In recent years, the demand for bone replacement materials used in the treatment of bone diseases has increased due to ongoing aging of the population. To date, β-tricalcium phosphate (β-Ca
3(PO
4)
2: β-TCP) has been employed clinically for this purpose because this material shows excellent biocompatibility along with a high degree of biosorption and can replace autologous bone when implanted in a bone defect [
1,
2,
3]. Even so, β-TCP has inferior osteogenic potential and lacks mechanical strength compared with autogenous bone. As an example, in the case that raw β-TCP powder is prepared via a solid phase reaction and subsequently sintered for 24 h at 1100 °C, which is below the alpha-beta transition temperature, grain growth can occur without an increase in density. The result is a body exhibiting approximately 80% sintering with a bending strength in the range of 40-60 MPa [
4]. It has been reported that sintered bodies having greater density and with bending strengths in the range of 150-200 MPa can be obtained by adding a trace oxide to prevent the crystal transition when sintering at high temperatures of 1150 to 1250 °C [
5]. However, the incorporation of these transition inhibitors may form a substitution-type solid solution with the oxide of β-TCP, thus suppressing the original solubility of β-TCP and resulting in reduced biosorption. It has also been demonstrated that densification can be promoted by hot pressing [
6,
7], hot isostatic pressing [
8,
9] and spark plasma sintering [
10], although the necessary equipment is expensive to purchase and to operate. The present work prepared composite sintered bodies in which nanoparticles were dispersed to generate a secondary phase [
11]. Specifically, colloidal silica (SiO
2) was added to β-TCP powder in the form of nanoparticles with the aim of improving the sintering characteristics and mechanical strength of the material.
Silicon is known to be essential for the growth and development of bone and cartilage [
12] and is found at concentrations on the order of 100 ppm in bone and ligaments and 200-600 ppm in cartilage and other connective tissues [
13]. The localized concentration of this element at active calcareous sites in the bones of young mice has also been noted, where it is involved in the early stages of biomineralization [
14].
Another approach to producing high-density, high-strength sintered bodies is to utilize very finely powdered raw materials. Therefore, the present study also assessed the use of the polymerized complex method. In this process, metal ions are complexed after which carboxyl and hydroxyl groups present in the complex are dehydrated and condensed by heating to prepare a polymeric gel in which metal ions are coordinated [
15]. This technique allows metal ions to be incorporated at an atomic level of dispersion and also permits the homogeneous dispersion of trace amounts of various additives. In addition, powders can be prepared rapidly and at low temperatures by sintering these gel precursors and hence the synthesis of raw material particles is facile [
16,
17].