In modern medicine, the treatment of implant-associated infections is still a central problem, as the number of such infections increases every year with the rising number of implantations. To avoid the drawbacks of a systemic treatment of such infections, a special drug-targeting set-up was developed. Here a magnetizable implant and an externally applied magnetic field are used to guide drug loaded superparamagnetic nanoporous silica nanoparticles (MNPSNPs) to the implant site. As the injected MNPSNP circulate in the body, they pass the implant where the strong local magnetic field causes an enhanced accumulation of the drug loaded MNPSNPs. Then the particles shall release their loaded drug and the infection can be treated. After this, the magnetic field is turned off and thus the particles are superparamagnetic, they will detach from the implant and are degraded by the body.
One aim in the design of suitable particles is to protect the particles from an early recognition of the immune system, which would lead to an early degradation of the particles. To obtained so called “stealth” particles different solutions are possible. For instance a poly(ethylene glycol) (PEG) functionalization is known to reduce the immunogenic reaction, where the PEG chain length has an key impact. Another very promising way to obtain “stealth” nanoparticles is the use of a protein which signals “self” to phagocytic cells and thereby prevents the phagocytosis. A protein with such a property is the cluster of differentiation 47 (CD47).
Another aspect in the design of the nanoparticles is the adjustment of their magnetizability. To ensure a high accumulation rate of the MNPSNPs at the implant site a high magnetizability is desired. This can be achieved by adjusting the size of either the magnetic magnetite core or by adjusting the size of the final core-shell particle.