M. Taheri

Modeling of various contact theories for the manipulation of different biological micro/nanoparticles based on AFM

In this article, the modeling of various contact theories to be applied in the biomanipulation of different micro/nanoparticles based on the atomic force microscope has been studied, and the effect of adhesion force in different contact models on indentation depth and contact angle between tip and substrate has been explored for the target biological micro/nanoparticle. The contact models used in this research include the Hertz, JKR, DMT, BCP, COS, PT, and the SUN models. Also, the target particles comprise the biological micro/nanoparticles of DNA, yeast, platelet, and nanobacterium. Previous research works have investigated the contact models for the manipulation of non-biological gold micro/nanoparticles in the air environment. Since in a real biomanipulation situation, the biological micro/nanoparticles are displaced in biological environments; in this article, various contact theories for the biomanipulation of biological micro/nanoparticles in different biological environments have been modeled and compared for the first time. The results of modeling indicate that the use of Hertz contact model in analyzing the biomanipulation of biological nanoparticles is not appropriate, because it does not take the adhesion force into consideration and thus produces a significant error. Also, all the six contact models developed in this article show larger deformations for studied bionanoparticles in comparison to the gold nanoparticles, which can be justified with regards to the mechanical properties of gold.

Manipulation with atomic force microscopy: DNA and yeast micro/nanoparticles in biological environments

Although significant attempts have been made to automate the manipulation of biological cells with atomic force microscopy, these efforts have faced many limitations and restrictions. Researchers have recently tried to measure the interacting forces in order to improve the reliability of manipulation operations with atomic force microscopy. By manipulation of micro/nanoparticles of different materials and shapes, as the target particles, in different biological environments, the interacting forces existing between these micro/nanoparticles and the biological environment will be different from those in the air medium. Therefore, in this paper, first, a general overview and simulation of the important forces acting in the biological environment was presented, and forces such as the adhesion force, hydration force and the electrostatic double-layer force were modeled and simulated in different environments (e.g. water, alcohol and blood plasma). After different biological environments (in comparison with the air medium) were explored and modeled, the manipulation operations with atomic force microscopy were simulated for different micro/nanoparticles such as gold, DNA and yeast by considering the forces existing in various biological environments. The results of manipulation in this paper indicate that in the air and liquid environments, the biological particles (DNA and yeast) will start to move after a longer time and by a higher magnitude force relative to the gold particles. This outcome is predictable, given the properties and stickiness of the biological particles. Also by comparing the obtained results, it is found that the critical force and critical time of manipulation with atomic force microscopy for gold nanoparticles slightly increase in water relative to air, which can be due to the properties of water and the existing forces in water that resist against the movement of nanoparticles. Finally, the obtained results were compared with the available empirical results. It can be seen that the obtained simulation values have a good correlation with the empirical results. The closeness of these two values confirms the validity of the performed simulation.

Dynamic modeling and simulation of rough cylindrical micro/nanoparticle manipulation with atomic force microscopy.

In this paper, the process of pushing rough cylindrical micro/nanoparticles on a surface with an atomic force microscope (AFM) probe is investigated. For this purpose, the mechanics of contact involving adhesion are studied first. Then, a method is presented for estimating the real area of contact between a rough cylindrical particle (whose surface roughness is described by the Rumpf and Rabinovich models) and a smooth surface. A dynamic model is then obtained for the pushing of rough cylindrical particles on a surface with an AFM probe. Afterwards, the process is simulated for different particle sizes and various roughness dimensions. Finally, by reducing the length of the cylindrical particle, the simulation condition is brought closer to the manipulation condition of a smooth spherical particle on a rough substrate, and the simulation results of the two cases are compared. Based on the simulation results, the critical force and time of manipulation diminish for rough particles relative to smooth ones. Reduction in the aspect ratio at a constant cross-section radius and the radius of asperities (height of asperities based on the Rabinovich model) results in an increase in critical force and time of manipulation.

Modeling of contact theories for the manipulation of biological micro/nanoparticles in the form of circular crowned rollers based on the atomic force microscope

This article has dealt with the development and modeling of various contact theories for biological nanoparticles shaped as cylinders and circular crowned rollers for application in the manipulation of different biological micro/nanoparticles based on Atomic Force Microscope. First, the effective contact forces were simulated, and their impact on contact mechanics simulation was investigated. In the next step, the Hertz contact model was simulated and compared for gold and DNA nanoparticles with the three types of spherical, cylindrical, and circular crowned roller type contact geometries. Then by reducing the length of the cylindrical section in the circular crowned roller geometry, the geometry of the body was made to approach that of a sphere, and the results were compared for DNA nanoparticles. To anticipatory validate the developed theories, the results of the cylindrical and the circular crowned roller contacts were compared with the results of the existing spherical contact simulations. Following t...

Three-dimensional modeling and simulation of the AFM-based manipulation of spherical biological micro/nanoparticles with the consideration of contact mechanics theories

By using an atomic force microscope as an ideal instrument for the manipulation of biological particles, the user deprives herself of the direct observation of the manipulation process in real time. In order to understand this process and to remove this limitation, an auxiliary method should be adopted which itself is not hampered by such a constraint. One of the approaches that has become of interest in this regard is the atomic force microscope based modeling and simulation of the manipulation process. Up to now, two-dimensional simulations have been performed using this technique; and as for three-dimensional modeling, only non-biological particles with cylindrical geometries have been investigated without the consideration of contact mechanics. For the first time, the present research has focused on the three-dimensional modeling and simulation of spherical biological particles in air medium while considering the mechanics of contact. Based on the simulation results, the manipulation force and indentation depth values that are produced in the contacts made during the manipulation process depend on the properties of the biological micro/nanoparticles involved; and in comparison with the two-dimensional case, increased values of manipulation force, contact radius and indentation depth have been observed in the three-dimensional models.

Investigating the effective parameters in the Atomic Force Microscope-based dynamic manipulation of rough micro/nanoparticles by using the Sobol sensitivity analysis method

Due to the substantial complexities of atomic force microscope (AFM)-based dynamic manipulation models, these models require the identification of many parameters and inputs with varying levels of sensitivity. Various sensitivity analysis (SA) methods can be used to achieve such a goal. The Sobol method is one of the famous SA approaches based on variance, which is widely used today in various study and scientific fields. The dynamic models for the manipulation of micro/nanoparticles, which have been investigated in previous works by means of the SA methods, have involved spherical nanoparticles with smooth surfaces. Since different micro/nanoparticles have a variety of geometries and since surface roughness plays a significant role in the contact of these particles with different surfaces, in this paper, the sensitivity of the AFM-based dynamic manipulation model of rough micro/nanorods has been analyzed. By considering more diverse geometrical conditions for the target micro/nanoparticle, including a cylindrical geometry and rough surfaces, many geometrical parameters enter the model. Therefore, in this study, simulations have been performed by the Sobol SA approach in order to determine the sensitivity of the input manipulation parameters to the critical output values of manipulation, for the two groups of AFM and environmental parameters. Based on the results obtained from these simulations, cantilever thickness constitutes the most sensitive parameter in the manipulation of rough cylindrical micro/nanoparticles. By analyzing the sensitivities of environmental parameters, it was found that the parameter of surface roughness in the range of 0–0.04 is highly sensitive for rough cylindrical micro/nanoparticles.

Simulating the impact between particles with applications in nanotechnology fields (identification of properties and manipulation)

The aim of this research is to study and simulate the Andrews impact theory and its potential in identifying the properties of soft biological particles and in manipulating these particles at nano scale by means of the atomic force microscope (AFM). The reason for employing the Andrews theory in this research is that this theory is unique in considering the plastic state of soft biological nanoparticles. First, the required equations for the estimation of two basic parameters (i.e., indentation depth and contact radius) used in the identification of properties and manipulation of these particles were derived. Since none of the previous works has considered the velocity of biological nanoparticles, and since the impact of biological particles with AFM tip and with substrate has been ignored in these works, the impacts between AFM tip and DNA particle and between DNA particle and substrate were simulated in this paper. The findings showed that before applying a load to a particle by a cantilever, due to the impact of AFM tip with the particle, a relatively noticeable deformation was created. This deformation, which has been disregarded in previous works up to now, can play an important role in identifying the properties of nanoparticles, in manipulation and even in controlling the cantilever of the atomic force microscope. The existing experimental results were used to validate the findings of this research.

Fabrication of Supports for Solid Oxide Fuel Cells by Powder Injection Molding

In this paper the processing steps for producing SOFC (Solid Oxide Fuel Cell) supports by means of PIM (Powder Injection Molding) technique were investigated. Injection molding parameters in this study were divided into pressure-related (injection pressure and packing pressure), temperature-related (nozzle temperature and mold temperature), and time-related (injection rate and holding time) parameters. Keeping the other parameters (pressure-related, temperature-related and time-related parameters) constant at an optimized value, the effects of each of the molding parameters above were investigated. The results show that the short shot, warpage, weld line and void are the most common defects in molded parts. According to the results the short shot could be seen in low values of injection pressure, injection rate, nozzle and mold temperature. Also, warpage could be seen in high values of mold temperature, injection and packing pressure. Poor weld line was another defect that could be seen in low values of injection pressure, injection rate, nozzle and mold temperature. Also the void was one of the most common defects that could be seen in high values of injection rate and nozzle temperatures. Finally, using optimized molding parameters, the molded parts underwent debinding and sintering processes. Based on the results of thermal shock tests and the porosity measurements of the sintered parts, these molded parts possessed relatively desirable characteristics.© 2011 ASME