Surface and in-depth characterization of bioresorbable poly(lactic acid) membranes and bioresorbable chitosan-based hydrogels for therapeutic drug release
Marchany Alfonso, Michelle D.
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One of the most attractive features of bioresorbable polymers is the ability to tune their properties to match a particular biomedical application. This dissertation aims to answer the following questions about the degradation and drug delivery rate of bioresorbable polymers for wound healing applications: (1) how is the surface degradation of poly(alpha-hydroxy ester) membranes affected by three-dimensional morphology, nanoscale confinement in one dimension, and molecular weight? (2) how does the degradation reaction of a poly(alpha-hydroxy ester) film proceed as a function of volume? and (3) what is the role of chemistry and charge in the protein loading and release behavior of chitosan-based hydrogels? The degradation behavior of poly(alpha-hydroxy ester) membranes was characterized with light and electron microscopy, and with time-of-flight secondary ion mass spectrometry (ToF-SIMS). It was found that morphological changes in micropatterned films were observed. But, contrary to what was expected, no spatial changes in the reaction progression were detected. In contrast, differences in the reaction progression through the depth of membranes, and in the surface degradation behavior as a function of nanoscale confinement and molecular weight, were detected by ToF-SIMS; these changes are not detectable by bulk characterization methods commonly used for polymer degradation studies, such as gel permeation chromatography. The chemistry and role of charge on the protein uptake and release behavior of chitosan-based hydrogels was tested using X-ray photoelectron spectroscopy (XPS), ToF-SIMS, and fluorescence spectroscopy. It was found that the protein loaded into the hydrogels was not detectable with XPS or ToF-SIMS, due to interference from impurities arising from the manufacturing process. However, certain moieties uptake more protein than others, regardless of their charge. More studies are needed on these hydrogels to draw more solid conclusions.