The Public Service Medal recognizes exceptional contributions to the mission of NASA by those who are not government employees.

An associate professor of mechanical engineering at the University of Houston Cullen College of Engineering, Kleis has worked with NASA for nearly 20 years to enhance the functionality of its bioreactors.

"It's an honor to receive this Public Service Medal," Kleis said.

"Designing vessels for growing cells in micro gravity requires quite a different view of fluid dynamics. The basic principles are the same, but a whole new set of forces dominates the motions of cell aggregates and bubbles in space."

"At the same time an interdisciplinary approach is needed to deal with cell biology, fluid dynamics, mass transport and mechanical design for micro gravity."

Steve Gonda, head of the Biotechnology Advanced Technology Development Laboratory at the NASA Johnson Space Center, nominated Kleis for the award, saying that part of NASA's focus is the development of space bioreactor systems that will support cell and tissue-based investigations in the space environment.

These investigations will advance the understanding of the effects of this unique, low-gravity environment at the cellular and tissue levels, and ultimately contributes to reducing space-related risks to astronauts during long-duration missions.

According to Gonda, NASA has a very comprehensive list of risks and questions associated with these risk areas, about 40 to 50 percent of which can be addressed by using cells and tissues.

"NASA has two decades of developing space bioreactors for operation on the Space Shuttle, Mir Station and the International Space Station in support of investigators from university, federal and medical-research institutions," Gonda said.

"We have a good number of successes under our belt, one of which was to have the longest duration, longest continuous operating tissue engineering experiment in a bioreactor in space."

"Our bioreactor system operated continuously for 130 days on the Mir Station, the longest tissue engineering experiment of its kind. Dr. Kleis contributed for many years to the overall capability of our program to have a very successful experiment."

After paving the way for the longest experiment, Kleis and his team followed with more work that ultimately helped resolve a new and difficult problem.

During the long-duration space experiment, the attending astronaut observed bubbles forming in the bioreactor vessel that could not be removed.

"That was unacceptable," Gonda said. "We have a very strong set of science requirements to which our bioreactors are designed and must meet. This is where the award for Dr. Kleis really focuses."

"He was team-lead for experimental strategies, and he did computer-based analysis in his laboratory looking for oxygen distribution and shear stress distributions in a new bioreactor system called the Hydrodynamic Focusing Bioreactor (HFB)."

Kleis and his team were able to take the HFB and conduct models in terms of shear stress and oxygen distribution. From these models, the team was able to develop ways to improve the design to optimize it to meet these science requirements.

They then took it to the next stage of testing its bubble-removal capability in a low-gravity environment on a series of KC-135 flights.

The tests were a complete success, and NASA now has a space bioreactor vessel that will meet its science requirements and also remove any bubbles that form or are introduced into the vessel.

"It's a major step forward for our program," Gonda said. "During that time, Dr. Kleis' teaching experience and his love of teaching came forward. He was very adept at working with members of a diverse team to fulfill our mission."

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