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A 3-Dimensional Large Deformation FEA of a Ligamentous C4-C7 Spine Unit
Published in J. Middleton, M. L. Jones, G. N. Pande, Computer Methods in Biomechanics & Biomedical Engineering – 2, 2020
F. Heitplatz, S. L. Hartle, C. R. Gentle
To show the model performance under large deformation the following boundary conditions were applied: the inferior aspect of the C7 vertebra body was restricted in all directions and a force of 400 N (i.e. 200 N for the half model) was applied in the anterior direction of the transverse plane at the superior aspect of the C4 vertebral body. Figure 3 shows the deformation of the model between the unloaded and the fully loaded states. Notice the 3D-sliding contact at the facet joints resulting in rotational movement of the vertebrae and therefore large strain at the inter-spinous ligament and the nuchal ligament. Last can only be fully modelled when the model is expanded to the occiput where it connects at its superior border. However this simple experiment shows the possibility of an involvement of the nuchal ligament in whiplash-type injuries.
Thermoplastic Elastomers
Published in Anil K. Bhowmick, Current Topics in ELASTOMERS RESEARCH, 2008
Francis R. Costa, Naba K. Dutta, Namita Roy Choudhury, Anil K. Bhowmick
A significant research has been dedicated in elastin–mimetic protein polymer and a versatile class of TPE based on block copolypeptide has been developed. It has been identified in early 1980s that the key structural feature that introduces elasticity to the protein of short repeat sequence contains proline and glycine residue. For example, the elastic proteins elastin and spider flagelliform silk are dominated by the pentapeptide repeats valine–proline–glycine–valine–glycine (VPGVG) [103,104] and glycine–proline–glycine–glycine–x (GPGGX) [105–107], respectively. Elastin is the major structural protein of those tissues, which required rapid extension and complete recovery (e.g., aorta, nuchal ligament). Thus significant focus has been placed on repeat sequence VPXYG [97,108]. It has been observed that the lower critical solution temperature (LCST) of this polypeptide can be manipulated by adjusting the identity of the fourth residue Y. In addition substitution of an ala residue for the consensus gly residue in the third position (X) of the repeat results in the change in the mechanical response of the biopolymer from elastomeric to plastic. The pentapeptide repeat residue has been the basis for the development of many ABA-type peptide-based triblock copolymer; some of them behave like hydrocarbon-based TPEs. Spontak and Patel [109] synthesized elastin–mimetic triblock polypeptides, ABA-type block copolymers using biological methods with a sequence based on the key elastin repeat sequence VPGVG that undergoes phase separation above a critical temperature. The gel reliquifies upon cooling and thus behaves like TPE. The A blocks chosen in the polymer are more hydrophobic than VPGVG. These hydrogels are also ionically and thermally responsive (i.e., they undergo large volume changes as a result of these responses). By combining polypeptide blocks with different inverse temperature transition values due to hydrophobicity differences of the blocks, it is possible to produce amphiphilic polypeptides that self-assemble into hydrogels and exhibit TPE-like behavior.
Contribution of injured posterior ligamentous complex and intervertebral disc on post-traumatic instability at the cervical spine
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
Marie-Hélène Beauséjour, Yvan Petit, Jeremy Hagen, Pierre-Jean Arnoux, Jean-Marc Mac Thiong, Eric Wagnac
The posterior ligamentous complex (PLC), which comprises the ligamentum flavum (LF), interspinous ligament (ISL) and nuchal ligament (NL) (Rasoulinejad et al. 2012) and the intervertebral disc (IVD) (Nadeau et al. 2012) play a critical role in cervical spine stability. Flexion-distraction injuries characterized by PLC and IVD disruption are frequent at the cervical spine and result in serious neurological consequences (Blauth et al. 2007).