“
“In this study, we examined the role of environmental parameters and physical structure in the aging process of poly(lactic acid) (PLA). The role of heating history on the aging behavior of the material was also investigated. PLA samples with a D-content of 4.25% were exposed to a relative humidity
of 80% at three different temperatures, 20, 40, and 50 degrees C (below the glass-transition temperature of the material), at various aging periods of 30, 60, 80, 100, and 130 days. Selected samples were subjected to two consecutive heating runs. The stability of PLA was monitored by a number of techniques, including size exclusion chromatography, differential scanning calorimetry, dynamic mechanical analysis, and tensile measurements. selleck screening library The initial thermal processing (150 degrees C) of the material resulted
in an overall molecular weight reduction. A substantial lowering of properties was observed for PLA samples aged at 20 degrees C for 30 days. No further loss of properties was observed for samples aged up to 40 degrees C for several time intervals. A major portion (80-90%) of the induced changes in the tensile properties could be reversed after drying. At 50 degrees C and 100 days of aging, a sharp decrease in the overall properties was noticed. The results seem to confirm the earlier finding that PLA degradation driven by hydrolysis needs a higher temperature (> 50 degrees C) in combination with ample time to take place. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 472-481, 2011″
“PURPOSE: To compare central and paracentral corneal curvature Selleck HDAC inhibitor measurements after myopic excimer laser surgery performed using a large optical zone (OZ) (6.5 mm).
SETTING: Private practice.
METHODS: The mean simulated keratometry (SimK) value, average central power, corneal power of Placido rings 1 to 9 and the average central corneal power over the central 3.0 mm (ACCP(3mm)) were measured using a TMS-2 corneal topographer.
RESULTS: Forty-two patients (mean correction -5.0 diopters [D] +/-
2.2 [SD]) were prospectively enrolled. The mean SimK value (38.82 D +/- 1.95) and the mean average central power (38.89 +/- 2.02 D) were not statistically significantly different, even when the sample was stratified according to the amount of induced correction (lower or higher than -5.00 D). Alvocidib solubility dmso The difference between the central and paracentral measurements was statistically significant when considering the ACCP(3mm), whose mean value was lower than the SimK value in eyes with a myopic correction less than -5.00 D (mean 39.53 +/- 1.92 D versus 39.67 +/- 1.82 D) (P = .0013) and in eyes with a myopic correction greater than -5.00 D (37.64 +/- 1.75 D versus 37.9 +/- 1.69 D) (P<.0001).
CONCLUSIONS: In eyes with a large OZ, the clinical relevance of the radius error was limited, especially with myopic corrections less than -5.00 D.