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Diagnosing Cartilage Degeneration via Mid-Infrared Spectroscopy: The future of Molecular Arthroscopy?

5 Feb '20 | By Biophotonics.World
Diagnosing Cartilage Degeneration via Mid-Infrared Spectroscopy: The future of Molecular Arthroscopy?
Image source: Ulm University, Institute of Analytical and Bioanalytical Chemistry (IABC)

By Julian Haas and Boris Mizaikoff*


Autor affiliation: Ulm University, Institute of Analytical and Bioanalytical Chemistry, Albert-Einstein Allee 11, 89081 Ulm, Germany


ORCID ID Julian Haas: https://orcid.org/0000-0001-9378-8922

ORCID ID Boris Mizaikoff: https://orcid.org/0000-0002-5583-7962

Researcher ID Boris Mizaikoff: G-9959-2013


Institute homepage: https://www.uni-ulm.de/en/nawi/iabc/

*Corresponding author contact: 


Tel.: +49-731-50-22751

Fax: +49-731-50-22763

Articular cartilage is a highly specialized connective tissue that is covering the ends of long bones. These tissues enable the smooth movement of joints. Articular cartilage consists mainly of a strongly hydrated matrix of collagen type II, and of proteoglycans such as chondroitin sulfate. 


Osteoarthritis is a common disease progressing appearing as a result of false posture, increased body weight, injuries, and increased average age of the population leading to pronounced degradation of articular cartilage. Next to the apparent cartilage damage, osteoarthritis is frequently accompanied by severe pain, and corresponding movement limitations.


Consequently, non- or minimally-invasive diagnostic tools enabling early recognition of the disease onset are demanded facilitating timely treatment of any cartilage alteration for promoting recovery rates, as has successfully been shown in a variety of animal models where such tools have readily proven their utility during successive treatments, as well as for post treatment evaluation.


For the evaluation of localized alterations of the cartilage matrix, the likewise localized evaluation of the cartilage matrix integrity is required, which is routinely executed via visual observation and manual probing of the cartilage elasticity during arthroscopy. However, if additional information in molecular detail could be obtained - such as via in vivoarthroscopic mid-infrared (MIR) spectroscopy – an additional dimension of information is provided enabling a more detailed cartilage damage evaluation. MIR spectroscopy provides detailed information on the molecular composition and molecular changes of cartilage based on pronounced and distinct vibrational transitions occurring in condensed phase media. In particular, attenuated total reflection (ATR) spectroscopy facilitates the analysis of otherwise opaque media, as light in the 3-20 µm (4000-500 cm-1) spectral regime penetrates only few micrometers via the evanescent field emanating at a waveguide-tissue interface into the adjacent sample matrix. ATR spectroscopy utilizes radiation leaking from a high-refractive-index waveguide (e.g., macroscopic ATR crystal, microscopic IR-transparent fiber or thin-film planar waveguide) into a lower-refractive-index sample for probing molecular transitions in close vicinity to the waveguide surface propagating radiation via total internal reflection. Hence, the IR spectrum of a sample within a penetration depth of few cubic-micrometers may be recorded via evanescent field absorption spectroscopy. Thereby, the IR signatures of molecular components comprising the organic tissue matrix remain evident despite the interference of the water signature ubiquitously present in hydrated biological samples. 


In the article “Surface analysis of sheep menisci after meniscectomy via infrared attenuated total reflection spectroscopy” published in the WILEYVCH Journal of Biophotonics, alterations of the molecular signature characteristic for sheep menisci after meniscectomy were evaluated via IR-ATR spectroscopy fundamentally demonstrating the utility of this analytical technique. Pronounced molecular signatures commonly referred to as the ‘molecular fingerprint’ of proteins in the MIR are the amide I band, the amide II band, and C-H bending bands along with spectral region characteristic for sugars. When applying additional 2D correlation strategies to the obtained IR spectra, even minute deviations between cartilage sample spectra before and after treatment may be derived.


Consequently, the ex vivo evaluation of cartilage samples using IR-ATR spectroscopy based on a conventional Fourier transform infrared (FTIR) spectrometer indicated a loss of highly ordered fibril structures and a decrease of the triple helical structure of the collagen matrix, which can be associated with a loss of structural integrity of the overall cartilage tissue. 


Thus obtained spectral characteristics may then be related to a commonly used OA grading systems classifying the degeneration status of the cartilage based on histological evaluations. While histological grading of extracted thin cartilage sections is certainly the diagnostic ‘gold standard’, it only enables the retrospective evaluation of OA tissue. Consequently, future correlation of in vivo acquired arthroscopic MIR spectroscopy may pave the way for a molecularly detailed and reliable determination of OA grades in real time during arthroscopic procedures.


Is this science fiction? No! The scope of the currently ongoing MIRACLE project (‘Mid-infrared arthroscopy innovative imaging system for real-time clinical in-depth examination and diagnosis of degenerative joint diseases’) funded by the EU H2020 program consolidated an exceptionally competent consortium for exploring novel diagnostic tools doing exactly that - evaluating joint cartilage degeneration via a highly integrated arthroscopic diagnostic tool based on MIR spectroscopy. Utilizing specialized quantum cascade lasers (QCL) in lieu of conventional IR spectrometers, it is anticipated to surpass current limitations of conventional IR spectroscopic approaches harnessing next-generation label-free in vivo diagnostics. For a more detailed description of the MIRACLE project see: http://miracleproject.eu/. The MIRACLE project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 780598. The project is an initiative of the Photonics Public Private Partnership.



Related journal article

López-Lorente Ángela I., Wang P, Stein S, et al. Surface analysis of sheep menisci after meniscectomy via infrared attenuated total reflection spectroscopy. J. Biophotonics. 2019; e201800429. https://doi.org/10.1002/jbio.201800429



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