Jinho Hyun

Nanocellulose-alginate hydrogel for cell encapsulation

TEMPO-oxidized bacterial cellulose (TOBC)-sodium alginate (SA) composites were prepared to improve the properties of hydrogel for cell encapsulation. TOBC fibers were obtained using a TEMPO/NaBr/NaClO system at pH 10 and room temperature. The fibrillated TOBCs mixed with SA were cross-linked in the presence of Ca(2+) solution to form hydrogel composites. The compression strength and chemical stability of the TOBC/SA composites were increased compared with the SA hydrogel, which indicated that TOBC performed an important function in enhancing the structural, mechanical and chemical stability of the composites. Cells were successfully encapsulated in the TOBC/SA composites, and the viability of cells was investigated. TOBC/SA composites can be a potential candidate for cell encapsulation engineering.

Doxorubicin-conjugated polypeptide nanoparticles inhibit metastasis in two murine models of carcinoma

Drug delivery vehicles are often assessed for their ability to control primary tumor growth, but the outcome of cancer treatment depends on controlling or inhibiting metastasis. Therefore, we studied the efficacy of our genetically encoded polypeptide nanoparticle for doxorubicin delivery (CP-Dox) in the syngeneic metastatic murine models 4T1 and Lewis lung carcinoma. We found that our nanoparticle formulation increased the half-life, maximum tolerated dose, and tumor accumulation of doxorubicin. When drug treatment was combined with primary tumor resection, greater than 60% of the mice were cured in both the 4T1 and Lewis lung carcinoma models compared to 20% treated with free drug. Mechanistic studies suggest that metastasis inhibition and survival increase were achieved by preventing the dissemination of viable tumor cells from the primary tumor.

Effect of negatively charged cellulose nanofibers on the dispersion of hydroxyapatite nanoparticles for scaffolds in bone tissue engineering

Nanofibrous 2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO)-oxidized bacterial cellulose (TOBC) was used as a dispersant of hydroxyapatite (HA) nanoparticles in aqueous solution. The surfaces of TOBC nanofibers were negatively charged after the reaction with the TEMPO/NaBr/NaClO system at pH 10 and room temperature. HA nanoparticles were simply adsorbed on the TOBC nanofibers (HA-TOBC) and dispersed well in DI water. The well-dispersed HA-TOBC colloidal solution formed a hydrogel after the addition of gelatin, followed by crosslinking with glutaraldehyde (HA-TOBC-Gel). The chemical modification of the fiber surfaces and the colloidal stability of the dispersion solution confirmed TOBC as a promising HA dispersant. Both the Youngs modulus and maximum tensile stress increased as the amount of gelatin increased due to the increased crosslinking of gelatin. In addition, the well-dispersed HA produced a denser scaffold structure resulting in the increase of the Youngs modulus and maximum tensile stress. The well-developed porous structures of the HA-TOBC-Gel composites were incubated with Calvarial osteoblasts. The HA-TOBC-Gel significantly improved cell proliferation as well as cell differentiation confirming the material as a potential candidate for use in bone tissue engineering scaffolds.

Spatial deformation of nanocellulose hydrogel enhances SERS

Bacterial cellulose hydrogels containing gold nanoparticles (AuNPs-BC) were prepared using a cost-effective and environment-friendly in situ synthesis method. Well-dispersed AuNPs were grown on the nanofiber surface of the BC hydrogel, forming substrates of surface-enhanced Raman spectroscopy (SERS). Increases in SERS-active sites in the AuNPs-BC hydrogel caused the enhancement of SERS intensity. The enhancement in SERS intensity of 4-fluorobenzenethiol and phenylacetic acid (PAA), used as test analytes, was compared with spatially-un-deformed AuNPs-BC hydrogels, as well as spatially-deformed AuNPs-BC hydrogels in which the BC layers had contracted during drying. Particularly noteworthy was the detection of PAA by the simple contraction of the substrate, despite a low affinity to surface gold.

Thermoresponsive pore structure of biopolymer microspheres for a smart drug carrier.

Triggering changes in surface porosity enabled the controlled release of biomolecules from elastin-like polypeptide (ELP) microspheres. The transition temperature (T(t)) of cross-linked microspheres was determined by differential scanning calorimetry, and T(t) was in agreement with the volume transition observed by changing the external temperature of the incubation media. The thermoresponsive pore structure of ELP microspheres and their surface morphology were examined by field-emission scanning electron microscopy. ELP microspheres were investigated as a smart drug carrier using model drug molecules, bovine serum albumin, and prednisone acetate. The release rate was accelerated by squeezing out the entrapped biomolecules as the temperature was increased above T(t) because of the development of micropores at the surface as well as in the bulk. In addition, the stepwise release confirmed that ELP microspheres could be progammed precisely to control the release of drugs by external stimuli.

Smart biopolymer for a reversible stimuli-responsive platform in cell-based biochips.

The rapid response of a smart material surface to external stimuli is critical for application to cell-based biochips. The sharp and controllable phase transition of elastin-like polypeptide (ELP) enabled reversible cell adhesion on the surface by changing the temperature or salt concentration in the system. First, ELP micropatterns were prepared on a glass surface modified into aldehyde. The lysine-containing ELP (ELP-K) was genetically synthesized from E. coli for conjugation with the aldehyde on the glass surface. The phase transition of ELP was monitored in PBS and cell culture media using UV-visible spectroscopy, and a significant difference in transition temperature (Tt) was observed between the two solution systems. The micropatterning of ELP on the glass surface was performed by microcontact printing a removable polymeric template on the aldehyde-glass followed by incubation in ELP-K aqueous solution. The ELP micropatterns were imaged with atomic force microscopy and showed a monolayer thickness of approximately 4 nm. Imaging from time-of-flight secondary ion mass spectroscopy confirmed that the ELP molecules were successfully immobilized on the highly resolved micropatterns. Cell attachment and detachment could be reversibly controlled on the ELP surfaces by external stimuli. The hydrophobic phase above Tt resulted in the adhesion of fibroblasts, while the detachment of cells was induced by lowering the incubation temperature below Tt. The smart properties of ELP were reliable and reproducible, demonstrating potential applications in cell-based microdevices.

Enhanced surface plasmon resonance by Au nanoparticles immobilized on a dielectric SiO2 layer on a gold surface

This paper introduces strategies for enhancement of a surface plasmon resonance (SPR) signal by adopting colloidal gold nanoparticles (AuNPs) and a SiO(2) layer on a gold surface. AuNPs on SiO(2) on a gold surface were compared with an unmodified gold surface and a SiO(2) layer on a gold surface with no AuNPs attached. The modified surfaces showed significant changes in SPR signal when biomolecules were attached to the surface as compared with an unmodified gold surface. The detection limit of AuNPs immobilized on a SPR chip was 0.1 ng mL(-1) for the prostate-specific antigen (PSA), a cancer marker, as measured with a spectrophotometer. Considering that the conventional ELISA method can detect approximately 10 ng mL(-1) of PSA, the strategy described here is much more sensitive (approximately 100 fold). The enhanced shift of the absorption curve resulted from the coupling of the surface and particle plasmons by the SiO(2) layer and the AuNPs on the gold surface.

Elastin-like polypeptide modified liposomes for enhancing cellular uptake into tumor cells

Polyethylene glycol-modified (PEGylated) liposomes have been widely used because of their long circulation time, but they have a major drawback of limited cellular uptake. In this study, liposomes modified with a thermosensitive biopolymer, elastin-like polypeptide (ELP), were prepared to enhance cellular uptake in tumor cells. Synthesized ELP exhibited an inverse transition temperature (T(t)) of 40°C in serum with hyperthermia treatment and contained a lysine residue for conjugation with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-[poly(ethylene-glycol)]-hydroxy succinamide, PEG MW 2000 (DSPE-PEG2000-NHS). ELP was covalently conjugated with liposomes encapsulating a high concentration of doxorubicin (Dox). Size and drug release properties of liposomes were investigated over a range of temperatures. ELP-modified liposomes tended to aggregate but did not show temperature-triggered release by phase transition of ELP molecules. Cellular uptake efficiency of liposomes was evaluated under normothermic and hyperthermic condition. Dox accumulation from liposomes was determined by flow cytometry and confocal microscopy. Higher internalization occurred in the ELP-modified liposomes than in ELP-unmodified liposomes. The results suggest that dehydration of ELP molecules on the liposomal surface can induce efficient cellular uptake, which can improve existing chemotherapeutic efficacy.

Amphiphilic comblike polymers enhance the colloidal stability of Fe3O4 nanoparticles

Stable colloidal dispersions of magnetite (Fe(3)O(4)) nanoparticles (MNPs) were obtained with the inclusion of an amphiphilic comblike polyethylene glycol derivative (CL-PEG) as an amphiphilic polymeric surfactant. Both the size and morphology of the resulting CL-PEG-modified MNPs could be controlled and were characterized by transmission electron microscopy (TEM). The interaction between MNPs and CL-PEG was confirmed by the presence of characteristic infrared absorption peaks, and the colloidal stability of the nanoparticle dispersion in water was evaluated by long-term observation of the dispersion using UV-visible spectroscopy. SQUID measurements confirmed the magnetization of CL-PEG-modified MNPs. The zeta potential of the CL-PEG-modified MNPs showed a dramatic conversion from positive to negative in response to the pH of the surrounding aqueous medium due to the presence of carboxyl groups at the surface. These carboxyl groups can be used to functionalize the MNPs with biomolecules for biotechnological applications. However, regardless of surface electrostatics, the flexible, hydrophilic side chains of CL-PEG-modified MNPs prevented the approach of adjacent nanoparticles, thereby resisting aggregation and resulting in a stable aqueous colloid. The cytotoxicity of MNPs and CL-PEG-modified MNPs was evaluated by a MTT assay.

Rapid analysis of matrix metalloproteinase-3 activity by gelatin arrays using a spectral surface plasmon resonance biosensor.

We developed a novel assay system using an array-based spectral surface plasmon resonance (SPR) biosensor for a high-throughput analysis of matrix metalloproteinase (MMP)-3 activity. Gelatin arrays were fabricated by immobilizing gelatin, a MMP-3 substrate, on amine-modified gold arrays. MMP-3 activity was determined by monitoring the shift of SPR wavelength caused by gelatin proteolysis. The gelatinolytic activity of MMP-3, which caused a decrease of the SPR wavelength, was verified by SPR spectroscopy, atomic force microscopy, and fluorescence-based protein arrays. MMP-3 activity increased by three non-ionic detergents in a dose-dependent manner, and Brij-35 was most effective. The array-based SPR biosensor was successfully applied to the rapid analysis of dose-dependent MMP-3 activity and its inhibition with tissue inhibitors of metalloproteinase 1 and GM6001, MMP inhibitors. Therefore, this new assay system using a spectral SPR biosensor is simple, label-free, and high-throughput, and is likely to have a strong potential for inhibitor screening.