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Key words: coatings, abrasion resistance, Taber Abraser
Based on the immediate need for information on thermal-based coatings from OSB (a required postmarket surveillance [RPS] issued last year) this project was developed toward finding a validated method for determining the quality of a thermal sprayed coating based on abrasion resistance. The most common, and not yet validated, method for qualifying the coatings abrasion durability is by using a Taber Abraser (manufacturer's name). Another test method that is still in development but is being used as a straw-man standard by ASTM is a reciprocating inverted pin on a sample method being developed at Howmedica. Both of these methods are being developed for evaluation in the Office of Science and Technology.
A Taber Abraser was purchased and set up over the past year. The appropriate sample abrasion wheels (used to abrade samples) were purchased and some test wheels developed by Taber were given to FDA for evaluation. Sample coupons (4"x4" flats of Ti) were purchased by the FDA and were coated by APS of Ohio (a thermal spray coating vendor to the industry). An engineering design was developed to minimize the likelihood of results being confounded by equipment parameters. Preliminary tests have been done to help develop appropriate protocols for the full battery of abrasion tests. The preliminary tests have forced OST to consider clearly identifying cleaning parameters and specifying equipment parameters that have not been positively identified in protocols submitted to the Agency by companies using the Taber as a test method. Samples are to be tested using a specific protocol developed in-house. This protocol will be introduced to the consensus standards process through ASTM.
Also under development has been a simpler, constructable model of the Howmedica inverted pin on sample method. A design was produced in the summer, and parts for the equipment were purchased. Unfortunately, new requirements make the current design less than optimal. The current design forces the load bearing on the sample to be no less than 20N, and it has become apparent within the past month that it may be necessary to run tests as low as 10N. Expectations are that the equipment will be redesigned and built over the next year. [Stds]
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Key words: absorbable sutures, mechanical testing, accelerated aging
An industrial complaint alleged that the packaging design for one type of absorbable suture does not maintain the integrity of seals in the packaging throughout the designed life of the product. This study was designed to determine whether the alleged health threat of epidemic wound dehiscence was genuine, and to develop a test method which can be used by ODE as part of a performancebased standard for the integrity of foil-type device packaging. An accelerated aging protocol and an in vitro test of retained strength after implantation for absorbable sutures are also being examined. The experimental design responds to concerns expressed by two Center Offices, OC and ODE.
For Phase II tests done in 1996, two sizes of braided and monofilament synthetic absorbable sutures from three manufacturers, plus two sizes of chromic gut sutures, were randomized into four treatment groups (5_C, 90% Relative Humidity (RH); 42_C, 90% RH; 5_C, 10% RH, and 42_C, 10% RH) for the accelerated aging test and placed into environmental chambers. Knot tensile strength was determined for sutures tested without being stored in environmental chambers and after four periods of aging in the environmental chambers (9, 18, 31, and 44 weeks, corresponding to 0.7, 1.4, 2.4, and 3.4 years of "accelerated time", where the last group of each suture type was near its accelerated expiration date when tested). An additional series of newly manufactured sutures of each type were also tested. Out-of-package testing and 1-, 2-, and 3-week in vivo and in vitro testing of untreated sutures and of all aged and new sutures has been completed and the data are being analyzed.
Tested sutures exceeded USP mandated 'out-of-package' mean minimum knot tensile strength. However, as was seen in Phase I testing (sutures of various ages retrieved from the field), some sutures did not meet label claims for retained strength after timed in vivo exposure. The behavior of the aged sutures did not echo data observed for naturally aged sutures in Phase I for all three types of sutures, demonstrating that this accelerated aging protocol is not an acceptable model for sutures aged naturally on the shelf. Preliminary analysis of data indicates that knot strength was not affected by the relative humidity; but for at least one type of suture, the knot strength was related to the package storage temperature and the time at elevated temperature. However, the preliminary analysis of the data does indicate that the in vitro test is an acceptable substitute for the in vivo test. Results from this project are being incorporated into a guidance document for the mechanical testing of sutures and will be the basis for a revision of the USP protocol for the mechanical testing of sutures. [Enf]
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Key words: latex gloves, environmental degradation, tensile test, chlorination
Latex gloves are widely used as a primary barrier to the spread of disease in various situations, including direct medical care, surgery, and emergency care. A federal-state contract study in the State of Washington recently evaluated the environmental degradation of latex condoms and determined that some formulations of condoms are susceptible to significant deterioration due to heat-accelerated and room temperature aging. Condoms and gloves are manufactured in a similar, but not identical manner. The purpose of this study was to evaluate the deterioration of latex gloves to determine if the mechanisms identified as important in the environmental degradation of condoms are relevant to gloves. This study focuses on whether differences in latex glove formulations are important factors in the resistance of the product to high-temperature deterioration, as might occur during shipment or shelf life storage in non-air-conditioned environments.
Sixteen latex glove styles were exposed to severely elevated temperature and low humidity (70°C, <15% RH) for periods of 7, 14, and 21 days. These conditions were selected to represent the most severe conditions that may be encountered during shipment and storage. The 16 styles represented various formulations of latex gloves (surgeons and exam, powdered and powder-free), manufactured from several sources in six different countries. Traditional tensile testing (ASTM D412) of the exposed gloves plus controls (0 days of exposure) was performed.
Our data were evaluated with respect to the effect of heat aging (70°C) on glove degradation over time, as well as the comparative effects of heat aging on different types of gloves (powdered vs. powder-free, exam vs. surgeons, and smooth vs. textured). The most notable difference was found between powdered and powder-free gloves. The powdered gloves, without exception, exhibited a moderate or no statistical decrease in tensile strength over 21 days of exposure. Four of the nine powdered glove styles showed no statistical degradation over time. The tensile strength of the other five types decreased a moderate 10-25%. The bulk of this degradation, depending on brand, occurred at various points throughout the 21-day exposure period.
In contrast, of the seven brands of powder-free gloves, the tensile strength of five brands significantly decreased (within only 7 days for four brands), followed by a more moderate rate of deterioration. The stress vs. time curves were generally quadratic in nature and the total deterioration in tensile strength ranged from 70% to over 90%. Two powder-free styles did not follow this pattern, but rather followed the more moderate linear degradation pattern characteristic of the powdered gloves, exhibiting total decreases in tensile strength of 15% and 25%. One of these two brands was found to be nonchlorinated. The powder removal process of the other brand is currently under investigation. Thus, these results suggest that the chlorination process, which is one of the most common processes used to render gloves free from surface powders, may have detrimental effects on the barrier ability of natural rubber latex.
Two direct comparisons could be made on the other glove characteristics mentioned above (texture and use) based on the assumptions that two glove types from the same manufacturer and country were made at the same site in that country and used in identical processes and formulations. (These assumptions may be difficult, if not impossible to verify.) Under these assumptions, smooth vs. textured gloves (powdered, exam, made in Thailand) were compared using a two-way analysis of variance (ANOVA). It was found that, although neither degraded significantly over time, the smooth gloves had significantly (p<0.0001) greater tensile strength (approximately 50%) than the textured gloves. It is not clear if lower tensile strength is a characteristic of textured gloves in general or is peculiar to this pair. A comparison of surgeons vs. exam gloves (smooth, powdered, made in the United States) showed no significant difference in tensile strength.
FDA currently accepts the performance limits for gloves (new and environmentally-aged) specified in ASTM D3577 and D3578. If it is determined that certain formulations of latex gloves are more susceptible to environmental degradation than others, and that the ASTM performance limits are inappropriate to assure adequate performance, FDA may need to impose additional requirements on the labeling for handling of gloves during shipment or strengthen the requirements for testing to assure adequate performance. [ProA]
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Key words: pyrolytic carbon, oxidative chemicals, surface morphology
A model to assess the potential for degradation of implant materials in an in vitro oxidizing environment was developed using pyrolytic carbon as a test material. Pyrolytic carbon was chosen because of its importance in cardiovascular applications. The model involves treating the pyrolytic carbon with various oxidative chemicals that occur as a result of cell activation, such as bleach, superoxide and hydrogen peroxide, as well as, human monocyte-derived macrophages. The test samples are then analyzed for the effects of these treatments on physical changes in the material and possible changes in the cell activation potential. The surfaces of the treated materials were analyzed by a variety of techniques, including, x-ray photoemission spectroscopy (XPS), Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FEM) and contact angle measurement. The in vitro biological response to the treated pyrolytic carbon was assessed by 1) a chemiluminescence assay that uses the chemiluminigenic probe, lucigenin, to measure the real-time production of superoxide by human monocyte-derived macrophages interacting with the biomaterial; and 2) complement activation to assess blood compatibility. The data indicated that some of the oxidizing treatments, particularly superoxide, hydrogen peroxide, bleach and monocyte-derived macrophages, result in surface morphology and oxygenation changes of the pyrolytic carbon. Biological activity was not increased by the oxidation treatments. Further work is in progress to validate the cellular results. This work was performed in collaboration with the Naval Research Lab. [ProA]