Silicate-Based Bioactive Ceramics for Bone Regeneration Application - Advanced Bioactive Inorganic Materials for Bone Regeneration and Drug Delivery - page 35

amorphous CSH gel is deposited on the original silicate materials, while
Ca(OH) 2 crystals nucleate and grow in the available capillary pore space and
the previously deposited CSH gel is well accepted. As time proceeds, the
CSH gels polymerize and harden. The self-setting progress of silicate mate-
rials is mainly attributed to the formation of a solid network, which is also
associated with the densification and increase of the mechanical strength
(Gou, Chang, Zhai, et al. 2005; Zhao et al. 2005). Our group has developed
a series of composite bone cements based on silicate and phosphate/CaSO 4
materials, which exhibit improved mechanical strength and setting proper-
ties for potential bone regeneration application (Huan and Chang 2007a,b,
2008, 2009; Zhao et al. 2008; Wu and Chang, forthcoming).
2.4 Biological Response of Bone-Forming
Cells to Silicate Ceramics
2.4.1 Cell Attachments
The attachment, adhesion, and spreading belong to the first phase of cell-
materials interactions and influence the cell's capacity to proliferate and dif-
ferentiate on contact with the implant (Anselme 2000). In the past several
years, we have conducted a series of cell experiments to evaluate cell attach-
ment on more than 20 silicate bioceramics. It is found that most of silicate
bioceramics support the attachment of osteoblast, bone marrow stromal cells
(BMSCs) and periodontal ligament cells (PDLCs), such as akermanite (see
Figure 2.5) (Wu, Chang, Ni, et al. 2006; Wu and Chang 2007; Wu, Ramaswamy,
Chang, et al. 2008; Wu, Ramaswamy, Soeparto, et al. 2008). For bone tis-
sue engineering application, osteoblasts have been found well attached on
the pore walls of porous silicate bioceramic scaffolds (see Figure 2.6) (Wu,
Chang, Zhai, et al. 2006; Wu et al. 2010). Generally, it is found that silicate
bioceramics and scaffolds, such as akermanite, diopside, and hardystonite,
with moderate or slow degradation benefit cell attachments, compared to
those with quick degradation, such as wollastonite, bredigite, and tricalcium
silicate. Therefore, it is speculated that the chemical composition of silicate
bioceramics is the main reason to influence cell attachment. Their chemical
compositions directly decide their surface degradation and further influence
cell attachment (Wu and Chang, forthcoming).
2.4.2 In Vitro Osteostimulation of Silicate Bioceramics
There is a common characteristic for silicate bioceramics, which the
Si-containing ionic products from silicate bioceramics significantly stimulate
the proliferation and osteogenic differentiation of several kinds of stem cells,