stored in different conditions. Changes in platelet adhesion and albumin adsorption have also been observed in the case of samples that underwent different sterilization methods. The effect of mediators like bromelain, an enzyme present in pineapple juice, on albumin adsorption and platelet adhesion on PEUU surfaces have been investigated. It seems the presence of pineapple juice increases the adsorption of albumin and reduces the adhesion of platelets on PEUU surfaces.

Correlation between the microstructure and properties of haemocompatible polyetherurethane ureas

The effect of the proportion of rigid blocks in segmented polyetherurethane ureas on their mechanical properties is studied. It is established that there are two critical points on the plots of the properties of the polymers against temperature, in which the nature of the behaviour of the system changes its character. It is shown by small angle X-ray scattering that at these points the type of supermolecular (domain) structure of the polyetherurethane urea changes.

Polyether Urethane Urea Membrane for An Improved Hemodialysis

This paper reviews our current activities of developing polyether urethane urea membranes for hemodialysis application. It is observed that the processing parameters such as precipitation medium, precipitation temperature etc. can influence the porosity of the membrane and subsequently the permeability property. Polyurethane/poly(methyl methacrylate) blended membranes have also shown high permeability. All the membranes are subjected to different sterilization processes and the pore sizes before and after sterilization are determined. The changes in the pore size due to sterilization seems to effect the permeability.

Albumin adsorption on to aluminium oxide and polyurethane surfaces

The changes in protein adsorption onto aluminium surfaces coated with different thicknesses of oxide layers were examined. The oxide layers on aluminium substrates were derived by the anodizing technique. Protein adsorption studies were conducted using 125l-labelled albumin and the amount of albumin adsorbed was estimated with the help of a gamma counter. An increase in albumin adsorption was observed on oxide layer coated aluminium surfaces. The effect of anti-Hageman factor on albumin and fibrinogen adsorption on to bare aluminium, oxide layer coated aluminium and bare polyether urethane urea surfaces was also investigated. It was observed that the presence of anti-Hageman factor increased the adsorption of albumin and fibrinogen on to all these substrates.

Hydrophobic and fibrillar microporous polyetherurethane urea prosthesis: an ESCA study on the internal and external surfaces of explanted grafts

The ESCA study gives a good qualitative and quantitative elemental analysis of internal and external surfaces of foreign materials. Microporous Hydrophobic Mitrathane® (a polyetherurethane urea) grafts were implanted as blood conduits in dogs for up to 6 month. Surface analysis of explanted grafts demonstrated the presence of different contaminants: sodium, chlorine, silicon, in patent grafts, i.e. those implanted for 1 month and less. The sulphur probably comes from the presence of proteins on the surface of the polymer and the high level of nitrogen is also protein-related. At 6 month implantation, the grafts were occluded and a decrease of proteins on the surface was observed. The values of N/C and O/C ratios are also reported. For the virgin material, these ratios correspond to the quantity of hard and soft segments; but, for the explanted grafts, these parameters are also influenced by the presence of proteins due to the Versaclean® washing which did not wash away all the proteins on the surface of the polymer. The SEM photographs showed a certain degradation of polyurethane after 6 month of implantation. However, by ESCA study, it is difficult to compare the surface of virgin and explanted grafts because it is masked by the presence of proteins.