Temperature-sensitive liposomal ciprofloxacin for the treatment of biofilm on infected metal implants using alternating magnetic fields

Figures & data

Figure 1. Schematic of ciprofloxacin release from temperature sensitive liposomes (TSL) in the vicinity of an infected metal implant heated by exposure to alternating magnetic field (AMF).

Figure 2. TEM images of (A) LTSL and (B) HTSL nanoparticles loaded with ciprofloxacin (arrow indicates liposomes) and size distribution curve of (C) LTSL and (D) HTSL measured with MQ water and (E) pH dependence of ciprofloxacin encapsulation by remote loading in LTSL nanoparticle in PBS.

Table 1. Composition, drug/lipid ratio, size (in MQ water and ammonium sulphate buffer), polydispersity index and zeta potential (in MQ water) of ciprofloxacin loaded LTSL, HTSL and PEG-HTSL (n = 3).

	LTSL	HTSL	PEG-HTSL
Composition	Molar ratio of 85.3:9.7:5.0 (DPPC:MSPC: DSPE-PEG)	Molar ratio of 2:8 (Chol:DPPC)	Molar ratio of 56:36:5.07 (DPPC, Cholesterol and DSPE-MPEG 2000)
Drug/lipid ratio	1:50	1:50	1:50
Size (nm) in MQ water	153.00 ± 56.50	185.00 ± 64.00	192.00 ± 2.88 nm
Size (nm) in ammonium sulphate buffer	148.80 ± 49.01	154.30 ± 56.54	185.20 ± 69.19
Size (nm) in 10% FBS	90.89 ± 4.13	105.72 ± 5.17	150.73 ± 1.50
Polydispersity index	0.13 ± 0.03	0.07 ± 0.03	0.11 ± 0.04
Zeta potential (mV) in MQ water	−40.22 ± 1.96	−43.03 ± 2.46	−34.69 ± 2.78
Zeta potential (mV) in 10% FBS	6.89 ± 8.6443.03 ± 2.46−34.69 ± 2.78	−8.27 ± 5.75	−4.15 ± 3.81
Phase transition temperature (Tm) (°C)	∼42.80 (in PBS) ∼ 42.73 (in 10% FBS)	No peak of transition (in PBS) No peak of transition (in 10% FBS)	Not determined

Figure 3. Thermoscan assay of ciprofloxacin loaded (A) LTSL (B) HTSL in PBS and FBS, ciprofloxacin release kinetics of LTSL in (A-1) PBS and (A-2) FBS and ciprofloxacin release kinetics of HTSL in (B-1) PBS and (B-2) FBS.

Figure 4. Ciprofloxacin release kinetics of PEG-HTSL in PBS and FBS at 25 and 37 °C.

Figure 5. (A) Experimental solenoid coil, (B) ciprofloxacin release vs. time for LTSL and HTSL under 20 W AMF exposure, (C) ciprofloxacin release vs. washer temperature for LTSL and HTSL during AMF exposure (20 W). [A fibre optic temperature sensor (Neoptix Inc., Quebec, Canada) was attached to the top surface of a metal washer using a thermally conductive epoxy (ASTA, Arctic Silver Inc., Visalia, CA).] (D) The bactericidal effect of alternating magnetic field (AMF) exposures on biofilm-associated bacteria associated with a metal washer for cipro-LTSL and cipro-HTSL. This assay demonstrates that the cipro-LTSL and HTSL keeps the antibiotic encapsulated until activated with heat from AMF.

Figure 6. Scanning electron microscopy (SEM) images of the surface of a stainless steel washer showing the influence of both cipro-LTSL and AMF exposures on bacteria and biofilms. (A) a negative control sample – washer with no bacteria, (B) a positive control sample – washer with biofilm but no treatment of cipro-LTSL and AMF exposure, (C) a control sample – washer with biofilm but treatment of cipro-LTSL and no AMF exposure, (D) sample – washer with biofilm with treatment of AMF exposure and (E) sample – washer with biofilm with treatment of both cipro-LTSL and AMF exposure. It was difficult to find any viable bacteria on the washer (E), and aggregates of material were visible on the washer surface. (Arrow indicates bacteria and arrow head indicates cipro-LTSL).

Figure 7. DSC thermograms of (A-1) LTSL in PBS, (A-2) LTSL in FBS, (A-3) Cipro-LTSL in PBS, (A-4) Cipro-LTSL in FBS, (B-1) HTSL in PBS, (B-2) HTSL in FBS, (B-3) Cipro-HTSL in PBS and (B-4) Cipro-HTSL in FBS.