The micro-domain provides excellent conditions for performing biological experiments on small populations of cells and has given rise to the proliferation of so-called lab-on-a-chip devices. In order to fully utilize the benefits of cell assays, means of retaining cells at defined locations over time are required. Here, the creation of scale-like cantilevers, inspired by biomimetics, on planar silicon nitride (Si3N4) film using focused ion beam machining is described. Using SEM imaging, regular tilting of the cantilever with almost no warping of the cantilever was uncovered. Finite element analysis showed that the scale-like cantilever was best at limiting stress concentration without difficulty in manufacture and having stresses more evenly distributed along the edge. It also had a major advantage in that the degree of deflection could be simply altered by changing the central angle. From a piling simulation conducted, it was found that a random delivery of simulated particles on to the scale-like obstacle should create a triangular collection. In the experimental trapping of polystyrene beads in suspension, the basic triangular piling structure was observed, but with extended tails and a fanning out around the obstacle. This was attributed to the aggregation tendency of polystyrene beads that acted on top of the piling behavior. In the experiment with bacterial cells, triangular pile up behind the cantilever was absent and the bacteria cells were able to slip inside the cantilever’s opening despite the size of the bacteria being larger than the gap. Overall, the fabricated scale-like cantilever architectures offer a viable way to trap small populations of material in suspension.
Micro-particle self-assembly provides an insight into the dynamics of particles in a well-understood force environment, interactions between particles, and processes where particles themselves modify the force environment. Various ways have been reported on creating microparticle assembly in optical traps. Yet the basis to understanding the nature of the assembly is to first comprehend trapping of a single sphere in a focused Gaussian laser beam. For spherical dielectric particles that are to be manipulated by a focused Gaussian laser beam, the axial trapping efficiency of this is a function of (i) the particle radius r, (ii) the ratio of the refractive index of particle over the medium, and (iii) the numerical aperture of the delivered light beam. From a comprehensive simulation conducted, we uncovered optical trapping regions in the 3D parameter space forming an iso-surface landscape with ridge-like contours. Using specific points in the parameter space, we drew attention to difficulties in using the trapping efficiency and stiffness metrics in defining how well particles are drawn into and held in the trap. An alternative calculation based on the maximum forward and restoration values of the trapping efficiency in the axial sense, called the trapping quality, was proposed. We also discuss the possibility of coupling optical trapping with other physical methods, notably capillary forces, in order to achieve effective microparticle assembly.
The modelling and simulation of periodic structures with defects define boundary value problems (BVPs) which
are conceptually and numerically difficult to solve. Innovative and problem-tailored analysis methods need to be
devised to solve defect problems efficiently and accurately. One possible attractive method is based on the ideas
related to the construction of Wannier functions. Wannier functions constitute a complete sequence of localised
orthogonal functions which are derived from associated periodic versions of defect problems. In this paper we
review general properties of Wannier functions from a linear algebra point of view, introduce an easy-to-use
symbolic notation for the diagonalisation of the governing equations and construct the Wannier functions for a
variety of phononic devices. Using certain distinguished properties inherent in the wavenumber-dependence of
the eigenvalues we prove the orthogonality and completeness of the Wannier functions in a conceptually novel