Kristofer J. Thurecht

Functional hyperbranched polymers: toward targeted in vivo 19F magnetic resonance imaging using designed macromolecules.

We have demonstrated the design and synthesis of hyperbranched molecules that can be successfully imaged in vivo using (19)F MRI in under 10 min. These polymers are cytocompatible following chain extension with PEGMA. In addition, functionalization of these macromolecules can be achieved in a facile manner and with accessible and correct ligand presentation. Such hyperbranched polymers hold promise as new generation tracking and targeting MRI contrast agents.

Multimodal Polymer Nanoparticles with Combined 19F Magnetic Resonance and Optical Detection for Tunable, Targeted, Multimodal Imaging in Vivo

Understanding the complex nature of diseased tissue in vivo requires development of more advanced nanomedicines, where synthesis of multifunctional polymers combines imaging multimodality with a biocompatible, tunable, and functional nanomaterial carrier. Here we describe the development of polymeric nanoparticles for multimodal imaging of disease states in vivo. The nanoparticle design utilizes the abundant functionality and tunable physicochemical properties of synthetically robust polymeric systems to facilitate targeted imaging of tumors in mice. For the first time, high-resolution (19)F/(1)H magnetic resonance imaging is combined with sensitive and versatile fluorescence imaging in a polymeric material for in vivo detection of tumors. We highlight how control over the chemistry during synthesis allows manipulation of nanoparticle size and function and can lead to very high targeting efficiency to B16 melanoma cells, both in vitro and in vivo. Importantly, the combination of imaging modalities within a polymeric nanoparticle provides information on the tumor mass across various size scales in vivo, from millimeters down to tens of micrometers.

A comparative study: the impact of different lipid extraction methods on current microalgal lipid research

Microalgae cells have the potential to rapidly accumulate lipids, such as triacylglycerides that contain fatty acids important for high value fatty acids (e.g., EPA and DHA) and/or biodiesel production. However, lipid extraction methods for microalgae cells are not well established, and there is currently no standard extraction method for the determination of the fatty acid content of microalgae. This has caused a few problems in microlagal biofuel research due to the bias derived from different extraction methods. Therefore, this study used several extraction methods for fatty acid analysis on marine microalga Tetraselmis sp. M8, aiming to assess the potential impact of different extractions on current microalgal lipid research. These methods included classical Bligh & Dyer lipid extraction, two other chemical extractions using different solvents and sonication, direct saponification and supercritical CO2 extraction. Soxhlet-based extraction was used to weigh out the importance of solvent polarity in the algal oil extraction. Coupled with GC/MS, a Thermogravimetric Analyser was used to improve the quantification of microalgal lipid extractions. Among these extractions, significant differences were observed in both, extract yield and fatty acid composition. The supercritical extraction technique stood out most for effective extraction of microalgal lipids, especially for long chain unsaturated fatty acids. The results highlight the necessity for comparative analyses of microalgae fatty acids and careful choice and validation of analytical methodology in microalgal lipid research.

Successful dispersion polymerization in supercritical CO2 using polyvinylalkylate hydrocarbon surfactants synthesized and anchored via RAFT.

New CO2-philic hydrocarbon molecules were synthesized by reversible addition fragmentation chain-transfer polymerization. These poly(vinyl alkylates) show the highest solubility in supercritical CO2 of any hydrocarbon reported to date. By utilizing the anchoring ability of the thiocarbonylthio end group, the dispersion polymerization of N-vinyl pyrrolidone was successfully achieved in scCO2 leading to high yields of well-defined spherical polymer particles.

One-pot synthesis of block copolymers in supercritical carbon dioxide: a simple versatile route to nanostructured microparticles.

We present a one-pot synthesis for well-defined nanostructured polymeric microparticles formed from block copolymers that could easily be adapted to commercial scale. We have utilized reversible addition-fragmentation chain transfer (RAFT) polymerization to prepare block copolymers in a dispersion polymerization in supercritical carbon dioxide, an efficient process which uses no additional solvents and hence is environmentally acceptable. We demonstrate that a wide range of monomer types, including methacrylates, acrylamides, and styrenics, can be utilized leading to block copolymer materials that are amphiphilic (e.g., poly(methyl methacrylate)-b-poly(N,N-dimethylacrylamide)) and/or mechanically diverse (e.g., poly(methyl methacrylate)-b-poly(N,N-dimethylaminoethylmethacrylate)). Interrogation of the internal structure of the microparticles reveals an array of nanoscale morphologies, including multilayered, curved cylindrical, and spherical domains. Surprisingly, control can also be exerted by changing the chemical nature of the constituent blocks and it is clear that selective CO(2) sorption must strongly influence the block copolymer phase behavior, resulting in kinetically trapped morphologies that are different from those conventionally observed for block copolymer thin films formed in absence of CO(2).

Bioerodable PLGA-based microparticles for producing sustained-release drug formulations and strategies for improving drug loading

Poly(lactic-co-glycolic acid) (PLGA) is the most widely used biomaterial for microencapsulation and prolonged delivery of therapeutic drugs, proteins and antigens. PLGA has excellent biodegradability and biocompatibility and is generally recognized as safe by international regulatory agencies including the United States Food and Drug Administration and the European Medicines Agency. The physicochemical properties of PLGA may be varied systematically by changing the ratio of lactic acid to glycolic acid. This in turn alters the release rate of microencapsulated therapeutic molecules from PLGA microparticle formulations. The obstacles hindering more widespread use of PLGA for producing sustained-release formulations for clinical use include low drug loading, particularly of hydrophilic small molecules, high initial burst release and/or poor formulation stability. In this review, we address strategies aimed at overcoming these challenges. These include use of low-temperature double-emulsion methods to increase drug-loading by producing PLGA particles with a small volume for the inner water phase and a suitable pH of the external phase. Newer strategies for producing PLGA particles with high drug loading and the desired sustained-release profiles include fabrication of multi-layered microparticles, nanoparticles-in-microparticles, use of hydrogel templates, as well as coaxial electrospray, microfluidics, and supercritical carbon dioxide methods. Another recent strategy with promise for producing particles with well-controlled and reproducible sustained-release profiles involves complexation of PLGA with additives such as polyethylene glycol, poly(ortho esters), chitosan, alginate, caffeic acid, hyaluronic acid, and silicon dioxide.

Molecular imaging with polymers

Polymers open up new possibilities in the field of molecular imaging, allowing sensitive and robust agents that can be imaged over long periods of time. This review highlights some recent advances in polymeric molecular imaging agents in both (pre)clinical and emerging applications.

Biodegradable core crosslinked star polymer nanoparticles as 19F MRI contrast agents for selective imaging

With the aim of developing stimuli-responsive imaging agents, we report here the synthesis of core crosslinked star (CCS) polymers and their evaluation as pH-sensitive 19F magnetic resonance imaging (19F MRI) contrast agents. Block copolymers consisting of poly(ethylene glycol)methyl ether methacrylate (PPEGMA) as the first block and a copolymer of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 2,2,2-trifluoroethyl methacrylate (TFEMA) as the second block were synthesised using RAFT polymerisation. The polymerisation kinetics were studied in detail. The block copolymers were then used as arm precursors for the arm-first synthesis of CCS polymers through RAFT dispersion polymerisation. The synthetic conditions were investigated and optimised. CCS polymers with a degradable core were also synthesised and evaluated as 19F MRI contrast agents. The degradation of the core was confirmed by treatment with various reducing agents. The particle size, 19F NMR signal and relaxation times as well as 19F MRI imaging performance of the CCS polymers were studied at a range of value of solution pH. Significant enhancement of the image intensity was observed when the pH was decreased from 8 to 5, indicating that the CCS nanoparticles could be used as 19F MRI contrast agents for the detection of the acidic environment within tumour tissue.

Enhanced uptake of nanoparticle drug carriers via a thermoresponsive shell enhances cytotoxicity in a cancer cell line

Polymer particles consisting of a biodegradable poly[lactide-co-glycolide] (PLGA) core and a thermoresponsive shell have been formulated to encapsulate the dye rhodamine 6G and the potent cytotoxic drug paclitaxel. Cellular uptake of these particles is significantly enhanced above the thermal transition temperature (TTT) of the polymer shells in the human breast carcinoma cell line MCF-7 as determined by flow cytometry and fluorescence microscopy. Paclitaxel-loaded particles display reduced and enhanced cytotoxicity below and above the TTT respectively compared to unencapsulated drug. The data suggests a potential route to enhanced anti-cancer efficacy through temperature-mediated cell targeting.

Modular Construction of Multifunctional Bioresponsive Cell-Targeted Nanoparticles for Gene Delivery

Multifunctional and modular block copolymers prepared from biocompatible monomers and linked by a bioreducible disulfide linkage have been prepared using a combination of ring-opening and atom-transfer radical polymerizations (ATRP). The presence of terminal functionality via ATRP allowed cell-targeting folic acid groups to be attached in a controllable manner, while the block copolymer architecture enabled well-defined nanoparticles to be prepared by a water-oil-water double emulsion procedure to encapsulate DNA with high efficiency. Gene delivery assays in a Calu-3 cell line indicated specific folate-receptor-mediated uptake of the nanoparticles, and triggered release of the DNA payload via cleavage of the disulfide link resulted in enhanced transgene expression compared to nonbioreducible analogues. These materials offer a promising and generic means to deliver a wide variety of therapeutic payloads to cells in a selective and tunable way.