The Impact of Gravity on Bone Cells: Experiments Heading to the International Space Station

The Impact of Gravity on Bone Cells: Experiments Heading to the International Space Station

Mechanical engineers from the University of Michigan are tackling the mysteries of bone density loss in space and on Earth


Nadab Wubshet, a doctoral student in mechanical engineering, stands near the launch site, holding a microfluidic chip like the ones sent to the International Space Station on Monday.  Image credit: Samuel Chen
Nadab Wubshet, a doctoral student in mechanical engineering, stands near the launch site, holding a microfluidic chip like the ones sent to the International Space Station on Monday. Image credit: Samuel Chen

Faculty Q&A

Early this morning, a pair of experiments exploring bone density, designed by University of Michigan engineers, left the Wallops Island, Virginia, launch pad aboard a Northrop Grumman Corp. Antares rocket for the International Space Station. (ISS).

allen liuUM associate professor of mechanical engineering, and members of his research team detail how experiments in space can shed light on osteoporosis, a condition that affects hundreds of millions of people worldwide, as well as how to maintain the safest astronauts.

What is the connection between bone density, osteoporosis, and gravity that makes this space research relevant to everyday people?

Allen Liu: Osteoporosis causes bones to become weak and brittle as people age, leading to fractures even with minor stresses and falls. There are an estimated 10 million cases in the US and another 43 million show signs of low bone density.

A weightless environment, or microgravity, can cause physiological changes in bones and presents a unique research environment without the typical mechanical stresses of gravity. It also rapidly alters the way cells grow and function without the use of drugs or genetic engineering.

The stiffness of a cell can tell us its biological age, predicting how its function may decline or its susceptibility to chronic disease over time. We’re testing the hypothesis that when cells don’t recoil against gravity, that reduction in stiffness makes them susceptible to the same kind of changes we see in osteoporosis. But we also think we can prevent those health impacts by mechanically compressing cells in a way that mimics gravity.

How are you going to see cell rigidity in space? What can that tell you about astronauts?

Nadab Wubshet, PhD student in mechanical engineering: We hypothesize that the absence of gravity can induce softening of cells, which could be behind the bone loss seen in astronauts after long stays on the ISS. Astronauts do resistance exercises on board to create the compression effect that doesn’t exist without gravity.

To test the stiffness of cells in the ISS, we used an automated microfluidic device that uses fluids to trap individual cells and slowly increase pressure on each cell to induce deformation. Fluorescent markers allow us to see its shape at each pressure level. Our device is also embedded in a system that takes snapshots and videos that allow us to collect data to measure cell stiffness.

How could this benefit human health?

Wubshet: If our hypothesis is proven correct, our results will provide great insight into how changes in physical forces, such as gravity, affect the mechanical characteristics of bone cells and bone formation. Having a better understanding of the impact of native forces, such as gravity, on bone formation could provide insights into better diagnosis and treatment for people dealing with bone decay.

But applications in space are also important, especially considering the growing interest in space exploration that could have astronauts in microgravity for longer periods of time. We hope to develop solutions to maintain the bone density of those astronauts.

In the second experiment, he tries to reduce the deterioration of bone cells. What do you hope to learn?

Grace Cai, Ph.D. student in applied physics: The cells we’ve been referring to as “bone cells” are osteoblasts, which lay down minerals and proteins to form bone when and where it’s needed most. In our study, we investigated how microgravity affects osteoblast activity.

Cells in microgravity experience low cell tension and we can increase cell tension by applying mechanical compression. By placing spherical clusters of human osteoblast cells in zero gravity and applying compression, we can test whether it promotes bone cell development and maintenance, while preventing bone loss.

How will the samples be returned to Earth, and how do you think their analysis will benefit future astronauts?

Cai: While the first experiment will be handled on the ISS, the samples for this second experiment will be returned to Earth on SpaceX CRS-26 in January for analysis. Our findings here should shed light on whether compressive space suits and clothing could prevent bone loss and improve bone health for astronauts exposed to microgravity conditions. These kinds of technologies could help protect crews traveling to and from the ISS, as well as other destinations.

In addition to informing osteoporosis research on Earth, we anticipate that our findings will likely be relevant to other age-related diseases and cancers. Cellular mechanics and the architectures that build cells, which are of fundamental importance to our own study, are also significant in these areas.

What are the most interesting things you have learned as a mechanical engineer preparing experiments for space?

Liu: One of the challenges of working in a microgravity environment is that everything is weightless, so handling fluids becomes extremely challenging. Everything has to be closed and our cells have to be kept in a bag instead of in a petri dish. And because space is at a premium on the ISS, each experiment is packed into a small CubeLab container, approximately 6.3″ tall, 8.2″ long and 12.3″ wide.

As a researcher, I think we are used to uncertainties, but this is very different. Many things can go wrong with an experiment on Earth, and it makes it even more difficult to do the experiment correctly in space. We are hopeful that the experiments will go smoothly and I am glad I made the flight!

The study is funded by the National Science Foundation and sponsored by the ISS National Laboratory, in collaboration with Space Tango.

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