Diffraction-Based Method To Evaluate Enzymatic Degradation Of Polylactic Acid Films

  • Author / Creator
    Hernandez-Salgado, Valeria Amellalli
  • Commodity plastics fate has become one of the most critical environmental concerns. Due to their resistance to degradation, plastics are accumulating into a massive amount of waste on land and in water. These materials are harming the ecosystems. Among the several alternatives studied, biodegradable bio-sourced polymers like polylactic acid (PLA) have been considered a potential replacement for oil-based plastics. PLA is a biopolymer that is not only biocompatible, but it presents physical properties that can be used in several areas like drug delivery, food packaging, agriculture and polymer thin films. Polymer thin films are used in applications in different areas. They can be used in microelectronics, functional coatings or optical components. Understanding degradation and stability are essential for their correct utilization. However, current characterization methods for the degradation of polymer thin films are mainly focus on gravimetric data. Polymer thin films
    present minuscule mass changes and these methods do not provide complete information about their stability. In this work, an optical technique that can be used to monitor the degradation of polymer thin films is explored. This technique was demonstrated previously in our group as a qualitative method to study the degradation of a semicrystalline biopolymer: polyhydroxybutyrate (PHB). In this technique, films are first patterned with a grating on their
    surface. The films are then immersed in degrading solutions under different conditions. During the immersion, a laser-irradiated the polymer surface, such that the grating diffracts the beam. A photodetector measures the beam intensity, and the degradation is monitored by observing the change in intensity of the first diffraction order spot. In current work, this method is firstly used to compare the degradation of polylactic acid thin films in various environments. PLA is known for being degraded by hydrolysis, and the
    presence of an enzyme can accelerate its biodegradation. The intensity decreased as the polymer is degraded by proteinase K. Atomic force microscope (AFM), images were collected at different degradation stages to determine the relationship between the PLA surface and the diffracted intensity. Optimized degradation conditions were identified using PLA films patterned with a triangular diffraction grating. These conditions were pH 8, 200 μg/mL and
    37ºC. This method was also able to demonstrate the effect of changes in pH, temperature and enzyme concentration in the degradation rate. The data obtained from the diffraction method allows qualitative comparisons of
    degradation rate, as shown by the change in intensity of the diffraction pattern over time. To extract quantitative information regarding etch rates from the intensity data collected using the optical diffraction method, a model was introduced in OmniSim software. This model provides the link between the intensity of the diffracted beam and the geometry of the grating. By applying the model, for the first time, it was possible to obtain quantitative information for polymer thin film degradation rates (nm/min) by measuring the diffraction intensity. The etch rate of this polymer thin film under optimum conditions, was 8.5 nm/min. By using gratings with different heights and cross-sectional profiles, the effect of different shapes on both the intensity and degradation rate was studied. Using this technique, biopolymers can be considered in polymer thin film applications since their stability can now be evaluated with a sensitive method. In the same manner, applications of polymer thin films can be expanded to biomedical areas where biodegradability is necessary since this method can be applied under a variety of conditions. Thus, these results provide an alternative to evaluating polymer thin film degradation that provides quantitative information.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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