NSF Award
1839762
NON-TECHNICAL ABSTRACT<br/><br/>Materials used in the biomedical industry find utility based on the relationship between their structure and the properties needed. Among polymer materials (plastics) the relevant properties often include strength, flexibility, the ability to break down in the body, etc. Two such polymer materials, PEO and PCL, already find a variety of uses in the biomedical field, e.g. in implant coatings and medication-delivery systems. The range of applications increases when these two materials are combined. To engineer a specific product, one must know how to develop specific structures in this combined material (PEO-PCL). This research aims to understand how these structures develop and how to control the variability of the resultant properties. By varying the temperature and characteristics of the solution from which these materials are processed, one is able to obtain desired properties including, but not limited to, strength, flexibility, and breakdown rate. Polymers are uniquely suited for a variety of applications because their properties may span a large range depending on their chemistry and structure. For example, plastics can be rigid and brittle or flexible and soft depending on their structure. Understanding the development of PEO-PCL structures should lead to an increase in possible uses for this inexpensive, widely prevalent, and robust material. Moreover, the results of this study could be applied to the study of the structures and properties of other biomedical, commodity, or sustainable plastics. A second, but no less important, goal of this work is to train students in the broad disciplines of polymer and materials sciences and prepare them for careers in technology-related areas.<br/><br/><br/>TECHNICAL ABSTRACT<br/><br/>Structural characterization is a critical component in predicting or tailoring the macroscopic properties of a material. In diblock copolymers, the structure involves phase separation between the two components and possible crystallization of one or both of the components. Poly(ethylene oxide)-block-poly(caprolactone) (PEO-b-PCL) copolymers are unique in several ways. First, they are both crystallizable with similar transition temperatures. Second, they are both prevalent in the biomedical field since they are biocompatible and since PCL is biodegradable. Lastly, by combining hydrophilic PEO and hydrophobic PCL into a block copolymer, the material is amphiphilic allowing for transport of hydrophobic drugs into the body. It is all of these traits that make these materials attractive for use in implant coatings and drug delivery systems. For these applications, the ability to manipulate the strength, elasticity, and degradation rate, amongst other properties, is important. These properties depend on how the material phase-separates and crystallizes from solution. Since phase separation is driven by crystallization, the focus of this research is to understand the crystallization mechanism and then control the crystallinity of the material by changing processing conditions such as temperature, casting solvent, and molecular weight. Using FTIR and DSC analyses, the crystallization of PEO and PCL blocks in samples with similar weight fractions or largely different weight fractions, cast from different solvents and/or annealed at different isothermal temperatures, will be monitored. Because the transition temperatures are similar, thermodynamic and kinetic considerations can be manipulated more easily by changes in these parameters. The goal is to pinpoint how each condition influences the crystallization mechanism, the overall crystallinity, and subsequent properties of interest in the biomedical field.
