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A segmented polyether urethane was used as the blood contacting surface in a series of 10 heart assist devices implanted in calves for periods up to 35 weeks. At termination, each was examined to correlate blood compatibility and device performance with surface properties, chemical purity, physical stability and affinity for lipid absorption.
The biocompatibility of porous implants made of Estane 5714 F1 polyether urethane, polypropylene oxide, and a poly(ethylene oxide hydantoin) and poly(tetramethylene terephthalate) segmented polyether polyester copolymer (HPOE/PBT copolymer), which were selected as candidates for an alloplastic tympanic membrane, was assessed after implantation in rat middle ears for periods of up to 1 year. Implantation of the materials led to tissue reactions initially associated with the wound-healing process, whereas after 1 month not only the presence of macrophages and foreign-body giant cells surrounding the implant materials but also implant degradation were characteristic for a foreign-body reaction. Macrophages and foreign-body giant cells dominated the picture of the tissue surrounding polypropylene oxide. The altered morphology of these cells, the persistent infiltration of the implantation sites by exudate cells, and the premature death of five rats in the 1-year group suggest that polypropylene oxide degradation was accompanied by the release of toxic substances. Estane and copolymer degradation did not induce tissue responses reflecting implant toxicity, and tympanic membranes given these alloplasts showed a normal healing pattern. Inclusions in the cytoplasm of macrophages associated with degradation and phagocytosis of all of the polymers under study were found to contain iron, silicon, titanium, and aluminum. Growth of fibrous tissue and bone, the latter into Estane and HPOE/PBT copolymer implants, indicated appropriate implant fixation by tissue, although macrophages and foreign-body giant cells were present as well. Especially the fixation of copolymer by ingrowth of bone seems promising in terms of the amount of bone in the pores and the electron-dense bone/copolymer interface. The latter is indicative for bonding osteogenesis. The HPOE/PBT copolymer is a better candidate for alloplastic tympanic membrane than Estane, and the use of polypropylene oxide cannot be recommended.
In vitro enzymatic degradation of non-porous films of segmented poly(ether urethane) (Pellethane 2363-80AE) was investigated by incubating the biomaterial in concentrated trypsin solutions for 5 months at room temperature. Chemical degradation of films was monitored by surface analysis techniques such as Fourier transform infrared spectroscopy-attenuated total reflectance and electron spectroscopy for chemical analysis. This latter technique proved to be much superior in detecting chemical changes. Extraction of films with methanol and characterization of the extracts by gel permeation chromatography revealed the presence of low-molecular-weight polymers. Results have shown that trypsin has the ability to induce degradation in PEU, the soft segment being most affected, particularly the CH2-O bond of the ether linkages.
We have studied the surface chemistry of two lots of Biomer (BSP067 and BSUA001), a widely used commercial poly(ether urethane) (PEU). Although transmission infrared adsorption studies revealed no differences in the bulk chemistry of the two lots, the surface chemistry, as seen by x-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS), was different. Lot BSP067 showed soft-segment enrichment at the surface, which is typical of PEU. Lot BSUA001 showed no evidence of either hard- or soft-segment PEU components at the surface. The surface of this lot was completely covered with a nonextractable additive identified as poly(diisopropyl amino ethyl methacrylate). Small amounts of a low-molecular-weight antioxidant were observed at the surface of both samples. Because the biological response to polymers is dependent on surface structure, these results are of considerable importance to biomaterials research.
A transparent poly (ether urethane) (PEU) was considered for use as a foldable intraocular lens material. The PEU was found to possess excellent mechanical, optical, and surface characteristics for this application. In vitro hydrolytic and ultraviolet aging studies suggested the PEU to be tolerant to conditions simulating 3-10 years of normal intraocular exposure. Different behavior was obtained, however, from intraocular and subcutaneous implantation of the PEU. After 6 months of intraocular exposure in the feline model, prototype PEU lenses had lost most or all of their optical resolving power. SEM analysis demonstrated scattered pitting and cracking on the lens surfaces. Degradation was found to be more extreme after as little as 30 days of subcutaneous exposure in rabbits. Severe pitting over the entire surface of implanted flat PEU specimens was observed by SEM. Macroscopic examination showed the samples to be frosty in appearance. It was postulated that the subcutaneous implant environment provides an accelerated in vivo model for materials intended for intraocular use. A minimum acceleration of 6-10x was estimated on a preliminary basis. The PEU studied here was found to be unsuitable for use as a foldable intraocular lens material.
Surface characterization and protein adsorption studies were carried out on a series of additive dispersed and additive coated poly(ether urethane ureas), PEUUs, to characterize early events in the blood compatibility of these materials. A hypothesis that is based on surface hydrophilicity, surface flexibility, and adsorption media has been developed to understand the modulated adsorption of plasma proteins by PEUU additives. Electron spectroscopy for chemical analysis (ESCA) and contact angle analysis were performed on two PEUU formulation as well as on PEUU formulations modified with Methacrol 2138F (co[diisopropylaminoethyl methacrylate (DIPAM)/decyl methacrylate (DM)][3/1]) or acrylate or methacrylate polymer or copolymer analogs of Methacrol 2138F. Methacrol 2138F is a commercially used amphiphilic copolymethacrylate. ESCA showed that the PEUUs loaded with Methacrol 2138F or with its hydrophilic component, homopoly (DIPAM) (h-(DIPAM)), had a higher percentage of nitrogen at their surfaces than did the base PEUUs. Contact angle analysis also showed that the air side of PEUU formulations loaded with Methacrol 2138F were more hydrophobic than was the air side of base PEUUs when films were cast from dimethylacetamide. However, during contact angle testing, the air side of PEUU films loaded with Methacrol 2138F rapidly became more hydrophilic than did the air side of the base PEUU films. A radioimmunoassay and whole or diluted human plasma were also used to characterize the presence of the proteins fibrinogen, immunoglobulin G, factor VIII/von Willebrand factor, Hageman factor (factor XII), and albumin, on the surface of the same PEUUs as analyzed by ESCA and contact angle. The protein adsorption assay showed that PEUU films loaded or coated with Methacrol 2138F, with a copolyacrylate analog of Methacrol 2138F (co(diisopropylaminoethyl acrylate [DIPAA]/decyl acrylate [DA]) [3/1]), or with the hydrophilic polyacrylate or polymethacrylate component analogs of Methacrol 2138F (h-DIPAM or h-DIPAA) adsorbed significantly lower amounts of the proteins than did either the base PEUU formulations or the homopoly(decyl methacrylate) (h-DM) or homopoly(decyl acrylate) (h-DA) coated or loaded PEUUs.
To understand better blood interactions with poly(ether urethane urea) (PEUU) materials, a radioimmunoassay and whole or diluted human plasma were used to characterize the presence of fibrinogen, immunoglobulin G, factor VIII/von Willebrand factor, Hageman factor (factor XII), and albumin on a PEUU formulation and on PEUU formulations modified with the amphiphilic additive Methacrol 2138F (co[diisopropylaminoethyl methacrylate (DIPAM)/decyl methacrylate] [3/1]), or with hydrophobic acrylate or methacrylate polymer or copolymer additives. The protein adsorption assay showed that PEUU films loaded or coated with Methacrol 2138F (Methacrol) or homopoly-DIPAM (h-DIPAM) adsorbed significantly lower amounts of the studied proteins than did either the base PEUU formulations or the PEUUs loaded with the more hydrophobic acrylate or methacrylate polymer additives. Experiments with Methacrol-loaded PEUUs, where the loading of Methacrol was varied from 0.25 wt% to 20.0 wt%, showed that the adsorption of each of the characterized proteins did not vary significantly throughout the Methacrol loading range, and that all Methacrol-loaded PEUU formulations adsorbed significantly lower amounts of the studied proteins than did the unloaded PEUU. Phase separation within the additive loaded PEUUs was characterized by scanning electron microscopy (SEM). The solubility parameters of the additives, as well as of the base PEUU, were calculated and used to interpret differences in phase separation of the additive modified PEUUs. The analysis showed that additives of lower solubility parameter phase-separated into fewer large microdroplets within the PEUU matrix. SEM analysis also showed that additive microdroplets were not present on the air side surface of loaded PEUUs. To explain the differences in protein adsorption to the air side of additive loaded PEUUs when compared to the base PEUU, it was assumed that the additives near this region of the solvent swollen PEUU matrix may have migrated to, at, or near the PEUU-air interface during film formation, creating an additive enriched PEUU surface region. Once at this surface region, it was suggested that dynamic surface reorientation in response to an aqueous medium ensured that the additives were able significantly to influence protein adsorption behavior only if they interacted with aqueous media more favorably than the PEUU.
To better understand endothelial cell interactions with poly(ether urethane urea) (PEUU) materials, and to assess bovine aortic endothelial cell attachment, films were incubated for 24 h with BAEC in media containing 5% fetal bovine serum. Other films were allowed to incubate for 4 more days in media containing 5% fetal bovine serum without cells to assess BAEC proliferation. The assay was performed on PEUU films modified with acrylate and methacrylate polymer and copolymer additives that spanned a wide range on the hydrophobicity/hydrophilicity scale. Tissue culture polystyrene (TCPS) was used as a control. The assay showed that PEUU films loaded with Methacrol 2138F [copoly(diisopropylaminoethyl methacrylate [DI-PAM]/decyl methacrylate [DM]) (3/1)] or with its hydrophilic component, DIPAM, in homopolymer form (i.e., h-DIPAM), significantly enhanced BAEC attachment (approximately 80% of TCPS values) and proliferation (approximately 80%) when compared to unloaded PEUU films (attachment 73%; proliferation, 47%) or to PEUU films loaded with the more hydrophobic acrylate or methacrylate polymer additives (attachment, 32-69%; proliferation, 18-57%). The assay also showed that PEUU films coated with homopoly(diisopropylaminoethyl acrylate) (h-DIPAA) significantly enhanced BAEC attachment and proliferation when compared to PEUU films coated with h-decyl acrylate (h-DA); films coated with the copolymer of these two acrylates (i.e., co-[DIPAA/DA] [3/1]) showed intermediate behavior. To explain the enhancement of BAEC interaction with films loaded with Methacrol 2138F or h-DIPAM, when compared to unmodified PEUU films or to PEUU films loaded with more hydrophobic acrylate and methacrylate polymer additives, it was assumed that the additives near the surface region of the solvent swollen PEUU matrix may have migrated to, or near to, the PEUU-air interface during film formation, creating an additive enriched PEUU surface region. It is suggested that, once at this surface region, dynamic reorientation in response to an aqueous medium ensured the additives were able significantly to influence protein adsorption, and concomitant endothelial cell behavior, but only if they interacted with aqueous media more favorably than the PEUU. The ability of Methacrol and h-DIPAM additives to enhance endothelial cell behavior is argued to be the result of increased hydrophilicity. This is the result of exposed, hydrogen-bonding DIPAM moieties and increased surface flexibility, which is itself due to the hydration of unhindered Methacrol chains, which may create an additive enriched PEUU-water interfacial zone.
To better understand vascular interactions with poly(ether urethane urea) (PEUU) materials, protein adsorption, and endothelial cell attachment and proliferation assays were performed on a base PEUU formulation, on PEUU formulations loaded with hydrophobic and amphiphilic poly(methylene-[polyphenyl isocyanate]) (PAPI) based additives, and on PEUU formulations in which some of the polymer chains had been endcapped with either diisopropylaminoethyl (DIPAA) or decyl (DA) moieties. Protein adsorption experiments with PAPI-based additives showed that additive loaded PEUU formulations adsorbed significantly lower amounts of the studied proteins than did the unloaded PEUU. Protein adsorption to the DA and DIPAA endcapped PEUU films was found not to vary consistently from that of the unloaded PEUU film. Endothelial cell attachment and proliferation experiments with PAPI-DA and polyethylene glycol-PAPI-DA (PEG-PAPI-DA) loaded PEUU films showed that many of the films exhibited attachment and proliferation that was significantly enhanced compared to PEUU A' and that approached or equaled that of the tissue culture polystyrene control. Experiments with PAPI-DIPAA and PEG-PAPI-DIPAA loaded PEUU films exhibited attachment and proliferation data that was often below 10% of the tissue culture polystyrene control values. Experiments with the DA and DIPAA endcapped PEUU films showed endothelial cell attachment and proliferation that was statistically indistinguishable from the PEUU A' values. Contact angle analysis was carried out on the endcapped PEUU films, on the PAPI-based additive loaded PEUU films, and on PEUU A' using the sessile drop method. The advancing and receding contact angle behavior of the PAPI-based additive loaded PEUU films deviated markedly from the behavior of PEUU A', suggesting that the additives were present at the PEUU-water interface. The contact angle behavior of the endcapped PEUUs was similar to that of PEUU A', suggesting that the DA and DIPAA endcap moieties did not exist at the hydrated PEUU surface in appreciable quantities. To explain the differences in protein adsorption and endothelial cell behavior on the air side of additive loaded PEUUs when compared to the base PEUU, it was assumed that the additives near this region of the solvent swollen PEUU matrix may have migrated to, at, or near the PEUU-air interface during film formation, creating an additive enriched PEUU surface region.(ABSTRACT TRUNCATED AT 400 WORDS)
Microthane foam, a poly(ester-urethane) (PU) used in the manufacture of Meme/Replicon breast implants, was analyzed by an HPLC method to determine whether 2,4- and 2,6-toluenediamine (TDA) were formed under a variety of physiological and nonphysiological extraction and hydrolytic conditions. At our detection limit of 20 ppb, no 2,4- or 2,6-TDA was observed in either methyl tert-butyl ether (MTBE), or aqueous buffer extracts of PU foam. The predominant extractable components identified by HPLC UV-analysis, were mixture of nonaromatic and aromatic PU fragments. Moreover, no detectable amounts of TDA were found in foam or MTBE extract of foam incubated in phosphate buffer, pH 7.4, at 37 degrees C for 5 days. By contrast, 2,4- and 2,6-TDA were found in foam and foam extracts exposed to low concentrations of either strong mineral acid or base; higher levels were found at higher acidity, treatment temperature, or durations of incubation. Moreover, 2,4- and 2,6-TDA were found in oligomers isolated by preparative HPLC and exposed to alkaline conditions. Finally, 1-2 ppm of 2,4-TDA was detected when PU foam extracts were prepared by the Snyder-Breder method, which employs acidic and alkaline conditions in the work-up procedure. Based on these findings, we suggest that published observations of 2,4-TDA formation from in vitro and ex vivo extractions of PU foam are artifacts resulting from pH effects on oligomeric PU fragments present in or extracted from the foam.
The effects of an oligomer, urethane dimethacrylate (UDMA), on two human cell lines were studied using flow cytometry (FCM). Untreated and treated cultures of propidium iodine-stained KB (epidermal oral carcinoma cells) and human foreskin fibroblast (HFF) cells were analyzed for cellular DNA content. Concentrations of 10 and 25 microM of UDMA slightly perturbed the KB cell cycle progression at 24 and 48 h of incubation. However, the effect of 50 microM was more pronounced at the latter incubation time period. In cell growth experiments, the sublethal concentrations (10 and 25 microM) produced inhibition of KB cell growth rate at a moderate level, which resulted in the prolongation of cell population doubling time. Significant inhibition of cell growth occurred when 50 microM (lethal concentration) was used. Data obtained from the cell cycle perturbation analysis, evidenced by FCM, correlated with the extent of inhibition in KB cell growth rates. The effects of sublethal concentrations were reversible during a 24 h period of oligomer withdrawal from culture medium. In contrast, the effects of 50 microM were not reversible. In HFF cells the depletion of S phase in the cell cycle was the major effect of 50 microM of UDMA. It was concluded that FCM technology is an ideal and practical approach for studying the cytotoxicity of components of dental composites.
Bioresorbable linear poly(ester-ether urethane)s with different hydrophilic character were synthesized from block copolymers of poly(epsilon-caprolactone)-poly(ethylene oxide)-poly(epsilon-caprolactone) (PCL-PEO-PCL) as macrodiols, and L-lysine diisocyanate (LDI). A series of PCL-PEO-PCL triblock copolymers with different PEO and PCL chain length was obtained by reacting PEO with epsilon-caprolactone. Polyurethanes were synthesized by reacting the triblock copolymers with LDI in solution using stannous 2-ethylhexanoate as catalyst. The prepared triblock copolymers and polyurethanes were fully characterized by proton nuclear magnetic resonance spectroscopy, size exclusion chromatography, differential scanning calorimetry, and wide-angle X-ray diffraction. Water uptake, hydrolytic stability, and tensile properties of polyurethanes with different composition were evaluated and discussed in terms of the chain length and molecular weight of the polymers and its block components. Water uptake seems to depend on the ethylene oxide unit content of the polyurethane regardless of the triblock structure. Mechanical properties of the synthesized polymers were strongly affected by the molecular weight achieved during polymerization. The use of triblock macrodiols with different hydrophilicity allowed the preparation of a series of polyurethanes having a broad range of properties.
Gly-Arg-Gly-Asp-Ser (GRGDS) was modified by conjugation to lauric acid (LA) to facilitate incorporation into the matrix of a poly(carbonate-urea)urethane (PCU) used in vascular bypass grafts. GRGDS and LA-GRGDS were synthesized using solid phase Fmoc chemistry and characterized by high performance liquid chromatography and Fourier transform infrared spectroscopy. LA-GRGDS was passively coated and incorporated as nanoparticle dispersion on the PCU films. Biocompatibility of the modified surfaces was investigated. Endothelial cells seeded on LA-GRGDS coated and incorporated PCU showed after 48 h and 72 h a significant (p < 0.05) increase in metabolism compared with unmodified PCU. The platelet adhesion and hemolysis studies showed that the modification of PCU had no adverse effect. In conclusion, LA-conjugated RGD derivatives, such as LA-GRGDS, that permit solubility into solvents used in solvent casting methodologies should have wide applicability in polymer development for use in coronary, vascular, and dialysis bypass grafts, and furthermore scaffolds utilized for tissue regeneration and tissue engineering.
Biomaterials respond to sterilization methods differently. Steam sterilization might decrease the performance of thermoplastic polyether-urethane (TPU); however, the effect of different gamma-radiation doses on this polymer is contradictory in present literature. The purpose of this study was to investigate the differences between irradiative doses in comparison with steam sterilization on a porous TPU scaffold produced by a new processing method. No significant differences in the surface chemical structure were found with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis when comparing with the sterilization methods. The molecular weight (M(w)) had a net increase from 11.5 +/- 0.039 to 13.2 +/- 0.072 kDa by gamma-sterilization from 10 to 60 kGy. The samples that were irradiated (>60 kGy) had also an increase in polydispersity index (PDI; 1.45 +/- 0.007) in comparison with the nonsterile ones (1.31 +/- 0.017), which indicate branching. Liquid chromatography/mass spectroscopy (LC/MS) analysis showed that there was a correlation between the concentration of the breakdown product, methyl dianiline, and cytotoxicity. The concentration of this compound was found to be four times higher in steam-sterilized sample (1.3 +/- 0.01 ppb) compared with that of the polymer sample gamma-sterilized at 10 kGy (0.3 +/- 0.01 ppb). The cytotoxicity of TPU was found to decrease with higher radiation doses, and was significantly higher for the steam-sterilized samples. It is recommended that TPU produced with the described foaming method should be sterilized by gamma-irradiation at 25 kGy or higher doses.
In this work, we synthesized six 4,4'-diphenylmethane diisocyanate (MDI)-based poly(carbonate urethanes) (PCU) by using the macrodiol poly(1,6-hexyl, 1,2-ethyl carbonate) diol (MW = 2,017) in different molar ratios to MDI. The bulk and surface properties of cast PCU films were analyzed. The glass transition temperatures measured by dynamic mechanical analysis (DMA) and surface images obtained from atomic force microscopy (AFM) indicated that these PCU had various degrees of nanophase separation that changed with the time and film casting temperatures. The degree of nanophase separation correlated very well with endothelial cell attachment and proliferation on PCU.
Nanophase separation has been suggested to influence the biological performance of polyurethane. In a previous work, six different 4,4'-diphenylmethane diisocyanate (MDI)-based poly(carbonate urethane)s (PCUs) that exhibited various degrees of nanophase separation were synthesized and characterized. In the present work, these PCUs were used as a model system to study the effect of nanometric structures on the biocompatibility of polyurethane. Human blood platelet activation, monocyte activation, protein adsorption, and bacterial adhesion on PCU were investigated in vitro. It was found that human blood platelets as well as monocytes were less activated on the PCU surfaces with a greater degree of nanophase separation in general. This phenomenon was closely associated with the lower ratio of human fibrinogen/albumin competitively adsorbed on these surfaces. Bacterial adhesion was also inhibited in some nanophase-separated PCUs. [diagram in text].
Glucose, pyruvate, and lactate of perilymph (PL), blood, and cerebrospinal fluid (CSF) of unexposed and sound-exposed guinea pigs under ethyl urethane anesthesia were examined with due consideration of the principal sources of error. The animals had fasted for 15--20 h before the experiment to stabilize the blood glucose level. The metabolites were determined enzymatically by means of fluorescence measurements. It was found that the glucose levels depend not only on ingestion but also on the duration of anesthesia of the animals before sampling. The mean values of the scala tympani and scala vestibuli PL and CSF did not differ significantly, being about half those of blood or plasma immediately (10--20 min) after introducing anesthesia (Table 2). This concentration difference is in disagreement with the original ultrafiltration hypothesis of PL, suggesting a blood-PL barrier for glucose. The dependence on the duration of anesthesia and on the animals' ingestion before sampling appears to be an important cause of the differences in glucose data published in literature hitherto. No influence of anesthesia on pyruvate and lactate concentrations was observed. Data obtained on unexposed control animals (Tables 3 and 4) confirmed our earlier metabolite findings (Scheibe et al. 1976, 1981). No major changes in glucose, pyruvate, and lactate concentration of PL, blood, and CSF were detectable immediately after 1 h of exposure to wide-band noise at an intensity of 120 dB SPL. The present lactate findings confirmed our earlier exposure experiments (Scheibe et al. 1976), but they did not agree with the information given by Schnieder (1974).
In vivo electrochemical detection of endogenous neurotransmitters was done in the dorsal raphe nucleus of urethane-anesthetized male Sprague-Dawley rats. Stereotaxically implanted carbon paste electrodes were scanned using a cyclic voltammetry amplifier with semiderivative signal processing over the potential range--0.2 to +0.5 V at the rate of 10 mV/s. Two distinct peaks were observed at +0.15 V (peak 1) and +0.25 V (peak 2), respectively. Peak identification was assessed by comparing the oxidation potential observed in vivo with those observed in in vitro experiments using pure catecholamines, indoleamines and their metabolites as well as ascorbic acid. Further characterization of in vivo peaks was done by observing changes in electrochemical peaks as well as tissue neurotransmitter concentrations after pharmacological manipulations. p-Chlorophenylalanine, m-hydroxybenzylhydrazine (NSD-1015), pargyline, alpha-methyl-p-tyrosine and fusaric acid were administered in an effort to block catecholamine or serotonin synthesis or degradation. Results of these experiments revealed that peak 1 primarily represents extracellular norepinephrine, while peak 2 is primarily produced by extracellular 5-hydroxyindoleacetic acid (5-HIAA).