Abstract
Treatments to alleviate chronic lower back pain, caused by intervertebral disc herniation as a consequence of degenerate annulus fibrosus (AF) tissue, fail to provide long-term relief and do not restore tissue structure or function. The future of AF tissue engineering relies on the production of its complex structure assisted by the many cells that are resident in the tissue. As such, this study aims to mimic the architecture and mechanical environment of outer AF tissue using electrospun fiber scaffolds made from a synthetic biopolymer blend of poly(ε-caprolactone) (PCL) and poly(L-lactic) acid (PLLA). Initially, an aligned bilayer PCL:PLLA scaffold was manually assembled at ±30° fibers direction to resemble the native AF lamellar layers; and bovine AF cells were used to investigate the effect of construct architecture on cell alignment and orientation. Bilayer scaffolds supported cell adhesion and influenced their orientation. Furthermore, significant improvements in tensile stiffness and strength were achieved, which were within the reported range for human AF tissue. Electrospun bilayer scaffolds are, however, essentially two-dimensional and fabrication of a complete three-dimensional (3D) circular construct to better replicate the AF's anatomical structure is yet to be achieved. For the first time, a custom-built Cell Sheet Rolling System (CSRS) was utilized to create a 3D circular lamellae construct that mimics the complex AF tissue and which overcomes this translational limitation. The CSRS equipment is a quick, automated process that allows the creation of multilayered, tube-like structures (with or without cells), which is ideal for mimicking human cervical AF tissue in term of tissue architecture and geometry. Tube-like structures (6 layers) were successfully created by rolling ±30° bilayer PCL:PLLA scaffolds seeded with bovine AF cells and subsequently cultured for 3 weeks. Cells remained viable, purposefully oriented with evidence of collagen type I deposition, which is the main structural component of AF tissue. This is the first study focused on applying CSRS technology for the fabrication of a more clinically-relevant, 3D tissue engineered scaffold for AF tissue regeneration.
Highlights
Treatments to alleviate chronic lower back pain, caused by intervertebral disc (IVD) degeneration and herniation, fail to restore IVD structure or function
The disc has heterogeneous biphasic structure that consists of fibrous concentric lamellar sheets, the annulus fibrosus (AF), surrounding a gel-like material, the nucleus pulposus (NP) (Hickey and Hukins, 1980; Raj, 2008)
The data suggested that, in addition to demonstrating biocompatibility, a bilayer scaffold made from a 50:50 blend of PCL and poly(L-lactic) acid (PLLA) with opposing fibers possessed similar structural and mechanical properties to human AF. This current study investigates the response of bovine AF cells seeded on ±30◦ bilayer fiber scaffolds and scalability of the blended scaffold into a more clinicallyrelevant 3D structure through the incorporation of an automated Cell Sheet Rolling System (CSRS) developed by Othman et al (2015) to create controlled 3D tubular scaffold architectures
Summary
Treatments to alleviate chronic lower back pain, caused by intervertebral disc (IVD) degeneration and herniation, fail to restore IVD structure or function. Tissue engineering is a promising approach for the treatment of degenerative IVD tissues (van Uden et al, 2017). Their complex architectural and mechanical properties make synthesis of a biomimetic, artificial substrate challenging. In the AF region, each lamellar sheet is angularly oriented at 30◦ and alternatively to each other, while the collagen fibers within every lamella are aligned parallel to each other (Figure 1A). This cross-aligned fibrous structure is critical for complex mechanical behavior that has non-linear anisotropic properties. Building on our previous work (Shamsah et al, 2019), structural evaluation of porcine IVD tissue, in particular the outer AF region, provided a detailed understanding of the tissue’s architecture (Figures 1B–E), which can be incorporated into the design and development of synthetic scaffolds
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