Safety of polyurethane-covered breast implants. Expert Panel on the Safety of Polyurethane-covered Breast Implants.
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Consumer Product Safety↗
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Evaluation of sunlight stability of polyurethane elastomers for maxillofacial use. I.
The evaluation of the efficiency of polymer additives with special emphasis on uv absorbers and antioxidants in polyurethane elastomers has been completed. Aliphatic polyurethanes were chosen for this study because their properties closely relate to the requirements of maxillofacial prosthesis. The polyurethane elastomers were either synthesized by ourselves or formulated according to the manufacturer's recommendation. Eleven different types of uv absorbes, coupled with one antioxidant, were incorporated into the polyurethane systems. The Atlas twin-lamp carbon arc Weatherometer was used as the source of uv. The samples were periodically withdrawn for examination of yellowing and tackiness. It was found that, although the incorporation of uv stabilizers enhanced the uv resistance of polyurethanes, the problem of tackiness resulting from uv aging was not solved satisfactorily. The phenomenon of yellowing, however, was significantly improved, mainly due to the aliphatic structure of polyurethanes. The most promising uv absorbers are Tinuvin 770 and the combination of Tinuvin 328, ZnO, and an antioxidant. Their effectiveness in other polyurethane systems is not known and further research is underway to explore this field. Hopefully, these findings will greatly assist the successful application polyurethane elastomers in maxillofacial prosthesis.
Biocompatible Materials↗
Effect of surface hydrophilicity on ex vivo blood compatibility of segmented polyurethanes.
The relationship between surface, bulk and ex vivo blood-contacting properties of segmented polyurethanes with various polyol soft segment was investigated. The polyols used in this study were poly(ethylene oxide), poly(tetramethylene oxide), hydrogenated poly(butadiene), poly(butadiene) and poly(dimethylsiloxane). The hard segment of these segmented polyurethanes was composed of 4,4' diphenylmethane diisocyanate and 1,4 butanediol, present at 50 wt%. An experimental polyurethane, Biostable PUR, which has shown excellent biostability, was used in this study. The segmented polyurethanes based on the hydrophobic polyols such as poly(dimethylsiloxane) and hydrogenated poly(butadiene) showed distinct microphase separation between hard and soft segments. X-ray photoelectron spectroscopy revealed the surface enrichment of the hydrophobic component at the air-solid interface. Dynamic contact angle measurements indicated that the poly(dimethylsiloxane)-based segmented polyurethane possessed a hydrophobic surface in water. The poly(dimethylsiloxane)-based segmented polyurethane had the lowest platelet adhesion among the segmented polyurethanes investigated in this study, whilst the platelet deposition on the poly(ethylene oxide)-based polymer increased with time.
Animals↗
Biostability and blood-contacting properties of sulfonate grafted polyurethane and Biomer.
Sulfonate-containing polyurethanes were evaluated for in vivo biodegradation using subcutaneously implanted tensile bars. In addition, these anionically charged polyurethanes were evaluated for in vivo activation of human complement C3a and ex vivo platelet deposition in arteriovenously-shunted canines. The sulfonate derivatized polymers included laboratory synthesized polyurethane and Biomer. Other polymers used for references included Intramedic polyethylene, Silastic and a poly(ethylene oxide) based polyurethane. The biodegradation results indicated that Biomer and the laboratory sulfonated Biomer (both manufactured with stabilizers), remained mechanically stable, retaining both tensile strength and elasticity after 4 weeks of subcutaneous implantation. The unstabilized polyurethanes (with or without sulfonation), however, showed marked cracking and a loss of mechanical properties after the same period of subcutaneous implantation. Sulfonated polyurethanes depressed human complement C3a activation in plasma, as indicated by decreased levels of anaphylatoxin production. The results of canine ex vivo blood contacting experiments were conducted in both an acute and chronic model and demonstrated decreased platelet deposition and activation for the sulfonated polyurethanes.
Absorption↗
Synthesis of a novel polyurethane co-polymer containing covalently attached RGD peptide.
The synthesis of a novel polyurethane block co-polymer containing a covalently attached, well-oriented RGD (Arg-Gly-Asp) peptide was explored. A poly(tetramethylene oxide) (PTMO)-based polyurethane was synthesized, and a bimolecular nucleophilic substitution reaction was then employed to incorporate ethyl carboxylate groups onto the polymer backbone (i.e. carboxylated polyurethane). Elemental analysis was used to determine the extent of carboxylation. The hexapeptide H-Gly-Arg-Gly-Asp-Ser-Tyr-OH was coupled to the carboxylated polyurethane via the formation of an amide bond. The attachment of the peptide was controlled by a protection-deprotection scheme. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies were used to monitor the reactions. Sakaguchi assay and amino acid analysis confirmed that the RGD-containing peptide was successfully grafted onto the carboxylated polyurethane. This reaction scheme provides a new route for grafting end-linked, bioactive peptides onto polyurethanes.
Amino Acid Sequence↗
Polyurethane-covered mammary prosthesis: a nine year follow-up assessment.
We have examined ten tissue capsules from patients ranging from five months to nine years of mammary implantation. Contrary to published reports of polyurethane foam "fragmentation" or "disappearance" in the capsules evaluated, the polyurethane foam was still present and embedded in the surrounding tissue capsule. The foam was nearly always invisible by gross observation, or manual palpation. Only after enzymatic digestion of the tissue capsule did the foam become clearly visible as continuous sheets. ESCA analyses show that explanted foams are devoid of nitrogen peaks. Only carbon, oxygen and silicone signals are observed. The same foams do show nitrogen peaks (due to urethane linkages) when probed by FTIR. Since ESCA only analyzes the first 40-50 Angstroms of a surface, we believe that a "protective coating" composed of soft segments has formed. Beneath this "coating" the original polyurethane composition is still present as evidenced by FTIR analysis. Three possible explanations are advanced: (1) The surface hydrolysis, which takes place within the soft segment of the polyurethane polymer, results in the formation of oligomer(s). These oligomers, devoid of urethane linkages, appear to protect the polymer from further bioresorption, by significantly retarding the rate of additional surface hydrolysis. (2) Chain cleavage occurs in the soft segment producing a hydrophilic polyester chain end which orients into the interfacial area. These chain ends then produce a skin effect which increases the distance from the surface to the hard segments, or urethane-containing linkages. (3) Macromolecular motion in the soft segment phases of the polymer could be reorienting under the influence of the in vivo environment, thus producing a surface layer or "coating" which is predominantly soft segment in composition. Regardless of which of the three hypotheses proves to be most plausible, we interpret the data as showing that the polyurethane foam cover undergoes very slow bioresorption, even after 9 years of human implantation. The data further suggests that the in vivo surface of the polyurethane foam cover is biocompatible and interfacial interactions with inflammatory cells are downregulated or reduced because of the apparent biocompatibility of the material.
Biocompatible Materials↗
Endothelial cell adhesion on polyurethanes containing covalently attached RGD-peptides.
Peptides based on cell-adhesive regions of fibronectin, Arg-Gly-Asp-Ser (RGDS), and vitronectin, Arg-Gly-Asp-Val (RGDV), were covalently bound to a polyurethane backbone via amide bonds. Nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectroscopies were used to monitor the reactions. The amount of grafted peptide was determined by amino acid analysis. X-ray photoelectron spectroscopy (XPS) suggested the presence of the grafted peptide at the polymer-air interface in vacuo. Dynamic contact angle analysis showed that, in water, the peptide-grafted polyurethane surfaces were more polar than the underivatized polyurethane indicating enrichment of peptide groups at the surface. The attachment and spreading of human umbilical vein endothelial cells (HUVECs) on the underivatized and peptide-grafted polyurethanes was investigated. The GRGDSY- and GRGDVY-grafted substrates supported cell adhesion and spreading even without serum in the culture medium. The GRGDVY-grafted substrate supported a larger number of adherent cells and a higher extent of cell spreading than the GRGDSY-grafted substrate. These RGD-containing peptide-grafted polyurethane copolymers may be useful in providing an easily prepared cell-adhesive substrate for various biomaterial applications.
Amino Acids↗
Long-term comparison of the electrical characteristics of polyurethane and polyethylene insulated ventricular leads.
Two types of pacing leads with different insulation material, polyurethane, and polyethylene, were followed for 44 months with respect to their electrophysiological characteristics and complications. In 48 patients, 32 polyurethane leads (Lifeline 493-03) and 16 polyethylene leads (EMT 588 D) were implanted and connected in all cases to the same type of programmable ventricular inhibited (VVI) pulse generator (Programalith, Pacesetter). There was a significant fall during the follow-up in lead impedance with the polyurethane leads (495 +/- 62 to 444 +/- 58 ohms, P less than 0.01), whereas the corresponding measurements for the polyethylene leads were essentially unchanged (360 +/- 58 to 378 +/- 71 ohm, ns). The energy of the stimulation threshold tended to increase in the polyurethane group, whereas an opposite tendency was observed in the polyethylene group. Pacing and/or lead failures were not observed in any case. The observed fall in impedance with the polyurethane leads was seemingly of no clinical significance.
Aged↗
[Studies on orthodontic polyurethane ringlets. (Part 1) Examination of its physical properties (author's transl)].
The purpose of this study was to develop orthodontic ringlets from polyurethane which have maximum flow resistance. The two types of polyurethane involved were thermoplastic and thermosetting polyurethane. The former included Paraprene 22, 25, 4805 + 4806, Biomer, Elastollan 585 (E-585) and improved Elastollan 590 (E-590). Thermosetting type incorporated Adiprene, Loyler 2170, Colonate 4080 and DC-4978. Using these materials as its base, a ring device was developed. Under two conditions, tests were conducted for tensile strength, aging effects on 50% and 100% modulus and permanent elongation. One group was stored in air at 20 degrees C and the other in water at 37 degrees C. The results were as follows; It was found that the thermoplastic polyurethane possessed high tensile strength. However, the modulus upon aging resulted in a lower reading with the exception of E-590 and Biomer. In the thermosetting polyurethane group, most of the rings except DC-4978 broke down during storage at 100% elongation in water at 37 degrees C. In the case of DC-4978, there was maximum flow resistance. Upon comparing it with E-590 and Biomer, it appeared that DC-4978 was the most effective for orthodontic purposes.
Elasticity↗
Tissue reactions to breast implants coated with polyurethane.
The histological features noted in the capsules from 7 polyurethane coated silicone breast prostheses are described. The polyurethane provoked a definite foreign body reaction and was slowly degraded, with some particles ejected from the capsule into the surrounding tissues. Separation of the polyurethane coating from the silicone prosthesis and the degradation of the polyurethane took about two years. Another much more resistant foreign material was found to occur in conjunction with the polyurethane in the capsules. It may be an adhesive or flakes off the silicone shell. Vacuolated spaces were noted in the inner layers of 3 capsules; it was assumed that they contained liquid silicone.
Breast↗
Thrombocytopenia associated with environmental exposure to polyurethane.
Few chemicals in the environment have been implicated as causes of isolated thrombocytopenia, and the evidence is usually less than convincing because the patients were not rechallenged with the chemical in vivo. In the present paper, a child is reported with the onset of thrombocytopenia in temporal association with environmental exposure to polyurethane. Five years after the initial thrombocytopenia had resolved, an inadvertent in vivo rechallenge with environmental polyurethane resulted in recurrence of the thrombocytopenia. This recurrence, together with the fact that only 1-4% of cases of idiopathic thrombocytopenic purpura in children recur, provided strong evidence for a causal role for the polyurethane exposure in this patient's thrombocytopenia. In summary, environmental exposure to polyurethane should be considered in the differential diagnosis of acquired thrombocytopenia in childhood.
Child, Preschool↗
Physical and blood-contacting properties of polyurethanes based on a sulfonic acid-containing diol chain extender.
Polyurethanes chain extended with N,N-bis (2-hydroxyethyl)-2-aminoethane-sulfonic acid (BES) were synthesized. The effect of the sulfonic acid group on the polymers' bulk, surface, and blood-contacting properties was evaluated by comparing the BES-based polymers with polyurethanes based on N-ethyldiethanolamine (EDEA). In addition, the effect of soft-segment polarity was addressed by comparing polyurethanes based on polytetramethylene oxide (PTMO) (MW = 1000) with polymers based on polyethylene oxide (PEO) (MW = 1000). The EDEA control samples had physical properties similar to a viscous fluid. The presence of the sulfonic acid group dramatically enhanced the degree of microphase separation and the mechanical strength of all the polymers. The more polar PEO soft segment resulted in polymers which were more phase mixed than the PTMO-based polyurethanes. Surface characterization studies revealed that in vacuum, all the surfaces were enriched in the polyether soft-segment phase. After 24-h equilibration in water, all the surfaces had similar surface polarities independent of the SO3H content. The canine ex vivo blood-contacting results showed that the sulfonic acid group in the PTMO-based polymers significantly reduced the number and activation of the adherent platelets. Fibrinogen deposition, however, increased with increasing sulfonic acid content. In contrast, platelet and fibrinogen deposition on the sulfonic acid-containing PEO-based polymers was greatly enhanced.
Adsorption↗
In vivo biocompatibility of an aliphatic crosslinked polyurethane in rabbit.
A cage implantation technique has been adopted in a rabbit animal model to investigate the biocompatibility of an aliphatic crosslinked polyurethane based on hexamethylene diisocyanate (HDI). In this study, four cages are represented; the cage containing the candidate polyurethane material, biomedical grade polyurethane (Tecoflex), the commercial grade polyvinylchloride (PVC), and an empty cage which were implanted subcutaneously in rabbits. Exudates were aspirated from these cages at 4, 7, 14, and 21 days postimplantation. Exudates were analyzed for variations in proteins, cell counts, and extracellular enzymes. Results with the four types of cage implants showed that the candidate polyurethane caused an inflammatory response comparable to that caused by medical-grade Tecoflex and the empty cage control.
Alkaline Phosphatase↗
Effect of sulfonation of segmented polyurethanes on the transient adsorption of fibrinogen from plasma: possible correlation with anticoagulant behavior.
The influence of polyurethane sulfonation on fibrinogen adsorption from plasma and on plasma coagulation has been investigated. Sulfonated polyurethanes were synthesized using a two-step solution polymerization in which a diamino disulfonic acid was used as chain extender, thus incorporating sulfonate groups into the hard segments. Polymer molecular weights were determined by size exclusion chromatography and weight average values were in the range of 50,000 to 200,000. Equilibrium water uptake of solid polymer specimens was substantial and was found to increase with increasing sulfonate content. Titration of sulfonate groups allowed an estimate of the retention of free sulfonate in the polymers which ranged from 50 to 85%. Loss of free sulfonate is attributed to reaction of isocyanate with sulfonate groups during chain extension. Both surface chemistry and hydrophilicity were assessed using a combination of ESCA and water contact angle measurements. The ESCA data indicate enrichment of soft segment in the surface. Contact angles show increasing hydrophilicity with increasing sulfur content. Fibrinogen adsorption from plasma to the sulfonated polyurethane surfaces was studied using radioiodine labeling. Fibrinogen surface concentration was found to increase strongly as sulfonate content increased. Fibrinogen adsorption behavior is quite different from that of conventional unsulfonated polyurethanes in the sense that the adsorption levels are much higher and there is little displacement of initially adsorbed fibrinogen (Vroman effect). The data are interpreted in terms of two mechanisms: fibrinogen uptake (i.e., absorption) into a polymer-plasma "gel" hypothesized to exist at the surface of these materials, and adsorption in the usual sense. Thrombin times of human plasma in which polymer particles were suspended were prolonged and were found to increase with increasing sulfonate content of the polymers, suggesting that sulfonate groups confer a measure of anticoagulant activity on these materials.
Adsorption↗
Polyurethane film (Opsite) vs. impregnated gauze (Jelonet) in the treatment of outpatient burns: a prospective, randomized study.
As it has been shown that re-epithelialization of partial skin thickness wounds can be accelerated if the wound is kept moist, a prospective, randomized clinical study compared the water vapour-semipermeable polyurethane film, Opsite, with the conventional impregnated gauze dressing, Jelonet, in the treatment of outpatient partial skin thickness burns. Fifty-five patients were included: 30 were treated with the polyurethane film and 25 with the conventional dressing. The patients were followed at regular intervals until healing had occurred and were seen 3 months later for evaluation of residual scars and pigmentation. The burns treated with polyurethane films healed with a median of 10 days, while the conventionally treated burns healed with a median of 7 days (P greater than 0.05). Residual scars were noted in 21 per cent of the patients treated with polyurethane films and in 8 per cent treated conventionally (P greater than 0.05). Prophylactic methods should be publicly stressed since one-quarter of the patients were children of 3 years or less who were scalded by split hot liquids. Furthermore the patients' wounds were only briefly cooled before attending medical care. With small burns we advise that cooling should be prolonged until the pain fades then professional assistance should be sought.
Adolescent↗
Comparative experience with smooth and polyurethane breast implants using the Kaplan-Meier method of survival analysis.
Smooth-walled silicone implants have been widely used in breast surgery. Capsular contracture, causing undesirable firmness and spherical deformity, has been a common problem. Recent studies suggest that polyurethane-covered breast implants are associated with a lower incidence of capsular contracture. The statistical methodology employed in some of these studies, however, may be subject to criticism. Between July of 1984 and June of 1990 (72 months), 427 polyurethane breast implants were used in 279 patients and 439 smooth prostheses were used in 250 patients for a variety of aesthetic and reconstructive procedures. The occurrence of capsular contracture was carefully monitored and then analyzed using the Kaplan-Meier method of survival analysis. This method is particularly well suited to analysis of these types of clinical data because it allows for the fact that contractures occur at varying intervals after surgery and that follow-up of patients is incomplete. The probability of capsular contracture with smooth-walled prostheses was found to be significantly greater than with polyurethane-covered implants in each group of patients studied (p less than 0.05). Other complications occurred at a similar rate regardless of prosthesis type. This study supports the belief that polyurethane breast implants have a lower contracture rate; furthermore, it introduces the Kaplan-Meier method for analyzing the outcome of alternative plastic surgical therapies.
Breast↗
The biomechanical and histopathologic effects of surface texturing with silicone and polyurethane in tissue implantation and expansion.
There has been considerable interest in determining the effect of morphologic alterations of prosthetic surfaces on capsule response in breast surgery. The purpose of this study was to provide a precise, three-dimensional evaluation of soft-tissue response to surface modifications in both implantation and expansion. Expandable 100-cc prostheses were designed with one of three surfaces: textured silicone (Biocell), standard smooth silicone, or polyurethane (Natural-Y, Meme). A new submuscular implantation site in the rabbit was developed. Each animal randomly received a smooth-surface device on one side and either a textured silicone or polyurethane device on the other. In one group of animals, the prostheses were expanded monthly. Capsular response was evaluated monthly in vivo using standardized techniques as well as biomechanical methods for up to 6 months in the expander group (n = 7 to 16) and 8 months in the implant group (n = 7 to 15). Analysis of biomechanical and histologic data revealed that prosthetic surface morphology can specifically alter capsular response. Polyurethane was the only effective surface in preventing capsular contracture in implantation. In expansion, both textured silicone and polyurethane surfaces resulted in significantly less capsular contracture and less resistance to expansion than comparable smooth-surfaced controls. Statistical comparisons reveal that the biomechanical methods utilized in this study provide the most precise and objective method of defining overall soft-tissue contracture around implanted biomaterials.
Animals↗
Cuff Cath: an initial experience of cuffed polyurethane central venous catheters in children.
The tendency of medium- and long-term silicone central venous catheters (CVCs) to block, fracture, and become displaced has led to the evaluation of a polyurethane CVC, Cuff Cath (Viggo Spectramed, Swindon, Wilts, United Kingdom) as a possible alternative because polyurethane is smoother and stronger. We report the first prospective study of polyurethane cuffed CVCs in children. Sixty Cuff Caths were placed in 53 children, mean age 4.7 years (range, 4 days to 16.3 years), mean weight 15.6 kg (range, 3.1 to 58 kg). All CVCs were tunnelled (mean tunnel length, 12 cm; range, 5 to 20 cm) and inserted either into the subclavian vein (n = 28) or internal jugular vein (n = 32). In a total of 6363 catheter days (mean, 111 days per patient; range, 15 to 364 days), three (5%) CVCs had to be removed because of sepsis and one (2%) because of blockage. All other Cuff Caths remained patent to infusion and blood sampling. No Cuff Caths were pulled or fell out, fractured, or migrated. This study demonstrates significant advantages of polyurethane compared with previous series using silicone CVCs with respect to blockage, fragmentation, and dislodgement. A prospective, randomized, controlled trial of Cuff Cath compared with a silicone CVCs in children is required.
Adolescent↗