Electrospray deposition (ESD) is a promising technique for depositing micro-/nano-scale droplets and particles with high quality and repeatability. It is particularly attractive for surface coating of costly and delicate biomaterials and bioactive compounds. While high efficiency of ESD has only been successfully demonstrated for spraying surfaces larger than the spray plume, this work extends its utility to smaller surfaces. It is shown that by architecting the local “charge landscape”, ESD coatings of surfaces smaller than plume size can be achieved. Efficiency approaching 100% is demonstrated with multiple model materials, including biocompatible polymers, proteins, and bioactive small molecules, on both flat and microneedle array targets. UV-visible spectroscopy and high-performance liquid chromatography measurements validate the high efficiency and quality of the sprayed material. Here, we show how this process is an efficient and more competitive alternative to other conformal coating mechanisms, such as dip coating or inkjet printing, for micro-engineered applications.

Electrospray deposition (ESD) uses charged droplets at the micro- and nano-scale to create a wide variety of particles and coatings. In ESD, an electrostatic force is applied to a solution, which then disperses charged droplets loaded with the materials to be deposited on a grounded target. Because the droplets carry charge, repulsive effects due to accumulation of charge in a coating (self-limiting electrospray) or “crowding” of the spray droplets can reduce the efficiency of the approach. This is especially the case when the targets are smaller than the characteristic size of the spray plume. For this reason, while many studies have presumed high efficiency in ESD, the actual measured efficiencies for small targets are much lower. Here, it is shown how architecting the local “charge landscape” can lead to ESD coatings approaching 100% deposition efficiency on both flat and microneedle array targets composed of multiple model materials, including biocompatible polymers, proteins, and bioactive small molecules. In this way, ESD can be considered a viable alternative to other conformal approaches, such as dip or inkjet coating.

Electrospray deposition (ESD) is a promising technique for depositing micro- and nano-scale droplets and particles with high quality and uniformity. It is a particularly attractive solution for surface coating of costly and delicate biomaterials and bioactive compounds. While high efficiency of ESD has only been successfully demonstrated for spraying surfaces larger than the spray plume, this work extends its utility to smaller surfaces. It is shown that by architecting the local “charge landscape”, ESD coatings of surfaces smaller than plume size can be achieved. Efficiency approaching 100% is demonstrated with multiple model materials, including biocompatible polymers, proteins, and bioactive small molecules, on both flat and microneedle array targets. UV-visible spectroscopy and HPLC measurements validate the high efficiency and quality of the sprayed material. This protocol for ESD can be considered an efficient and more competitive alternative to other conformal coating mechanisms, such as dip coating or inkjet printing, for micro-engineered applications.