Collagen is a ubiquitous biomaterial in vertebrate animals. Although each of its 28 subtypes contributes to the functions of many different tissues in the body, most studies on collagen or collagenous tissues have focused on only one or two subtypes. With recent developments in analytical chemistry, especially mass spectrometry, substantial advances have been made towards quantifying the different collagen subtypes in various tissues; however, high-throughput and low-cost methods for collagen-subtype quantification do not yet exist. In this Review, we introduce the roles of collagen subtypes and crosslinks and describe modern assays that enable a deep understanding of tissue physiology and disease states. Using cartilage as a model tissue, we describe the roles of major and minor collagen subtypes in detail, discuss known and unknown structure–function relationships and show how tissue engineers may harness the functional characteristics of collagen to engineer robust neotissues.
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Whitslar, W. H. A study of the chemical composition of the dental pulp. Am. J. Dent. Sci. 23, 350–355 (1889).
Lin, S. & Gu, L. Influence of crosslink density and stiffness on mechanical properties of type I collagen gel. Materials 8, 551–560 (2015).
Eleswarapu, S. V., Responte, D. J. & Athanasiou, K. A. Tensile properties, collagen content, and crosslinks in connective tissues of the immature knee joint. PLoS ONE 6, e26178 (2011).
Brüel, A., Ørtoft, G. & Oxlund, H. Inhibition of cross-links in collagen is associated with reduced stiffness of the aorta in young rats. Atherosclerosis 140, 135–145 (1998).
Fang, M., Yuan, J., Peng, C. & Li, Y. Collagen as a double-edged sword in tumor progression. Tumour Biol. 35, 2871–2882 (2014).
Xu, S. et al. The role of collagen in cancer: from bench to bedside. J. Transl. Med. 17, 309 (2019).
Poole, A. R. et al. Type II collagen degradation and its regulation in articular cartilage in osteoarthritis. Ann. Rheum. Dis. 61, ii78–ii81 (2002).
Landewé, R. B. M. et al. Arthritis instantaneously causes collagen type I and type II degradation in patients with early rheumatoid arthritis: a longitudinal analysis. Ann. Rheum. Dis. 65, 40–44 (2006).
Kuivaniemi, H., Tromp, G. & Prockop, D. J. Mutations in collagen genes: causes of rare and some common diseases in humans. FASEB J. 5, 2052–2060 (1991).
Arseni, L., Lombardi, A. & Orioli, D. From structure to phenotype: impact of collagen alterations on human health. Int. J. Mol. Sci. 19, 1407 (2018).
Sorushanova, A. et al. The collagen suprafamily: from biosynthesis to advanced biomaterial development. Adv. Mater. 31, e1801651 (2019).
Kadler, K. E., Hill, A. & Canty-Laird, E. G. Collagen fibrillogenesis: fibronectin, integrins, and minor collagens as organizers and nucleators. Curr. Opin. Cell Biol. 20, 495–501 (2008).
Shoulders, M. D. & Raines, R. T. Collagen structure and stability. Annu. Rev. Biochem. 78, 929–958 (2009). This review paper describes the structure and characteristics of collagen triple helices.
Responte, D. J., Natoli, R. M. & Athanasiou, K. A. Collagens of articular cartilage: structure, function, and importance in tissue engineering. Crit. Rev. Biomed. Eng. 35, 363–411 (2007).
Lin, K. et al. Advanced collagen-based biomaterials for regenerative biomedicine. Adv. Funct. Mater. 29, 1804943 (2019).
Chang, S.-W. & Buehler, M. J. Molecular biomechanics of collagen molecules. Mater. Today 17, 70–76 (2014).
Ricard-Blum, S. The collagen family. Cold Spring Harb. Perspect. Biol. 3, a004978 (2011).
Sharma, U. et al. Structural basis of homo- and heterotrimerization of collagen I. Nat. Commun. 8, 14671 (2017).
An, B. et al. Definition of the native and denatured type II collagen binding site for fibronectin using a recombinant collagen system. J. Biol. Chem. 289, 4941–4951 (2014).
Pihlajamaa, T. et al. Characterization of recombinant human type IX collagen. Association of alpha chains into homotrimeric and heterotrimeric molecules. J. Biol. Chem. 274, 22464–22468 (1999).
Eyre, D. R., Weis, M. A. & Wu, J.-J. Advances in collagen cross-link analysis. Methods 45, 65–74 (2008). This paper highlights methods for analysing crosslinked collagen peptides with LC-MS/MS and shows intermolecular crosslinks between collagen types IX and II.
Siegel, R. C. Biosynthesis of collagen crosslinks: increased activity of purified lysyl oxidase with reconstituted collagen fibrils. Proc. Natl Acad. Sci. USA 71, 4826–4830 (1974).
Barnard, K., Light, N. D., Sims, T. J. & Bailey, A. J. Chemistry of the collagen cross-links. Origin and partial characterization of a putative mature cross-link of collagen. Biochem. J. 244, 303–309 (1987).
Robins, S. P. in Dynamics of Bone and Cartilage Metabolism (eds Seibel, M. J., Robins, S. P. & Bilezikian, J. P.) 41–53 (Elsevier, 2006).
Avery, N. C., Sims, T. J. & Bailey, A. J. Quantitative determination of collagen cross-links. Methods Mol. Biol. 522, 103–121 (2009).
Saito, M. & Marumo, K. Effects of collagen crosslinking on bone material properties in health and disease. Calcif. Tissue Int. 97, 242–261 (2015).
Eyre, D. R., Weis, M. A. & Wu, J.-J. Maturation of collagen ketoimine cross-links by an alternative mechanism to pyridinoline formation in cartilage. J. Biol. Chem. 285, 16675–16682 (2010).
Willett, T. L., Kandel, R., De Croos, J. N. A., Avery, N. C. & Grynpas, M. D. Enhanced levels of non-enzymatic glycation and pentosidine crosslinking in spontaneous osteoarthritis progression. Osteoarthr. Cartil. 20, 736–744 (2012).
Steinhart, H., Bosselmann, A. & Moeller, C. Determination of pyridinolines in bovine collagenous tissues. J. Agric. Food Chem. 42, 1943–1947 (1994).
Tan, C. I., Kent, G. N., Randall, A. G., Edmondston, S. J. & Singer, K. P. Age-related changes in collagen, pyridinoline, and deoxypyridinoline in normal human thoracic intervertebral discs. J. Gerontol. A. Biol. Sci. Med. Sci. 58, B387–B393 (2003).
Delmas, P. D., Schlemmer, A., Gineyts, E., Riis, B. & Christiansen, C. Urinary excretion of pyridinoline crosslinks correlates with bone turnover measured on iliac crest biopsy in patients with vertebral osteoporosis. J. Bone Miner. Res. 6, 639–644 (1991).
Lindert, U. et al. Urinary pyridinoline cross-links as biomarkers of osteogenesis imperfecta. Orphanet J. Rare Dis. 10, 104 (2015).
Takeuchi, S., Arai, K., Saitoh, H., Yoshida, K. & Miura, M. Urinary pyridinoline and deoxypyridinoline as potential markers of bone metastasis in patients with prostate cancer. J. Urol. 156, 1691–1695 (1996).
Siegfried, M. Reticulin and collagen. J. Physiol. 28, 319–324 (1902).
Tebb, M. C. Reticulin and collagen. J. Physiol. 27, 463–472 (1902).
Neuman, R. E. & Logan, M. A. The determination of hydroxyproline. J. Biol. Chem. 184, 299–306 (1950).
Reddy, G. K. & Enwemeka, C. S. A simplified method for the analysis of hydroxyproline in biological tissues. Clin. Biochem. 29, 225–229 (1996).
Cissell, D. D., Link, J. M., Hu, J. C. & Athanasiou, K. A. A modified hydroxyproline assay based on hydrochloric acid in Ehrlich’s solution accurately measures tissue collagen content. Tissue Eng. Part C Methods 23, 243–250 (2017). This paper describes the most recent edition of the photometric hydroxyproline assay, which uses safer and less expensive materials, without sacrificing assay sensitivity.
Caetano, G. F., Fronza, M., Leite, M. N., Gomes, A. & Frade, M. A. C. Comparison of collagen content in skin wounds evaluated by biochemical assay and by computer-aided histomorphometric analysis. Pharm. Biol. 54, 2555–2559 (2016).
Kliment, C. R., Englert, J. M., Crum, L. P. & Oury, T. D. A novel method for accurate collagen and biochemical assessment of pulmonary tissue utilizing one animal. Int. J. Clin. Exp. Pathol. 4, 349–355 (2011).
Stoilov, I., Starcher, B. C., Mecham, R. P. & Broekelmann, T. J. Measurement of elastin, collagen, and total protein levels in tissues. Methods Cell Biol. 143, 133–146 (2018).
Khan, T. et al. Metabolic dysregulation and adipose tissue fibrosis: role of collagen VI. Mol. Cell. Biol. 29, 1575–1591 (2009).
Wu, J. et al. Extraction and isolation of type I, III and V collagens and their SDS-PAGE analyses. Trans. Tianjin Univ. 17, 111–117 (2011).
Hayashi, T. & Nagai, Y. Separation of the α chains of type I and III collagens by SDS-polyacrylamide gel electrophoresis. J. Biochem. 86, 453–459 (1979).
Vincent, S. G., Cunningham, P. R., Stephens, N. L., Halayko, A. J. & Fisher, J. T. Quantitative densitometry of proteins stained with coomassie blue using a Hewlett Packard scanjet scanner and Scanplot software. Electrophoresis 18, 67–71 (1997).
Eyre, D. R., Koob, T. J. & Van Ness, K. P. Quantitation of hydroxypyridinium crosslinks in collagen by high-performance liquid chromatography. Anal. Biochem. 137, 380–388 (1984).
Saito, M., Marumo, K., Fujii, K. & Ishioka, N. Single-column high-performance liquid chromatographic-fluorescence detection of immature, mature, and senescent cross-links of collagen. Anal. Biochem. 253, 26–32 (1997).
Robins, S. P., Stewart, P., Astbury, C. & Bird, H. A. Measurement of the cross linking compound, pyridinoline, in urine as an index of collagen degradation in joint disease. Ann. Rheum. Dis. 45, 969–973 (1986).
Robins, S. P. et al. Direct, enzyme-linked immunoassay for urinary deoxypyridinoline as a specific marker for measuring bone resorption. J. Bone Miner. Res. 9, 1643–1649 (1994).
Taneda, S. & Monnier, V. M. ELISA of pentosidine, an advanced glycation end product, in biological specimens. Clin. Chem. 40, 1766–1773 (1994).
Sutandy, F. X. R., Qian, J., Chen, C.-S. & Zhu, H. Overview of protein microarrays. Curr. Protoc. Protein Sci. 72, 27.1.1–27.1.16 (2013).
Kuschel, C. et al. Cell adhesion profiling using extracellular matrix protein microarrays. Biotechniques 40, 523–531 (2006).
Baker, H. N., Murphy, R., Lopez, E. & Garcia, C. Conversion of a capture ELISA to a Luminex xMAP assay using a multiplex antibody screening method. J. Vis. Exp. 65, e4084 (2012).
Elshal, M. F. & McCoy, J. P. Multiplex bead array assays: performance evaluation and comparison of sensitivity to ELISA. Methods 38, 317–323 (2006).
Kim, C. H. et al. Stability and reproducibility of proteomic profiles measured with an aptamer-based platform. Sci. Rep. 8, 8382 (2018).
Coghlan, R. F. et al. A degradation fragment of type X collagen is a real-time marker for bone growth velocity. Sci. Transl. Med. 9, eaan4669 (2017).
Koolmees, P. A. & Bijker, P. G. Histometric and chemical methods for determining collagen in meats. Vet. Q. 7, 84–90 (1985).
Grimm, P. C. et al. Computerized image analysis of Sirius Red-stained renal allograft biopsies as a surrogate marker to predict long-term allograft function. J. Am. Soc. Nephrol. 14, 1662–1668 (2003).
Brigger, D. & Muckle, R. J. Comparison of Sirius red and Congo red as stains for amyloid in animal tissues. J. Histochem. Cytochem. 23, 84–88 (1975).
Coelho, P. G. B., de Souza, M. V., Conceição, L. G., Viloria, M. I. V. & Bedoya, S. A. O. Evaluation of dermal collagen stained with picrosirius red and examined under polarized light microscopy. An. Bras. Dermatol. 93, 415–418 (2018).
Nagai, M. et al. Alteration of cartilage surface collagen fibers differs locally after immobilization of knee joints in rats. J. Anat. 226, 447–457 (2015).
Schmid, T. M. & Linsenmayer, T. F. Immunohistochemical localization of short chain cartilage collagen (type X) in avian tissues. J. Cell Biol. 100, 598–605 (1985).
Agarwal, P. et al. Collagen XII and XIV, new partners of cartilage oligomeric matrix protein in the skin extracellular matrix suprastructure. J. Biol. Chem. 287, 22549–22559 (2012).
Yakovlev, D. D. et al. Quantitative mapping of collagen fiber alignment in thick tissue samples using transmission polarized-light microscopy. J. Biomed. Opt. 21, 071111 (2016).
Chen, X., Nadiarynkh, O., Plotnikov, S. & Campagnola, P. J. Second harmonic generation microscopy for quantitative analysis of collagen fibrillar structure. Nat. Protoc. 7, 654–669 (2012).
Keikhosravi, A. et al. Quantification of collagen organization in histopathology samples using liquid crystal based polarization microscopy. Biomed. Opt. Express 8, 4243–4256 (2017).
Ghazanfari, S., Driessen-Mol, A., Strijkers, G. J., Baaijens, F. P. T. & Bouten, C. V. C. The evolution of collagen fiber orientation in engineered cardiovascular tissues visualized by diffusion tensor imaging. PLoS ONE 10, e0127847 (2015).
Starborg, T., Lu, Y., Kadler, K. E. & Holmes, D. F. Electron microscopy of collagen fibril structure in vitro and in vivo including three-dimensional reconstruction. Methods Cell Biol. 88, 319–345 (2008).
Starborg, T. et al. Using transmission electron microscopy and 3View to determine collagen fibril size and three-dimensional organization. Nat. Protoc. 8, 1433–1448 (2013).
Changoor, A. et al. Structural characteristics of the collagen network in human normal, degraded and repair articular cartilages observed in polarized light and scanning electron microscopies. Osteoarthr. Cartil. 19, 1458–1468 (2011).
Ruozi, B. et al. Intact collagen and atelocollagen sponges: characterization and ESEM observation. Mater. Sci. Eng. C 27, 802–810 (2007).
Snellman, A. et al. A short sequence in the N-terminal region is required for the trimerization of type XIII collagen and is conserved in other collagenous transmembrane proteins. EMBO J. 19, 5051–5059 (2000).
Manferdini, C. et al. Immunoelectron microscopic localization of collagen type XV during human mesenchymal stem cells mineralization. Connect. Tissue Res. 59, 42–45 (2018).
Plumb, D. A. et al. Collagen XXVII is developmentally regulated and forms thin fibrillar structures distinct from those of classical vertebrate fibrillar collagens. J. Biol. Chem. 282, 12791–12795 (2007).
Ranjit, S. et al. Imaging fibrosis and separating collagens using second harmonic generation and phasor approach to fluorescence lifetime imaging. Sci. Rep. 5, 13378 (2015).
Haudenschild, A. K. et al. Nondestructive fluorescence lifetime imaging and time-resolved fluorescence spectroscopy detect cartilage matrix depletion and correlate with mechanical properties. Eur. Cell. Mater. 36, 30–43 (2018).
Haudenschild, A. K. et al. Non-destructive detection of matrix stabilization correlates with enhanced mechanical properties of self-assembled articular cartilage. J. Tissue Eng. Regen. Med. 13, 637–648 (2019).
Sherlock, B. E. et al. Nondestructive assessment of collagen hydrogel cross-linking using time-resolved autofluorescence imaging. J. Biomed. Opt. 23, 1 (2018).
de Campos Vidal, B. & Mello, M. L. S. Collagen type I amide I band infrared spectroscopy. Micron 42, 283–289 (2011).
Belbachir, K., Noreen, R., Gouspillou, G. & Petibois, C. Collagen types analysis and differentiation by FTIR spectroscopy. Anal. Bioanal. Chem. 395, 829–837 (2009).
Bergholt, M. S., Serio, A. & Albro, M. B. Raman spectroscopy: guiding light for the extracellular matrix. Front. Bioeng. Biotechnol. 7, 303 (2019).
Albro, M. B. et al. Raman spectroscopic imaging for quantification of depth-dependent and local heterogeneities in native and engineered cartilage. NPJ Regen. Med. 3, 3 (2018).
Ye, H. et al. Burn-related collagen conformational changes in ex vivo porcine skin using Raman spectroscopy. Sci. Rep. 9, 19138 (2019).
Nguyen, T. T. et al. Characterization of type I and IV collagens by Raman microspectroscopy: identification of spectral markers of the dermo-epidermal junction. J. Spectrosc. 27, 421–427 (2012).
Marcu, L., Cohen, D., Maarek, J.-M. I. & Grundfest, W. S. Characterization of type I, II, III, IV, and V collagens by time-resolved laser-induced fluorescence spectroscopy. Optical Biopsy III 3917, 93–101 (2000).
Sun, Y. et al. Development of a dual-modal tissue diagnostic system combining time-resolved fluorescence spectroscopy and ultrasonic backscatter microscopy. Rev. Sci. Instrum. 80, 065104 (2009).
Colgrave, M. L., Allingham, P. G., Tyrrell, K. & Jones, A. Multiple reaction monitoring for the accurate quantification of amino acids: using hydroxyproline to estimate collagen content. Methods Mol. Biol. 2030, 33–45 (2019).
Nimptsch, A. et al. Quantitative analysis of denatured collagen by collagenase digestion and subsequent MALDI-TOF mass spectrometry. Cell Tissue Res. 343, 605–617 (2011). This paper uses MALDI-TOF mass spectrometry to quantify glycine–proline–hydroxyproline tripeptides as a more sensitive method than the hydroxyproline assay.
Yoshida, K. et al. Quantitative evaluation of collagen crosslinks and corresponding tensile mechanical properties in mouse cervical tissue during normal pregnancy. PLoS ONE 9, e112391 (2014).
Naffa, R. et al. Rapid analysis of pyridinoline and deoxypyridinoline in biological samples by liquid chromatography with mass spectrometry and a silica hydride column. J. Sep. Sci. 42, 1482–1488 (2019).
Kovacevic, I., Pokrajac, M., Miljkovic, B., Jovanovic, D. & Prostran, M. Comparison of liquid chromatography with fluorescence detection to liquid chromatography–mass spectrometry for the determination of fluoxetine and norfluoxetine in human plasma. J. Chromatogr. B 830, 372–376 (2006).
Lin, H., Goodin, S., Strair, R. K., DiPaola, R. S. & Gounder, M. K. Comparison of LC-MS assay and HPLC assay of busulfan in clinical pharmacokinetics studies. ISRN Anal. Chem. 2012, 198683 (2012).
Santa, T. Recent advances in analysis of glutathione in biological samples by high-performance liquid chromatography: a brief overview. Drug Discov. Ther. 7, 172–177 (2013).
Dreisewerd, K., Rohlfing, A., Spottke, B., Urbanke, C. & Henkel, W. Characterization of whole fibril-forming collagen proteins of types I, III, and V from fetal calf skin by infrared matrix-assisted laser desorption ionization mass spectrometry. Anal. Chem. 76, 3482–3491 (2004).
Pataridis, S., Eckhardt, A., Mikulikova, K., Sedlakova, P. & Miksik, I. Determination and quantification of collagen types in tissues using HPLC-MS/MS. Curr. Anal. Chem. 5, 316–323 (2009).
Wang, Y. et al. Quantitative proteomics analysis of cartilage response to mechanical injury and cytokine treatment. Matrix Biol. 63, 11–22 (2017).
Kumazawa, Y., Taga, Y., Iwai, K. & Koyama, Y.-I. A rapid and simple LC-MS method using collagen marker peptides for identification of the animal source of leather. J. Agric. Food Chem. 64, 6051–6057 (2016).
Wiese, S., Reidegeld, K. A., Meyer, H. E. & Warscheid, B. Protein labeling by iTRAQ: a new tool for quantitative mass spectrometry in proteome research. Proteomics 7, 1004–1004 (2007).
Lanucara, F. & Eyers, C. E. Mass spectrometric-based quantitative proteomics using SILAC. Methods Enzymol. 500, 133–150 (2011).
Zhang, L. & Elias, J. E. Relative protein quantification using tandem mass tag mass spectrometry. Methods Mol. Biol. 1550, 185–198 (2017).
Ye, X., Luke, B., Andresson, T. & Blonder, J. 18O stable isotope labeling in MS-based proteomics. Brief. Funct. Genomic. Proteomic. 8, 136–144 (2009).
Zhu, W., Smith, J. W. & Huang, C.-M. Mass spectrometry-based label-free quantitative proteomics. J. Biomed. Biotechnol. 2010, 840518 (2010).
Dresner, E. & Schubert, M. The comparative susceptibility to collagenase and trypsin of collagen, soluble collagens and renal basement membrane. J. Histochem. Cytochem. 3, 360–368 (1955).
Krey, J. F. et al. Accurate label-free protein quantitation with high- and low-resolution mass spectrometers. J. Proteome Res. 13, 1034–1044 (2014).
Cox, J. et al. Accurate proteome-wide label-free quantification by delayed normalization and maximal peptide ratio extraction, termed MaxLFQ. Mol. Cell. Proteom. 13, 2513–2526 (2014).
Önnerfjord, P., Khabut, A., Reinholt, F. P., Svensson, O. & Heinegård, D. Quantitative proteomic analysis of eight cartilaginous tissues reveals characteristic differences as well as similarities between subgroups. J. Biol. Chem. 287, 18913–18924 (2012). This paper shows a wide proteomics analysis on several types of cartilage. iTRAQ and LC-MS/MS technologies were used for relative quantification of many ECM molecules.
Lourido, L. et al. Quantitative proteomic profiling of human articular cartilage degradation in osteoarthritis. J. Proteome Res. 13, 6096–6106 (2014).
Frantzi, M. et al. Discovery and validation of urinary biomarkers for detection of renal cell carcinoma. J. Proteomics 98, 44–58 (2014).
van Huizen, N. A. et al. Up-regulation of collagen proteins in colorectal liver metastasis compared with normal liver tissue. J. Biol. Chem. 294, 281–289 (2019).
Huey, D. J., Hu, J. C. & Athanasiou, K. A. Unlike bone, cartilage regeneration remains elusive. Science 338, 917–921 (2012).
Athanasiou, K. A., Darling, E. M., Hu, J. C., DuRaine, G. D. & Hari Reddi, A. Articular Cartilage (CRC Press, 2017).
Sophia Fox, A. J., Bedi, A. & Rodeo, S. A. The basic science of articular cartilage: structure, composition, and function. Sports Health 1, 461–468 (2009). This review paper provides a thorough overview of articular cartilage, its zonal variations and its biomechanical functions.
Almarza, A. J. & Athanasiou, K. A. Design characteristics for the tissue engineering of cartilaginous tissues. Ann. Biomed. Eng. 32, 2–17 (2004).
Makris, E. A., Hadidi, P. & Athanasiou, K. A. The knee meniscus: structure–function, pathophysiology, current repair techniques, and prospects for regeneration. Biomaterials 32, 7411–7431 (2011).
Kuroda, S. et al. Biomechanical and biochemical characteristics of the mandibular condylar cartilage. Osteoarthr. Cartil. 17, 1408–1415 (2009).
Singh, M. & Detamore, M. S. Biomechanical properties of the mandibular condylar cartilage and their relevance to the TMJ disc. J. Biomech. 42, 405–417 (2009).
Mithoefer, K., McAdams, T., Williams, R. J., Kreuz, P. C. & Mandelbaum, B. R. Clinical efficacy of the microfracture technique for articular cartilage repair in the knee: an evidence-based systematic analysis. Am. J. Sports Med. 37, 2053–2063 (2009).
Bos, E. J. et al. Structural and mechanical comparison of human ear, alar, and septal cartilage. Plast. Reconstr. Surg. Glob. Open. 6, e1610 (2018).
Griffin, M. F., Premakumar, Y., Seifalian, A. M., Szarko, M. & Butler, P. E. M. Biomechanical characterisation of the human auricular cartilages; implications for tissue engineering. Ann. Biomed. Eng. 44, 3460–3467 (2016).
Naumann, A. et al. Immunochemical and mechanical characterization of cartilage subtypes in rabbit. J. Histochem. Cytochem. 50, 1049–1058 (2002).
Madsen, K., von der Mark, K., van Menxel, M. & Friberg, U. Analysis of collagen types synthesized by rabbit ear cartilage chondrocytes in vivo and in vitro. Biochem. J. 221, 189–196 (1984).
Setton, L. A., Elliott, D. M. & Mow, V. C. Altered mechanics of cartilage with osteoarthritis: human osteoarthritis and an experimental model of joint degeneration. Osteoarthr. Cartil. 7, 2–14 (1999).
Miosge, N., Hartmann, M., Maelicke, C. & Herken, R. Expression of collagen type I and type II in consecutive stages of human osteoarthritis. Histochem. Cell Biol. 122, 229–236 (2004).
Lahm, A. et al. Changes in content and synthesis of collagen types and proteoglycans in osteoarthritis of the knee joint and comparison of quantitative analysis with Photoshop-based image analysis. Arch. Orthop. Trauma Surg. 130, 557–564 (2010).
Hosseininia, S. et al. Evidence for enhanced collagen type III deposition focally in the territorial matrix of osteoarthritic hip articular cartilage. Osteoarthr. Cartil. 24, 1029–1035 (2016).
Heinemeier, K. M. Type II collagen; designed to last a lifetime? Osteoarthr. Cartil. 25, S5 (2017).
Owings, M. F. & Kozak, L. J. Ambulatory and inpatient procedures in the United States, 1996. Vital Health Stat. 13, 1–119 (1998).
Moseley, J. B. et al. A controlled trial of arthroscopic surgery for osteoarthritis of the knee. N. Engl. J. Med. 347, 81–88 (2002).
Koh, J. L., Wirsing, K., Lautenschlager, E. & Zhang, L.-O. The effect of graft height mismatch on contact pressure following osteochondral grafting: a biomechanical study. Am. J. Sports Med. 32, 317–320 (2004).
Khan, I. M., Gilbert, S. J., Singhrao, S. K., Duance, V. C. & Archer, C. W. Cartilage integration: evaluation of the reasons for failure of integration during cartilage repair. A review. Eur. Cell. Mater. 16, 26–39 (2008).
Makris, E. A., Gomoll, A. H., Malizos, K. N., Hu, J. C. & Athanasiou, K. A. Repair and tissue engineering techniques for articular cartilage. Nat. Rev. Rheumatol. 11, 21–34 (2015).
Zhang, Z. et al. Matrix-induced autologous chondrocyte implantation for the treatment of chondral defects of the knees in Chinese patients. Drug Des. Devel. Ther. 8, 2439–2448 (2014).
Frisbie, D. D. et al. Early events in cartilage repair after subchondral bone microfracture. Clin. Orthop. Relat. Res. 407, 215–227 (2003).
Barber, F. A. What is the terrible triad? Arthroscopy 8, 19–22 (1992).
LeResche, L. Epidemiology of temporomandibular disorders: implications for the investigation of etiologic factors. Crit. Rev. Oral Biol. Med. 8, 291–305 (1997).
Murphy, M. K., MacBarb, R. F., Wong, M. E. & Athanasiou, K. A. Temporomandibular joint disorders: a review of etiology, clinical management, and tissue engineering strategies. Int. J. Oral Maxillofac. Implants 28, e393–e414 (2013).
Urban, J. P. G. & Roberts, S. Degeneration of the intervertebral disc. Arthritis Res. Ther. 5, 120 (2003).
Luoma, K. et al. Low back pain in relation to lumbar disc degeneration. Spine 25, 487–492 (2000).
Maniadakis, N. & Gray, A. The economic burden of back pain in the UK. Pain 84, 95–103 (2000).
Ha, A. Y., Shalvoy, R. M., Voisinet, A., Racine, J. & Aaron, R. K. Controversial role of arthroscopic meniscectomy of the knee: a review. World J. Orthop. 7, 287–292 (2016).
Miloro, M. & Henriksen, B. Discectomy as the primary surgical option for internal derangement of the temporomandibular joint. J. Oral Maxillofac. Surg. 68, 782–789 (2010).
Thorlund, J. B. et al. Patient reported outcomes in patients undergoing arthroscopic partial meniscectomy for traumatic or degenerative meniscal tears: comparative prospective cohort study. BMJ 356, j356 (2017).
Illien-Jünger, S. et al. Detrimental effects of discectomy on intervertebral disc biology can be decelerated by growth factor treatment during surgery: a large animal organ culture model. Spine J. 14, 2724–2732 (2014).
Kwon, H. et al. Surgical and tissue engineering strategies for articular cartilage and meniscus repair. Nat. Rev. Rheumatol. 15, 550–570 (2019).
Higashioka, M. M., Chen, J. A., Hu, J. C. & Athanasiou, K. A. Building an anisotropic meniscus with zonal variations. Tissue Eng. Part A 20, 294–302 (2014).
Cao, Y., Vacanti, J. P., Paige, K. T., Upton, J. & Vacanti, C. A. Transplantation of chondrocytes utilizing a polymer-cell construct to produce tissue-engineered cartilage in the shape of a human ear. Plast. Reconstr. Surg. 100, 297–302 (1997).
Little, C. J., Bawolin, N. K. & Chen, X. Mechanical properties of natural cartilage and tissue-engineered constructs. Tissue Eng. Part B Rev. 17, 213–227 (2011).
Salinas, E. Y., Hu, J. C. & Athanasiou, K. A guide for using mechanical stimulation to enhance tissue-engineered articular cartilage properties. Tissue Eng. Part B Rev. 24, 345–358 (2018).
Pulkkinen, H. J. et al. Repair of osteochondral defects with recombinant human type II collagen gel and autologous chondrocytes in rabbit. Osteoarthr. Cartil. 21, 481–490 (2013).
Matsiko, A., Levingstone, T. J., O’Brien, F. J. & Gleeson, J. P. Addition of hyaluronic acid improves cellular infiltration and promotes early-stage chondrogenesis in a collagen-based scaffold for cartilage tissue engineering. J. Mech. Behav. Biomed. Mater. 11, 41–52 (2012).
Munir, N. & Callanan, A. Novel phase separated polycaprolactone/collagen scaffolds for cartilage tissue engineering. Biomed. Mater. 13, 051001 (2018).
Corradetti, B. et al. Immune tuning scaffold for the local induction of a pro-regenerative environment. Sci. Rep. 7, 17030 (2017).
Boehler, R. M., Graham, J. G. & Shea, L. D. Tissue engineering tools for modulation of the immune response. Biotechniques 51, 239–240 (2011).
Irawan, V., Sung, T.-C., Higuchi, A. & Ikoma, T. Collagen scaffolds in cartilage tissue engineering and relevant approaches for future development. Tissue Eng. Regen. Med. 15, 673–697 (2018).
Moutos, F. T. & Guilak, F. Composite scaffolds for cartilage tissue engineering. Biorheology 45, 501–512 (2008).
Eyre, D. Collagen of articular cartilage. Arthritis Res. 4, 30–35 (2002).
Eyre, D. R. & Wu, J. J. Collagen of fibrocartilage: a distinctive molecular phenotype in bovine meniscus. FEBS Lett. 158, 265–270 (1983).
Luo, Y. et al. The minor collagens in articular cartilage. Protein Cell 8, 560–572 (2017). This review paper describes the minor collagens found in articular cartilage, including the molecules to which they bind, and which collagens may be used as biomarkers of joint diseases.
Johns, D. E. & Athanasiou, K. A. Design characteristics for temporomandibular joint disc tissue engineering: learning from tendon and articular cartilage. Proc. Inst. Mech. Eng. H 221, 509–526 (2007).
Eyre, D. R. & Muir, H. E. Types I and II collagens in intervertebral disc. Interchanging radial distributions in annulus fibrosus. Biochem. J. 157, 267–270 (1976).
Han, S. et al. Molecular mechanism of type I collagen homotrimer resistance to mammalian collagenases. J. Biol. Chem. 285, 22276–22281 (2010).
Li, L. P., Herzog, W., Korhonen, R. K. & Jurvelin, J. S. The role of viscoelasticity of collagen fibers in articular cartilage: axial tension versus compression. Med. Eng. Phys. 27, 51–57 (2005).
Aryaei, A., Vapniarsky, N., Hu, J. C. & Athanasiou, K. A. Recent tissue engineering advances for the treatment of temporomandibular joint disorders. Curr. Osteoporos. Rep. 14, 269–279 (2016).
Bozec, L., van der Heijden, G. & Horton, M. Collagen fibrils: nanoscale ropes. Biophys. J. 92, 70–75 (2007).
Orgel, J. P. R. O., San Antonio, J. D. & Antipova, O. Molecular and structural mapping of collagen fibril interactions. Connect. Tissue Res. 52, 2–17 (2011).
Holmes, D. F. & Kadler, K. E. The 10+4 microfibril structure of thin cartilage fibrils. Proc. Natl Acad. Sci. USA 103, 17249–17254 (2006).
Gottardi, R. et al. Supramolecular organization of collagen fibrils in healthy and osteoarthritic human knee and hip joint cartilage. PLoS ONE 11, e0163552 (2016).
Eryilmaz, E., Teizer, W. & Hwang, W. In vitro analysis of the co-assembly of type-I and type-III collagen. Cell. Mol. Bioeng. 10, 41–53 (2017).
Gelse, K., Pöschl, E. & Aigner, T. Collagens—structure, function, and biosynthesis. Adv. Drug Deliv. Rev. 55, 1531–1546 (2003).
Petersen, W. & Tillmann, B. Collagenous fibril texture of the human knee joint menisci. Anat. Embryol. 197, 317–324 (1998).
Inoue, H. & Takeda, T. Three-dimensional observation of collagen framework of lumbar intervertebral discs. Acta Orthop. Scand. 46, 949–956 (1975).
Hickey, D. S. & Hukins, D. W. Collagen fibril diameters and elastic fibres in the annulus fibrosus of human fetal intervertebral disc. J. Anat. 133, 351–357 (1981).
Armiento, A. R., Alini, M. & Stoddart, M. J. Articular fibrocartilage - Why does hyaline cartilage fail to repair? Adv. Drug Deliv. Rev. 146, 289–305 (2019).
Karuppal, R. Current concepts in the articular cartilage repair and regeneration. J. Orthop. 14, A1–A3 (2017).
Zhang, L., Hu, J. & Athanasiou, K. A. The role of tissue engineering in articular cartilage repair and regeneration. Crit. Rev. Biomed. Eng. 37, 1–57 (2009).
Han, E., Chen, S. S., Klisch, S. M. & Sah, R. L. Contribution of proteoglycan osmotic swelling pressure to the compressive properties of articular cartilage. Biophys. J. 101, 916–924 (2011).
Grynpas, M. D., Eyre, D. R. & Kirschner, D. A. Collagen type II differs from type I in native molecular packing. Biochim. Biophys. Acta 626, 346–355 (1980).
Liu, X., Wu, H., Byrne, M., Krane, S. & Jaenisch, R. Type III collagen is crucial for collagen I fibrillogenesis and for normal cardiovascular development. Proc. Natl Acad. Sci. USA 94, 1852–1856 (1997).
Wu, J.-J., Weis, M. A., Kim, L. S. & Eyre, D. R. Type III collagen, a fibril network modifier in articular cartilage. J. Biol. Chem. 285, 18537–18544 (2010).
Birk, D. E., Fitch, J. M., Babiarz, J. P. & Linsenmayer, T. F. Collagen type I and type V are present in the same fibril in the avian corneal stroma. J. Cell Biol. 106, 999–1008 (1988).
Wenstrup, R. J. et al. Type V collagen controls the initiation of collagen fibril assembly. J. Biol. Chem. 279, 53331–53337 (2004).
Sun, M. et al. Collagen V is a dominant regulator of collagen fibrillogenesis: dysfunctional regulation of structure and function in a corneal-stroma-specific Col5a1-null mouse model. J. Cell Sci. 124, 4096–4105 (2011).
Olsen, B. R. Collagen IX. Int. J. Biochem. Cell Biol. 29, 555–558 (1997).
Eyre, D. R., Pietka, T., Weis, M. A. & Wu, J.-J. Covalent cross-linking of the NC1 domain of collagen type IX to collagen type II in cartilage. J. Biol. Chem. 279, 2568–2574 (2004).
Opolka, A. et al. Collagen IX is indispensable for timely maturation of cartilage during fracture repair in mice. Matrix Biol. 26, 85–95 (2007).
Fässler, R. et al. Mice lacking alpha 1 (IX) collagen develop noninflammatory degenerative joint disease. Proc. Natl Acad. Sci. USA 91, 5070–5074 (1994).
Oxford, J. T., Doege, K. J., Horton, W. E. Jr & Morris, N. P. Characterization of type II and type XI collagen synthesis by an immortalized rat chondrocyte cell line (IRC) having a low level of type II collagen mRNA expression. Exp. Cell Res. 213, 28–36 (1994).
Wu, J.-J., Weis, M. A., Kim, L. S., Carter, B. G. & Eyre, D. R. Differences in chain usage and cross-linking specificities of cartilage type V/XI collagen isoforms with age and tissue. J. Biol. Chem. 284, 5539–5545 (2009).
Fichard, A., Kleman, J.-P. & Ruggiero, F. Another look at collagen V and XI molecules. Matrix Biol. 14, 515–531 (1995).
Fernandes, R. J., Weis, M., Scott, M. A., Seegmiller, R. E. & Eyre, D. R. Collagen XI chain misassembly in cartilage of the chondrodysplasia (cho) mouse. Matrix Biol. 26, 597–603 (2007).
Chiquet, M., Birk, D. E., Bönnemann, C. G. & Koch, M. Collagen XII: protecting bone and muscle integrity by organizing collagen fibrils. Int. J. Biochem. Cell Biol. 53, 51–54 (2014).
Taylor, D. W. et al. Collagen type XII and versican are present in the early stages of cartilage tissue formation by both redifferentating passaged and primary chondrocytes. Tissue Eng. Part A 21, 683–693 (2015).
Gregory, K. E., Keene, D. R., Tufa, S. F., Lunstrum, G. P. & Morris, N. P. Developmental distribution of collagen type XII in cartilage: association with articular cartilage and the growth plate. J. Bone Miner. Res. 16, 2005–2016 (2001).
Zou, Y. et al. Recessive and dominant mutations in COL12A1 cause a novel EDS/myopathy overlap syndrome in humans and mice. Hum. Mol. Genet. 23, 2339–2352 (2014).
Ansorge, H. L. et al. Type XIV collagen regulates fibrillogenesis: premature collagen fibril growth and tissue dysfunction in null mice. J. Biol. Chem. 284, 8427–8438 (2009). This paper shows a structure–function relationship of collagen type XIV in skin and immature tendons in a mouse knockout. Cartilage mechanics were not tested but may display similar weakening.
Bell, P. A. et al. Analysis of the cartilage proteome from three different mouse models of genetic skeletal diseases reveals common and discrete disease signatures. Biol. Open 2, 802–811 (2013).
Kassner, A. et al. Discrete integration of collagen XVI into tissue-specific collagen fibrils or beaded microfibrils. Matrix Biol. 22, 131–143 (2003).
Grässel, S. & Bauer, R. J. Collagen XVI in health and disease. Matrix Biol. 32, 64–73 (2013).
Kassner, A. et al. Molecular structure and interaction of recombinant human type XVI collagen. J. Mol. Biol. 339, 835–853 (2004).
Kvist, A. J. et al. The major basement membrane components localize to the chondrocyte pericellular matrix–a cartilage basement membrane equivalent? Matrix Biol. 27, 22–33 (2008).
Foldager, C. B. et al. Collagen type IV and laminin expressions during cartilage repair and in late clinically failed repair tissues from human subjects. Cartilage 7, 52–61 (2016).
Sudhakar, A. et al. Human alpha1 type IV collagen NC1 domain exhibits distinct antiangiogenic activity mediated by alpha1beta1 integrin. J. Clin. Invest. 115, 2801–2810 (2005).
Poschl, E. Collagen IV is essential for basement membrane stability but dispensable for initiation of its assembly during early development. Development 131, 1619–1628 (2004).
Pfaff, M. et al. Integrin and Arg-Gly-Asp dependence of cell adhesion to the native and unfolded triple helix of collagen type VI. Exp. Cell Res. 206, 167–176 (1993).
Gara, S. K. et al. Three novel collagen VI chains with high homology to the alpha3 chain. J. Biol. Chem. 283, 10658–10670 (2008).
Zelenski, N. A. et al. Type VI collagen regulates pericellular matrix properties, chondrocyte swelling, and mechanotransduction in mouse articular cartilage. Arthritis Rheumatol. 67, 1286–1294 (2015).
Shen, G. The role of type X collagen in facilitating and regulating endochondral ossification of articular cartilage. Orthod. Craniofac. Res. 8, 11–17 (2005).
Gress, C. J. & Jacenko, O. Growth plate compressions and altered hematopoiesis in collagen X null mice. J. Cell Biol. 149, 983–993 (2000).
Sund, M. et al. Distinct expression of type XIII collagen in neuronal structures and other tissues during mouse development. Matrix Biol. 20, 215–231 (2001).
Ylönen, R. et al. Type XIII collagen strongly affects bone formation in transgenic mice. J. Bone Miner. Res. 20, 1381–1393 (2005).
Koch, M. et al. A novel marker of tissue junctions, collagen XXII. J. Biol. Chem. 279, 22514–22521 (2004).
Zwolanek, D. et al. Collagen XXII binds to collagen-binding integrins via the novel motifs GLQGER and GFKGER. Biochem. J. 459, 217–227 (2014).
Charvet, B. et al. Knockdown of col22a1 gene in zebrafish induces a muscular dystrophy by disruption of the myotendinous junction. Development 140, 4602–4613 (2013).
Hjorten, R. et al. Type XXVII collagen at the transition of cartilage to bone during skeletogenesis. Bone 41, 535–542 (2007).
Plumb, D. A. et al. Collagen XXVII organises the pericellular matrix in the growth plate. PLoS ONE 6, e29422 (2011).
Exposito, J.-Y., Valcourt, U., Cluzel, C. & Lethias, C. The fibrillar collagen family. Int. J. Mol. Sci. 11, 407–426 (2010).
Gonzaga-Jauregui, C. et al. Mutations in COL27A1 cause Steel syndrome and suggest a founder mutation effect in the Puerto Rican population. Eur. J. Hum. Genet. 23, 342–346 (2015).
Pfeiffer, E., Vickers, S. M., Frank, E., Grodzinsky, A. J. & Spector, M. The effects of glycosaminoglycan content on the compressive modulus of cartilage engineered in type II collagen scaffolds. Osteoarthr. Cartil. 16, 1237–1244 (2008).
Rieppo, J. et al. Structure-function relationships in enzymatically modified articular cartilage. Cells Tissues Organs 175, 121–132 (2003).
Lee, J.-H. & Cho, J.-Y. Proteomics approaches for the studies of bone metabolism. BMB Rep. 47, 141–148 (2014).
Sato, N. et al. Proteomic analysis of human tendon and ligament: solubilization and analysis of insoluble extracellular matrix in connective tissues. J. Proteome Res. 15, 4709–4721 (2016).
Deshmukh, A. S. et al. Deep proteomics of mouse skeletal muscle enables quantitation of protein isoforms, metabolic pathways, and transcription factors. Mol. Cell. Proteom. 14, 841–853 (2015).
Hosseininia, S., Önnerfjord, P. & Dahlberg, L. E. Targeted proteomics of hip articular cartilage in OA and fracture patients. J. Orthop. Res. 37, 131–135 (2019).
Merl-Pham, J. et al. Quantitative proteomic profiling of extracellular matrix and site-specific collagen post-translational modifications in an in vitro model of lung fibrosis. Matrix Biol. Plus 1, 100005 (2019).
Ko, J. et al. Machine learning to detect signatures of disease in liquid biopsies – a user’s guide. Lab Chip 18, 395–405 (2018).
Saha, S. et al. Automated detection and classification of early AMD biomarkers using deep learning. Sci. Rep. 9, 10990 (2019).
Banaei, N. et al. Machine learning algorithms enhance the specificity of cancer biomarker detection using SERS-based immunoassays in microfluidic chips. RSC Adv. 9, 1859–1868 (2019).
Van Camp, G. et al. A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene. Am. J. Hum. Genet. 79, 449–457 (2006).
Hafez, A. et al. Col11a1 regulates bone microarchitecture during embryonic development. J. Dev. Biol. 3, 158–176 (2015).
Alexopoulos, L. G., Youn, I., Bonaldo, P. & Guilak, F. Developmental and osteoarthritic changes in Col6a1-knockout mice: Biomechanics of type VI collagen in the cartilage pericellular matrix. Arthritis Rheum. 60, 771–779 (2009). This paper describes the structure–function relationship of collagen type VI and cartilage pericellular matrix stiffness.
Bayer, M. L. et al. Release of tensile strain on engineered human tendon tissue disturbs cell adhesions, changes matrix architecture, and induces an inflammatory phenotype. PLoS ONE 9, e86078 (2014).
Pu, X. & Oxford, J. T. Proteomic analysis of engineered cartilage. Methods Mol. Biol. 1340, 263–278 (2015). This paper is the first and only proteomics study of engineered tissue that identifies collagen type XIV.
Fawzi-Grancher, S., De Isla, N., Faure, G., Stoltz, J. F. & Muller, S. Optimisation of biochemical condition and substrates in vitro for tissue engineering of ligament. Ann. Biomed. Eng. 34, 1767–1777 (2006).
Richardson, S. M. et al. The differentiation of bone marrow mesenchymal stem cells into chondrocyte-like cells on poly-l-lactic acid (PLLA) scaffolds. Biomaterials 27, 4069–4078 (2006).
Kurobe, H. et al. Development of small diameter nanofiber tissue engineered arterial grafts. PLoS ONE 10, e0120328 (2015).
Ashjian, P. et al. Noninvasive in situ evaluation of osteogenic differentiation by time-resolved laser-induced fluorescence spectroscopy. Tissue Eng. 10, 411–420 (2004).
Lee, J. K. et al. Tension stimulation drives tissue formation in scaffold-free systems. Nat. Mater. 16, 864–873 (2017).
Kutsuna, T. et al. Noninvasive evaluation of tissue-engineered cartilage with time-resolved laser-induced fluorescence spectroscopy. Tissue Eng. Part C Methods 16, 365–373 (2010).
Bergholt, M. S., Albro, M. B. & Stevens, M. M. Online quantitative monitoring of live cell engineered cartilage growth using diffuse fiber-optic Raman spectroscopy. Biomaterials 140, 128–137 (2017).
Riesle, J., Hollander, A. P., Langer, R., Freed, L. E. & Vunjak-Novakovic, G. Collagen in tissue-engineered cartilage: types, structure, and crosslinks. J. Cell. Biochem. 71, 313–327 (1998).
Murdoch, A. D., Hardingham, T. E., Eyre, D. R. & Fernandes, R. J. The development of a mature collagen network in cartilage from human bone marrow stem cells in Transwell culture. Matrix Biol. 50, 16–26 (2016).
Lee, J. K., Link, J. M., Hu, J. C. Y. & Athanasiou, K. A. The self-assembling process and applications in tissue engineering. Cold Spring Harb. Perspect. Med. 7, a025668 (2017).
Ofek, G. et al. Matrix development in self-assembly of articular cartilage. PLoS ONE 3, e2795 (2008).
Makris, E. A., Hu, J. C. & Athanasiou, K. A. Hypoxia-induced collagen crosslinking as a mechanism for enhancing mechanical properties of engineered articular cartilage. Osteoarthr. Cartil. 21, 634–641 (2013).
Makris, E. A., Responte, D. J., Paschos, N. K., Hu, J. C. & Athanasiou, K. A. Developing functional musculoskeletal tissues through hypoxia and lysyl oxidase-induced collagen cross-linking. Proc. Natl Acad. Sci. USA 111, E4832–E4841 (2014).
Yan, D. et al. The impact of low levels of collagen IX and pyridinoline on the mechanical properties of in vitro engineered cartilage. Biomaterials 30, 814–821 (2009).
Setiawati, R. & Rahardjo, P. Bone development and growth. Osteogenesis Bone Regeneration 13 https://doi.org/10.5772/intechopen.82452 (2018).
Budde, B. et al. Altered integration of matrilin-3 into cartilage extracellular matrix in the absence of collagen IX. Mol. Cell. Biol. 25, 10465–10478 (2005).
Zhang, R.-Z. et al. Recessive COL6A2 C-globular missense mutations in Ullrich congenital muscular dystrophy: role of the C2a splice variant. J. Biol. Chem. 285, 10005–10015 (2010).
Schmid, T. M. & Linsenmayer, T. F. Immunoelectron microscopy of type X collagen: Supramolecular forms within embryonic chick cartilage. Dev. Biol. 138, 53–62 (1990).
This work was funded by NIH grant nos. R01DE015038, R01AR071457 and R01AR067821.
The authors declare no competing interests.
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Bielajew, B.J., Hu, J.C. & Athanasiou, K.A. Collagen: quantification, biomechanics and role of minor subtypes in cartilage. Nat Rev Mater (2020). https://doi.org/10.1038/s41578-020-0213-1