The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Complex coacervates can form through the electrostatic complexation of oppositely charged polymers. The material properties of the resulting coacervates can change based on the polymer chemistry and the complex interplay between electrostatic interactions and water structure, controlled by salt. We examined the effect of varying the polymer backbone chemistry using methacryloyl- and acryloyl-based complex coacervates over a range of polymer chain lengths and salt conditions. We simultaneously quantified the coacervate phase behavior and the linear viscoelasticity of the resulting coacervates to understand the interplay between polymer chain length, backbone chemistry, polymer concentration, and salt concentration. Time-salt superposition analysis was used to facilitate a broader characterization and comparison of the stress relaxation behavior between different coacervate samples. Samples with mismatched polymer chain lengths highlighted the ways in which the shortest polymer chain can dominate the resulting coacervate properties. A comparison between coacervates formed from methacryloyl vs acryloyl polymers demonstrated that the presence of a backbone methyl group affects the phase behavior, and thus the rheology in such a way that coacervates formed from methacryloyl polymers have a similar phase behavior to those of acryloyl polymers with ∼10× longer polymer chains.

Sulfonium sulfonate, or sulfothetin, zwitterionic monomers were synthesized by ring-opening of 1,3-propanesultone with dialkyl sulfides containing styrenic or methacrylic moieties. Reversible addition-fragmentation chain-transfer polymerization of these monomers was achieved in water or trifluoroethanol, and the resulting polymers exhibited higher upper critical solution temperatures than the analogous sulfobetaine polymers. Unlike typical polymer zwitterions, these polymeric sulfothetins possess an inherent reactivity that proved tunable based on their chemical structures. This reactivity makes them amenable to post-polymerization modification by nucleophilic dealkylation to rapidly access novel substituted polymers and gels. V C 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 83-92

Polymer zwitterions are generally regarded as hydrophilic and repellant or "slippery" materials. Here, a case is described in which the polymer zwitterion structure is tailored to decrease water solubility, stabilize emulsion droplets, and promote interdroplet adhesion. Harnessing the upper critical solution temperature of sulfonium- and ammonium-based polymer zwitterions in water, adhesive droplets are prepared by adding organic solvent to an aqueous polymer solution at elevated temperature, followed by agitation to induce emulsification. Droplet aggregation is observed as the mixture cools. Variation of salt concentration, temperature, polymer concentration, and polymer structure modulates these interdroplet interactions, resulting in distinct changes in emulsion stability and fluidity. Under attractive conditions, emulsions encapsulating 50-75% oil undergo gelation. By contrast, emulsions prepared under conditions where droplets are nonadhesive remain fluid and, for oil fractions exceeding 0.6, coalescence is observed. The uniquely reactive nature of the selected zwitterions allows their in situ modification and affords a route to chemically trigger deaggregation and droplet dispersion. Finally, experiments performed in a microfluidic device, in which droplets are formed under conditions that either promote or suppress adhesion, confirm the salt-responsive character of these emulsions and the persistence of adhesive interdroplet interactions under flow.

Polymer-based gene delivery relies on the binding, protection, and final release of nucleic acid cargo using polycations. Engineering polymeric vectors, by exploring novel topologies and cationic moieties, is a promising avenue to improve their performance, which hinges on the development of simple synthetic methods that allow facile preparation. In this work, we focus on cationic micelles formed from block polymers, which are examined as promising gene compaction agents and carriers. In this study, we report the synthesis and assembly of six amphiphilic poly(n-butyl acrylate)-b-poly(cationic acrylamide) diblock polymers with different types of cationic groups ((dialkyl)amine, morpholine, or imidazole) in their hydrophilic corona. The polycations were obtained through the parallel postpolymerization modification of a poly(n-butyl acrylate)-b-poly(pentafluorophenyl acrylate) reactive scaffold, which granted diblock polymers with equivalent degrees of polymerization and subsequent quantitative functionalization with cations of different pK a . Ultrasound-assisted direct dissolution of the polycations in different aqueous buffers (pH = 1−7) afforded micellar structures with low size dispersities and hydrodynamic radii below 100 nm. The formation and properties of micelle−DNA complexes ("micelleplexes") were explored via DLS, zeta potential, and dye-exclusion assays revealing that binding is influenced by the cation type present in the micelle corona where bulkiness and pK a are the drivers of micelleplex formation. Combining parallel synthesis strategies with simple direct dissolution formulation opens opportunities to optimize and expand the range of micelle delivery vehicles available by facile tuning of the composition of the cationic micelle corona.

Antisense oligonucleotides (ASOs) are an important emerging therapeutic; however, they struggle to enter cells without a delivery vehicle, such as a cationic polymer. To understand the role of polymer architecture for ASO delivery, five linear polymers and five diblock polymers (capable of self-assembly into micelles) were synthesized with varying cationic groups. After complexation of each polymer/micelle with ASO, it was found that less bulky cationic moieties transfected the ASO more effectively. Interestingly, however the ASO internalization trend was the opposite of the transfection trend for cationic moiety, indicating internalization is not the major factor in determining transfection efficiency for this series. Micelleplexes (micelle–ASO complexes) generally enable higher transfection efficacy as compared to polyplexes (linear polymer–ASO complexes). Additionally, the order of addition of cells and complexes was explored. Linear polyplexes showed better transfection efficiency in adhered cells, whereas micelleplexes delivered the ASO more efficiently when the cells and micelleplexes were added simultaneously. This phenomenon may be due to increased cell-complex interactions as micelleplexes have increased colloidal stability compared to polyplexes. These findings emphasize the importance of polymer composition and architecture in governing the cellular interactions necessary for transfection, thus allowing advancement in the design principles for nonviral nucleic acid delivery formulations.

Oil-in-water droplets stabilized with polymer zwitterions (PZWs) exhibit salt-responsive aggregationdisaggregation behavior. In this paper, we describe a method to shape these droplets, starting from their aggregated state, into supracolloidal fibers by simply extruding them into aqueous media. The effect of salt concentration, in both the initial emulsion and the aqueous media, on the ability of the emulsions to form fibers is examined. After fiber formation, a transition from well-defined macroscopic fibers to non-interacting droplet dispersions can be triggered, simply by increasing the salt concentration of the aqueous environment. The inter-droplet energy of adhesion and emulsion rheology correlate qualitatively with salt concentration and thus impact the ability of the emulsions to be shaped by extrusion. The inter-droplet adhesion is dependent on both salt concentration and polymer composition, which allows tailoring of conditions to trigger fiber disaggregation. Finally, fibers with variable compositions along their length are prepared by sequential loading and extrusion of emulsions containing oil phases of differing densities.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

The ability to safely and precisely deliver genetic materials to target sites in complex biological environments is vital to the success of gene therapy. Numerous viral and nonviral vectors have been developed and evaluated for their safety and efficacy. This study will feature progress in synthetic polymers as nonviral vectors, which benefit from their chemical versatility, biocompatibility, and ability to carry both therapeutic cargo and targeting moieties. The combination of synthetic gene carrying constructs with advanced delivery techniques promises new therapeutic options for treating and curing genetic disorders. This article is characterized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies