For many decades, titanium and titanium alloys have been used to develop various medical applications due to their unique characteristics of strength, biocompatibility, resistance to the effects of body fluids, flexibility, and resistance to corrosion.
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These properties have led the material to be relied on for over half a century to create medical implants.
To this day, titanium remains a prominent material in the engineering of biomedical applications. Presently, numerous research teams are determining how the next generation of biomedical systems can be enhanced or even made possible through the use of the newly emerging titanium nanostructures.
Recently, studies have uncovered that the large surface area offered titanium nanostructures offer the properties of increased antibacterial properties, osseointegration, and protein interaction that medical implants benefit from. Below, we discuss in detail the various applications of titanium nanostructures in biomedical applications, with a focus on their main use in implants.
Hydroxyapatite formation
Studies have shown that titanium dioxide (TiO2) nanotube surfaces can speed up the formation of hydroxyapatite (HAp) from body fluids on the surface of implants. The effect is more strongly observed in TiO2 nanotubes in comparison to flat TiO2 surfaces. This is significant because HAp is commonly used as a replacement for bone or as a coating to encourage bone ingrowth in the case of prosthetic implants.
Protein interactions with nanotubes and cell adhesion
The adsorption of proteins in the tissue encompassing the implant is a vital stage for ensuring the implant’s success, with the level of adsorption being impactful on success. Scientists have proposed a rough titanium implant surface to encourage the adhesion of cells.
It works because an attraction is formed between the negatively charged osteoblast and the negatively charged titanium surface which is mediated by charged proteins.
Likewise, fibronectin molecules in the extracellular matrix and the titanium oxide surface form a cation-mediated attraction, which facilitates integrin-mediated osteoblast adhesion.
It is theorized that stronger binds could be formed between the osteoblasts and the sharp edges of the nano rough titanium oxide surfaces where the negative charge density is greatest, promoting more adhesion of osteoblasts.
Antibacterial activity
Bacterial infection presents a major challenge to the use of medical devices and implants because increasing antimicrobial resistance and biofilm formation mean that traditional antibiotics are becoming ineffective against these infections.
Fortunately, studies have shown that controlling the size of nanotubes may prevent implant and other medical device-related infections, with evidence revealing that the behavior of various common medical device-related pathogens being impacted by the nanotubes. Larger diameter nanotubes seem to reduce the persistence of pathogens. Research has also shown a similar effect is had on bacteria. However, when specifically using titanium nanostructures, evidence shows that smaller-diameter nanotubes have the impact of increasing the antibacterial effect.
Dental and orthopedic implants
Titanium dioxide nanotubes have proven themselves to be better than conventionally used surfaces at improving the bone-bonding strength to dental and orthopedic implants. Studies have shown this can be up to nine times better with nanotubular surfaces.
Also, titanium dioxide nanotubes produce better bone-implant contact as well as collagen type I expression (essential for bone and connective tissue health). These results have been found both in vitro and in vivo.
Drug delivery
Presently, the expected lifetime of orthopedic implants is just 10 to 15 years due to several limitations. The main factor being the likeliness of infection impacting the implant. To tackle this, scientists have developed a coating that is applied to the titanium nanostructures used in the implants which include infection-reducing drugs and inflammation-reducing drugs.
Following this, researchers have taken this further and discovered that magnetic Fe3O4 particles can be carried inside of titanium dioxide nanotubes, allowing them to be guided magnetically to their intended locations.
These filled nanotubes can also be used directly to create photocatalytic reactions with certain cell types, such as cancer types, establishing a new technique for targeting and destroying cancer.
Overall, titanium nanostructures are currently benefitting several biomedical applications, with a focus on implants. However, research is still in the early days and we can expect much more from titanium nanostructures in the future.
Sources:
https://iopscience.iop.org/article/10.1088/0957-4484/26/6/062002#nano501931s4
https://www.elsevier.com/books/titanium-in-medical-and-dental-applications/froes/978-0-12-812456-7
https://www.sciencedirect.com/science/article/pii/B9780080994451000092
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