Fabrication of multi-component tissue for intervertebral disc tissue engineering

Abstract

Intervertebral disc tissue engineering is challenging because it involves the

integration of multiple tissues with distinct structures and compositions such as

lamellar annulus fibrosus, gel?like nucleus pulposus and cartilage endplate. Each

of them has different compositions and different structures. It is hypothesized

that integration of tissues can be enhanced with appropriate mechanical and

biological stimuli. Meanwhile, effect of torsional stimulus on cell re?orientation

in mesenchymal stem cell?collagen tubular constructs is investigated in this study.

Furthermore, it is proposed that these findings can be used to fabricate a multicomponent

unit for intervertebral disc tissue engineering. It has been

demonstrated that mechanical and biological stimuli can stabilize the interface

between osteogenic and chondrogenic differentiated constructs with enhanced

ultimate tensile stress while the phenotype of osteogenic and chondrogenic

differentiated constructs were maintained. Scanning electronic microscopic

images have shown aligned collagen fibrils and presence of calcium at the

interface, indicating the possibility of the formation of a calcified zone. In

addition, it is proven that torsional stimulus triggered re?orientation of

mesenchymal stem cells in collagen lamellae towards a preferred angle. Cell

alignments were confirmed by using a MatLab?based program to analyze the

actin filament and the cell alignment via Phalloidin and Hematoxylin staining,

respectively. Cells and actin filaments were inclined around 30o from the vertical

axis, while cells and filaments in the control group (static loading) aligned along

the vertical axis. Furthermore, a double?layers bioengineered unit was fabricated,

with intact osteogenic differentiated parts at both ends. Comparatively higher

cell density was observed at the interface between layers, demonstrating the

interactions between layers, while the phenotype of each part was maintained in

14 days culture. This study concludes that a multi?components bioengineered

unit with preferred cell alignments can be fabricated. This provides new insights

to future development of bioengineered spinal motion segment for treating late

stage disc degeneration.