Crystallization and sintering of borosilicate bioactive glasses for application in tissue engineering

Abstract

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...

In Vitro Degradation of Borosilicate Bioactive Glass and Poly(l-lactide-co-ε-caprolactone) Composite Scaffolds

“…It is generally accepted that the presence of the vibration bands at ~1020 cm −1 along with a vibration band at 875 cm −1 can be attributed to Ca deficient HA [ 37 ]. This was further confirmed in [ 38 ] where it was demonstrated that scaffolds from the bioactive glass used in this study precipitated an HA layer with a Ca/P ratio close to 1.67. The Figure 6 c presents the spectra of all scaffolds and of the corresponding bioactive glass particles immersed for 336 h. With an increase in the the bioactive glass content within the scaffolds, the signal of the HA layer at the surface of the scaffold was enhanced.…”

Bioactive Glasses: Where Are We and Where Are We Going?

“…It has also been found that most of silicate-based BGs readily undergo devitrification during the processing of porous scaffolds as a result of sintering temperature. This crystallization at large amounts can result in reduced bioactivity of the glasses, as well as an uncontrolled release of ions [ 115 ]. For instance, Jones and colleagues have shown that an increase in the final sintering temperature from 600 to 800 °C leads to a decrease in dissolution rate of scaffolds and, thereby, reduced ions release [ 76 ].…”

Glass and Glass-Ceramic Scaffolds: Manufacturing Methods and the Impact of Crystallization on In-Vitro Dissolution

“…Nevertheless, the in-vivo outcome of these materials was positive [52]. Other researcher are attempting to develop borosilicate glass based on the fast dissolving bioactive 45S5 and S53P4 [53].…”