Tokyo | Scientists have grown protein crystals and measured their growth in a specially-designed chamber onboard the International Space Station (ISS) to better examine the effects of microgravity on the crystals.
Scientists monitored the very slow growth and dissolution rate – approximately one centimetre per second of the crystals by laser interferometry. This was the first time the technique had been used onboard the ISS to measure the growth rate of the crystals at various temperatures.
To observe this, researchers developed unique growth cells suitable for long-term projects, for about six months. We are interested in the growth mechanisms of a space-grown protein crystal – a lysozyme crystal – as a model crystal to understand why space-grown crystals sometimes do show better quality than the Earth-grown crystals, said Tomoya Yamazaki from Tohoku University in Japan.
The experimental process, known as NanoStep, was performed in the Japanese Experimental Module (KIBO) of the ISS in 2012, researchers said. They had previously measured the growth rates of protein crystals under simulated microgravity by using a Russian recoverable satellite and aircraft in parabolic flights.
Researchers took precise measurements of the growth rate of the lysozyme crystals versus their driving force, supersaturation – the natural logarithm of the protein’s concentration divided by its solubility – with measurements of the solution’s refractive index distribution obtained through interferometry. This also yielded crucial information about the growth mechanism. They opted to modify the supersaturation of the solution by increasing or decreasing the growth cell’s temperature, which can easily be done remotely. This took place over a range of 10 to 40 degrees Celsius, which necessitated building a closed growth cell to withstand the stresses caused by the thermal expansion of the growth solution.
The closed, cube-like growth cell was constructed out of quartz glasses with different thickness, an essential component for laser interferometry due to its high chemical and mechanical resistances with a protein seed crystal glued to the top of the sample holder.
To relieve the thermal stress on the glass, the researchers attached tubes made out of an elastomer, low-moisture- permeability thermoelastic polymer. This was selected to mitigate evaporation of water in the crystal growth solution. They also employed a special spring tension system to reduce stress by keeping the gap between the glass cell and thermal control modules constant amid thermal expansion. The growth cell could also be used to fine-tune the measurements of extremely small growth or dissolution rates of insoluble minerals on the order of 0.001 nanometres per second of insoluble minerals, researchers said.
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