Picture of athlete cycling

Open Access research with a real impact on health...

The Strathprints institutional repository is a digital archive of University of Strathclyde's Open Access research outputs. Strathprints provides access to thousands of Open Access research papers by Strathclyde researchers, including by researchers from the Physical Activity for Health Group based within the School of Psychological Sciences & Health. Research here seeks to better understand how and why physical activity improves health, gain a better understanding of the amount, intensity, and type of physical activity needed for health benefits, and evaluate the effect of interventions to promote physical activity.

Explore open research content by Physical Activity for Health...

The strain-dependent osmotic pressure and stiffness of the bovine nucleus pulposus apportioned into ionic and non-ionic contributors

Heneghan, P. and Riches, P.E. (2008) The strain-dependent osmotic pressure and stiffness of the bovine nucleus pulposus apportioned into ionic and non-ionic contributors. Journal of Biomechanics, 41 (11). pp. 2411-2416. ISSN 0021-9290

Full text not available in this repository. Request a copy from the Strathclyde author

Abstract

Elucidation of the load-bearing mechanism of the nucleus pulposus (NP) facilitates understanding of the mechanical and metabolic functioning of the intervertebral disc and provides key data for mathematical models. Negatively charged proteoglycans in the NP generate an ionic osmotic pressure, πi, which contributes to the tissue's resistance to load and, moreover, is the main mechanism by which the unloaded disc rehydrates. Functionally important, πi has seldom been investigated in situ and, crucially, its variation with strain has not been reported. In a confined compression apparatus, we aimed to apportion the strain-dependent load-bearing mechanism of the NP at equilibrium to the tissue matrix and ionic osmotic pressure; and to determine whether any proteoglycan loss occurs during confined compression testing. Forty-eight confined compression experiments were conducted in isotonic (0.15 M NaCl) and hypertonic (3.0 and 6.1 M NaCl) external solutions in single and multiple step-strain protocols. The 6.1 M NaCl external solution was needed to eliminate as much of the ionic effects as possible. The ionic osmotic pressure was well described by πi=19.1λ−1.58 (R2=0.992), and was approximately 70% of the applied load at equilibrium, independent of λ. The effective aggregate modulus, , also increased with strain: . Concentrations of sulphated glycosaminoglycans were obtained for the samples tested in isotonic NaCl with no proteoglycan loss detected from the confined compression tests. These results highlight the non-linearity of the stress-strain response of NP tissue and the necessity to include a non-linear function for osmotic pressure in mathematical models of this tissue.