Boron nitride (BN) is a compound of boron and nitrogen with a structure analogous to carbon-based materials. It exists in several crystalline forms, with hexagonal boron nitride (hBN) being the most stable and widely studied for biomedical applications. Its unique properties, including chemical inertness, thermal stability, and mechanical strength, make it a promising candidate for various medical uses. This article explores BN's biocompatibility, drug delivery capabilities, and applications in bioimaging and tissue engineering.

Biocompatibility is a critical factor for any material intended for biomedical applications. Studies have demonstrated that BN exhibits low cytotoxicity and high biocompatibility with various cell types. In vitro experiments with human cells, including fibroblasts and endothelial cells, show minimal adverse effects even at relatively high concentrations. The inert nature of BN reduces inflammatory responses, making it suitable for implants and other in vivo applications. Unlike some nanomaterials that induce oxidative stress or membrane damage, BN maintains cellular integrity, promoting long-term compatibility in biological environments. Animal studies further support these findings, with no significant immune reactions or tissue damage observed upon implantation or injection of BN-based materials.

Drug delivery systems benefit from BN's structural and chemical properties. Its high surface area allows for efficient loading of therapeutic agents, including small-molecule drugs, proteins, and nucleic acids. The surface of BN can be functionalized with various chemical groups to enhance drug binding and controlled release. For example, BN nanosheets modified with polyethylene glycol (PEG) show improved dispersion in physiological fluids and prolonged circulation time in the bloodstream. This functionalization also enables targeted delivery by attaching ligands that recognize specific cell receptors. BN's thermal stability is advantageous for stimuli-responsive drug release, where external triggers such as near-infrared light or pH changes can initiate the discharge of encapsulated drugs. Research indicates that BN-based carriers can deliver chemotherapeutic agents to tumor sites with reduced off-target effects, enhancing treatment efficacy while minimizing side effects.

In bioimaging, BN's optical properties are leveraged for diagnostic purposes. While BN itself is not fluorescent, its combination with other imaging agents enhances contrast and resolution. For instance, BN nanosheets doped with rare-earth elements or conjugated with quantum dots exhibit strong luminescence under specific wavelengths, making them suitable for fluorescence imaging. Additionally, BN's high atomic number contributes to X-ray contrast, enabling its use in computed tomography (CT) imaging. The material's stability ensures that these imaging modalities remain effective over extended periods without degradation. BN-based probes have been tested in preclinical models, demonstrating clear visualization of tissues and organs with minimal background noise. The ability to functionalize BN with targeting moieties further improves imaging specificity, allowing for early detection of diseases such as cancer.

Tissue engineering applications capitalize on BN's mechanical strength and biocompatibility. BN scaffolds provide structural support for cell growth and tissue regeneration. The material's porous structure facilitates nutrient exchange and cell migration, critical for the formation of functional tissues. In bone tissue engineering, BN composites with hydroxyapatite or polymers enhance mechanical properties while promoting osteoblast adhesion and proliferation. Similarly, BN-reinforced hydrogels mimic the extracellular matrix, supporting the growth of soft tissues like cartilage and skin. Electrical insulation properties of BN are beneficial for neural tissue engineering, where unwanted electrical interference must be avoided. Studies report successful integration of BN-based scaffolds in animal models, with new tissue formation and minimal fibrous encapsulation.

BN's role in combination therapies is also noteworthy. Its ability to carry both drugs and imaging agents enables theranostic approaches, where diagnosis and treatment occur simultaneously. For example, BN nanosheets loaded with anticancer drugs and labeled with fluorescent markers allow real-time monitoring of drug distribution while delivering therapy. This multifunctionality reduces the need for separate diagnostic and therapeutic agents, streamlining clinical procedures. The material's stability under physiological conditions ensures that these combined functions remain effective throughout the treatment period.

Despite these advantages, challenges remain in optimizing BN for widespread biomedical use. Scalable synthesis methods are needed to produce uniform BN materials with consistent properties. Long-term biodistribution and degradation studies are necessary to fully understand its behavior in the body. Regulatory approvals will require extensive preclinical and clinical testing to confirm safety and efficacy. However, the progress so far highlights BN's potential to advance drug delivery, bioimaging, and tissue engineering, offering new solutions for complex medical challenges.

The versatility of BN in biomedical applications stems from its unique combination of physical and chemical properties. Its biocompatibility ensures safe interaction with biological systems, while its structural characteristics enable innovative approaches to drug delivery and tissue repair. As research continues, BN is poised to play a significant role in the development of next-generation medical technologies, improving outcomes in diagnostics, therapeutics, and regenerative medicine. The ongoing exploration of BN's capabilities will likely uncover even more applications, solidifying its place in the future of biomedicine.