Water loss is an early onset indicator of osteoarthritis. Although Raman spectroscopy (RS) holds the potential for measurement of cartilage hydration, the knowledge of Raman OH-stretch bands of biological tissue is very limited. We assesed here the sensitivity of RS to identify and classify water types in the cartilage. Raman spectrum measurements over the high wavenumber range were employed to identify different water fractions in articular cartilage. Raman spectra were collected from wet and sequentially dehydrated cartilage along with pure collagen type II and chondroitin sulfate standards. OH-stretch band of cartilage is dominated by mobile water, up to 95% of total intensities. We identified six peaks in cartilage spectrum using second-derivative analysis: peaks at 3200 and 3650 cm−1 are associated with organic matrix (both collagen and proteglycan) and matrix-bound water molecules. Peaks at 3250, 3453, and 3630 cm−1 are associated with collagen and collagen-related water molecules, whereas the peak at 3520 cm−1 is associated with proteoglycan (PG) and PG-related water molecules. The current work is the first thorough analysis of the Raman OH-stretch band of the cartilage and with the knowledge generated by this study, it may now be possible to study on cartilage hydration by RS.
Given that bone is an intriguing nanostructured dielectric as a partially disordered complex structure, we apply an elastic light scattering-based approach to image prefailure deformation and damage of bovine cortical bone under mechanical testing. We demonstrate that our imaging method can capture nanoscale deformation in a relatively large area. The unique structure, the high anisotropic property of bone, and the system configuration further allow us to use the transfer matrix method to study possible spectroscopic manifestations of prefailure deformation. Our sensitive yet simple imaging method could potentially be used to detect nanoscale structural and mechanical alterations of hard tissue and biomaterials in a fairly large field of view.
Image subtraction has been an extremely useful tool for capturing subtle changes in pixel intensity with extremely high
temporal resolution, and has been used for decades in the astronomy and metal corrosion fields. However, to date, image
subtraction has not been used as a mainstream technique for investigating morphological changes in cells, tissues, or
whole organisms. We introduce a user-friendly differential imaging technique for monitoring real time (~msec) changes
in morphology within the micrometer to millimeter spatial scale. The technique is demonstrated by measuring
morphological changes morphology for biomedical (bone stress), agricultural (crop root elongation), and environmental
(zooplankton ecotoxicology) applications. Subtle changes in growth that would typically only be observed by highly
skilled experts are easily resolved via image subtraction and the use of convolution kernels. When coupled with
techniques characterizing real time biochemical transport (e.g., respiration, ion/substrate transport), physiology can be
directly quantified with a high temporal and spatial resolution. Because of the ease of use, this technique can be readily
applied to any field of science concerned with bridging the gap between form and function.
There is a relatively deep understanding of macro and meso scale failure processes taking place in bone. Bone has
multiple orders of structural hierarchy and damage has to evolve through molecular, supramolecular and micron scales
before giving forth to fractures. Raman spectroscopy is known to be an efficient technique to provide information on the
failure processes at these scales. We used Raman microspectroscopy to assess the deformation of bone at the
supramolecular level and Digital Image Correlation (DIC) was applied to relate local strains to observed shifts in the
wavenumber of phosphate symmetric stretch band. DIC analysis of notched samples loaded in tension showed the
presence of compressive as well as tensile residual strains. Tensile strain however, was more predominant near the notch.
Raman analysis corroborated DIC observations such that the majority of the samples displayed negative shifts in mineral
band indicating tensile deformations. The results support Raman based observation of deformations in bone and indicate
that heterogeneity and anisotropy of bone complicate the expected stress patterns.
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