Bokyung Jung

Hydrogel swelling as a trigger to release biodegradable polymer microneedles in skin.

Biodegradable polymeric microneedles were developed as a method for achieving sustained transdermal drug release. These microneedles have potential as a patient-friendly substitute for conventional sustained release methods. However, they have limitations related to the difficulty of achieving separation of the needles into the skin. We demonstrated that microneedle separation into the skin was mediated by hydrogel swelling in response to contact with body fluid after the needles were inserted into the skin. The hydrogel microparticles were synthesized by an emulsification method using poly-N-isopropylacrylamide (PNIPAAm). The microneedles were fabricated by micromolding poly-lactic-co-glycolic acid (PLGA) after filling the cavities of the mold with the hydrogel microparticles. The failure of microneedle tips caused by hydrogel swelling was studied in regard to contact with water, insertion of microneedles into porcine cadaver skin in vitro, stress-strain behavior, and insertion into the back skin of a hairless mouse in vivo. The drug delivery property of the hydrogel particles was investigated qualitatively by inserting polymer microneedles into porcine cadaver skin in vitro, and the sustained release property of PLGA microneedles containing hydrogel microparticles was studied quantitatively using the Franz cell model. The hydrogel particles absorbed water quickly, resulting in the cracking of the microneedles due to the difference in volume expansion between the needle matrix polymer and the hydrogel particles. The swollen particles caused the microneedles to totally breakdown, leaving the microneedle tips in the porcine cadaver skin in vitro and in the hairless mouse skin in vivo. Model drugs encapsulated in biodegradable polymer microneedles and hydrogel microparticles were successfully delivered by releasing microneedles into the skin.

A direct surface modification of iron oxide nanoparticles with various poly(amino acid)s for use as magnetic resonance probes

Water soluble and biocompatible iron oxide nanoparticles coated with poly(aspartic acid) (PAsp), poly(asparagines) (PAsn), poly(2-hydroxy-ethyl L-aspartamide) (PHEA), and poly-α,β-(N-2-dimethylaminoethyl L-aspartamide) (PDMAEA) were prepared by hydrophobic interaction between hydrophobic iron oxide nanoparticles and each amphiphilic poly(amino acid)s graft polymer. The octadecyl side chain grafted poly(succinimide)(PSI-g-C(18)), used as a precursor polymer, was easily aminolyzed with nucleophilic compounds to form various poly(amino acid)s graft polymer (PAsp-g-C(18), PAsn-g-C(18), PHEA-g-C(18), PDMAEA-g-C(18),) and simultaneously stabilize the dispersion of iron oxide nanoparticles in aqueous solution. The diameters of the poly(amino acid)s coated iron oxide nanoparticles (PAIONs) were smaller than 30 nm in aqueous solution, extremely stable in aqueous solutions with a wide range of pH and salt concentrations. Further, all the PAIONs showed excellent MR signal intensities (high r(2) values) and the cellular uptake property of the PAIONs was also evaluated.

Tumor-binding prodrug micelles of polymer–drug conjugates for anticancer therapy in HeLa cells

An interesting phytosphingosine (PHS), a natural sphingolipid metabolite comprising ceramides, is believed to play a vital role in strong anticancer therapeutic efficacy for various types of cancer cells, which is based on a programmed cellular death mechanism, so called apoptosis. However, extremely low water-solubility has been an obstacle to its usage as an anticancer drug via the systemic administration route. To utilize the benefits of PHS, we developed tumor-targeting polymer–drug conjugates wherein hydrophobic PHS was connected to the folate-grafted hydrophilic and biocompatible polymer through pH-sensitive linkages. The polymer–drug conjugates formed nano-sized (10–20 nm) spherical micelles spontaneously in aqueous media and they were found to have high drug contents (10.3 wt%). We present a systematic study of in vitro anticancer therapy in HeLa cells treated by tumor-targeting micelles in terms of anti-proliferation. The anticancer effect was analyzed by apoptotic cell death as well as the preferential distribution of loaded drug in the cancer cells. The synergistic effect by loading the commercial drug of doxorubicin was also studied.

Reaction-controlled diffraction grating of photopolymer for use of phase stable holographic optical element

Herein we propose control of polymerization kinetics to prevent inherent scattering problem of holographic photopolymer system that is caused by a phase separation between matrix and photopolymerized grating polymers. To elucidate this, in this letter, phase stability of the photopolymer system was studied with molecular dynamic simulation of Flory–Huggins theory and was investigated in the respect of polymerization kinetics. It was controlled with the variables of monomer conversion and degree of polymerization by varying both reaction time and rates. In addition, volume grating fixing effect of post ultraviolet treatment on photopolymer was examined.

Self-Assembled Nanoparticles of Ribozymes with Poly(ethylene glycol)-b-Poly(L-lysine) Block Copolymers

Complex nanoparticle formation of poly(ethylene glycol)-b-poly(L-lysine) (PEG-b-PLL) block copolymers with ribozyme (Rzs) in an aqueous solution was studied. Nanoparticles formed from PEG-b-PLL and Rzs have about 100 nm in an effective diameter with the hydrophilic PEG segments stabilizing and surrounding the core of complexes formed between the PLL segments and Rzs. The block copolymer having a higher positive charge formed relatively smaller complex nanoparticles. The profile of the ethidum bromide (EtBr) displacement assay and images of agarose gel electrophoresis revealed the condensation of Rzs to form complex nanoparticles above a critical weight ratio, r (r: 4.0 for PEG5000-b-PLL1920 and 3.0 for PEG5000-b-PLL3840). Furthermore, the PEG-b-PLL/Rz complex nanoparticle showed high resistance against RNase attack in biological fluids.

Blue laser-sensitized photopolymer for a holographic high density data storage system.

We present a new blue-sensitized photopolymer to achieve a higher storage density compared to green/red-recordable media. Photopolymers are prepared based on a two-chemistry system and their holographic recording properties are investigated. A matrix of long and flexible ether units of an epoxy precursor and a multi-crosslinkable amine hardener enhances energetic sensitivity and suppresses volume shrinkage effectively. Page-wise recording of 961 bits/page of digital data is demonstrated and long term recording stability is also verified for a period of roughly 2 months.

Robust interpenetrating network photopolymer containing hyper-branched photoreactive nanoparticle for holographic data storage

Herein we report an interpenetrating network (IPN) photopolymer containing an inorganic hyper-branched photoreactive polyhedral oligomeric silsesquioane (POSS) nanoparticle (NP) which can address the problem of light scattering induced by the aggregation of nanoparticles and can allow writing-induced shrinkage to be successfully reduced to the extent of negligible values for 500-μm-thick film. Holographic optical properties including diffraction efficiency (DE), sensitivity, and volume shrinkage are investigated as a function of POSS concentration. Angle multiplexing and page-wise recording are also demonstrated by using an amplitude spatial light modulator (SLM).