Binh T. T. Pham

Synthesis of polymeric janus nanoparticles and their application in surfactant-free emulsion polymerizations

A robust and simple synthesis of nano-size oblate to dumbbell shaped polymeric anisotropic particles using RAFT mediated emulsion polymerization is presented. The particle synthesis relies on the property that monomer swollen cross-linked polymer seed particles shrink and expel some of the monomer when heated. Thus, upon heating for polymerization, some of the swelling monomer is expelled and subsequently polymerizes to form a bulge on the side of the original crosslinked seed particle. The shape of the bulge, and the degree of contact that the expelled monomer maintains with the original seed particle, is controlled by controlling the wettability of the seed surface by the expelled monomer. Very small monodisperse cross-linked polymer particles are initially prepared by RAFT mediated emulsion polymerization, then swollen with monomer and further polymerized to form anisotropic particles with a long dimension as little as 25 nm. Both the shape of the anisotropic bulge and the polymer composition, of each end of the final Janus nanoparticle can be finely controlled. The surface active properties of the Janus nanoparticles are demonstrated by their ability to contribute as stabilizers and influence particle formation in a surfactant free ab-initio emulsion polymerization. The method provides a simple and reproducible process for the production of Janus colloidal nanoparticles readily achievable in a normal latex plant where batch size would be limited only by the size of the reactor.

Ultrasmall superparamagnetic iron oxide nanoparticle prelabelling of human neural precursor cells

Stem cells prelabelled with iron oxide nanoparticles can be visualised using magnetic resonance imaging (MRI). This technique allows for noninvasive long-term monitoring of migration, integration and stem cell fate following transplantation into living animals. In order to determine biocompatibility, the present study investigated the biological impact of introducing ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) into primary human fetal neural precursor cells (hNPCs) inxa0vitro. USPIOs with a mean diameter of 10-15xa0nm maghemite iron oxide core were sterically stabilised by 95% methoxy-poly(ethylene glycol) (MPEG) and either 5% cationic (NH2) end-functionalised, or 5% Rhodamine B end-functionalised, polyacrylamide. The stabilising polymer diblocks were synthesised by reversible addition-fragmentation chain transfer (RAFT) polymerisation. Upon loading, cellular viability, total iron capacity, differentiation, average distance of migration and changes in intracellular calcium ion concentration were measured to determine optimal loading conditions. Taken together we demonstrate that prelabelling of hNPCs with USPIOs has no significant detrimental effect on cell biology and that USPIOs, when utilised at an optimised dosage, are an effective means of noninvasively tracking prelabelled hNPCs.

Using mechanisms to make seemingly impossible latexes and polymers

It is possible to create latex particles wherein the molecular architecture, on the micro- or nano-scale, appears thermodynamically unfavourable. This can be brought about by exploiting both the topology of an emulsion polymerization (i.e., it takes place in a dispersed medium) combined with appropriate free-radical chemistry. Some examples include creating latexes by seeded emulsion polymerization wherein there is (a) extensive grating between hydrophobic and hydrophilic entities, (b) sufficient graft copolymer is created in situ to compatibilize two polymers with significantly different solubility parameters, and (c) graft copolymers between styrene and aniline with interesting electrical properties.

Lysozyme depolymerization of photo-activated chitosan adhesive films

Effective tissue bioadhesion of rose bengal-chitosan films can be achieved by photoactivation using a green laser. In this study, lysozyme was incorporated in these films to enhance the rate of depolymerization and assess the laser impact on lysozyme. The lysozyme loaded films exhibited a 21% mass loss after 4 weeks implantation in rats while control films (without lysozyme) had only 7% mass loss. Capillary electrophoresis-mass spectroscopy showed that chitosan degraded into monomers and oligomers of glucosamine and N-acetyl-glucosamine. Irradiation with laser did not affect the depolymerization of adhesive by lysozyme suggesting that the inclusion of lysozyme in the bioadhesive is a viable technique for tailoring the depolymerization.

The composition and end-group functionality of sterically stabilized nanoparticles enhances the effectiveness of co-administered cytotoxins

Diffusion of active cytotoxic agents throughout an entire solid tumour is a particular challenge to successful drug delivery. Here we show the simple and robust generation of non-toxic, 10-15 nm superparamagnetic iron oxide nanoparticles (SPIONs) that have been sterically stabilized by either 100% anionic or 100% cationic or 100% neutral end-functionalized steric stabilizers or by novel combinations of cationic and neutral end-functionalized polymer. When these nanoparticles were co-administered with various anti-cancer drugs, a significant increase in the diffusion and effectiveness of the cytotoxin in a 3-dimensional model of a solid tumour was shown for specific combinations of surface functionality and cytotoxin. The critical determinant of enhanced cytotoxin diffusion and effectiveness was the end functionality of the steric stabilizers and not the core composition (either iron oxide, silica or gold). We provide evidence that SPIONs stabilized with heterogeneous steric stabilizers enhance nuclear uptake of doxorubicin across multiple cell layers.

Preparation of inert polystyrene latex particles as microRNA delivery vectors by surfactant-free RAFT emulsion polymerization

We present the preparation of 11 nm polyacrylamide-stabilized polystyrene latex particles for conjugation to a microRNA model by surfactant-free RAFT emulsion polymerization. Our synthetic strategy involved the preparation of amphiphilic polyacrylamide-block-polystyrene copolymers, which were able to self-assemble into polymeric micelles and grow into polystyrene latex particles. The surface of these sterically stabilized particles was postmodified with a disulfide-bearing linker for the attachment of the microRNA model, which can be released from the latex particles under reducing conditions. These nanoparticles offer the advantage of ease of preparation via a scaleable process, and the versatility of their synthesis makes them adaptable to a range of applications.

Tunable and noncytotoxic PET/SPECT-MRI multimodality imaging probes using colloidally stable ligand-free superparamagnetic iron oxide nanoparticles

Physiologically stable multimodality imaging probes for positron emission tomography/single-photon emission computed tomography (PET/SPECT)-magnetic resonance imaging (MRI) were synthesized using the superparamagnetic maghemite iron oxide (γ-Fe2O3) nanoparticles (SPIONs). The SPIONs were sterically stabilized with a finely tuned mixture of diblock copolymers with either methoxypolyethylene glycol (MPEG) or primary amine NH2 end groups. The radioisotope for PET or SPECT imaging was incorporated with the SPIONs at high temperature. 57Co2+ ions with a long half-life of 270.9 days were used as a model for the radiotracer to study the kinetics of radiolabeling, characterization, and the stability of the radiolabeled SPIONs. Radioactive 67Ga3+ and Cu2+-labeled SPIONs were also produced successfully using the optimized conditions from the 57Co2+-labeling process. No free radioisotopes were detected in the aqueous phase for the radiolabeled SPIONs 1 week after dispersion in phosphate-buffered saline (PBS). All labeled SPIONs were not only well dispersed and stable under physiological conditions but also noncytotoxic in vitro. The ability to design and produce physiologically stable radiolabeled magnetic nanoparticles with a finely controlled number of functionalizable end groups on the SPIONs enables the generation of a desirable and biologically compatible multimodality PET/SPECT-MRI agent on a single T2 contrast MRI probe.

Biodistribution and Clearance of Stable Superparamagnetic Maghemite Iron Oxide Nanoparticles in Mice Following Intraperitoneal Administration

Nanomedicine is an emerging field with great potential in disease theranostics. We generated sterically stabilized superparamagnetic iron oxide nanoparticles (s-SPIONs) with average core diameters of 10 and 25 nm and determined the in vivo biodistribution and clearance profiles. Healthy nude mice underwent an intraperitoneal injection of these s-SPIONs at a dose of 90 mg Fe/kg body weight. Tissue iron biodistribution was monitored by atomic absorption spectroscopy and Prussian blue staining. Histopathological examination was performed to assess tissue toxicity. The 10 nm s-SPIONs resulted in higher tissue-iron levels, whereas the 25 nm s-SPIONs peaked earlier and cleared faster. Increased iron levels were detected in all organs and body fluids tested except for the brain, with notable increases in the liver, spleen, and the omentum. The tissue-iron returned to control or near control levels within 7 days post-injection, except in the omentum, which had the largest and most variable accumulation of s-SPIONs. No obvious tissue changes were noted although an influx of macrophages was observed in several tissues suggesting their involvement in s-SPION sequestration and clearance. These results demonstrate that the s-SPIONs do not degrade or aggregate in vivo and intraperitoneal administration is well tolerated, with a broad and transient biodistribution. In an ovarian tumor model, s-SPIONs were shown to accumulate in the tumors, highlighting their potential use as a chemotherapy delivery agent.

The interaction of sterically stabilized magnetic nanoparticles with fresh human red blood cells

Sterically stabilized superparamagnetic iron oxide nanoparticles (SPIONs) were incubated with fresh human erythrocytes (red blood cells [RBCs]) to explore their potential application as magnetic resonance imaging contrast agents. The chemical shift and linewidth of 133Cs+ resonances from inside and outside the RBCs in 133Cs nuclear magnetic resonance spectra were monitored as a function of time. Thus, we investigated whether SPIONs of two different core sizes and with three different types of polymeric stabilizers entered metabolically active RBCs, consuming glucose at 37°C. The SPIONs broadened the extracellular 133Cs+ nuclear magnetic resonance, and brought about a small change in its chemical shift to a higher frequency; while the intracellular resonance remained unchanged in both amplitude and chemical shift. This situation pertained over incubation times of up to 90 minutes. If the SPIONs had entered the RBCs, the intracellular resonance would have become broader and possibly even shifted. Therefore, we concluded that our SPIONs did not enter the RBCs. In addition, the T2 relaxivity of the small and large particles was 368 and 953 mM−1 s−1, respectively (three and nine times that of the most effective commercially available samples). This suggests that these new SPIONs will provide a superior performance to any others reported thus far as magnetic resonance imaging contrast agents.

A study of porosity of synthetic polymer nanoparticles using PALS

Positron annihilation lifetime spectroscopy (PALS) has been used to study the free volume in dry synthetic polymer nanoparticles of various sizes. A series of poly(styrene/divinyl benzene) particles with diameters in the range of 100 to 500 nm were synthesized and then carefully chemically treated using the sulfonation process, to increase their porosity. The particles were characterised by Scanning Electron Microscopy (SEM), light scattering and PALS. Light scattering gave larger size for the treated particles, reflecting the hydration effect and therefore the increase in porosity. PALS spectra of untreated and treated particles gave four and three life-time components, respectively. Analysis by PAScual version 1.3.0 program indicated there was a reduction in the intensity and the type of the micropores in the treated particles. The data suggest PALS is a sensitive tool for detecting changes in microporosity in particles. The conflicting results obtained for light scattering compared to PALS for chemically treated particles is difficult to resolve and suggests sample preparation of polymeric materials for PALS is the critical factor.