Macromolecular Engineering by Surface-Initiated ATRP: New Nanomaterials for Bioapplications

The objective of this thesis is to investigate the synthesis of well-defined polymer nanohybrid materials bearing desirable functionality via surface-initiated atom transfer radical polymerization (SI-ATRP) for potential bioapplications.

SI-ATRP is an excellent controlled radical polymerization (CRP) method for the synthesis of polymer nanohybrid by growing polymer brushes (chains) from an interface, which allows precise control over polymer composition, topology, and functionality. Polymer brushes have proven to be attractive platforms for applications spanning drug delivery, tissue engineering, biosensors as well as bioseparation.

Copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click reaction has been widely applied for the design, fabrication and post-polymerization modification of polymer nanohybrid due to some important features: high reaction yields, benign reaction conditions, and tolerance to diverse functional groups.

One aim of this thesis is to grow polymer brushes from inorganic nanoparticles via SI-ATRP in organic solvent followed by post-polymerization functionalization of the polymer brushes via click reaction for different applications. Specifically, thermo-responsive polymer brushes composed of poly(N-isopropylacrylamide) (pNIPAm) and poly(glycidyl methacrylate) (pGMA) were grafted from silica nanoparticles via SI-ATRP. A high amount of boronic acid ligands and iminodiacetate (IDA) ligands were introduced into the polymer brushes through the high-efficiency click reaction for the enrichment of glycoproteins and histidine-tagged proteins, respectively. The polymer nanohybrids were characterized to determine the particle size, morphology, organic content, densities of polymer chains and the affinity ligands via techniques including dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis, thermogravimetric analysis (TGA), and gel permission chromatography (GPC). The nanocomposites showed high adsorption capacity and selectivity towards the target proteins due to the dense ligands immobilized on the long and flexible polymer brushes that are able to provide rapid protein transport to binding sites. The synthetic approaches developed in this thesis have a great potential for the development of more efficient adsorbents for biological samples.

Another focus of this thesis is to investigate the possibility of growing polymer chains from biological interface via SI-ATRP in an aqueous solvent. Specifically, ATRP initiators were first selectively immobilized on amelogenin (AMEL), which is a pH-responsive protein, followed by growing thermo-responsive pNIPAm chains in an aqueous solution via SI-ATRP, leading to a pH and temperature dually responsive bioconjugate. The bioconjugate was characterized in terms of particle size, molecular weight of polymer, and self-assembly behavior in response to pH and temperature. The bioconjugates may serve as a promising platform for bioapplications such as drug delivery and biosensing.