Dispersion of silicate in tricalcium phosphate elucidated by solid-state NMR

The dispersion of silicate in tricalcium phosphate, a resorbable bioceramics for bone replacement, has been investigated by various solid-state nuclear magnetic resonance (NMR) methods. In samples prepared with 5 and 10 mol % of both (SiO2)-Si-29 and ZnO, three types of silicate have been detected: (i) SiO44- (Q(0) sites) with long longitudinal (T-1,T-Si) relaxation times (similar to 10 000 s), which substitute for similar to 1% of PO43-; (ii) silicate nanoinclusions containing Q(2), Q(1), and Q(0) sites with T-1,T-Si similar to 100 s, which account for most of the silicon; and (iii) crystalline Q(4) (SiO2) with long T-1,T-Si. Sensitivity was enhanced > 100-fold by Si-29 enrichment and refocused detection. The inclusions in both samples have a diameter of similar to 8 nm, as proved by Si-29{P-31} REDOR dephasing on a 30-ms time scale, which was simulated using a multispin approach specifically suited for nanoparticles. Si-29 CODEX NMR with 30-s Si-29 spin diffusion confirms that an inclusion contains >10 Si (consistent with the REDOR result of >100 Si per inclusion). Overlapping signals of silicate Q(2), Q(1), and Q(0) sites were spectrally edited based on their J-couplings, using double-quantum filtering. The large inhomogeneous broadening of the Q(2), Q(1), and Q(0) Si-29 subspectra indicates that the nanoinclusions are amorphous.