Laser-Powered Microbots Gently Transport Live Cells

Laser-Powered Microbots Gently Transport Live Cells

This project involves the manipulation and the assembly of micro-objects using optically controlled microrobots. Light patterns are used to control the movement of the microrobots. Objectives include the micro-assembly of objects, including live cells, and the parallel, independent control of multiple microrobots in one system.

The UH microrobot (visible in the top center of the image) was used to position these 100-µm-diameter glass beads to form “UH”.

Cell culturing devices

The cell culturing device project involves the trapping of cells in hydrogel scaffold in order to promote the cultivation of cells in 3D. Advances in cell culturing technology could lead to improved drug and therapy development, along with alternative ways to test live subjects. The project will also give a further insight into cell behavior, which could lead to the cure of various diseases.

For more information, see:

K. S. Ishii, W. Hu, S. A. Namekar, and A. T. Ohta, “An optically controlled 3D cell culturing system,” Advances in OptoElectronics, vol. 2011, Article ID 253989, 8 pages, 2011. doi:10.1155/2011/253989

Optoelectronic tweezers

Optoelectronic tweezers (OET) can be used to manipulate micro- and nano-scale particles, such as cells, carbon nanotubes, and nanowires. OET uses light-induced dielectrophoresis to enable this optically controlled manipulation. Dielectrophoresis is an electrokinetic force induced upon particles in a non-uniform electric field. OET integrates the flexibility and control of optical manipulation with the parallel manipulation and sorting capabilities of dielectrophoresis.

OET simulationElectric field profile of a circular OET particle trap.

We are exploring the use of optoelectronic tweezers for live / dead cell sorting for in vitro fertilization. A treatment available to men with sperm of limited mobility or viability is intracytoplasmic sperm injection (ICSI), where fertilization is achieved by injecting a single sperm directly into the oocyte (egg). Thus, the quality of the individual sperm that is selected is of paramount importance, and the challenge is how to distinguish viable from non-viable sperm. Current sperm viability assays are limited by subjectivity, sensitivity, and potential toxicity. Optoelectronic tweezers can non-invasively distinguish between live and dead cells and provide a means of sorting them. We have demonstrated the separation of live and dead sperm even in the absence of motility, as viable non-motile sperm are attracted to OET-induced electric fields, while non-viable sperm are repelled by the same electric fields. Thus, OET sorting is a potential method by which to identify viable non-motile sperm for assisted reproductive technologies.

We’re used to thinking of robots as mechanical entities, but at very small scales, it sometimes becomes easier to use existing structures (like microorganisms that respond to magnetic fields or even swarms of bacteria) instead of trying to design and construct one (or lots) of teeny tiny artificial machines. Aaron Ohta’s lab at the University of Hawaii at Manoa has come up with a novel new way of creating non-mechanical microbots quite literally out of thin air, using robots made of bubbles with engines made of lasers.

To get the bubble robots to move around in this saline solution, a 400 mW 980nm (that’s infrared) laser is shone through the bubble onto the heat-absorbing surface of the working area. The fluid that the bubbles are in tries to move from the hot area where the laser is pointing towards the colder side of the bubble, and this fluid flow pushes the bubble towards the hot area. Moving the laser to different sides of the bubble gives you complete 360 degree steering, and since the velocity of the bubble is proportional to the intensity of the laser, you can go as slow as you want or as fast as about 4 mm/s.

This level of control allows for very fine manipulation of small objects, and the picture below shows how a bubble robot has pushed glass beads around to form the letters “UH” (for University of Hawaii, of course):

Besides being able to create as many robots as you want of differing sizes out of absolutely nothing (robot construction just involves a fine-tipped syringe full of air), the laser-controlled bubbles have another big advantage over more common microbots in that it’s possible to control many different bubbles independently using separate lasers or light patterns from a digital projector. With magnetically steered microbots, they all like to go wherever the magnetic field points them as one big herd, but the bubbles don’t have that problem, since each just needs its own independent spot of light to follow around.

The researchers are currently investigating how to use teams of tiny bubbles to cooperatively transport and assemble microbeads into complex shapes, and they hope to eventually develop a system that can provide real-time autonomous control based on visual feedback. Eventually, it may be possible to conjure swarms of microscopic bubble robots out of nothing, set them to work building microstructures with an array of thermal lasers, and then when they’re finished, give each one a little pop to wipe it completely out of existence without any mess or fuss.

Cooperative Micromanipulation Using Optically Controlled Bubble Microrobots by Wenqi Hu, Kelly S. Ishii, and Aaron T. Ohta of the the Department of Electrical Engineering, University of Hawaii at Manoa, was presented last week at the 2012 IEEE International Conference on Robotics and Automation in St. Paul, Minn.

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