title: Engineering zonal cartilage through bioprinting collagen type II hydrogel constructs with biomimetic chondrocyte density gradient.
abstract: Cartilage tissue engineering is a promising approach for repairing and regenerating cartilage tissue. To date, attempts have been made to construct zonal cartilage that mimics the cartilaginous matrix in different zones. However, little attention has been paid to the chondrocyte density gradient within the articular cartilage. We hypothesized that the chondrocyte density gradient plays an important role in forming the zonal distribution of extracellular matrix (ECM).
  
  
  
  In this study, collagen type II hydrogel/chondrocyte constructs were fabricated using a bioprinter. Three groups were created according to the total cell seeding density in collagen type II pre-gel: Group A, 2 × 10(7) cells/mL; Group B, 1 × 10(7) cells/mL; and Group C, 0.5 × 10(7) cells/mL. Each group included two types of construct: one with a biomimetic chondrocyte density gradient and the other with a single cell density. The constructs were cultured in vitro and harvested at 0, 1, 2, and 3 weeks for cell viability testing, reverse-transcription quantitative PCR (RT-qPCR), biochemical assays, and histological analysis.
  
  
  
  We found that total ECM production was positively correlated with the total cell density in the early culture stage, that the cell density gradient distribution resulted in a gradient distribution of ECM, and that the chondrocytes' biosynthetic ability was affected by both the total cell density and the cell distribution pattern.
  
  
  
  Our results suggested that zonal engineered cartilage could be fabricated by bioprinting collagen type II hydrogel constructs with a biomimetic cell density gradient. Both the total cell density and the cell distribution pattern should be optimized to achieve synergistic biological effects.
authors.affiliation: Center for Joint Surgery, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, People's Republic of China.|Orthopedic Department, 452nd Hospital Chinese PLA, Chengdu, 610021, Sichuan, People's Republic of China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Ren
authors.affiliation: Center for Joint Surgery, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, People's Republic of China.
authors.forename: Fuyou
authors.initials: F
authors.lastname: Wang
authors.affiliation: Center for Joint Surgery, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, People's Republic of China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Chen
authors.affiliation: Center for Joint Surgery, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, People's Republic of China.
authors.forename: Xiaoyuan
authors.initials: X
authors.lastname: Gong
authors.affiliation: Center for Joint Surgery, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, People's Republic of China.
authors.forename: Li
authors.initials: L
authors.lastname: Yin
authors.affiliation: Center for Joint Surgery, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, People's Republic of China. jointsurgery@sina.cn.
authors.forename: Liu
authors.initials: L
authors.lastname: Yang
mesh_terms: D000818:Animals; D040761:Biomimetic Materials / Q000737:chemistry; D062028:Bioprinting / Q000295:instrumentation / Q000379:methods*; D002358:Cartilage, Articular / Q000166:cytology / Q000502:physiology*; D002452:Cell Count; D018929:Cell Culture Techniques; D002470:Cell Survival; D019902:Chondrocytes / Q000737:chemistry*; D024043:Collagen Type II / Q000737:chemistry*; D005109:Extracellular Matrix; D020100:Hydrogels / Q000737:chemistry*; D007719:Knee Joint / Q000166:cytology; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction; D023822:Tissue Engineering / Q000295:instrumentation / Q000379:methods*
chemical_list: D024043:Collagen Type II; D020100:Hydrogels
keywords: Biofabrication; Cell density gradient; Chondrocyte; Collagen type II; Hydrogel; Total cell density