Hydrothermal synthesis of hydroxyapatite from natural source

Area of Science:

• Materials Science
• Biomaterials Engineering
• Inorganic Chemistry

Background:

• Dicalcium phosphate dihydrate (DCPD) and anhydrous dicalcium phosphate (DCPA) are readily available from bovine bone gelatin by-products.
• Hydroxyapatite (HA) is a crucial biomaterial with applications in bone regeneration and dental implants.
• Efficient synthesis routes for HA from accessible precursors are of significant interest.

Purpose of the Study:

• To investigate the hydrothermal synthesis of hydroxyapatite (HA) from dicalcium phosphate dihydrate (DCPD) and anhydrous dicalcium phosphate (DCPA).
• To determine the optimal conditions for achieving a single HA phase with specific crystal morphologies.
• To explore the influence of Ca/P molar ratio and pH on the conversion process.

Main Methods:

• Hydrothermal synthesis of HA from DCPD and DCPA at 160-200°C and 1-2 MPa.
• Adjustment of Ca/P molar ratios using calcium hydroxide (Ca(OH)2).
• Analysis of reaction products across a range of pH values (4.6 and 12.3).

Main Results:

• Hydrothermal synthesis of HA from DCPA and DCPD was achieved.
• A single phase of needle-like HA crystals was obtained only after adjusting the Ca/P molar ratio to 1.50 or 1.67 with Ca(OH)2.
• DCPA whiskers formed in DCPD suspension, but addition of Ca(OH)2 resulted in a mixture of DCPA and HA.
• Incomplete conversion to HA occurred without Ca(OH)2 addition, with coexistence of DCPA and HA observed across acidic and basic pH ranges.

Conclusions:

• Complete conversion of DCPA and DCPD to HA via hydrothermal synthesis necessitates the addition of Ca(OH)2 to control the Ca/P molar ratio.
• The Ca/P molar ratio is a critical factor in achieving a single-phase HA product with desired morphology.
• Understanding the phase behavior of dicalcium phosphates under hydrothermal conditions is essential for controlled HA synthesis.