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PubMed1979

Mechanical properties of antibacterial silicone rubber for hydrocephalus shunts.

In an effort to find a solution to the serious problem of bacterial colonization of cerebrospinal-fluid shunting devices, room-temperature and heat-vulcanizing silicone rubbers were impregnated with gentamicin sulphate. The effects on the mechanical properties of the two rubbers were studied. Results show that the tensile strength and extensibility of the room-temperature-vulcanizing silicone rubber reduced with increasing concentration of the drug. For the heat-vulcanizing silicone rubber, the tensile strength was also found to decrease with increasing drug content. The extensibility after an initial reduction at low concentrations was found to increase at drug concentrations in excess of 10 mg/g. Nevertheless, the changes in mechanical properties measured are considered not to be so great as to preclude the application of drug-impregnated silicone rubbers to cerebrospinal-fluid shunting devices.

Bacteria↗
PubMed2004

Biosurfactant from Lactococcus lactis 53 inhibits microbial adhesion on silicone rubber.

The ability of biosurfactant obtained from the probiotic bacterium Lactococcus lactis 53 to inhibit adhesion of four bacterial and two yeast strains isolated from explanted voice prostheses to silicone rubber with and without an adsorbed biosurfactant layer was investigated in a parallel-plate flow chamber. The microbial cell surfaces and the silicone rubber with and without an adsorbed biosurfactant layer were characterized using contact-angle measurements. Water contact angles indicated that the silicone-rubber surface with adsorbed biosurfactant was more hydrophilic (48 degrees) than bare silicone rubber (109 degrees). The results showed that the biosurfactant was effective in decreasing the initial deposition rates of Staphylococcus epidermidis GB 9/6 from 2,100 to 220 microorganisms cm(-2) s(-1), Streptococcus salivarius GB 24/9 from 1560 to 137 microorganisms cm(-2) s(-1), and Staphylococcus aureus GB 2/1 from 1255 to 135 microorganisms cm(-2) s(-1), allowing for a 90% reduction of the deposition rates. The deposition rates of Rothia dentocariosa GBJ 52/2B, Candida albicans GBJ 13/4A, and Candida tropicalis GB 9/9 were far less reduced in the presence of the biosurfactant as compared with the other strains. This study constitutes a step ahead in developing strategies to prevent microbial colonization of silicone-rubber voice prostheses.

Bacterial Adhesion↗
PubMed2004

Measurement of bite force variables related to human discrimination of left-right hardness differences of silicone rubber samples placed between the incisors.

This study was designed to examine human subjects' ability to discriminate between spatially different bite pressures. We measured actual bite pressure distribution when subjects simultaneously bit two silicone rubber samples with different hardnesses using their right and left incisors. They were instructed to compare the hardness of these two rubber samples and indicate which was harder (right or left). The correct-answer rates were statistically significant at P < 0.05 for all pairs of different right and left silicone rubber hardnesses. Simultaneous bite measurements using a multiple-point sheet sensor demonstrated that the bite force, active pressure and maximum pressure point were greater for the harder silicone rubber sample. The difference between the left and right was statistically significant (P < 0.05) for all pairs with different silicone rubber hardnesses. We demonstrated for the first time that subjects could perceive and discriminate between spatially different bite pressures during a single bite with incisors. Differences of the bite force, pressure and the maximum pressure point between the right and left silicone samples should be sensory cues for spatial hardness discrimination.

Adult↗
PubMed2003

Skim and cream natural rubber particles: colloidal properties, coalescence and film formation.

Cream and skim fractions of freshly tapped natural rubber latex have been studied using atomic force microscopy and scanning electric potential microscopy to elucidate the topology and charge properties in film formation. Elemental distribution maps of the particles have also been obtained using electron energy-loss imaging in a low-energy transmission electron microscope. The two rubber fractions are obtained by centrifugation. The cream fraction is stable while rapid coagulation occurs in the skim fraction. After removal of the coagulum, no further coagulation occurs and the remaining skim rubber particles are stable. The rubber particles from the cream rubber particles contain higher amount of adsorbed protein-phospholipid materials compared to those in the "self-cleaned" skim fraction. This difference in membrane property has a significant impact on the spreading of the cis-1,4-polyisoprene cores, their coalescence and film formation behavior. Coalescence of cream particles appears to be hindered by the membrane materials, forming a rough film that retains the topology of individual particles. Skim particles coalesce more readily, forming relatively smooth films.

Journal Article↗
PubMed2006

Viscoelasticity evaluation of rubber by surface reflection of supersonic wave.

The main characteristic of rubber is a viscoelasticity. So it is important to research the characteristic of the viscoelasticity of the high frequency band for the friction between a rubber material and the hard one with roughness, for instance, the tire and the road. As for the measurement of the viscoelasticity of rubber, DMA (dynamic mechanical analysis) is general. However, some problems are pointed out to the measurement of the high frequency band by DMA. Then, we evaluated the viscoelasticity characteristic by the supersonic wave measurement. However, attenuation of rubber is large, and when the viscoelasticity is measured by the supersonic wave therefore, it is inconvenient and limited in a past method by means of bottom reflection. In this report, we tried the viscoelasticity evaluation by the method of using complex surface reflection coefficient and we compared with the friction coefficient under wide-range friction velocity. As a result, some relationships had been found for two properties. We report the result that character of viscoelasticity of rubber was comparable to friction coefficient.

Algorithms↗
PubMed2003

Biocompatibility of layer-by-layer self-assembled nanofilm on silicone rubber for neurons.

Electrostatic layer-by-layer (LbL) self-assembly, a novel method for ultrathin film coating has been applied to silicone rubber to encourage nerve cell adhesion. The surfaces studied consisted of precursor layers, with alternating cationic poly(ethyleneimine) (PEI) and anionic sodium poly(styrenesulfonate) (PSS) followed by alternating laminin and poly-D-lysine (PDL) layers or fibronectin and PDL layers. Film growth increased linearly with the number of layers. Every fibronectin/PDL and laminin/PDL bilayer was 4.4 and 3.5 nm thick, respectively. All layers were more hydrophilic than the unmodified silicone rubber surface, as determined from contact angle measurements. Of the coatings studied, a PDL layer was the most hydrophilic. A multilayer film with composition [PSS/PEI]3+[fibronectin/PDL]4 or [PSS/PEI]3+[laminin/PDL]4 was highly favorable for neuron adhesion, in contrast to bare silicone rubber substrate. The film coated on silicone rubber is biocompatible for cerebellar neurons with active viability, as shown by lactate dehydrogenase (LDH) assay and fluorescence cellular metabolism observations. These results demonstrate that LbL self-assembly provides an effective approach to apply films with nanometer thickness to silicone rubber. Such only few nanometer thick films are biocompatible with neurons, and may be used to coat devises for long-term implant in the central nervous system.

Animals↗
PubMed2001

Effects of a rubber-slatted flooring system on cleanliness and foot health in tied dairy cows.

Effects on animal cleanliness and foot health of a new rubber-slat system for tied dairy cows, with the ability to drain faeces and urine, were studied in a 2-year controlled quasi-randomised trial in a Swedish university herd. Swedish Red and White cows were kept tied in 42 traditional long-stalls with rubber mats. In total, 82 cows were observed. In 21 stalls, the rearmost 0.74m of the solid stall floor was replaced with nine rubber-coated 53mm wide slats, divided by 29mm slots. The cleanliness was assessed subjectively weekly (year 1) or bi-weekly (year 2) by observations of the hind part of the body. Claw measurements and foot health in hind feet were assessed in connection with hoof trimmings at the beginning, middle and end of the housing period. The foot-health recordings were blinded to flooring. For the analysis of both cleanliness (1781 records, 73 cows) and foot health (240 records, 79 cows), logistic regression was applied, using marginal models and cow observations as repeated measures within each year. The risk of getting dirty on the rubber-slatted floor was significantly lower (odds ratio 0.12 for hind feet when short stall dividers were used, 0.39 for hind legs and 0.38 for thighs and udder), comparing with the solid stall floor. The prevalence of foot diseases in hind feet at trimming was significantly lower on the rubber slats (odds ratio 0.23 for dermatitis, 0.09 for heel horn erosion, and 0.34 for sole ulcer or sole or white line haemorrhage).

Animal Welfare↗
PubMed2003

Surface modification of an experimental silicone rubber maxillofacial material to improve wettability.

OBJECTIVES: Good wettability of maxillofacial prosthetic materials is important so that a lubricating layer is formed with supporting tissues thus reducing patient discomfort. The purpose of the study was to surface modify an experimental silicone rubber material in order to improve wettability. METHODS: Samples of experimental silicone rubber were surface modified by first argon plasma treatment followed by chemisorption of ethyleneoxy functional silanes. These were compared with the same silicone rubber which had ethyleneoxy functional surfactants incorporated into the polymer matrix. In all cases contact angles, tear strength and water uptake were measured. RESULTS: Surface modified materials had comparable contact angles to surfactant modified silicone rubber all being significantly lower than the unmodified material. Surface modified materials, however, had a significantly higher tear strength and lower water uptake in comparison to surfactant modified materials. CONCLUSIONS: Argon plasma treatment followed by chemisorption of ethyleneoxy functional silanes proved an effective way of improving the wettability of an experimental silicone rubber maxillofacial prosthetic material without altering bulk properties.

Materials Testing↗
PubMed1986

Silicone rubber carpal implants: a study of the incidence of late osseous complications.

This clinical review of 53 silicone rubber carpal implants done by the senior author (P. R. C.) between 1976 and 1983 determines the incidence of so-called "silicone rubber synovitis." Although previously reported in small series, the true incidence of this complication of wear of the implant has not been documented. In this study late radiographic follow-up demonstrated lytic lesions adjacent to the carpal implants in 75% of the scaphoid implants, 55% of the lunate implants, and 75% of the scapholunate implants. In patients with x-ray film evidence of lytic lesions, more than half (56%) complained of pain, and more than one fourth (27%) have already had revision surgery. In every patient who had reoperation in this study, the histologic examination of the tissue in the wrist showed a chronic granulomatous process identical to that previously reported in cases of so-called "silicone rubber synovitis". These "lytic lesions" must be differentiated from "degenerative cysts" that are a part of the natural progression of degenerative arthritis. Four cases were submitted for mass spectrophotometric analysis, and the positive identification of the silica atom was made in all four. This study shows that the wear of carpal bone implants of silicone rubber and subsequent "silicone rubber synovitis" are common occurrences and not rare as has been previously inferred from isolated case report studies. This study suggests that implantation of these implants in young, healthy individuals is rarely indicated, and careful follow-up of patients who already have these implants in place is important.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2003

Comparative evaluation of Type 1 latex hypersensitivity in patients with chronic urticaria, rubber factory workers and healthy control subjects.

Latex hypersensitivity manifests itself most commonly with contact urticaria. In this study, we investigated the frequency of latex hypersensitivity as a possible aetiological factor in patients with chronic urticaria (CU) and compared latex hypersensitivity of CU patients (n = 50) with that of rubber factory workers (n = 50) and healthy controls (n = 50). Prick test with latex and fruit extracts and determination of latex-specific immunoglobulin E (IgE) were performed. As a risk factor, contact dermatitis due to rubber additives was tested by patch test. Latex hypersensitivity was detected in 14% of CU patients, 12% of rubber factory workers and 12% of healthy controls (P > 0.05). Positive patch test with rubber additives was detected in 6% of CU and 4% of rubber factory workers. 3 of 7 CU patients had sensitivity to fruits in addition to latex hypersensitivity. In 1 patient with CU, the clinical complaints were found to be related to latex hypersensitivity. These findings suggest that the frequency of latex hypersensitivity in CU patients is no higher than that in healthy individuals. However, CU patients should be carefully asked about latex allergy, as we demonstrated that 1 of the CU patients had undiagnosed symptomatic latex allergy.

Adult↗
PubMed2005

The rubber tree (Hevea brasiliensis Muell. Arg.) homologue of the LEAFY/FLORICAULA gene is preferentially expressed in both male and female floral meristems.

The rubber tree (Hevea brasiliensis Muell. Arg.) is an important source of natural rubber in tropical regions and, as with many woody species, shows a long juvenile phase. To understand the genetic and molecular mechanisms underlying the reproductive process in rubber trees, H. brasiliensis RRIM600 flower and inflorescence development have been characterized, the rubber tree FLORICAULA/LEAFY (FLO/LFY) orthologue, HbLFY, cloned, and its expression patterns were analysed during vegetative and reproductive development. The rubber tree, similar to other Euphorbiaceae species, produces lateral inflorescences containing male, female, and bisexual flowers. HbLFY is expressed in lateral meristems that give rise to inflorescences and in all flower meristems, consistent with a role in reproductive development. Complementation studies using Arabidopsis lfy mutants indicated that the biological function of LFY might be conserved among Brassicaceae and Euphorbiaceae species.

Arabidopsis↗
PubMed2003

Laser diffraction: A new tool for identification and studies of physiological effectors involved in aggregation-coagulation of the rubber particles from Hevea latex.

Latex coagulation is the main limiting factor of rubber yield in Hevea brasiliensis (rubber tree). Using laser diffraction, we set up and optimized a new method for monitoring the kinetics of rubber particle (RP) aggregation, a prerequisite for latex coagulation. In contrast to any previous method used, laser diffraction allows continuous monitoring changes in size of RP aggregates, thereby allowing characterization and quantification of the processes involved in latex coagulation. Using this technique, we confirm that RP aggregating factors are proteins compartmentalized within latex cell vacuoles (lutoids), which, especially at relatively acidic physiological pH, can induce formation of RP aggregates large enough to induce plugging of severed latex vessel extremities. Conversely, latex cytosol was found to harbor anti-aggregating proteins. Further, we were able to titrate the RP-aggregating efficiency of the intralutoidic serum and the anti-aggregating efficiency of the cytosol. Preliminary assays showed that these two parameters were correlated with the yield potential of the tested rubber clones. This method will allow identification and characterization of proteins involved in latex coagulation, hence in rubber yield. We suggest that laser diffraction could be used to monitor the kinetics and characterize the physiological processes involved in aggregation of any particles, organelles or cells.

Chemical Precipitation↗
PubMed2000

A randomized controlled trial of rubber band ligation versus infra-red coagulation in the treatment of internal haemorrhoids.

OBJECTIVE: Despite the presence of numerous non-surgical therapies for the treatment of haemorrhoids, none of these therapies has clearly been proven to be superior. The effectiveness and patient tolerance of rubber band ligation (RBL) and infra-red coagulation (IRC) in the treatment of haemorrhoids was assessed. DESIGN: Prospective randomized trial. SETTING: Academic hospital (tertiary care). PARTICIPANTS: A total of 133 consecutive patients (73 males, 60 females, mean age 48 years (range 19-82)) with internal haemorrhoids, and without concomitant anorectal disease, were randomized to rubber band ligation (RBL, n = 65) or infra-red coagulation (IRC, n = 68). INTERVENTIONS: Rubber band ligation or infra-red coagulation was performed in one or more sessions with four-week intervals until symptoms had resolved. Treatment outcome and side-effects were assessed after each treatment session and one month after the last treatment by proctological examination and a questionnaire, including a pain score (visual analogue scale from 0 to 10). Recurrence of complaints was assessed by telephone questionnaire [mean follow-up of 19.2 months (SD 7.8)]. RESULTS: Treatment outcome was assessed in 124 patients (60 RBL, 64 IRC). The mean number of treatment sessions was 1.6 (SD 0.9) for both therapies. For RBL, 58 patients (97%), and for IRC, 59 patients (92%) were symptom-free or had satisfactorily improved. Only third-degree haemorrhoids seemed to respond better to RBL (five of five patients symptom-free) than to IRC (two of four patients symptom-free). Pain following treatment was more common and more severe after RBL (VAS 5.5 +/- 3.7) than after IRC (VAS 3.3 +/- 3.3, P= 0.018). The telephone questionnaire was answered by 105 patients. Nine of 50 patients (18%) treated with RBL and 11 of 55 patients (20%, P= 0.81) treated with IRC had experienced symptomatic relapse to pre-treatment levels. CONCLUSIONS: Infra-red coagulation and rubber band ligation are equally effective in the treatment of haemorrhoids. The rate and severity of pain is higher after rubber band ligation. Infra-red coagulation should be the first-line treatment for haemorrhoids.

Adult↗
PubMed2005

Strain-induced nonlinearity of filled rubbers.

Dynamic strain-induced nonlinearity in the modulus of filled rubbers shows a striking similarity to what is known about the glass transition of solid materials and the jamming transition of granular materials. This analogy stems from the reality that shear strain in dynamic mechanical measurements introduces fluctuations in a filler network by forcing the system to explore different configurations. Such fluctuations can be described by an "effective temperature" that has many attributes of a true temperature, and particularly is proportional to the strain amplitude. Thus, filled rubbers with respect to strain will display many unusual phenomena that are usually observed in glass-forming materials, but now demonstrated in filled rubbers, including asymmetric kinetics, crossover effects, and glasslike kinetic transitions. The nonlinearity in the modulus of filled rubbers simply reflects a dejamming transition of fillers in rubber matrices. The agglomeration of filler in an elastomeric matrix shares a common ground of physics with the jamming process and glass formation.

Journal Article↗
PubMed1987

Impairment of Photorespiratory Carbon Flow into Rubber by the Inhibition of the Glycolate Pathway in Guayule (Parthenium argentatum Gray).

Cut shoots of guayule (Parthenium argentatum Gray) were treated with four inhibitors of the glycolate pathway (alpha-hydroxypyridinemethanesulfonic acid; isonicotinic acid hydrazide, glycine hydroxamate, and amino-oxyacetate, AOA) in order to evaluate the role of photorespiratory intermediates in providing precursors for the biosynthesis of rubber. Photorespiratory CO(2) evolution in guayule leaves was severely inhibited by AOA. Application of each of the four inhibitors has resulted in a significantly decreased incorporation of (14)C into rubber fractions suggesting that the glycolate pathway is involved in the biosynthesis of rubber in guayule. However, the application of each of the glycolate pathway inhibitors showed no significant effect on photosynthetic CO(2) fixation in the leaves. The inhibitors individually also reduced the incorporation of labeled glycolate, glyoxylate, and glycine into rubber, while the incorporation of serine and pyruvate was not affected. The effective inhibition of incorporation of glycolate pathway intermediates in the presence of AOA was due to an inhibition of glycine decarboxylase and serine hydroxymethyltransferase. It is concluded that serine is a putative photorespiratory intermediate in the biosynthesis of rubber via pyruvate and acetyl coenzyme A.

Journal Article↗
PubMed2006

Interference in adhesion of bacteria and yeasts isolated from explanted voice prostheses to silicone rubber by rhamnolipid biosurfactants.

AIMS: The effects and extent of adhesion of four different bacterial and two yeast strains isolated from explanted voice prostheses to silicone rubber with and without an adsorbed rhamnolipid biosurfactant layer obtained from Pseudomonasaeruginosa DS10-129 was studied. METHODS AND RESULTS: The ability of rhamnolipid biosurfactant to inhibit adhesion of micro-organisms to silicone rubber was investigated in a parallel-plate flow chamber. The anti-adhesive activity of the biosurfactant at different concentrations was significant against all the strains and depended on the micro-organism tested. The results showed an effective reduction in the initial deposition rates, and the number of bacterial cells adhering after 4 h, for all micro-organisms tested at the 4 g l(-1) undiluted rhamnolipid solution. Maximum initial reduction of adhesion rate (an average of 66%) occurred for Streptococcus salivarius GB 24/9 and Candida tropicalis GB 9/9. The number of cells adhering after 4 h on silicone rubber conditioned with biosurfactant was reduced to 48% for Staphylococcus epidermidis GB 9/6, Strep. salivarius GB 24/9, Staphylococcus aureus GB 2/1 and C. tropicalis GB 9/9 in comparison to controls. Perfusing the flow chamber with biosurfactant containing solution followed by the passage of a liquid-air interface, to investigate detachment of micro-organisms adhering to silicone rubber, produced high detachment (96%) of adhered cells for all micro-organisms studied, except for Staph. aureus GB 2/1 (67%). SIGNIFICANCE AND IMPACT OF THE STUDY: It is concluded that biosurfactant represent suitable compounds that should be considered in developing future strategies to prevent the microbial colonization of silicone rubber voice prostheses.

Actinomycetaceae↗
PubMed1981

The treatment of second degree haemorrhoids by injection, rubber band ligation, maximal anal dilatation, and haemorrhoidectomy: a prospective clinical trial.

One hundred and twenty patients with confirmed second degree haemorrhoids were randomly allocated to four treatment groups; injection, rubber band ligation, maximal anal dilatation, and haemorrhoidectomy. Each groups consisted of 30 patients. All patients were regularly followed up for at least one year. Assessment at one year showed that haemorrhoidectomy "cured" the haemorrhoids in 29 out of 30 patients. Rubber band ligation relieved 25 out of 30 and maximal anal dilatation 24 out of 30. Injection was the least effective treatment, and relieved 18 of the 30 patients, with a cure rate of 60% only. Haemorrhoidectomy caused pain in all cases, anal stenosis in two, postoperative haemorrhage in two, and the patients required an average hospital stay of 11.5 days and an average of a further 15.5 days off work. Rubber band ligation was painless in 26 patients out of 30, and maximal anal dilatation was painless in 25 our of 30. There were no postoperative complications in the latter two treatment groups. Haemorrhoidectomy is good in "curing" the disease, but the higher possibility of postoperative pain and complications and longer hospital stay would not justify its use in the treatment of second degree haemorrhoids. Both rubber band ligation and maximal anal dilatation are effective and relatively free from complications. Rubber band ligation has the additional advantage of not requiring hospital stay or anaesthesia and is therefore considered to be the most appropriate method of treatment for second degree haemorrhoids.

Adult↗
PubMed1999

The problems of rubber hypersensitivity (Types I and IV) in chronic leg ulcer and stasis eczema patients.

The prevalence of Type I and Type IV hypersensitivity to rubber allergens in patients with stasis eczema and/or venous leg ulcers over an 18-month period was studied by prick and patch testing. Results from 109 patients were analysed. Positive patch tests were found in 71 patients (65%). Delayed-type hypersensitivity to rubber chemicals was found in 17 patients (15.6%). However, only 1 patient who had additional risk factors showed Type I hypersensitivity to natural rubber latex. We therefore conclude that, although Type IV hypersensitivity to rubber chemicals is relatively common in our patients, Type I hypersensitivity to natural rubber latex remains rare.

Adult↗