Biomedical Engineering Reference
In-Depth Information
In an alternative approach to utilization of alginate scaffolds for NP TE, Gaetani
investigated the use of semipermeable alginate microcapsules with a liquid core for
the co-culture of human NP cells and ADSCs to create NP tissue in vitro [
121
].
Using a one-step process, a cell suspension in 40 mM barium chloride was created
and added drop-wise into a 0.5% (w/v) sodium alginate solution in DMEM.
The authors cite the advantages of using barium due to its reduced involvement
in biological processes compared to that of calcium and an observed increase in
alginate mechanical integrity. Culture for 7 days resulted in a pseudo-tissue struc-
ture in which tightly aggregated and elongated spindle-shaped cells resided at the
liquid core-alginate interface, with rounded cells evenly distributed throughout
the core itself. Interestingly, the authors also found that the matrix surrounding the
rounded cells stained positively for aggrecan and collagen type I. The authors
theorized that using a liquid-core scaffold may be advantageous because cells are
not trapped in a gel matrix, but rather are suspended in liquid media. Careful
consideration of this theory, however, is warranted as most cells derived from
tissues are anchorage-dependent. The observed production of collagen type I by
the cells within the scaffold in this study suggests that the cells are attempting to
create their own substrate for attachment; however, the production of collagen type
I would probably not result in an appropriate NP-like tissue. Additionally, since the
authors used NP cells harvested from herniated discs, long-term studies with
healthy cells are certainly warranted.
8.2.5 Miscellaneous Scaffolds
The use of chitosan, a cationic polysaccharide derived from depolymerization
and deacytlation of chitin found in crustacean shells, has been investigated by
Roughly as an alternative scaffold for NP TE [
122
]. The authors hypothesize that
the thermoresponsive cationic chitosan hydrogels would be able to trap and retain
anionic proteoglycan molecules produced by encapsulated NP cells, an ability
significantly lacking in many other hydrogel systems. The authors found that gels
made of 1.5% chitosan crosslinked with glycerophosphate in the presence of
hydroxyethyl cellulose allowed bovine NP cell proliferation while retaining nearly
75% of synthesized GAG within the constructs after 20 days of in vitro culture. This
resulted in a total GAG content that was 8-12% of GAG levels found in the native
bovine NP. With the addition of TGF-
b
to the culture media, total GAG content
approached but never exceeded 15% of native NP values, despite increased time in
culture. Moreover, the rate of proteoglycan accumulation eventually diminished,
which may have been due to a potential inhibitory effect of the surrounding
proteoglycan on the cells, as suggested by the authors.
Reza et al. illustrated the feasibility of using methacrylating carboxymethyl-
cellulose (CMC), a water-soluble polysaccharide derivative of cellulose, to yield a
photo-crosslinkable hydrogel scaffold for encapsulating NP cells [
123
]. The authors
utilized this material due to the fact that carboxylic acid on the CMC molecule
becomes deprotonated at physiologic pH, resulting in a negative charge similar to
