Crystal Growth Studied in Space
Brent D. Johnson
Insulin is perhaps one of the most studied proteins in medical science. Understanding how its structure folds and unfolds could lead to new forms of insulin that would have greater therapeutic value for the millions of people afflicted with Type I diabetes, but analyzing its complex crystalline structure has been a persistent challenge.
Researchers at NASA's Marshall Space Flight Center plan to use a novel miniature camera to analyze the growth of insulin crystals in microgravity aboard the International Space Station. Space-grown protein crystals, far left, on Spacelab II are larger and of greater optical clarity than their Earth-grown counterparts, left.
Hoping to meet this challenge, researchers at NASA's Marshall Space Flight Center in Huntsville, Ala., have developed Delta-L, an apparatus for measuring macromolecule crystal growth rates in microgravity. They plan to image the growth of ultrapure insulin crystals in microgravity aboard the International Space Station. It is believed that the crystals will be larger and more ordered than those that have been grown in Earth's gravity, making detailed analysis much simpler.
To view these crystals, the scientists needed a miniature microscope that could scan a 15- to 20-mm observation area and resolve crystals ranging in size from 50 to 500 µm with a point-to-point accuracy of ±2.0 µm within a quartz growth cell.
Lead avionics designer Eric Corder said that initial attempts to visualize the crystals were thwarted because the images would wash out on the edge of the growth cell.
The researchers related the problem to Robert Urstadt of Creative Devices Inc., whose solution was to couple a Pulnix 5LC black-and-white camera to an SL20× objective from Mitutoyo America Corp. of Aurora, Ill., that had a working distance of 30 mm. The system gave them an aspect ratio of 4:3 and 500-µm resolution. It also allowed them to reduce the relay lens from 3 inches to 2 and to get by with 10× magnification rather than 20×.
In addition, they folded an in-line LED through a collimator, which produced 3000 mc at 5 V, increasing contrast by 30 percent. Eventually, they were able to bring the contrast up to 60 or 70 percent.
The group is fabricating the flight hardware for the Delta-L experiment and should have the complete system ready soon. Corder said that the results of tests of the system have been excellent. The fully integrated system will undergo four to five months of environmental testing and may fly in November 2003 in the Microgravity Science Glovebox.
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