End-capping Star-like Polycaprolactone with Different Functional Groups and the Interaction with Smooth Muscle Cells

Polycaprolactone (PCL) is a PDA-approved biodegradable polymer with excellent biocompatibility and flexibility. My work has been designed to find out how different functional end groups in star-like PCL samples affect the surface properties (such as hydrophilicity, morphology) and bulk properties (such as thermal, mechanical, rheological properties, and crystallization), and consequently the behavior and functions of primary rat aortic smooth muscle cells (SMCs).

I focused on the synthesis of PCL with different functional groups and their characterizations. In chapter 2, PCL samples with four or six hydroxyl end groups were synthesized with different molecular weights ranging from 8,000 to 30,000 g/mol [gram per mole]. The hydroxyl end groups in PCL were converted into carboxyl, methyl, amino, and acrylate groups, with conversion percentage confirmed by nuclear magnetic resonance (NMR) spectra. Thermal properties of these PCL samples were determined with a Differential Scanning Calorimeter (DSC). In chapter 3, the different spherulitic morphologies formed by 4-arm and 6-arm star-like PCL in isothermal crystallization were explored. In chapter 4, the rheological properties of linear and star-like polymers were determined by using a strain controlled rheometer, which aims to find out the dependence of viscosity on frequency and molecular weight. The rheological properties of star like polymers were compared with the linear ones. In chapter 5, cytotoxicity tests of the star-PCL samples using SMCs were performed, and cell study of SMC attachment, spreading, proliferation on the star-PCL samples with different functional groups were also performed.