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
P3HB-3HV.
5.4
Applications in Tissue Engineering
Bone and Cartilage Repair
Based on the results of the in vitro cell compatibility testing (see Sect. 5.2),
whichshowedimprovedattachment,proliferationanddifferentiationofrab-
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.
