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Posted: Jun 05, 2015

New technique precisely controls size and shape of polymeric nanoparticles

(Nanowerk Spotlight) Over the last twenty years, scientists have developed many techniques to synthesize polymeric nanoparticles for a wide range of applications including surface coating, sensor technology, catalysis, and nanomedicine.
These so-called reversible-deactivation radical polymerization (RDRP) techniques have provided researchers with powerful tools to synthesize well-defined macromolecules with predetermined molecular weight, low polydispersity, and precisely defined end groups.
However, the precise control of the size and shape of polymer nanoparticles remains challenging, and RDRP techniques still fall well short of producing large, well-defined macromolecules with the same size and degree of precision as nature (proteins, nucleic acids, etc.).
In new work, researchers at The Australian Research Council Centre of Excellence in Convergent Bio-Nano Science & Technology (CBNS) at Monash University, led by Professor Thomas Davis, have developed a new technique to precisely control the size and shape of polymeric nanoparticles.
The scientific core of these findings lies in a novel stabilizer of nanoparticles that provide the precise control over particle size and a novel self-assembly method for the synthesis of various nanoparticle shapes. In combination with traditional techniques, this new method provides a useful approach for reproducibly generating an extensive library of nanostructured particles with different sizes and shapes.
The team reports their findings in recent online editions of Polymer Chemistry ("Rapid synthesis of ultrahigh molecular weight and low polydispersity polystyrene diblock copolymers by RAFT-mediated emulsion polymerization") and in ACS Macro Letters ("Reproducible Access to Tunable Morphologies via the Self-Assembly of an Amphiphilic Diblock Copolymer in Water").
nanoparticle shapes
Various nanoparticle shapes synthesized by The Australian Research Council Centre of Excellence in Convergent Bio-Nano Science & Technology at Monash University.
By using a novel macromolecular chain transfer agents (CTA) in reversible addition fragmentation chain transfer polymerization (RAFT)-mediated emulsion polymerization, the researchers have overcome a long-standing challenge in the synthesis of UHMW polymers and created a new nanomaterial with promising potential.
"Our synthesis technique has the following advantages," Nghia Truong Phuoc, a Postdoctoral Research Fellow at CBNS, tells Nanowerk: "1) ultrafast synthesis; 2) narrow distribution of particle sizes; 3) precise control over both molecular weight and particle size; 4) no use of organic solvents; 5) high solids content; 6) excellent stability; and 7) tunable morphologies."
This makes the method very useful for the preparation of polymeric nanoparticles with predetermined size (from 20 nm to 200 nm) and shape (e.g., sphere, vesicle, worm, flower, etc.), opening the door to novel industrial, sensing and medical applications.
Beside traditional applications, polymeric nanoparticles made via this novel technique could have great potential in biomedical engineering. For example, as Truong explains, worm-like nanoparticles can evade clearance by the immune system and achieve prolonged circulation time, which is a special feature similar to that of certain rod-shaped bacteria, viruses, and fungi found in nature.
"They also have the ability to accumulate in tumors to a very high concentration – i.e., up to 30 wt % of the injected dose – and achieve a higher antitumor efficacy when compared to spheres and vesicles," he points out. "In addition, nanoparticles with rare morphologies such as large compound vesicles and flower-like vesicles are rapidly taken up by cells and able to escape endolysosomal cellular transport compartments."
Going forward, the researchers plan to study the structure-property relationship of nano-bio interactions occurring between these novel nanoparticles with biological systems, which could eventually provide highly efficient nanocarriers for drug and gene delivery.
The ultimate goal for researchers in this field is to synthesize a library of polymeric nanoparticles possessing different sizes, shapes, surfaces, and cores to render different physicochemical properties which could support vastly different applications in biotechnology and medicine.
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