Creating tissue with intervertebral disc-like characteristics using gdf5 functionalized silk scaffolds and human mesenchymal stromal cells
1 Tissue Engineering for Orthopaedic & Mechanobiology, Bone & Joint Program, Department for BioMedical Research (DBMR), Medical Faculty, University of Bern, CH-3008 Bern, Switzerland
2 Graduate School for Cellular and Biomedical Sciences (GCB), University of Bern, CH-3012 Bern, Switzerland
3 Institute of Textile Machinery and High Performance Material Technology, TUD University of Technology, Dresden, Hohe Str. 6, 01069 Dresden, Germany
4 Department of Orthopaedic Surgery & Traumatology, Inselspital, Bern University Hospital, Medical Faculty, University of Bern, CH-3010 Bern, Switzerland
Abstract
For years, researchers have searched for a suitable biomaterial to regenerate the intervertebral disc (IVD). A promising candidate is silk, as there have been several approaches in the past where silk fibroin was used to repair the IVD's nucleus pulposus (NP) and annulus fibrosus (AF). However, to date, nobody has attempted to recreate IVD tissue with dimensions and cell densities comparable to a human IVD using silk and human mesenchymal stromal cells (MSC). Therefore, silk scaffolds were produced from Bombyx mori yarn. To mimic the AF, the yarn was embroidered into a ring-like structure or patch. To mimic the NP, fibre-additive manufacturing was applied to create highly porous constructs. Half of the NP scaffolds were functionalized with the growth differentiation factor 5 (GDF5). The scaffolds were seeded with MSCs from five human donors in a density of one-third of the density found in the human IVD and cultured for 7, 14 or 21 days in transforming growth factor β1 (TGF-β1)-enriched medium. All scaffolds were biocompatible as cell numbers increased by a factor 4-5. Furthermore, the scaffolds generally showed an anabolic phenotype, which was positively influenced by GDF5, and tissue-like characteristics were promoted based on the scaffolds' morphology. In conclusion, the here proposed silk scaffolds showed IVD-like characteristics with a size and cell density comparable to human IVD tissue.
Graphical Abstract

Keywords
- Silk
- Bombyx mori
- intervertebral disc
- growth and differentiation factor 5
- mesenchymal stromal cells
- scaffolds
- nucleus pulposus regeneration
- annulus fibrosus regeneration
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