Bone tissue compositional differences in women with and without osteoporotic fracture.

It is generally accepted that the hallmark of osteoporosis is a reduction in bone mass. There is significant overlap, however, in bone mineral density between osteoporotic and normal individuals. This study examined the chemical composition of bone tissue obtained from women who had sustained a fracture and women without fracture to determine if there are differences between the two groups. Nineteen fractured and eleven non-fractured proximal femurs were obtained, matched for age and bone volume fraction obtained from micro-computed tomography. Trabecular bone specimens were examined by Raman spectroscopy to determine measures of chemical composition. A subset of the specimens was utilized to compare locations at the fracture and regions at least 2 mm away from apparent tissue damage using Raman spectroscopy. In addition, fifteen iliac crest biopsies each were obtained from women who had sustained a fracture and from normal controls. Raman spectroscopy was used to determine measures of chemical composition of trabecular and cortical bone. The results demonstrated that femoral bone tissue in the region of visible damage had a trend towards differences compared to regions at least 2 mm from visible damage. Femoral trabecular bone in fractured women had a higher carbonate/amide I area ratio than in unfractured women. Iliac crest biopsies revealed a higher carbonate/phosphate ratio in cortical bone from women who had sustained a fracture. Results suggest that the chemical composition of bone tissue may be an additional risk factor for osteoporotic fracture.

Reexamination of hexafluorosilicate hydrolysis by 19F NMR and pH measurement.

The dissociation of hexafluorosilicate has been reinvestigated due to recent suggestions that fluorosilicate intermediates may be present in appreciable concentrations in drinking water. 19F NMR spectroscopy has been used to search for intermediates in the hydrolysis of hexafluorosilicate. No intermediates were observable at 10(-5) M concentrations under excess fluoride forcing conditions over the pH range of 3.5-5. A single intermediate species, assigned as SiF5(-) or its hydrate, was detected below pH 3.5. At moderate pH values of 4 and 5 silica oligomerization in the solutions studied made it difficult to directly determine the hexafluorosilicate equilibrium constant. Under more acidic conditions the average pKd, or negative log of the dissociation constant Kd, determined by 19F NMR measurements, was 30.6. We also investigated the behavior of hexafluorosilicate in common biological buffer reagents including phosphate/citrate, veronal/HCI buffers, and Ringer's solution. The buffer capacity of all of these systems was found to be insufficient to prevent acidic shifts in pH when hexafluorosilicate was added. The pH change is sufficient explanation for the observed inhibition of acetylcholinesterase that was previously attributed to hexafluorosilicate hydrolysis intermediates.

Subsurface Raman spectroscopy and mapping using a globally illuminated non-confocal fiber-optic array probe in the presence of Raman photon migration.

We report the use of a fiber-optic probe with global illumination and an array of 50 collection fibers (PhAT probe, Kaiser Optical Systems, Inc.) to obtain Raman spectra and 50 spatial element maps of polymers through overlayers of other polymers that are highly scattering. Band target entropy minimization (BTEM) is used to recover the spectra of the subsurface components and generate maps of their distributions. This approach to subsurface mapping is tested with model systems consisting of two or three layers of polyethylene, polytetrafluoroethylene (Teflon), and polyoxymethylene (Delrin) arranged in different geometries. Raman spectra and maps were obtained through overlayer thicknesses of up to 13 mm. Subsurface spatial resolution is achieved because each fiber views an asymmetric distribution of Raman scattered light from surface and subsurface components that depends on the position of the fiber relative to the depth and position of a component and the extent of photon diffusion through the system.

Classification of spectroscopically encoded resins by Raman mapping and infrared hyperspectral imaging.

Barcoded resins (BCRs) were recently introduced as a potential platform for pre-encoded multiplexed synthesis, screening, and biomedical diagnostics. A key step toward the development of this strategy is the ability to rapidly interrogate and classify the BCRs in a high-throughput, noninvasive manner. Here, we describe a one-step strategy based on Raman mapping and Fourier transform infrared imaging to classify and spatially resolve randomly distributed BCRs. To illustrate this methodology, mixtures of up to 25 different BCRs were imaged and classified with 100% confidence. This strategy can be readily extended to a larger pool of resins, provided each BCR features a unique vibrational fingerprint (spectroscopic barcode). We have also established that reliable single-bead Raman spectra can be recorded in 10 ms, thus confirming that Raman mapping, in particular, could be a very fast method to classify the BCRs.

Bone tissue ultrastructural response to elastic deformation probed by Raman spectroscopy.

Raman spectroscopy is used as a probe of ultrastructural (molecular) changes in both the mineral and matrix (protein and glycoprotein, predominantly type I collagen) components in real time of murine cortical bone as it responds to elastic deformation. Because bone is ia composite material, its mechanical properties are dependent on the structure and composition at a variety of dimensional scales. At the ultrastructural level, crystal structure and protein secondary structure distort as the tissue is loaded. These structural changes are followed as perturbations to tissue spectra. We load murine femora in a custom-made mechanical tester that fits on the stage of a Raman microprobe and can accept hydrated tissue specimens. As the specimen is loaded in tension, the shifts in mineral P-O4 v1 are followed with the microprobe. Average load and strain are measured using a load cell. These devices ensure that specimens are not loaded to or beyond the yield point. Changes occur in the mineral component of bone as a response to loading in the elastic regime. We propose that the mineral apatitic crystal lattice is deformed by movement of calcium and other ions. Raman microspectroscopy shows that bone mineral is not a passive contributor to tissue strength. The mineral active response to loading may function as a local energy storage and dissipation mechanism, thus helping to protect tissue from catastrophic damage.