title: Acrylamide Polymer Double-Network Hydrogels: Candidate Cartilage Repair Materials with Cartilage-Like Dynamic Stiffness and Attractive Surgery-Related Attachment Mechanics.
abstract: BACKGROUND
  In focal repair of joint cartilage and meniscus, initial stiffness and strength of repairs are generally much less than surrounding tissue. This increases early failure potential. Secure primary fixation of the repair material is also a problem. Acrylamide polymer double-network (DN) hydrogels are candidate-improved repair materials. DN gels have exceptional strength and toughness compared to ordinary gels. This stems from the double-network structure in which there is a high molar ratio of the second network to the first network, with the first network highly crosslinked and the second loosely crosslinked. Previous studies of acrylic PAMPS/PDMAAm and PAMPS/PAAm DN gels demonstrated physicochemical stability and tissue compatibility as well as the ability to foster cartilage formation.
  
  
  METHODS
  Mechanical properties related to surgical use were tested in 2 types of DN gels.
  
  
  RESULTS
  Remarkably, these >90%-water DN gels exhibited dynamic impact stiffness (E*) values (~1.1 and ~1.5 MPa) approaching swine meniscus (~2.9 MPa). Dynamic impact energy-absorbing capability was much lower (median loss angles of ~2°) than swine meniscus (>10°), but it is intriguing that >90%-water materials can efficiently store energy. Also, fine 4/0 suture tear-out strength approached cartilage (~2.1 and ~7.1 N v. ~13.5 N). Initial strength of attachment of DN gels to cartilage with acrylic tissue adhesive was also high (~0.20 and ~0.15 N/mm(2)).
  
  
  CONCLUSIONS
  DN gel strength and toughness properties stem from optimized entanglement of the 2 network components. DN gels thus have obvious structural parallels with cartilaginous tissues, and their surgical handling properties make them ideal candidates for clinical use.
authors.affiliation: Department of Orthopedic Surgery and Skeletal Traumatology, Kantonsspital Bruderholz, Bruderholz, Switzerland.
authors.forename: Markus P
authors.initials: MP
authors.lastname: Arnold
authors.affiliation: Laboratory of Biomechanics and Biocalorimetry, Faculty of Medicine, University of Basel, Basel, Switzerland.
authors.forename: Alma U
authors.initials: AU
authors.lastname: Daniels
authors.affiliation: Laboratory of Biomechanics and Biocalorimetry, Faculty of Medicine, University of Basel, Basel, Switzerland.
authors.forename: Sarah
authors.initials: S
authors.lastname: Ronken
authors.affiliation: Biomedical Engineering Section, Department of Engineering, Universidad Iberoamericana, Mexico City, Mexico.
authors.forename: Helena Ardura
authors.initials: HA
authors.lastname: García
authors.affiliation: Department of Orthopedic Surgery and Skeletal Traumatology, Kantonsspital Bruderholz, Bruderholz, Switzerland.
authors.forename: Niklaus F
authors.initials: NF
authors.lastname: Friederich
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan ; Creative Research Institution "Sousei", Hokkaido University, Sapporo, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kurokawa
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
authors.forename: Jian P
authors.initials: JP
authors.lastname: Gong
authors.affiliation: Department of Orthopedic Surgery and Skeletal Traumatology, Kantonsspital Bruderholz, Bruderholz, Switzerland ; Laboratory of Biomechanics and Biocalorimetry, Faculty of Medicine, University of Basel, Basel, Switzerland.
authors.forename: Dieter
authors.initials: D
authors.lastname: Wirz
keywords: cartilage repair; gels; loss angle; modulus; suturing