title: Spontaneous hyaline cartilage regeneration can be induced in an osteochondral defect created in the femoral condyle using a novel double-network hydrogel.
abstract: BACKGROUND
  Functional repair of articular osteochondral defects remains a major challenge not only in the field of knee surgery but also in tissue regeneration medicine. The purpose is to clarify whether the spontaneous hyaline cartilage regeneration can be induced in a large osteochondral defect created in the femoral condyle by means of implanting a novel double-network (DN) gel at the bottom of the defect.
  
  
  METHODS
  Twenty-five mature rabbits were used in this study. In the bilateral knees of each animal, we created an osteochondral defect having a diameter of 2.4-mm in the medial condyle. Then, in 21 rabbits, we implanted a DN gel plug into a right knee defect so that a vacant space of 1.5-mm depth (in Group I), 2.5-mm depth (in Group II), or 3.5-mm depth (in Group III) was left. In the left knee, we did not apply any treatment to the defect to obtain the control data. All the rabbits were sacrificed at 4 weeks, and the gross and histological evaluations were performed. The remaining 4 rabbits underwent the same treatment as used in Group II, and real-time PCR analysis was performed at 4 weeks.
  
  
  RESULTS
  The defect in Group II was filled with a sufficient volume of the hyaline cartilage tissue rich in proteoglycan and type-2 collagen. The Wayne's gross appearance and histology scores showed that Group II was significantly greater than Group I, III, and Control (p < 0.012). The relative expression level of type-2 collagen, aggrecan, and SOX9 mRNAs was significantly greater in Group II than in the control group (p < 0.023).
  
  
  CONCLUSIONS
  This study demonstrated that spontaneous hyaline cartilage regeneration can be induced in vivo in an osteochondral defect created in the femoral condyle by means of implanting the DN gel plug at the bottom of the defect so that an approximately 2-mm deep vacant space was intentionally left in the defect. This fact has prompted us to propose an innovative strategy without cell culture to repair osteochondral lesions in the femoral condyle.
authors.affiliation: Department of Sports Medicine and Joint Surgery, Hokkaido University School of Medicine, Sapporo, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Yokota
authors.forename: Kazunori
authors.initials: K
authors.lastname: Yasuda
authors.forename: Nobuto
authors.initials: N
authors.lastname: Kitamura
authors.forename: Kazunobu
authors.initials: K
authors.lastname: Arakaki
authors.forename: Shin
authors.initials: S
authors.lastname: Onodera
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kurokawa
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Gong
mesh_terms: D053674:Aggrecans / Q000378:metabolism; D000818:Animals; D020219:Chondrogenesis / Q000502:physiology*; D024043:Collagen Type II / Q000378:metabolism; D005260:Female; D005269:Femur / Q000378:metabolism / Q000601:surgery*; D051457:Hyaline Cartilage / Q000502:physiology*; D020100:Hydrogels / Q000627:therapeutic use*; D023421:Models, Animal; D011509:Proteoglycans / Q000378:metabolism; D011817:Rabbits; D012038:Regeneration / Q000502:physiology*; D055758:SOX9 Transcription Factor / Q000378:metabolism
chemical_list: D053674:Aggrecans; D024043:Collagen Type II; D020100:Hydrogels; D011509:Proteoglycans; D055758:SOX9 Transcription Factor