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<p>The success of gene medicine ultimately depends on the efficient intracellular
delivery and sustained expression of nucleic acid therapeutics, yet nonviral gene
delivery performed with cationic polymer carriers has been chronically hindered by
the slow release of nucleic acid payloads at their targets, as well as the transient
nature of exogenous transgene expression. Polymer-nucleic acid nanocomplexes made
with passive gene carriers using traditional bulk methods have proven inadequate for
most translational applications. The objective of this work is to improve nonviral
gene delivery through the selection, formulation, and application of improved nanoparticles.
</p><p> After screening a number of number of cationic polymer delivery systems
ranging from natural to synthetic, high molecular weight to low, binary and ternary,
we identified a bioreducible linear poly(amido amine) able to give sustained, robust
expression of both DNA and RNA through serial dosing. We next turned our attention
to the process of nanocomplex assembly. Traditional assembly via bulk mixing is poorly
controlled, and the poor quality of these nanocomplexes is a significant impediment
to both the establishment of robust structure-function relationships and the advancement
of nonviral gene delivery. So, we developed an emulsion-based microfluidic nanomanufacturing
platform to better control the self-assembly process, and thus the physical properties
of nanocomplexes. Confined mixing within picoliter droplets generates self-assembled
nanocomplexes that are more uniform and more effective. This microfluidic nanomanufacturing
approach possesses broad utility in the production of polymer-nucleic acid nanocomplexes;
we demonstrated that its benefits extend to multiple gene carriers, a range of nucleic
acid payloads, and translationally relevant cell types. Then, we applied the improved
nanomanufactured particles to begin to address an unmet clinical need, namely the
lack of a safe and ethical source of cells to treat neurodegenerative diseases. Nonviral
cellular reprogramming strategies eliminate the integration of viral DNA sequences
and represent a potentially safer alternative to viral transdifferentiation methods
to generate therapeutic cells. Using nanomanufactured polymer-nucleic acid nanocomplexes,
we improved the efficiency of the nonviral cellular reprogramming of fibroblasts directly
to functional induced neuronal cells. </p><p> Nonviral gene therapy will continue
to demand more sophisticated delivery systems to continue to progress. Microfluidic
nanomanufacturing represents a reproducible and scalable platform to synthesize more
uniform and effective nanocomplexes that not only improves their functional performance,
but may also help establish clearer structure-function relationships that will inform
future gene carrier design. Complementing the innovative chemical and biological approaches
to create multifunctional nanoparticles, this study indicates that microfluidic nanomanufacturing
can serve as a parallel physical strategy to both optimize the properties of polymer-nucleic
acid nanocomplexes and improve their performance in applications with important clinical
implications.</p>
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