Selective Enzymatic Digestion of Proteoglycans and Collagens Alters Cartilage T1rho and T2 Relaxation Times

  • Amber T. Collins
  • Courtney C. Hatcher
  • Sophia Y. Kim
  • Sophia N. Ziemian
  • Charles E. Spritzer
  • Farshid Guilak
  • Louis E. DeFrate
  • Amy L. McNulty


Our objective was to determine the relationship of T1rho and T2 relaxation mapping to the biochemical and biomechanical properties of articular cartilage through selective digestion of proteoglycans and collagens. Femoral condyles were harvested from porcine knee joints and treated with either chondroitinase ABC (cABC) followed by collagenase, or collagenase followed by cABC. Magnetic resonance images were acquired and cartilage explants were harvested for biochemical, biomechanical, and histological analyses before and after each digestion. Targeted enzymatic digestion of proteoglycans with cABC resulted in elevated T1rho relaxation times and decreased sulfated glycosaminoglycan content without affecting T2 relaxation times. In contrast, extractable collagen and T2 relaxation times were increased by collagenase digestion; however, neither was altered by cABC digestion. Aggregate modulus decreased with digestion of both components. Overall, we found that targeted digestion of proteoglycans and collagens had varying effects on biochemical, biomechanical, and imaging properties. T2 relaxation times were altered with changes in extractable collagen, but not changes in proteoglycan. However, T1rho relaxation times were altered with proteoglycan loss, which may also coincide with collagen disruption. Since it is unclear which matrix components are disrupted first in osteoarthritis, both markers may be important for tracking disease progression.


MRI Validation Osteoarthritis Articular cartilage Collagens Proteoglycan Biomarkers 



The authors would like to thank the National Institutes of Health (AR065527, AR066477, AG15768, AG028716, AG46927), the Veteran’s Affairs Rehabilitation Research Service Award, the Orthopaedic Research and Education Foundation, and the AO Foundation for financial support of this work. Additionally, the authors would like to thank the Duke Center for Advanced Magnetic Resonance Development (CAMRD) for their assistance with MR imaging.

Conflict of interest

The authors have no conflicts of interest.


  1. 1.
    Akella, S. V., R. R. Regatte, A. J. Gougoutas, A. Borthakur, E. M. Shapiro, J. B. Kneeland, J. S. Leigh, and R. Reddy. Proteoglycan-induced changes in T1rho-relaxation of articular cartilage at 4T. Magn. Reson. Med. 46(3):419–423, 2001.CrossRefPubMedGoogle Scholar
  2. 2.
    Armstrong, C. G., and V. C. Mow. Variations in the intrinsic mechanical properties of human articular cartilage with age, degeneration, and water content. J. Bone Joint Surg. Am. 64(1):88–94, 1982.CrossRefPubMedGoogle Scholar
  3. 3.
    Bank, R., M. Krikken, B. Beekman, R. Stoop, A. Maroudas, F. Lafeber, and J. te Koppele. A simplified measurement of degraded collagen in tissues: application in healthy, fibrillated and osteoarthritic cartilage. Matrix Biol. 16(5):233–243, 1997.CrossRefPubMedGoogle Scholar
  4. 4.
    Billinghurst, R. C., L. Dahlberg, M. Ionescu, A. Reiner, R. Bourne, C. Rorabeck, P. Mitchell, J. Hambor, O. Diekmann, H. Tschesche, J. Chen, H. Van Wart, and A. R. Poole. Enhanced cleavage of type II collagen by collagenases in osteoarthritic articular cartilage. J Clin Invest 99(7):1534–1545, 1997.CrossRefPubMedPubMedCentralGoogle Scholar
  5. 5.
    Borthakur, A., A. Wheaton, S. R. Charagundla, E. M. Shapiro, R. R. Regatte, S. V. Akella, J. B. Kneeland, and R. Reddy. Three-dimensional T1rho-weighted MRI at 1.5 Tesla. J. Magn. Reson. Imaging 17(6):730–736, 2003.CrossRefPubMedGoogle Scholar
  6. 6.
    Carter, T. E., K. A. Taylor, C. E. Spritzer, G. M. Utturkar, D. C. Taylor, C. T. Moorman, 3rd, W. E. Garrett, F. Guilak, A. L. McNulty, and L. E. DeFrate. In vivo cartilage strain increases following medial meniscal tear and correlates with synovial fluid matrix metalloproteinase activity. J. Biomech. 48(8):1461–1468, 2015.CrossRefPubMedPubMedCentralGoogle Scholar
  7. 7.
    Catterall, J. B., T. V. Stabler, C. R. Flannery, and V. B. Kraus. Changes in serum and synovial fluid biomarkers after acute injury (NCT00332254). Arthritis Res Ther. 12(6):R229, 2010.CrossRefPubMedPubMedCentralGoogle Scholar
  8. 8.
    Choi, J. A., and G. E. Gold. MR imaging of articular cartilage physiology. Magn. Reson. Imaging Clin. N. Am. 19(2):249–282, 2011.CrossRefPubMedPubMedCentralGoogle Scholar
  9. 9.
    David-Vaudey, E., S. Ghosh, M. Ries, and S. Majumdar. T2 relaxation time measurements in osteoarthritis. Magn. Reson. Imaging 22(5):673–682, 2004.CrossRefPubMedGoogle Scholar
  10. 10.
    Detamore, M. S., and K. A. Athanasiou. Effects of growth factors on temporomandibular joint disc cells. Arch. Oral Biol. 49(7):577–583, 2004.CrossRefPubMedGoogle Scholar
  11. 11.
    Duvvuri, U., S. Kudchodkar, R. Reddy, and J. Leigh. T(1rho) relaxation can assess longitudinal proteoglycan loss from articular cartilage in vitro. Osteoarthritis Cartilage 10(11):838–844, 2002.CrossRefPubMedGoogle Scholar
  12. 12.
    Duvvuri, U., R. Reddy, S. D. Patel, J. H. Kaufman, J. B. Kneeland, and J. S. Leigh. T1rho-relaxation in articular cartilage: effects of enzymatic degradation. Magn. Reson. Med. 38(6):863–867, 1997.CrossRefPubMedGoogle Scholar
  13. 13.
    Farndale, R. W., C. A. Sayers, and A. J. Barrett. A direct spectrophotometric microassay for sulfated glycosaminoglycans in cartilage cultures. Connect. Tissue Res. 9(4):247–248, 1982.CrossRefPubMedGoogle Scholar
  14. 14.
    Fazaeli, S., S. Ghazanfari, V. Everts, T. H. Smit, and J. H. Koolstra. The contribution of collagen fibers to the mechanical compressive properties of the temporomandibular joint disc. Osteoarthritis Cartilage 24(7):1292–1301, 2016.CrossRefPubMedGoogle Scholar
  15. 15.
    Fleck, A. K. M., U. Kruger, K. Carlson, C. Waltz, S. A. McCallum, X. Lucas Lu, and L. Q. Wan. Zonal variation of MRI-measurable parameters classifies cartilage degradation. J. Biomech. 65:176–184, 2017.CrossRefPubMedGoogle Scholar
  16. 16.
    Grenier, S., M. M. Bhargava, and P. A. Torzilli. An in vitro model for the pathological degradation of articular cartilage in osteoarthritis. J. Biomech. 47(3):645–652, 2014.CrossRefPubMedGoogle Scholar
  17. 17.
    Guilak, F., A. Ratcliffe, N. Lane, M. P. Rosenwasser, and V. C. Mow. Mechanical and biochemical changes in the superficial zone of articular cartilage in canine experimental osteoarthritis. J. Orthop. Res. 12(4):474–484, 1994.CrossRefPubMedGoogle Scholar
  18. 18.
    Harris, Jr, E. D., H. G. Parker, E. L. Radin, and S. M. Krane. Effects of proteolytic enzymes on structural and mechanical properties of cartilage. Arthritis Rheum. 15(5):497–503, 1972.CrossRefPubMedGoogle Scholar
  19. 19.
    Hatcher, C. C., A. T. Collins, S. Y. Kim, L. C. Michel, W. C. Mostertz, 3rd, S. N. Ziemian, C. E. Spritzer, F. Guilak, L. E. DeFrate, and A. L. McNulty. Relationship between T1rho magnetic resonance imaging, synovial fluid biomarkers, and the biochemical and biomechanical properties of cartilage. J. Biomech. 55:18–26, 2017.CrossRefPubMedPubMedCentralGoogle Scholar
  20. 20.
    Hollander, A. P., I. Pidoux, A. Reiner, C. Rorabeck, R. Bourne, and A. R. Poole. Damage to type II collagen in aging and osteoarthritis starts at the articular surface, originates around chondrocytes, and extends into the cartilage with progressive degeneration. J. Clin. Invest. 96(6):2859–2869, 1995.CrossRefPubMedPubMedCentralGoogle Scholar
  21. 21.
    Hosseininia, S., L. R. Lindberg, and L. E. Dahlberg. Cartilage collagen damage in hip osteoarthritis similar to that seen in knee osteoarthritis; a case–control study of relationship between collagen, glycosaminoglycan and cartilage swelling. BMC Musculoskelet. Disord. 14:18, 2013.CrossRefPubMedPubMedCentralGoogle Scholar
  22. 22.
    Hosseininia, S., M. A. Weis, J. Rai, L. Kim, S. Funk, L. E. Dahlberg, and D. R. Eyre. Evidence for enhanced collagen type III deposition focally in the territorial matrix of osteoarthritic hip articular cartilage. Osteoarthritis Cartilage 24(6):1029–1035, 2016.CrossRefPubMedPubMedCentralGoogle Scholar
  23. 23.
    Janusz, M. J., A. M. Bendele, K. K. Brown, Y. O. Taiwo, L. Hsieh, and S. A. Heitmeyer. Induction of osteoarthritis in the rat by surgical tear of the meniscus: inhibition of joint damage by a matrix metalloproteinase inhibitor. Osteoarthritis Cartilage 10(10):785–791, 2002.CrossRefPubMedGoogle Scholar
  24. 24.
    Karsdal, M. A., S. H. Madsen, C. Christiansen, K. Henriksen, A. J. Fosang, and B. C. Sondergaard. Cartilage degradation is fully reversible in the presence of aggrecanase but not matrix metalloproteinase activity. Arthritis Res. Ther. 10(3):R63, 2008.CrossRefPubMedPubMedCentralGoogle Scholar
  25. 25.
    Keenan, K. E., T. F. Besier, J. M. Pauly, E. Han, J. Rosenberg, R. L. Smith, S. L. Delp, G. S. Beaupre, and G. E. Gold. Prediction of glycosaminoglycan content in human cartilage by age, T1rho and T2 MRI. Osteoarthritis Cartilage 19(2):171–179, 2011.CrossRefPubMedGoogle Scholar
  26. 26.
    Kurkijarvi, J. E., M. J. Nissi, I. Kiviranta, J. S. Jurvelin, and M. T. Nieminen. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) and T2 characteristics of human knee articular cartilage: topographical variation and relationships to mechanical properties. Magn. Reson. Med. 52(1):41–46, 2004.CrossRefPubMedGoogle Scholar
  27. 27.
    Lark, M. W., E. K. Bayne, J. Flanagan, C. F. Harper, L. A. Hoerrner, N. I. Hutchinson, I. I. Singer, S. A. Donatelli, J. R. Weidner, H. R. Williams, R. A. Mumford, and L. S. Lohmander. Aggrecan degradation in human cartilage. Evidence for both matrix metalloproteinase and aggrecanase activity in normal, osteoarthritic, and rheumatoid joints. J. Clin. Invest. 100(1):93–106, 1997.CrossRefPubMedPubMedCentralGoogle Scholar
  28. 28.
    Larsson, S., L. S. Lohmander, and A. Struglics. Synovial fluid level of aggrecan ARGS fragments is a more sensitive marker of joint disease than glycosaminoglycan or aggrecan levels: a cross-sectional study. Arthritis Res. Ther. 11(3):R92, 2009.CrossRefPubMedPubMedCentralGoogle Scholar
  29. 29.
    Lawrence, R., D. Felson, C. Helmick, L. Arnold, H. Choi, R. Devo, S. Gabriel, R. Hirsch, M. Hochberg, M. Hunder, J. Jordan, J. Katz, H. Kremers, and F. Wolfe. Estimates of the prevalence of arthritis and other rheumatic conditions in the United States. Part II. Arthritis Rheum. 58(1):26–35, 2008.CrossRefPubMedPubMedCentralGoogle Scholar
  30. 30.
    Li, X., C. Benjamin Ma, T. M. Link, D. D. Castillo, G. Blumenkrantz, J. Lozano, J. Carballido-Gamio, M. Ries, and S. Majumdar. In vivo T(1rho) and T(2) mapping of articular cartilage in osteoarthritis of the knee using 3 T MRI. Osteoarthritis Cartilage 15(7):789–797, 2007.CrossRefPubMedPubMedCentralGoogle Scholar
  31. 31.
    Li, X., J. Cheng, K. Lin, E. Saadat, R. I. Bolbos, B. Jobke, M. D. Ries, A. Horvai, T. M. Link, and S. Majumdar. Quantitative MRI using T1rho and T2 in human osteoarthritic cartilage specimens: correlation with biochemical measurements and histology. Magn. Reson. Imaging 29(3):324–334, 2011.CrossRefPubMedGoogle Scholar
  32. 32.
    Li, X., A. Pai, G. Blumenkrantz, J. Carballido-Gamio, T. Link, B. Ma, M. Ries, and S. Majumdar. Spatial distribution and relationship of T1rho and T2 relaxation times in knee cartilage with osteoarthritis. Magn. Reson. Med. 61(6):1310–1318, 2009.CrossRefPubMedPubMedCentralGoogle Scholar
  33. 33.
    Liu, B., N. K. Lad, A. T. Collins, P. K. Ganapathy, G. M. Utturkar, A. L. McNulty, C. E. Spritzer, C. T. Moorman, III, E. G. Sutter, W. E. Garrett, and L. E. DeFrate. In vivo tibial cartilage strains in regions of cartilage-to-cartilage contact and cartilage-to-meniscus contact in response to walking. Am. J. Sports Med. 45(12):2817–2823, 2017.CrossRefPubMedPubMedCentralGoogle Scholar
  34. 34.
    Lu, X. L., V. C. Mow, and X. E. Guo. Proteoglycans and mechanical behavior of condylar cartilage. J. Dent. Res. 88(3):244–248, 2009.CrossRefPubMedPubMedCentralGoogle Scholar
  35. 35.
    Lyyra, T., J. P. Arokoski, N. Oksala, A. Vihko, M. Hyttinen, J. S. Jurvelin, and I. Kiviranta. Experimental validation of arthroscopic cartilage stiffness measurement using enzymatically degraded cartilage samples. Phys. Med. Biol. 44(2):525–535, 1999.CrossRefPubMedGoogle Scholar
  36. 36.
    Madsen, S. H., E. U. Sumer, A. C. Bay-Jensen, B. C. Sondergaard, P. Qvist, and M. A. Karsdal. Aggrecanase- and matrix metalloproteinase-mediated aggrecan degradation is associated with different molecular characteristics of aggrecan and separated in time ex vivo. Biomarkers 15(3):266–276, 2010.CrossRefPubMedGoogle Scholar
  37. 37.
    Maroudas, A., I. Ziv, N. Weisman, and M. Venn. Studies of hydration and swelling pressure in normal and osteoarthritic cartilage. Biorheology 22(2):159–169, 1985.CrossRefPubMedGoogle Scholar
  38. 38.
    Martin, J. A., and J. A. Buckwalter. Roles of articular cartilage aging and chondrocyte senescence in the pathogenesis of osteoarthritis. Iowa Orthop. J. 21:1–7, 2001.PubMedPubMedCentralGoogle Scholar
  39. 39.
    McNulty, A. L., N. E. Rothfusz, H. A. Leddy, and F. Guilak. Synovial fluid concentrations and relative potency of interleukin-1 alpha and beta in cartilage and meniscus degradation. J. Orthop. Res. 31(7):1039–1045, 2013.CrossRefPubMedPubMedCentralGoogle Scholar
  40. 40.
    Mosher, T. J., H. E. Smith, C. Collins, Y. Liu, J. Hancy, B. J. Dardzinski, and M. B. Smith. Change in knee cartilage T2 at MR imaging after running: a feasibility study. Radiology 234(1):245–249, 2005.CrossRefPubMedGoogle Scholar
  41. 41.
    Mow, V. C., S. C. Kuei, W. M. Lai, and C. G. Armstrong. Biphasic creep and stress relaxation of articular cartilage in compression? Theory and experiments. J. Biomech. Eng. 102(1):73–84, 1980.CrossRefPubMedGoogle Scholar
  42. 42.
    Nieminen, M. T., J. Rieppo, J. Toyras, J. M. Hakumaki, J. Silvennoinen, M. M. Hyttinen, H. J. Helminen, and J. S. Jurvelin. T2 relaxation reveals spatial collagen architecture in articular cartilage: a comparative quantitative MRI and polarized light microscopic study. Magn. Reson. Med. 46(3):487–493, 2001.CrossRefPubMedGoogle Scholar
  43. 43.
    Nieminen, M. T., J. Toyras, M. S. Laasanen, J. Silvennoinen, H. J. Helminen, and J. S. Jurvelin. Prediction of biomechanical properties of articular cartilage with quantitative magnetic resonance imaging. J. Biomech. 37(3):321–328, 2004.CrossRefPubMedGoogle Scholar
  44. 44.
    Nieminen, M. T., J. Toyras, J. Rieppo, J. M. Hakumaki, J. Silvennoinen, H. J. Helminen, and J. S. Jurvelin. Quantitative MR microscopy of enzymatically degraded articular cartilage. Magn. Reson. Med. 43(5):676–681, 2000.CrossRefPubMedGoogle Scholar
  45. 45.
    Nishioka, H., J. Hirose, E. Nakamura, Y. Oniki, K. Takada, Y. Yamashita, and H. Mizuta. T1rho and T2 mapping reveal the in vivo extracellular matrix of articular cartilage. J. Magn. Reson. Imaging 35(1):147–155, 2012.CrossRefPubMedGoogle Scholar
  46. 46.
    Nissi, M. J., E. N. Salo, V. Tiitu, T. Liimatainen, S. Michaeli, S. Mangia, J. Ellermann, and M. T. Nieminen. Multi-parametric MRI characterization of enzymatically degraded articular cartilage. J. Orthop. Res. 34(7):1111–1120, 2016.CrossRefPubMedGoogle Scholar
  47. 47.
    Regatte, R. R., S. V. Akella, A. Borthakur, J. B. Kneeland, and R. Reddy. Proteoglycan depletion-induced changes in transverse relaxation maps of cartilage: comparison of T2 and T1rho. Acad. Radiol. 9(12):1388–1394, 2002.CrossRefPubMedGoogle Scholar
  48. 48.
    Rowland, C. R., D. P. Lennon, A. I. Caplan, and F. Guilak. The effects of crosslinking of scaffolds engineered from cartilage ECM on the chondrogenic differentiation of MSCs. Biomaterials 34(23):5802–5812, 2013.CrossRefPubMedPubMedCentralGoogle Scholar
  49. 49.
    Sah, R. L., A. S. Yang, A. C. Chen, J. J. Hant, R. B. Halili, M. Yoshioka, D. Amiel, and R. D. Coutts. Physical properties of rabbit articular cartilage after transection of the anterior cruciate ligament. J. Orthop. Res. 15(2):197–203, 1997.CrossRefPubMedGoogle Scholar
  50. 50.
    Sanchez-Adams, J., H. A. Leddy, A. L. McNulty, C. J. O’Conor, and F. Guilak. The mechanobiology of articular cartilage: bearing the burden of osteoarthritis. Curr. Rheumatol. Rep. 16(10):451, 2014.CrossRefPubMedPubMedCentralGoogle Scholar
  51. 51.
    Setton, L. A., D. M. Elliott, and V. C. Mow. Altered mechanics of cartilage with osteoarthritis: human osteoarthritis and an experimental model of joint degeneration. Osteoarthritis Cartilage 7(1):2–14, 1999.CrossRefPubMedGoogle Scholar
  52. 52.
    Setton, L. A., W. Zhu, and V. C. Mow. The biphasic poroviscoelastic behavior of articular cartilage: role of the surface zone in governing the compressive behavior. J. Biomech. 26(4–5):581–592, 1993.CrossRefPubMedGoogle Scholar
  53. 53.
    Shingleton, W. D., D. J. Hodges, P. Brick, and T. E. Cawston. Collagenase: a key enzyme in collagen turnover. Biochem. Cell Biol. 74(6):759–775, 1996.CrossRefPubMedGoogle Scholar
  54. 54.
    Souza, R. B., D. Kumar, N. Calixto, J. Singh, J. Schooler, K. Subburaj, X. Li, T. M. Link, and S. Majumdar. Response of knee cartilage T1rho and T2 relaxation times to in vivo mechanical loading in individuals with and without knee osteoarthritis. Osteoarthritis Cartilage 22(10):1367–1376, 2014.CrossRefPubMedPubMedCentralGoogle Scholar
  55. 55.
    Stoop, R., P. Buma, P. M. van der Kraan, A. P. Hollander, R. C. Billinghurst, T. H. Meijers, A. R. Poole, and W. B. van den Berg. Type II collagen degradation in articular cartilage fibrillation after anterior cruciate ligament transection in rats. Osteoarthritis Cartilage 9(4):308–315, 2001.CrossRefPubMedGoogle Scholar
  56. 56.
    Subburaj, K., D. Kumar, R. Souza, H. Alizai, X. Li, T. Link, and S. Majumdar. The acute effect of running on knee articular cartilage and meniscus magnetic resonance relaxation times in young healthy adults. Am. J. Sports Med. 40(9):2134–2141, 2012.CrossRefPubMedPubMedCentralGoogle Scholar
  57. 57.
    Sutter, E. G., M. R. Widmyer, G. M. Utturkar, C. E. Spritzer, W. E. Garrett, Jr, and L. E. DeFrate. In vivo measurement of localized tibiofemoral cartilage strains in response to dynamic activity. Am. J. Sports Med. 43(2):370–376, 2015.CrossRefPubMedGoogle Scholar
  58. 58.
    Tang, S. Y., R. B. Souza, M. Ries, P. K. Hansma, T. Alliston, and X. Li. Local tissue properties of human osteoarthritic cartilage correlate with magnetic resonance T(1) rho relaxation times. J. Orthop. Res. 29(9):1312–1319, 2011.CrossRefPubMedPubMedCentralGoogle Scholar
  59. 59.
    Temple-Wong, M. M., W. C. Bae, M. Q. Chen, W. D. Bugbee, D. Amiel, R. D. Coutts, M. Lotz, and R. L. Sah. Biomechanical, structural, and biochemical indices of degenerative and osteoarthritic deterioration of adult human articular cartilage of the femoral condyle. Osteoarthritis Cartilage 17(11):1469–1476, 2009.CrossRefPubMedPubMedCentralGoogle Scholar
  60. 60.
    Tsushima, H., K. Okazaki, Y. Takayama, M. Hatakenaka, H. Honda, T. Izawa, Y. Nakashima, H. Yamada, and Y. Iwamoto. Evaluation of cartilage degradation in arthritis using T1rho magnetic resonance imaging mapping. Rheumatol. Int. 32(9):2867–2875, 2012.CrossRefPubMedGoogle Scholar
  61. 61.
    Wayne, J. S., K. A. Kraft, K. J. Shields, C. Yin, J. R. Owen, and D. G. Disler. MR imaging of normal and matrix-depleted cartilage: correlation with biomechanical function and biochemical composition. Radiology 228(2):493–499, 2003.CrossRefPubMedGoogle Scholar
  62. 62.
    Wei, B., X. T. Du, J. Liu, F. Y. Mao, X. Zhang, S. Liu, Y. Xu, F. C. Zang, and L. M. Wang. Associations between the properties of the cartilage matrix and findings from quantitative MRI in human osteoarthritic cartilage of the knee. Int. J. Clin. Exp. Pathol. 8(4):3928–3936, 2015.PubMedPubMedCentralGoogle Scholar
  63. 63.
    Wheaton, A. J., G. R. Dodge, A. Borthakur, J. B. Kneeland, H. R. Schumacher, and R. Reddy. Detection of changes in articular cartilage proteoglycan by T(1rho) magnetic resonance imaging. J. Orthop. Res. 23(1):102–108, 2004.CrossRefGoogle Scholar
  64. 64.
    Wheaton, A. J., G. R. Dodge, D. M. Elliott, S. B. Nicoll, and R. Reddy. Quantification of cartilage biomechanical and biochemical properties via T1rho magnetic resonance imaging. Magn. Reson. Med. 54(5):1087–1093, 2005.CrossRefPubMedGoogle Scholar
  65. 65.
    Widmyer, M. R., G. M. Utturkar, H. A. Leddy, J. L. Coleman, C. E. Spritzer, C. T. Moorman, III, L. E. Defrate, and F. Guilak. High body mass index is associated with increased diurnal strains in the articular cartilage of the knee. Arthritis Rheum. 65(10):2615–2622, 2013.PubMedPubMedCentralGoogle Scholar
  66. 66.
    Wilusz, R. E., S. Zauscher, and F. Guilak. Micromechanical mapping of early osteoarthritic changes in the pericellular matrix of human articular cartilage. Osteoarthritis Cartilage 21(12):1895–1903, 2013.CrossRefPubMedGoogle Scholar
  67. 67.
    Woessner, Jr, J. F. The determination of hydroxyproline in tissue and protein samples containing small proportions of this imino acid. Arch. Biochem. Biophys. 93:440–447, 1961.CrossRefPubMedGoogle Scholar

Copyright information

© Biomedical Engineering Society 2018

Authors and Affiliations

  • Amber T. Collins
    • 1
  • Courtney C. Hatcher
    • 1
  • Sophia Y. Kim
    • 1
    • 4
  • Sophia N. Ziemian
    • 1
  • Charles E. Spritzer
    • 2
  • Farshid Guilak
    • 6
  • Louis E. DeFrate
    • 1
    • 4
    • 5
  • Amy L. McNulty
    • 1
    • 3
  1. 1.Department of Orthopaedic SurgeryDuke University School of MedicineDurhamUSA
  2. 2.Department of RadiologyDuke University School of MedicineDurhamUSA
  3. 3.Department of PathologyDuke University School of MedicineDurhamUSA
  4. 4.Department of Biomedical EngineeringDuke UniversityDurhamUSA
  5. 5.Department of Mechanical Engineering and Materials ScienceDuke UniversityDurhamUSA
  6. 6.Department of Orthopaedic SurgeryWashington University and Shriners Hospital for ChildrenSt. LouisUSA

Personalised recommendations