title: Changes in triphasic mechanical properties of proteoglycan-depleted articular cartilage extracted from osmotic swelling behavior monitored using high-frequency ultrasound.
abstract: This study aims to obtain osmosis-induced swelling strains of normal and proteoglycan (PG) depleted articular cartilage using an ultrasound system and to investigate the changes in its mechanical properties due to the PG depletion using a layered triphasic model. The swelling strains of 20 cylindrical cartilage-bone samples collected from different bovine patellae were induced by decreasing the concentration of bath saline and monitored by the ultrasound system. The samples were subsequently digested by a trypsin solution for approximately 20 min to deplete proteoglycans, and the swelling behaviors of the digested samples were measured again. The bi-layered triphasic model proposed in our previous study (Wang et al., J Biomech Eng-Trans ASME 2007; 129: 413-422) was used to predict the layered aggregate modulus Ha from the data of depth-dependent swelling strain, fixed charge density and water content. It was found that the region near the bone, for the normal specimens, had a significantly higher aggregate modulus (Ha1 = 20.6 +/- 18.2 MPa) in comparison with the middle zone and the surface layer (Ha2 = 7.8 +/- 14.5 MPa and Ha3 = 3.6 +/- 3.2 MPa, respectively) (p < 0.001). The normalized thickness of the deep layer h1 was 0.68 +/- 0.20. After the trypsin digestion, the parametric values decreased to Ha1 = 13.6 +/- 9.6 MPa, Ha2 = 6.7 +/- 11.5 MPa, Ha3 = 2.7 +/- 3.2 MPa, and h1 = 0.57 +/- 0.28. Other models were also used to analyze data and the results were compared. This study showed that high-frequency ultrasound measurement combined with the triphasic modeling was capable of nondestructively quantifying the alterations in the layered mechanical properties of the proteoglycan-depleted articular cartilage.
authors.affiliation: Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
authors.forename: Q
authors.initials: Q
authors.lastname: Wang
authors.forename: Y P
authors.initials: YP
authors.lastname: Zheng
authors.forename: H J
authors.initials: HJ
authors.lastname: Niu
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000000981:diagnostic imaging / Q000502:physiology*; D002417:Cattle; D066298:In Vitro Techniques; D008954:Models, Biological; D009997:Osmotic Pressure; D010329:Patella / Q000000981:diagnostic imaging / Q000502:physiology; D011509:Proteoglycans / Q000302:isolation & purification / Q000502:physiology*; D014463:Ultrasonography
chemical_list: D011509:Proteoglycans