Biomedical Engineering Reference
In-Depth Information
polyamide biocomposites [310, 311]. In certain cases, a mechano-
chemical route [312], emulsions [313-316], freeze-drying [317] and
freeze-thawing techniques [318], flame-sprayed technique [319],
or gel-templated mineralization [320] might be applied to produce
calcium othophosphates-based biocomposites. Various fabrication
procedures are well described elsewhere [36, 63, 297], where the
interested readers are referred.
The interfacial bonding between a calcium orthophosphate and
a polymer is an important issue of any biocomposite. Four types of
mutual arrangements of nanodimensional particles to polymer chains
have been classified by Kickelbick (Fig. 6.1): (1) inorganic particles
embedded in inorganic polymer, (2) incorporation of particles by
bonding to the polymer backbone, (3) an interpenetrating network
with chemical bonds, (4) an inorganic-organic hybrid polymer [321].
If adhesion among the phases is poor, the mechanical properties of
a biocomposite suffer. To solve the problem, various approaches
have been already introduced. For example, a diisocyanate coupling
agent was used to bind PEG/PBT (Polyactive
TM
) block copolymers
to HA filler particles. Using surface-modified HA particles as a filler
in a PEG/PBT matrix significantly improved the elastic modulus and
strength of the polymer as compared to the polymers filled with
ungrafted HA [293, 322]. Another group used processing conditions
to achieve a better adhesion of the filler to the matrix. Ignjatovic et al.
prepared PLLA/HA composites by pressing blends of varying PLLA
and HA content at different temperatures and pressures [158, 159,
323]. They found that maximum compressive strength was achieved
at ~15 wt.% of PLLA. By using blends with 20 wt.% of PLLA, the
authors also established that increasing the pressing temperature
and pressure improved the mechanical properties. The former was
explained by decrease in viscosity of the PLLA associated with a
temperature increase, hence leading to improved wettability of HA
particles. The latter was explained by increased compaction and
penetration of pores at higher pressure, in conjunction with a greater
fluidity of the polymer at higher temperatures. The combination of
high pressures and temperatures was found to decrease porosity and
guarantee a close apposition of a polymer to the particles, thereby
improving the compressive strength [286] and fracture energy [324]
of the biocomposites. The PLLA/HA biocomposites scaffolds were
found to improve cell survival over plain PLLA scaffolds [325].
Search WWH ::
Custom Search