Research On Characterization Of Principle Components And In-vivo Detection Method Of Articular Cartilage By Infrared Spectroscopy

Collagen and proteoglycan(PG)are two main components in articular cartilage(AC),accounting for more than 90% of dry weight.The organic combination of their components maintains the water content and the ion exchange with synovial fluid,which make the AC elastic,compressive and enduring.Their content and structure change are also considered as the primary marks of early-stage osteoarthritis(OA).Fourier transform infrared spectroscopy imaging(FTIRI)can obtain the composition and structure information of the samples with high resolution and has been applied in biomedical photonics field.FTIRI combined with chemometric methods have been applied to the content prediction of collagen and PG both in the healthy and OA cartilage in the previous report.They have also been use to identify the healthy and early OA cartilages.Attenuated total reflection(ATR)is a new method in FTIR technology from last 20 years.It is a powerful tool to detect the sample spectrum.Advantages include simple sample treatment,nondestructive measurement and detecting samples containing water.Especially,it has a potential to become a new tool to monitor tissue spectrum during the operation if couple with the fiber.Base on the above research,this research aims to explore the method to represent the collagen and PG content of AC by using FTIRI technology.Moreover,a device for AC in vivo infrared spectrum detection is aimed to be designed,which based on the Attenuated total reflection and fiber technology.Firstly,FTIRI was employed to analyze the characteristic bands of principal components of 5 ACs and their attribution by integrated and second derivative methods.The depth dependent profiles of integrated absorbance and second derivative spectral intensity of these IR bands were lineally fitted to those of the concentrations of collagen and PG that were predicted by principal component regression algorithms.The correlation coefficients by linear fit suggest that the correlation coefficient(R)between the integrated absorbance of Amide I(II)and collagen concentration(RA-amide I & RA-amide II)is much higher than that between amide III absorbance and collagen concentration(RA-amide III),meaning Amide I(II)are very suitable to qualitatively represent the depth dependence content of collagen.As well as the correlation coefficient between the second derivative spectral intensity of sugar band and PG concentration(RD-sugar)is better than that between integrated absorbance of sugar band and PG concentration(RA-sugar),suggesting the second derivative spectral intensities of sugar band is much fit to represent the depth dependences contents of PG.Secondly,combining with the above research,the FTIRI with polarization technique was used to investigate the anisotropic change of collagen fiber in formalin fixed AC through the absorbance change of Amide I and Amide II with immersing time and polarization direction.The degree of anisotropy of collagen fiber in cartilage was characterized with the fitting determination coefficient of absorbance.The anisotropy of Amide I and Amide II became stronger with immersing extension of AC in formalin,and the Amide I showed anisotropy more remarkable.It was concluded that the formalin solution induced new crosslink of collagen,which gradually strengthened the collagen fiber anisotropy and was helpful for the structural analysis of the AC.Finally,the paper also offered an easy handing FTIR-ATR optical fiber probe and a device to couple the probe with the FTIR spectrometer,which can be used to measure the biological tissue,like AC tissues,spectrum in vivo easily.This device combining with the above method to detect and represent the content and structure of collagen and PG in AC has a potential to become a new tool for the OA diagnosis and AC research.