Bone material responds to mechanical stresses such as experienced during load-bearing, or its opposite weightlessness, to form new bone or break down existing bone by complex signals. These signals are believed to be sent and received from bone cells (osteocytes) housed within mineralized cavities called lacunae, via cell processes that pass nutrients and other signals within mineralized channels (canaliculi) extending from the lacunae (Duncan & Turner 1995, Khosla et al. 2008). Therefore, obtaining the 3D structure of lacunae and canaliculi at the nanoscale will help our understanding of healthy bone tissue and the changes that occur with aging and disease.

A team that included scientists from NASA Ames Research Center, Cornell University, Xradia, Inc. and the Stanford Synchrotron Radiation Lightsource (SSRL) has conducted imaging experiments of bone using the transmission x-ray microscope (TXM) on SSRL beam line 6-2. They imaged trabeculae from mice that were hindlimb unloaded, a method developed by NASA to simulate weightlessness, reducing the functional loads experienced by the hindlimbs. 2D images show detailed structures of lacunae and the associated canaliculi (Figure 1), and tomography provided a 3D view of these structures (Figure 2, and supplemental movie). Tomography was obtained by rotating the bony trabecula and taking images at successive angles from -90 to 90 degrees. These images were reconstructed mathematically to provide a 3D image, and 2D slices from the 3D data (Fig. 2 b and c) provide detail of the lacuna and canaliculi extending from the cell cavity.

	Fig. 2. Projection (a) and slices (b and c) from tomography of single bone trabecula imaged from -90 to 90 degrees shows lacuna and canaliculi extending from it.