title: Hydrogels for nucleus replacement--facing the biomechanical challenge.
abstract: Hydrogels are considered promising for disc regeneration strategies. However, it is currently unknown whether the destruction of the natural interface between nucleus and surrounding structures caused by nucleotomy and an inadequate annulus closure diminishes the mechanical competence of the disc. This in vitro study aimed to clarify these mechanisms and to evaluate whether hydrogels are able to restore the biomechanical behaviour of the disc. Nucleus pressure in an ovine intervertebral disc was measured in vivo during day and night and adapted to an in vitro axial compressive diurnal (15min) and night (30min) load. Effects of different defects on disc height and nucleus pressure were subsequently measured in vitro using 30 ovine motion segments. Following cases were considered: intact; annulus incision repaired by suture and glue; annulus incision with removal and re-implantation of nucleus tissue; and two different hydrogels repaired by suture and glue. The intradiscal pressure in vivo was 0.75MPa during day and 0.5MPa during night corresponding to an in vitro axial compressive force of 130 and 58N, respectively. The compression test showed that neither the implantation of hydrogels nor the re-implantation of the natural nucleus, assumed as being the ideal implant, was able to restore the mechanical functionality of an intact disc. Results indicate the importance of the natural anchorage of the nucleus with its surrounding structures and the relevance of an appropriate annulus closure. Therefore, hydrogels that are able to mimic the mechanical behaviour of the native nucleus may fail in restoring the mechanical behaviour of the disc.
authors.affiliation: Institute of Orthopaedic Research and Biomechanics, Center of Musculoskeletal Research, University of Ulm, Helmholtzstrasse 14, 89081 Ulm, Germany. sandra.reitmaier@uni-ulm.de
authors.forename: Sandra
authors.initials: S
authors.lastname: Reitmaier
authors.forename: Uwe
authors.initials: U
authors.lastname: Wolfram
authors.forename: Anita
authors.initials: A
authors.lastname: Ignatius
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Wilke
authors.forename: Antonio
authors.initials: A
authors.lastname: Gloria
authors.forename: José M
authors.initials: JM
authors.lastname: Martín-Martínez
authors.forename: Joana
authors.initials: J
authors.lastname: Silva-Correia
authors.forename: Joaquim
authors.initials: J
authors.lastname: Miguel Oliveira
authors.forename: Rui
authors.initials: R
authors.lastname: Luís Reis
authors.forename: Hendrik
authors.initials: H
authors.lastname: Schmidt
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D020100:Hydrogels / Q000737:chemistry; D007403:Intervertebral Disc / Q000502:physiology* / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000502:physiology / Q000601:surgery; D008422:Materials Testing; D055595:Mechanical Phenomena; D012756:Sheep; D059145:Total Disc Replacement; D016474:Weight-Bearing
chemical_list: D020100:Hydrogels