Light-triggered switching of liposome surface charge directs delivery of membrane impermeable payloads in vivo

Surface charge plays a fundamental role in determining the fate of a nanoparticle, and any encapsulated contents, in vivo. Herein, we describe, and visualise in real time, light-triggered switching of liposome surface charge, from neutral to cationic, in situ and in vivo (embryonic zebrafish). Prior to light activation, intravenously administered liposomes, composed of just two lipid reagents, freely circulate and successfully evade innate immune cells present in the fish. Upon in situ irradiation and surface charge switching, however, liposomes rapidly adsorb to, and are taken up by, endothelial cells and/or are phagocytosed by blood resident macrophages. Coupling complete external control of nanoparticle targeting together with the intracellular delivery of encapsulated (and membrane impermeable) cargos, these compositionally simple liposomes are proof that advanced nanoparticle function in vivo does not require increased design complexity but rather a thorough understanding of the fundamental nano-bio interactions involved.


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All studies must disclose on these points even when the disclosure is negative. No statistical methods were used to calculate sample size. For all experiments in embryonic zebrafish, the sample size was >20. This sample size was determined based on similar reported studies and balances the practicalities involved in maintaining strict confocal imaging timeframes with the need for a large enough population to ensure reproducible results. Where liposome fate was analyzed before and after UV activation, the same injected embryo was imaged before and after UV irradiation.
With the exception of unsuccessfully injected embryos, no data was excluded from the analysis.
All experiments were repeated at least twice, with the exception of data presented in Figure 6b,c and Supplementary Figures 1 and 9. All replicate experiments were performed using freshly prepared liposomes. Unless clearly stated in the manuscript text (e.g. varying macrophage uptake prior to UV activation), all replicate experiments were successful and confirmed the presented data.
For all experiments in embryonic zebrafish, at least four embryos were randomly selected for imaging from a pool of >20 successfully injected embryos.
Blinding was not applied in this proof-of-concept study as all experiments were performed without prior knowledge of the experimental outcome. Key results were observed by more than two different investigators. This study does not involve wild animals.
This study does not involve samples collected from the field.
Adult zebrafish (Danio rerio, strain AB/TL) were maintained and handled according to the guidelines described in (Aleström, P. et al. Zebrafish: Housing and husbandry recommendations. Lab. Anim. (2019)) and in compliance with the directives of the local animal welfare committee of Leiden University. No ethical approval was required for experiments in embryonic zebrafish as all embryos used in this study were < 120 hours post-fertilisation.