Biomedical subjects

Tung Siu

Publications and source records attributed to Tung Siu.

5 recordsLinked to original sources

PubMed2007

Microdevice-based delivery of gene products using sonoporation.

This paper presents a proof-of-concept miniature device for delivery of antisense oligonucleotides (ASO). A piezoelectric, lead zirconate titanate (PZT) plate (0.5 cm(2) x 0.75 mm) is used to transfect cells using cavitation-induced sonoporation. Both human umbilical vein endothelial cells (HUVEC) and human prostate cancer cells (PC3) are investigated in vitro. Preliminary results show that after sonication, the transfection rate for HUVEC increases by 96% compared to controls (p < 0.01). For PC3, the transfection rate increases by 31% compared to controls (p < 0.02). This research can potentially be applied in realizing a microelectromechanical system (MEMS)-based device for gene therapy in cancer treatment.

Cell Line, Tumor↗

PubMed2006

Comparison of cellular strain with applied substrate strain in vitro.

Strain magnitudes within tenocytes undergoing substrate tensile strain are not well defined. It was hypothesized that strain magnitudes at the cellular level would reflect those of the applied substrate (equibiaxial or uniaxial) strain. A vacuum-operated device was used to apply equibiaxial or uniaxial tension to a flexible substrate upon which tenocytes were cultured in monolayer. Images of tenocytes labeled with Fura-2, to detect free intracellular calcium ions, and MitoFluor Green, to detect mitochondria, were taken prior to strain and for 20 min during application of static strain. A custom-written, texture correlation program computed strain magnitudes in the cell based on the change in pixel pattern displacements between images of non-strained and strained cells. On average, cellular strain was approximately 37+/-8% and 63+/-11% of the applied equibiaxial and uniaxial substrate strain, respectively. The largest cell strains were detected in cells oriented parallel to the direction of applied uniaxial tensile strain. However, strain magnitudes within a cell were heterogeneous. The variance in strain magnitude within and among tenocytes is dependent on cell orientation, cell stiffness, cytoskeleton organization, subcellular organelles, or placement and type of cell-substrate contacts. Results of the present study indicate that cultured tenocytes experience a moderate fraction of the applied substrate strain.

Animals↗

PubMed2005

Development of electrochemical processes for nitrene generation and transfer.

An electrochemical strategy for running nitrogen-transfer reactions on chemically inert anode surfaces has been developed. The generation and trapping of highly reactive nitrene-transfer reagents can be accomplished under mild conditions on platinum electrodes. The key factor that accounts for the high levels of chemoselectivity in this process is the phenomenon of overpotential. We have found that molecules that are similar in terms of propensity toward oxidation can be differentiated on the basis of their affinity to a given electrode surface. Thereby, reactive species can be selectively generated in the presence of acceptor molecules of interest. Specifically, a wide range of structurally dissimilar olefins can be transformed into the corresponding aziridines in the presence of N-aminophthalimide. Likewise, nitrene generation in the presence of sulfoxides leads to their chemoselective transformation into the corresponding sulfoximines. In this paper we discuss the underlying mechanistic foundation of these reactions.

Journal Article↗

PubMed2002

Electrochemical imination of sulfoxides using N-aminophthalimide.

[reaction: see text] A novel electrochemical sulfoxide imination process is described. Our approach starts with a highly selective nitrene transfer from N-aminophthalimide to a variety of sulfoxides. This oxidative treatment is followed by reductive N-N bond cleavage under the controlled current conditions, which leads to a range of parent NH sulfoximines. In addition to solving the challenging problem of removing the N-phthalimido group, the overall process avoids the use of toxic oxidants and metal additives.

Electrochemistry↗

PubMed2002

Practical olefin aziridination with a broad substrate scope.

The present study illustrates the possibility of a rational approach that bypasses the requirement for stoichiometric amounts of toxic oxidants and metal additives (including reagents and catalysts) in organic redox reactions. We describe an aziridination process that delivers a nitrene functionality to olefins from a readily available N-aminophthalimide. Remarkably, both electron-rich and electron-poor olefins are converted to aziridines with high efficiency. The continuum of applied potentials and the heterogeneous nature of reactions at electrode surfaces allow for the electrochemical discrimination of substrates which have similar redox potentials and therefore cannot be selectively reduced or oxidized using soluble reagents. This selectivity is due to the phenomenon of overpotential, the kinetic inhibition of electron transfer on a particular electrode surface.

Journal Article↗