Phase Transformation and Mechanical Optimization of Eggshell-Derived Hydroxyapatite across a Wide Sintering...

Area of Science:

• Biomaterials Science
• Materials Engineering
• Bioceramics

Background:

• Hydroxyapatite (HA) is crucial for biomedical applications due to its similarity to bone mineral.
• Developing cost-effective and sustainable HA sources is essential for widespread use.
• Eggshells offer a readily available and biocompatible source for HA production.

Purpose of the Study:

• To synthesize and characterize hydroxyapatite (HA) from eggshells using a precipitation method.
• To investigate the effect of sintering temperature on the mechanical properties of eggshell-derived HA (E-HA).
• To evaluate the antibacterial efficacy of E-HA against *Streptococcus mutans*.

Main Methods:

• HA synthesis via precipitation using eggshells as a raw material.
• Press-forming and sintering of HA powder at various temperatures (800–1400 °C).
• Mechanical property testing (hardness, compressive strength, fracture toughness) and statistical analysis (ANOVA, Tukey's test).
• Antibacterial assays using *Streptococcus mutans* culture on E-HA, chemically synthesized HA (Chem-HA), and commercial HA (Comm-HA).

Main Results:

• Increasing sintering temperature led to HA transformation into β-TCP and α-TCP, and increased relative density.
• Optimal sintering at 1200–1300 °C yielded maximum relative density (94.5%).
• E-HA sintered at 1200 °C showed superior mechanical properties: hardness (5.08 GPa), compressive strength (255.79 MPa), and fracture toughness (1.21 MPa·m^0.5).
• All tested HA samples exhibited significant antibacterial efficacy against *Streptococcus mutans* (OD < 0.2).

Conclusions:

• Eggshell-derived HA is a viable and cost-effective alternative for biomedical applications.
• Sintering temperature critically influences the phase composition, density, and mechanical performance of E-HA.
• E-HA possesses comparable antibacterial properties to chemically synthesized and commercial HA, highlighting its potential in bone regeneration and dental applications.