The crystallization behavior of phosphate glasses of the composition 50P 2 O 5 -(40-x)CaO-xSrO10Na 2 O with x = 0, 20, and 40 was investigated using non-isothermal differential thermal analysis. The study was performed on three different size fractions (fine powder (\45 lm), intermediate (300-500 lm), and coarse particles ([500 lm)). The DTA thermograms recorded for all glasses exhibited a single and symmetrical crystallization peak. The position and shape of the crystallization varies with the particles size. The activation energy for crystallization, E c , was calculated using equations proposed by Kissinger and Friedman. The calculated E c values were similar for both techniques. E c decreased with increasing the particle size for all glass compositions. The JohnsonMehl-Avrami exponent n expressing the crystal growth dimensionality was quantified using the methods proposed by Augis-Bennett (AB) and Ozawa. In general, the AB method gave higher value than the Ozawa technique. For all glass composition the n value for the coarse powder suggested bulk crystallization whereas with decreasing particle size, the value of n indicated a complex surface crystallization. Glass monoliths were heat treated in electric oven at several temperatures for various times. XRD suggested crystallization of two phases: Ca(PO 3 ) 2 and NaCa(PO 3 ) 3 for the glass with x = 0, Sr(PO 3 ) 2 and NaSr(PO 3 ) 3 for the glass with x = 40, and a solid solution of (Ca,Sr)(PO 3 ) 2 and Na(Ca,Sr)(PO 3 ) 3 for the glass with x = 20. All crystals were found to preferentially nucleate and grow from the surface. Partially to fully crystallized glass particles were immersed in simulated body fluid for 24, 48, and 72 h. SEM/EDS of the particles and changes in the pH and ion concentrations of the solution (ICP-OES) suggested that crystallization prevents the CaP layer formation for all partially crystallized glasses.

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Typical silicate bioactive glasses are known to crystallize readily during the processing of porous scaffolds. While such crystallization does not fully suppress the bioactivity, the presence of significantly large amounts of crystals leads to a decrease in the rate of reaction of the glass and an uncontrolled release of ions. Furthermore, due to the non-congruent dissolution of silicate glasses, these materials have been shown to remain within the surgical site even 14 years postoperation. Therefore, a need for bioactive materials that can dissolve with higher conversion rates and more effectively are required. Within this work, boron was introduced, in the FDA approved S53P4 glass, at the expense of SiO2. The crystallization and sintering-ability of the newly developed glasses were investigated by differential thermal analysis. All the glasses were found to crystallize primarily from the surface, and the crystal phase precipitating was dependent upon the quantity of B2O3 incorporated. The rate of crystallization was found to be lower for the glasses were 25, 50 and 75 % of the SiO2 was replaced with B2O3. These glasses were further sintered into porous scaffolds using simple heat sintering. The impact of glass particles size and heat treatment temperature on the scaffolds porosity and average pore size was investigated. Scaffolds with porosity ranging from 10 to 60 % with compressive strength ranging from 1 to 35 MPa, were produced. The scaffolds remained amorphous during processing and their ability to rapidly precipitate hydroxycarbonated apatite was maintained. This is of particular interest in the field of tissue engineering as the scaffolds degradation and reaction was generally faster and offers higher controllability as opposed to current partially/fully crystallized scaffolds obtained from the FDA approved bioactive glasses. IntroductionAs of today, autografts are still the gold standard for the repair of large bone defects. However, with the aging and growing population, the number of surgical intervention to regenerate bone defects are increasing. The limited supply and patient site morbidity is a well-known disadvantage and problem [1][2]. Allografts are an option. However, the limited tissue bank as well as the higher risk for infection and cellular and humoral immune reactions limits their usage [3]. The quest for synthetic biomaterials to replace the autografts is more than two decades old. However, as of today no materials have shown as promising a result as autografts. Q. Chen et al. have reported the optimum characteristic that the synthetic materials should have to find great potential as bone grafts [4]. The bone graft should be a 3D construct (3D scaffold) not only biocompatible, but ultimately biodegradable and osteoconductive with highly interconnected porosity. Pore size should be no less than 100 µm to allow cell and fluid penetration as well as angiogenesis. In general, interconnected pores of at least 100 µm and an open porosity of over 50% is considered the minimum requirement for ti...