Inorganic process for wet silica-doping of calcium phosphate.

Yuki Sugiura,Yasuko Saito,Masanori Horie,Kodai Niitsu,Takashi Endo

doi:10.1039/d1ra00288k

Abstract

Silica is not only a biocompatible trace element but also an essential element for bone formation and metabolism. Therefore, it is often doped into bioceramics such as calcium phosphate and calcium carbonate for enhancing biomaterial ability. Heretofore, organic silica materials are employed as silica sources, but the residual organic matter is a significant drawback in biomaterial applications. Therefore, in this study, we introduce a one-pot inorganic synthesis method for the formation of silica-doped octacalcium phosphate (OCP) using Na2SiO3 as the silica source. Silica was intercalated into the OCP unit lattice, replacing its hydrous layer structure, and then a layer-by-layer structure of apatite and silica was formed. Furthermore, by immersing the fabricated silica-doped OCP into suitable solutions, both silica-doped hydroxyapatite and carbonate apatite were fabricated through a one-step inorganic processes.

Highlights

Heretofore, organic silica materials are employed as silica sources, but the residual organic matter is a significant drawback in biomaterial applications
Organic silica materials such as tetraethyl orthosilicate (TEOS) and hexamethyldisilane have been employed as silica sources for doping via in situ hydrolysis, the residual organic matter from silica sources might exhibit toxicity.[7,8,11,12]
A technique for fabricating silica-doped octacalcium phosphate (OCP) in sodium silicate (Na2SiO3) solutions would be valuable for the silicadoping of calcium phosphate; in this study, we investigated silica-doped OCP formed through hydrolysis process in inorganic Na2SiO3 solutions

Summary

Introduction

Since the 1960s, silica (SiO44À) has been known to stimulate and enhance bone cell activities and upregulate the bone remodelling process.[1,2,3] Especially, silica enhances the activity and puri cation of osteoblasts as reinforcing alkali phosphatase and type-I collagen generation and inhibits the activity of osteoclasts.[4,5,6] silica-doped biomaterials, due to their excellent biocompatibility, are considered attractive for bone substitutes. Various works have investigated silica-doped biocompatible ceramics, such as calcium carbonate and calcium phosphate.[7,8,9,10] For example, silica-doped vaterite, a metastable phase of calcium carbonate, has been found to signi cantly upregulate osteoblast activities such as alkali phosphatase generation and viability.[7,11] silica-doping processes of calcium carbonate and calcium phosphates based on wet-chemical systems have signi cant drawbacks. Octacalcium phosphate [OCP: Ca8H2(PO4)6$5H2O] exhibits excellent biocompatibility and can function as a bone aHealth and Medical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Kagawa, 761-0395, Japan. A technique for fabricating silica-doped OCP in sodium silicate (Na2SiO3) solutions would be valuable for the silicadoping of calcium phosphate; in this study, we investigated silica-doped OCP formed through hydrolysis process in inorganic Na2SiO3 solutions

Material and methods

Results and discussions

Conclusion