Introduction

 

Hydroxyapatite (HAp, Ca₁₀(PO₄)₆(OH)₂) is a bioactive calcium phosphate mineral extensively studied for its structural similarity to human enamel and bone. This unique characteristic makes HAp a versatile material, not only in toothpaste and food additives but also in biomedical engineering, drug delivery systems, and composite materials. Recent advances in nanostructuring, ion doping, and surface functionalization have expanded its applications across multiple research fields, highlighting its importance as a multifunctional biomaterial.

 

Material Properties Relevant to Multiple Applications

 

The functional performance of h ydroxyapatite is closely related to its crystallinity, particle size, morphology, and surface chemistry. Nanostructured HAp provides higher surface area and enhanced bioactivity compared to microcrystalline forms. Ion substitution with elements such as magnesium, zinc, strontium, or fluoride can modulate mechanical strength, bioactivity, antimicrobial properties, and solubility. These tunable properties make HAp suitable for applications ranging from enamel remineralization to controlled calcium release in functional foods and osteoconductive scaffolds for tissue engineering.

 

Hydroxyapatite in Toothpaste

 

In oral care, HAp functions as a remineralizing agent in toothpaste. Nano-HAp particles penetrate enamel micro-defects, acting as nucleation sites for hydroxyapatite deposition, which restores mineral density and reduces sensitivity. Studies show that regular use of HAp-containing toothpaste increases enamel microhardness and provides a non-fluoride alternative for preventive dentistry. Doped HAp formulations, such as zinc-substituted HAp, also exhibit antibacterial effects against Streptococcus mutans, enhancing their clinical potential. Analytical techniques including AFM, SEM, and microhardness testing are commonly used to quantify surface restoration and particle interaction with enamel.

 

Hydroxyapatite as a Food Additive

 

HAp is increasingly applied as a functional food additive, primarily for calcium fortification. Particle size, morphology, and crystallinity influence solubility and bioavailability, making these parameters critical in food applications. HAp can be integrated into beverages, dairy alternatives, or dietary supplements, providing controlled calcium release without altering taste or texture. Trace-element doping with magnesium or strontium can further mimic natural bone mineral composition, potentially improving nutritional uptake. Characterization methods such as XRD, FTIR, TEM, and ICP-OES are essential for evaluating HAp structure and composition in complex food matrices.

 

Hydroxyapatite in Bone and Tissue Engineering

 

Beyond oral care and food applications, HAp is widely used in bone regeneration and tissue engineering. Its osteoconductivity supports bone cell attachment and proliferation, while its biodegradability allows gradual integration into the host tissue. Researchers have developed HAp scaffolds, porous ceramics, and composite materials combined with polymers like PLGA or chitosan to improve mechanical properties and control degradation rates. Nanostructured HAp coatings on metallic implants enhance osseointegration and reduce implant failure. In these contexts, surface chemistry, porosity, and crystallinity are carefully optimized to balance bioactivity with mechanical stability.

 

Hydroxyapatite in Drug Delivery and Functional Coatings

 

HAp nanoparticles are increasingly explored as drug carriers, leveraging their biocompatibility and surface functionalization potential. Drugs can be adsorbed onto HAp surfaces or incorporated into HAp-based composites for controlled release, targeting bone or oral tissues. HAp coatings on dental and orthopedic implants also serve as carriers for antimicrobial agents, reducing infection risks while promoting tissue integration. Functionalization strategies include polymer grafting, ion doping, and co-encapsulation of bioactive molecules, which allow researchers to tune release kinetics and target specificity.

 

Current Research Trends

 

Recent studies focus on nanostructured HAp, ion doping, composite development, and mechanistic understanding of its interactions with biological tissues. Researchers are exploring high-throughput screening and computational modeling to predict the effects of particle size, crystallinity, and doping on remineralization, bioavailability, and osteoconductivity. Integration with bioactive polymers, peptides, or growth factors is also being investigated to create multifunctional biomaterials with applications spanning oral care, nutrition, and regenerative medicine.

 

Conclusion

 

Hydroxyapatite remains a highly versatile and scientifically significant material. Its applications in toothpaste and food additives are complemented by a wide array of research in bone regeneration, drug delivery, and composite biomaterials. The material’s tunable properties—including particle size, crystallinity, and ion doping—allow researchers to optimize performance for diverse biological and nutritional applications. As nanostructuring, surface functionalization, and composite technologies advance, HAp continues to offer rich opportunities for materials science research and translational applications.