Efficient electrospray deposition of surfaces smaller than the spray plume.

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.

A click chemistry-based, free radical-initiated delivery system for the capture and release of payloads.

Click chemistries are efficient and selective reactions that have been leveraged for multi-stage drug delivery. A multi-stage system allows independent delivery of targeting molecules and drug payloads, but targeting first-phase materials specifically to disease sites remains a challenge. Stimuli-responsive systems are an emerging strategy where common pathophysiological triggers are used to target payloads. Oxidative stress is widely implicated in disease, and we have previously demonstrated that reactive oxygen species (ROS) can crosslink and immobilize polyethylene glycol diacrylate (PEGDA) in tissue mimics. To build on these promising results, we present a two-step, catch-and-release system using azide-DBCO click chemistry and demonstrate the capture and eventual release of a fluorescent payload at defined times after the formation of a PEGDA capturing net. The azide component is included with radical-sensitive PEGDA, and the payload is conjugated to the DBCO group. In cell-free and cell-based tissue mimic models, azides were incorporated at 0-30% in the first-phase polymer net, and DBCO was delivered at 2.5-10 µM in the second phase to control payload delivery. The payload could be captured at multiple timepoints after initial net formation, yielding a flexible and versatile targeting system. Matrix metalloproteinase (MMP)-degradable peptides were incorporated into the polymer backbone to engineer fluorescent payload release by MMPs, which are broadly upregulated in diseases, through degradation of the capture net and directly from the DBCO. Taken together, this research demonstrates proof-of-principle for a responsive and clickable biomaterial to serve as a multi-potent agent for the treatment of diseases compounded by high free radicals.

Alternative Chemistries for Free Radical-Initiated Targeting and Immobilization.

Stimuli-responsive biomaterials are an emerging strategy that leverage common pathophysiological triggers to target drug delivery to limit or avoid toxic side effects. Native free radicals, such as reactive oxygen species (ROS), are widely upregulated in many pathological states. We have previously demonstrated that native ROS are capable of crosslinking and immobilizing acrylated polyethylene glycol diacrylate (PEGDA) networks and coupled payloads in tissue mimics, providing evidence for a potential targeting mechanism. To build on these promising results, we evaluated PEG dialkenes and dithiols as alternative polymer chemistries for targeting. The reactivity, toxicity, crosslinking kinetics, and immobilization potential of PEG dialkenes and dithiols were characterized. Both the alkene and thiol chemistries crosslinked in the presence of ROS, generating high molecular weight polymer networks that immobilized fluorescent payloads in tissue mimics. Thiols were especially reactive and even reacted with acrylates in the absence of free radicals, and this motivated us to explore a two-phase targeting approach. Delivering thiolated payloads in a second phase, after the initial polymer net formation, allowed greater control over the payload dosing and timing. Two-phase delivery combined with a library of radical-sensitive chemistries can enhance the versatility and flexibility of this free radical-initiated platform delivery system.

Free radical-mediated targeting and immobilization of coupled payloads.

Targeted drug delivery is a promising approach to enhance the accumulation of therapies in diseased tissues while limiting off-site effects. Ligand-receptor interactions are traditionally identified to deliver therapies, and although specific, this can be costly and often suffers from limited sensitivity. An emerging approach is to target intermediary species that modulate disease progression. Here, we propose novel methods of targeting therapies by using native free radicals as a homing signal. Elevated concentrations of free radicals are a characteristic comorbidity of many different diseases. In polymer chemistry, free radicals are frequently used to initiate crosslinking reactions. We proposed that free radicals elevated in injury sites are capable of inducing crosslinking of acrylate groups on polymer chains. Coupling payloads to the polymer then allow for specific targeting of therapies to areas with elevated free radicals. We demonstrate in vitro proof-of-principle of this approach. Reactive oxygen species (ROS) initiated crosslinking of acrylated PEGs, which immobilized a fluorescent payload within tissue mimics. The cross-linking efficiency and immobilization potential varied with the polymer chain length, suggesting that a tuneable platform can be achieved. Together these results provide promising proof-of-concept for using free radicals to specifically target and sustain nearly endless payloads to disease sites.