Spectroscopic Evaluation of Water in Hyaline Cartilage

Abstract

Articular cartilage is hypocellular, aneural, alymphatic, and avascular. In diseased conditions such as osteoarthritis, there is an increase in water content from the average normal of 60-85% to greater than 90%. As cartilage has very little capability for self repair, methods of early detection of degeneration are required, and assessment of water could prove to be a useful diagnostic method. The most explored method for the assessment of water content in cartilage is MRI, but it cannot detect small changes in water content. Other methods such as dry/wet analysis and Karl Fischer titration are destructive. Infrared spectroscopy is extremely sensitive to the chemical composition and molecular structure of the sample. The technique of near infrared spectroscopy (NIRS) has been used for analyses of water in food, pharmaceuticals and skin. The hypothesis that NIR spectra can be used to assess water content in cartilage was investigated here. A model system using bovine nasal cartilage (BNC) to assess water content in hyaline cartilage was developed. The water content was initially determined by finding the integrated areas under the absorbance bands attributable to water centered at 5190 cm-1 and 6890 cm-1, and compared to the gold standard method for water measurement, gravimetric analysis of wet and dry weights.. The integrated areas of the absorbance bands at 5190 cm-1 and 6890 cm-1 , reflective of a combination of bound plus free water, and free water, in the tissues, respectively, were found to correlate with the absolute water content of the tissue. A model system of gelatin with varying amounts of water, representing the primary components of cartilage, collagen and water, was also developed. Regression analysis and partial least square (PLS) models using data from BNC tissues were successfully developed, and demonstrate that NIR spectroscopy can be utilized to quantitatively determine water content in articular cartilage.