The deleterious effects of microgravity are undeniable: reduced bone mineral density, muscle atrophy, vascular remodeling, etc. These health issues may derive from both systemic factors, and from direct alterations to intracellular components and in the local microenvironment around cells. To understand the biological mechanisms at play, detailed studies have been performed in spaceflight. However, because experiments on the International Space Station (ISS) can be prohibitively expensive, clinostats are an alternative ground-based analogue for cellular studies. Clinostats “randomize” the orientation of gravity with respect to the cell fixed-frame, thereby simulating microgravity by eliminating a preferential gravity direction.

Fig. 1 – The clinochip system has a rotating platform to simulate microgravity through the time-averaged nullification of the gravity vector. In addition, a static platform serves as a control.
Conventional clinostats are not ideal experimental tools for several reasons. First, cells seeded on microcarriers need to be rotated at optimal speeds that balance centrifugal effects with fluid shear and sedimentation forces. This difficult balancing act may yield unrepeatable experimental results. Additionally, the large radius in conventional clinostat vessels imposes a wide variation in residual gravity on the cells, which may further confound results. Finally, cells cannot be continuously monitored in this vessel, which severely limits the types of assays that can be performed.

With the recently developed clinochip system, clinorotation time-lapse micros - copy is possible and enables time-lapse imaging of cells in simulated microgravity. The clinochip is a lab-on-chip configuration that accommodates elastic substrates, complex microfluidics, and same-cell tracking requirements to enable a wide range of science investigations. Cells can be cultured in monolayer, in suspension, or in 3D constructs. In all, the compact system provides not only traditional endpoint outcomes, but also dynamic cellular processes, while offering the ability to precisely modulate the microenvironment and fluid flow around cells. (See Figure 1)

Fig. 2 – Traction force microscopy in simulated microgravity. hMSC is shown in a retracted state on the micropost array. Micropost defections are used to evaluate force interactions between cells and their substrate.
Specifically, detailed studies have been performed to yield the first-ever traction force measurements in simulated microgravity. These measurements are important because they help elucidate fundamental biophysics that may influence cell processes, such as lineage commitment in stem cells, which may ultimately impede bone maintenance and repair in spaceflight. Force-sensing substrates were created using a regular array of polydimethylsiloxane (PDMS) micro-posts, with dimensions of 2 μm diameter, 5 μm periodicity, and 10 μm height. Standard cantilever beam bending equations were used to derive cellsubstrate forces. Micro-post arrays are not new; however, in combination with the clinochip system, this development provides the first clinorotation-based capabilities for force sensing.

Results derived from this force-sensing clinochip innovation are important for determining possible gravisensing mechanisms in cells. Eventually, therapeutic countermeasures could potentially be developed. Other complex cell assays are also possible by adapting the current configuration with other labon-chip devices. (See Figure 2)

Finally, the clinochip system could potentially be commercialized and an entity may offer several different system configurations targeting various science investigations (i.e., microgravity research vs. tissue engineering), and provide different interface adapters for peripheral devices (e.g., microscope, pump, control electronics, etc.).

This work was performed by Alvin Yew of NASA Goddard Space Flight Center; and Javier Atencia, Adam Hsieh, and Carlos Luna of the University of Maryland, College Park. GSC-16834-1

This Brief includes a Technical Support Package (TSP).
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Live-Cell Microscopy and Traction Force Measurements with Simulated Microgravity “Clinochip”

(reference GSC-16834-1) is currently available for download from the TSP library.

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