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J Mech Behav Biomed Mater. 2020 Apr;104:103639. doi: 10.1016/j.jmbbm.2020.103639. Epub 2020 Jan 17.

Comparison of water, hydroxyproline, uronic acid and elastin contents of bovine knee ligaments and patellar tendon and their relationships with biomechanical properties.

Author information

1
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland. Electronic address: aapo.ristaniemi@uef.fi.
2
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland.
3
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
4
Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland.
5
School of Medicine, University of Eastern Finland, Kuopio, Finland.
6
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Diagnostic Imaging Center, Kuopio University Hospital, Kuopio, Finland; School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia.

Abstract

Mechanical material properties of ligaments originate from their biochemical composition and structural organization. However, it is not yet fully elucidated how biochemical contents vary between knee ligaments and patellar tendon (PT) and how they relate with mechanical properties. The purpose of this study was to compare water, collagen, proteoglycan and elastin contents between bovine knee ligaments and PT and correlate them with tensile material properties. Hydroxyproline (collagen), uronic acid (proteoglycan) and elastin contents per wet and dry weights were measured using colorimetric biochemical methods for bovine knee ligament and PT samples (n = 10 knees). Direct comparison and correlation with multiple linear regression were performed against biomechanical properties measured in our earlier study. Anterior cruciate ligament (ACL) and PT exhibited lower hydroxyproline content per wet weight compared with other ligaments (p < 0.05). Cruciate ligaments had higher uronic acid content per dry weight compared with collateral ligaments (p < 0.05). Posterior cruciate ligament had higher elastin content than ACL (p < 0.05). Higher hydroxyproline content per wet weight implied higher Young's modulus, strength and toughness. Quantitatively, higher elastin content per wet weight predicted higher toe region nonlinearity and Young's modulus whereas higher uronic acid content per dry weight predicted lower Young's modulus, yield stress and toughness. Differences between ligaments in biochemical composition highlight differences in their physiological function and loading regimes. As expected, collagen content showed similar trend with stiffness and strength. The predictive role of proteoglycan and elastin contents on the mechanical properties might indicate their important functional role in ligaments.

KEYWORDS:

Elastin; Hydroxyproline; Knee joint; Ligament; Patellar tendon; Uronic acid

Conflict of interest statement

Declaration of competing interest Authors declare no conflicts of interest. Acknowledged funding sources had no involvement in the study design; in the collection, analysis and interpretation of data; in the writing of the manuscript; and in the decision to submit the manuscript for publication.

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