Tailored Mesoporous Silica Nanoparticles and the Chick Chorioallantoic Membrane: A Promising Strategy and Model for Efficient Blood-Brain Barrier Crossing

Crossing the blood-brain barrier (BBB) remains a major challenge for brain-targeted drug delivery. Mesoporous silica nanoparticles (MSNs) with tunable size and surface properties are promising vehicles for crossing the BBB. In this study, we explored the potential applications of the chick chorioallantoic membrane (CAM) model in combination with nanotherapeutics. We synthesized ∼25 nm MSNs and RITC-conjugated MSNs (RMSNs) with short PEG chains and varying amounts of positively charged molecules, specifically tertiary amine (polyethylenimine, PEI) or quaternary amine (trimethylammonium, TA), to investigate the positive charge effects on BBB penetration. Strongly positively charged TA-modified RMSNs (s-RMSN@PEG/TA, where s denotes strongly positively charged) effectively crossed the chick embryo BBB, whereas PEI-modified RMSNs did not. Although the weakly positively charged formulation (w-MSN@PEG/TA, where w denotes weakly positively charged) exhibited higher Dox loading capacity and a faster release rate, s-MSN@PEG/TA demonstrated superior BBB penetration and drug permeability. Consistent with chick CAM results, RMSN@PEG/TA also penetrated the BBB in mice. Long-chain PEG-modified RMSN@PEG/TA (RMSN@PEG_(L)/TA, where L denotes long-chain PEG) showed reduced BBB penetration due to steric hindrance, possibly shielding TA molecules. This study highlights the effectiveness of optimizing short PEG chain density and TA modification for MSN-based BBB crossing without additional biological ligands. Furthermore, the chick CAM model proves to be a valuable alternative to mouse models for assessing BBB crossing of nanoparticles, offering significant research opportunities.