Biomedical Engineering Reference
In-Depth Information
main component of the mollusc shell) and alginate emerges, among others.
Chitosan seems to have a poor biomineralisation potential. A significant HA
formation could be observed
in vitro
only when chitosan films were immersed
in pseudo-SBFs, the ion concentrations of which are doubled in respect to
other SBFs (Beppu
et al
., 2005). therefore, pseudo-SBFs do not genuinely
simulate the ion composition of the
in vivo
bone repair environment. X-ray
diffractograms showed that deposits are poorly crystalline (like biological
apatites) and a higher crystallinity was shown in those pseudo-SBFs where
the phosphorous concentration was higher.
therefore, chitosan biomineralisation
in vitro
has been pursued through
modifications of this polysaccharide. For example, electrospun nanofibrous
scaffolds which were prepared by using chitosan/polyvinyl alcohol (CS/PVa)
and n-carboxyethyl chitosan/PVa (CECS/PVa) supported the deposition of
Ha when immersed in a supersaturated CaCl
2
and KH
2
PO
4
solution (Yang
et al
., 2008). the presence of poly(acrylic acid) in the ionic solution and
the use of matrix with carboxylic acid groups promoted crystal deposition
and growth.
Similar substrate potentials for cell adhesion and Ha formation were
observed in the case of alginate. Satisfactory adhesion, proliferation and
differentiation of osteoblasts was found only when gels of this polysaccharide
were functionalised with specific bioligands (for more details see Section
14.2.3) (Evangelista
et al
., 2007).
the effect of soluble sodium alginate on Ha crystal growth has been
investigated in supersaturated ion solutions (Malkaj
et al
., 2005). Sodium
alginate was found to inhibit Ha crystal growth and kinetic studies seem
to show that this inhibition is caused by a Langmuir-type adsorption of
the alginate on the forming Ha surface which may impede Ha crystal
growth.
Synthetic polymers
as biopolymer physicochemical properties and batch-to-batch variability
are difficult to control, biomaterial scientists have tried to develop synthetic
polymers able to support tissue repair. as a result, a large number of
degradable synthetic polymers has been developed which have been later
tested for their potential in tissue engineering and, among the various
clinical applications, for bone tissue engineering. the currently available
biodegradable synthetic polymers have been optimised for tuneable and safe
degradation processes. Conversely, their potential for supporting cell adhesion
and biomineralisation relies on the presence of suitable functional groups
in their structure rather than in attempting to mimic accurately the features
of the extracellular matrix. Only in the last decade, has the importance of
their specific functionalisation with biomimetic molecules been considered.
