Physicochemical properties and in vitro biocompatibility of PEO/PTMO multiblock copolymer/segmented polyurethane blends

A multiblock copolymer composed of poly(ethylene oxide) (PEO) and poly(tetramethylene oxide) (PTMO) and which forms a physical hydrogel was blended with Pellethane®, a commercial segmented polyurethane (SPU) developed for various biomedical devices, to provide a PEO-rich surface with improved stability. The effect of the copolymer blending was evaluated with respect to surface hydrophilicity, long-term stability, mechanical properties, in vitro protein adsorption, and platelet adhesion. A small amount of the copolymer additive (5 wt%) significantly improved surface hydrophilicity, which was then gradually enhanced by increasing the amount of the copolymer in the blends. The blend films exhibited minimal extraction of the copolymer additive when exposed to a buffer solution for 2 months at 37°C, resulting in less than 1 wt% weight loss of the films even with 30 wt% content of the copolymer in the blends. Although a certain degree of alteration in the mechanical properties was observed by increasing the copolymer content, the mechanical properties were well maintained for up to 10 wt% addition of the copolymer, when compared with the bare SPU. Protein adsorption was significantly reduced with a small amount of copolymer additive as low as 5 wt%. Fibrinogen, an adhesive protein for further cellular adhesion and activation, was effectively repelled by increasing the amount of copolymer additive. The platelet adhesion test revealed that the blend film surface reduced platelet adhesion and the degree of inhibition was proportional to the content of the additive, up to 30 wt%. The high molecular weight (M_w = 66 000) and compatible chemical structure of the copolymer with SPU made the surfaces PEO-rich and stable in an aqueous environment, resulting in an enhancement of the resistance to protein adsorption and platelet adhesion without a significant deterioration in physical properties.     

Assessment of PEO/PTMO multiblock copolymer/segmented polyurethane blends as coating materials for urinary catheters: in vitro bacterial adhesion and encrustation behavior

The effective long-term use of indwelling urinary catheters has often been hindered by catheter-associated infection and encrustation. In this study, the suitability of poly(ethylene oxide) (PEO)-based multiblock copolymer/segmented polyurethane (SPU) blends as coating materials for the commercial urinary catheters was assessed by measuring swellability, bacterial adhesion, and encrustation behavior. When exposed to PBS (pH 7.4), the blends absorbed a significant amount of water, which was proportional to the copolymer content. It was demonstrated from bacterial adhesion tests that compared to bare SPU, the blend surfaces could significantly reduce the adhesion of E. coli, P. mirabilis, and S. epidermidis; the number of adherent bacteria correlated with the amount of copolymer additive. indicating that the swellability of the blends affected bacterial adhesion. Of the bacteria studied, the greatest effect of the copolymer additive was observed in S. epidermidis adhesion, in which there was an 85% decrease compared to bare SPU with a small amount of copolymer additive as low as 5% based on a dried blend. By using an artificial bladder model, allowing the catheter to be blocked by encrustation, it was revealed that the blend surfaces could effectively resist encrustation. The duration of patency was extended up to 20 +/- 3.1 h on the blend surface containing 10% of the copolymer additive, whereas the silicone-coated catheter, a control, required the least time for blockage, 7.8 +/- 3.1 h. The superior characteristics of the blends compared to other surfaces might be attributed to their PEO-rich surfaces, produced by the migration of PEO phase in the copolymer chain of the blends in an aqueous environment, and provide promising potential as a coating material on the urinary catheter for long-term catheterization.     

Gas plasma etching of PEO/PBT segmented block copolymer films

A series of poly(ethylene oxide)/poly(butylene terephthalate) (PEO/PBT) segmented block copolymer films was treated with a radio-frequency carbon dioxide (CO(2)) or with argon (Ar) plasma. The effects of (preferential) etching on surface structure, topography, chemistry, and wettability were studied by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. In all cases, a granular-type nanostructure was formed after prolonged CO(2) plasma etching. Ar plasma etching generally did not lead to significant changes in surface structure. Regarding surface chemistry, CO(2) plasma treatment caused surface oxidation and oxidative degradation of the films while Ar plasma etching resulted mainly in the preferential removal of PEO blocks. The wettability of all films significantly increased after plasma treatment because of the creation of polar functional groups at the surface. Preliminary goat bone-marrow cell compatibility experiments have shown that all plasma-treated PEO/PBT films induced a greatly enhanced cell adhesion and/or growth compared to untreated biomaterials. This improvement was attributed to changes in surface chemistry during plasma etching rather than to changes in surface structure. These results show that plasma-treated PEO/PBT copolymers have a high potential as scaffolds for bone tissue regeneration.     

Physicochemical properties and in vitro biocompatibility of a hydraulic calcium silicate/tricalcium aluminate cement for endodontic use

This study sought to prepare a calcium silicate cement (CSC) with varying additions of tricalcium aluminate (Ca(3)Al(2)O(6), C(3)A), and to find an optimal amount of C(3)A by evaluating the effect of C(3)A on the physicochemical and in vitro biological properties of the CS/C(3)A cement. The results indicated that the addition of C(3)A into CSC reduced the setting time and improved the compressive strength especially at the early stage of setting. However, the 15% C(3)A was too much for the CS/C(3)A system and did harm to its strength development. Furthermore, the CS/C(3)A cement was bioactive and biocompatible in vitro, and had a stimulatory effect on the cell growth, when the content of C(3)A was 5 or 10%. When compared with the commercially available Dycal(?), the CS/C(3)A cement was notably more compatible with the human dental pulp cells. Therefore, the CS/C(3)A cement with 5-10% C(3)A produced the best compromise between setting and in vitro biological properties, and may be a promising candidate for endodontic use.     

Synthesis and in vitro biocompatibility of injectable polyurethane foam scaffolds

The development of therapeutics for orthopedic clinical indications exploiting minimally invasive surgical techniques has substantial benefits, especially for treatment of fragility fractures in the distal radius of osteoporotics and vertebral compression fractures. We have designed six formulations of injectable polyurethane foams to address these clinical indications. The polyurethanes were prepared by mixing two liquid components and injecting the reactive liquid mixture into a mold where it hardens in situ. Porous polyurethane foams were synthesized from lysine methyl ester diisocyanate, a poly(epsilon-caprolactone-co-glycolide) triol, a tertiary amine catalyst, anionic and non-ionic stabilizers, and a fatty acid pore opener. The rise time of the foams varied from 8-20 min. The porosity was approximately 95% and the pores varied in size from 100-1000 microm. The polyurethane foams supported attachment of viable (>95%) MG-63 cells under dynamic seeding conditions. We anticipate compelling opportunities will be available as a consequence of the favorable biological and physical properties of the injectable polyurethane foams.     

In vitro biocompatibility assessment of sulfonated polyrotaxane-immobilized polyurethane surfaces

Sulfonated polyrotaxanes (PRx-SO(3)'s), in which sulfonated alpha-cyclodextrins (alpha-CDs) were threaded onto the poly(ethylene glycol) (PEG) segments in a PEG-b-poly(propylene glycol) (PPG)-b-PEG triblock copolymer (Pluronic) capped with benzyloxycarbonyl (Z)-L-phenylalanine (Z-L-Phe), were prepared as a novel surface-modifying biomaterial. Surface modification of the polyurethane (PU) was carried out by blending the PRx-SO(3)'s with a PU solution, followed by solution casting. The incorporated PRx-SO(3)'s led to the enhanced hydrophilicity by changing the surface properties of the PU matrix. Modified PUs showed the stable entrapment of the PRx-SO(3)'s with little extraction into water and enhanced mechanical properties after exposure to water compared to the PU control. The incorporated PRx-SO(3)'s repelled the proteins and kept them from closely approaching the surface areas, prevented platelet activation by thrombin, and effectively repelled bacteria. These results suggest that both the supramolecular structure of the polyrotaxanes and exposure of the sulfonated groups onto the surfaces contribute to these phenomena. Thus, surface modification with PRx-SO(3)'s is suggested to be useful for the fabrication of biocompatible medical devices.     

Durable modification of segmented polyurethane for elastic blood-contacting devices by graft-type 2-methacryloyloxyethyl phosphorylcholine copolymer

We propose a novel application of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers for enhancing the performance of modified segmented polyurethane (SPU) surfaces for the development of a small-diameter vascular prosthesis. The SPU membranes were modified by random-type, block-type, and graft-type MPC polymers that were prepared using a double-solution casting procedure on stainless steel substrates. Among these MPC polymers, the graft-type poly(MPC-graft-2-ethylhexyl methacrylate [EHMA]), which is composed of a poly(MPC) segment as the main chain and poly(EHMA) segments as side chains, indicated a higher stability on the SPU membrane after being peeled off from the stainless steel substrate, as well as after immersion in an aqueous medium. This stability was caused by the intermiscibility in the domain of the poly(EHMA) segments and the soft segments of the SPU membrane. Each SPU/MPC polymer membrane exhibited a dramatic suppression of protein adsorption from human plasma and endothelium cell adhesion. Based on these results, the performance of SPU/poly(MPC-graft-EHMA) tubings 2?mm in diameter as vascular prostheses was investigated. Even after blood was passed through the tubings for 2?min, the graft-type MPC polymers effectively protected the blood-contacting surfaces from thrombus formation. In summary, SPU modified by graft-type MPC polymers has the potential for practical application in the form of a non-endothelium, small-diameter vascular prosthesis.     

A long-term in vitro biocompatibility study of a biodegradable polyurethane and its degradation products

The biological safety of degradation products from degradable biomaterials is very important. In this study a new method is proposed to test the cytotoxicity of these degradation products with the aim to save time, laboratory animals, and research funds. A biodegradable polyurethane (PU) foam was subjected to this test method. The PU had soft segments of DL-lactide/epsilon-caprolactone and hard segments synthesized from butanediol and 1,4-butanediiosocyanate. Copolymer foams without urethane segments, consisting of DL-lactide/epsilon-caprolactone, were tested as well. Accumulated degradation products were collected by degrading the foams in distilled water at 60 degrees C up to 52 weeks. Cell-culture medium was prepared from powder medium with this water. In different tests the cytotoxicity of this medium was established. The first signs of cytotoxicity were observed after 3-5 weeks of degradation. This accounts for both materials and reestablishes the good short-term biocompatibility of these materials. The PU showed more toxicity toward the end stages of degradation in comparison with the copolymer. This is probably related to the accumulation of degradation products of the urethane segments. In the in vivo situation the degradation of the PU and the metabolism and excretion of degradation products may differ. Therefore, long-term in vivo studies will have to establish whether these in vitro results are representative for the in vivo behavior of the degrading PU.     

The biocompatibility evaluation of mPEG-PLGA-PLL copolymer and different LA/GA ratio effects for biocompatibility

Biomaterial poly(lactic-co-glycolic acid) (PLGA), a FDA-approved material for clinical application, showed broad prospects in the past, but gradually can no longer meet present clinical developments and requirements, which we synthesized monomethoxy(polyethylene glycol)-poly(d,l-lactic-co-glycolic acid)-poly(l-lysine) (mPEG-PLGA-PLL) (PEAL) and have had some relevant reports. But studies on biocompatibility and the impacts of LA and GA ratio (LA/GA?=?60/40, 70/30, and 80/20) in main material have not yet been reported. Hemolysis experiment indicates that the hemolysis rate of PEAL extraction medium is less than 5%. Whole blood clotting time (CT), plasma recalcification time, activated partial thromboplastin time, prothrombin time evaluations, and dynamic CT assay show that the anticoagulant time of PEAL copolymer for blood is longer than that under negative and positive control. Protein adsorption assay indicates that PEAL films adsorb less protein than PLGA films (p?p?>?0.05). Complement activation test shows that PEAL surface does not induce complement activation. CCK8 measurement shows that the relative growth rates of Huh7, L02, and L929 cells co-incubated with PEAL nanoparticles (NPs) are more than 90%. PEAL NPs co-incubated with 5% foetal bovine serum or 2% bovine serum albumin, through dynamic light scattering assay, remain stable. Different concentrations of PEAL NPs co-incubated with zebrafish embryos at 6–72?h post fertilization show that comparing with negative control, 10, 100, or 500?μM of NPs for embryos development has no significant effects (p?>?0.05), only 1000 or 2000?μM of NPs has some effects (p?in vivo.     

Mechanical properties and in vitro biocompatibility of porous zein scaffolds

A porous scaffold utilizing hydrophobic protein zein was prepared by the salt-leaching method for tissue engineering. The scaffolds possessed a total porosity of 75.3-79.0%, compressive Young's modulus of (28.2+/-6.7)MPa-(86.6+/-19.9)MPa and compressive strength of (2.5+/-1.2)MPa-(11.8+/-1.7)MPa, the percentage degradation of 36% using collagenase and 89% using pepsin during 14 days incubation in vitro. The morphology of pores located on the surface and within the porous scaffolds showed good pore interconnectivity by scanning electron microscopy (SEM). Rat mesebchymal stem cells (MSCs) could adhere, grow, proliferate and differentiate toward osteoblasts on porous zein scaffold. With the action of dexamethasone, the cells showed a relative higher activity of alkaline phosphatase (ALP) and a higher proliferating activity (p<0.05) than those of MSCs without dexamethasone.     

Fibrinogen adsorption by PS latex particles coated with various amounts of a PEO/PPO/PEO triblock copolymer

Polystyrene (PS) latex particles of different sizes were adsorption coated with the polymeric surfactant Pluronic F108 (PEO₁₂₉-PPO₅₆-PEO₁₂₉). The commercial surfactant was found to have a bimodal molecular weight distribution. However, the maximum surface concentrations resulting from adsorption of either the purified high molecular weight component or the composite were identical. An increase in the copolymer surface concentration on 252-nm particles was found to decrease their fibrinogen uptake exponentially. At maximum copolymer surface concentration, the fibrinogen uptake was two orders of magnitude lower than that of bare particles (down from 3.3 mg/m² to 0.03 mg/m²). This surface protection was equally effective whether the adsorption involved the bimodal polymer surfactant or the purified high molecular weight fraction. The PEO tail mobility was investigated with electron paramagnetic resonance (EPR), and found to increase with an increase in polymer surface concentration. The comparatively slow motion of the PEO chains at low surface concentration indicated that not only the PPO block, but also the PEO blocks interacted hydrophobically with the PS surface. When the copolymer surface concentration was increased, the PEO tails were gradually being released, acquiring higher mobility as the surface became covered by the more strongly binding PPO blocks. Results obtained with F108 coated particles of different sizes showed that particle size had a significant effect on the fibrinogen uptake, with larger particles showing larger fibrinogen uptakes.     

Fibrinogen adsorption by PS latex particles coated with various amounts of a PEO/PPO/PEO triblock copolymer

Polystyrene (PS) latex particles of different sizes were adsorption coated with the polymeric surfactant Pluronic F108 (PEO129-PPO56-PEO129). The commercial surfactant was found to have a bimodal molecular weight distribution. However, the maximum surface concentrations resulting from adsorption of either the purified high molecular weight component or the composite were identical. An increase in the copolymer surface concentration on 252-nm particles was found to decrease their fibrinogen uptake exponentially. At maximum copolymer surface concentration, the fibrinogen uptake was two orders of magnitude lower than that of bare particles (down from 3.3 mg/m2 to 0.03 mg/m2). This surface protection was equally effective whether the adsorption involved the bimodal polymer surfactant or the purified high molecular weight fraction. The PEO tail mobility was investigated with electron paramagnetic resonance (EPR), and found to increase with an increase in polymer surface concentration. The comparatively slow motion of the PEO chains at low surface concentration indicated that not only the PPO block, but also the PEO blocks interacted hydrophobically with the PS surface. When the copolymer surface concentration was increased, the PEO tails were gradually being released, acquiring higher mobility as the surface became covered by the more strongly binding PPO blocks. Results obtained with F108 coated particles of different sizes showed that particle size had a significant effect on the fibrinogen uptake, with larger particles showing larger fibrinogen uptakes.     

Composite scaffolds of dicalcium phosphate anhydrate /multi-(amino acid) copolymer: in vitro degradability and osteoblast biocompatibility

This study aims to evaluate in vitro degradability and osteoblast biocompatibility of dicalcium phosphate anhydrate/multi-(amino acid) (DCPA/MAA) composites prepared by in situ polymerization method. The results revealed that the composites could be slowly degraded in PBS solution, with weight loss of 9.5 ± 0.2?wt.% compared with 12.2 ± 0.2?wt.% of MAA copolymer after eight weeks, and the changes of pH value were in the range of 7.18–7.4 and stabilized at 7.24. In addition, the compressive strength of the composite decreased from 98 to 62 MPa while that of MAA copolymer from 117 to 86 MPa. Furthermore, with non-toxicity demonstrated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide assay, the addition of DCPA to the MAA copolymer evidenced an enhancement of osteoblast differentiation and attachment compared with pure MAA materials regarding to alkaline phosphatase activity as well as initial cell adhesion. The results indicated that the DCPA/MAA scaffolds with good osteoblast biocompatibility, degradability, and sufficient strength had promising potential application in bone tissue engineering.     

Extraction of polyurethane block copolymers: effects on bulk and surface properties and biocompatibility

In order to study changes occurring in polyurethane block copolymers upon solvent extraction, a base polymer containing approximately 50% polyurethane hard segment based on 4,4'-bis(p-phenyl isocyanate), 1,4-butanediol, and poly(tetramethylene oxide) of MW 1000 was synthesized. Portions of this polymer were extracted using methanol, toluene, and acetone. Multidetector gel permeation chromatography was used to characterize the effect of extraction on molecular weight and molecular weight distribution. Extraction also affected bulk and surface properties and the blood compatibility as assessed using a canine ex vivo blood-contacting experiment. Extracted materials possessed a higher molecular weight than the base polymer and had narrower molecular weight distributions. Acetone extraction resulted in the polymer with the highest ultimate tensile strength. Contrary to expectations, the surface properties and blood compatibility of the material studied were affected minimally by extraction.     

Structural features and mechanical properties of in situ-bonded meshes of segmented polyurethane electrospun from mixed solvents

The relationships between the structural features and mechanical properties of electrospun segmented polyurethane (SPU) meshes and electrospinning parameters such as formulation (e.g., polymer concentration and solvent mixing ratio) and operation parameters (e.g., applied voltage, air gap, and flow rate) were studied with the use of a mixed-solvent system of tetrahydrofuran (THF) and N,N-dimethylacrylamide (DMF). After the relationships between the structure of electrospun SPU and the operation parameters under a fixed SPU concentration of single THF solution were established, SPU was electrospun from the mixed solvent of THF and DMF with different mixing ratios [DMF content: 5, 10, and 30% (v/v)]. Scanning electron microscopy showed that an increase in DMF ratio significantly enhances the degree of bonding between SPU fibers at contact sites and decreases the diameter of fibers formed. The porosimetric characterization showed the following: (1) The porosity of the electrospun SPU meshes decreased with an increase of DMF ratio. (2) The pore size distribution exhibited three representative peaks of different void sizes (i.e., approximately 5, 20, and 70 microm). (3) The proportion of the 20-microm void markedly decreased with an increase in DMF ratio. A tensile test on the meshes showed that an increase in DMF ratio induces an increase in elasticity of the mesh. Such a regulation of the structural features and mechanical properties of electrospun SPU meshes using a mixed-solvent system with low- and high-boiling-point solvents may be useful in the engineering of SPU-fiber based matrices or scaffolds.     

Studies on the effect of surface properties on the biocompatibility of polyurethane membranes

To study the effect of surface properties on the biocompatibility of biomaterials based on the same material, polyurethane membranes with different surface properties were prepared. Myoblast culture and interleukin-1 (IL-1) generation in an air pouch model and in vitro monocyte culture were used to examine biocompatibility of different polyurethane membranes. Polyurethane membranes were found to exhibit significant differences depending on their surface properties prepared by different fabrication processes. When myoblasts were cultured on polyurethane surfaces, the smooth and hydrophobic membrane (F1), prepared by the solvent evaporation process, showed the greatest inhibition of myoblast adhesion compared with other porous and hydrophilic membranes (F2, F3 and F4), prepared by immersing the polymer solution into a precipitation bath. In contrast, IL-1 generation by monocytes/macrophages on the membrane F1 was more severe than those on the porous and hydrophilic membranes. Based on our results, the interaction of biomaterials with various cells is discussed.     

Polyamide 6 composite membranes: properties and in vitro biocompatibility evaluation

The aim of the present study was to develop polyamide 6 membrane blended with gelatin and chondroitin sulfate using the phase precipitation method and evaluate its in vitro biocompatibility. Morphology of membranes was studied by laser scanning confocal microscopy which allowed the nondestructive visualization of internal bulk morphology of membranes. Membranes exhibited porous morphology with pores spanning across the membrane width with interconnections at various depths. Membranes showed adequate mechanical properties with tensile strengths of 20.10 +/- 0.64 MPa, % strain of 3.01+/-0.07, and modulus of 1082.50+/-23.50 MPa. In vitro biocompatibility of membranes by direct contact test did not show degenerative effects on NIH3T3 cells and also its leach-out products (LOP), as determined by tetrazolium (MTT) and neutral red uptake (NRU) assay. Mouse peritoneal macrophage cultured in contact with membranes and PTFE control showed comparable expression of activation markers such as CD11b/CD18, CD45, CD14, and CD86 suggesting the membranes' non-activating nature. Membrane LOP did not induce excessive proliferation of mouse splenocytes suggesting its non-antigenic nature. Preliminary blood compatibility of membranes was observed with no detectable hemolysis in static incubation assay. Taken collectively, the present data demonstrate that polyamide 6 composite membranes are biocompatible and prospective candidates for tissue engineering applications.     

Properties and biocompatibility of polypropylene graft copolymer films

Modifying the surfaces of polymers has received a great deal of attention, because it could bring about specific surface characteristics such as antithrombogenic property. Therefore, N-vinyl pyrrolidone/sodium acrylate (NVP/Na-AAc) binary monomers were introduced onto polypropylene (PP) films by a radiation grafting method. The effect of solvent and comonomer composition on the degree of grafting was determined. Studies of the mechanical properties and water content of such graft copolymers showed that as the grafting yield increases the elongation percent decreases. However, the water content increases with increasing grafting yield. The blood compatibility of the original PP and PP-g-NVP/Na-AAc films was evaluated by determination of the extent of platelet adsorption and thrombus formation. The blood compatibility of PP-g-NVP/Na-AAc seems to be better than that of original PP.     

Surface modification with PEO-containing triblock copolymer for improved biocompatibility: in vitro and ex vivo studies

Poly(ethylene oxide) (PEO) has been frequently used to modify biomaterial surfaces for improved biocompatibility. We have used PEO-polybutadiene-PEO triblock copolymer to graft PEO to biomaterials by gamma-irradiation for a total radiation dose of 1 Mrad. The molecular weight of PEO in the block copolymer was 5000. In vitro study showed that fibrinogen adsorption to Silastic, polyethylene, and glass was reduced by 70 to approximately 95% by PEO grafting. On the other hand, the reduction of fibrinogen adsorption was only 30% on expanded polytetrafluoroethylene (e-PTFE). In vitro platelet adhesion study showed that almost no platelets could adhere to PEO-coated Silastic, polyethylene, and glass, while numerous platelet aggregates were found on the ePTFE. The platelet adhesion in vitro corresponded to the fibrinogen adsorption. When the PEO-grafted surfaces were tested ex vivo using a series shunt in a canine model, the effect of the grafted PEO was not noticeable. Platelet deposition on ePTFE was reduced by PEO grafting from 8170 +/- 1030 to 5100 +/- 460 platelets 10(-3) microm2, but numerous thrombi were still present on the PEO-grafted surface. The numbers of platelets cumulated on Silastic, polyethylene, and glass were 100 +/- 80, 169 +/- 35, and 24 +/- 22 platelets 10(-3) microm2, respectively. This is about 35% reduction in platelet deposition by PEO grafting. While the numbers of deposited platelets were small, the decreases were not as large as those expected from the in vitro study. This may be due to a number of reasons which have to be clarified in future studies, but it appears that in vitro platelet adhesion and fibrinogen adsorption studies may not be a valuable predictor for the in vivo or ex vivo behavior of the PEO-grafted surfaces.