Shilpa Sivashankar

Enhanced cell viability and cell adhesion using low conductivity medium for negative dielectrophoretic cell patterning.

Negative dielectrophoretic (n‐DEP) cell manipulation is an efficient way to pattern human liver cells on micro‐electrode arrays. Maintaining cell viability is an important objective for this approach. This study investigates the effect of low conductivity medium and the optimally designed microchip on cell viability and cell adhesion. To explore the influence of conductivity on cell viability and cell adhesion, we have used earlier reported dielectrophoresis (DEP) buffer with a conductivity of 10.2 mS/m and three formulated media with conductivity of 9.02 (M1), 8.14 (M2), 9.55 (M3) mS/m. The earlier reported isotonic sucrose/dextrose buffer (DEP buffer) used for DEP manipulation has the drawback of poor cell adhesion and cell viability. A microchip prototype with well‐defined positioning of titanium electrode arrays was designed and fabricated on a glass substrate. The gap between the radial electrodes was accurately determined to achieve good cell patterning performance. Parameters such as dimension of positioning electrode, amplitude, and frequency of voltage signal were investigated to optimize the performance of the microchip.

3D biomimetic chip integrated with microvascular system for studying the liver specific functions

We describe the design and fabrication of 3D chip that enables the cell co-culture under continuous flow perfusion and repeated in situ observation by light microscopy. Thin polydimethylsiloxane (PDMS) membrane was etched to create an array of through-holes, and sandwiched between two PDMS channels to form an upper chamber and lower chamber. In the upper chamber hepatocytes (HepG2) and fibroblasts (3T3) were co-cultured to mimic the liver whereas in the lower structure endothelial cells (HMEC-1) were cultured to mimic the vascular system at the cellular scale for providing nutrients to the in vitro liver mimicked in the upper channel.

Experimental investigation of bulk response of cells on optoelectronic dielectrophoresis chip

The mechanism of the particle interactions is still inconclusive, even though many researchers have tried to figure out the particle-particle interactions under the influence of electric field. In this paper we report an experimental investigation of electrostatic attraction and repulsion of endothelial cells in an image-driven light induced dielectrophoresis (DEP) apparatus. The optoelectronic tweezers (OET) device consists of a planar structure having one or more portions which are photoconductive to convert incoming light to a change in the electric field pattern. When the cells are manipulated in OET chip at a frequency near the threshold of electrolysis, cells exhibits numerous interesting phenomena such as spinning, collision, rotation and pearl chain effect in three-dimensional (3D) space. All of these cell behaviors at such critical frequencies on this OET chip are reported.

3D microstructure integrated bioreactor system for transgenic mice thick liver tissue culture

A bioreactor system with 3-diementional (3D) Poly ethylene glycol diacrylate (PEGDA) structures in the culture-well to provide 3D culturing conditions is proposed here. The culture medium diffused through the tissue cause of the nozzle shaped flow channel at the outlet of each bioreactor and tissue being held between PEGDA microstructures. This helps in delivering the required nutrients to core of the tissue, eliminating the mass transfer problem. Presence of PEGDA based microstructures resulted in better circulation of medium around the liver tissue and mesothelial cells providing 3D microenvironment and to retain intact architecture. The flow rate was 20 μl/min and the flow direction is changed every 12hrs for effective removal of waste products and toxins. Tissues slices of 2mm thick have been cultured for 12 days with 76% viable cells.

Emulated circulatory system integrated with lobule-mimetic liver to enhance the liver function

In the proposed paper, we report dielectrophoresis (DEP) liver lab chip integrated with Poly ethylene glycol diacrylate (PEGDA) based blood vessel within the microfluidic system for reconstructing the engineered liver tissue with the feature of liver function enhancement. The titanium (Ti) electrodes are well designed to provide positive dielectrophoresis (pDEP) and negative dielectrophoresis (nDEP) force to pattern HepG2 and 3T3 fibroblast cells. To mimic the blood flow direction of the liver lobule in vivo, we have integrated the reconstructed liver lobule with hydrogel encapsulated blood vessel. As smooth muscle cells and endothelial cells are the main components of blood vessel, we have utilized these cells and encapsulated within PEGDA hydrogel to mimic blood vessels. When assayed for urea concentration in cultured medium for five time points, the trend illustrated the enhanced metabolism of hepatocytes via blood vessel integrated lobule-mimetic pattern.

In-vitro transgenic mice liver tissue culture via hydrodynamic flow perfusion bioreactor

We report a Poly methyl methacrylate (PMMA) bioreactor in which hepatitis B virus (HBV) infected transgenic mice liver tissue has been cultured for long term with the continuous flow of culture medium, surrounded by mesothelial cells to provide 3-dimensional culturing conditions with adequate nutrient exchange. PDMS membrane was fabricated and a layer of mesothelial cells were cultured on it. Further this membrane was deformed and positioned on the microchannel by suction through the holes at the bottom of the channel. Liver tissue of transgenic mice was introduced on PDMS membrane. The experimental results proved that the proposed bioreactor portrays the in-vivo conditions better, with substantial improvement of liver-specific functions such as sufficient antigen expression, better structural integrity when compared to conventional static culture method. The in-vitro culture period of sliced liver tissue in our bioreactor was extended for 9 days to facilitate drug screening applications.

Dielectrophoretic concentrator for enhanced performance of poly-silicon nanowire field effect transistor for biosensing application

Biological and medical fields have authenticated stupendous advancement in the development of biosensors and biochips. The development of highly sensitive biological sensors is need of the hour. This research work utilizes the dielectrophoretic concentrator chip with titanium (Ti) electrodes to shape the electric field, to pre-concentrate deoxyribo nucleic acid (DNA) within microfluidic channel onto nanowire region of poly-silicon nanowire field effect transistor (poly-Si NWFET). Preconcentration of biomolecules at the constriction site was demonstrated by focusing the DNA with negative dielectrophoresis (nDEP) manipulation technique. After integrating the DEP device with poly-Si NWFET, the I-VG curve was plotted to ensure n-type behavior.