Biomedical Engineering Reference
In-Depth Information
(sGAG); however, these molecules did not appear to be retained within the scaffold
itself.
In a similar fashion, Yang et al. developed a 70% porous hydrogel scaffold with
average pore diameter of 100
m
m using a formulation of gelatin, chondroitin-6-
sulfate, and hyaluronic acid. Hydrogels were assembled via multiple freeze-dry
cycles and crosslinked with glutaraldehyde [
101
,
102
]. Studies using these gels
indicated that human NP cells remained viable over a 4-week culture period and
appeared to proliferate significantly for between 2 and 4 weeks. Immunohisto-
chemistry for collagen type II stained positive within the scaffold, and gene
expression illustrated the upregulation of NP phenotype markers including collagen
type II, aggrecan, and Sox-9 in comparison to NP cells cultured in monolayer.
Interestingly, a downregulation in interleukin 1 (IL-1), which has been implicated
in increasing MMP activity and proteoglycan degradation, was observed along with
an upregulation of TIMP-1. In general, the scaffolds developed by Yang appear to
be conducive to repopulation, with NP cells maintaining their viability,
proliferative, and synthetic capacity. However, both control scaffolds (those with-
out cells) and scaffolds with NP cells were only able to maintain approximately half
their initial GAG content at best.
Li et al. have developed a porcine collagen type II, hyaluronate, chondroitin-6-
sulfate tri-copolymer sponge [
103
]. Unlike Yang et al. who utilized glutaraldehyde,
which does not have the ability to crosslink GAGs, Li utilized a 1-ethyl-3-
(3-dimethylaminopropyl)-carbodiimide (EDC) and
N
-hydroxysuccinimide (NHS)
crosslinking system to stabilize GAGs within their scaffolds. Evaluation of hydrogel
cytotoxicity carried out using rabbit NP cells indicated no significant difference in
DNA synthesis of NP cells in monolayer and scaffold. Histocompatibility following
implant in Sprague-Dawley rats indicated a foreign-body reaction, with inflammatory
cell infiltration at day 3 within and around the implant followed by a gradual
replacement of these cells with fibroblasts at day 14. The scaffold was almost
completely degraded after 84 days and fully replaced with vascularized granulation
tissue. There was no difference in circulating antibodies towards the porcine collagen,
as noted via ELISA between implant, untreated, and sham-operated groups.
In an attempt to mimic the physiological ratio of collagen type II to hyaluronan
in the healthy human NP, Calderon et al. constructed hydrogels scaffolds composed
of these two elements in a 9:1 (w/w) ratio [
104
]. Scaffolds were crosslinked
with various concentrations of EDC/NHS, but it was found that 8 mM EDC/NHS
resulted in a confined compressive modulus on the order of the native NP, while
allowing for optimal rat mesenchymal stem cell (rMSC) viability and proliferation.
Additionally, real time PCR results from rMSCs seeded on the scaffolds for 21 days
indicated that the scaffolds promoted increased aggrecan expression and inhibited
collagen type I expression compared to rMSCs cultured on monolayers.
Sakai et al. investigated the influence of three different atelocollagen scaffolds
(3% atelocollagen I, 0.3% atelocollagen I, 0.3% atellocollagen II) on human NP
cell proliferation and proteoglycan synthesis compared to 1.2% alginate hydrogels
[
105
]. In general, the results indicate varied influence of scaffold material on NP
cells. Cells in atelocollagen I scaffolds showed significantly more [3H]-thymidine
