Biomineralization of electrospun poly(l-lactic acid)/gelatin composite fibrous scaffold by using a supersaturated simulated body fluid with continuous CO2 bubbling

To promote the biomineralization, supersaturated simulated body fluids (SBFs), e.g. five times SBF (5 × SBF), were usually applied. In these SBFs, however, homogeneous nucleation of Ca-P mineralites and deposition unavoidably took place owing to the HCO3− decomposition and the pH value increment, which made the prediction of bone bioactivity of substrates controversial. In this study, the classically prepared 5 × SBF was continuously bubbled with CO2 to keep the pH value stable at 6.4 and the solution transparent, and a kind of electrospun poly(l-lactic acid)/gelatin composite fibers was used for the biomineralization study. In such a modified 5 × SBF, heterogenenous nucleation occurred dominantly and thermodynamical unstable brushites (dicalcium phosphate dihydrate, DCPD) were detected shortly on both electrospun PLLA fibers and PLLA/gelatin (1:1 in weight) composite fibers. In comparison with electrospun PLLA fibers, the sheet-like DCPD mineralites transformed into flaky carbonated calcium-deficient hydroxyapatite (CDHA) within 24 h on the PLLA/gelatin composite fibers due to the accelerating effect of gelatin component. The formed apatite coating contained much less Mg2+ ions than that deposited in the classical 5 × SBF. The results of this study showed that supersaturated SBFs buffered with gassy CO2 were expected good choices for the accelerated biomineralization, and for the prediction of the bone bonding bioactivity of substrates.

In classical five times simulated body fluid (5 × SBF), homogeneous nucleation of Ca-P mineralites and deposition unavoidably took place owing to the HCO3− decomposition and the pH value increment, which made the prediction of bone bioactivity of substrates controversial. In this study, the classically prepared 5 × SBF was continuously bubbled with CO2 to keep the pH value stable at 6.4. The biomineralization results of a kind of coelectrospun poly(l-lactic acid)/gelatin composite fibers in the modified 5 × SBF demonstrated that heterogenenous nucleation occurred dominantly. Thermodynamical unstable brushites (dicalcium phosphate dihydrate, DCPD) were detected shortly on the composite fibers. The sheet-like DCPD mineralites transformed into flaky carbonated calcium-deficient hydroxyapatite (CDHA) within 24 h on the PLLA/gelatin composite fibers due to the accelerating effect of gelatin component. And the formed apatite coating contained much less Mg2+ ions than that deposited in the classical 5 × SBF. These findings suggested that supersaturated SBFs buffered with CO2 could be expected as a good choice for the prediction of the bone bonding bioactivity of substrates.Highlights► Electrospun poly(l-lactide)/gelatin composite fibers as substrates for biomineralization. ► Five times simulated body fluid bubbled with gassy CO2 is used for biomineralization. ► Gelatin component in composite fibers enhances apatite formation and transformation.