Intervertebral Disk Tissue Engineering Using Biphasic Silk Composite Scaffolds

Abstract

Scaffolds composed of synthetic, natural, and hybrid materials have been investigated as options to restore intervertebral disk (IVD) tissue function. These systems fall short of the lamellar features of the native annulus fibrosus (AF) tissue or focus only on the nucleus pulposus (NP) tissue. However, successful regeneration of the entire IVD requires a combination approach to restore functions of both the AF and NP. To address this need, a biphasic biomaterial structure was generated by using silk protein for the AF and fibrin/hyaluronic acid (HA) gels for the NP. Two cell types, porcine AF cells and chondrocytes, were utilized. For the AF tissue, two types of scaffold morphologies, lamellar and porous, were studied with the porous system serving as a control. Toroidal scaffolds formed out of the lamellar, and porous silk materials were used to generate structures with an outer diameter of 8 mm, inner diameter of 3.5 mm, and a height of 3 mm (the interlamellar distance in the lamellar scaffold was 150-250 mm, and the average pore sizes in the porous scaffolds were 100-250 mm). The scaffolds were seeded with porcine AF cells to form AF tissue, whereas porcine chondrocytes were encapsulated in fibrin/ HA hydrogels for the NP tissue and embedded in the center of the toroidal disk. Histology, biochemical assays, and gene expression indicated that the lamellar scaffolds supported AF-like tissue over 2 weeks. Porcine chondrocytes formed the NP phenotype within the hydrogel after 4 weeks of culture with the AF tissue that had been previously cultured for 2 weeks, for a total of 6 weeks of cultivation. This biphasic scaffold simulating in combination of both AF and NP tissues was effective in the formation of the total IVD in vitro.

Biaxial mechanics and inter‐lamellar shearing of stem‐cell seeded electrospun angle‐ply laminates for annulus fibrosus tissue engineering

“…[6][7][8][9][10][11][12] However, most of these efforts focus on replication of disk biochemical content and distribution, rather than multi-lamellar microstructure and function. We have previously adopted an electrospinning-based approach to generate scaffolds for multi-lamellar AF tissue engineering.…”

The challenge and advancement of annulus fibrosus tissue engineering

“…The mechanical tests revealed that POM has an excellent deformability: the compressive stress, young's modulus, and tensile strength markedly increased as the polymerization time increased. There was no permanent deformation after 500 press-loading and release cycles with Poly-D-L-lactide/Bioglass [90,91] Silk [92,93] Genipin crosslinked fibrin [94] Single unit with fiber orientation Aligned alginate/chitosan [88] Polycarbonate polyurethane linked with dihydroxyl oligomer [95,96] Polycaprolactone [97,98] Poly-L-Lactide [99] Silk fibers/chondroitin sulphate [100] Collagen fibrils [101] Biphasic scaffold Poly (polycaprolactone triol malate)/DBM [102] Composite scaffold Poly-L-Lactide as AF and hyaluronic acid hydrogel as NP [24] Polyglycolic Acid/poly-l-lactic as AF and alginate hydrogel as NP [103] Silk scaffold as AF and silicon as NP or hyaluronic acid as NP [104,105] 30 % maximum strain. When implanted into mice back subcutaneous pocket, there were no inflammation responses were found [89].…”

“…They showed that the fibril alignment was formed, the chondrocytes were well distributed around the boundary of NP and AF, and the composite scaffolds had strong mechanical properties than that of agarose gel alone [32]. A different group created the AF/NP composite constructs with silk protein as an AF material and fibrin/hyaluronic acid gel as a NP tissue, and the composites were cultured in vitro up to 6 weeks [105].…”

A novel culture platform for fast proliferation of human annulus fibrosus cells

“…In the last decade, tissue engineering has proved to be a promising solution for replacing structure and restoring function of degenerated IVD (Yang et al 2009; Park et al 2012; Jin et al 2013). However, such approaches usually require a large number of seed cells, and thus the slow proliferation rate and consequential phenotypic alternation are key limiting factors (Gruber et al 1997).…”

“…It is understood that 2D cultures generally yield greater numbers of cells, but phenotypic stability is compromised (Gruber et al 2000). By contrast, 3D culture systems may favor disc matrix production and phenotype maintenance by incorporating various scaffolds such as collagen sponge, fibrin gel, agarose, and alginate (Yang et al 2009; Park et al 2012; Jin et al 2014). However, 3D culture procedures may be time consuming, technically demanding, and costly.…”