One-Pot Method for Preparation of Magnetic Multi-Core Nanocarriers for Drug Delivery

The development of various magnetically-responsive nanostructures is of great importance in biomedicine. The controlled assembly of many small superparamagnetic nanocrystals into large multi-core clusters is needed for effective magnetic drug delivery. Here, we present a novel one-pot method for the preparation of multi-core clusters for drug delivery (i.e., magnetic nanocarriers). The method is based on hot homogenization of a hydrophobic phase containing a nonpolar surfactant into an aqueous phase, using ultrasonication. The solvent-free hydrophobic phase that contained tetradecan-1-ol, γ-Fe2O3 nanocrystals, orlistat, and surfactant was dispersed into a warm aqueous surfactant solution, with the formation of small droplets. Then, a pre-cooled aqueous phase was added for rapid cooling and the formation of solid magnetic nanocarriers. Two different nonpolar surfactants, polyethylene glycol dodecyl ether (B4) and our own N1,N1-dimethyl-N2-(tricosan-12-yl)ethane-1,2-diamine (SP11), were investigated for the preparation of MC-B4 and MC-SP11 magnetic nanocarriers, respectively. The nanocarriers formed were of spherical shape, with mean hydrodynamic sizes <160 nm, good colloidal stability, and high drug loading (7.65 wt.%). The MC-B4 nanocarriers showed prolonged drug release, while no drug release was seen for the MC-SP11 nanocarriers over the same time frame. Thus, the selection of a nonpolar surfactant for preparation of magnetic nanocarriers is crucial to enable drug release from nanocarrier.


S1.1. Synthesis of tricosan-12-one (laurone).
The synthesis of tricosan-12-one was carried out as reported by J. C. Sauer. (Sauer, J. C. (2003). Laurone. In Organic Syntheses, (Ed.). doi:10.1002/0471264180.os031.24). Lauroyl chloride (10 mL, 42 mmol, 1 equiv) was dissolved in diethyl ether (75 mL) and the solution was cooled on an ice bath. Et3N (5.82 mL, 42 mmol, 1 equiv) was then added dropwise and the reaction mixture was stirred on an ice bath for one hour. The stirring was then discontinued and the reaction mixture was left at room temperature overnight. The reaction mixture was transferred to a separatory funnel, washed with 2 % sulfuric acid (2× 30 mL) and the solvents were removed under reduced pressure. 2 % KOH solution (60 mL) was added to the residue, the mixture was heated to the boiling point and then cooled on an ice bath. The waxy cake that formed on top of the aqueous layer was collected, washed with water and dried to yield the desired product (58 %) as a white solid.

S2. NMR data
Nuclear magnetic resonance spectra were measured on a Bruker Avance III NMR spectrometer at 400 MHz for proton spectra and at 101 MHz for carbon 13 spectra, using deuterated chloroform (CDCl3) as solvent. As internal standard it was used the residual nondeuterated solvent peak (chloroform, CHCl3).

S3. High resolution mass spectrometry data
High resolution mass spectrometry measurements were performed on a Thermo Scientific QExactive Plus mass spectrometer with ESI ionisation.

S4. Representative HPLC chromatograph of orlistat
For measuring concentrations of orlistat to determine the drug loading and drug release profile HPLC was used as described within methods. As shown in Figure S9 typical retentive time of orlistat is 4.390 minutes. Area under the curve or height of the peak is related to the concentration of orlistat, which enables calculating the concentration of it according to standard samples with known concentration. Figure S9: Representative HPLC chromatograph of orlistat.

S5. Zeta-potential measurements
Both magnetic nanocarrier suspensions were monitored with the measurements of their zetapotentials by laser Doppler anemometry using the Zetasizer Nano ZS (Malvern Instruments, UK). The graphs in Figure S10 show representative distributions of apparent zeta-potentials. Figure S10: Representative zeta-potential distributions for the formulations MC-B4 (A) and MC-SP11 (B).

S6. Determination of the hydrodynamic sizes of magnetic nanocarriers
The determination of the hydrodynamic size of magnetic nanocarriers was performed by photon correlation spectroscopy using Zetasizer Nano ZS (Malvern Instruments, UK). Each individual sample was measured three-times and the corresponding standard deviations (SD) were calculated. The intensity-weighted distributions of the hydrodynamic sizes including SDs for both samples are shown in Figure S11 and Figure S12.  MC-SP11