Browsing by Author "Valenzuela, Loreto M."
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- ItemEffect of laser scanning angle and atmospheric oxygen on mechanical properties and microstructural morphology of selective laser-sintered aluminum-filled polyamide monolayers(2021) Alamos, Fernando J.; Ramos Grez, Jorge; Valenzuela, Loreto M.
- ItemImproving myoblast differentiation on electrospun poly(ε-caprolactone) scaffolds(2017) Abarzua-Illanes, Phammela N.; Padilla, Cristina; Ramos, Andrea; Isaacs, Mauricio; Ramos Grez, Jorge; Olguin, Hugo C.; Valenzuela, Loreto M.
- ItemMultiscale analysis of water uptake and erosion in biodegradable polyarylates(ELSEVIER SCI LTD, 2012) Valenzuela, Loreto M.; Zhang, Guojin; Flach, Carol R.; Murthy, N. Sanjeeva; Mendelsohn, Richard; Michniak Kohn, Bozena; Kohn, JoachimThe role of hydration in degradation and erosion of materials, especially biomaterials used in scaffolds and implants, was investigated by studying the distribution of water at length scales from 0.1 nm to 0.1 mm using Raman spectroscopy, small-angle neutron scattering (SANS). Raman confocal imaging, and scanning electron microscopy (SEM). The measurements were demonstrated using L-tyrosine derived polyarylates. Bound- and free- water were characterized using their respective signatures in the Raman spectra. In the presence of deuterium oxide (D2O), H-D exchange occurred at the amide carbonyl but was not detected at the ester carbonyl. Water appeared to be present in the polymer even in regions where there was little evidence for NH to ND exchange. SANS showed that water is not uniformly dispersed in the polymer matrix. The distribution of water can be described as mass fractals in polymers with low water content (similar to 5 wt%), and surface fractals in polymers with larger water content (15-60 wt%). These fluctuations in the density of water distribution are presumed to be the precursors of the similar to 20 mu m water pockets seen by Raman confocal imaging, and also give rise to the 10-50 mu m porous network seen in SEM. The surfaces of these polymers appeared to resist erosion while the core of the films continued to erode to form a porous structure. This could be due to differences in either the density of the polymer or the solvent environment in the bulk vs. the surface, or a combination of these two factors. There was no correlation between the rate of degradation and the amount of water uptake in these polymers, and this suggests that it is the bound water and not the total amount of water that contributes to hydrolytic degradation. (c) 2011 Elsevier Ltd. All rights reserved.
- ItemVariability of Water Uptake Studies of Biomedical Polymers(WILEY-BLACKWELL, 2011) Valenzuela, Loreto M.; Michniak, Bozena; Kohn, JoachimWater uptake influences many properties of polymers and has been widely studied. In the context of polymeric biomaterials, several publications reported an unusual high variability of analytical results, without further investigating the cause for this phenomenon. Using selected polymers from the library of L-tyrosine-derived polyarylates and poly(D,L lactic acid), we showed that nonaged and nonannealed compression molded film samples exhibit the typical large variation in water uptake observed in previous reports. The introduction of an annealing step allows accurate and reproducible water uptake measurements for these polymers. We evaluated the use of 3 H-radiolabeled water for the determination of water uptake, finding that the use of radiolabeled water yields statistically indistinguishable measurements, compared to gravimetric methods, while providing significant advantages in throughput and sensitivity. Using the recommended methods of annealing and (3)H-radiolabled water, the water uptake profiles of 24 polymers of the library of L-tyrosine-derived polyarylates are reported. This article addresses experimental concerns related to water uptake studies and may assist other researchers in improving the accuracy of their water uptake results. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 1311-1320, 2011