Background: Nanoparticles (NPs) suffer from rapid clearance from body and require frequent
dosing if long treatment is required.
Method: In order to solve this problem for solid lipid nanoparticles (SLN) and prolong their action,
SLNs were incorporated into thermo-responsive Poloxamer sol-gels and their fate was investigated invivo
and in-vitro using a near infrared lipophilic fluorescent dye; dialkylcarbocyanin . Leakage test,
release of intact SLNs from sol-gel and SLN size and zeta potential were investigated. Biodistribution
of DiR formulations (solution, free SLN and SLN-Gel) was investigated by whole-body and ex-vivo
organ imaging after intraperitoneal injection in mice. SLN showed particle size of about 165 nm and a
negative zeta potential of about -36 mV.
Results: Leakage studies indicated that fluorescent probe does not release from SLNs. Imaging results
revealed a steady profile for SLN-Gel over time, while the fluorescence intensity of solution and free
SLN showed a burst followed by rapid clearance. Results also showed that SLN release occurs after gel
erosion and follows a zero order profile.
Conclusion: Our results indicate that NP-incorporated gel can be used to control the release of SLNs
from application site and prolong their action in a sustained manner.
Keywords: Controlled release, fluorescence reflectance imaging, in-situ forming gels, solid lipid nanoparticle, SLN, thermoresponsive,
tissue imaging, whole-body imaging.
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