Degradable thiomethacrylate core-crosslinked star-shaped polymers

Degradable polymers are considered to present a promising solution to combat plastic pollution. However, many polymers are based on ester and amide bonds, which often require high temperatures and acidic/basic...

Dynamic Manipulation of DNA-Programmed Crystals Embedded in a Polyelectrolyte Hydrogel

DNA is a powerful tool for programming the three-dimensional organization of nanomaterials, where the specificity of nucleotide base-pairing can enable precise, complex, and dynamically addressable structures like colloidal crystals. However, because these DNA-programmed materials are often only stable in solution, their organization can be easily disrupted by changes to its local environment. Methods to stabilize these materials have been developed, but often come at the expense of altering or permanently fixing the materials' structures, removing many of the benefits of using DNA interactions to program assembly. Thus, these methods limit the application of DNA-assembled structures as dynamic and programmable material components. Here, a method is presented to resolve these drawbacks for DNA-grafted nanoparticles, also known as Programmable Atom Equivalents (PAEs), by embedding assembled lattices within a hydrogel matrix. The preformed lattices are exposed to polymerizable residues that electrostatically bind to the charged backbone of the DNA ligands and form a continuous, permeating gel network that stabilizes the colloidal crystals upon introduction of a radical initiator. After embedding PAEs in a hydrogel, deformation of the macroscopic matrix results in concomitant deformation of the PAE lattices, allowing superlattice structural changes to be induced by chemical methods (such as changing solute concentration to alter swelling pressure) or by application of mechanical strain. Changes to the structure of the PAE lattices are reversible and repeatable over multiple cycles and can be either isotropic (such as by swelling) or anisotropic (such as by mechanical deformation). This method of embedding nanoparticle crystals inside of a flexible and environmentally responsive hydrogel is therefore a useful tool in extending the utility of PAEs and other micro- and nanostructures assembled with DNA.

Charge-Shifting Polycations Based on N,N-(dimethylamino)ethyl Acrylate for Improving Cytocompatibility During DNA Delivery

Synthetic polycations are studied extensively as DNA delivery agents because of their ease of production, good chemical stability, and low cost relative to viral vectors. This report describes the synthesis of charge-shifting polycations based on N,N-(dimethylamino)ethyl acrylate (DMAEA) and 3-aminopropylmethacryamide (APM), called PAD copolymers, and their use for in vitro DNA delivery into HeLa cells. PAD copolymers of varying compositions were prepared by RAFT polymerization to yield polymers of controlled molecular weights with low dispersities. Model hydrolysis studies were carried out to assess the rate of charge-shifting of the polycations by loss of the cationic dimethylaminoethanol side chains. They showed reduction in the net cationic charge by about 10-50% depending on composition after 2 days at pH 7, forming polyampholytes comprising permanent cationic groups, residual DMAEA, as well as anionic acrylic acid groups. HeLa cells exposed for 4 h to PAD copolymers with the greatest charge-shifting ability showed comparable or higher viability at high concentrations, relative to the noncharge shifting polycations PAPM and polyethyleneimine (PEI) 2 days post-exposure. Cell uptake efficiency of PAD/60bp-Cy3 DNA polyplexes at 2.5:1 N/P ratio was very high (>95%) for all compositions, exceeding the uptake efficiency of PEI polyplexes of equivalent composition. These results suggest that these PAD copolymers, and in particular PAD80 containing 80 mol % DMAEA, have suitable rates of charge-shifting hydrolysis for DNA delivery, as PAD80 showed reduced cytotoxicity at high concentrations, while still retaining high uptake efficiencies. In addition, the polyampholytes formed during DMAEA hydrolysis in PAD copolymers can offer enhanced long-term cytocompatibility.

Hydrogen-Bond Cyclization Programming of Ultrasensitive Esters and Its Application in Gene Delivery

The ester bond as a universal linker has recently been applied in gene delivery systems owing to its efficient gene release by electrostatic repulsion after its cleavage. However, the ester bond is nonlabile and is difficult to cleave in cells. This work reports a method in which a secondary amine was introduced to the β-position of the ester bond to generate a hydrogen-bond cyclization (HBC) structure that can make the ester bond hydrolysis ultrafast. A series of molecules comprising ultrasensitive esters that can be activated by H₂ O₂ were synthesized, and it was found that those able to form an HBC structure showed complete ester hydrolysis within 5 h in both water and phosphate-buffered saline solution, which was several times faster than other methods reported. Then, a series of amphiphilic poly(amidoamine) dendrimers were constructed, comprising the ultrasensitive ester groups for gene delivery; it was found that they could effectively release genes under quite a low concentration of H₂ O₂ (<200 μm) and transport them into the nucleus within 2 h in Hela cells with high safety. Their gene transfection efficiencies were higher than that of PEI_25k . The results demonstrated that the hydrogen-bond-induced ultrasensitive esters could be powerfully applied to construct gene delivery systems.

Efficient Binding, Protection, and Self-Release of dsRNA in Soil by Linear and Star Cationic Polymers

Double stranded RNA (dsRNA) exhibits severe degradation within 3 days in live soil, limiting its potential application in crop protection. Herein we report the efficient binding, protection, and self-release of dsRNA in live soil through the usage of a cationic polymer. Soil stability assays show that linear poly(2-(dimethylamino)ethyl acrylate) can delay the degradation of dsRNA by up to 1 week while the star shaped analogue showed an increased stabilization of dsRNA by up to 3 weeks. Thus, the architecture of the polymer can significantly affect the lifetime of dsRNA in soil. In addition, the hydrolysis and dsRNA binding and release profiles of these polymers were carefully evaluated and discussed. Importantly, hydrolysis could occur independently of environmental conditions (e.g., different pH, different temperature) showing the potential for many opportunities in agrochemicals where protection and subsequent self-release of dsRNA in live soil is required.

Exploring the Long-Term Hydrolytic Behavior of Zwitterionic Polymethacrylates and Polymethacrylamides

The hydrolytic stability of polymers to be used for coatings in aqueous environments, for example, to confer anti-fouling properties, is crucial. However, long-term exposure studies on such polymers are virtually missing. In this context, we synthesized a set of nine polymers that are typically used for low-fouling coatings, comprising the well-established poly(oligoethylene glycol methylether methacrylate), poly(3-(N-2-methacryloylethyl-N,N-dimethyl) ammoniopropanesulfonate) ("sulfobetaine methacrylate"), and poly(3-(N-3-methacryamidopropyl-N,N-dimethyl)ammoniopropanesulfonate) ("sulfobetaine methacrylamide") as well as a series of hitherto rarely studied polysulfabetaines, which had been suggested to be particularly hydrolysis-stable. Hydrolysis resistance upon extended storage in aqueous solution is followed by ¹H NMR at ambient temperature in various pH regimes. Whereas the monomers suffered slow (in PBS) to very fast hydrolysis (in 1 M NaOH), the polymers, including the polymethacrylates, proved to be highly stable. No degradation of the carboxyl ester or amide was observed after one year in PBS, 1 M HCl, or in sodium carbonate buffer of pH 10. This demonstrates their basic suitability for anti-fouling applications. Poly(sulfobetaine methacrylamide) proved even to be stable for one year in 1 M NaOH without any signs of degradation. The stability is ascribed to a steric shielding effect. The hemisulfate group in the polysulfabetaines, however, was found to be partially labile.