Infrared fiber optic spectroscopy detects bovine articular cartilage degeneration

Abstract

Articular cartilage (AC) is a soft connective tissue that covers the ends of articulating bones. Joint injuries may lead to degeneration of cartilage tissue and initiate development of post-traumatic osteoarthritis (OA). Arthroscopic surgeries can be used to treat joint injuries, but arthroscopic evaluation of cartilage quality is subjective. Therefore, new methods are needed for objective assessment of cartilage degeneration. Fourier transform infrared (FTIR) spectroscopy can be used to assess tissue composition based on the fundamental molecular vibrations. When combined with fiber optics and attenuated total reflectance (ATR) crystal, the measurements can be done flexibly without any sample processing. We hypothesize that Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy can detect enzymatically and mechanically induced changes similar to changes occurring during progression of OA. Fresh bovine patellar cartilage plugs (n = 60) were extracted and degraded enzymatically and mechanically. Adjacent untreated control samples (n = 60) were utilized as controls. Enzymatic degradation was implemented by 90-min and 24-hour collagenase as well as 30-min trypsin treatments. Mechanical damage was induced by: 1) dropping a weight impactor on the cartilage plugs, and 2) abrading the cartilage surface with a rotating sandpaper. Fiber optic FTIR-ATR spectroscopic measurements were conducted for control and degraded samples, and spectral changes were assessed with random forest (RF), partial least squares discriminant analysis (PLS-DA), and support vector machine (SVM) classifiers. RF (accuracy 93.1 % to 79.2 %), PLS-DA (accuracy 95.8% to 81.9%), and SVM (accuracy 91.7% to 80.6%) all had excellent classification performance for detecting the different enzymatic and mechanical damage on cartilage matrix. The results suggest that fiber optic FTIR-ATR spectroscopy is a viable way to detect minor degeneration of AC.

Applications of Vibrational Spectroscopy for Analysis of Connective Tissues

“…Santos et al have shown that silica core-silica clad fibers, with acrylate coating and a black nylon jacket, provided low background signal and good signal quality in in vitro measurements of brain tissue of a 6-month old pig [ 100 ]. The versatility of fiber optic probes in cartilage assessment has been shown for in vitro studies of engineered cartilage development [ 54 , 55 , 83 , 91 , 101 ], ex vivo studies of cartilage degradation [ 81 , 102 ], and in vivo arthroscopic evaluation of articular cartilage and subchondral bone [ 51 ]. Similarly, Raman spectroscopic probes have also been used to assess articular cartilage quality [ 103 ], and have been used to monitor the development of tissue engineered cartilage in vitro [ 91 ].…”

“…Additionally, polarized infrared light can be used with FTIR imaging to reveal the zonal distribution of differently oriented collagen fibers based on the ratio of the amide I to amide II absorbances [ 69 ]. The information in these foundational studies of native cartilage has subsequently been applied in many areas of cartilage research, including towards understanding of degraded osteoarthritic tissues [ 102 , 114 , 115 , 116 ], and characterization of developing engineered constructs [ 60 , 117 , 118 , 119 ].…”