Enzyme-Responsive Nanoparticles and Coatings Made from Alginate/Peptide Ciprofloxacin Conjugates as Drug Release System

Abstract

Infection-controlled release of antibacterial agents is of great importance, particularly for the control of peri-implant infections in the postoperative phase. Polymers containing antibiotics bound via enzymatically cleavable linkers could provide access to drug release systems that could accomplish this. Dispersions of nanogels were prepared by ionotropic gelation of alginate with poly-l-lysine, which was conjugated with ciprofloxacin as model drug via a copper-free 1,3-dipolar cycloaddition (click reaction). The nanogels are stable in dispersion and form films which are stable in aqueous environments. However, both the nanogels and the layers are degraded in the presence of an enzyme and the ciprofloxacin is released. The efficacy of the released drug against Staphylococcus aureus is negatively affected by the residues of the linker. Both the acyl modification of the amine nitrogen in ciprofloxacin and the sterically very demanding linker group with three annellated rings could be responsible for this. However the basic feasibility of the principle for enzyme-triggered release of drugs was successfully demonstrated.

Keywords: ciprofloxacin; copper-free click chemistry; drug release system; enzyme triggered release; implant coating; nanoparticle; peri-implantitis.

Figure 1

Reaction scheme for the preparation of ciprofloxacin conjugated to a poly-l-lysin sequence which can be used as linker.

Figure 2

(a) Dependence of the size of nanogels prepared with different PLL-ciprofloxacin/alginate ratios at RT in deionized water; (b) size of the nanoparticles (PLL-ciprofloxacin/alginate 1/3) as a function of incubation time in phosphate buffer saline (pH 7.4) at 37 °C. The particle size for the 1/3 mixture here was somewhat higher because of the buffer and the higher temperature.

Figure 3

Size of the nanoparticles (PLL-ciprofloxacin/alginate 1/3) as function of incubation time in phosphate buffer saline (pH 7.4) at 37 °C after addition of trypsin (final concentrations of 2.5 µg/mL).

Figure 4

Absorbance at 278 nm, which corresponds to the ciprofloxacin concentration in the dialysate as function incubation time in PBS buffer (pH 7.4) without, with 2 µg/mL or 5 µg/mL trypsin, respectively, at 37 °C.

Figure 5

Dry layer thickness of PLL-cipro/alginate coatings as determined by ellipsometry after incubation in PBS buffer with or without addition of trypsin (5 μg/mL) at pH 7.4 and at 37 °C.

Figure 6

Bacterial growth in the presence of ciprofloxacin modifications. (a) Chemical structures of the ciprofloxacin modifications 4, 5, and 6. (b) Percentage growth of S. aureus (mean ± SD) in the presence of different concentrations of ciprofloxacin modifications (4, 5, 6), unmodified ciprofloxacin, or water.