The epidermal growth factor receptor (EGFR) is overexpressed on a high percentage of human carcinomas. EGFR is an attractive therapeutic target for tissue-specific targeting by non-viral vectors in cancer gene therapy. In this study we analyzed and compared the effects of EGFR-targeted and untargeted polyplexes in respect to internalization into EGFR overexpressing HuH7 cells. Uptake kinetics and internalization dynamics were evaluated by flow cytometry and single-particle tracking. Our results clearly show that EGFR targeting leads to faster and more efficient internalization compared with untargeted particles. After 5 minutes 50% of the EGFR-targeted polyplexes were internalized, whereas untargeted polyplexes reached only approximately 20% internalization even after 20 minutes. In addition, single-particle tracking revealed a three-phase dynamics of the internalization process, and this was generally observed for polyplexes independent of targeting. Phase I was characterized by slow, actin cytoskeleton-mediated movement of the particles with drift, and included the internalization process. During phase II particles displayed increased velocities with normal and confined diffusion in the cytoplasm. Phase III was characterized by fast active transport along microtubules. Targeting of polyplexes for receptor-mediated endocytosis by the EGFR resulted in shortening of phase I and strongly accelerated internalization.

When a droplet hits a surface fast enough, droplet splashing can occur: Smaller secondary droplets detach from the main droplet during impact. While droplet splashing on smooth surfaces is by now well understood, the surface roughness also affects at which impact velocity a droplet splashes. In this paper, the influence of the surface roughness on droplet splashing is investigated. By changing the root-mean-square roughness of the impacted surface, we show that the droplet splashing velocity is only affected when the droplet roughness is large enough to disrupt the spreading droplet lamella and change the droplet splashing mechanism from corona to prompt splashing. Finally, using Weber and Ohnesorge number scaling models, we also show that the measured splashing velocity for both water and ethanol on surfaces with different roughnesses and water-ethanol mixtures collapses onto a single curve, showing that the droplet splashing velocity on rough surfaces scales with the Ohnesorge number defined with the surface roughness length scale.

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