Hierarchal coatings for biological building blocks via electrospray deposition

Electrospray deposition (ESD) is a spray coating process that utilizes a high voltage to atomize a flowing solution into charged microdroplets. These self-repulsive droplets evaporate as they travel to a target grounded substrate, depositing the solution solids as thin films. These thin films can be utilized in biomedical applications including drug and therapeutics delivery in addition to the fabrication of medical implants and biosensors. Our lab has categorized various modes of ESD, including self-limiting electrospray deposition (SLED). In SLED, the material arrives onto a target as a dried spray, carrying a charge that eventually begins to repel itself over time. The charged spray is redirected to regions that are uncoated such that manipulation of the electrostatic repulsion, hydrodynamic forces, and evaporation kinetics can be employed to conformally cover 3D architectures with micro-coatings. The generated coatings are hierarchical, possessing either nano-shell, nanoparticle, or nanowire microstructure, which can be smoothed through further post processing. We envision SLED as being a replacement for dip or conventional-spray coating, where its greatest advantage would be the potential for much higher materials utilization. While many studies have presumed high efficiency in ESD, this is rarely quantified. Here, we show how architecting the local charge landscape can lead to SLED coatings approaching 100% deposition efficiency on microneedle arrays and other complex substrates of relevant therapeutics with the building blocks and signals for synthetic biology, including DNA vaccines, proteins, amino acids, bioactive small molecules, and biocompatible conductors.