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Objective: To evaluate effects of a common CT contrast agent (iohexol) on the mechanical behaviors of cartilage and meniscus., Methods: Indentation responses of juvenile bovine cartilage and meniscus were monitored following exposure to undiluted contrast agent (100% CA), 50% CA/water, 50% CA/Phosphate Buffered Saline (PBS) or PBS alone, and during re-equilibration in PBS. The normalized peak force (F pk ¯), effective osmotic strain (ε osm ), and normalized effective contact modulus (E c ¯) were calculated for every cycle, with time constants determined for both exposure and recovery via mono- or biexponential fits to F pk ¯., Results: All cartilage CA groups exhibited long-term increases in F pk ¯ following exposure, although the hyperosmolal 100% CA and 50% CA/PBS groups showed an initial transient decrease. Meniscus presented opposing trends, with decreasing F pk ¯ for all CA groups. Re-equilibration in PBS for 1hr after exposure to 100% CA produced recovery to baseline F pk ¯ in cartilage but not in meniscus, and extended tests indicated that meniscus required ∼2.5 h to recover halfway. E c ¯ increased with CA exposure time for cartilage but decreased for meniscus, suggesting an increased effective stiffness for cartilage and decreased stiffness for meniscus. Long-term changes to ε osm in both tissues were consistent with changes in E c ¯., Conclusion: Exposure to iohexol solutions affected joint tissues differentially, with increased cartilage stiffness, likely relating to competing hyperosmotic and hypotonic interactions with tissue fixed charges, and decreased meniscus stiffness, likely dominated by hyperosmolarity. These altered tissue mechanics could allow non-physiological deformation during ambulatory weight-bearing, resulting in an increased risk of tissue or cell damage., (Copyright © 2020 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.)

Determining the influence of tissue composition on the osmotic swelling stress of articular cartilage and meniscus fibrocartilage is important to enhance our understanding of physiology and disease. This osmotic swelling stress is critical for the load-bearing capability of both tissues and results in part due to the interactions between the negatively charged sulfated glycosaminoglycan (sGAG) chains and the ionic interstitial fluid. Changes in sGAG content, as those occurring during the progression of degenerative joint disease, alter such interactions. Here, we compare the time-varying effects of altered osmotic environments on the confined compression swelling behavior of bovine tissues spanning a range of sGAG concentrations: juvenile articular cartilage, juvenile and adult meniscus, and juvenile cartilage enzymatically degraded to reduce its sGAG content. The transient response to changes in bath conditions was evaluated for explants assigned to one of three compressive offsets (5%, 10%, or 15% strain) and one of three bath conditions (0.1X, 1X, or 10X phosphate-buffered saline). Our results show that relative responses to alterations to the osmotic environment are consistent across native tissues but differ for degraded juvenile cartilage, demonstrating that changes in sGAG do not completely recapitulate the native swelling behaviors. Further, we found a strong correlation between aggregate modulus and sGAG/collagen, as well as between sGAG and collagen contents across native tissue types, suggesting some conservation of composition-function relationships across a range of tissue types with varying sGAG concentrations. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:785-792, 2020., (© 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.)