Abstract
After the implantation of endoprotheses or osteosynthesis devices, implant-related infections are one of the major challenges. The surface of implants offers optimal conditions for the formation of a biofilm. Effective carrier systems for the delivery of adequate therapeutics would reduce the concentrations needed for successful treatment and improve cure rates. In cancer diagnosis and therapy, magnetic nanoparticles are concentrated in the target area by an external magnetic field. For orthopaedic applications, in vitro examinations showed that the addition of a magnetic implant in combination with an external magnetic field could increase the amount of MNPSNPs that accumulated in direct vicinity to the implant. The present examinations implemented an electromagnet to increase magnetic field strength and should show if the in vitro set up can be transferred to an in vivo mouse model. Additionally, the loading capacity of the MNPSNPs with enrofloxacin and its release kinetics were determined.
Fluorescein-isothiocyanate (FITC) was covalently attached to MNPSNPs. For the in vitro set up, a peristaltic pump was used to establish a closed circuit which contained the MNPSNP dispersion and a magnetic platelet. After 5 minutes fluid samples were taken from the area around the magnetic platelet and analysed using a microplate reader. For the in vivo set up, a BALB/c mouse was implanted subcutaneously with the metallic platelet at the hind leg. The MNPSNP dispersion was injected into the tale vein and the hind leg of the mouse was placed immediately in a magnetic field of 1.9 T. After one week the implant was retrieved and examined by confocal laser scanning microscopy (CLSM). Liver, spleen and kidneys of the mouse were examined by magnetic resonance imaging (MRI). The loading capacity of the MNPs with enrofloxacin was examined by quantification of the enrofloxacin content in the incubation and washing solution after incubation. The release kinetics weres tested in PBS using UV/Vis-spectrometry.
The solution in the remaining tube contained no detectable MNPs while the concentration in the vicinity of the platelet was 150 µg/ml. The mouse showed no clinical adverse effects. The CLSM examination revealed a considerable accumulation of the MNPs at the implant surface. MRI could show neither accumulated MNPs nor changes of organ structure. The loading capacity of the MNPs for enrofloxacin was approximately 95 µg/mg. A burst release of nearly a third of the loaded antibiotic occurred within the first 6 hours followed by a further steady release.
Conclusion
Loading and release of enrofloxacin showed appropriate results. For future studies antibiotics like rifampicin or vancomycin will be implemented. This first in vivo trial demonstrated an implant-directed targeting of the MNPs and successfully transferred the principle into an in vivo model so that a main study with statistically significant animal numbers has started including histological examinations.
