Fourier-Transformed Infrared Spectroscopy
Washed and dried samples were mixed with potassium bromide (Sigma) to obtain a ratio of 1∶100 (w/w). The samples were compressed with a hand press to form a thin transparent pellicle. FTIR spectra were acquired with a Nicolet 5700 FTIR spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) equipped with a deuterated triglycine sulfate (DTGS) detector. The spectra were obtained at a resolution of 4 cm−1 and at wavelengths ranging between 4,000 cm−1 to 400 cm−1. Each spectrum represented an average of 32 consecutive scans. For comparison, the commercially available controls of CaCO3, Ca3(PO4)2, and HAP described earlier were diluted and washed in either double-distilled water (shown in Fig. 13J, K, L, respectively) or DMEM (data not shown), followed by processing for FTIR analysis. The use of DMEM produced dampening of signals and significant depressions/troughs that could not be explained at this time.