Anthony M. Granville

One-pot polymer brush synthesis via simultaneous isocyanate coupling chemistry and “grafting from” RAFT polymerization

One-pot ‘grafting from’ of polystyrene on polydopamine coated SiO2 particles was investigated using a newly developed carbonyl-azide reversible addition–fragmentation chain transfer (RAFT) agent. Simultaneously during the RAFT polymerization of styrene, the carbonyl-azide group of the CTA rearranges into an isocyanate moiety permitting the one-pot coupling to functional surfaces. The one-pot coupling to the polydopamine surfaces was investigated, separately, using both the non-catalyzed amine–isocyanate coupling and the metal catalyzed alcohol–isocyanate coupling. Thermogravimetric analysis showed that the catalyzed one-pot ‘grafting from’ process produced nearly double the weight increase, and thus higher grafting density, when compared to the uncatalyzed system. These results are consistent with more available hydroxyl groups on the polydopamine surface. Finally, both one-pot ‘grafting from’ approaches exhibited higher grafting density when compared to their analogous ‘grafting to’ strategies using α-isocyanate terminated polystyrene and thus superseding previous ‘grafting from’ processes where two-steps were normally required.

Surface modification of polydopamine coated particles via glycopolymer brush synthesis for protein binding and FLIM testing

Glycopolymer brushes were successfully synthesized on polydopamine coated silicon dioxide particles using a one-step ‘grafting from’ method to produce high density polymer brushes. This one-step ‘grafting from’ method uses an azide-terminated RAFT agent that simultaneously grows polymer chains and attaches to the polydopamine coating. The azide group rearranges via an in situ Curtius rearrangement to form an isocyanate group. This reacts with the hydroxyl and amine groups on the polydopamine coating while simultaneously growing a polymer chain. Poly(pentafluorostyrene) polymer brushes were grown and attached to the polydopamine coating, then converted to glycopolymer brushes using a thiol substitution reaction. This creates a surface that facilitates protein binding. Fluorescently tagged Concanavalin A proteins were bound to the surface and the binding ability was investigated using Fluorescence Lifetime Imaging Microscopy (FLIM). This reports the facile preparation of particles that are biocompatible, and can be used in vivo as drug carrier systems. The use of polydopamine coatings, one-step ‘grafting from’ polymer brush synthesis and ‘click’ chemistry to create glycopolymers, collectively are an improved and simple way to prepare particles for biomedical applications.

Incorporation of 5-Hydroxyindazole into the Self-Polymerization of Dopamine for Novel Polymer Synthesis

Investigation into the mussel-inspired polymerization of dopamine has led to the realization that other compounds possessing potential quinone structures could undergo similar self-polymerizations in mild buffered aqueous conditions. To this end, 5-hydroxyindazole was added to a dopamine polymerization matrix in varying amounts, to study its incorporation into a polydopamine coating of silica particles. Solid-state (13) C NMR spectroscopy confirmed the presence of the indazole in the polymer shell when coated onto silica gel. SEM and DLS analysis also confirmed that the presence of the indazole in the reaction matrix yielded monodisperse polymer-coated particles, which retained their polymer shell upon HF etching, except when high levels of the indazole were used. Characterization data and examination of incorporation mechanism suggests that the 5-hydroxyindazole performs the function of a chain-terminating agent. Cytotoxicity studies of the polymer particles containing 5-hydroxyindazole showed dramatically lower toxicity levels compared to polydopamine alone.

Copolymerization of an indazole ligand into the self-polymerization of dopamine for enhanced binding with metal ions

5,6-Dihydroxy-1H-indazole (DHI) is able to self-polymerize through the same mussel-inspired chemistry responsible for generating poly(dopamine) (PDA), demonstrating the potential to expand this class of catecholamine-exclusive chemistry onto heterocyclic catechol derivatives for the preparation of functional materials. Although DHI exhibits slower polymerization kinetics compared to dopamine, the two chemical species are compatibly polymerizable under the same reaction conditions and allow the preparation of copolymer coatings in different molar ratios. Of these copolymers, the 1 : 3-copolymer (DHI-to-dopamine ratio) has demonstrated adequate structural stability as a polymer coating. While PDA performs as an intact framework, the incorporated DHI enhances the colloidal stability and provides additional coordinating functionality through the pyrazole moieties. The 1 : 3-copolymer was fabricated into polymer capsules which exhibit negligible cytotoxicity towards murine dermal fibroblasts (L929) and enhanced binding behaviour towards copper(ii). This represents a new channel for fabricating cargo carriers for biomedical applications that involve the use of transition metal-based species.

Thin film hydrophilic electroactive polymer coatings for bioelectrodes

Hybrids of conducting polymers (CPs) and hydrogels have been explored as soft electroactive coatings for improving the mechanical and electrical performance of metallic implant electrodes. However, hydrogel fabrication methods pose a significant challenge to producing thin (sub-micron) coatings, resulting in bulky implants, which displace a large volume of tissue. To address this issue, polymer brushes of poly(2-hydroxyethyl methacrylate) (pHEMA) were covalently bound to a gold electrode using surface initiated atom-transfer radical-polymerization (SI-ATRP). The CP poly(3,4-ethylene dioxythiophene) (PEDOT) was electropolymersied through the brush layer to form a thin hydrophilic coating. The electrical properties of the hybrid were shown to be superior to homogenous CPs and the surface chemistry was varied as a function of PEDOT deposition time to present a graded composition of pHEMA and PEDOT. The resulting material was shown to support the attachment and differentiation of model neural cells, signifying the potential of these hybrid coatings for bioelectrode applications.

Surface Property Modification of Silver Nanoparticles with Dopamine-Functionalized Poly(pentafluorostyrene) via RAFT Polymerization

This research aims to synthesize a dopamine-functionalized macromolecular anchor to perform surface modification on the target nanostructures. A molecular anchor, 3,4-dichloro-1-[2-(3,4-dihydroxyphenyl)ethyl]-1H-pyrrole-2,5-dione, was successfully synthesized from dopamine and 2,3-dichloromaleic anhydride. The anchor acted as a linkage to couple the chains of poly(pentafluorostyrene) (PPFS) which were synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. Modification was successfully performed to silver nanoparticles (AgNPs) by deposition of the dopamine-functionalized coupled PPFS onto the surface of the particles. The modified AgNPs had demonstrated improved dispersibility in organic solvent due to the hydrophobic nature of PPFS. To modify the surface chemistry of the nanoparticles further, thioglucose was grafted onto the structure of the coupled PPFS via thiol-fluoro nucleophilic substitution at the para-position of the pentafluorophenyl groups on the monomer units. The presence of sugar moieties on the coupled PPFS increased its hydrophilicity, which allowed the modified AgNPs to be readily dispersed in aqueous solvent.

The role of algal organic matter in the separation of algae and cyanobacteria using the novel “Posi” - Dissolved air flotation process

Algae and cyanobacteria frequently require separation from liquid media in both water treatment and algae culturing for biotechnology applications. The effectiveness of cell separation using a novel dissolved air flotation process that incorporates positively charged bubbles (PosiDAF) has recently been of interest but has been shown to be dependent on the algae or cyanobacteria species tested. Previously, it was hypothesised that algal organic matter (AOM) could be impacting the separation efficiency. Hence, this study investigates the influence of AOM on cell separation using PosiDAF, in which bubbles are modified using a commercially available cationic polyelectrolyte poly(N, N-diallyl-N,N-dimethylammonium chloride) (PDADMAC). The separation of Chlorella vulgaris CS-42/7, Mychonastes homosphaera CS-556/01 and two strains of Microcystis aeruginosa (CS-564/01 and CS-555/1), all of which have similar cell morphology but different AOM character, was investigated. By testing the cell separation in the presence and absence of AOM, it was determined that AOM enhanced cell separation for all the strains but to different extents depending on the quantity and composition of carbohydrates and proteins in the AOM. By extracting AOM from the strain for which optimal separation was observed and adding it to the others, cell separation improved from <55% to >90%. This was attributed to elevated levels of acidic carbohydrates as well as glycoprotein-carbohydrate conjugations, which in turn were related to the nature and quantity of proteins and carbohydrates present in the AOM. Therefore, it was concluded that process optimisation requires an in-depth understanding of the AOM and its components. If culturing algae for biotechnology applications, this indicates that strain selection is not only important with respect to high value product content, but also for cell separation.

Expanding the aqueous-based redox-facilitated self-polymerization chemistry of catecholamines to 5,6-dihydroxy-1H-benzimidazole and its 2-substituted derivatives

Aqueous-base redox-facilitated self-polymerization can be performed with 5,6-dihydroxy-1H-benzimidazole (DHBI) to generate polymeric material that is analogous to poly(dopamine) (PDA), proving the possibility to expand the catecholamine-exclusive chemistry to N-heterocyclic catechol derivatives. DHBI underwent similar reaction pathways as dopamine to self-polymerize into the lightly cross-linked, π-conjugated poly(5,6-dihydroxy-1H-benzimidazole) (PDHBI). However, it was observed that the polymerization of DHBI proceeded faster than dopamine, and can be further enhanced under UV-stimulation, similar to dopamine polymerization. When coated on various substrates, the PDHBI coatings were capable of promoting surface wettability similar to PDA, but exhibited lower thermal stability due to a reduced cross-link density. Copolymerization compatibility between DHBI and dopamine was demonstrated, and it was possible to enhance the thermal stability of PDHBI by incorporating dopamine as a comonomer/cross-linker. Despite the high level of similarity between the two polymers, PDHBI possesses the imidazole moieties as unique features. Because of the versatile chemistry of o-benzenediamine employed for the monomer synthesis, DHBI-based monomers with specific functionality at the 2-carbon position of the imidazole ring can be prepared by choosing a desirable carboxylic acid. Two 2-substituted derivatives of DHBI were synthesized to demonstrate the ability to intrinsically modify the properties of PDHBI-based polymeric materials in terms of solubility, structure, and thermal stability.

Surface Modification of Polydivinylbenzene Microspheres with a Fluorinated Glycopolymer Using Thiol-Halogen Click Chemistry

Distillation-precipitation polymerization of divinylbenzene was applied to obtain uniform-sized polymeric microspheres. The microspheres were then modified with polypentafluorostyrene chains utilizing surface-initiated atom transfer radical polymerization techniques. The hydrophobic fluoropolymer-coated microsphere was then converted to a hydrophilic biopolymer by performing thiol-halogen click chemistry between polypentafluorostyrene and 1-thio-β-D-glucose sodium salt. The semi-fluorinated glycopolymer showed good binding ability with Concanavalin A as determined by confocal microscopy and turbidity experiments.