Two-stage repeat sintering: A modified method for fabricating hydroxyapatite scaffolds with enhanced mechano-therapeutic properties

A modified two-stage repeat sintering (TSRS) technique has been used to produce hydroxyapatite (HAp) from non-separated animal bones, and the energy consumption per cycle of the proposed TSRS was calculated. The TSRS technique was compared to the conventional one-step sintering method. The energy consumption per cycle of the proposed TSRS was calculated considering economies of scale and typical energy consumption billing in Nigeria. The synthesized powders from both techniques underwent comprehensive characterization through X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and scanning electron microscopy (SEM). The XRD analysis revealed the main reflections of HAp in the (112), (300), and (202) planes. The FT-IR spectra exhibited characteristic bands representative of HAp at all measurement points. Notably, the TSRS-derived sample during the second sintering step showed carbonate bands, suggesting relevance in the bone structure makeup. SEM images unveiled varying crystal morphologies, ranging from irregular shapes in the raw bone (RB) sample to rounded shapes with nucleation in aggregates and agglomerates at micro and macro levels in the TSRS-derived samples. The samples obtained from the TSRS technique demonstrated a high Ca/P ratio that is potentially beneficial for osteoblast adhesion in vivo. The cost analysis of electricity consumption per TSRS cycle, factoring in economies of scale and typical energy consumption billing in Nigeria, amounted to approximately $8 with consideration of the exchange rates at the time of the study. The microhardness measured using the TSRS technique was 0.5 GPa with a 1 MPa compaction pressure, while the samples prepared using the conventional sintering method were too fragile to handle and measure. The obtained microhardness using the modified technique surpassed values reported in various studies. In conclusion, the samples produced using the TSRS technique exhibited promising results regarding energy efficiency, material characteristics, and microhardness compared to the samples produced through conventional sintering. The distinct crystal morphologies observed suggest potential advantages for biomedical applications, particularly in enhancing osteoblast adhesion.