Samo Penič

Morphological alterations of T24 cells on flat and nanotubular TiO2 surfaces.

Aim To investigate morphological alterations of malignant cancer cells (T24) of urothelial origin seeded on flat titanium (Ti) and nanotubular titanium dioxide (TiO2) nanostructures. Methods Using anodization method, TiO2 surfaces composed of vertically aligned nanotubes of 50-100 nm diameters were produced. The flat Ti surface was used as a reference. The alteration in the morphology of cancer cells was evaluated using scanning electron microscopy (SEM). A computational model, based on the theory of membrane elasticity, was constructed to shed light on the biophysical mechanisms responsible for the observed changes in the contact area of adhesion. Results Large diameter TiO2 nanotubes exhibited a significantly smaller contact area of adhesion (P < 0.0001) and had more membrane protrusions (eg, microvilli and intercellular membrane nanotubes) than on flat Ti surface. Numerical membrane dynamics simulations revealed that the low adhesion energy per unit area would hinder the cell spreading on the large diameter TiO2 nanotubular surface, thus explaining the small contact area. Conclusion The reduction in the cell contact area in the case of large diameter TiO2 nanotube surface, which does not enable formation of the large enough number of the focal adhesion points, prevents spreading of urothelial cells.

Characterization of integrated thin film Pt heater and temperature sensors on Si platform

In this paper the design, fabrication methods and characterization of thin film meandered Pt resistive heater (size 20 × 20 mm2) with integrated Pt sensors on Si platform is presented. Pt heaters and temperature sensors were fabricated simultaneously by DC sputtering method. It was found that the fabrication process has significant influence on the electrical properties of the realized thin film resistive layers, which also explains the discrepancies between the calculated and measured values that were obtained during this work. Annealing temperature of the Pt layers was found to influence significantly the final resistance of the deposited layer and was performed at 500°C. To reduce the heat loss, the heater and temperature sensors were covered by Pyrex glass with prefabricated cavity. By this new approach, the power consumption was reduced due to improved thermal insulation. A comparative study was performed and showed that we can decrease the power consumption by more than 25% only by this approach. Measured temperature coefficient of resistance (TCR) for temperature sensors and the heater was between 1400-1700 ppm and showed that also the heater can be used as temperature sensing element.

On the role of external force of actin filaments in the formation of tubular protrusions of closed membrane shapes with anisotropic membrane components

Biological membranes are composed of different components and there is no a priori reason to assume that all components are isotropic. It was previously shown that the anisotropic properties of membrane components may explain the stability of membrane tubular protrusions even without the application of external force. Our theoretical study focuses on the role of anisotropic membrane components in the stability of membrane tubular structures generated or stabilized by actin filaments. We show that the growth of the actin cytoskeleton inside the vesicle can induce the partial lateral segregation of different membrane components. The entropy of mixing of membrane components hinders the total lateral segregation of the anisotropic and isotropic membrane components. Self-assembled aggregates formed by anisotropic membrane components facilitate the growth of long membrane tubular protrusions. Protrusive force generated by actin filaments favors strong segregation of membrane components by diminishing the opposing effect of mixing entropy.

Thermal Fluctuations of Phospholipid Vesicles Studied by Monte Carlo Simulations

Abstract This work presents the theoretical basis for Monte Carlo simulations of thermally fluctuating lipid bilayers. The purpose of such simulations is to obtain additional insight into the mechanical processes involved in thermal fluctuations of lipid bilayers and to test and limit some of the assumptions used in established theoretical models employed in measurements of the elastic properties of lipid membranes. The two-dimensional and three-dimensional models are explained and discussed. A dynamically triangulated surface model of the membrane is adapted to the thermally fluctuating vesicle with constant volume and local membrane stretching. The microstates of the vesicle are sampled according to the Metropolis algorithm, where fluctuations that conserve the volume of the vesicle are produced, while the energy of any given microstate of the vesicle consists of the bending and stretching energies of the vesicle. The vesicle shape is then approximated by a set of spherical harmonics. The results of the spectral analysis of thermally fluctuating vesicles in our simulations open questions that are discussed in the concluding section.

Modeling of closed membrane shapes

Closed biological membranes were considered within the spontaneous curvature model. Ground state membrane shapes were compared with Monte Carlo simulations in the thermal equilibrium, where membranes are subject to thermal uctuations. The results of the two approaches correspond well with each other. The oblate discocyte membrane shapes are obtained in the ground state but can become metastable when thermal uctuations are taken into account. The nematic ordering in oblate and stomatocyte vesicle membranes was also studied. It was conrmed

Improvements of Roughness Control in Micromachining of Silicon Microchannels

Investigation of wet anisotropic etching of silicon microchannels on (100) silicon is presented with the emphasis to simultaneously fabricate bifurcated silicon channels in and directions. Silicon crystal planes that are playing major role of microchannels sidewalls are characterized for their roughness and etch rates. Beside the standardly smooth {111} crystal planes, microroughness of {110} sidewalls is of particular interest. It is shown that by implementing TMAH-Triton etchant, the roughness of {110} sidewalls was significantly improved over the standard KOH-IPA or TMAH-IPA etching system without affecting the neighboring crystal plane sidewalls. Agitation of the etching solution is found to have significant influence on both, the etch rate and surface roughness. Optimal etching conditions were determined to obtain smooth microchannel sidewalls in two major directions. Furthermore, reduced convex corner underetching was obtained compared to other etching system. Two viable solutions for the connecting through holes or vias are presented by using single or double mask layer photolithography prior to performing the etching step.© 2007 ASME