Effects of polydimethylsiloxane grafting on the calcification,physical properties,and biocompatibility of polyurethane in a heart valve

Segmented polyurethane (PU) has proven to be the best biomaterial for artificial heart valves, but the calcification of polyurethane surfaces causes serious problems in long‐term implants. This work was undertaken to evaluate the effects of polydimethylsiloxane (PDMS) grafting on the calcification, biocompatibility, and blood compatibility of polyurethane. A grafted polyurethane film was compared with virgin polyurethane surfaces. Physical properties of the samples were examined using different techniques. The hydrophobicity of the polyurethane films increased as a result of silicone modification. The effects of surface modification of polyurethane films on their calcification and fibroblast cell (L 929) and platelet behavior were evaluated in vitro. Fourier transform infrared spectroscopy indicated the direct involvement of the polyether soft segments of the polymer in the calcification process. Scanning electron microscopy of films indicated that grafting of silicone rubber to the surface of polyurethane successfully prevented the calcification process. The morphology of fibroblast cells that adhered to the PU films and modified films was similar to that of controls and showed the same proliferation. On the other hand, grafting PDMS onto PU did not affect the amount of platelets that adhered to the polyurethane surfaces. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 758–766, 2005     

Anticoagulant surface prepared by the heparinization of ionic polyurethane film

We present a new method for heparinization on the surface of polyurethane. The segmented polyurethane was first modified with an epoxide monomer and followed by a ring‐opening reaction with diethanolamine to introduce sufficient hydroxyl groups on the surface of cast film. On this film surface, a cationic monomer was grafted by using tetravalent Cerium salt as an initiator. Heparin was immobilized in high efficiency on the ionized surface through static interactions in aqueous solution. The structure of ionized and heparinized surfaces were characterized by attenuated total reflectance infrared spectroscopy (ATR–FTIR) and electron spectroscopy for chemical analysis (ESCA) spectra. The platelet‐rich plasma (PRP) contacting test and the platelet‐poor plasma (PPP) clotting time measurements showed that the immobilized heparin retained its strong anticoagulant property. The release of heparin from film into salt solution was also studied, and it was found that only a small portion of heparin (10–20%) was released over a period as long as 10 h. It is expected that this new method for surface heparinization can be used to prepare antithrombogenic materials with long‐term stability. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 382–390, 2000     

Heparin‐immobilized poly(2‐hydroxyethylmethacrylate)‐based microspheres

Poly(2‐hydroxyethylmethacrylate) (PHEMA)‐based microspheres (150–200 µm in diameter) were produced by a modified suspension polymerization of different type of comonomers—namely, acrylic acid, dimethylaminoethyl‐methacrylate, and methylmethacrylate. These microspheres were activated with cyanogen bromide (CNBr) at pH 11.5, and heparin molecules were then immobilized through covalent bonds. The amount of immobilized heparin was controlled by changing the initial concentration of CNBr and heparin. The increase in the initial concentrations of both CNBr and heparin caused an increase in the amount of heparin immobilized onto microspheres for all polymer surfaces. The maximum heparin immobilization was observed on the PHEMA homopolymer microspheres (180 mg/g). The plain and heparin‐immobilized microspheres were contacted with blood in in vitro systems and in ex vivo animal experiments. Loss of the blood cells and clotting times were followed. Anticoagulant effect of the immobilized heparin was clearly observed with blood coagulation experiments. Loss of cells in the blood contacting with heparin‐immobilized microspheres was significantly lower than those observed with the plain microspheres. Bovine serum albumin adsorption onto the microspheres containing heparin on their surfaces was also studied. High albumin adsorption values (up to 127 mg/g) were observed in which the heparin‐immobilized PHEMA microspheres were used. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 655–662, 1999     

Antibacterial oil‐based polyurethane films for wound dressing applications

As an alternative to petroleum‐based polyol, hydroxyl containing material was prepared from linseed oil for polyurethane synthesis. Hexamethylene di‐isocyanate (HMDI) and/or 4, 4′‐methylene diphenyl di‐isocyanate (MDI) were used as isocyanate source. The polymerization reaction was carried out without catalyst. Polymer films were prepared by casting‐evaporation technique. The MDI/HMDI‐based polyurethane and its films had higher T_g and better thermal property than that of the HMDI‐based one because of the existence of benzene ring in the polymer chain. Static water contact angle was determined to be 74° and 77.5° for HMDI and MDI/HMDI‐based films, respectively. Water adsorption was found to be around 2.6–3.6% for both films. In vitro degradation of polyurethanes in phosphate buffered saline at 37°C was investigated by gravimetric method. Fourier transform infrared spectroscopy and scanning electron microscopy were used for confirmation of degradation on the polymer surface. The degradation rate of the HMDI‐based polyurethane film was found higher than that of the MDI/HMDI‐based film. Both the direct contact method and the MMT test were applied for determination of cytotoxicity of polymer films, and the polyurethane films investigated here was not cytotoxic. Silver‐containing films were prepared using Biocera A® as filler and were screened for their antibacterial performance against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and/or Bacillus subtilis. The films prepared with and without Biocera A® exhibited antibacterial activity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of hydrolytically stable low elastic modulus polyurethane‐urea for biomedical applications

Polyurethane‐urea without ether linkages was synthesised using dicyclohexyl‐methane diisocyanate (SMDI), hydroxy‐terminated polybutadiene (HTPBD) and m‐phenylenediamine (PDA). The hydrolytic stability of this polymer was investigated under in vitro conditions using Ringer's solution and phosphate‐buffered saline, and the stability of candidate polyurethane‐urea polymers was compared with that of polyurethane prepared with SMDI, HTPBD and 1,4‐butanediol [BD]. The change of tensile properties, hardness and surface properties in the aged polymer is significant for polyurethane when compared with those of polyurethane‐urea polymer. The in vitro study revealed possible applications of polyurethane‐urea for long‐term biomedical applications. © 2000 Society of Chemical Industry     

Surface modification of poly(vinyl chloride) for antithrombogenicity study

A process was established to conduct heparinization on the surface of poly(vinyl chloride) for antithrombogenicity utilization. A bifunctional monomer, glycidyl methacrylate (GMA), was grafted onto the surface of PVC by gas‐phase photografting polymerization without degassing first; then heparin was immobilized onto the poly(glycidyl methacrylate) segments. The branch structure of GMA and heparin were characterized by Fourier transfer infrared (FTIR) spectroscopy and electron spectroscopy (ESCA). It was confirmed that the bifunctional monomer GMA and heparin were grafted successfully onto the surface of PVC. The antithrombogenicity of the samples was tested both in vitro and in vivo, respectively. Results indicated that the blood compatibility of those products was improved greatly. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1013–1018, 2002     

Modification of poly(octadecene‐alt‐maleic anhydride) films by reaction with functional amines

Thin films of poly(octadecene‐alt‐maleic anhydride) on top of Si wafers and glass plates were modified by reactions with different functional amines to be used in future studies on the relevance of certain molecular surface properties for the covalent immobilization of proteins. For that aim, a strategy was developed and applied to convert the anhydride moieties of the copolymer by functional amines into side chains bearing hydrophilic groups of acidic (carboxylic acid, sulfonic acid), basic (amines), or neutral (poly(ethylene oxide) (PEO), glucose) character. The modification of the copolymer films was achieved through the two‐step formation of a cyclic imide, which was very stable in aqueous solution. Depending on the reactivity of the applied amine, the adjustment of the reaction time was suitable for the preparation of partially converted surfaces of the polymer film. Degrees of modification between 5 and 30% (according to X‐ray photoelectron spectroscopy data) were obtained. Annealing the modified polymer films induced efficient back‐formation of the anhydride groups. By reaction of the layered polyanhydrides with highly crosslinked diamines, amine‐functionalized polymer films were produced that were capable of binding secondary polyanhydride layers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1255–1266, 2003     

Structure and composition of the surface of urethane/acrylic composite latex films

Polyurethane dispersions were prepared and urethane/acrylic composite latices were synthesized with polyurethane dispersions as the seed, and core‐shell emulsion polymerization. Fourier‐transform infrared spectroscopy coupled with attenuated total reflectance (FTIR‐ATR) analyses showed that the films obtained from the composite latices were rich in polyurethane component or segments at air‐facing and substrate‐facing surfaces, in comparison with their average composition. Moreover, the substrate‐facing surface contained even more polyurethane component or segments than the air‐facing surface. X‐ray photoelectron spectroscopy (XPS) detection also indicated that the polyurethane component or segments preferentially migrated to the surface layer of the films from the bulk, and that the films from blend latices displayed more polyurethane component or segments near the surface layer. Both FTIR‐ATR and XPS analyses suggested that some reorientation had happened in synthesizing the composite latices and/or after film formation. This structure and composition endow urethane/acrylic composite films with both surface properties (such as mar‐resistance, adhesion, wettability) from pure polyurethane, and film hardness from acrylic copolymers. © 2001 Society of Chemical Industry     

Temperature‐ and pH‐sensitive IPNs grafted onto polyurethane by gamma radiation for antimicrobial drug‐eluting insertable devices

Temperature‐ and pH‐sensitive interpenetrating polymer networks (IPNs) and semi‐interpenetrating polymer networks (s‐IPNs) were γ‐ray grafted onto polyurethane (Tecoflex^®; TFX) to obtain vancomycin‐eluting implantable medical devices with minimized risk of infections. N‐isopropylacrylamide (NIPAAm) was grafted onto TFX catheters and films via a preirradiation oxidative method (method P) or via a direct method (method D). The PNIPAAm network facilitated acrylic acid (AAc) inclusion and subsequent polymerization/crosslinking, under specific reaction conditions. IPNs and s‐IPNs systems were characterized regarding the amount of grafted polymers, surface properties (FTIR‐ATR, ESEM, EDX), thermal behavior (DSC), and their temperature‐ and pH‐responsiveness. Loading and release of vancomycin for preventing in vitro growth of Staphylococcus aureus were also evaluated. Antimicrobial activity tests and hemo‐ (hemolysis, protein adsorption, thrombogenicity) and cyto‐compatibility (cell viability and production of cytokines and NO) assays indicated that the modification of TFX by γ‐radiation may improve the performance of polyurethanes for biomedical applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39992.     

A multiscale investigation on controlling bovine serum albumin adsorption onto polyurethane films

Our previous study on castor oil (CO) and poly(ethylene glycol) (PEG)‐based shape memory polyurethane (PU) films indicated that cell spreading on the polymer surface, cell morphology, and adhesion of fibroblast are closely related to the composition of the polymer that influences surface properties. This integrated experimental and computational study is designed to investigate the effect of important parameters such as surface roughness, crystallinity, hydrophilicity, distribution of hard/soft segments, and topology of the surface on protein adsorption for CO‐ and PEG‐based PUs. Analyses indicate that the crystallinity percentage highly promotes bovine serum albumin (BSA) adsorption. Roughness together with topological features determines BSA adsorption rate and concentration. Hydrophilicity and hard segment content seem to have less critical effect on adsorption. Distribution of hard segments into the soft segments emerges as another important factor for protein adsorption. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45669.     

Polystyrene-based diazonium salt as adhesive: A new approach for enzyme immobilization on polymeric supports

In this work, a new way for enzyme immobilization was explored and properties of the enzyme immobilized on different polymer films were investigated. In the process, a polystyrene-based diazonium salt (PS-DAS) was synthesized and used as molecular adhesive to immobilize β-glucosidase on the polymeric supports (films of polyethylene, polypropylene and poly(ethylene terephthalate)). The immobilization of β-glucosidase on the polymer surfaces was achieved by sequential depositions of a piece of the polymer films in PS-DAS and the enzyme solutions. The surface modification was investigated by X-ray photoelectron spectroscopy (XPS), water contact angle measurement, and atomic force microscopy (AFM). The activity of the immobilized β-glucosidase was evaluated by measuring its enzymatic activity to the hydrolysis of p-nitrophenyl-β-d-glucopyranoside (pNPG). The optimized reaction conditions (such as pH and temperature), thermal stability, and reusability of the immobilized enzyme on PE films were assayed by using the enzyme-catalyzed reaction. Results show that the polymeric diazonium salt is firmly adhered on the polymer surfaces and the modified surfaces can react with the enzyme to form covalent bonds. The immobilized enzyme shows changes in the optimized pH and temperature for the hydrolysis reaction catalyzed by β-glucosidase. The kinetic parameter (K_m) of the immobilized β-glucosidase is lower than that of its free counterpart. The immobilized enzyme shows significant enhancement in the thermal stability and reasonable reusability. This new approach can be used as a simple and versatile method for protein immobilization.     

Effects of crosslinking density on structure and properties of interpenetrating polymer networks from polyurethane and nitroguar gum

Semi‐interpenetrating polymer networks (semi‐IPNs) of castor oil‐based polyurethane prepolymer and nitroguar gum (NGG) with different crosslinking density of the PU network, coded as UNG films, were prepared through varying the trimethanol propane (TMP)/1,4‐butanediol (BDO) molar ratios in the chain extender mixture. The effects of crosslinking density on the structure and properties of the UNG films was investigated by attenuated total reflection Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, scanning electron microscopy, crosslinking density measurements, solvent‐extracting tests, and tensile tests. The experimental results revealed that incorporation of TMP crosslinker into the hard segments of polyurethane resulted in a decrease in the aggregation of hard segments. With an increase of the TMP/BDO molar ratios, the semi‐IPN films exhibited the higher crosslinking density, glass temperature (T_g), stiffness, and tensile strength (σ_b). Furthermore, the experimental results also indicated that NGG restricted the formation of crosslinking networks when the TMP content is relatively high, which led to the negative deviation of the theoretically predicted crosslinking density and Dibenedetto's equation. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Conjugated poly(pyridinium salt)s as fluorescence light‐up probes for heparin sensing

Because of its interaction with diverse proteins, heparin plays an important role in the regulation of various normal physiological and pathological processes. However, heparin overdose can induce some complications such as hemorrhages and thrombocytopenia. Therefore, it is critical to detect and quantify heparin accurately and quickly. Recently, conjugated polyelectrolytes (CPEs)‐based fluorescent probes for heparin sensing have attracted considerable interests. Unfortunately, only few kinds of CPEs such as polyfluorenes derivatives, polythiophene derivatives, are reported and effective in fluorescent assays of heparin by now. This contribution aims to develop a new kind of polyelectrolytes based on poly(pyridinium salt)s derivatives for heparin detection with a light‐up signature. An alternative conjugated poly(pyridinium salt)s ( P1 ) containing carbazole segments in the main chain was designed and synthesized, which are weakly emissive in solution but highly luminescent upon binding with heparin. Fluorescence light‐up probes for heparin detection based on P1 were developed with high selectivity. P1 shows the similar fluorescence response toward heparin both in a broad pH range of about 3–12 and in the presence of various competing anions. Heparin quantification with a practical calibration range (0–14 µM) covering the whole therapeutic dosing levels (0.2–1.2 U mL^?1, 1.7–10 µM) is realized based on the polymer probe. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40933.     

High-Elastic Blood Compatible Material

Abstract

Materials with unique complex of the properties of elasticity and tensile strength processed from the natural rubber latex (NRL) were modified to improve their blood compatibility. ESCA, ATR-IR, UV-spectroscopy and other methods were used for appraisement of the grade of modification, structure and properties of material. Thromboresistancy was studied in in vivo and ex vivo tests. It was shown that blood compatibility is raised after thorough purification of the material from non-rubber components by means of two-stage extraction changing the physical-chemical parameters of the surface. Two different principles were used in the process of modification: 1) coating by thin polyurethane (PU) coverings with improved thromboresistant properties-thus the problem of providing high adhesion interaction of covering with the latex base was solved; 2) heparin surface immobilization-higher efficiency of modification of latex material in gel-form without preliminary protein adsorption was shown. Modification allows to increase blood compatibility of the latex materials preserving at the same time their elasticity and tensile strength.     

COVALENT IMMOBILIZATION OF HEPARIN ON POLYMETHYLACRYLATE SURFACES

Heparin, a natural anticoagulant, was immobilized via covalent bonds on the surface of polymethylacrylate (PMA) beads to create a blood-compatible surface. Two chemical routes were utilized for immobilization. In the first route, PMA was hydrolyzed to produce functional carboxyl groups on its surface and heparin was covalently linked to these surface carboxyl groups by making use of carbodiimide chemistry. This method utilizes the free amino groups on heparin: the coupling occurs in minutes. In the second route, free amino groups were fixed to surface-hydrolyzed PMA by coupling one end of a suitable alkyl diamine with a water-soluble carbodiimide. Heparin was first ionically adsorbed to this aminated surface and then attached by glutaraldehyde fixation. This process occurs within one hour. In both techniques, more crude heparin (“Stage 14”) was bound than highly purified heparin due to larger number of free amino groups in crude heparin. The extent of heparin coupling was determined with ¹⁴C-labelled heparin. In vitro blood tests indicate that these surfaces are platelet compatible and are good candidates for nonthrombogenic materials.     

Surface changes in polyhydroxyalkanoate films during biodegradation and biofouling

BACKGROUND: Despite the recognition that microbial biofilms play a role in environmental degradation of bioplastics, few studies investigate the relationship between bioplastic biodegradation and microbial colonisation. We have developed protocols based on a combination of confocal laser scanning microscopy and contact angle goniometry to qualitatively and quantitatively map surface changes due to biofilm formation and biopolymer degradation of solvent cast poly(3‐hydroxyalkanoate) films in an accelerated in vitro biodegradation system. RESULTS: A significant regression relationship between biofilm formation and polymer biodegradation (R² = 0.96) was primarily conducted by cells loosely attached to the film surfaces (R² = 0.95), rather than the strongly attached biofilm (R² = 0.78). During biodegradation the surface rugosity of poly(3‐hydroxybutyrate) and poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] increased by factors of 1.5 and 1.76, respectively. In contrast, poly(3‐hydroxyoctanoate) films showed little microbial attachment, negligible weight loss and insignificant changes in surface rugosity. CONCLUSION: A statistically significant link is established between polymer weight loss and biofilm formation. Our results suggest that this degradation is primarily conducted by cells loosely attached to the polymer rather than those strongly attached. Biofilm formation and its type are dependent upon numerous factors; the flat undifferentiated biofilms observed in this study produce a gradual increase in surface rugosity, observed as an increase in waviness. Copyright © 2008 Society of Chemical Industry     

Development of antimicrobial‐loaded polyurethane films for drug‐eluting catheters

To prepare antibacterial, polymeric catheters for preventing catheter‐induced infections, sulfathiazole was loaded into polyurethane by solubilizing with solvents and the resultant films were cast. Fourier transform infrared spectroscopy confirmed the presence of sulfathiazole in the drug‐loaded polyurethane films. The thermal and mechanical properties of the films were assessed using differential scanning calorimetry and dynamic mechanical analysis. The drug‐loaded films were immersed in constantly stirred, deionized water at 37 °C for in vitro drug release study. The experimental data obtained from the in vitro drug release study were fit into mathematical models. Antibacterial efficiency of released sulfathiazole was evaluated by Escherichia coli growth inhibition test. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46467.     

Design strategy for waterborne polyurethane with sodium sulfonate groups on the soft segments

The field of waterborne polyurethane (WPU) is gaining a great deal of momentum from both a commercial and academic sense because of increasing environmental and sustainable awareness. For polyurethane (PU) to be dispersible in water, the hydrophilic groups are very important in the design of the polymer chains. Herein, we present a design strategy for WPU having hydrophilic groups on the soft segments through the reaction of as‐synthesized OH‐terminated poly(ε‐caprolactone) diols containing a sodium sulfonate group with diisocyanate. A stable aqueous dispersion was then obtained, and this was followed by a subsequent chain extension reaction and emulsification. We found that the PU dispersion particles were a core–shell structure with a good particle size distribution, and the obtained films exhibited a low tensile strength and a high elongation at break. This approach provided valuable information for fundamental research in the production, modification, property enhancement, and new applications of these materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39657.     

Surface modification of linear low‐density polyethylene film by amphiphilic graft copolymers based on poly(higher α‐olefin)‐graft‐poly(ethylene glycol)

In this article, a series of amphiphilic graft copolymers, namely poly(higher α‐olefin‐co‐para‐methylstyrene)‐graft‐poly(ethylene glycol), and poly(higher α‐olefin‐co‐acrylic acid)‐graft‐poly(ethylene glycol) was used as modifying agent to increase the wettability of the surface of linear low‐density polyethylene (LLDPE) film. The wettability of the surface of LLDPE film could be increased effectively by spin coating of the amphiphilic graft copolymers onto the surface of LLDPE film. The higher the content of poly(ethylene glycol) (PEG) segments, the lower the water contact angle was. The water contact angle of modified LLDPE films was reduced as low as 25°. However, the adhesion between the amphiphilic graft copolymer and LLDPE film was poor. To solve this problem, the modified LLDPE films coated by the amphiphilic graft copolymers were annealed at 110° for 12 h. During the period of annealing, heating made polymer chain move and rearrange quickly. When the film was cooled down, the alkyl group of higher α‐olefin units and LLDPE began to entangle and crystallize. Driven by crystallization, the PEG segments rearranged and enriched in the interface between the amphiphilic graft copolymer and air. By this surface modification method, the amphiphilic graft copolymer was fixed on the surface of LLDPE film. And the water contact angle was further reduced as low as 14.8°. The experimental results of this article demonstrate the potential pathway to provide an effective and durable anti‐fog LLDPE film. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

In vitro production of polyhydroxyalkanoates: achievements and applications

The mechanisms of polyhydroxyalkanoate (PHA) production have been studied for over half a century. However, despite numerous improvements in the control of monomer composition, genetically‐engineered host organisms, fermentation strategies and polymer recovery processes they remain uncompetitive compared with petrochemical plastics. Recently, interest has developed in the enzyme‐catalysed production of PHAs in vitro. This has allowed the study of enzyme kinetics and properties, and represents another strategy for the economic production of PHAs on the industrial scale. It also presents an opportunity to coat other materials in thin films of PHA so as to modify the surface properties. In vitro production offers advantages over in vivo methods as it enables greater control over monomer composition and molecular weight, does not require a biomass‐accumulation phase, simplifies downstream processing and can utilise a wider range of monomeric subunits. Copyright © 2009 Society of Chemical Industry