Kyunga Na

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.

Gadolinium-based cancer therapeutic liposomes for chemotherapeutics and diagnostics.

Gadolinium (Gd)-based cancer therapeutic liposomes can be used for chemotherapeutics and diagnostics. In this study, dual functional liposomes co-encapsulating doxorubicin (Dox) and Gd were prepared by Dox-transition metal complexation. Preparation conditions were optimized to obtain liposomes containing high concentrations of Dox and Gd. The optimized liposomes Gd250 co-encapsulated 3.6 mM of Dox and 1.9 mM of Gd. The magnetic resonance (MR) properties of Gd250 liposomes were determined using a 4.7 T MR system. Cellular uptake of Dox was determined using a flow cytometer and a confocal microscopy and that of Gd was measured using an inductively coupled plasma-atomic emission spectrometer. Although encapsulated Gd exhibited lower relaxivity than MRbester®, which is widely used for clinical diagnosis, because of limited diffusion across the liposome membrane, Gd250 liposomes showed much higher cellular uptake than that of MRbester®. In Gd250 liposomes, Gd was highly accumulated in B16F10 cells, which could provide improved contrast sensitivity for molecular imaging. Additionally, in Gd250 liposomes, Dox was highly internalized, which could enhance its cancer therapeutic effects. Consequently, we suggest that dual functional liposomes can be used as therapeutic and diagnostic carriers.

Simple fabrication of a smart microarray of polystyrene microbeads for immunoassay

We describe a simple method to fabricate an array of polystyrene microbeads (PS microbeads) conjugated with an elastin-like polypeptide (ELP) on a glass surface using a removable polymer template (RPT). A thin layer of adhesive was spun-cast on glass and cured by UV radiation. Micropatterns of an RPT were then transferred onto the surface by microcontact printing. The adhesion of PS microbeads on the surface depended on the adhesion performance of the adhesive layer, which could be adjusted by irradiation time. An array of PS microbeads conjugated with ELP was used for a smart immunoassay of prostate-specific antigen (PSA), a cancer marker. By controlling the phase transition of ELP molecules, PSA molecules were selectively adhered or released from the bead surface. The selective and reversible binding of PSA molecules on the bead surface was characterized with fluorescence microscopy.

Gd(III)-DOTA-modified sonosensitive liposomes for ultrasound-triggered release and MR imaging

Ultrasound-sensitive (sonosensitive) liposomes for tumor targeting have been studied in order to increase the antitumor efficacy of drugs and decrease the associated severe side effects. Liposomal contrast agents having Gd(III) are known as a nano-contrast agent system for the efficient and selective delivery of contrast agents into pathological sites. The objective of this study was to prepare Gd(III)-DOTA-modified sonosensitive liposomes (GdSL), which could deliver a model drug, doxorubicin (DOX), to a specific site and, at the same time, be capable of magnetic resonance (MR) imaging. The GdSL was prepared using synthesized Gd(III)-DOTA-1,2-distearoyl-sn-glycero-3-phosphoethanolamine lipid. Sonosensitivity of GdSL to 20-kHz ultrasound induced 33% to 40% of DOX release. The relaxivities (r1) of GdSL were 6.6 to 7.8 mM−1 s−1, which were higher than that of MR-bester®. Intracellular uptake properties of GdSL were evaluated according to the intensity of ultrasound. Intracellular uptake of DOX for ultrasound-triggered GdSL was higher than that for non-ultrasound-triggered GdSL. The results of our study suggest that the paramagnetic and sonosensitive liposomes, GdSL, may provide a versatile platform for molecular imaging and targeted drug delivery.

Polypeptide-Mediated Switchable Microarray of Bacteria

This paper describes a feasible solution for the bacterial cell death and contamination from cell division that occurs in microfluidic applications. The method adopts a smart thermoresponsive surface, highly resolved micropatterns, and surface-functionalized bacteria tagged with thermoresponsive molecules. We developed a method for controllable bacterial attachment and detachment using an elastin-like polypeptide (ELP). To create a smart surface with switchable properties, the surface of a glass substrate was conjugated with thermoresponsive ELP molecules. The attachment of bacterial cells to the ELP surface was induced by the hydrophobic affinity of the ELPs on the glass surface to tagged ELPs on the bacterial surface. A cell-repellent polymer was micropatterned to create a highly resolved space for specific bacterial adhesion. Reversible bacterial attachment and detachment was achieved by controlling the thermoresponsive phase transition of ELP molecules. Five different types of bacteria were successfully conjugated with ELPs and arrayed on the surface. The viability of the bacteria that had attached to the surface was evaluated by determining colony forming units of released bacteria on an agar plate.

“Smart” microspheres for self-renewal of embryonic stem cells

Abstract