Cartilage and collagen mechanics under large-strain shear within in vivo and at supraphysiogical temperatures. (March 2020)

• Record Type: Journal Article
• Authors: Marshall, Lauren; Tarakanova, Anna; Szarek, Phoebe; Pierce, David M.
• Is Part Of: Journal of the mechanical behavior of biomedical materials. Volume 103(2020)
• Publication Date: 2020-03
• Subjects: Articular Cartilage -- Collagen -- Large strain -- Shear -- Temperature -- Denaturation; Biomedical materials -- Periodicals; Biomedical materials -- Mechanical properties -- Periodicals; Biomedical materials; Biomedical materials -- Mechanical properties; Periodicals; Electronic journals; 610.28
• DOI: 10.1016/j.jmbbm.2019.103595
• Languages: English
• ISSNs: 1751-6161

Abstract

Abstract: Human joints, particularly those of extremities, experience a significant range of temperatures in vivo . Joint temperature influences the mechanics of both joint and cartilage, and the mechanics of cartilage can affect the temperature of both joint and cartilage. Thermal treatments and tissue repairs, such as thermal chondroplasty, and ex vivo tissue engineering may also expose cartilage to supraphysiological temperatures. Furthermore, although cartilage undergoes principally compressive loads in vivo, shear strain plays a significant role at larger compressive strains. Thus, we aimed to determine whether and how the bulk mechanical responses of cartilage undergoing large-strain shear change (1) within the range of temperatures relevant in vivo, and (2) both during and after supraphysiological thermal treatments. We completed large-strain shear tests (10 and 15%) at four thermal conditions: 24 ∘ C and 40 ∘ C to span the in vivo range, and 70 ∘ C and 24 ∘ C repeated after 70 ∘ C to explore mechanics during and after potential treatments. We calculated the bulk mechanical responses (strain-energy dissipation densities, peak-to-peak shear stresses, and peak-effective shear moduli) as of function of temperature and used statistical methods to probe significant differences. To probe the mechanisms underlying differences we assessed specimens, principally the type II collagen, with imaging (second harmonic generation and transmission electron microscopies, and histology) and assessed the temperature-dependent mechanics of type II collagen molecules within cartilage using steered molecular dynamics simulations. Our results suggest that the bulk mechanical responses of cartilage depend significantly on temperature both within the in vivo range and at supraphysiological temperatures, showing significant reductions in all mechanical measures with increasing temperature. Using imaging and simulations we determined that one underlying mechanism explaining our results may be changes in the molecular deformation profiles of collagen molecules versus temperature, likely compounded at larger length scales. These new insights into the mechanics of cartilage and collagen may suggest new treatment targets for damaged or osteoarthritic cartilage. Graphical abstract: Image 1 Highlights: ● Significant differences in cartilage mechanics at range of in vivo temperatures. ● Cartilage dissipates less strain energy and is more compliant at higher temperatures. ● TEM images after thermal treatments show fiber swelling from thermal damage. ● Simulations of collagen extension at temp. show tensile unwinding then shear slipping. ● Temp.-dependent ratios of molecular forces correspond to ratios of bulk mechanics.