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PubMed2026

Preparation and study of non-thrombotic and biostable sulfobetaine-modified small-diameter polyurethane vascular grafts.

A novel sulfobetaine-modified polysiloxane-polycarbonate polyurethane (ZSiPCU) was synthesized. In vitro characterizations revealed that polysiloxane surface enrichment endowed the material with excellent biostability. Importantly, sulfobetaine zwitterions formed a robust hydration layer, effectively suppressing protein adsorption and platelet adhesion to ensure outstanding hemocompatibility. Furthermore, the material supported the adhesion and proliferation of vascular endothelial cells, confirming its cytocompatibility, while its elastomeric matrix provided rapid mechanical self-sealing capabilities. Electrospun ZSiPCU grafts were evaluated in a 3-month rat abdominal aorta model, maintaining high patency rates and facilitating in situ luminal endothelialization and smooth muscle cell remodeling. Additionally, superior puncture resistance of the grafts was demonstrated by puncture tests, with complete hemostasis achieved within 2 mins through mechanical self-sealing.

Polyurethanes↗

PubMed1979

In vivo comparison of replamineform, Silastic, and bioelectric polyurethane arterial grafts.

The replamineform process allows fabrication of microporous prostheses with control of both pore diameter and structural geometry by means of a variety for biomaterials. Tubular prostheses 3 cm long, 6 mm inside diameter, and 1 mm wall thickness were made of Silastic or Bioelectric Polyurethane (BEP) with use of a template of the echinoderm Heterocentrotus mammillatus. Pore diameter of the prosthesis wall was 18 to 25 mu. Light and scanning-electron microscopy of grafts removed between 1 and 32 weeks demonstrated that organization and endothelialization of neointima were similar for both polymers, being complete by 4 to 8 weeks. However, the character of prosthesis wall ingrowth was strikingly different: the microporous lattice of BEP was completely ingrown early, but was apparently fragmented by continued granulomatous inflammation by 32 weeks, while Silastic generated minimal inflammatory response and slower fibrous tissue and capillary ingrowth. Thus, with Silastic and BEP, similarities in neointima organization appeared independent of distinct differences in wall ingrowth. The replamineform process is a unique means of studying surface healing and wall ingrowth of different biomaterials as microporous vascular prostheses in a controlled fashion.

Arteries↗

PubMed1979

A clinical and laboratory evaluation of a polyurethane foam: a new donor site dressing.

A polyurethane foam (Lyofoam) has been reported to accelerate epithelization of a wound. The purpose of this study was to evaluate its efficacy as a donor-site dressing for thermally injured patients. Thus, partial-thickness injuries were made in ten pigs and covered with Lyofoam, Xeroform, Telfa, Scarlet Red, and fine-mesh gauze. Gross and histologic examinations failed to show accelerated healing under the Lyofoam dressing but did show that Scarlet Red covered donor sites healed the fastest. On clinical evaluation, nine patients only showed that Lyofoam separated earlier from the underlying wound but there was no evidence to suggest that the wound was more mature than that covered with fine-mesh gauze.

Animals↗

PubMed1997

Use of a non-porous polyurethane membrane as a sample support for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of peptides and proteins.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) of proteins and peptides was performed on samples deposited onto non-porous ether-type polyurethane (PU) membranes. Spectra obtained using PU membranes showed that mass resolution and accuracy were equivalent to values observed using a metal target, and superior to those obtained using poly(vinylidene difluoride) (PVDF) membranes. A small apparent increase in the mass of proteins and also loss of resolution were observed at very high laser irradiance due to charging, but were not observed under normal conditions. Analysis of NaCl-doped standards demonstrated that PU membranes yielded better results than a metallic target for salt-containing solutions. Relatively strong hydrophobic interactions between the proteins and peptides and the PU membrane allowed the incorporation of a washing step. This step allowed for the removal of salts and buffer components and thus provided an increase in resolution and mass accuracy. Digestion of citrate synthase (a protein of molecular weight 47,886) with trypsin was performed directly on the surface of the membrane for variable periods of time, and characteristic peptide fragments were observed by MALDI-TOFMS. Delayed extraction was used to increase the resolution and to permit more accurate mass assignments for those fragments. The use of PU membranes for MALDI-TOFMS analysis of proteins with higher molecular weights is also demonstrated.

Citrate (si)-Synthase↗

PubMed1996

Novel compliant and tissue-permeable microporous polyurethane vascular prosthesis fabricated using an excimer laser ablation technique.

A small-diameter vascular prosthesis with a multiply pored structure could have great potential to elevate the patency rate, for the following two reasons: 1) increased flexibility of the graft may increase compliance matching, consequently minimizing intimal hyperplasia; and 2) enhanced transmural tissue ingrowth may accelerate endothelialization. In this study, we fabricated a polyurethane (PU)-based artificial graft with well-controlled micropores in terms of their diameter and distribution, which was achieved using a computer-aided excimer laser (KrF) ablation technique. Three types of microporous PU tubes (2 mm in internal diameter, 100 microns in wall thickness) were designed: pore size (100 microns) and longitudinal pore-to-pore distance (200 microns) were constant, and circumferential pore-to-pore intervals were 60 degrees (type 1), 30 degrees (type 2), and 15 degrees (type 3). The fabricated prostheses were coated with photoreactive gelatin, which was photogelled and chemically fixed on PU surfaces upon ultraviolet light irradiation. Scanning electron microscopy showed that pore size and arrangement were precisely controlled as designed, and that a gelatinous hydrogel layer was formed over the entire luminal surface. The stiffness parameter (beta), inversely related to compliance, was determined from the change in external diameter against intraluminal pressure. An increase in the number of pores around the circumference decreased the beta value. The type 3 graft, the stiffness parameter of which was very close to that of human coronary artery, was the most compliant among the three types. The combination of excimer laser-directed microporing and photochemical surface processing techniques enabled the development of a novel compliant small-caliber vascular prosthesis, which is expected to show enhanced transmural tissue in growth in vivo.

Blood Vessel Prosthesis↗

PubMed1996

Surface microarchitectural design in biomedical applications: in vitro transmural endothelialization on microporous segmented polyurethane films fabricated using an excimer laser.

We describe the preparation of segmented polyurethane (SPU) films with round micropores and present a quantitative assay method of endothelial cell (EC) migration through micropores of and growth on microprocessed SPU films as an in vitro model of transmural endothelialization in open-cell-structured small-diameter vascular grafts. The micropored films, pores of which ranged from 9 to 100 microns in diameter, were microfabricated using an excimer laser. Time-dependent processes of EC ingrowth through micropores of SPU films with different pore sizes, which have a confluent monolayer sheet on one face and are cell free on the other, and subsequent endothelialization were quantitatively studied. The circular cellular sheet centered at the micropores expanded as incubation proceeded. Markedly retarded migration was found for the smallest pore size (9 microns in diameter). The larger the pore, the higher was the endothelialization rate. The endothelialization characteristics were studied on multiply microspored films of different pore sizes and densities, each of which was prepared so as to provide a fixed total pore area per unit area (0.01 mm2 per mm2). The highest endothelialization rates in an early incubation period were found on films with microspores between 18 and 50 microns in diameter.

Animals↗

PubMed1996

Improved blood compatibility of segmented polyurethanes by polymeric additives having phospholipid polar groups. I. Molecular design of polymeric additives and their functions.

To improve the blood compatibility of a segmented polyurethane (SPU), 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was blended with the SPU. The MPC was copolymerized with cyclohexyl methacrylate (CHMA) or 2-ethylhexyl methacrylate (EHMA), and the MPC polymers obtained could be dissolved in the same solvent as the SPU (Tecoflex 60). The blended membranes composed of SPU and MPC polymers were prepared by a solvent evaporation method. A small amount of MPC polymer in the blended membrane leached out after immersion in water for 10 days. The X-ray photo electron spectra indicated that the MPC moieties were located at the surface of the SPU membrane blended with poly(MPC-co-CHMA). On the other hand, the poly-(MPC-co-EHMA) was located homogeneously in the SPU membrane. The mechanical properties of the SPU membrane, as determined by tensile stress-strain measurements, changed very little even after addition of the MPC polymers. Blood compatibility of the blended membrane was evaluated by blood-cell adhesion on the surface when the membranes were placed in contact with rabbit whole blood or platelet-rich plasma. The addition of MPC polymer in the SPU membrane dramatically reduced cell adhesion. It is concluded that the blending of the MPC polymer in the SPU membrane is an effective method for imparting nonthrombogenicity.

Animals↗

PubMed1996

Improved blood compatibility of segmented polyurethane by polymeric additives having phospholipid polar group. II. Dispersion state of the polymeric additive and protein adsorption on the surface.

To improve the blood compatibility of a segmented polyurethane (SPU), phospholipid polymer, i.e., 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymerized with cyclohexyl methacrylate or 2-ethylhexyl methacrylate, was blended into SPU as a polymeric additive. The blending was achieved by a solvent-evaporation technique from a homogeneous solution containing both the SPU and the MPC polymer. Surface analysis of the SPU membrane blended with the MPC polymer (SPU/MPC polymer membrane) revealed that the MPC polymer was concentrated at the surface of the SPU membrane which contacted the substrate, Teflon, compared with that which contacted air during the membrane-formation period. The dispersion state of the MPC polymer in the SPU membrane was evaluated in detail by staining the MPC unit with osmium tetraoxide. When sonication was applied during preparation of the mixed solution containing SPU and the MPC polymer, the dispersion of the MPC polymer in the SPU membrane was different from that without sonication. That is, the size of the domains of the MPC polymer became smaller but the number of the domains increased. The amount of the MPC polymer mixed with SPU affected the dispersion state. Plasma proteins adsorbed on the SPU/MPC polymer membrane surface after contact with human plasma were detected by gold-colloid-labeled immunoassay. Both albumin and fibrinogen were observed on the SPU membrane; however, the amount of these proteins was reduced on the SPU/MPC polymer membrane. Thus it was concluded that the blood compatibility of the SPU was effectively improved by the blending of the MPC polymer.

Adsorption↗

PubMed1996

Effect of forms of collagen linked to polyurethane on endothelial cell growth.

Collagen has been widely coated or grafted onto polymer surfaces to improve the biocompatibility of materials. To better support the growth of endothelial cells on polyurethane (PU), collagen was grafted to the carboxyl group enriched PU through 1,2-bis(2,3-epoxypropoxy)ethane linking. Our results demonstrated that collagen in various conditions may result in different forms being grafted to the PU substrate, which subsequently affected the growth of endothelial cells. Collagen predialyzed against physiological phosphate buffered saline (PBS) could be reconstituted into native type fibrils with a bigger diameter at 37 degrees C than could collagen neutralized by titration with NaOH. At low temperature, titrated collagen formed floss-like fibrils packed in a ball with cobblestone-like morphology. The amount of collagen grafted was related to the condition of the collagen used, which in consequence affected the diameter of the collagen fibril formed and the growth of endothelial cells. In conclusion, reconstituted collagen fibrils formed from collagen in PBS at 37 degrees C grafted in the highest amounts to an epoxy-PU substrate and that optimally supported the growth of endothelial cells. Such prepared materials may be potentially good vascular bioprosthetic materials and may provide a wide range of biological applications.

Animals↗

PubMed1997

Enhanced vascularization in a microporous polyurethane graft impregnated with basic fibroblast growth factor and heparin.

Rapid and controlled neoarterial regeneration via perianastomotic as well as transmural tissue ingrowth is critical to patency of implanted small-caliber artificial vascular grafts. Microporous polyurethane (PU) grafts (inner diameter, 1.5 mm; wall thickness, 100 microns; length, 20 mm; pore size, 100 microns), fabricated using an excimer laser ablation technique, were coated with a mixed solution of photoreactive gelatin, basic fibroblast factor (bFGF), and heparin, and were photocured by ultraviolet irradiation. Control grafts were treated with only photoreactive gelatin. An in vitro study showed that coimmobilization of bFGF and heparin (bFGF/heparin) in a crosslinked gelatin gel significantly enhances proliferation of endothelial cells. The bFGF/heparin-impregnated grafts (n = 6) and nonimpregnated (control) grafts (n = 9) were implanted in aortas of rats for 4 weeks. All the implanted grafts were patent, but there was a marked difference in the extent of neoarterial regeneration between the two groups. Irrespective of group, endothelialization proceeded from anastomotic sites and little occurrence of transmural capillary ingrowth was observed. The extent of endothelialization was much greater for bFGF/heparin-immobilized grafts than that for controls. In subendothelial tissues for the impregnated group, a significantly profound peripheral transmural tissue ingrowth including recruits of smooth muscle cells and fibroblasts from adjacent native tissue was observed near anastomotic sites; subendothelial tissue regeneration was noticed at the midportions of the grafts. However, only a fibrin layer was formed on control grafts. Thus, coimmobilization of bFGF and heparin significantly accelerated neoarterial regeneration via both perianastomotic and transmural tissue ingrowth. The former was more extensive than the latter.

Animals↗

PubMed1997

Tissue reactions to bacteria-inoculated rat lead samples. II. Effect of local gentamicin release through surface-modified polyurethane tubing.

A surface modification technique was developed to achieve controlled release of gentamicin from implanted polyurethane (PU) rat lead samples. PU tubing first was provided with an acrylic acid/acrylamide copolymer surface graft and then loaded with gentamicin. This surface modification technique resulted in release of gentamicin base (GB) and was applied either to the inner luminal surface only (PU-GB-1x) or to both the inner and outer surfaces (PU-GB-2x). First we investigated whether the early tissue response was harmfully compromised when surface-modified rat lead samples were implanted without any infectious challenge. Additionally, the efficacy of this type of local gentamicin therapy was investigated by establishing its effect on tissue response and its ability to prevent lead-related infections after inoculation with Staphylococcus aureus. It was demonstrated that the applied surface modification(s) did not induce adverse effects although an increase in the infiltration of granulocytes and macrophages and an increase in the formation of wound fluid and fibrin were observed. This effect was stronger with PU-GB-2x than with PU-GB-1x. With bacterial inoculation the applied surface modification successfully suppressed the infectious challenge, PU-GB-2x more effectively than PU-GB-1x. PU-GB-2x also was more effective when compared to the gentamicin-delivery methods discussed in the first part of this two-part study, i.e., release through a vicinal gentamicin-containing collagen sponge and preoperative gentamicin solution-dipping of rat lead samples.

Animals↗

PubMed1997

Effect of single-chain and two-chain high molecular weight kininogen on adsorption of fibrinogen from binary mixtures to glass and sulfonated polyurethane surfaces.

The adsorption of fibrinogen from a single protein solution and from binary mixtures of fibrinogen and high-molecular-weight kininogen (HK) to glass and four sulfonated polyurethane surfaces is reported. The effect of the single-chain (SCHK) and two-chain (TCHK) forms of HK on fibrinogen adsorption was investigated. Using radiolabeling methods, fibrinogen adsorption from a series of mixtures having the same weight ratio of fibrinogen to HK as in plasma (50:1), but varying in total concentration, was measured. Fibrinogen adsorption from the mixtures was reduced on all surfaces compared to the single-protein solution, confirming the highly surface-active nature of this protein. However, except for glass, there was no significant difference between the SCHK and TCHK forms. Polyacrylamide gel electrophoresis and immunoblotting analysis of the proteins eluted from the surfaces after contact with the fibrinogen-SCHK solutions indicated that although intact SCHK was essentially conserved, some transformation of SCHK to TCHK on the surface occurred during the course of the experiment. It is hypothesized that in purified form, in which HK is not complexed to prekallikrein or factor XI, the surface-binding domain is more available than in the complexed forms which are present in plasma. If so, then the removal of bradykinin by kallikrein, as occurs in generating TCHK, may not be required for the expression of surface-binding domain activity.

Adsorption↗

PubMed1997

Significance of porosity and compliance of microporous, polyurethane-based microarterial vessel on neoarterial wall regeneration.

The microporous structure of artificial vascular grafts, which increases compliance and porosity simultaneously, may enhance neoarterial regeneration. In order to differentiate these effects, three models of segmented polyurethane grafts (inner diameter, 1.5 mm; wall thickness, 100 microns) with or without micropores fabricated using an excimer laser ablation technique, were prepared, and their neoarterial regenerative potentials were studied upon implantation: Model I (microporous, permeable, compliant); Model II (smooth-surfaced, impermeable, compliant); and Model III (smooth-surfaced, impermeable, noncompliant). In Models I and II, the pore or groove size (diameter, 100 microns) and pore or groove arrangement were fixed, and consequently their compliances were almost identical. Irrespective of model, the luminal surfaces were coated with benzophenone-derivatized gelatin and subsequently photocured. Twenty grafts (length, 20 mm) of each model were implanted in the aortas of rats. Predetermined implantation periods were 4, 12, and 24 weeks. Total patency rate decreased in the order Model I (100%), II (87%), and III (59%) grafts. All patent grafts were completely endothelialized after 12 weeks of implantation, irrespective of model. After 12- and 24-week implantations, in Model I grafts, the neoarterial wall was thin, and smooth muscle cells (SMCs) were of the contractile phenotype. In Model II grafts, the neoarterial wall exhibited considerable thickening. In Model III grafts, the neoarterial wall exhibited marked thickening, and SMCs were of the synthetic phenotype. The neoarterial wall thickness at the midportion of the grafts after 24 weeks of implantation increased in the order Model I (48 +/- 8 microns), II (146 +/- 87 microns), and III (385 +/- 21 microns) grafts. These results strongly suggest that compliance matching and porosity synergistically resulted in neoarterial wall restoration without appreciable thickening.

Animals↗

PubMed1998

Comparison of epoxides on grafting collagen to polyurethane and their effects on cellular growth.

The current study investigated the effects of vary epoxides on linking capacity of collagen to carboxyl-group-enriched polyurethane (PU) and the consequent effects on the growth of endothelial cells. Epoxides of EX-810, 1,4BDE, DER732, DER331, and DER332 were initially reacted with the carboxyl groups of PU substrates at 110 degrees C for 20 h. Free epoxy rings of epoxide-PU substrates, characterized by Fourier transform infrared spectroscopy and quantified by titration with HCl and NaOH, were available for collagen grafting. The amounts of collagen grafted were in accordance with the amounts of free epoxy rings detected and correlated with the growth of endothelial cells on the substrates. Our results indicated that epoxides with shorter aliphatic intermediate chain can graft more collagen to the epoxide-PU substrates than epoxides with longer intermediate chain or with aromatic groups. Epoxides were also demonstrated to be nontoxic linking agents for biomaterials.

Cell Division↗

PubMed1998

Platelet adhesion onto segmented polyurethane surfaces modified by PEO- and sulfonated PEO-containing block copolymer additives.

Polyethylene oxide (PEO) surfaces were prepared by the addition of PEO- and sulfonated PEO-containing amphiphilic block copolymers as surface-modifying additives in a segmented polyurethane (PU). PEO-PPO-PEO triblock copolymers (Pluronics) with different PEO chain lengths (from 2 to 80) were used as additives. The prepared film surfaces were characterized by the measurement of dynamic water contact angles and electron spectroscopy for chemical analysis. It was observed that the PU films containing 10 wt% of PEO additives were surface-saturated with the additives regardless of their PEO chain length, but the PEO chains were more projected from the film surfaces containing the additives with longer PEO chains. The water absorption of the films increased largely with the increasing PEO chain length of the additives. The addition of PEO additives produced film surfaces that were in a gel-like state. The films demonstrated some extraction of the PEO additives. However, the additives with higher molecular weights were entrapped more stably into the PU matrix. The mechanical properties (tensile strength and elongation) of the films were changed by the addition of PEO additives, but the differences were not significant compared to the control PU. The platelet adhesion on the film surfaces decreased with increasing PEO chain length of the additives. The film surface containing additives with long PEO chains (chain length of 80) was particularly effective in preventing platelet adhesion. The effect of negatively charged sulfonate groups on the prevention of platelet adhesion appeared only on the film surfaces containing additives with short PEO chains. For longer PEO chains, the chain mobility effect was more dominant than the negative charge effect on the prevention of platelet adhesion.

Animals↗

PubMed1999

A new generation of polyurethane vascular prostheses: rara avis or ignis fatuus?

Three polyurethane (PU) vascular grafts with novel designs were investigated and compared in terms of the microporous structure, reinforcement technology, polymer chemistry, microphase separation, and mechanical properties. The Corvita graft, composed of a poly(carbonate urethane) polymer, displayed a helically wound filament structure with communicating inter-fiber spaces. The reinforced model contained an external PET mesh impregnated with a protein sealant, and displayed good microphase separation, the highest Young's modulus in the longitudinal direction, and the second highest in the radial direction. The Thoratec graft was made of a polyetherurethaneurea with an average micropore size of 15 microns. Silicone was observed on both surfaces of the graft. The Thoratec device displayed a low degree of hydrogen-bonding among the urethane groups and had no well-organized hard-segment domains. Its mechanical strength was superior to that of the Pulse-Tec graft. A solid PU layer underneath the luminal surface precluded any communication between the luminal and adventitial sides. The Pulse-Tec prosthesis was composed of polyetherurethane, with an average micropore size of 28 microns. It offered the highest radial compliance, a high degree of hydrogen-bonding, a narrow molecular weight distribution, and a certain degree of microphase separation. Its tensile strength and hysteresis loss were inferior to those of the other two grafts.

Animals↗

PubMed1999

Preparation of poly(acrylic acid) modified polyurethane membrane for biomaterial by UV radiation without degassing.

Poly(acrylic acid) modified polyurethane (AA/PU) membranes were prepared by UV radiation without degassing. The chemical composition of the AA/PU membrane was studied by IR spectroscopy. In addition to those absorption peaks associated with pure PU, the absorption peak at 2400 cm-1 of poly(AA) was also found. The morphology of AA/PU membrane was studied by optical polarizing microscopy. We also measured the glass transition temperature and the decomposition temperature of the AA/PU membrane by differential scanning calorimetry and thermogravimetric analysis. A significant domain was found in the AA/PU membrane, which resulted in different glass transition temperature and decomposition temperature between AA/PU and pure PU membrane. The effect of AA content on the contact angle and water absorption of the AA/PU membrane was determined. It was found that the water content of AA/PU membrane increased with increasing AA content, whereas the contact angle decreased. By using Kaeble's equation and the contact angle data, the surface free energy of AA/PU membrane was determined. The increase of surface free energy resulted from the increase of the dispersion (gammad) term and polar (gammap) term. In order to evaluate the biocompatibility of these membranes, a cytotoxicity test and a cell adhesion and proliferation assay were conducted in cell culture. Immortal cells and primary lymphocytes were both used in this study. The results showed that these AA/PU membranes exhibited very low cytotoxicity and could support cell adhesion and growth. An animal primary test was also done in this study. It was found that the AA/PU membrane could possibly be employed in the treatment of bowel defect.

Acrylic Resins↗

PubMed1999

Surface photograft polymerization on segmented polyurethane using the iniferter technique.

A segmented polyurethane (SPU) film was chloromethylated and subsequently dithiocarbamated. The treated films were immersed in solutions containing poly(ethylene glycol) methacrylate (PEGMA) or N, N-dimethyl-acryl amide (DMAAm) and irradiated with ultraviolet (UV) light. The resultant surfaces were highly wettable with water. The surface chemical compositions, as determined by X-ray photoelectron spectroscopy, indicated that surface graft polymerization, initiated from surface-derivatized dithiocarbamate, had occurred and had altered the surface properties and the composition of SPU. The platelet adhesion test using platelet-rich plasma showed minimal adhesion for the poly(PEGMA)-grafted surface, followed by the poly(DMAAm)-grafted surface.

Animals↗