Table 3.
Composite strategies for anulus fibrosus/nucleus pulposus replacement
| Anulus fibrosus | Nucleus pulposus | Bone | Outcome | Reference(s) |
|---|---|---|---|---|
| PGA/PLA, ovine AF cells (isotropic) | Alginate, ovine NP cells | NA | First research to demonstrate tissue-engineered composite IVD, ECM production, and compressive mechanical properties on the order of native ovine IVD | 140 |
| PLLA/HA, MSCs (isotropic) | HA, MSCs | NA | First paper to demonstrate a composite IVD structure using electrospun fibers; in vitro study demonstrated histological evidence of an AF and NP region with collagen I, II, and aggrecan production | 116 |
| Demineralized bone matrix rabbit AF cells (isotropic) | Collagen (II)/hyaluronate/chondroitin-6-sulfate rabbit NP cells | NA | Composite IVD subcutaneously implanted into aythmic mice demonstrated NP and AF region with collagen and proteoglycan deposition | 114 |
| Contracted collagen gel, ovine AF cells (anisotropic) | Alginate, ovine NP cells | NA | Composite IVD implanted in a rat-tail and lumbar model showed integration, disc height maintenance, and mechanical properties on the order of the native controls in all implants in the tail model, and disc height maintenance in 50% of the implants in the lumbar model | 66, 70, 76, 121 |
| Toroidal scaffolds of porous silk | Fibrin/hyaluron crosslinked hydrogel | NA | In vitro study demonstrated histological evidence of an AF from implanted AF cells, and NP from implanted chondrocytes, with phenotypically appropriate gene expression | 77, 141 |
| Multiple lamellae of photocrosslinked collagen membranes | Collagen-glycosaminoglycan co-precipitate | NA | Composite IVD tested mechanically in compression for comparison to native IVD; results showed a role for collagen lamellae in preserving height recovery following loading, and transient behaviors in creep and recovery. | 120 |
| Electrospun PCL, MSCs (anisotropic) | Agarose, MSCs | NA | Composite IVD with AF and NP regions showed aligned PCL fiber and lamella AF organization that mimicked those of the native IVD; in vitro study demonstrated organization and appropriate ECM deposition in the composite IVD constructs | 80, 115 |
| Electrospun PCL, acellular (anisotropic) | No material acellular | NA | Construct with organized AF architecture was implanted in a rat-tail model showing maintenance of disc height in 50% of samples without fixation and 100% with fixation | 81 |
| Contracted collagen gel, MSCs (anisotropic) | Collagen–GAG coprecipitate MSC | Collagen gel, osteogenically differentiated MSCs | Created an engineered IVD with AF/NP/osteochondral subunits with appropriate histological features of each region | 123 |
Abbreviations: AF, anulus fibrosus; ECM, extracellular matrix; GAG, glycosaminoglycan; HA, hyaluronic acid; IVD, intervertebral disc; MSC, mesenchymal stem cell; NA, not applicable; NP, nucleus pulposus; PCL, poly(ε-caprolactone); PGA, polyglycolic acid; PLA, polylactic acid.