Is a collagen scaffold for a tissue engineered nucleus replacement capable of restoring disc height and stability in an animal model?

Abstract

The idea of a tissue engineered nucleus implant is to seed cells in a three-dimensional collagen matrix. This matrix may serve as a scaffold for a tissue engineered nucleus implant. The aim of this study was to investigate whether implantation of the collagen matrix into a spinal segment after nucleotomy is able to restore disc height and flexibility. The implant basically consists of condensed collagen type-I matrix. For clinical use, this matrix will be used for reinforcing and supporting the culturing of nucleus cells. In experiments, matrixes were concentrated with barium sulfate for X-ray purposes and cell seeding was disclaimed in order to evaluate the biomechanical performance of the collagen material. Six bovine lumbar functional spinal units, aging between 5 and 6 months, were used for the biomechanical in-vitro test. In each specimen, an oblique incision was performed, the nucleus was removed and replaced by a collagen-type-I matrix. Specimens were mounted in a custom-built spine tester, and subsequently exposed to pure moments of 7.5 Nm to move within the three anatomical planes. Each tested stage (intact, nucleotomy and implanted) was evaluated for range of motion, neutral zone and change in disc height. Removal of the nucleus significantly reduced disc height by 0.84 mm in respect to the intact stage and caused an instability in the segment. Through the implantation of the tissue engineered nucleus it was possible to restore this height and stability loss, and even to increase slightly the disc height of 0.07 mm compared with the intact stage. There was no statistical difference between the stability provided by the implant and intact stage. Results of movements in lateral bending and axial rotation showed the same trend compared to flexion/extension. However, implant extrusions have been observed in three of six cases during the flexibility assessment. The results of this study directly reflect the efficacy of vital nucleus replacement to restore disc height and to provide stability to intervertebral discs. However, from a biomechanical point of view, the challenge is to employ an appropriate annulus fibrosus sealing method, which is capable to keep the nucleus implant in place over a long-time period. Securing the nucleus implant inside the disc is one of the most important biomechanical prerequisites if such a tissue engineered implant shall have a chance for clinical application.

Scaffolding in tissue engineering: general approaches and tissue-specific considerations

“…Subcutaneous implantation was used and the implant was never exposed to physiological loading. Recently, there is one ex vivo study reporting collagen nucleus replacement in bovine discs under mechanical loading [121]. Although restoration of disc height is possible, extrusion of the whole implant after a few loading cycles have been reported.…”

“…A wide range of biomaterials dominated by natural biomaterials has been used for nucleus replacement. These materials include collagen [121], atellocollagen [98,99], alginate [70,76], gelatin [118], chitosan [33], collagen/ glycosaminoglycan [97], collagen/hyaluronan [2] and poly-L-lactic acid [94]. Reviews for nucleus replacements have been reported elsewhere [29,103].…”

Injection of a polymerized hyaluronic acid/collagen hydrogel matrix in an in vivo porcine disc degeneration model

“…Injected cells and fibrin matrix (without UVL polymerization) get lost easily through this annular lesion [3,4,6,7]. Consequently, the nucleus is exposed to the immune system and to detrimental degenerative cascades with upregulation of MMPs [31,32].…”

“…However, at present such approaches to humans are still rare and limited due to remaining concerns about safety and biological potency. Although tremendous efforts have been made to improve disc cell therapy, today's results are rather disappointing with early loss of implanted cells caused by annular damage at the injection site and cell death due to the harsh intradiscal environment characterized by insufficient nutrition, accumulation of waste products and high intradiscal pressures [3][4][5][6][7]. Additionally, cell-based strategies are expensive, time demanding, and invasive with potentially more complications, since autologous cells have to be collected in a first operation, with the need for processing and cultivation, and then application to the disc in a second operative procedure.…”

Intervertebral Disc Regeneration

“…The three main components of IVD aimed at tissue regeneration are: 1) AF (Sato et al, 2003;Chang et al, 2007;Helen and Gough, 2007;Nerurkar et al, 2007;Shao and Hunter, 2007;Wan et al, 2007;Nerurkar et al, 2008;Wang et al, 2008;Nerurkar et al, 2009); 2) NP (Baer et al, 2001;Sakai et al, 2003;Seguin et al, 2004;Bertram et al, 2005;Wilke et al, 2006;Roughley et al, 2006;Cloyd et al, 2007;Chou et al, 2008;Halloran et al, 2008;Richardson et al, 2008;Vernengo et al, 2008;Bron et al, 2009;Chou et al, 2009;Sawamura et al, 2009;Calderon et al, 2010;Silva-Correia et al, 2010a;Silva-Correia et al, 2010b;Reza and Nicoll, 2010;); and 3) both NP and AF by means of using biphasic scaffolds (Mizuno et al, 2004;Hamilton et al, 2005;Mizuno et al, 2006;Nerurkar et al, 2008;Nesti et al, 2008). It has been proposed that for producing a tissue resembling natural IVD, total IVD replacement could be required.…”