Boon M. Teo

Sonochemical synthesis of magnetic Janus nanoparticles

The sonochemical synthesis of nanosized surface-dissymmetrical (Janus) particles is described. The Janus particles were composed of silica and polystyrene, with the polystyrene portion loaded with nanosized magnetite particles. It is shown that the Janus particles can be used to form kinetically stable oil-in-water emulsions that can be spontaneously broken on application of an external magnetic field. The one-pot synthetic process used to prepare the Janus particles has several advantages over other conventional methods of producing such particles.

Novel One-Pot Synthesis of Magnetite Latex Nanoparticles by Ultrasound Irradiation

A simple and efficacious procedure for the synthesis of magnetite nanoparticles has been achieved via a sonochemical miniemulsion polymerization process. The sonochemically synthesized magnetite encapsulated polymer latex particles exhibit excellent colloidal stability and strong magnetic properties, and are of a size that makes them technologically relevant. This novel method may be readily extended to the preparation of multiple combinations of different polymers and encapsulated materials.

Assembly of Poly(dopamine)/Poly(N-isopropylacrylamide) Mixed Films and Their Temperature-Dependent Interaction with Proteins, Liposomes, and Cells

Many biomedical applications benefit from responsive polymer coatings. The properties of poly(dopamine) (PDA) films can be affected by codepositing dopamine (DA) with the temperature-responsive polymer poly(N-isopropylacrylamide) (pNiPAAm). We characterize the film assembly at 24 and 39 °C using DA and aminated or carboxylated pNiPAAm by a quartz crystal microbalance with dissipation monitoring (QCM-D), X-ray photoelectron spectroscopy, UV-vis, ellipsometry, and atomic force microscopy. It was found that pNiPAAm with both types of end groups are incorporated into the films. We then identified a temperature-dependent adsorption behavior of proteins and liposomes to these PDA and pNiPAAm containing coatings by QCM-D and optical microscopy. Finally, a difference in myoblast cell response was found when these cells were allowed to adhere to these coatings. Taken together, these fundamental findings considerably broaden the potential biomedical applications of PDA films due to the added temperature responsiveness.

Liposome-containing polymer films and colloidal assemblies towards biomedical applications

Liposomes are important components for biomedical applications. Their unique architecture and versatile nature have made them useful carriers for the delivery of therapeutic cargo. The scope of this minireview is to highlight recent developments of biomimetic liposome-based multicompartmentalized assemblies of polymer thin films and colloidal carriers, and to outline a selection of recent applications of these materials in bionanotechnology.

Highly-branched poly(N-isopropylacrylamide) as a component in poly(dopamine) films

Mixed one-step poly(dopamine) (PDA)/highly branched poly(N-isopropylacrylamide) (pNiPAAm) coatings have been assembled and characterized by X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, atomic force microscopy, and quartz crystal microbalance with dissipation monitoring (QCM-D) depending on the deposition temperature below and above the lower critical solution temperature (LCST) of the pNiPAAm. Mixed films were confirmed. The protein adsorption at 24 °C was found to be reduced with increasing amount of pNiPAAm in the mixed coatings, while there was no difference observed for proteins deposition at 39 °C. Further, the ability of these mixed coatings in comparison to the pure PDA and pNiPAAm films to serve as capping layer for surface-immobilized zwitterionic or positively charged liposomes has been assessed by QCM-D. The adhesion of hepatocytes, macrophages, and myoblast to these liposomes-containing hybrid coatings and the uptake of fluorescent lipids from the surface by the adhering cells depending on the capping layers were compared. The latter aspect was found to be dependent on the used capping layer and the type of liposome as carrier for the fluorescent lipid, with the highest uptake found for positive liposomes and pure pNiPAAm as capping layer. Taken together, the assembled hybrid coatings have the potential to be used as functional coatings toward surface-mediated drug delivery.

Antimicrobial and Biosensing Ultrasound-Responsive Lysozyme-Shelled Microbubbles

Air-filled lysozyme microbubbles (LSMBs) were engineered as a support for the immobilization of gold nanoparticles and an enzyme, alkaline phosphatase, in order to develop micro-antimicrobial and biosensing devices. Gold nanoparticles immobilized on LSMBs significantly improved the antimicrobial efficacy of the microbubbles against M. lysodeikticus. The surface functionalization of the microbubbles with gold nanoparticles did not affect their echogenicity when exposed to an ultrasound imaging probe. Alkaline phosphatase was conjugated on the surface of microbubbles without compromising its enzymatic activity. The functionalized microbubbles were used for the detection of paraoxon in aqueous solutions.

Recent progress of liposomes in nanomedicine

Liposomes, spherical vesicles consisting of one or more lipid bilayer membrane(s) encapsulating an aqueous medium, are among the prominent players in the field of nanomedicine. Herein, we highlight the newest, atypical applications of liposomes towards their use in biomedicine. In particular, we put special emphasis on innovative chemical modification of liposomes, the interactions of liposomes with cells under the influence of shear stress, and the utilisation of liposomes as drug deposits in polymeric films and as components in synthetic cell mimics.

Cargo delivery to adhering myoblast cells from liposome-containing poly(dopamine) composite coatings

Designing surfaces to deliver therapeutic compounds to adhering cells is of paramount importance for both implantable devices and tissue engineering. We report the assembly of composite films consisting of liposomes as drug deposits in a poly(dopamine) matrix. We monitor the film assembly using a quartz crystal microbalance with dissipation. We assess the response of adhering myoblast cells to these films containing fluorescent lipids in terms of uptake efficiency and cell mean fluorescence using flow cytometry. The viability of adhering myoblast cells, when the hydrophobic cytotoxic compound thiocoraline is entrapped in the lipid membrane, is assessed for different films. Coatings with one or two liposome deposition steps are considered. Further, the effect of the polymer separation layers between the liposome layers is determined. We found that it is possible to use the different nano-engineered composite coatings to impose a corresponding cellular response, e.g., a higher amount of embedded liposomes leads to higher uptake efficiency of the fluorescent lipids and cell mean fluorescence or a higher reduction in the viability of the adhering cells. Assessment of the uptake efficiency and cell mean fluorescence over time reveals a decrease in both parameters over 48 h. Our results demonstrate the ability to affect the cell response depending on the properties of the films, opening up a variety of opportunities for biomedical applications in substrate-mediated drug delivery.

Synthesis of temperature responsive poly(N-isopropylacrylamide) using ultrasound irradiation.

Ultrasound was employed to synthesize poly(N-isopropylacrylamide) [poly(NIPAM)] either as aqueous solutions or microgels in the absence of a chemical initiator. Poly(NIPAM) of different microstructures can be readily prepared via ultrasound irradiation by varying the reaction temperature. At a preparation temperature of 20 degrees C, poly(NIPAM) was formed in aqueous solutions, whereas, at a higher preparation temperature (beyond the lower critical solution temperature of approximately 32 degrees C), poly(NIPAM) microgels were formed. In addition, the high shear gradients generated by the acoustic cavitation process aid to control or vary the molecular weights of poly(NIPAM) formed in aqueous solutions. The swelling behavior of poly(NIPAM) at different concentrations of sodium dodecyl sulfate (SDS) was also studied. An increase in the transition temperature and hydrodynamic size of the particles was attributed to SDS binding to the polymer network through hydrophobic interactions. Light scattering data reflected the formation of larger microgels at low cross-linker concentrations. The encapsulation of rhodamine B within the microgels was achieved by sonicating the monomer containing the dye. The subsequent release of the dye was consistent with Fickian diffusion and the diffusion coefficient of the dye was estimated as 4.0 x 10(-12) and 3.6 x 10(-11) m(2) s(-1) at 20 and 40 degrees C, respectively. From the diffusion coefficients, the viscosities of the polymer samples at 20 and 40 degrees C were determined using the Stokes-Einstein equation to be 77 and 10 cP, respectively.

Microemulsion Polymerizations via High-Frequency Ultrasound Irradiation

The synthesis of nanosized polymer latex particles using high-frequency ultrasound (213 kHz) has been successfully performed. The effects of surfactant type and concentration of surfactants on the rates of polymerization, latex size, and molecular weights of the polymers produced are presented.