The focus of this dissertation is synthesis and applications of amorphous alkaline earth
phosphate such as magnesium-calcium phosphate and magnesium phosphate.
Phosphates of alkaline earths such as calcium phosphates, are of great interest as bone
replacement materials because they are biocompatible and resorbable in physiological
conditions. As such, they have been studied for a long time. With growing research
interest in magnesium alloys, magnesium phosphates have been gaining attention as a
bone substitute material with comparable or in some cases, better properties than
calcium phosphates. The compositional similarities between calcium phosphates (Ca
Ps) and natural bone matrix prompted vigorous research activities in calcium
phosphates. By comparison, research on magnesium-calcium phosphates are rare.
Among the Ca P, amorphous calcium phosphates (ACP), have found applications as
an important class of materials since their presence is important in commercial
products such as plasma sprayed coatings on implants to self-setting CaP cements, or
the fact that amorphous phase is as an intermediate phase in the synthesis of various crystalline phases of CaP. On the other hand, an understanding of the amorphous
phases of magnesium phosphate or magnesium-calcium phosphate, or their
transformation into their relevant crystalline phases is rare. For instance, it is shown
that doping magnesium (small amount) in calcium phosphate can stabilize amorphous
calcium phosphate prior to conversion to hydroxyapatite, However, not much
information is available on amorphous magnesium phosphate as reports of synthesis
of amorphous magnesium phosphate is scarce in the literature.
Accordingly, this dissertation is broadly divided into five sub-sections. The first
section reviews the state-of-the-art on processing of porous biomaterials. Porous
biomaterials are an important class of materials and important goal of this research is
to be able fabricate them in a cost-effective way. The second section discusses the
synthesis and applications of amorphous magnesium-calcium phosphate, and
amorphous magnesium phosphate as promising biomaterials in comparison to
amorphous calcium phosphates or other relevant crystalline phases of calcium
phosphates. The focus is on the mechanisms of formation and functional properties
such as biocompatibility. In general, several methods have been proposed on the
synthesis of amorphous phase, including synthesis from aqueous medium (wet route),
using high energy processing or high temperatures (dry route) etc. Among them
precipitation (wet route) was chosen in this study, because it is relatively simple and
reproducible. Additionally, based on the method of the formation and experimental
conditions (solution supersaturation, pH, etc.) different ratios of Ca/P, Mg/P,
(Ca+Mg)/P ranging from 1 to 2 or even higher can be produced.The as-synthesized materials were characterized using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). In vitro studies were conducted on mouse osteoblasts, and SEM was used as the imaging methods.
In the next of the work, the theme is to investigate the applications of amorphous magnesium-calcium phosphate, and amorphous magnesium phosphate as dense bodies (sintered bioceramic), as cement and also as porous cement scaffold in orthopedic applications. We show that amorphous magnesium phosphate, and amorphous magnesium-calcium phosphate can be produced through ethanol-assisted precipitation method. They are also shown to be biocompatible for relevant applications. The sinterability of amorphous magnesium-calcium phosphate and magnesium phosphate was studied. The results indicate that the amorphous phase of magnesium magnesium-calcium phosphates was able to transform into relevant crystalline phases upon sintering using microwave sintering technique. Next, the development of cement composite consisting of amorphous magnesium phosphate and hydrophilic poly vinyl alcohol (PVA) biopolymer, was carried. Finally, the ability of amorphous magnesium phosphate in fabrication of macroporous composite scaffold through gas-foaming technique was studied. Biodegradable Mg-particles were used as the porogen to produce macroporous structure. This method uses the fast corrosion kinetics of Mg to create macro pores in real time during the setting of the cement.