Biodegradable drug-eluting nanofiber-enveloped implants for sustained release of high bactericidal concentrations of vancomycin and ceftazidime: in vitro and in vivo studies

Abstract

We developed biodegradable drug-eluting nanofiber-enveloped implants that provided sustained release of vancomycin and ceftazidime. To prepare the biodegradable nanofibrous membranes, poly(D,L)-lactide-co-glycolide and the antibiotics were first dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol. They were electrospun into biodegradable drug-eluting membranes, which were then enveloped on the surface of stainless plates. An elution method and a high-performance liquid chromatography assay were employed to characterize the in vivo and in vitro release rates of the antibiotics from the nanofiber-enveloped plates. The results showed that the biodegradable nanofiber-enveloped plates released high concentrations of vancomycin and ceftazidime (well above the minimum inhibitory concentration) for more than 3 and 8 weeks in vitro and in vivo, respectively. A bacterial inhibition test was carried out to determine the relative activity of the released antibiotics. The bioactivity ranged from 25% to 100%. In addition, the serum creatinine level remained within the normal range, suggesting that the high vancomycin concentration did not affect renal function. By adopting the electrospinning technique, we will be able to manufacture biodegradable drug-eluting implants for the long-term drug delivery of different antibiotics.

Keywords: antibiotics; biodegradable nanofiber-enveloped plates; electrospinning; release characteristics.

Figure 1

Photos of drug-eluting membrane-enveloped plate and screws. Notes: (A) process of the plate enveloping; (B) process of the screw enveloping.

Figure 2

Schematic of the tissue-sampling sites: Site 1 – proximal side, Site 2 – right side, Site 3 – distal side, Site 4 – left side, Site 5 – above the implant, Site 6 – under the implant, Site 7 – inside the bone canal, Site 8 – blood.

Figure 3

Morphology of the nanofibrous membrane elucidated by scanning electron microscopy.

Figure 4

In vitro release characteristic of vancomycin (Van). Abbreviations: Ceft, ceftazidime; MIC50, minimum inhibitory concentration required to inhibit the growth of 50% of organisms; MIC90, minimum inhibitory concentration required to inhibit the growth of 90% of organisms; PLGA, poly(D,L)-lactide-co-glycolide.

Figure 5

In vitro release characteristic of ceftazidime (Ceft). Abbreviations: Van, vancomycin; MIC50, minimum inhibitory concentration required to inhibit the growth of 50% of organisms; MIC90, minimum inhibitory concentration required to inhibit the growth of 90% of organisms; PLGA, poly(D,L)-lactide-co-glycolide.

Figure 6

Bioactivity of the eluted antibiotics: (A) vancomycin, (B) ceftazidime.

Figure 7

In vivo release behavior of vancomycin. Abbreviations: MIC50, minimum inhibitory concentration required to inhibit the growth of 50% of organisms; MIC90, minimum inhibitory concentration required to inhibit the growth of 90% of organisms.

Figure 8

In vivo release behavior of ceftazidime. Abbreviations: MIC50, minimum inhibitory concentration required to inhibit the growth of 50% of organisms; MIC90, minimum inhibitory concentration required to inhibit the growth of 90% of organisms.

Figure 9

Histological examination of muscle tissue surrounding the plate at days 1, 3, 7, 14, 21, and 28 after surgery. Microscopic examination of hematoxylin-and-eosin-stained specimens showed significant mononuclear cell infiltrates of lymphocytes, plasma cells, and eosinophils in the muscle tissue surrounding the plate at day 1 after surgery. The number of polymorphonuclear leukocytes gradually decreased over time to day 28 post-surgery. Note: Original magnification 200×.