title: Macromer density influences mesenchymal stem cell chondrogenesis and maturation in photocrosslinked hyaluronic acid hydrogels.
abstract: OBJECTIVE
  Engineering cartilage requires that a clinically relevant cell type be situated within a 3D environment that supports cell viability, the production and retention of cartilage-specific extracellular matrix (ECM), and eventually, the establishment of mechanical properties that approach that of the native tissue. In this study, we investigated the ability of bone marrow derived mesenchymal stem cells (MSCs) to undergo chondrogenesis in crosslinked methacrylated hyaluronic acid hydrogels (MeHA) of different macromer concentrations (1, 2, and 5%).
  
  
  METHODS
  Over a 6 week culture period under pro-chondrogenic conditions, we evaluated cartilage-specific gene expression, ECM deposition within constructs and released to the culture media, and mechanical properties in both compression and tension. Further, we examined early matrix assembly and long term histological features of the forming tissues, as well as the ability of macromolecules to diffuse within hydrogels as a function of MeHA macromer concentration.
  
  
  RESULTS
  Findings from this study show that variations in macromer density influence MSC chondrogenesis in distinct ways. Increasing HA macromer density promoted chondrogenesis and matrix formation and retention, but yielded functionally inferior constructs due to limited matrix distribution throughout the construct expanse. In 1% MeHA constructs, the equilibrium compressive modulus reached 0.12MPa and s-GAG content reached nearly 3% of the wet weight, values that matched or exceeded those of control agarose constructs and that are 25 and 50% of native tissue levels, respectively.
  
  
  CONCLUSIONS
  These data provide new insight into how early matrix deposition regulates long term construct development, and defines new parameters for optimizing the formation of functional MSC-based engineered articular cartilage using HA hydrogels.
authors.affiliation: McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: I E
authors.initials: IE
authors.lastname: Erickson
authors.forename: A H
authors.initials: AH
authors.lastname: Huang
authors.forename: S
authors.initials: S
authors.lastname: Sengupta
authors.forename: S
authors.initials: S
authors.lastname: Kestle
authors.forename: J A
authors.initials: JA
authors.lastname: Burdick
authors.forename: R L
authors.initials: RL
authors.lastname: Mauck
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D020219:Chondrogenesis / Q000502:physiology*; D005109:Extracellular Matrix / Q000378:metabolism*; D006820:Hyaluronic Acid / Q000378:metabolism*; D020100:Hydrogels / Q000378:metabolism; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism*; D023822:Tissue Engineering / Q000379:methods*
chemical_list: D020100:Hydrogels; D006820:Hyaluronic Acid