Biomedical Engineering Reference
In-Depth Information
Studies with rabbit bone marrow stromal cells have shown that these
cells can attach, proliferate, and differentiate into osteoblasts when seeded
on P3HB-11%3HH films. However, no phosphate deposits could be detected
in the 28-day study [279]. A comparison of cell viabilities on P3HB, P3HB-
3HH and PLLA films had the order: P3HB-12%3HH
>
P3HB-5%3HH
>
P3HB
>
P3HB-20%3HH
>
PLLA. This order is different to that found for
fibroblasts and was attributed to the appropriate surface roughness pro-
moting attachment and differentiation of osteoblasts-like cells, while fibrob-
lasts prefer smoother surfaces [94]. Porous scaffolds made by solution-
casting/salt-leaching confirmed the good cell compatibility of P3HB-3HH
matrices, which showed higher cell viabilities and osteoblast differentiation
(as determined by alkaline phosphatase activity) than scaffolds made from
P3HB and PLLA. Additionally, a significant mineralization has been observed
in this study [49]. Addition of HA to P3HB-3HH scaffolds resulted in reduced
osteoblast growth, while the growth on P3HB/HA scaffolds was enhanced in
comparison to the unmodified materials [124].
Rabbit articular cartilage-derived chondrocytes have been seeded on
solution-cast films made from P3HB, P3HB-12%3HH, and their blends.
Blends containing equal amounts of both polymers, possessing the highest
surface free energy of the samples tested, had the highest amount of pro-
tein adsorbed and number of chondrocytes adhered [129]. Studies on porous
scaffolds showed more chondrocyte growth on P3HB/P3HB-3HH blends than
on the individual polymers alone within the 28-day culture period [48, 89].
Microscopic analysis revealed that large quantities of chondrocytes grew ini-
tially on the surface and, after 7 days, also into the open pores of the polymer
scaffolds. Morphologically, cells found on the surface of the scaffold exhib-
ited a fibroblast-like appearance and slowly formed confluent cell multilayers
starting from 14-28 days of incubation. In contrast, proliferating chondro-
cytes, which maintain their morphology and phenotype for up to 28 days,
have been found inside the polymer matrices [48]. High amounts of gly-
cosaminoglycans and ECM (collagen) were produced in scaffolds made from
the polymer blends. The level of collagen II that is secreted by maturating
chondrocytes as cartilage-specific ECM protein was higher in P3HB-3HH or
P3HB/P3HB-3HH than in P3HB scaffolds [130, 131]. Analysis of the ECM
formed during cell culture with a scaffold containing 40%P3HBand60%
P3HB-3HH demonstrated high levels of calcium and phosphorus in a molar
ratio of Ca
/
P = 1.66, which is similar to that of natural HA (Ca
/
P = 1.67), the
major inorganic component of bone and cartilage [90].
5.3
Biodegradability
The (nonenzymatic) degradation of P3HB-3HH has not yet been tested sys-
tematically either in vitro or in vivo. Data has been reported from a short-
