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At least 973 records · Page 54Linked to original sources

PubMed1989

Patch testing with nickel chloride in a hydrogel.

Various concentrations of NiCl2 in a hydrogel were evaluated as a possible alternative to the standard patch test material of 5% NiSO4 pet. Patch test responses were recorded on a total of 430 patients with known or suspected contact allergy. A NiCl2 concentration of 1% or less in the hydrogel failed to elicit a response in some patients who reacted to 5% NiSO4 pet. The 2% NiCl2 hydrogel produced a small increase in response frequency and may reduce false-negative reactions. Along with the ability of the material to improve the topical bioavailability of nickel ions, more irritant reactions were observed. However, in cases with a positive history and a negative patch test with petrolatum, the hydrogel prepared from Methocel-E-4M seems to be a useful alternative vehicle for water-soluble allergens.

Dermatitis, Contact↗

PubMed2000

Suppression of bacterial adherence by experimental root canal sealers.

To prevent reinfection after root canal treatment, root filling materials should be antimicrobial. This study assessed the antimicrobial efficacy of KT-308, a modified glass ionomer cement sealer, and three formulations of ZUT, a combination of KT-308 and three different concentrations of a silver-containing zeolite. Discs prepared from the test materials and paper controls were incubated in Brain Heart Infusion broth for 12 wk. At 2-wk intervals, 18 discs from each group were inoculated with Enterococcus faecalis and incubated for periods of 1 to 30 h. After further processing, a 200 microliters aliquot of the broth immersing each disc was plated on agar and assessed for bacterial growth. The remaining broth was measured for optical density. All ZUT discs demonstrated no bacterial growth after 15 h of interaction, in contrast to abundant growth with the KT-308 and paper discs. Thus ZUT effectively suppressed adherent E. faecalis after 15 h, irrespective of its concentration and age.

Anti-Infective Agents, Local↗

PubMed1995

Bioprosthetic valve tissue viscoelasticity: implications on accelerated pulse duplicator testing.

Most of our knowledge of heart valve mechanics has been gained from low strain-rate studies much lower than physiologic levels. Using a high-speed materials testing system, we compared the low and high strain-rate viscoelastic behavior of porcine aortic valve cusps at extension rates of up to 40 mm/s. Circumferential and radial strips were stretched and then held in their stretched configuration to measure their "stress-relaxation" behavior. During low strain-rate stretching, only 6% of the initial stress dissipated or relaxed after 1 second, whereas 25% of the stress dissipated during high strain-rate stretching. This considerable difference in stress relaxation suggests a rate-dependent viscoelastic behavior that has not been accounted for in valve design and may have important implications for accelerated pulse testing. Even though the valve cusp is loaded for only 0.4 seconds during each heartbeat, at least 15% of the stress may relax over that period. During accelerated pulse testing, however, sufficient time may not be available to allow the tissue fibers to relax back to their natural state before the subsequent loading cycle, leading to a higher baseline preload. In addition, because valve tissue is not given sufficient time to relax before the next cycle, pulse testing subjects the valves to lower-magnitude cyclic stresses than does physiologic loading. Because both the baseline preload and the magnitude of cyclic stresses may lead to early fatigue failure, accelerated wear testing may either overestimate or underestimate valve durability. Clearly, the mechanism of stress-induced failure of biologic tissues must be elucidated before too much validity is placed on pulse duplicator studies.

Animals↗

PubMed1983

The effects of cyclic stress on dental polymethylmethacrylate. I. Thermal and environmental fluctuation.

Alternative resins to traditional denture base acrylic need to be assessed for both short- and long-term performance before their potential can be evaluated. Much dental materials testing is carried out on fresh material and a baseline of knowledge about the properties of aged material is incomplete. Studies have been carried out to examine the effects of thermal and environmental fluctuation on dental acrylic, with testing procedures reconsidered so as to resemble service conditions as closely as possible. Thermal cycling proved detrimental to the resin only when superimposed on intermittent partial drying out and resaturation.

Denture Bases↗

PubMed2005

[Edit and evaluation of Mandarin sentence materials for Chinese speech audiometry].

OBJECTIVE: To edit the sentence list for mandarin speech test materials (MSTM) and to test their equivalence in order to use the list as routine clinical speech tests for evaluation of cochlear implants and hearing aids in different stages of the intervention and rehabilitation. METHODS: Firstly, two groups of professionals were set up: one for establishing the principles of the edit, another for experiments. The criteria to guide the selection of spoken sentences were as following: (1) suitable for everyday speech audiometry, esp. clinically usage; (2) a normal sampling of everyday spoken sentences in mandarin. Totally, 300 sentences were selected in 30 lists for the experiment. The record cassette was used by a male speaker. The college students (54 persons,54 ears) with normal hearing participated in the equivalence test. Two statistic methods were used for equivalence analysis. RESULTS Through speech tests and statistic analysis, 2 sets with 29 lists (290 sentences) were selected as our equivalent lists for further evaluation and clinical trial. CONCLUSIONS: By setting up the strict criteria of selecting sentences, speech test method and statistic analysis, 2 sets of 29 lists (290) sentences were chosen as our speech evaluation materials, but it was necessary for further analysis in different laboratories and clinics. The sentence lists should also get used for hearing impaired subjects, hearing aid users and cochlear implant recipients.

Adult↗

PubMed2006

Spatially varying material properties of the rat caudal intervertebral disc.

STUDY DESIGN: The use of a microscopy based material testing technique to assess the local material properties of rat caudal intervertebral discs under uniaxial compression. OBJECTIVES: To better understand the cell environment of rat caudal intervertebral discs during mechanical loading and elucidate better the role of the nucleus pulposus to the overall disc material properties. SUMMARY OF BACKGROUND DATA: Rat tail models of disc degeneration have been widely used for their similarity with the degeneration phenomena in human beings. Degenerative patterns in the disc are often inhomogeneous, however, only average material properties of rodent discs have been studied. Knowledge of the spatially varying properties within the disc is necessary to understand the disc cell milieu during tissue loading. METHODS: Rat caudal motion segments were tested intact, sectioned, and with alterations of nucleus pulposus using microscopy based techniques. Local displacements and strains were obtained using digital image correlation. Strains and load measurements were used to get the average apparent Young's modulus, peak stress, local Young's modulus, and local Poisson's ratio. RESULTS: There was no difference observed in the average apparent Young's modulus among experimental groups. Peak stresses decreased significantly when the nucleus pulposus was replaced with extremely fluid-like materials. The axial displacement field showed 3 distinct linear distributions in samples which were sectioned. The center region in all groups had significantly smaller axial strain and showed a higher local Young's modulus. CONCLUSIONS: The average equilibrium Young's modulus may be dependent on short-range ultrastructural organization. Spatially varying material properties within the intervertebral disc may be caused by orientation of fiber bundles in the different regions of the anulus fibrosus. The fiber bundles are better able to resist compressive loads when oriented parallel rather than perpendicular to the loading direction. At equilibrium, the anulus fibrosus also appears to have a shielding effect independent of the material filling up the nucleus pulposus space.

Animals↗

PubMedDate not supplied

Effect of placement agitation and placement time on the shear bond strength of 3 self-etching adhesives.

This study measured the shear bond strength (SBS) of 3 self-etching bonding agents to enamel and dentin with and without agitation at 3 different application times. The null hypotheses tested were that agitation and application time have no effect on bond strength. Occlusal surfaces of 180 recently extracted caries-free human molars were wet ground with 600 grit wet-dry silica carbide abrasive paper to obtain a flat enamel surface. The teeth were divided into 18 groups of 10 teeth. Three self-etching bonding agents, Clearfil SE BOND (Kuraray America), Xeno III (Dentsply) and AdheSE (Ivoclar-Vivadent) were applied using application times of 10, 20 or 30 seconds with or without agitation, thinned with a gentle stream of air and cured for 10 seconds, according to manufacturers' directions. Z100 (3M ESPE) composite, A2 shade, was placed over the cured adhesive and cured for 40 seconds. The samples were stored in distilled water at room temperature until testing. The samples were tested in shear to failure with a 1-mm/minute crosshead speed. After enamel shear bond strength testing, the teeth were again ground with 400 and 600-grit wet-dry SiC paper to obtain a flat dentin surface. The protocol used for preparing the enamel bond test samples was repeated, and the teeth were stored until testing in distilled water at room temperature. The samples were again tested in shear at a 1-mm/minute crosshead speed. Values were converted to MPa and data analyzed for intergroup differences using ANOVA and Tukey post-hoc tests. Agitation did not improve enamel SBS for any of the materials tested, but there was a significant difference in enamel SBS among materials: Clearfil SE Bond shear bond strength was greater than Xeno III, which was greater than AdheSE. At 10 seconds application time on dentin, agitation improved the Clearfil SE Bond SBS and, at 20 seconds application time on dentin, agitation significantly improved SBS to dentin for all systems tested. Agitation had no affect when the adhesive was applied to dentin for 30 seconds. Clearfil SE Bond SBS to dentin was significantly higher than the other self-etching adhesives tested except at 10 seconds without agitation.

Acrylic Resins↗

PubMed2001

Evaluation of biomechanical properties of Expanded-Polytetrafluoroethylene Soft Tissue Patch after dorsal implantation in the rat to mimic TMJ lateral reconstruction.

Clinically, Gore-Tex Expanded-Polytetrafluoroethylene (E-PTFE) has been used to reconstruct the lateral temporomandibular joint (TMJ) ligament. The purpose of this study was to assess changes in the biomechanical properties of implanted E-PTFE over time with respect to tissue infiltration. Ninety-six specimens of implants were divided into four groups. Group A was the experimental group. Thirty-six autoclave-sterilized specimens were subcutaneously implanted into the backs of 36 rats. The rats were randomly sacrificed at 2 (n = 12), 7 (n = 12) and 12 (n = 12) weeks. The implants were tested for mechanical properties including maximal stress, strain and Young's modulus of elasticity (E) using the servo-hydraulic material testing system (MTS). Group B was the in vitro control group. Thirty-six specimens were placed in tissue culture media at 37 degrees C for a time period equivalent to the experimental group to simulate the effect of a moist, warm environment on biomechanical properties. Group C was the temperature and pressure control group. Twelve specimens were autoclave-sterilized to determine the changes of tensile strength under high temperature and pressure. Control group D (no treatment) was tested to determine the initial tensile strength. The results showed significantly larger maximal stress as well as an increase in E and smaller maximal strain in experimental group A than in control groups B, C and D. There was no significant difference among control groups B, C and D. Histological examination of implants at 12 weeks demonstrated that 0.2-0.3 mm of 1-mm thick implants were occupied by connective tissue from each side. It may be concluded that E-PTFE implants become stronger and less flexible after implantation in vivo.

Analysis of Variance↗

PubMed1994

Comparison of the resistance of miniplates and microplates to various in vitro forces.

A comparison of the Luhr Mini System (Howmedica, Inc, Rutherford, NJ) and the Luhr Micro System (Howmedica, Inc) was undertaken to determine resistance to various forces using a biomechanical model. Miniplates and microplates were first tested to determine their resistance to forces of displacement on flat bend, edge bend, tension, and compression generated by a materials testing system machine. Then, miniplates and microplates were attached to fresh porcine ribs, fixed to a custom-made jig, and subjected to the same forces of displacement. The load was applied to the bone plate to permanent deformation in all tests. The mini and microplate systems resisted 14.50 and 1.14 kg, respectively, on edgewise bending, 2.65 and 1.10 kg, respectively, on flat bending, 92.03 and 16.44 kg, respectively, on tension, and 127.9 and 27.02 kg, respectively, on compression. The mini and microsystem biomechanical model resisted 1.89 and 0.94 kg, respectively, on edgewise bending, 5.20 and 0.85 kg, respectively, on flat bending, 37.60 and 15.72 kg, respectively, on tension, and 53.55 and 16.0 kg, respectively, on compression. The results suggest that the Luhr Mini Fixation System provides a significant amount of resistance to tensile and compressive forces, but is weakest when large forces are applied at 90 degrees to the flat portion of the plate. The system showed decreased force resistance in the biomechanical model except on flat bending. The Luhr Micro Fixation System has significantly less resistance to deformation, but shows no decrease in ability to resist forces of displacement in the biomechanical model.

Animals↗

PubMed1994

A study on reference standard for cytotoxicity assay of biomaterials.

The objective of the present study was to find a standard substance for use as a reference in the cytotoxicity assay of biomaterials, as an alternative to animal experiments in recent years. Eight kinds of rubber were made in a plate shape to keep their surface area at 1 cm2 against 10 ml of extract volume. They were extracted by the following three extraction methods (a) dynamic extraction at 200 rpm gyration on alumina balls at 37 degrees C for 24 h; (b) static extraction at 37 degrees C for 24 h and (c) extraction by heating in an autoclave at 121 degrees C for 60 min. At the end of each period each extract was examined for cell viability based on an evaluation by neutral red uptake. These methods were repeated up to seven times. Two kinds of chemicals were also tested. The extracts obtained were used to treat human gingival fibroblasts that have been cultured with DMEM supplemented with 5% fetal bovine serum into a 96 well tissue culture plate by 1 x 10(5) cells/ml, in an incubator aerated with 5% CO2, and 95% humidified air at 37 degrees C for 48 h. The extracts of ethylene-propylene, butyl, nitrile rubbers, and two kinds of chemicals yielded strong cytotoxicity in all three kinds of extraction methods, while chloroprene, fluorine-contained, isoprene, India, and silicone rubbers showed little cytotoxicity. The results obtained by the three kinds of extraction methods revealed no differences in the order of cytotoxicity of the materials tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Testing Alternatives↗

PubMed1999

Intrinsic 'soft-start' polymerisation shrinkage-kinetics in an acrylate-based resin-composite.

OBJECTIVES: A resin-composite based on multi-acrylate monomers was to be evaluated for any differences in the setting shrinkage-strain kinetics relative to more conventional formulations based on di-methacrylate monomers. METHODS: Four resin-composites were examined for shrinkage-strain over time periods up to 60 min, from initial irradiation, using a 'bonded disk' measurement device. One material was evaluated with a standard and also a two-level (low to high) blue light irradiation regime. The test material (Solitaire), and the other two controls were studied under fixed-(normal) level irradiation by blue light. Measurements were made at 23 and 37 degrees C. RESULTS: The low-high light irradiation applied to one di-methacrylate composite led to a highly significant (p < 0.001) reduction in shrinkage-strain to a minimal level for the initial 0.2 min. The fixed-level irradiation with the acrylate-composite also led to a formally identical, but intrinsic 'soft-start' shrinkage-delay regime; significant at p < 0.001. Di-methacrylate composites under the same fixed-level light regime did not exhibit shrinkage delay. Both di-methacrylate and multi-acrylate composites exhibited increases in the range 18-29% in final equilibrium shrinkage-strain by increase of specimen temperature. SIGNIFICANCE: Reductions in the rate of initial shrinkage of light-cured restoratives may have clinical benefits for restoration bond-integrity nearly as important as reductions in the final equilibrium shrinkage-strain. This may be achieved either by special light irradiation regimes (low to high, or ramped) or in favourable cases by novel monomer-composite formulations and setting chemistry (e.g. Solitaire). The bonded disk shrinkage-strain measurement technique is suitable for the elucidation of such rapid kinetic and temperature-dependent events during photo-polymerisation setting processes.

Acrylic Resins↗

PubMed2002

An evaluation of the viscoelastic characteristics of soft denture liners.

PURPOSE: The purpose of this study was to evaluate the viscoelastic characteristics of a group of soft denture liners by means of a creep test. MATERIALS AND METHODS: The materials evaluated included a silicone rubber base direct liner (Sofreliner MS), a polyolefin base indirect liner (Molteno S), and a conventional tissue conditioner (Coe Soft) as a control. Cylindrical specimens of each material were fabricated using a metal mold. Half of the specimens were subjected to mechanical fatigue with a 75-N load at 1.2 Hz for 200,000 cycles. The creep test was performed on each material and condition with and without a fatigue test using low-load conditions to achieve a 10% strain on all specimens. Viscosity and elasticity were measured, and the data were statistically analyzed using 1-way analysis of variance and Fisher's Protected Least Significant Difference (PLSD) test (p < 0.05). RESULTS: The silicone rubber direct liner (1.31 +/- 2.1 MPa) exhibited a similar mean elastic property as the conventional tissue conditioner (0.90 +/- 0.22 MPa) and an intermediate viscosity between the conventional tissue conditioner (0.11 +/- 0.01 GPa. s) and polyolefin base indirect liner (9.84 +/- 1.08 GPa. s). The elasticity did not change for polyolefin and silicone rubber after the fatigue process. Significant differences in the viscosity of silicone rubber were seen with and without fatigue testing (p < or = 0.05). CONCLUSIONS: The silicone rubber was as soft as the tissue conditioner and softer than the polyolefin liner. The stiffer the material, the lower the permanent deformation observed.

Analysis of Variance↗

PubMed2005

Concepts of skin protection: considerations for the evaluation and terminology of the performance of skin protective equipment.

This article proposes a common language for better understanding processes involved in dermal exposure and skin protection. A conceptual model has been developed that systematically describes the transport of agent mass from sources, eventually resulting in "loading" of the skin surface or the skin contaminant layer. In view of a harmonized glossary of exposure terminology this is considered the exposure surface. Loading is defined as agent mass present in this layer divided by the exposure surface area. Skin protective equipment (SPE) is meant to reduce uptake, that is, an agent crosses the absorption barrier of the skin, by intervening in the processes of loading the exposure surface; however, the design of the equipment may fail to cover skin surface entirely. In addition, part of the mass intercepted by the SPE may reach the skin surface either by permeation, penetration, or by transfer when touching the contaminated exterior of the SPE. Evaluation of SPE performance has earlier focused on chemical resistance performance testing for permeation, penetration, or degradation of SPE-materials. In use-scenario practice, however, all processes will occur concurrently. Thus, SPE field performance evaluation including user-SPE interaction complementary to material testing is warranted. Results of laboratory testing for SPE-materials are reported as substance-specific breakthrough times and permeation rates. SPE field performance should be evaluated for reduction of either uptake or parameters that reflect the outcome of dermal exposure. Ideally, this should be based on the results of intervention-type workplace studies, for (e.g., assessment of exposure loading). The level of reduction can be expressed as a protection factor (ratio without/with SPE) for different parameters of dermal exposure or uptake. It is concluded that for evaluation of SPE-type performance, generic protection factors can be derived for substance-independent processes (e.g., reduction of exposure loading) but not for substance-specific reduction of uptake.

Environmental Monitoring↗

PubMed1989

Abrasion resistance of microwave-curing denture base resin.

This study was designed to test the abrasion resistance of microwave-curing denture base resin. We also studies the effects of surface smoothing treatment on abrasion resistance. Test resin was allowed to polymerize, and then buff polished or treated by surface smoothing. Knoop hardness was measured both prior to and following surface treatment. Then, the test material was subjected to brushing using a newly developed toothbrushing machine. Volume and surface roughness of the material were measured before and after brushing, and the surface structure of the material was examined with SEM. Microwave-curing denture base resin is equal in Knoop hardness and abrasion resistance to its conventional heat-curing counterpart, although it is smoother at the surface. The resin improved both in hardness and abrasion resistance when it underwent surface smoothing treatment regardless of whether it was heat-cured or microwave-cured. As was evident from SEM observations that both types of resins suffered superficial chipping following severe brushing, which is in accordance with our previous clinical findings.

Acrylic Resins↗

PubMed1990

Screening of in vitro cytotoxicity by the adhesive film test.

A novel procedure, the adhesive film test, is proposed as a screening method to predict potential cytotoxicity of biomaterials. This in vitro test utilizes a sterile strip of acrylate-based medical adhesive as an anchorage substrate in cytotoxicity studies. The adhesive film allows direct fixation of test samples to the base of the petri dish, ensuring close contact between sample and cells. The test is based on the principle that toxic components present in the test material will readily leach out into the culture medium and adversely affect the local cell population. The main advantage of the adhesive film test is that a viable cell population can be added directly to the test plate and after an incubation period of 24 h, the cellular response can be recorded as either cytotoxic or cytocompatible. Microscopic examination can be followed by quantifying the results using a micrometer to measure cellular attachment areas, migration distances and zones of inhibition. In addition, the adhesive film used to attach the test samples is shown to support extensive fibroblast growth and attachment to its surface and hence can also function as a negative nontoxic control in cytotoxicity studies.

Adhesives↗

PubMed1990

Biconvex intraocular lenses and Nd:YAG capsulotomy: experimental comparison of surface damage with different poly(methyl methacrylate) formulations.

Biconvex posterior chamber lenses have optical advantages and decrease the risk of capsular opacification, but they are more likely to be pitted during ND:YAG capsulotomy because of apposition of the lens to the capsule. This study reports the likelihood of surface damage to different formulations of poly(methyl methacrylate) at the energy levels required to open posterior capsules. Molded lenses are more easily damaged than higher molecular weight lathe-cut materials (P less than .01), as expected. However, by keeping energy output low, even injection-molded lenses showed minimal damage, with mean pit size 39 +/- 39 microns at 1 mJ. By using a converging contact lens, low power, and keeping the focus behind the capsule, damage to all materials tested should be clinically insignificant.

Lasers↗

PubMed1999

[Modification of bacterial growth by alloplastic bone substitutes].

BACKGROUND: To determine the applicability of alloplastic materials as bone substitutes it is now standard procedure to test materials for possible toxic effects and to study their behavior in animal models and cell cultures. This is especially important with respect to middle ear implants that can be put at risk by recurrent infections and require additional testing in a bacterially contaminated environment. MATERIALS AND METHODS: In the present study ionomeric cement (V-O CEM), bioactive glass ceramic and hydroxyapatite were subjected to contamination with S. aureus, E. coli, Pr. mirabilis, Ps. aeruginosa and Enterococci using agar diffusion and microbial suspension tests and examined for their antibacterial activity. A special feature of V-O CEM that had to be considered was that it could be implanted in two physical states (as a viscous substance and a fully hardened material). RESULTS: The agar diffusion test showed that an antibacterial effect of freshly mixed V-O CEM was demonstrable for up to 60 min. In the microbial suspension test growth of E. coli was found to be promoted after 48-h incubation by V-O CEM set for 1 h. S. aureus exhibited a depressed growth, while Pseudomonas cultures demonstrated cell death after 48 h. V-O CEM set for 24 h and 7 days, respectively, exerted a similar though less pronounced effect. Using the microbial suspension test, a comparison was also made of the antibacterial activities of 24-h V-O CEM, bioactive glass ceramic and hydroxyapatite against cultures of S. aureus, Pseudomonas and E. coli. The inhibitory effect of hydroxyapatite on the growth of S. aureus was found to persist beyond the 48-h incubation period. There was slight growth of E. coli in the presence of bioactive glass ceramic after 48 h, whereas hydroxyapatite produced inhibition of microbial growth. V-O CEM inhibited the growth of Pseudomonas, unlike bioactive glass ceramic and hydroxyapatite, which transiently promoted bacterial growth. DISCUSSION AND CONCLUSIONS: Our findings showed that V-O CEM, bioactive glass ceramic and hydroxyapatite exhibited material-dependent bacterial colonization and thus resembled polymeric bone substitutes (susceptible to invasion by S. epidermidis) and metals (sensitive to S. aureus). In general, users of bone substitutes should conduct preclinical tests in order to obtain advance information on the properties of possible replacement material. Since there can be varying interactions between the materials studied and bacterial growth, material-specific effects on bacterial growth should be investigated. While it is recognized that in vitro studies are an inadequate simulation of the clinical situation, they still provide some insight into the likely behavior of a bone substitutes in human sites.

Bacteriological Techniques↗

PubMed1976

[Mutual relations between plastic materials and bacteria (author's transl)].

The complex problems of microbiological degradation of synthetic plastics and a fairly wide variety of 62 testing materials, belonging to 14 major groups of plastics, are described. Adaequate and reliable testing techniques had to be devised. Drawing on the experiences of H. Braun, 1930, and of Bushnell and Haas, 1941, as to the metabolism of bacteria and the utilization of certain hydrocarbons by microorganisms, and previous research work by A. Schwartz in Berlin, 1959-60, on microbial corrosion of plastics, methods of laboratory testing were developed. The bacteriological technique was based on selection of aerobic microorganisms, which were, by starvation, adapted to use the plastic materials as their only carbon source; foreign carbon sources had to be strictly eliminated; emphasis was laid on proper, double control cultures. The test organisms involved included P. aeruginosa and fluorescens strains, also a certain species of Candida, and mixtures of soil, sewage and garbage organisms grown on exposed plastic surfaces. By means of series of passages the selective adaptation and conservation of these organisms was continued up to 4 1/2 years. An anaerobic adaptation method for Desulfovibrio desulfuricans was developed and used successfully. After preliminary experimentation (Soil burial, sewage and garbage exposure tests) in the laboratory as well as in the open, a large scale Field testing programme under realistic and to some extent extreme conditions was implemented: Nine different plastic materials comprising eight plain high polymer plastics and for comparison one synthetic Cellulose derivate, together with glass control samples, were exposed in twelve different sewage, garbage, and soil media over a period of 3 months to 2 years, and subsequently examined. On the basis of the bacteriological results obtained from the adaptation series the test materials were classified into three categories, corresponding to the stimulation of bacterial growth: Group one, which allowed strong proliferation, included certain types of plasticized P.V.C. and Cellulose esters, as expected, and, as a new result, Polyurethane rubber; the latter showed clear signs of surface corrosion. Group two, which induced a clear but moderate growth, comprised a nylon trade type of Polyamide. Gruop three, allowing weak but still recognisable growth, included Formaldehyde pressure resing (Bakelite). This was surprising as it was thought that the formaldehyde and phenol components would exert a bacteriocidic or at least bacteriostatic effect. The results of the long and time consuming adaptation series with Pseudomonas aeruginosa were confirmed by the manometric dissimilation method of O. Warburg by means of the Braun/Melsungen apparatus. With this subtle but elegant procedure results and graphical recordings were obtained within hours and days...

Candida↗