Joo-Woon Lee

Neuroactive conducting scaffolds: nerve growth factor conjugation on active ester-functionalized polypyrrole.

Electrically conductive and biologically active scaffolds are desirable for enhancing adhesion, proliferation and differentiation of a number of cell types such as neurons. Hence, the incorporation of neuroactive molecules into electroconductive polymers via a specific and stable method is essential for neuronal tissue engineering applications. Traditional conjugation approaches dramatically impair conductivities and/or stabilities of the scaffolds and ligands. In this study, we developed copolymers (PPy-NSE) of N-hydroxyl succinimidyl ester pyrrole and regular pyrrole, which can be immobilized with nerve growth factor (NGF) without significantly hindering electroconductivity. The presence of active ester groups was confirmed using reflectance infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) from the copolymers prepared from different monomer compositions. We selected PPy-NSE50 (polymerized from a 50 : 50 monomer ratio of pyrrole : pyrrole-NSE) for further modification with NGF because this copolymer retains good conductivity (approx. 8 S cm−1) and presents active ester groups for NGF immobilization. We tethered NGF on the PPy-NSE50 surface, and found that PC12 cells extended neurites similarly to cells cultured in NGF-containing medium. XPS and enzyme-linked immunosorbent assay confirmed that NGF immobilized via the active ester on the PPy-NSE50 film was stable for up to 5 days in phosphate-buffered saline solution. Also, application of an external electrical potential to NGF-immobilized PPy films did not cause a significant release of NGF nor reduce their neurotrophic activity. This novel scaffold, providing electroconductive and neurotrophic activities, has potential for neural applications, such as tissue engineering scaffolds and biosensors.

Analysis of the Initial Burst of Drug Release Coupled with Polymer Surface Degradation

AbstractPurpose. Local pH effect on the release of a model pH-inert hydrophobic drug coupled with polymer degradation is described at the induction phase of biodegradable polymer erosion for better understanding the nature of initial burst of a drug. Methods. Using a novel approach with time-of-flight secondary ion mass spectrometry, both surface concentration of Ph3N and degradation kinetics of PLLA are simultaneously and independently determined from a model Ph3N/PLLA (20:80 wt%) blend matrix (t ≈ 0.4 μm on 1.0 cm2). In vitro hydrolysis of the model blend matrix is investigated for short-term periods (<24 h) at physiologic pH and temperature and compared to basic pH. Results. The rate of PLLA degradation is accelerated by a factor of ∼3 when using basic pH in vitro, but the rate of Ph3N accumulation at the surface is accelerated by a factor of ∼6. Conclusions. A new quantitative method has been developed to examine the earliest stages of polymer degradation and drug release. It was applied to a model system that could not be examined by traditional in vitro methods. For the model system studied the release of a low molecular weight hydrophobic drug at the induction phase of polymer erosion is related to but not singularly dependent on degradation kinetics.

Crystalline trigonal micropyramids composed of potassium carbamate moiety

Generating nanoand microstructured crystalline materials has become an important field in nanoscience, nanotechnology, and microtechnology for the practical processing of electronic, sensory, and optical devices. A wide range of biomineralization processes has been developed for creating hierarchical materials with exquisite structures and shapes at various range of length scales. In principle, an important requirement in the ‘synthesis with construction’ of biomimetic materials is control over crystallization, which can be guided by specific molecular recognition at interfaces. Although the morphogenetic foundations for the diversity and evolution of biomineralization remain largely unrealized, controlling crystallization processes can direct the unique shapes, sizes, patterns, polymorphs, and properties. Therefore, mimicking biomineralization may become a way of synthesizing crystalline materials with complexity of form and structure. Lee and White previously reported mineralization processes to give specific polymorphs and morphologies of carbonate derivatives at the air interface of aminosiloxane-based nanomatrixes under mild conditions. The nucleation and growth of crystalline materials were matrix-mediated on mesoporous poly(γ-aminopropyl triethoxysilane) (PAPS), where CO2 (0.03%) from air was utilized as a carbon source in the mineralization process under relative humidity 50%~ 60%. Mineralization from the matrixes (ca. 40-μm thick) of NaOH-catalyzed PAPS, denoted as Na/PAPS, led to the formation of crystalline Na3(CO3HCO3)·2H2O with exquisite floral shape. White et al. also reported self-organized fibrous nanostructures at the interface with air of the thin film (ca. 50-nm thick) of PAPS matrix spin-cast on sodalime glass substrates. The phenomenon was related to dissolved CO2 (aq) from air and Na ions leached out from the substrates. The growth of fibrous nanonetworks was directly dependent on the Na concentration segregated at the air interface of PAPS matrixes. It was explained that the selfassembly of nanofibers was attributed to hydrogen bonding and electrostatic interaction between Na and carbamate (-NHCO2) ions. While, when replacing NaOH with KOH, the growth of HCO2K-filled fibrous KHCO3 microtubes was mediated from the thick film (ca. 40-μm thick) of K/ PAPS deposited on boron-doped SiO2/Si(100) wafers. The proposed mineralization mechanism involved both a catalytic cycle via the reproduction of potassium carbamate (-NHCO2K) as a key intermediate for growing KHCO3 microtubes at the exposed interface with air and the photoelectrochemical reduction of CO3 to HCO2 at the buried interface with the substrate, e.g., a p-type SiO2 semiconductor, followed by the capillary action of the microtubes to collect ionic HCO2. Here, this research presents the results from the further exploration in the thin film version (ca. 50nm thick) of the K/PAPS matrix system, leading to the growth of trigonal micropyramids composed of crystalline carbamates matrix-mediated at the air-matrix interface.

Aptamer-based optical switch for biosensors

In this review, we will discuss aptamer technologies including in vitro selection, signal transduction mechanisms, and designing aptamers and aptazyme for label-free biosensors and catalysts. Dye-displacement, a typical label-less method, is described here which allows avoiding relatively complex labeling steps and extending this application to any aptamers without specific conformational changes, in a more simple, sensitive and cost effective way. We will also describe most recent and advanced technologies of signaling aptamer and aptazyme for the various analytical and clinical applications. Quantum dot biosensor (QDB) is explained in detail covering designing and adaptations for multiplexed protein detection. Application to aptamer array utilizing self-assembled signaling aptamer DNA tile and the novel methods that can directly select smart aptamer or aptazyme experimentally and computationally will also be finally discussed, respectively.