RUI: Role of Crystallinity and Morphology in Degradation and Drug Release of PEO-b-PCL Films

Lafayette College, Easton PA

Investigators

Abstract

NON-TECHNICAL: Additives are a crucial component in engineering advantageous properties in plastics. One example is in therapeutic medical treatments, which rely on the ability to deliver drugs in a controlled way. Understanding the interactions between additives and polymer molecules,is critical for modeling how the molecules might leach or release from the final product. Factors that contribute to the additive’s release rate include how they are distributed among the polymer molecules, how those polymer molecules are arranged, and how the polymers break down. This research aims to determine how these interactions impact the release and degradation behavior in a two-component polymer, poly(ethylene oxide)-poly(caprolactone) (PEO-b-PCL). PEO-b-PCL has two differing components: one that is hydrophilic, or water-soluble, and one that is hydrophobic, or water-insoluble. Additionally, both components can assemble in crystalline phases (having tightly structured arrangements) or amorphous phases (more random and spacious molecular arrangements). Because of the duality of the polymer, additives may partition into different sections of the material. Using common drug molecules of varying hydrophobicity, PEO and PCL crystallinity will be monitored to determine the impact of additives on crystal formation. A decrease in crystallinity or crystal size could be observed whether the additive exists in the polymer as individual molecules (good dispersion) or as large crystalline structures (poor dispersion) and whether it segregates into PEO or PCL partially, primarily, or exclusively. Preparation of the additive-polymer mixture will be varied to see how changes in the polymer crystal structure impacts the additive assembly. Not only will changes in the crystalline structure impact the additive release, it will impact the plastic’s erosion and degradation in water. A comprehensive analysis of structure-property relationships is needed to appropriately understand the role of polymer physical structure in the process of additive release and polymer breakdown over time. In addition to scientific discovery, this research provides training and development for undergraduates - our future scientists and engineers - and promotes inclusion in STEM for all. Outreach activities including hosting a local high school student as a research assistant and engagement in a K-6 community outreach program that brings students to campus for engineering activities are also included in this project. TECHNICAL: Controlled drug release relies on the chemical or physical structure and interactions between drug molecules and the polymeric carrier. Molecular dispersion of the drug and complex interactions among drug, polymer, and water are primary factors that contribute to the rate of release and its control. One underlying factor that impacts the diffusion of both drug and water molecules is the physical structure of the polymer where crystalline lamellae provide physical barriers and microphase separation provides inhomogeneous dispersion of small molecules. Amphiphilic poly(ethylene oxide)-block-poly(-caprolactone) (PEO-b-PCL) is a model copolymer with hierarchical physical structures, including crystallization of both blocks and subsequent phase separation. These structures are impacted by preparation techniques and the inclusion of small molecule additives. Spectroscopic and thermal analysis techniques will be used to evaluate the polymers’ and drug’s structures using differing preparation methods, thermal treatments, drug loading, and drug hydrophobicity. PEO and PCL domains should exhibit changes in crystal size and/or crystallinity as it correlates to the drug’s structure and dispersion (molecular or crystalline solid) and partitioning in each domain. More hydrophobic molecules are expected to segregate into the PCL domain; however, interactions during the assembly process may be more complicated. Previously determined techniques for tailoring the crystal morphology from edge-on spherulites to flat-on structures will be utilized to evaluate the crystal stability in the presence of drug additives or aqueous environments. Conversely, the absorption of water in the PEO domains should be impacted by PEO crystallites. Similar techniques will be used to monitor the diffusion of water into the film and subsequent dissolution of PEO crystals of varying metastability. Complimentary experimental procedures in chromatography and gravimetric analysis will be used to measure controlled release and degradation profiles to gain insight into the role of the polymer’s physical structure in the macroscopic properties. Understanding the interplay between the PEO and PCL crystal size, crystallinity, and morphology and resultant water absorption, degradation, and drug release properties is important for controlled delivery. . This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.