Biomedical Engineering Reference
In-Depth Information
In general, both bioactivity and biodegradability of any
biocomposite and/or hybrid biomaterial are determined by the same
properties of the constituents. Both processes are very multi-factorial
because, during implantation, the surface of any graft contacts with
biological fluids and, shortly afterwards, is colonized by cells. Much
more biology, than chemistry and material science altogether, is
involved into these very complex processes and many specific details
still remain unknown. To simplify the task, the biodegradability
of the biologically relevant calcium orthophosphates might be
described by a chemical dissolution in slightly acidic media (calcium
orthophosphates are almost insoluble in alkaline solutions [111-
117]), which, in the case of CDHA, might be described as a sequence
of four successive chemical Eqs. (5.15-5.18) [519, 1161, 1162] (see
sections
, as well as Chapter 7 for details). Further details
on bioactivity and biodegradability of calcium orthophosphates are
available in section
5.5
and
4.6.3
.
Biodegradability of polymers generally depends on the following
factors: (1) chemical stability of the polymer backbone, (2)
hydrophobicity of the monomer, (3) morphology of the polymer,
(4) initial molecular weight, (5) fabrication processes, (6) geometry
of the implant, (7) properties of the scaffold such as porosity and
pore diameter [328]. A summary on degradation of PLA and PGA,
as well as that of SEVA-C is available in literature [Ref. 178, p. 798
and p. 803, respectively], where the interested readers are referred
to. Biodegradation of HA/PLLA and CDHA/PLLA biocomposite rods
in subcutis and medullary cavities of rabbits were investigated
mechanically and histologically; the degradation was found to be
faster for the case of using uncalcinated CDHA instead of calcinated
HA [1163]. In a more detailed study, new bone formation was
detected at 2 weeks after implantation, especially for formulations
with a high HA content [1164]. More to the point, a direct contact
between bones and these composites without intervening fibrous
tissue was detected in this case [1164, 1165]. Both SEVA-C and
SEVA-C/HA biocomposite were found to exhibit a non-cytotoxic
behavior [1166, 1167] inducing a satisfactory tissue response when
implanted as shown by
4.6.4
studies [1167]. Furthermore, SEVA-C/
HA biocomposites induce a positive response on osteoblast-like
cells to what concerns cell adhesion and proliferation [1166]. An
in vivo
in
vivo
study on biodegradation of microspheres (PLGA, gelatin, and
poly(trimethylene carbonate) were used)/calcium orthophosphate
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