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The particular interest of studies in the Polymer Nanomaterials Laboratory at Chung-Ang University is to control the interfaces between neutral and charged (or highly polar) species in preparing organic (or hybrid) nanomaterials for electro-optic and biomedical applications.

 

On-going researches

 
 

 

Aqueous-Based Applications using Conjugated Polymer Nanomaterials

 

Highly Ordered Structures in Conjugated Polymer Nanoparticles Assembled with Phospholipids for Enhanced Stability

Revealing the nature of chain packing in conjugated polymer nanoparticles (CPNs) is one of the important issues to polymer physics research. Surfactant-stabilized CPNs in water show significantly enhanced luminescence intinsity in comparison to small molecular organic dyes and single polymer chains dissolved in solvents. The importance of the conjutated polymer structure in nanomaterials is undoubted. However, details of the relationship between alignment of conjugated backbone in CPNs and its luminescent property have not been estabilished. Furthermore, there are yet no methods that can predict the atom-resolved structure of conjugated polymer in the CPNs. We empoly coarse-grained (CG) molecular dynaic simulations to investigate the structure of phase-separated film and the film shattering process for a mixture of a conjugated polymer and a phospholipid. The pi-pi stacked structure of the conjugated polymer is significantly enhanced when the ratio of the phospholipid increases in both dried and water exposed film. We also show that the amount of the phospholipid is at least 2.5 times larger than that of the conjugated polymer to wrap the conjugated polymer chain. We confirmed that conjugated backbones inside the nanoparticles were completely shielded from the aqueous solution by the dense layers of alkyl chains, resulting in remarkably enhanced chain packing. These simulated results are correlated with experimentally observed structure through UV-vis-near infrared (UV-vis-NIR) spectrometry, scanning electron microscopy (SEM), particle size analysis, transmission electron microscopy (TEM), and grazing-incidence X-ray diffraction (GIXD). [Macromolecules 2017, 50, 6935; Copyright 2017, ACS Publications]

 

Conjugated Polymer Nanoparticle (CPN) assembled via the Phase-Separated Film Shattering (PSFS) Route for Photothermal Therapy

We develop nanoparticles of conjugated polymers from phase-separated thin films. When a conjugated polymer and a phospholipid are dissolved in a cosolvent and the cosolvent is evaporated, it is clearly anticipated that the resulting films will show a phase-separated morphology because of immiscibility between the hydrophobic polymer and the polar heads of the phospholipids. Furthermore, nanometer-scale associations can be formed when the alkyl tail length of the phospholipid is comparable to the alkyl side chain length of the conjugated polymer. Ultrasonication of the solution after adding water enables the water molecules to penetrate into the thin films due to the existence of polar regions in the phospholipid heads, thus breaking the thin films and ultimately dispersing nanoparticles of conjugated polymers into the aqueous media. Nanoparticles with primary amines at their surface can be formed, thus widely opening applications for biology and medicine by post-functionalization on demands. [Adv. Mater. 2014, 26, 4559; Copyright 2014, John Wiley & Sons]

 

Conjugated Oligoelectrolyte as Molecular Wires in Photoelectrodes for Solar Energy Conversion

Lipid assemblies of natural and artificial light-harvesting complexes on electrodes have been widely investigated as subcomponents in electronic and optoelectronic devices to mimic photosynthesis in nature. Conjugated oligoelectrolytes (COEs), that is, oligomers having backbones with -delocalized electronic structures and pendant groups with ionic functionalities, have proven their usefulness for optoelectronic applications. As a result of their unique molecular structures, which combine hydrophobic conjugated backbones with hydrophilic moieties, COEs can be incorporated into lipid bilayers and is assumed to have a perpendicular alignment of its long molecular axis with respect to the membrane surface because of charge compensation between the zwitterions in phospholipids and the terminal ionic groups in COEs, together with hydrophobic attraction between the neutral parts of COEs and the alkyl chains in phospholipids. Phospholipid-assembled COEs significantly facilitates transmembrane electron transfer across lipid bilayers, possibly by a charge-tunneling mechanism through the -delocalized structure. We show that Forster resonance energy transfer (FRET) between a COE and Nile red can enhance photocurrent generation when the photoagents are assembled vertically on gold electrodes. COE and Nile red intercalated into phospholipid membranes of unilamellar vesicles were found to form a useful FRET system because of the solvatochromic properties of COE, and the accompanying photophysical properties were suitable for FRET with Nile red. As a result, a FRET efficiency of 93~94% was achieved. When Nile red was tethered in a selfassembled monolayer on gold electrodes and phospholipid-assembled COE was sequentially organized on the SAM layer, the anodic photocurrent increased notably, reaching about 815 nA/cm2 by virtue of FRET between the vertically aligned dyes. [J. Phys. Chem. C 2013, 117, 3293; Copyright 2013, American Chemical Society]

 

 

Cosmetic Applications

 

Microencapsulation by Pectin Shells for Multi-Component Carriers

Oil/water microencapsulation by microfluidic systems has been a prominent delivery method to prepare functional microcapsules in the food, cosmetic, and pharmaceutical industries because it is an easy way to control the shape and size of structures and functionalities. We prepared biocompatible and multi-component microcapsules using the precipitation and ionic crosslinking of pectin in a poor solubility environment and with multivalent cations, respectively. When the aqueous solution (including calcium ions and ethanol) in a sheath flow met the flow of a pectin aqueous solution containing oil droplets, ethanol-gelation and ionic cross-linking occurred, enclosing the inner oil phase droplets by solidified pectin shells. Furthermore, the resulting microcapsules stabilized by pectin shells exhibited functionalities using a hydrophobic agent and nanoparticles of a hydrophilic species that were dissolved and dispersed, respectively, in the oil phase.[Carbohydrate Polymers 2018, 182, 172; Copyright 2018, Elsevier]

 

Polyssacharide Hydrogel Nanoparticles for Enhanced Transdermal Delivery

 

 

Lipid bilayers self-assembled on micro- and nano-spheres have received considerable attention for over the last two decades due to their potential in biomedical applications. Pharmaceutical agents or biofunctional proteins could be embedded inside such sphere-liposome assemblies within the sphere or supported lipid membranes while maintaining mechanical stability. So-called lipobeads or lipogels have been used as artificial biological cells to study membrane biopysics as well as for biosensors coupled with microfluidics, drug delivery, and dermatologic applications. Decreases in sphere size to the nanometer scale will be required for future pharmaceutical and cosmetic applications. When the size of a colloidal system decreases, it would be expected that circulation time in the blood would increase or that the response time for swelling or shrinking under stimulus would decrease, improving targeting, transmembrane delivery, and controlled release of drugs. Nanohydrogels are also useful for transdermal delivery and cosmetics. The stratum corneum, the outermost layer of skin, has a morphology that can be represented by a brick (corneocyte) and mortar (intercellular lipid layer) model. Smaller-sized colloids show enhanced permeation into these microstructures and allow for transport of hydrophobic drugs or cosmetic components through the intercellular lipid layers. We develop a new type of hydrogel-liposome assemblies with a nanogel core using the hydrophobic anchoring group of a phospholipid. We modified a polyssacharide with a phospholipid moeity, and with UV-crosslinkable methacrylic anhydride. It is anticipated that the modified polyssacharide can form nanospheres in an inverse emulsion media without the use of surfactants, generating nanogel particles upon UV irradiation with phospholipid moieties displayed on the nanogel surfaces. Thus, the phospholipid bilayers, which have a similar chemical structure to that of the surface-anchoring moieties and can accommodate hydrophobic or amphiphilic agents, can self-assemble on the surface of nanogels. [Chem. Eng. J. 2015, 263, 38; Copyright 2015, Elsevier]

 

Polymer Nanomaterials Laboratory, School of Chemical Engineering and Materials Science, Chung-Ang University

Room 529, Building 207, 84 Heokseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea, Phone +82-2-822-7772