Effect of thermal treatment on bioactive glass microstructure, corrosion behavior, ? potential, and protein adsorption

Abstract

Bioactive glass ceramic is characterized by high mechanical strength and a slow rate of bone bonding. To understand the factors contributing to a decrease in the rate of bone bonding to bioactive glass ceramic, we evaluated the effect of different percentages of bioactive glass crystallization on corrosion behavior, zeta potential, and serum protein adsorption. X-ray diffraction analysis showed that heat treatment of bioactive glass in the temperature range 550 degrees -700 degrees C resulted in the precipitation of Na(2)Ca(2)Si(3)O(9) crystals in the glass matrix. The percentage of crystallization increased in the order: 5%, 8%, 45%, and 83% after thermal treatment at 550 degrees, 600 degrees, 650 degrees, and 700 degrees C/1 h, respectively. Scanning electron microscopic analyses of bioactive glass treated at 550 degrees C showed major glass in glass-phase separation. Moreover, energy-dispersive X-ray analyses indicated that during crystallization P is concentrated in the glassy phase. Induced-coupled plasma analyses showed that after 24 h immersion in simulated body fluid, the concentration of the released P ion increased as the crystallization percentage of bioactive glass increased. zeta potential of bioactive glass samples containing 5% crystallization had a statistically significant higher negative value than control untreated bioactive glass (p <.02). Control untreated bioactive glass adsorbed a statistically significant higher amount of serum protein than bioactive glass samples containing 5% crystallization (p <.02). Results of our study suggest that inhibition of protein adsorption might be responsible for the slow rate of bone bonding to bioactive glass ceramic. It is also possible that conformation changes inhibit the activity of the protein adsorbed onto thermally treated bioactive glass.

Structural variations of bioactive glasses obtained by different synthesis routes

“…An earlier study indicated that the apatite-forming ability of glasses is higher than glass-ceramics with the same chemical composition, due to lower solubility of crystalline phase. This could be attributed to the strong bond between atoms in the crystal lattice [2,70].…”

“…dissolution of silica phase and phosphate phase, affecting the glass bioactivity. It was shown that phase separation reduced the solubility of Si and Ca ions from the bioactive glass, which can be attributed to the increase in viscosity of the phase-separated glass compared to the homogeneous one [70].…”

Factors affecting crystallization of bioactive glasses

“…1 The first bioactive glasses made of sodium oxide, calcium oxide, phosphorous pentoxide and silicon dioxide were found to phase separate and crystallize easily during working processes in the temperature range between glass transformation and liquidus. 2 The energy provided from heating during working processes assists in breaking bondings in the glass network structure and thus facilitates arranging the melt into crystal structures in this instable region. Compared to traditional glasses bioactive glasses have a high amount of network modifiers and a low amount of silica network formers, thus giving smaller structural units.…”

Crystallization Behavior and Microstructure of Bio Glass-Ceramic System

“…They are excellent biomaterials because they are nontoxic, they match the composition of natural bone, and show excellent integration with bone in the framework of in vitro and in vivo studies.1 Unfortunately, the low toughness of bioactive glass has limited its use to non-load-bearing applications [8,9]. Crystallization of bioactive glasses may be the best way to improve their mechanical properties [8,10,11]. It has been reported [12] that some glass-ceramics in the CaO-SiO 2 -P 2 O 5 -Na 2 O system, containing apatite and wollastonite phases, with good mechanical properties and the ability of forming tight chemical bonds with living bone can be produced through sintering and subsequent crystallization of glass powders.…”