Biomedical Engineering Reference
In-Depth Information
1983). Ca-P-based bioceramics, such as conventional hydroxyapatite (HAp)
(El-Ghannam et al. 1997), β-tricalcium phosphate (β-TCP), and HAp/β-TCP
composites, have been used as bone regeneration materials. However, a major
drawback of these materials is the lack of sufficient mechanical strength,
rendering them unsuitable as a load-bearing bone substitute (Hench 1998).
Previous studies have shown that the sintered Ca-P-based bioceramics,
especially HAp, lack full biodegradability after implantation (Ducheyne et
al. 1993; Lu et al. 2002). Although β-TCP ceramics have been regarded as bio-
degradable materials, their degradation kinetic tends to be slow
in vitro
and
in vivo
(Ni et al. 2008; Xu et al. 2008; Wang et al. 2012). In addition, it is gener-
ally accepted that conventional sintered Ca-P ceramics lack osteoinductivity.
In the early 1970s, Hench and his colleagues developed a new class of
biomaterials, SiO
2
-CaO-Na
2
O-P
2
O
5
glasses 45S5. One of the significant
characteristics of Ca-Si-based bioactive glasses is that they can induce the
formation of HAp layer or hydroxyl carbonated apatite (HCA) similar to the
mineral phase of bone on their surface in simulated body fluids (SBF) (Hench
1973; Hench and Paschall 1973). This class of Ca-Si-based glasses was able to
osseointegrate with host bone (Hench 1991). Further studies have also shown
that the Ca and Si containing ionic products released from the Bioglass 45S5
contribute to its bioactivity, as both Ca and Si are found to stimulate osteo-
blast proliferation and differentiation (Xynos et al. 2000; Gough, Jones, et al.
2004; Gough, Notingher, et al. 2004; Valerio et al. 2004; Hoppe et al. 2011).
Xynos et al. (2000) using cDNA microarray analysis showed that the expres-
sion of a potent osteoblast mitogenic growth factor, insulin-like growth fac-
tor II (IGF-II), was increased to 32% upon exposure of the osteoblasts to the
bioactive glass stimuli. Results indicated that Ca and Si ionic products from
bioglass might increase IGF-II in osteoblasts by inducing the transcription of
the growth factor and its carrier protein, and also by regulating the dissocia-
tion of this factor from the binding protein. The unbound IGF-II was likely
to be responsible for the increase in cell proliferation observed in cell culture
experiments. Similar bioactive induction of the transcription of extracellu-
lar matrix components and their secretion and self-organization into min-
eralized matrix might be responsible for the rapid formation and growth of
bone nodules and differentiation of the mature osteocyte phenotype in the
presence of bioglass (Hench et al. 2004). For this reason, Hench proposed
the new concept of “third generation biomaterials” in which bioactive mate-
rials should stimulate cell and tissue growth. Recently, Hench suggested
that bioactive glasses possess osteostimulation properties and they can be
one of typical third generation biomaterials (Hench and Thompson 2010).
However, the major disadvantages of bioglass are its high brittleness, low
bending strength, fracture toughness, and workability, which limits its clini-
cal application.
Silicon (Si) is one of the important trace elements in the human body. Si was
found at a level of 100 ppm in bone and 200-550 ppm bound to extracellular
matrix compounds (Schwarz 1973). It is reported that Si is located at active
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