Biomedical Engineering Reference
In-Depth Information
In order to improve the mechanical properties of calcium
orthophosphate cements, numerous researchers blended various
polymers with the cements. For example, gelatin might be added to
calcium orthophosphate cement formulations, primarily to stabilize
the paste in aqueous solution before it develops adequate rigidity
and, secondly, to improve the compressive strength [473, 521, 554].
Adding rod-like fillers to the cement formulations also caused an
improvement in the mechanical properties [554]. For example, PAA
and PVA were successfully used to improve the mechanical properties
of a TTCP + DCPD cement but, unfortunately, with an inevitable and
unacceptable reduction of both workability and setting time [555,
556]. Similar findings were reported in the presence of sodium
alginate and sodium polyacrylate [557]. Other polymers, such as
polyphosphazene, might be used as well [558-560]. Other examples
of polymer/calcium orthophosphate cement formulations might be
found elsewhere [561, 562].
Porous calcium orthophosphate scaffolds with interconnected
macropores (~1 mm), micropores (~5 μm), and of high porosity
(~80%) were prepared by coating polyurethane foams with a TTCP
+ DCPA cement, followed by firing at 1200 °C. In order to improve
the mechanical properties of the scaffolds, the open micropores
of the struts were then infiltrated by a PLGA solution to achieve
an interpenetrating bioactive ceramic/biodegradable polymer
composite structure. The PLGA filled struts were further coated
with a 58S bioactive glass/PLGA composite coating. The obtained
complex porous biocomposites could be used as tissue engineering
scaffolds for low-load bearing applications [563]. A more complicated
construction, in which the PLGA macroporous phase has been
reinforced with a bioresorbable TTCP + DCPA cement, followed
by surface coating of the entire construct by a non-stoichiomentic
CDHA layer, has been designed as well [564]. The latter approach
has culminated in a unique, three-phase biocomposite that is simple
to fabricate, osteoconductive and completely biodegradable.
A porosity level of 42-80% was introduced into calcium
orthophosphate cement/chitosan biocomposites by addition of
the water-soluble mannitol [565]. Chitosan significantly improved
the mechanical strength of the entire biocomposite [566]. A similar
approach was used by other researchers who studied the effect of the
addition of PLGA microparticles [567-570] (which can also be loaded
with drugs or growth factors [571-573]) to calcium orthophosphate
Search WWH ::
Custom Search