We demonstrate control of multiscale structure and drug delivery function for paclitaxel (PAX)-loaded polycaprolactone-block-poly(ethylene oxide) (PCL-b-PEO) polymeric nanoparticles (PNPs) via synthesis and flow-directed shear processing in a two-phase gas-liquid microfluidic reactor. This strategy takes a page from the engineering of commodity plastics, where processing rather than polymer chemistry provides an experimental handle on properties and function. PNPs formed from copolymers with three different PCL block lengths show sizes, morphologies, and loading efficiencies that depend on both the PCL block length and the microfluidic flow rate. By varying flow rate and comparing with a conventional bulk method of PNP preparation, we show that flow-variable shear processing provides control of PNP sizes and morphologies and enables slower PAX release times (up to 2 weeks) compared to bulk-prepared PNPs. Antiproliferative effects against cultured MCF-7 breast cancer cells were greatest for PNPs formed at an intermediate flow rate, corresponding to small and low-polydispersity spheres formed uniquely at this flow condition. Formation and flow-directed nanoscale shear processing in gas-liquid microfluidic reactors provides a manufacturing platform for drug delivery PNPs that could enable more effective and selective nanomedicines through multiscale structural control.

Hierarchical block copolymer self-assembly is used to produce "polyplex-in-hydrophobic-core" (PIHC) micelles for gene delivery. The unique PIHC micelle structure provides nuclease protection and controlled release by embedding nucleic acids in the micelle core surrounded by condensed hydrophobic polymer chains. PIHC micelles are generated through a simple, two-step process using commercially available polymers: (1) electrostatic binding between the nucleic acid cargo and poly(ε-caprolactone)block-poly(2-vinyl pyridine) (PCL-b-P2VP) (SA1), followed by (2) microprecipitation of the polyplex with poly(ε-caprolactone)block-poly(ethylene glycol) (SA2). The resulting vectors possess poly(ethylene glycol) (PEG) coronae and nucleic acid−P2VP polyplexes embedded within condensed PCL hydrophobic cores. Using a two-phase microfluidic reactor for the SA2 step, we produce mainly spherical PIHC micelles with ∼30 nm PCL cores and ∼15 nm PEG shells. Plasmids encapsulated in PIHC micelles show resistance to DNase I degradation compared to plasmids located outside the micelle cores. PIHC micelles containing pUC18 show enhanced transformation efficiencies in competent Escherichia coli with a linear time dependence over 8 h associated with slow plasmid release via hydrolytic degradation of PCL cores. Finally, we show that PIHC micelles are readily taken into the cytosol of MDA-MB-231 (human breast cancer) cells.

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Microfluidic manufacturing of advanced gene delivery vectors necessitates consideration of the effects of microfluidic shear forces on the structural integrity of plasmid DNA (pDNA). In this paper, we expose pDNA to variable shear forces in a two-phase, gas–liquid microfluidic reactor and apply gel electrophoresis to analyze the products of on-chip shear-induced degradation. The effects of shear rate, solvent environment, pDNA size, and copolymer complexation on shear-induced degradation are investigated. We find that small naked pDNA (pUC18, 2.7 kb) exhibits shear rate-dependent shear degradation in the microfluidic channels in a mixed organic solvent (dioxane/water/acetic acid; 90/10/<0.1 w/w/w), with the extents of both supercoil isoform relaxation and complete fragmentation increasing as the maximum shear rates increase from 4 × 105 to 2 × 106 s–1. However, over the same range of shear rates, the same pDNA sample shows no evidence of microfluidic shear-induced degradation in a pure aqueous environment. Quiescent control experiments in the same mixed organic solvent prove that a combination of solvent and shear forces is involved in the observed shear-induced degradation. Furthermore, we show that shear degradation effects in mixed organic solvents can be significantly attenuated by complexation of pDNA with the block copolymer polycaprolactone-block-poly­(2-vinylpyridine) prior to exposure to microfluidic shear. Finally, we demonstrate that medium (pDSK519, 8.1 kb) and large (pRK290, 20 kb) naked pDNA are more sensitive to shear-induced microfluidic degradation in the mixed organic solvent environment than small pDNA, with both plasmids showing complete fragmentation even at the lowest shear rate, although we found no evidence of shear-induced damage in water for the largest investigated naked pDNA even at the highest flow rate. The resulting understanding of the interplay of the solvent and shear effects during microfluidic processing should inform microfluidic manufacturing routes to new gene therapy formulations.