Biomedical Engineering Reference
In-Depth Information
and US-tube/PPF scaffolds exhibit a diffuse cell density at the earlier (4 week) time point and a
denser cell population at the later (12 week) time point. Lin et al.
[27]
prepared biodegradable poly
(lactic-co-glycolic acid) (PLGA)/carboxyl-functionalized MWCNT (c-MWCNT) nanocomposites
via solvent casting technique and assessed the biocompatibility of the nanocomposites in vitro by
using rat BMSCs. The presence of c-MWCNTs not only increased the mechanical properties of the
nanocomposites but also promoted cell adhesion, viability, and production levels of alkaline phos-
phatase (ALP). These results demonstrated that CNT-modified polymer composites were beneficial
for promoting cell growth and inducing BMSCs to differentiate into osteoblasts.
In addition to use of CNTs as reinforcement, some studies intended to culture cells directly on
CNT films or scaffolds. An earlier study on metabolic activity and adhesion of human osteoblasts
on SWCNT films demonstrated that the SWCNT films were nontoxic for osteoblast activity and
adhesion, which were in the same range as Ti6Al4V alloy control group used in the study
[28]
.
When the maturation of human osteoblast-like SaoS-2 cells on MWCNT compact substrate was
evaluated using assays for osteonectin, osteopontin, and osteocalcin gene expression, total protein
(TP) amount, and ALP activity, the results indicated that the CNTs induced osteogenic maturation
of the osteoblasts
[29]
. Zanello et al.
[9]
prepared CNT-coated glass coverslips by spraying differ-
ent CNT dispersions onto preheated (ca. 80
o
C) glass coverslips. These coverslips were used for
cell culture after dry sterilization directly. The CNTs in the study included as-prepared CNTs
(AP-CNTs), as well as nitric acid-treated SWNTs (SWNT-COOH), poly(m-aminobenzene sulfonic
acid) functionalized SWNTs (SWNT-PABS), and poly(ethylene glycol) (PEG) functionalized
SWNTs (SWNT-PEG), on the basis of their net negative, zwitterionic, and neutral electric charge,
respectively, at the pH of the experiment. The authors studied osteoblastic ROS 17/2.8 cells prolif-
eration on these CNTs in 5-day-old cultures and found that the CNTs supported ROS 17/2.8 cell
growth in the order of electrically neutral AP-CNTs and SWNT-PEG, and then the negative
SWNT-COOH and zwitterionic SWNT-PABS. The results suggested the surface charge of CNTs
was a vital property necessary for adequate secretion of bone matrix, although one could not say
that it alone was responsible for osteoblast growth. Furthermore, the cells cultured on SWNTs pro-
duced plate-shaped crystals (100
1000 nm in length and approximately 20 nm in thickness) similar
in shape to hydroxyapatite (HA) crystals found in woven bone, which aggregated in clusters. These
results indicated that SWNTs could facilitate the deposition of mineralized matrix (
Figure 18.4
).
To make CNTs, which are of relatively short aspect ratio, into three-dimensional scaffolds,
Zhang et al.
[30]
wrapped natural polysaccharides such as amylose (AMY), alginate (ALG), and
chitosan (CHI) onto SWCNTs to give a series of SWCNT scaffolds. The polysaccharide-wrapped
SWCNTs well mimicked the natural nanofibrous ECM and significantly enhanced cell adhesion
and proliferation. The surface properties of the SWCNT scaffolds, such as functional groups, sur-
face charge, and hydrophilicity, directly influenced the protein adsorption, which led to significant
changes in the expression of cellular focal adhesion kinase (FAK) and thus affected the mammalian
cell morphology and proliferation. Hirata et al.
[31]
coated 3-D collagen scaffold surface with
MWCNTs to obtain porous structures (MWCNT-coated sponge) for bone tissue engineering. They
cultured rat primary osteoblasts on MWCNT-coated sponge in a 3-D dynamic flow cell culture
system and measured differentiation markers. The measurements showed that ALP activity,
calcium and osteopontin contents of cells on the MWCNT-coated sponges at 7 days were signifi-
cantly higher than those on uncoated ones. This confirmed the earlier differentiation of osteoblasts
on the MWCNT-coated sponges. By using 12-week-old Wistar rats as the animal model, the bone
