Attenuated total reflectance/Fourier transform infrared (ATR/FTIR) mapping coupled with principal component analysis for the study of in vitro degradation of porous polylactide/hydroxyapatite composite material

Abstract

Attenuated total reflectance/Fourier transform infrared (ATR/FTIR) mapping was used to characterize the degradation of porous polylactide/hydroxyapatite (PLLA/HA) composite material. The ATR/FTIR images were acquired using a Continuum XL FTIR imaging microscope coupled with a slide-on Si ATR accessory at a resolution of 8 cm⁻¹ with eight co-added scans in the wavenumber range of 4000–650 cm⁻¹. Principal component analysis (PCA) was used to analyze the FTIR image data. Four principal components (PCs) were identified by analyzing both the scree plot and the loading spectra. The degradation at various days was clearly described by the curve of the intensity ratio of the band at 1026 cm⁻¹ to the one at 1755 cm⁻¹ (I₁₀₂₆/I₁₇₅₅) in the first PC's (PC1's) loading plot versus the number of days. The shape and position of the second PC (PC2) was similar to the IR spectrum of water, indicating that it comes from the contribution of water absorbed on the porous sample. The variations of the bands at 1755 cm⁻¹ and 1026 cm⁻¹ in PC3's loading plots reflected the changes in PLLA and HA on different days, respectively, while the fourth PC (PC4) suggested a transition from the abstract signal to noise. These results demonstrate that ATR/FTIR mapping coupled with PCA could effectively characterize the degradation process of porous PLLA/HA composite materials.