Anyone who has been sick before knows you want relief as quickly as possible. An investigation soon taking place aboard the International Space Station could help bring that relief by improving design of tablets used to deliver medicine into the human body. The Hard to Wet Surfaces research looks at liquid-solid interactions and how certain pharmaceuticals dissolve, which may lead to more potent and effective medicines in space and on Earth.

Dissolving a solid such as a medicine tablet involves two key factors: wettability and float effect. "Wettability is how well a liquid spreads over the surface of a solid," said principal investigator Richard Cope, who holds a doctorate in chemical engineering and is the associate engineering advisor at Eli Lilly and Company. "Float effect refers to how solids that are less dense float on the surface of a liquid."

Both factors commonly play a role in how quickly and how well a solid dissolves on Earth, and the goal of this research is to better understand each by separating their effects in microgravity. Differences in density become negligible in microgravity, so researchers expect float effect to essentially disappear.

"We hypothesize that tablets that float on Earth will dissolve more quickly in microgravity because they will not float in space. More of the surface will be in contact with the liquid," said Alison Campbell, who holds a doctorate in chemistry and is a senior research scientist at Lilly.

How microgravity may affect wettability is more of an unknown. But with many pharmaceutical ingredients considered "hard to wet," understanding microgravity's effect on this characteristic is important in the fundamental approach to dissolving these substances.

"This work is foundational," said Kenneth Savin, who holds a doctorate in organic chemistry and is an advisor in Lilly's clinical innovation group. "We're looking at a basic property - how to get a solid to dissolve."

Tablets and pills that don't dissolve easily might slow a drug's release into the body, but wettability's role in drug performance is not well understood. Results will help guide ingredient choices for future pharmaceutical formulations, improving delivery to a drug's intended target.

"Looking forward, we don't know if this particular experiment will lead to sweeping changes," said Campbell. "But it is all about building a foundation of knowledge so we can develop a better product."

Some medications seem to be less effective when taken in space. Understanding whether microgravity changes the way solids dissolve also may help explain this phenomenon.

The Center for the Advancement of Science in Space (CASIS), which manages the International Space Station U.S. National Laboratory, helped the researchers from Lilly prepare their investigation for launch.

"The liquid-solid interface is an important concept to understand," said Jonathan Volk, who holds a doctorate in chemical engineering and is the CASIS commercial innovation manager. "We hope this is just the first in this kind of work."

CASIS will continue to support the investigation by helping to maximize use of data and to develop future experiments. In the future, thanks to tiny tablets that went to space, better ones could show up in our medicine cabinets here on Earth.