title: Long-Term Creep Behavior of the Intervertebral Disk: Comparison between Bioreactor Data and Numerical Results.
abstract: The loaded disk culture system is an intervertebral disk (IVD)-oriented bioreactor developed by the VU Medical Center (VUmc, Amsterdam, The Netherlands), which has the capacity of maintaining up to 12 IVDs in culture, for approximately 3 weeks after extraction. Using this system, eight goat IVDs were provided with the essential nutrients and submitted to compression tests without losing their biomechanical and physiological properties, for 22 days. Based on previous reports (Paul et al., 2012, 2013; Detiger et al., 2013), four of these IVDs were kept in physiological condition (control) and the other four were previously injected with chondroitinase ABC (CABC), in order to promote degenerative disk disease (DDD). The loading profile intercalated 16 h of activity loading with 8 h of loading recovery to express the standard circadian variations. The displacement behavior of these eight IVDs along the first 2 days of the experiment was numerically reproduced, using an IVD osmo-poro-hyper-viscoelastic and fiber-reinforced finite element (FE) model. The simulations were run on a custom FE solver (Castro et al., 2014). The analysis of the experimental results allowed concluding that the effect of the CABC injection was only significant in two of the four IVDs. The four control IVDs showed no signs of degeneration, as expected. In what concerns to the numerical simulations, the IVD FE model was able to reproduce the generic behavior of the two groups of goat IVDs (control and injected). However, some discrepancies were still noticed on the comparison between the injected IVDs and the numerical simulations, namely on the recovery periods. This may be justified by the complexity of the pathways for DDD, associated with the multiplicity of physiological responses to each direct or indirect stimulus. Nevertheless, one could conclude that ligaments, muscles, and IVD covering membranes could be added to the FE model, in order to improve its accuracy and properly describe the recovery periods.
authors.affiliation: Center for Mechanical and Materials Technologies, Department of Mechanical Engineering, University of Minho , Guimarães , Portugal ; INSIGNEO Institute for in silico Medicine, Department of Mechanical Engineering, University of Sheffield , Sheffield , UK.
authors.forename: A P G
authors.initials: AP
authors.lastname: Castro
authors.affiliation: Department of Orthopaedic Surgery, VU Medical Center , Amsterdam , Netherlands ; Research Institute MOVE, Faculty of Human Movement Sciences, VU Medical Center , Amsterdam , Netherlands.
authors.forename: C P L
authors.initials: CP
authors.lastname: Paul
authors.affiliation: Department of Orthopaedic Surgery, VU Medical Center , Amsterdam , Netherlands ; Research Institute MOVE, Faculty of Human Movement Sciences, VU Medical Center , Amsterdam , Netherlands ; Skeletal Tissue Engineering Group Amsterdam, VU Medical Center , Amsterdam , Netherlands.
authors.forename: S E L
authors.initials: SE
authors.lastname: Detiger
authors.affiliation: Department of Orthopaedic Surgery, VU Medical Center , Amsterdam , Netherlands ; Research Institute MOVE, Faculty of Human Movement Sciences, VU Medical Center , Amsterdam , Netherlands ; Skeletal Tissue Engineering Group Amsterdam, VU Medical Center , Amsterdam , Netherlands.
authors.forename: T H
authors.initials: TH
authors.lastname: Smit
authors.affiliation: Department of Orthopaedic Surgery, VU Medical Center , Amsterdam , Netherlands ; Research Institute MOVE, Faculty of Human Movement Sciences, VU Medical Center , Amsterdam , Netherlands ; Skeletal Tissue Engineering Group Amsterdam, VU Medical Center , Amsterdam , Netherlands.
authors.forename: B J
authors.initials: BJ
authors.lastname: van Royen
authors.affiliation: Center for Mechanical and Materials Technologies, Department of Mechanical Engineering, University of Minho , Guimarães , Portugal.
authors.forename: J C
authors.initials: JC
authors.lastname: Pimenta Claro
authors.affiliation: Department of Orthopaedic Surgery, VU Medical Center , Amsterdam , Netherlands ; Research Institute MOVE, Faculty of Human Movement Sciences, VU Medical Center , Amsterdam , Netherlands ; Department of Plastic, Reconstructive and Hand Surgery, VU Medical Center , Amsterdam , Netherlands.
authors.forename: M G
authors.initials: MG
authors.lastname: Mullender
authors.affiliation: Center for Mechanical and Materials Technologies, Department of Mechanical Engineering, University of Minho , Guimarães , Portugal.
authors.forename: J L
authors.initials: JL
authors.lastname: Alves
keywords: circadian variations; creep behavior; custom finite element solver; intervertebral disk; loaded disk culture system