Inexpensive silicon microteeth that open and close like jaws to harmlessly deform red blood cells have been developed at Sandia.
The patent-pending microdevices, because of their constant munching, bear a strong resemblance to the computer game hero Pac-Man as their upper teeth slide back and forth in piston-like action across microchannels to momentarily trap unaware red blood cells against the lower teeth.
"We’ve shown we’ve created a micromachine that can interact at the scale of cells," says Sandia researcher Murat Okandan (1749).
The capability could add an extra tool to the growing capabilities of microfluidic devices, a billion-dollar industry. Microfluidic devices typically are limited in capabilities to examination of materials. But, says Murat, "We’re trying to create conditions in which, on a massive scale, cells may be altered as well as examined."
The prototype device offers the possibility of considerable mechanical intervention at the cellular level because it operates rapidly and is so small that many units could operate in parallel in a small space. Ten complete units can fit in an area smaller than a household electric plug prong, and each microdevice can puncture 10 cells per second.
An immediate goal of Murat, who developed the device with Paul Galambos, Sita Mani, and Jay Jakubczak (all 1749), is to see whether the masticated red blood cells absorb fluorescent material.
If the material is readily absorbed, it means that Sandia researchers have created the first example of a continuous flow, mechanical cellular-membrane disrupter ever reported.
Enter, the needle
A near-time goal is to replace the microteeth with a hollow silicon needle now in development. The needles would rapidly inject DNA, RNA, or proteins (including drug molecules) into living cells at precise points of their anatomies and in large numbers, possibly changing the course of a disease or restoring lost functions.
Even if punctures have not occurred, "We’ve created a demonstration tool with very flexible technology that we hope will enable many designs and concepts," says Murat. "This device itself may generate considerable interest from the agriculture or genetic engineering marketplaces."
The cells punctured do not need to be blood cells but could be, say, stem cells — cells able to change, given suitable direction — possibly by gene implantation — into many of the tissues of the human body, says Murat.
In terms of the number of living cells altered, the method potentially compares favorably with electrical or chemical techniques used to open cell walls for drug insertion; either of the latter methods kills large numbers of cells.
Also, microelectromechanical insertion is less expensive than these other methods. The devices — powered by electrostatic actuators — and the microchannels in which they function are so cheap to fabricate that, when mass-produced, a device could be thrown away after it is used once.
The depth and precise position of molecular insertion would be controlled by researchers who have located the cell’s "sweet spot" by observing effects of the insertions.
Hundreds or thousands of units assembled in parallel, puncturing cells at the rate of 10 a second, could create a sizeable supply of enhanced material.
Why the device could be built
Inexpensive fabrication of the device became possible for two reasons: the capabilities of the Sandia MEMS SUMMiT V fabrication process — a sequence of deposition, patterning, and etching — to create complicated micromachines, and the use of silicon nitride to build insulated microchannels in that process.
An effective insulator is needed because microchannels of silicon, an electrical conductor, would short out electrodes that create electrical and magnetic fields used to analyze or manipulate the contents of the channel. By fabricating channels instead out of a version of silicon nitride, the researchers were able to avoid these problems.
Silicon nitride’s other advantages are that it is transparent, allowing researchers optical examination of the experiments, and that it is a material commonly used in microelectronic device fabrication — an important consideration.
Although the microdevices are fabricated step by step with lithographic processes well known to the semiconductor industry, the ability to easily make this complicated device is credited to the Sandia SUMMiT V fabrication process, which allows five-level micromachine construction to be quickly designed and implemented. The SUMMiT V process is the only one available worldwide that can construct five-level micromachine devices.
Another invisible ingredient in the mix was the expert MESA (Microsystems and Engineering Sciences Applications complex) fabrication teams that physically created the device.