Inverted Quasi-Spherical Droplets on Polydopamine–TiO₂ Substrates for Enhancing Gene Delivery

Devising efficient gene delivery systems is crucial to enhancing the therapeutic efficacy of gene–cell therapy approaches. Herein, inverted quasi-spherical (iQS) droplet systems, which enhance gene delivery efficiencies by reducing the path lengths of gene vectors, mediating motions of vectors at early stages, and raising the contact frequencies of vectors with cells, are developed by adopting the principle of 3D hanging-drop cell culture. Micrometer-sized polydopamine (pDA) holes are created on superhydrophobic titanium isopropoxide (TiO₂)-coated substrates by physical scraping; droplets are loaded on the pDA holes, and inversion of the substrate generates iQS droplets with large contact angles. Both human neural stem cells (hNSCs) and adeno-associated viral vectors are simultaneously incorporated into the iQS droplets to assess gene delivery efficiencies. The steep angles of iQS droplets and enhanced cell/vector contact frequencies facilitate the viral association with hNSCs and enhancing cell–cell interactions, thereby significantly promoting gene delivery efficiencies. Even with reduced viral quantities/exposure times and cell numbers, the iQS droplet systems elicit sufficient gene expression (i.e., interleukin-10). The ability of the iQS droplet systems to maximize beneficial gene delivery effects with minimal materials (e.g., medium, cells, and vectors) should enable their extensive use as a platform for preparing genetically stimulated cellular therapeutics.