title: Sliding indentation enhances collagen content and depth-dependent matrix distribution in tissue-engineered cartilage constructs.
abstract: BACKGROUND
  Current tissue-engineered cartilage constructs contain insufficient amounts of collagen, whose function is to resist tension. We postulate that dynamic tension is necessary to stimulate collagen formation. Another shortcoming is that tissue-engineered cartilage does not possess native zonal variations. We hypothesize that applying depth-varying mechanical cues would stimulate extracellular matrix (ECM) synthesis depth dependently. We developed a dedicated loading regime called sliding indentation, which enables us to apply dynamic tension as well as depth-varying strain fields to the chondrocyte-seeded agarose constructs.
  
  
  OBJECTIVE
  In 2 study designs, we explored whether sliding indentation would increase collagen content and induce depth-varying ECM distribution.
  
  
  METHODS
  In the first study, we developed an agarose-sandwich model that involves embedding of a thin chondrocyte-seeded 0.5% agarose layer between two cell-free 3% agarose layers. In the second study, 3-mm-thick chondrocyte-seeded agarose constructs were created. Sliding indentation at 10% depth and 1 Hz was applied to constructs in both studies for 4 h/day during 28 days, and unloaded constructs served as control.
  
  
  RESULTS
  Sliding indentation resulted in an increased amount of collagen in the produced cartilage layer. Further, sliding indentation for 7 days resulted in a depth-dependent response at gene expression levels, with the highest response in the regions that received highest strains. Analysis of protein expression after 28 days showed a similar depth-dependent distribution in all constructs, which further enhanced by sliding indentation.
  
  
  CONCLUSIONS
  Sliding indentation can increase collagen content and enhances depth-dependent ECM distribution, and is therefore a promising strategy for culturing cartilage with improved properties.
authors.affiliation: Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
authors.forename: Linda M
authors.initials: LM
authors.lastname: Kock
authors.forename: Keita
authors.initials: K
authors.lastname: Ito
authors.forename: Corrinus C
authors.initials: CC
authors.lastname: van Donkelaar
mesh_terms: D019149:Bioreactors; D002356:Cartilage / Q000166:cytology*; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism*; D005109:Extracellular Matrix / Q000378:metabolism; D006801:Humans; D013314:Stress, Mechanical; D023822:Tissue Engineering / Q000379:methods*
chemical_list: D003094:Collagen