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Rheological characterization of the nucleus pulposus and dense collagen scaffolds intended for functional replacement
J.L. Bron 1 3, G.H. Koenderink 4, V. Everts 3 5, T.H. Smit 2 3 *
1Department of Orthopaedic Surgery, VU University Medical Center, Amsterdam, The Netherlands 2Department of Physics and Medical Technology, VU University Medical Center, Postbox 7057, 1007 MB, Amsterdam, The Netherlands 3Skeletal Tissue Engineering Group Amsterdam (STEGA) and Research Institute Move, Amsterdam, The Netherlands 4Institute for Atomic and Molecular Physics (AMOLF), Amsterdam, The Netherlands 5Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University, Amsterdam, The Netherlands
*Correspondence to T.H. Smit, Department of Physics and Medical Technology, VU University Medical Center, Postbox 7057, 1007 MB, Amsterdam, The Netherlands. T: +31-20-444-8023; F: +31-20-444-2357.
Lumbar discectomy is an effective therapy for neurological decompression in patients suffering from sciatica due to a herniated nucleus pulposus (NP). However, high numbers of patients suffering from persisting postoperative low back pain have resulted in many strategies targeting the regeneration of the NP. For successful regeneration, the stiffness of scaffolds is increasingly recognized as a potent mechanical cue for the differentiation and biosynthetic response of (stem) cells. The aim of the current study is to characterize the viscoelastic properties of the NP and to develop dense collagen scaffolds with similar properties. The scaffolds consisted of highly dense (0.5%-12%) type I collagen matrices, prepared by plastic compression. The complex modulus of the NP was 22 kPa (at 10 rad s-1), which should agree with a scaffold with a collagen concentration of 23%. The loss tangent, indicative of energy dissipation, is higher for the NP (0.28) than for the scaffolds (0.12) and was not dependent of the collagen density. Gamma sterilization of the scaffolds increased the shear moduli but also resulted in more brittle behavior and a reduced swelling capacity. In conclusion, by tuning the collagen density, we can approach the stiffness of the NP. Therefore, dense collagen is a promising candidate for tissue engineering of the NP that deserves further study, such as the addition of other proteins. Published by Wiley Periodicals, Inc. J Orthop Res 27: 620-626, 2009
