Altered composition of bone as triggered by irradiation facilitates the rapid erosion of the matrix by both cellular and physicochemical processes.

Radiation rapidly undermines trabecular architecture, a destructive process which proceeds despite a devastated cell population. In addition to the 'biologically orchestrated' resorption of the matrix by osteoclasts, physicochemical processes enabled by a damaged matrix may contribute to the rapid erosion of bone quality. 8w male C57BL/6 mice exposed to 5 Gy of Cs(137) γ-irradiation were compared to age-matched control at 2d, 10d, or 8w following exposure. By 10d, irradiation had led to significant loss of trabecular bone volume fraction. Assessed by reflection-based Fourier transform infrared imaging (FTIRI), chemical composition of the irradiated matrix indicated that mineralization had diminished at 2d by -4.3±4.8%, and at 10d by -5.8±3.2%. These data suggest that irradiation facilitates the dissolution of the matrix through a change in the material itself, a conclusion supported by a 13.7±4.5% increase in the elastic modulus as measured by nanoindentation. The decline in viable cells within the marrow of irradiated mice at 2d implies that the immediate collapse of bone quality and inherent increased risk of fracture is not solely a result of an overly-active biologic process, but one fostered by alterations in the material matrix that predisposes the material to erosion

Dynamic Full-Field Infrared Imaging with Multiple Synchrotron Beams

Microspectroscopic imaging in the infrared (IR) spectral region allows for the examination of spatially resolved chemical composition on the microscale. More than a decade ago, it was demonstrated that diffraction-limited spatial resolution can be achieved when an apertured, single-pixel IR microscope is coupled to the high brightness of a synchrotron light source. Nowadays, many IR microscopes are equipped with multipixel Focal Plane Array (FPA) detectors, which dramatically improve data acquisition times for imaging large areas. Recently, progress been made toward efficiently coupling synchrotron IR beamlines to multipixel detectors, but they utilize expensive and highly customized optical schemes. Here we demonstrate the development and application of a simple optical configuration that can be implemented on most existing synchrotron IR beamlines to achieve full-field IR imaging with diffraction-limited spatial resolution. Specifically, the synchrotron radiation fan is extracted from the bending magnet and split into four beams that are combined on the sample, allowing it to fill a large section of the FPA. With this optical configuration, we are able to oversample an image by more than a factor of 2, even at the shortest wavelengths, making image restoration through deconvolution algorithms possible. High chemical sensitivity, rapid acquisition times, and superior signal-to-noise characteristics of the instrument are demonstrated. The unique characteristics of this setup enabled the real-time study of heterogeneous chemical dynamics with diffraction-limited spatial resolution for the first time

Trabecular and cortical bone parameters in the tibiae of irradiated mice compared to the age-matched control at 2d, 10d, and 8w.

<p>By 10d following irradiation, although there was a deficit to the trabecular bone architecture compared to non-irradiated control, no significant differences were apparent in the cortical bone between the irradiated mice and the age-matched control.</p

Light microscope image of mouse tibiae stained with Modified Wright Giemsa at 10d following irradiation.

<p>Image on the left is a control, and on the right is an irradiated mouse. The empty spaces in the marrow of the irradiated bone correspond to the rapid infiltration of fat cells, a consequence of which is that there is less space for immune cells to occupy the bone marrow space. Scale bar represents 1 mm.</p

Trabecular bone chemical composition using FTIRI.

<p>A) Level of mineralization as a proportion of the inorganic to organic matrix, in the trabecular bone of irradiated mice compared to control at 2d, 10d, and 8w following irradiation. *p<0.05 compared to age-matched control. B) A typical FTIRI heat map of the level of mineralization in a control (left) and an irradiated (right) trabecular strut at 2d. Increased intensity corresponds to increased degree of mineralization.</p

Mechanical properties of trabecular bone at 2d, 10d, and 8w following irradiation.

<p>As early as 2d following irradiation, alterations in the trabecular bone led to an increase in hardness and elastic modulus which was no longer present at 10d. *p<0.05 compared to control.</p