Vibrational spectroscopy and thermal analysis for the characterization of poly(epsilon-caprolactone)-apatite scaffolds.

Poly(epsilon-caprolactone) (PCL) is used as long-term biodegradable scaffold for bone repair. Addition of apatite (Ap), the inorganic component of bone tissue, should improve the mechanical properties of the biomaterial and also its bone compatibility. Scaffolds with different PCL/Ap ratio, identified as PCL/Ap 75:25, PCL/Ap 60:40, PCL/Ap 50:50 and PCL/Ap 100:0 (pure PCL), synthesised at the Istituto per la Tecnologia dei Materiali Compositi-CNR, Università di Napoli, Italy, using phase-inversion and salt-leaching technique were analysed by IR and Raman spectroscopies, thermogravimetry (TG) and differential scanning calorimetry (DSC). The samples were investigated before and after in vitro degradation in different media: saline phosphate buffer at pH 7.4 (SPB), simulated body fluid (SBF) at pH 7.4, esterase in SPB and NaOH solution at pH 12. The results of the IR and Raman analysis showed that the crystallinity of PCL decreased along the series PCL/Ap 50:50>PCL/Ap 60:40>PCL/Ap 75:25>PCL/Ap 100:0. This fact was demonstrated by the decrease of the bandwidth of the C=O and the increase in intensity of the crystalline PCL Raman marker bands at 1419, 1285, 1110 and 912 cm-1. The results of thermal analysis confirmed this trend. As regards degradation, after 28 days only PCL/Ap 60:40 sample showed a slight increase in PCL crystallinity in all degradation media while the other samples did not show significant changes. The samples containing Ap, after 28 days of degradation in SBF solution, showed an increase in intensity of the bands attributable to Ap both in IR and Raman spectra and also a weight gain, suggesting a deposition of an apatitic phase on the surface of the scaffold. This deposition is more pronounced on the PCL/Ap 50:50 scaffold which contain the highest amount of Ap.