Hydroxyapatite is an inherent calcium phosphate mineral that closely resembles the mineral constituent of bones and teeth 1. Hydroxyapatite (HAp) innate biocompatibility renders it a highly sought-after substance in diverse therapeutic domains. The widespread usage of this material in various medical and dental applications is due to its distinct characteristics, such as bioactivity, biocompatibility, and osteoconductivity. 2 The significance of HAp in healthcare lies in its capacity to stimulate bone development and regeneration. HAp serves as a scaffold in orthopaedic applications, promoting the growth of fresh bone tissue. Furthermore, the capacity of HAp to directly adhere to bone renders it a highly suitable substance for implants and coatings, guaranteeing their enduring durability and seamless integration with the body 3.

This review will examine the various applications of HAp in the field of healthcare, including its utilization in bone tissue engineering, dental care, drug delivery systems, wound healing, cancer treatment, and antimicrobial applications. In addition, we will examine the biocompatibility and probable toxicity of HAp, along with the difficulties and future prospects of this adaptable biomaterial.

Hydroxyapatite can be produced using many techniques, such as wet chemical precipitation, hydrothermal treatment, and sol-gel processing 2, 4. The selection of the synthesis technique often relies on the intended characteristics of the HAp, including factors like particle size, shape, and level of crystallinity. Furthermore, HAp can undergo functionalization with diverse materials to augment its characteristics and broaden its range of uses. For example, HAp can be integrated with polymers to produce composites that possess enhanced mechanical characteristics. Additionally, HAp can be altered with pharmaceuticals or bioactive substances to provide regulated administration of medications 3.

The nHAp is the nanoscale version of hydroxyapatite, has gained considerable interest in recent times because of its exceptional bioactivity, large surface area, and similarity to the natural apatite present in bones and teeth. The references cited are Pushpalatha et al., 2023 and Mazumder et al., 2019 1, 5. Precise control over the size, morphology, and crystallinity of nHAp is essential for its effective utilization in diverse domains including as biomedicine, dentistry, and environmental remediation.

The objective of bone tissue engineering is to restore and rejuvenate impaired or diseased bone tissue, thereby enhancing the quality of life for numerous individuals afflicted with bone abnormalities resulting from trauma, infection, or illness. The nHAp is a highly promising material in this sector because of its exceptional biocompatibility, bioactivity, and osteoconductivity. It closely resembles the composition and structure of genuine bone mineral. The references cited are Abere et al. (2022), Noor (2013), and Fu et al. (2021) 19, 20, 21. The nHAp, a scaffold material, mimics the structure of natural bone apatite. It serves as a framework for cell adhesion, proliferation, and differentiation, according to Munir et al. (2022) 22. The research has demonstrated that nHAp scaffolds have the ability to improve the attachment, growth, and specialization of osteoblasts, which are cells responsible for bone production. This ultimately results in the creation of new bone 19. The nanoscale characteristics of nHAp offer an expanded surface area that enhances protein adsorption and cellular interactions, hence facilitating the process of bone rebuilding.

The nHAp has exceptional biocompatibility, its mechanical characteristics, specifically its brittleness, may restrict its use in load-bearing bone defects. The references cited are Munir et al. (2022) and Tsai et al. (2018) 22, 23. In order to address this constraint, researchers have investigated the integration of nHAp into several composite materials. The mechanical strength and toughness of the scaffolds can be enhanced by incorporating nHAp with polymers like as chitosan, collagen, and polylactic acid, without compromising their biocompatibility 24, 25. nHAp can function as a transporter for bioactive compounds, including growth factors and medicines, to promote bone repair. 26 The porous nature of nHAp scaffolds enables the absorption and gradual release of these substances, which stimulates the growth, specialization, and creation of blood vessels at the site of injury.

HAp, due to its striking resemblance to the mineral composition of natural bone and teeth, has become a versatile biomaterial in the field of dentistry. The extensive utilization of this material in diverse dental applications is due to its biocompatibility, osteoconductivity, and capacity to stimulate tissue regeneration. HAp is a vital component in implant dentistry since it significantly improves the process of osseointegration for dental implants. Implants covered with hydroxyapatite (HAp) provide enhanced bone-to-implant contact and increased stability in comparison to implants without coating, as reported by Karamian et al. (2014) 43. The improved osseointegration results in increased rates of implant success, decreased risk of implant loosening, and greater long-term outcomes for patients 44, 45.

Periodontal regeneration involves the use of HAp in several forms such as granules, pastes, and membranes 44. The osteoconductive qualities of this substance facilitate the development of new bone and the attachment of the periodontal ligament, hence aiding in the regeneration of periodontal tissues that have been lost 19. Research has demonstrated that materials containing HAp can successfully decrease the depth of gum pockets, boost the level of connection between the gum and tooth, and promote the regeneration of gum tissue in individuals with periodontitis 1. HAp is commonly employed in operations to enhance the alveolar ridge. This helps to correct insufficient alveolar ridges, making it easier to install dental implants or enhance the durability of dentures 46. HAp-based bone graft substitutes serve as a framework for the development of new bone, improving the size and strength of the alveolar ridge. This enhances the visual appeal and operational effectiveness of dental prostheses 47.

Dentin hypersensitivity is commonly treated using dentifrices and dental care products that contain HAp 48. Nano-HAp's small particle size enables it to block exposed dentinal tubules, hence limiting fluid flow and relieving sensitivity49 (Pei et al., 2019). Enamel remineralization is promoted by including Hydroxyapatite (HAp), a crucial element of tooth enamel, into oral care products. According to Okada and Furuzono (2012) 3, formulations of HAp that contain fluoride improve the process of remineralization and reinforce the enamel, providing protection against dental cavities.

The nHAp has gained considerable interest as a potential material for drug delivery applications due to its excellent biocompatibility, bioactivity, and similarity to the mineral component of bone 19, 50, 5. This review explores the existing literature on the utilization of nHAp in drug delivery systems, emphasizing its benefits, drawbacks, and recent progress. Its exhibits excellent biocompatibility and biodegradability, indicating that it does not cause any negative responses in the body and can be gradually decomposed and assimilated over a period of time 51, 22. The feature of nHAp makes it an appealing material for the development of secure and efficient medication delivery systems 19.

The small size of nHAp particles leads to a large surface area and porosity, allowing for efficient drug loading and regulated release 51. It demonstrates an inherent attraction to bone tissue, rendering it highly appropriate for precise administration of drugs to bone cells and tissues. This focused strategy can improve the effectiveness of therapy while reducing the occurrence of unintended effects 51, 52. The surface of nHAp can be readily changed with different functional groups, enabling the conjugation of specific medicines or targeting ligands. The ability to adapt allows for the creation of tailored drug delivery systems to address specific therapeutic requirements 51.

Hydroxyapatite is primarily recognized for its ability to regenerate bones, but it is also gaining attention for its potential in wound healing and treating soft tissues. This review examines the current body of literature that investigates the possible advantages and drawbacks of HAp in various areas. The HAp's biocompatibility is essential for soft tissue applications, as it helps to minimize adverse reactions and promote integration with the body, similar to its role in bone 3. The HAp's porosity structure serves as a scaffold for cell adhesion, proliferation, and migration, which are crucial activities in wound healing and tissue regeneration 33.

The research indicates that HAp, especially in its nano-scale form, may possess antibacterial capabilities, which might potentially decrease the likelihood of infection in wounds 54. Presently, ongoing investigations and practical uses: wound dressings containing HAp have demonstrated promise in accelerating healing, diminishing inflammation, and improving tissue regeneration in animal models, as reported by Vivcharenko et al. (2021) 55. The research is currently investigating the potential of HAp-based scaffolds as temporary skin substitutes for the treatment of burns and chronic wounds. These scaffolds serve as a framework for the creation of new tissue 56. The potential of HAp to serve as a medication carrier is now being studied for targeted administration of antibacterial drugs or growth factors to enhance wound healing 23.

The nHAp, commonly used in bone regeneration, is now being considered as a potential treatment for cancer due to its distinct characteristics. This study examines the existing research that investigates the many uses of nHAp in fighting cancer.

The HAp, a calcium phosphate ceramic known for its ability to interact well with living tissue and its likeness to the mineral found in bones, has gained attention for its potential to fight against microorganisms and germs. This comprehensive review examines the current body of literature, investigating the mechanisms, uses, and future prospects of HAp in fighting against microbial diseases.

The HAp, surfaces can possess a positive charge, which has the ability to attract bacterial cell walls that are negatively charged. This attraction can lead to the disruption of the integrity of the bacterial cell walls 61. This interaction has the potential to cause membrane damage, resulting in the release of cellular contents and, ultimately, the death of bacteria. It has the ability to release calcium (Ca²⁺) and phosphate (PO^43-) ions. These ions can hinder bacterial metabolism and disturb crucial cellular processes 62, 63. Elevated levels of these ions can have a harmful effect on bacteria.

Certain studies indicate that HAp, especially in its nano-form, has the ability to produce reactive oxygen species such as hydroxyl radicals (•OH) under specific conditions 64. These extremely reactive compounds have the ability to harm bacterial DNA, proteins, and lipids, resulting in the death of the cell. The HAp has synergistic effects when combined with antibacterial drugs, such as antibiotics or silver ions, resulting in an enhanced efficacy of these medicines. The observed synergistic impact can be ascribed to three factors: enhanced medication delivery, heightened local concentration of antibacterial drugs, or increased bacterial sensitivity 65, 66, 67.

Hydroxyapatite is a calcium phosphate ceramic that closely resembles the mineral component of bone. It is well-known for its ability to be compatible with living tissues and its ability to promote bone growth. These characteristics have resulted in its widespread utilization in diverse biomedical applications, including as orthopaedic implants, dental materials, and drug delivery systems. This review examines the current body of literature on the biocompatibility and potential toxicity of HAp, investigating how it interacts with biological systems and addressing any relevant problems. The high biocompatibility of HAp is derived from its chemical resemblance to the mineral found in genuine bone. After being implanted, HAp demonstrates exceptional integration with nearby tissues, resulting in a low immune response and facilitating the formation of new bone.

The nHAp shows great potential in many healthcare fields such as orthopaedics, dentistry, and drug delivery, and it has exceptional biocompatibility, bioactivity, and similarity to genuine bone mineral. Nevertheless, there are still numerous obstacles and subjects for further investigation that need to be addressed in order to fully unlock its potential.

Synthesized nano-hydroxyapatite (nHAp) exemplifies the intersection of material science and medicine, providing a flexible framework for tackling a wide range of healthcare obstacles. The intrinsic biocompatibility, osteoconductivity, and ability to distribute drugs in a customized manner have sparked a significant increase in research and development, generating confidence for its potential to bring about transformation. Nevertheless, the journey from the laboratory bench to the patient's bedside is filled with obstacles. It is crucial to develop synthesis methods that can produce nHAp with uniform physicochemical properties, while also being scalable and reproducible. To address issues regarding the long-term stability, control of degradation, and potential nanotoxicity, it is necessary to conduct thorough investigations and develop creative solutions. Moreover, it is crucial to navigate the intricate aspects of clinical translation, regulatory obstacles, and cost-effectiveness considerations in order to fully achieve the clinical benefits of nHAp-based medicines.

Notwithstanding these difficulties, the prospects for synthesized nHAp in healthcare are highly promising. The extensive potential of targeted drug delivery systems, biomimetic scaffolds for bone tissue creation, and antibacterial/anti-inflammatory applications is highlighted by ongoing research. As we go further into the field of personalized medicine and nanomedicine, the capacity to customize the characteristics of nHAp to meet unique patient requirements presents extraordinary opportunities for diagnostics and therapies. Despite the remaining obstacles, synthesized nHAp possesses exceptional qualities and a wide range of uses, making it a leading force in healthcare innovation. Through ongoing research, interdisciplinary collaboration, and a resolute dedication to overcoming current obstacles, the use of nHAp has the potential to transform the field of medicine and introduce a new age of patient care.