Engineering a Multicomponent Spinal Motion Segment-Like Construct from Mesenchymal Stem Cells
Authors: Chik T. K. , Chooi W. H. , Cheng H. W. , Choy T. H. , Sze K. Y. , Luk K. , Cheung K. , Chan B. P. 
Published: May 2014

Introduction

The task of engineering the intervertebral disc is challenging as the complex tissue needs to integrate with the host tissue and perform its function after the implantation. The vertebrae connected to the endplates are essential to integrate with the host vertebrae tissue which had been shown by Luk et al in whole disc transplantation.1 Hence, engineering the complex tissue needs to integrate the different components of the vertebrae (VB), cartilaginous endplate (CEP), nucleus pulposus (NP), and annulus fibrosus (AF); both biologically and mechanically. In this study, the multiple component spinal motion segments were fabricated by integrating these components. The construct was then loaded in a bioreactor and supplied with mechanical and biological stimulation. The functional aspect of the fabricated endplate-like construct was evaluated by a permeability test.

Materials and Methods

Rabbit mesenchymal stem cells (rMSCs) were encapsulated in collagen and induced to differentiate toward osteogenic and chondrogenic lineages before fabricating trilayered osteochondral (OC) constructs as previously mentioned. To test the nutritional function of the OC construct which acts as the endplate, rabbit nucleus pulposus cells (rNPCs)-encapsulated collagen microspheres were trapped in a sealed chamber formed with the OC construct such that the nutrients have to diffuse through the OC construct to reach the inside of the chamber. Cell viability of the rNPCs was then evaluated. To fabricate the multiple component construct, a rMSCs encapsulated collagen-GAG precipitate was added in between two OC construct and placed in between the shaft of the bioreactor. Then a layer of rMSC encapsulated collagen was formed around the construct to form the AF-like lamella. Torsional loading was applied onto the construct to study its effect on cell alignment in the AF-like lamella. Finally, one to three layers of AF-like lamellae were added to the spinal motion segment construct and cultured in the bioreactor with complex loading for 14 days. Histological, ultrastructural, and mechanical evaluation was done on the construct.

Results

In the custom developed functionality test for nutrient transport, the rNPCs in the chamber were viable at the end of the culture showed that nutrients were able to diffuse through the OC construct. For the effect of torsional loading on cell alignment in the AF-like lamella, alignment analysis showed that the cells were aligned along a preferred axis under torsional loading compared with control group without loading. However, no collagen fibers alignment was found in this study. The multiple component construct was fabricated with each component similar to the spinal motion segment. The different components of the construct were well integrated throughout the culture and were shown by histology. Mean torsional stiffness of the constructs significantly increased as the number of rMSC encapsulated AF-like layer increased.

Conclusion

This study demonstrated the feasibility to engineer a spinal motion segment-like tissue with collagen and MSC. The OC constructs demonstrated its nutritional function and can be used as a vertebra-endplate construct in this model. rMSC encapsulated in collagen gel can be induced to re-orientate and align in a certain direction by applying cyclic torsional force on the tubular structure. This can be a tissue engineered model to study the effects of various strategies in functional remodeling and maturation of the intervertebral disc. Disclosure of Interest None declared Reference Luk KD, Ruan DK. Intervertebral disc transplantation: a biological approach to motion preservation. Eur Spine J 2008;17(Suppl 4):504–510