Crystallization and sintering of borosilicate bioactive glasses for application in tissue engineering
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 decrease in the rate of reaction of the material and 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 post-operation. Therefore, a need for bioactive materials that could convert more efficiently and fully to hydroxyapatite are needed. In this paper, 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 found to depend on the B2O3 content. 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 60 to 10 % and compressive strength ranging from 35 to 1 MPa, were processed. 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 is generally faster and can be better controlled as opposed to partially/fully crystallized scaffolds obtained from the FDA approved bioactive glasses.