PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Elastomers”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1977

Development of blood-compatible elastomers. V. Surface structure and blood compatibility of avcothane elastomers.

The Avcothane 51 elastomer, a member of a series of proprietary materials best characterized as polyurethane/poly(dialkylsiloxane) block copolymers, displays considerable hemocompatibility without any incorporated anticoagulants. In the form of intra-aortic balloons, the elastomer was implanted in several thousands of cardiac patients without intolerable hematologic effects. Hemocompatibility has been assumed to result from a predominantly dispersion-type surface force field whose intensity fluctuates within small domains, maintaning adsorbed blood proteins in an unstable state. The relative hemocompatibility of films, which were obtained from a prepolymer solution cast on substrates impenetrable to the solvent, is a function of the effective surface molecular structure. This can vary as a function of preparative conditions (temperature and rate of evaporation), and has been correlated with an anisotropic distribution of the silicone component in cured films. The concentration of this component in surface layers was quantified independently by IRATR spectroscopy and electron-microprobe analysis, giving consistent results. An IRATR index, which is computed from the ratio of absorptivities measured at 13.00 and 12.62 mu and is inversely proportional to the relative silicone content of surface layers, was found to correlate with the apparent hemocompatibility determined by different in vitro methods. Optimized reproducible hemocompatibility is attained by strict process controls.

Assisted Circulation↗
PubMed2003

New concepts in thermoplastic elastomers: the case of syndiotactic polypropylene, an unconventional elastomer with high crystallinity and large modulus.

Syndiotactic polypropylene (sPP), despite high crystallinity, shows unusual elastic properties, associated with a reversible crystal-crystal phase transition. The mechanism behind the crystal-crystal phase transition involved during cyclic elongation and recovery and the time scale of this process is here investigated, to unravel the origin of the elasticity of such an unconventional elastomer. The structural transformation of fibers of sPP during deformation has been studied by wide-angle X-ray diffraction measurements, using the high flux available on the beamline ID11 at the European Syncrotron Radiation Facility (ESRF), Grenoble, France, performing a time-resolved analysis of structural changes occurring while cyclically stretching and relaxing sPP fibers. This analysis indicates that the stress-induced phase transition is a martensitic transformation. As in martensitic phase transitions it occurs readily and directly, supporting the idea that elasticity in sPP is partially of enthalpic nature.

Journal Article↗
PubMed2003

Fluoridated elastomers: in vivo versus in vitro fluoride release.

OBJECTIVES: To compare (i) the in vivo release of fluoride from fluoridated elastomers to the in vitro release, and (ii) the residual fluoride content of the elastomers after 1 week in the mouth with and without fluoride toothpaste and mouthrinse. DESIGN: A prospective, longitudinal, cross-over study. SUBJECTS AND METHOD: Six subjects were recruited by poster to take part in the study. Each subject had one premolar in each quadrant to which a bracket could be fixed and exemplary oral hygiene. Elastomers were then placed on these brackets. INTERVENTION: The study was divided into two parts: (i) subjects used oral hygiene products with fluoride and (ii) oral hygiene products with fluoride were excluded. Both groups of elastomers were left in the mouth for 1 week. After collection the elastomers were stored in distilled water. MAIN OUTCOME MEASURES: The amount of residual fluoride in the ligatures after they have been placed in the mouth for 1 week was compared with the cumulative fluoride release in vitro over 1 week and 6 months. RESULTS: Only 13 per cent of the total amount of fluoride in fluoridated elastomers was released during the first week in vitro, compared with 90 per cent in vivo. There was a significantly greater amount (P = 0.001) of residual fluoride when the elastomers were in the mouth for 1 week in the presence of fluoride toothpaste and mouthrinse, than when fluoride supplements were excluded. CONCLUSIONS: (1) Higher levels of fluoride are lost from the fluoride elastomers in vivo than in vitro during the first week. (2) A significantly greater amount of residual fluoride was released from the elastomers placed in the mouth when fluoride toothpaste and mouthrinse were used.

Cariostatic Agents↗
PubMed2004

Fluoridated elastomers: effect on disclosed plaque.

OBJECTIVE: To investigate the effect of fluoridated elastomers on the quantity of disclosed dental plaque surrounding an orthodontic bracket in vivo. DESIGN: A randomized, prospective, longitudinal clinical trial, employing a split mouth, crossover design. SETTING: The Orthodontic Departments of Liverpool and Sheffield Dental Hospitals. SUBJECTS AND METHODS: The subjects were 30 individuals about to start fixed orthodontic treatment. The study consisted of two experimental periods of 6 weeks with a washout period between. Fluoridated elastomers were randomly assigned at the first visit to be placed around brackets on 12, 11, 33 or 22, 21, 43. Non-fluoridated elastomers were placed on the contra-lateral teeth. After 6 weeks (visit 2) the elastomers were removed, the teeth disclosed and a photograph taken. Non-fluoridated elastomers were placed on all brackets for one visit to allow for a washout period. At visit 3, fluoridated elastomers were placed on the contra-lateral teeth to visit 1. At visit 4, the procedures at visit 2 were repeated. The photographs were scanned, then the area and proportion of the buccal surface covered with disclosed plaque was measured using computerized image analysis. A mixed-effects ANOVA was carried out with the dependent variable being the area or percentage area of disclosed plaque. RESULTS: There was no evidence of a systematic error and substantial agreement for the repeat readings of the same images. The only significant independent variable for the area of disclosed plaque was the subject (p < 0.001). The significant independent variables for the proportion of disclosed plaque were the subject (p < 0.001) and the tooth type (p = 0.002). The independent variable describing the use of fluoridated or non-fluoridated elastomers was not significant for either the area or the proportion of disclosed plaque. CONCLUSION: Fluoridated elastomers do not affect the quantity of disclosed plaque around an orthodontic bracket.

Adolescent↗
PubMed1993

Permeability of latex and thermoplastic elastomer gloves to the bacteriophage phi X174.

BACKGROUND: Most studies challenging the integrity of the glove barrier have compared the permeability of vinyl and latex gloves. However, no studies of a new nonlatex, nonvinyl thermoplastic elastomer have been reported. This pilot study therefore compared the protective barriers provided by latex and thermoplastic elastomer surgical gloves against penetration of the bacteriophage phi X174. METHODS: Twenty thermoplastic elastomer gloves and 25 commercially available latex gloves (20 brand 1, 5 brand 2) were filled with a sterile serum surrogate and exposed to the phi X174 virus in a flask, with shaking for 180 minutes at 37 degrees C. Aliquots of 5 ml were withdrawn at baseline, 30, 60, 120, and 180 minutes and assayed by a standard plaque assay. The remaining contents of the gloves were then tested by an extremely sensitive qualitative assay (plaque assay without dilution of the sample). RESULTS: With the standard plaque assay, virus was detected in 30% of the brand 1 latex gloves, in 80% of the brand 2 latex gloves, but in none of the thermoplastic elastomer gloves. The qualitative assay, which can detect even a single virus in the entire glove contents, had positive results for 30% of the thermoplastic elastomer gloves, 70% of the brand 1 gloves, and 100% of the brand 2 gloves. CONCLUSIONS: Despite the small sample, the results of this stringent assay suggest that the mechanical barrier offered by thermoplastic elastomer gloves is equal to or better than that provided by the latex gloves tested. Clinical studies are needed to evaluate thermoplastic elastomer gloves, which may withstand mechanical stress better than latex or vinyl. Thermoplastic elastomer gloves may therefore be a desirable alternative for health care workers in high-risk settings or for individuals with latex allergies.

Bacteriophages↗
PubMed1991

In vivo study of an elastomer end-coated polytetrafluoroethylene vascular prosthesis.

Polyurethane end-coated polytetrafluoroethylene (PTFE) grafts (elastomer PTFE grafts) were implanted in 12 female adult mongrel dogs to assess patency, intimalization, tissue incorporation, and technical suitability of the material as a vascular graft. Each dog had bilateral aortoiliac grafts placed, one a standard PTFE and the other an elastomer PTFE graft. The length of the grafts was 7-8 cm and the diameter was 6 mm. The grafts were harvested at intervals to 120 days postoperatively. The elastomer PTFE grafts showed superior longitudinal elasticity, retention of shape, and no graft tearing with suture tension; however, no significant difference in bleeding was noted at the anastomoses between the standard and elastomer PTFE grafts. Satisfactory patency was obtained with both standard (8/10) and elastomer PTFE grafts (9/10) at 90-120 days. No significant difference in the thickness of intima and the length of pannus ingrowth was noted between the standard and elastomer PTFE grafts. No outer tissue incorporation was seen at the elastomer-treated graft segments as opposed to the well-incorporated untreated segments. In conclusion, elastomer end-coating of a PTFE vascular prosthesis provided excellent handling characteristics without detracting from patency; however, the lack of outer tissue incorporation may be a potential disadvantage in its clinical use.

Anastomosis, Surgical↗
PubMed1995

Clinical effectiveness of fluoride-releasing elastomers. I: Salivary Streptococcus mutans numbers.

The purpose of this study was to examine the effect of fluoride-releasing elastomers on salivary Streptococcus mutans numbers. Twenty-four patients with fixed orthodontic appliances were randomly divided into experimental and control groups consisting of 12 patients each. Conventional elastomers were in place while two baseline whole saliva samples were collected from each subject in both groups at their regular appointments. After the second baseline sample was taken, conventional elastomers were replaced with fluoride-releasing elastomers in the experimental group, whereas conventional elastomers were continued in the control group. Three saliva samples were then collected from all subjects at 1-week intervals. Conventional elastomers were placed in all subjects while two postexperimental saliva samples were collected at regular appointments. Results showed that the control group demonstrated no significant changes (p > 0.05) in the percentage of S. mutans over the 13-week study period. However, after the fluoride-releasing elastomers were placed, the percent of salivary S. mutans decreased significantly (p < 0.01) in the experimental group. There was no significant effect after the fluoride-releasing elastomers were in place for 2 or more weeks.

Adolescent↗
PubMed2004

Fluoridated elastomers: effect on the microbiology of plaque.

The objective of this study was to investigate the effect of fluoridated elastomeric ligatures on the microbiology of local dental plaque in vivo. This randomized, prospective, longitudinal, clinical trial had a split-mouth crossover design. The subjects were 30 patients at the beginning of their treatment with fixed orthodontic appliances in the orthodontic departments of the Liverpool and the Sheffield dental hospitals in the United Kingdom. The study consisted of 2 experimental periods of 6 weeks with a washout period between. Fluoridated elastomers were randomly allocated at the first visit to be placed around brackets on tooth numbers 12, 11, 33 or 22, 21, 43. Nonfluoridated elastomers were placed on the contralateral teeth. Standard nonantibacterial fluoridated toothpaste and mouthwash were supplied. After 6 weeks (visit 2), the elastomers were removed, placed in transport media, and plated on agar within 2 hours. Nonfluoridated elastomers were placed on all brackets for 1 visit to allow for a washout period. At visit 3, fluoridated elastomers were placed on the teeth contralateral to those that received them at visit 1. At visit 4, the procedures at visit 2 were repeated. Samples were collected on visits 2 and 4. A logistic regression was performed, with the presence or absence of streptococcal or anaerobic growth as the dependent variable. A mixed-effects analysis of variance was carried out with the percentage of streptococcal or anaerobic bacterial count as the dependent variable. The only significant independent variables were the subject variable (P =<.001) for the percentage of streptococcal and anaerobic bacterial count and the visit variable for the percentage of streptococcal count (P =<.001). The use of fluoridated or nonfluoridated elastomers was not significant for percentage of either streptococcal (P =.288) or anaerobic count (P =.230). Fluoridated elastomers are not effective at reducing local streptococcal or anaerobic bacterial growth after a clinically relevant time in the mouth.

Adolescent↗
PubMed1999

Color stability and colorant effect on maxillofacial elastomers. Part III: weathering effect on color.

STATEMENT OF PROBLEM: Maxillofacial prostheses are serviceable for approximately 6 months, after which they need to be refabricated because of the deterioration of color and physical properties. PURPOSE: This third article in a 3-part series evaluated the color stability of commonly used colorant-elastomer combinations as a result of exposure to weathering. METHODS AND MATERIAL: Fifteen specimens were fabricated for each of the 3 elastomers (Silastic medical adhesive type A, Silastic 4-4210, and Silicone A-2186) and 6 colorants (dry earth pigments, rayon fiber flocking, artist's oil paints, kaolin, liquid cosmetics, and no colorant) for a total of 270 specimens (18 groups of 15 specimens). The 15 specimens of each elastomer-colorant combination were separated into 3 test condition groups (control, time passage, and natural weathering) of 5 specimens per test condition group. Control specimens were evaluated within 1 month of fabrication. The time passage group was sealed in glass containers and kept in the dark for 6 months before testing. The natural weathering groups were placed on the roof of the dental school for 6 months and exposed to sunlight and weathering. Color and optical density data for each elastomer-colorant combination were subjected to a 1-way analysis of variance to examine effects among test conditions (control, time passage, and weathering). When significant differences were observed, the Student-Newman-Keuls multiple range test was performed to identify differences in elastomer-colorant combinations among each test condition at a significance level of .05. RESULTS: Changes in color, as a result of weathering, were noted in many of the colorant-elastomer combinations. Also, color change occurred not only to the colored, but also to uncolored materials over time without exposure to weathering. CONCLUSION: Clinically, the addition of colorants could have a stabilizing effect on the elastomer color when it is exposed to weathering.

Analysis of Variance↗
PubMed2001

Accelerated color change in a maxillofacial elastomer with and without pigmentation.

STATEMENT OF PROBLEM: Maxillofacial prostheses require frequent replacement because the elastomer and its color additives undergo changes. PURPOSE: This study attempted to determine whether predictable color changes occur when 3 pigments are individually incorporated into a specific silicone elastomer. MATERIAL AND METHODS: The materials included an RTV elastomer; 1 natural inorganic pigment, burnt sienna; and 2 synthetic organic pigments, Hansa yellow and alizarin red. Eight test groups of 10 polymerized specimens were established. Groups 1 and 2, acting as the control, involved only the elastomer. Groups 3 and 4 were composed of elastomer and burnt sienna. Groups 5 and 6 consisted of elastomer and Hansa yellow. Groups 7 and 8 comprised elastomer and alizarin red. Odd-numbered groups were assigned to a test site in Miami, Fla., whereas the even numbered groups went to Phoenix, Ariz. Specimens weathered in Miami and Phoenix received sunlight exposures of 1305.7 MJ/m2 and 1310.2 MJ/m2, respectively, over time. Before and after weathering, the L* a* b* color parameter (DeltaE*) of each specimen was determined spectrophotometrically. RESULTS: Mean color changes that occurred in Arizona were larger than those produced in Florida. Specifically, these differences ranged from 0.4 (alizarin red groups) to 2.36 units for the 2 unpigmented control groups. Other differences showed significance for the unpigmented (P=.001), burnt sienna (P=.006), and Hansa yellow groups (P=.001). CONCLUSION: Outdoor weathering tests in which documented ASTM methods were used provided a valid baseline for future research on color changes in maxillofacial prostheses.

Analysis of Variance↗
PubMed2003

Relationship between the fluoride concentration of the fluoride-releasing elastomers and the acquired acid resistance of human enamel in vitro.

The objective of the study was to evaluate the relationship between the fluoride concentration of the fluoride-releasing elastomers and the acquired acid resistance of human enamel. Four kinds of fluoride concentration of the experimental fluoride-releasing elastomers were 1.25, 2.5, 3.75 and 5.0 wt%. An enamel block was cut into two smaller enamel blocks, one of which was set with an elastomer, the other as a control not set with elastomer. A plastic block that had the same shape as the small enamel block was also set with elastomer. Fluoride release and acid resistance tests were carried out. The mineral loss of the demineralized enamel was measured by microradiography. The results showed that the fluoride-releasing ability significantly increased with the increase of fluoride concentration in the elastomer (p < 0.05). The acid resistance of the enamel appeared to be enhanced greatly, however, its change was not proportional to the fluoride concentration in the elastomers.

Absorption↗
PubMed2005

Highly active, lipase silicone elastomers.

Lipase Candida rugosa was entrapped in silicone rubber via condensation-cure room temperature vulcanization of silanol-terminated poly(dimethylsiloxane) with tetraethyl orthosilicate as a crosslinker, to give a highly active silicone-enzyme elastomer. The effect on enzyme activity of addition of water and hydrophilic polymeric moieties based on poly(ethylene oxide) 2 was examined, as were crosslinker concentration, enzyme concentration, and elastomer thickness. It was demonstrated that lipase is most active in silicone elastomers and more active in silicone oils than simple hydrocarbons. Crosslink density in these elastomers was not an important factor in the reactivity of the rubber. However, the addition of hydrophilic species prior to elastomer formation decreased the efficiency both of the dispersion of the enzyme and the resulting activity of the elastomer. This effect could be moderated by prior exposure of the lipase to silicone oil. Thus, hydrophobic silicones play a protective/activating role for lipase.

Biocompatible Materials↗
PubMed2006

Interactions of pigments and opacifiers on color stability of MDX4-4210/type A maxillofacial elastomers subjected to artificial aging.

STATEMENT OF PROBLEM: The color instability and degradation of maxillofacial elastomers limit the function and cosmetic quality of facial prostheses. PURPOSE: The purpose of this study was to measure the interactions of oil pigments plus dry earth opacifiers at 5%, 10%, and 15% by volume in stabilizing the color of MDX4-4210/type A silicone elastomers before and after artificial aging. MATERIAL AND METHODS: In the first part of the study, each of 5 opacifiers (Georgia kaolin powder neutral, kaolin powder calcined, Artskin white, dry pigment titanium (Ti) white, or Ti white artists' oil color) at 10% concentrations were combined with each of 5 oil pigment types (no pigment, cadmium-barium red deep, yellow ochre, burnt sienna, or a mixture of the 3 pigments), for a total of 25 experimental groups of elastomers. In the second part of the study, 50 experimental groups of elastomers were made by combining 1 of 5 opacifiers at 5% and 15% concentrations with 1 of 5 oil pigments as in Part 1. Five specimens of each elastomer were tested, for a total of 375 specimens. In each part of the study, all specimens were aged in an artificial aging chamber. CIE L*a*b* values were measured by a spectrophotometer. The color differences (DeltaE*) were subjected to repeated-measures analysis of variance. Mean values were compared by Tukey-Kramer intervals (alpha = .05). RESULTS: In Part 1, when the opacifiers were tested at 10% concentration, Ti white oil color had the most color change, and dry pigment Ti white had the least; all other opacifiers were not significantly different from each other. In Part 2, at 5%, Ti white oil color had the most color change; all other opacifiers were not significantly different from the others. At 15%, Ti white oil color again had the most color change, followed by Artskin white, kaolin powder calcined, and Georgia kaolin; Ti white dry earth pigment had the least color change. Overall, 5% Artskin white had less color change than the 15%, whereas 15% dry pigment Ti white had less color change than the 5% (P < .001). The 5% and 15% of other opacifiers were not significantly different. CONCLUSIONS: At all 3 concentrations, oil pigments mixed with opacifiers helped protect the MDX4-4210/type A silicone elastomer from color degradation over time. Dry pigment Ti white remained the most color stable over time, followed by the pigments mixed with kaolin powder calcined, Georgia kaolin, Artskin white, and Ti white artists' oil color.

Barium Sulfate↗
PubMed1999

Color stability and colorant effect on maxillofacial elastomers. Part II: weathering effect on physical properties.

STATEMENT OF PROBLEM: The clinical life of a maxillofacial prosthesis averages about 6 months, before it needs to be refabricated. Degradation of the color and physical properties of the prosthesis are the principle reasons for replacement. PURPOSE: This second part of a 3-part in vitro investigation evaluated the change in physical properties of popular colorant-elastomer combinations as a result of weather exposure. MATERIAL AND METHODS: Fifteen dumbbell-shaped and 15 trouser-shaped specimens were fabricated for each of the 3 elastomers (Silastic medical adhesive type A, Silastic 4-4210, and Silicone A-2186) and 6 colorant combinations (dry earth pigments, rayon fiber flocking, artist's oil paints, kaolin, liquid cosmetics, and no-colorants) for a total of 540 specimens. The 15 dumbbell-shaped and trouser-shaped specimens of each elastomer colorant combination were separated into 5 of each shape among 3 test condition groups (control, time passage, and natural weathering). Control specimens were evaluated within 1 month of fabrication. The time passage group was sealed in glass containers and kept in the dark for 6 months before testing. The natural-weathering groups were placed on the roof of the dental school for 6 months and exposed to sunlight and weathering. Evaluations of hardness and tear strength were made on trouser-shaped specimens, and evaluations of the ultimate tensile strength and percentage elongation on dumbbell-shaped specimens. Physical property data for each elastomer-colorant combination were subjected to a 1-way analysis of variance to examine effects among the test conditions. When significant differences were observed, the Student-Newman-Keuls multiple range test was performed to identify differences in elastomer-colorant combinations among each test condition at a significance level of .05. RESULTS: Exposure to weathering and time changes of the physical properties of many colorant-elastomer combinations indicated that properties of a clinical prosthesis can change with time. CONCLUSION: The addition of colorants to the silicones altered the effects of weathering. In addition, the silicones were not as stable as previously assumed.

Analysis of Variance↗
PubMedDate not supplied

Synthesis and characterization of a photo-cross-linked biodegradable elastomer.

The synthesis and characterization of a photocurable biodegradable elastomer as a potential biomaterial for the delivery of thermosensitive drugs are described. The elastomer was prepared from UV initiated cross-linking of an acrylated star-poly(epsilon-caprolactone-co-D,L-lactide) prepolymer. The influence of the molecular weight of the acrylated prepolymer on the final elastomer mechanical and thermal properties was determined. The glass-transition temperature of the elastomers was independent of the prepolymer molecular weight and was from -6 to -8 degrees C. The Young's modulus and stress at break of the elastomers was proportional to the inverse of the prepolymer molecular weight, while the strain at break increased in a linear fashion with the prepolymer molecular weight. Over a degradation period of 12 weeks in phosphate buffered saline, the elastomers exhibited little mass loss, appreciable mechanical strength loss, and little dimensional or strain at break change.

Biocompatible Materials↗
PubMed2006

In vivo degradation behavior of photo-cross-linked star-poly(epsilon-caprolactone-co-D,L-lactide) elastomers.

We have recently reported on the preparation of biodegradable elastomers through photo-cross-linking acrylated star-poly(epsilon-caprolactone-co-D,L-lactide). In this paper we assess the change in their physical properties during in vivo degradation in rats after subcutaneous implantation over a 12 week period. These parameter changes were compared to those observed in vitro. Two different cross-link densities were examined, representing the range from a high Young's modulus to a low Young modulus. Elastomers having a high cross-link density exhibited degradation behavior consistent with a surface erosion mechanism, and degraded at the same rate in vivo as observed in vitro. Young's modulus and the stress at break of these elastomers decreased linearly with the degradation time, while the strain at break decreased slowly. Elastomers having a low cross-link density exhibited a degradation mechanism consistent with bulk erosion. Young's modulus and the stress at break of these elastomers decreased slowly initially, followed by a marked increase in mechanical strength loss after 4 weeks. The elastomers were well tolerated by the rats over the 12 week period in vivo.

Absorbable Implants↗
PubMed2004

Study on rat subcutaneous reaction to experimental polyurethane elastomers.

The purpose of the study was to investigate the biocompatibility of experimental elastomers, E580 and E590. The experimental elastomers and the control--a clinically used elastomer--were implanted into the subcutaneous tissue of rats. The tissue reactions were examined histologically on the 3rd, 7th, 14th, 28th, and 56th day after implantation. It was found that there were some irritant responses in the tissues adjacent to the implanted elastomers during the first week. However, the inflammatory tissue reaction subsided substantially from the second week onwards. The stable fibrous capsule surrounding the elastomer was formed after eight weeks. The tissue responses of the control, E580, and E590 were similar. The results suggested that the long-term tissue irritation of the experimental elastomers was so low such that they have the potential to be applied clinically.

Animals↗