Hydroxyapatite (HAp) is a naturally occurring mineral form of calcium apatite that closely resembles the composition of human bone and teeth. With the chemical formula Ca₁₀(PO₄)₆(OH)₂, hydroxyapatite has become one of the most important biomaterials in the fields of orthopedics, dentistry, and tissue engineering. Its biocompatibility, bioactivity, and ability to bond directly with bone make it a cornerstone in the development of advanced medical implants and regenerative therapies.

The primary appeal of hydroxyapatite lies in its exceptional biocompatibility. Because it mimics the mineral phase of bone, the body readily accepts HAp without triggering adverse immune responses. This makes it ideal for coating metal implants such as titanium hip and dental implants, where it encourages bone cells to grow directly on the implant surface—a process known as osseointegration. This tight bonding helps reduce implant loosening and improves long-term stability.

In bone grafting applications, hydroxyapatite serves as a scaffold that supports the growth of new bone tissue. It can be used in pure powder form or combined with polymers and other ceramics to form composite materials that enhance both strength and biofunctionality. These materials are often used to fill bone voids after trauma, tumor removal, or congenital defects, helping to restore structure and function with minimal risk of rejection.

Dental applications of hydroxyapatite are also expanding. It is used in toothpaste formulations to remineralize enamel, treat sensitivity, and promote overall oral health. In cosmetic dentistry, HAp is applied in bone fillers and coatings for implants to improve aesthetics and integration.

One of the most promising areas of research involves nanostructured hydroxyapatite. Nanoscale HAp particles more closely resemble natural bone mineral in size and structure, offering improved surface area and better interaction with cells. These nanoparticles are being investigated for use in drug delivery systems, where they can carry antibiotics or growth factors directly to bone tissue, enhancing healing and reducing infection risks.

Environmentally, hydroxyapatite is a sustainable choice. It can be synthesized from natural sources like coral, animal bones, and eggshells, or produced synthetically under controlled conditions. Researchers are also exploring green synthesis techniques using plant extracts to lower the environmental impact of production.