Biomedical Engineering Reference
In-Depth Information
When typical formulations of these copolymers (75:25 and 50:50 PLA-PGA)
were evaluated as substrates for primary human osteoblasts in direct contact
tests for 14 days, it was found that there was neither detectable cytotoxicity
nor inhibition of cell adhesion and proliferation. the degree of differentiation
measured as aLP activity and osteocalcin synthesis was also not affected.
indeed, osteoblast adhesion on these copolymers was found to be mainly b
(1)/a(v)/b(1) integrin complex-dependent and only partially dependent on
a(v) integrin.
in a similar study, three injectable and biodegradable PLa/PGa 50150
copolymers dispersed in different matrices were tested (tschon
et al
., 2007).
The PLA/PGA-based bone filler Fisograft-gel (GEL) was dispersed in an
aqueous matrix of polyethylglycole (PEG), Slurry2 (SL2) was dispersed in an
aqueous matrix of PEG and dextran and Slurry6 (SL6) was dispersed in a 3%
agarose matrix. GEL and SL2 induced similar effects on MG-63 osteoblast-
like human osteosarcoma cells in terms of viability and differentiation after 7
days in culture, while SL6 caused a higher production of both interleukin-6
and type i collagen. none of these biomaterials showed cytotoxicity. these
data were corroborated by
in vivo
studies showing that SL6 was supporting
bone repair with more physiological histological features.
Biomineralisation strategies should reproduce the dimension and structural
hierarchy of apatite deposits within a demineralised collagen matrix. However,
none of the biodegradable synthetic polymers is able to mimic this process.
As a consequence, polymers like PLA/PGA, PCL and others have been
surface-modified by physical and chemical methods to improve their ability
to catalyse the formation of hydroxyapatite crystals.
For example, PLA/PGA (70/30) films and scaffolds have been treated
with oxygen plasma to enhance their biomineralisation potential tested in
SBF (Qu
et al
., 2007). It has been hypothesised that the acquired ability of
this modified polymer in inducing hydroxyapatite formation was due to the
combined effect of the changed surface chemistry and surface topography.
it was also observed that the presence of newly formed hydroxyapatite layer
enhanced the adhesion and proliferation of OCt-1 osteoblast-like cells, but
had no significant effect on their ALP activity after 7 days in culture.
PCL has also been modified to improve its biomineralisation potential.
For instance, the polymer surface has been modified by phosphate salts (i.e.
naH
2
PO
4
, na
2
HPO
4
KH
2
PO
4
or K
2
HPO
4
) (Puska
et al
., 2008). the results
showed that the addition of phosphate salts led to an improvement in the
compression strength of PCL as a result of their mineralisation process with
a new apatite-like phase.
More information can be found in Chapter 8 of this topic and in a
comprehensive review paper published by Sokolsky-Papkov
et al
. (2007).
