Isamu Oh

Trapping and manipulation of a single micro-object in solution with femtosecond laser-induced mechanical force

A nondestructive and noncontact method to trap and manipulate a microparticle in solution is proposed by utilizing femtosecond laser-induced nonlinear phenomena. A 90μm diameter polystyrene bead in solution was trapped and manipulated by scanning femtosecond laser pulses around it, which was ascribed to shockwave, cavitation bubble, and jet flow. The maximum mechanical force exerted by laser irradiation was estimated to be over 1μN. In comparison with conventional optical tweezers, this method provides not only a much larger trapping force but also a noninvasive advantage.

Identification of small molecular compounds and fabrication of its aqueous solution by laser-ablation, expanding primordial cartilage

OBJECTIVE The discovery of small molecular compounds that expand cartilage is needed. We searched for small molecular compounds that expand cartilage or enhance the actions of bone morphogenetic proteins (BMPs) on cartilage. DESIGN Metatarsal primordial cartilage explants prepared from 14.5 days postcoitum (d.p.c.) mouse embryos were organ-cultured in the presence or absence of BMPs and/or 4-(5-Benzol[1,3]dioxol-5-yl-4-pyrldin-2-yl-1H-imidazol-2-yl)-benzamide hydrate (BPIB) and its related molecules. The perichondrium was removed from some of the cartilage explants by partial digestion with collagenase. BPIB aqueous solution was prepared by fragmenting BPIB crystals in water with laser irradiation and then added to cartilage explants in organ culture. RESULTS We found that small molecular compounds, BPIB, available as SB431542 from Sigma and its related molecules, expand primordial cartilage explants in organ culture. These molecules are transforming growth factor-β (TGF-β) inhibitors, and the addition of excess TGF-β reduced cartilage expansion induced by these molecules. The co-administration of BPIB and BMPs synergistically expanded cartilage explants. Removal of the perichondrium abolished BIPB-induced cartilage expansion but not BMP-induced cartilage-expansion, suggesting that BPIB, but not BMPs, expands cartilage through the perichondrium. Furthermore, we used the laser-ablation technique to generate BPIB aqueous solution in the presence of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) without the use of hazardous dimethyl sulfoxide (DMSO). The laser-ablation-generated BPIB aqueous solution was more stable, expanded cartilage explants more effectively than BPIB colloidal solution prepared with DMSO, and synergistically enhanced BMP-induced cartilage expansion. CONCLUSIONS A small molecular compound, BPIB, expands primordial cartilage explants. A BPIB aqueous solution was created by laser-ablation without using DMSO and proved to be biologically active.

SECONDARY CONVERGENCE IN FEMTOSECOND LASER TRAPPING

When femtosecond laser pulses pass through a trapped polystyrene bead, water breakdown is induced even though the energy of laser pulse is much lower compared to the threshold value of breakdown when the femtosecond laser directly irradiates in water. This mechanism is assigned to the secondary convergence of the laser by the trapped bead.

Femtosecond Laser Manipulation Techniques for Individual Patterning of Biological Micro-object

Several kinds of manipulation of biological cells were performed utilizing regeneratively amplified femtosecond laser system. When single-shot pulse of an amplified Ti: Sapphire femtosecond laser pulse is focused on a culture medium, shockwave and cavitation bubble are generated with little heating. An impulsive force resulting in these phenomena was applied to pttern specific cells form a culture substrate. Furthermore, laser trapping of cells was realized using high-repetition rate pulses from the laser oscillator. Although the cell was trapped stably when the laser power was less than 100 mW, the cell was burst above the threshold laser power. The bursting would be due to heating inside cell, on which the laser was focused and multiphoton absorption was induced. On the bases of these results, we propose a new methodology to pattern biological cells, which is speedy and flexible when compared with previous micropatterning methods.

SPATIAL LIGHT MODULATING AND MULTI-TRAPPING WITH A DMD

Although the digital micromirror device (DMD) has been considered to be a spatial light modulator (SLM) for a long time, it is seldom utilized for holographic tweezers practically because of its energy loss. In this work, a multi-trapping system built with a DMD is demonstrated. But a problem of dispersion is found when the DMD is applied to femtosecond laser, and its mechanism is studied.