Biomechanics plays a central role in breast epithelial morphogenesis. In this study we have used 3D cultures in which
normal breast epithelial cells are able to organize into rounded acini and tubular ducts, the main structures found in the
breast tissue. We have identified fiber organization as a main determinant of ductal organization. While bulk rheological
properties of the matrix seem to play a negligible role in determining the proportion of acini versus ducts, local changes
may be pivotal in shape determination. As such, the ability to make microscale rheology measurements coupled with
simultaneous optical imaging in 3D cultures can be critical to assess the biomechanical factors underlying epithelial
morphogenesis. This paper describes the inclusion of optical tweezers based microrheology in a microscope that had
been designed for nonlinear optical imaging of collagen networks in ECM. We propose two microrheology methods and show preliminary results using a gelatin hydrogel and collagen/Matrigel 3D cultures containing mammary gland
We demonstrate how optical trapping and manipulation can be used to assemble microstructures. The microstructures we
show being automatically recognized and manipulated are produced using the two-photon polymerization (2PP)
technique with submicron resolution. In this work, we show identical shape-complementary puzzle pieces being
manipulated in a fluidic environment forming space-filling tessellations. By implementation of image analysis to detect
the puzzle pieces, we developed a system capable of assembling a puzzle with no user interaction required. This allows
for automatic gathering of sparsely scattered objects by optical trapping when combined with a computer controlled
motorized sample stage.
With the aid of phase-only spatial light modulators (SLM), generalized phase contrast (GPC) has been applied with great
success to the projection of binary light patterns through arbitrary-NA microscope objectives for real-time threedimensional
manipulation of microscopic particles. Here, we review the analysis of the GPC method with emphasis on
efficiently producing speckle-free two-dimensional grey-level light patterns. Numerical simulations are applied to
construct 8-bit grey-level optical potential landscapes with high fidelity and optical throughput via the GPC method.
Three types of patterns were constructed: geometric block patterns, multi-level optical trap arrays, and optical obstacle
arrays. Non-periodic patterns were accurately projected with an average of 80% diffraction efficiency. Periodic patterns
yielded even higher diffraction efficiencies, averaging 94%, by the utilization of large-aperture phase contrast filters.
Three-dimensional light structures can be created by modulating the spatial phase and
polarization properties of an an expanded laser beam. A particularly promising technique is
the Generalized Phase Contrast (GPC) method invented and patented at Risø National
Laboratory. Based on the combination of programmable spatial light modulator devices and
an advanced graphical user-interface the GPC method enables real-time, interactive and
arbitrary control over the dynamics and geometry of synthesized light patterns. Recent
experiments have shown that GPC-driven micro-manipulation provides a unique technology
platform for fully user-guided assembly of a plurality of particles in a plane, control of
particle stacking along the beam axis, manipulation of multiple hollow beads, and the
organization of living cells into three-dimensional colloidal structures. Here we present
GPC-based optical micromanipulation in a microfluidic system where trapping experiments
are computer-automated and thereby capable of running with only limited supervision. The
system is able to dynamically detect living yeast cells using a computer-interfaced CCD
camera, and respond to this by instantly creating traps at positions of the spotted cells
streaming at flow velocities that would be difficult for a human operator to handle.
Using a single phase-only spatial light modulator (SLM), we present a compact GPC-based optical trapping system for
interactively manipulating microscopic particles in three dimensions (3D) and in real-time. We employ only one GPC 4<i>f</i>
setup, which transforms 2D phase into intensity patterns, and utilize the SLM to form two phase-encoding regions
defined by two equally sized apertures - one centered at x = x<sub>0</sub> and the other at x = -x<sub>0</sub> (with the optical axis centered at
x = 0). Reconfigurable intensity patterns associated with the two independently addressable SLM-apertures are relayed
to the sample volume to form a dynamic array of counterpropagating-beam traps. We discuss the experimental
demonstrations showing 3D trapping of microparticles using the presented optical setup.
Helico-conical optical beams are a recently introduced class of beams that multiplicatively combine helical and conical phase fronts. Focusing these beams leads to a spiral intensity distribution at the focal plane of the lens. Further theoretical and experimental examination reveals interesting three-dimensional intensity patterns near the focal region, including a cork-screw structure around the optical axis. Variations on these light distributions based on the superposition of multiple helico-conical beams are also presented here. These beams are expected to yield interesting dynamics when applied to the optical trapping of microscopic particles, such as dielectric microspheres or even biological cells.
Recently, a new type of beam termed "spiral optical beam" has been introduced [Alonzo, <i>et al.</i>, Opt. Express <b>13</b>, 1749 (2005)]. Spiral beams are created from multiplicative mixtures of helical and conical phase distributions. Helico-conical phase fronts that generate these novel beams are not achieved with a sequence of a corkscrew wave-plate and an axicon (as this sequence gives a sum of helical and conical phase terms). Nevertheless, the availability of phase-only spatial light modulators (SLM) allows one to directly imprint helico-conical phase functions on an incident plane wave and provides an easy way to modify the profile of the encoded phase. Focusing the phase-modified field results in spiral intensity distributions that may find use for optical manipulation of mesoscopic particles. In this paper, we have extended the discussion to translation and rotation (as well as chirality switching) of the spiral beams using SLM control.