Biomedical Engineering Reference
In-Depth Information
term in vitro study of P3HB-12%3HV porous scaffolds showing 7%mass
loss after 50 days of incubation in simulated body fluid (pH 7.4, 37 C), in
comparison to 3% for P3HB [124]. Two opposite effects on the hydrolysis
process have to be considered when comparing the degradability of P3HB-
3HH with that of the P3HB homopolymer. Firstly, the introduction of 3HH
side-chains into P3HB increases the hydrophobicity of the polymer, thus hin-
dering the penetration of water into the polymer bulk and slowing down
the hydrolysis. Secondly, 3HH groups decrease the polymer crystallinity [63],
which would result in an accelerated hydrolysis compensating the effect of the
more hydrophobic side-chains. Overall, it can be assumed that the degrada-
tion rate of P3HB-3HH is comparable or slightly faster than that of P3HB or
Applications in Tissue Engineering
Bone and Cartilage Repair
Based on the results of the in vitro cell compatibility testing (see Sect. 5.2),
bit bone marrow cells on P3HB-3HH films [94, 279] and porous matrices [49,
124] in comparison to P3HB or PLLA, it was concluded that P3HB-3HH has
potential as scaffold material in bone tissue engineering. However, there is
still a lack of in vivo data. In vitro, a strong alkaline phosphatase activity as an
early marker of osteoblast differentiation has been reported; however, phos-
phate deposits as a late marker of osteoblast differentiation could be detected
only on porous materials but not on dense polymer films after 28 days of
cell culture [49, 279]. Composite scaffolds made from P3HB-3HH and HA as
a bioactive and osteoconductive additive did not enhance osteoblast growth
in vitro [124]. Ultimately, P3HB-3HH matrices have to be tested in vivo to
confirm their potential for bone repair.
Similarly, despite a number of in vitro studies demonstrating the po-
tential of P3HB-3HH films [129] and porous matrices [48, 89, 90, 130, 131]
for engineering of cartilage (see Sect. 5.2) no in vivo results have been re-
ported so far. In vitro, blends made from P3HB and P3HB-3HH showed most
promise, in comparison to P3HB and P3HB-3HH alone, as they enhanced not
only adhesion and proliferation of rabbit chondrocytes but also allowed for
preservation of the cell phenotype, which is required for chondrogenesis [48].
Additionally, these materials allow for synthesis of hyaline cartilage-specific
collagen II, which is the major component of the solid matrix of human
articular cartilage [130, 131]. Another major ECM protein secreted by chon-
drocytes at the late stage of cartilage development, collagen X, could also be
detected [129]. These important indicators of functional tissue development
observed in vitro have to be confirmed in vivo to assess the potential of P3HB-
3HH in cartilage engineering.
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