bioavailability of silicon markedly depends on the chemical form of the silicon
compound. Therefore, various formulations have been applied to increase the bioavailability of silicic acid. These formulations include choline-stabilized orthosilicic
acid (a mixture of orthosilicic acid and choline chloride) (Calomme and Van den
Berghe 1997; Spector et al. 2008) and arginine silicate inositol complex (Nielsen
2008). Supplementation of ovariectomized rats with choline-stabilized orthosilicic
acid partially prevented femoral bone loss in aged animals (Calomme et al. 2006).
Administration of arginine silicate inositol complex has been shown to improve
mineralization of bone tissue in quail (Sahin et al. 2006). Choline-stabilized
orthosilicic acid has also been added to food supplements as source of silicon in
human diet (EFSA 2009). Studies on dietary intake of silicon in postmenopausal
women aged over 60 years did not reveal major variations by age (McNaughton et al.
2005), which could affect the usefulness of silicon supplements.
Silicon-containing implant materials such as silicon-substituted HA and bioglass
have attracted great attention as bone substitutes (Hench and Paschall 1973; Hench
and Wilson 1984; Hench 1998; Hench and Polak 2002; Lo ´pez-Alvarez et al. 2009;
Zou et al. 2009). Bioglass has been considered as “bioactive” because it becomes
intimately bound to bone tissue (Chen et al. 2006; Bretcanu et al. 2009). This implant
material has been reported to show osteoinductive and osteoconductive properties
(Hench 2006).
First prototypic bioactive implant materials comprising silicatein and a silica
precursor have bee prepared. The results of first preclinical tests are promising
(Wiens et al. 2010a). To facilitate the application of silicatein in bone (and dental)
replacement materials, a bioengineered recombinant silicatein has been developed,
which contains an oligo-glutamate sequence (Glu-tagged silicatein) that allows
immobilization of the enzyme onto HA surfaces and the formation of biosilica
coatings after addition of substrate (Natalio et al. 2010; Wiens et al. 2010b);
Fig. 10.10c.
A schematic presentation of the proposed application of the materials for
treatment of vertebral fractures (compression fractures) of osteoporotic patients is
shown in Fig. 10.10. The material, comprising either biosilica-formed ex vivo or
tagged silicatein protein administered together with a suitable biosilica precursor,
is injected into the fractured vertebra either alone or together with some other
material used in vertebroplasty (Fig. 10.10a). Fig. 10.10b shows the application in
kyphoplasty. A balloon (bone tamp) is inserted into the vertebral body by means of
two bone biopsy needles. When inflated, the bone tamp re-expands the vertebral
body. The restructured vertebral body is then stabilized by the injected polymeric
material after hardening. Recruitment of osteoblasts and restoration of the balance
between bone formation (osteoblasts) and bone resorption (osteoclasts) by the
modulatory effect of the biosilica material on the RANK/RANKL/OPG system
and its osteoinductive activity finally result in replacement of the injected material
by autologous bone. Figure 10.10c shows a schematic presentation of biosilica
formation by the injected Glu-tagged silicatein in the presence of substrate.
Silicatein binds via its Glu-tag to the trabeculae. Following its immobilization on
the Ca-P substrate (trabecular HA), silicatein facilitates biosilica formation in the
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H.C. Schr€ oder et al.
compound. Therefore, various formulations have been applied to increase the bioavailability of silicic acid. These formulations include choline-stabilized orthosilicic
acid (a mixture of orthosilicic acid and choline chloride) (Calomme and Van den
Berghe 1997; Spector et al. 2008) and arginine silicate inositol complex (Nielsen
2008). Supplementation of ovariectomized rats with choline-stabilized orthosilicic
acid partially prevented femoral bone loss in aged animals (Calomme et al. 2006).
Administration of arginine silicate inositol complex has been shown to improve
mineralization of bone tissue in quail (Sahin et al. 2006). Choline-stabilized
orthosilicic acid has also been added to food supplements as source of silicon in
human diet (EFSA 2009). Studies on dietary intake of silicon in postmenopausal
women aged over 60 years did not reveal major variations by age (McNaughton et al.
2005), which could affect the usefulness of silicon supplements.
Silicon-containing implant materials such as silicon-substituted HA and bioglass
have attracted great attention as bone substitutes (Hench and Paschall 1973; Hench
and Wilson 1984; Hench 1998; Hench and Polak 2002; Lo ´pez-Alvarez et al. 2009;
Zou et al. 2009). Bioglass has been considered as “bioactive” because it becomes
intimately bound to bone tissue (Chen et al. 2006; Bretcanu et al. 2009). This implant
material has been reported to show osteoinductive and osteoconductive properties
(Hench 2006).
First prototypic bioactive implant materials comprising silicatein and a silica
precursor have bee prepared. The results of first preclinical tests are promising
(Wiens et al. 2010a). To facilitate the application of silicatein in bone (and dental)
replacement materials, a bioengineered recombinant silicatein has been developed,
which contains an oligo-glutamate sequence (Glu-tagged silicatein) that allows
immobilization of the enzyme onto HA surfaces and the formation of biosilica
coatings after addition of substrate (Natalio et al. 2010; Wiens et al. 2010b);
Fig. 10.10c.
A schematic presentation of the proposed application of the materials for
treatment of vertebral fractures (compression fractures) of osteoporotic patients is
shown in Fig. 10.10. The material, comprising either biosilica-formed ex vivo or
tagged silicatein protein administered together with a suitable biosilica precursor,
is injected into the fractured vertebra either alone or together with some other
material used in vertebroplasty (Fig. 10.10a). Fig. 10.10b shows the application in
kyphoplasty. A balloon (bone tamp) is inserted into the vertebral body by means of
two bone biopsy needles. When inflated, the bone tamp re-expands the vertebral
body. The restructured vertebral body is then stabilized by the injected polymeric
material after hardening. Recruitment of osteoblasts and restoration of the balance
between bone formation (osteoblasts) and bone resorption (osteoclasts) by the
modulatory effect of the biosilica material on the RANK/RANKL/OPG system
and its osteoinductive activity finally result in replacement of the injected material
by autologous bone. Figure 10.10c shows a schematic presentation of biosilica
formation by the injected Glu-tagged silicatein in the presence of substrate.
Silicatein binds via its Glu-tag to the trabeculae. Following its immobilization on
the Ca-P substrate (trabecular HA), silicatein facilitates biosilica formation in the
302
H.C. Schr€ oder et al.