Biomedical Engineering Reference
In-Depth Information
scaffolds composed of a thermoresponsive 3% chitosan-0.5 M glycerophosphate
crosslinked hydrogel [
74
]. Others have shown that direct injection of BMSCs into
the lumbar IVDs of New Zealand white rabbits resulted in an initial increase
proteoglycan content [
94
]. However, by 24 weeks, injected BMSCs had migrated
to the transition zone between the NP and AF and had developed spindle-shaped
morphologies reminiscent of AF cells. These interesting aspects definitely necessi-
tate further studies. In a similar approach, Sakai et al. injected allogenic BMSCs
encapsulated in atellocollagen type II hydrogels into rabbit degenerated IVDs with
outstanding results [
95
]. Similar to studies on BMSCs, several reports have
documented the potential of ADSCs to differentiate into NP-like cells using indirect
co-culture systems with NP cells [
96
,
97
].
8.2 Biopolymeric Scaffolds for Tissue Engineering of the NP
Although it has been shown that there are many feasible cell sources for TE of the
human NP, it is clear that a suitable scaffold to support these cells is required for
successful tissue regeneration. In the event that the NP is severely degenerated,
creating an environment rich in destructive enzymes [
27
], one could speculate that
removal of the degraded NP could prove advantageous in allowing for the best
possible outcome for any alternative cell source to rescue the NP. Accordingly, the
use of a scaffold on which to seed cells would be advantageous not only for aiding
in the restoration of the mechanical function of the NP, but also in facilitating the
maintenance or re-establishment of a proper NP cell phenotype. An ideal NP
scaffold would include the use of a material that could (1) protect cells from
loads experienced by the IVD, (2) supports either the re-differentiation of cell
sources that may de-differentiate during monolayer expansion or induce the out-
right differentiation of cells, (3) is non-cytotoxic, and (4) ideally degrades into non-
cytotoxic components [
74
,
98
-
100
]. To this list one could add that the chosen
scaffold material should be able to be implanted using a minimally invasive
approach and should mimic the biochemical and mechanical properties found in
the native NP while allowing for cell proliferation and infiltration. To date, numer-
ous scaffolds have been developed from biopolymers in attempts to support cell-
driven regeneration of a healthy NP.
8.2.1 Collagen-Glycosaminoglycan-Based Scaffolds
One of the more recent attempts at developing a scaffold that mimics the native
ECM of human NP was investigated by Halloran et al. [
73
]. Using a blend of
atellocollagen II, aggrecan, and hyaluronic acid crosslinked with a calcium-depen-
dent enzyme (microbial transglutaminase), the authors' were able to form an in situ
curing hydrogel. The authors demonstrated that bovine NP cells remained viable
throughout
the 7 day study and were producing sulfated glycosaminoglycan
