title: The effects of glycosaminoglycan content on the compressive modulus of cartilage engineered in type II collagen scaffolds.
abstract: OBJECTIVE
  The current study determined the unconfined compressive modulus of tissue-engineered constructs with varying sulfated glycosaminoglycan (GAG) density produced by goat articular chondrocytes in type II collagen scaffolds prepared with a range of cross-link densities and various times in culture. The purpose of this work is to establish a basis for future studies employing constructs of selected maturity (e.g., 25%, 50%, or 75% normal GAG content) for cartilage repair in vivo.
  
  
  METHODS
  Porous scaffolds (8 mm diameter by 2 mm thick) were fabricated from porcine type II collagen by freeze-drying, followed by dehydrothermal treatment and carbodiimide cross-linking. In a pilot study, passage 3 adult caprine articular chondrocytes isolated from one goat were grown in scaffolds with six cross-link densities for 2, 3, 4, and 6 weeks (n=3). The goal was to select scaffold cross-link densities and times in culture that would produce constructs with approximately 25%, 50% and 75% the GAG density of native articular cartilage. Based on the results of the pilot study, chondrocytes from three goats were grown in scaffolds with two cross-link densities for three time periods: 3, 5, and 9 weeks (n=6; one of the cross-link groups was run in quadruplicate). The equilibrium modulus from unconfined compression testing of these samples was correlated with GAG content.
  
  
  RESULTS
  There was a notable increase in GAG density with decreasing cross-link density. Histological analysis verified a chondrogenic phenotype and revealed various amounts of GAG and type II collagen-containing cartilage. The correlation between modulus and GAG density had a linear coefficient of determination of 0.60. One group with a mean GAG density of 22 microg/mm(3), which was 140% the GAG density of normal caprine articular cartilage, averaged a compressive modulus of 31.5 kPa, which was 10% of caprine articular cartilage tested in this study.
  
  
  CONCLUSIONS
  The GAG density and modulus of tissue-engineered constructs can be controlled by the degree of cross-linking of type II collagen scaffolds and time in culture.
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: E
authors.initials: E
authors.lastname: Pfeiffer
authors.forename: S M
authors.initials: SM
authors.lastname: Vickers
authors.forename: E
authors.initials: E
authors.lastname: Frank
authors.forename: A J
authors.initials: AJ
authors.lastname: Grodzinsky
authors.forename: M
authors.initials: M
authors.lastname: Spector
mesh_terms: D000818:Animals; D002356:Cartilage / Q000378:metabolism*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism*; D024043:Collagen Type II / Q000378:metabolism*; D019245:Compressive Strength / Q000502:physiology*; D006025:Glycosaminoglycans / Q000378:metabolism*; D006041:Goats; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013552:Swine; D023822:Tissue Engineering / Q000379:methods*
chemical_list: D024043:Collagen Type II; D006025:Glycosaminoglycans