Using methacrylated gellan gum in combination with novel silk to repair the annulus fibrosus in a dynamically loaded bovine organ culture model

Abstract

INTRODUCTION: Annulus fibrosus (AF) rupture within the intervertebral disc (IVD) can lead to herniation and is a key contributor to low back pain [1]. A potential solution could be implementing a methacrylated gellan gum (MA-GG) hydrogel. MA-GG is a polysaccharide produced by the bacterium Sphingomonas paucimobilis and is considered as a promising biomaterial for IVD tissue engineering applications [2]. Therefore, we aimed to create an AF repair approach using 2% MA-GG as a filler material and sealing it with an embroidered silk yarn fabric, miming the AF’s morphology.

METHODS: For this ex vivo organ culture model, coccygeal IVDs were isolated from fresh bovine tails. Next, the AF was injured using a biopsy puncher ( ⌀ 2 mm) [3]. The damaged site was either left untreated or filled with 2% MA-GG and then sealed with an embroidered silk yarn fabric sutured directly onto the IVD. Then, the IVDs were cultured for 14 days under different loading profiles, i.e. i) no load, ii) static load at 0.2 MPa, and iii) dynamic load at 0.2 ± 0.1 MPa and a superimposed torsion of 2° (Figure 1a). After the culture period, changes in the IVDs’ height were recorded, the AF was dissected, and the tissue and the culture medium were harvested. The AF tissue was further analysed for its metabolic activity, glycosaminoglycan (GAG) content, nitric oxide (NO) content, and relative gene expression.

RESULTS: After 14 days of culture, no IVD herniation occurred, and the silk ribbon successfully managed to seal the repaired site regardless of the loading profile (Figure 1b). Moreover, repaired IVDs showed a better disc height recovery than damaged samples under the dynamic loading profile. However, the

metabolic activity and the amount of GAG and NO remained mostly unchanged. Furthermore, repaired samples generally showed a higher expression of anabolic genes like Aggrecan and Collagen type II compared to damaged samples under dynamic load, and also inflammatory genes were often more highly expressed in the repaired samples than in the damaged ones.

Fig. 1: a) Daily dynamic loading profile, repeated for 14 days. b) Injured bovine IVD, repaired with MA-GG, sealed with silk and cultured for14 days under dynamic load.

DISCUSSION & CONCLUSIONS: The presented approach using MA-GG and silk fibroin to repair an AF injury was a success as no displacement of the biomaterials and no IVD herniation was observed. Furthermore, the cytocompatible properties of MA-GG and silk were confirmed as the tissue’s metabolic activity remained stable. Nevertheless, results should be viewed with caution as the data are still preliminary due to the small sample size of N = 1-2.

ACKNOWLEDGEMENTS: We thank the Swiss National Science Foundation # 310030E_192674/1 for funding.

REFERENCES: 1 Adams, M.A. and P.J. Roughley, Spine (Phila Pa 1976), 2006. 31(18): p. 2151-61. 2 Silva-Correia, J., et al., J Tissue Eng Regen Med, 2011. 5(6): p. e97-107. 3 Li, Z., et al., Eur Spine J, 2016. 25(9)