The purpose of this work is to generate a theoretical model for the dynamics of a polystyrene microsphere under the influence of Gaussian beam optical tweezers (OTs) in the ray-optics regime. OTs use the radiation pressure from a focused laser beam to manipulate microscopic objects as small as atoms [1]. They have been used in the biological sciences to measure nanometer-range displacements, apply picoNewton-range forces, and determine the mechanical properties of DNA, cell membranes, whole cells, and microtubules. The proposed model takes into account the forces and moments imparted onto the microbead by the OTs beam, and uses a Newton-Euler Dynamics framework to generate the equations of motion. Although examination of dimensionless numbers and other indicators including, Reynolds number 10 −9 ≤ Re ≤ 10 −4 , Knudsen number 0.0001875, and the disproportionality between the mass and the viscous drag co-efficients O (10 −4 ), does not clearly indicate whether this is a multiscale problem or not; but, a numerical integration of the original model leads to a long simulation run-time, a few days. Moreover, investigation of the step size showed that the adaptive numerical integrator was proceeding with a picosecond step size in order to achieve the requested accuracy. This situation implies a multiscale feature involved in the dynamics of optical trapping process of the small bead. To address this issue, a multiscale model is developed that helps to significantly reduce the simulation run-time and reveals underdamped behavior of the bead. In order to verify the theoretical model, experiments were carried out on a microsphere bead with 1.6 μm diameter. A comparison of experimental data and simulation data indicate that this approach closely models microparticle behavior to the accuracy of the experiment under Gaussian beam optical tweezers.

Hierarchical designs of biological structures have remarkable physical, chemical mechanical and biological properties and functionalities over the wide range of length scales [1–4]. Man-made nanocomposites have dramatic improvement of the structural and mechanical properties but however they have very limited hierarchy [5]. Fish scales are bone-like tissues, which form a protective layer on the body of the fish and enable the fish to swim efficiently. Bones and bone-like parts in living organism are formed as tissues by self-assembly of bio-minerals and protein matrix. These tissues are bio-nanocomposites and have hierarchical structure ranging from nanoscale to macroscale [2–4]. Bio-hierarchy contains different bio-macromolecules, bio-minerals, interfacial bonds and porosity which result in gradient mechanical properties at multiple length scales [1–6]. Fish scale consists of inorganic bio-minerals and organic collagens [3,4]. Multilevel hierarchy influences elasticity, hardness and fracture toughness of fish scale. They have additional functions related to movement including reduction or increase of drag [7] and rapid manoeuvre while they are hunting or avoiding predators. In this article we report comparison studies of hierarchical nanocomposite of sardina pilchardus(sp) fish scale and man-made SiO 2 nanoparticles filled nanocomposites.

This article shows that the added mass due to fluid structure interaction significantly affects the vibrational dynamics of cilia-based devices. Our main contribution is to show that such damping effects cannot explain the substantial reduction in the resonant vibrational frequency of the cilia operating in liquid when compared to the natural frequency of the cilia in air. It is shown that an added-mass approach (that accounts for the inertial loading of the fluid) can explain this reduction in the resonant vibrational frequency when operating the cantilever-type devices in liquids. Additionally, it is shown that the added-mass effect can explain why the cilia-vibration amplitude is not substantially reduced in a liquid by the hydrodynamic drag force. Thus, this article shows the need to model the added-mass effect, both, theoretically and by using experimental results.

Micro swimming robots that mimic the motion of micro organisms can carry out a variety of medical tasks including drug delivery, micro surgery and minimally invasive diagnostic tasks. Micro organisms such as spermatozoa and bacteria use their flagella to propel themselves. The artificial micro swimmer presented in this study is composed of a body that carries a medical payload, and one wave propagating tail attached to it. In this study, forces and torques exerted on the tail structure by the surrounding fluid are computed with the help of corresponding force coefficients. Rigid body dynamics computations are carried out by four-dimensional quaternion configuration to eliminate numerical error accumulation during matrix integrations, and, hence, instantaneous rotation matrix for rigid body rotation is extracted from the quaternion. Propulsive force obtained by waving tail is balanced by the drag force on the micro swimmers’ total wet surface and dynamic behavior of the micro swimmer is obtained as a rigid body motion. The effect of swimmer and waving geometry is parameterized to study the swimming behavior. Simulations carried out to explore the effect of wave length, wave amplitude, driving frequency. Translational and rotational velocities and hydrodynamic power requirements are presented for each individual set of design parameters. Validity of the model is tested by comparing the numerical results and finite element simulation results. Lastly, the model is modified to utilize the mobility matrix coefficients obtained from inertia eliminated finite element simulations governed by time dependent Navier-Stokes equations.