Biomedical Engineering Reference
In-Depth Information
cement formulations up to ~ 30 MPa; however, the kinetics of CDHA
formation and, thus, the bioactivity of the material were decreased
[110, 422]. Xu et al
reported that incorporation of long carbon fibers
at a volume fraction of 5.7% increased the flexural strength about 4
times and work of fracture ~100 times, if compared to un-reinforced
formulations [423]. The reinforcement mechanisms were found to
be crack bridging and fiber pullout, while fiber length and volume
fraction were key microstructural parameters that determined the
concrete properties [426]. Although addition of polypropylene, nylon
and carbon fibers was found to reduce the compression strength of a
double-setting calcium orthophosphate cement because of increased
porosity, it strongly increased the cement's fracture toughness and
tensile strength, relative to the values for the un-reinforced variant
of this formulation [415]. A knitted two-dimensionally oriented
polyglactin fiber-mesh was found to be effective in improving load-
bearing behavior of a calcium orthophosphate cement for potential
structural repair of bone defects [199]. To make the material stronger,
fast setting and anti-washout, chitosan might be added [178, 344,
403, 424-434]. Furthermore, anti-washout properties might
appear by adding sodium alginate [435]. Calcium orthophosphate
concretes containing SiO
.
particles showed a significant
(~ 80-100 MPa) increase in the compressive strength, whilst no
change in the mechanical behavior of the formulations was observed
when ZrO
and TiO
2
2
particles were added [416]. Additional examples of the
properties improving comprise addition of calcium silicates [67],
polypeptide copolymers [436] and collagen [437-443]. A strength
improvement was found when DCPA and TiO
2
crystals were used
as fillers for mechanically activated α-TCP cements [444]. Calcium
orthophosphate concretes reinforced by whiskers of calcium
carbonate [55] have been also developed.
Yet another team examined the effects of varying fiber type,
fiber length and volume fraction of fiber-reinforced calcium
orthophosphate concretes [424, 445]. Four fiber types were studied:
aramid, carbon, E-glass and polyglactin. Fiber length ranged within
3-200 mm and fiber volume fraction ranged within 1.9-9.5%. The
results indicated that a self-setting calcium orthophosphate cement
was substantially strengthened via fiber reinforcement. Aramid
contributed to the largest increase in the concrete strength, followed
by carbon, E-glass and polyglactin. Fiber length, fiber volume
fraction and fiber strength were found to be key microstructural
2
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