Photo of the implant: a miniaturized additively manufactured Ti6Al4V implant for testing of the efficacy of the biofunctionalized surfaces. (Image credit: Marieke de Lorijn.)
An overview of the approach to creating multi-functional titanium implants.Orthopedic implants have revolutionized the lives of millions, replacing worn out or damaged joints. But even state-of-the-art titanium implants have a limited service life, with devices losing their attachment to bone, causing pain and limiting patient mobility. Ultimately, replacement is necessary. Various tactics have been explored to extend the lifetime of implants, including using different materials, especially those with bone-mimicking properties, surface functionalization, and delivering active agents to promote bone growth and ward off infection. The ideal implant, therefore, needs to have multiple functions to last a lifetime.
“Although orthopedic implants are usually very successful, many patients face major complications: implant-associated infections and loosening of the implant. As many patients receive their first implant after 60 years of age and the life expectancy of patients increases, this is a major concern for future implants,” explains Ingmar A. J. van Hengel of Delft University of Technology, who together with colleagues at University Medical Center Utrecht and Erasmus Medical Center, has developed a new titanium implant.
The prototype porous titanium implant could prevent these complications, the researchers believe [van Hengel et al., Materials Today Bio 7 (2020) 100060, https://doi.org/10.1016/j.mtbio.2020.100060 ]. The team used rational design principles and additive manufacturing to create an ordered interconnected porous microstructure in medical-grade titanium ideal for in-growing bone. The bone-mimicking mechanical properties can be readily adjusted, while additive manufacturing allows bespoke implants of different shapes and sizes to be easily fabricated. The porous structure increases surface area by a factor of three compared with solid implants so that surface functionalization, which both stimulates differentiation of stem cells into bone (or osteogenic) cells and prevents bacterial infection, is more effective.
“We applied a surface modification, namely plasma electrolytic oxidation (PEO), to incorporate strontium and silver nanoparticles into the surface of [our] highly porous implants,” says van Hengel.
Silver nanoparticles have long been known to have an antibacterial effect, but the team found that this action is enhanced by strontium ions, which were added to combat osteoporosis and encourage long-term bone formation and resorption. Moreover, the combination is also effective against bacterial strains such as methicillin-resistant Staphylococcus aureus (MRSA), which have developed resistant to common antibiotics.
“We discovered an unexpected synergistic antibacterial behavior between silver and strontium,” van Hengel told Materials Today. “This was quite unexpected but may facilitate the production of even stronger antibacterial implants, minimizing the chance of infection.”
The prototype implants were tested in a model system that mimics the clinical environment, but the researchers are confident that the approach could be easily scaled to human-sized devices.
“Patients may benefit both from mechanically-optimized implants and surface properties, which will contribute to enhanced implant longevity,” says van Hengel.