Systematic study of hydrophobic and hydrophilic modifications to poly(N-isopropylacrylamide) elucidates design rules for control over cloud point and aqueous self-assembly.

Herein, we report a family of mechanically tunable, nonswellable hydrogels that are based on a 2hydroxyethylcellulose (HEC) scaffold grafted with amphiphilic diblock copolymers. Poly[(oligo(ethylene glycol)methyl ether methacrylate]-b-poly(methyl methacrylate) (POEGMA-b-PMMA) diblock copolymers of different compositions were created via RAFT polymerization using an alkyne terminated macro chain transfer agent (CTA). 2-Hydroxyethylcellulose (HEC) was modified with azide groups and the diblock copolymers were attached to the backbone via the coppercatalyzed click reaction to yield HEC-g-(POEGMA-b-PMMA) graft terpolymers. The resulting conjugates were soluble in DMF and able to form hydrogels upon simple solvent exchange in water. By increasing the concentration of the conjugates in DMF, the storage moduli of the hydrogels increased and the pore size in the gel decreased. After hydrogel formation, the structures were also found to be nonswellable (no macroscopic volume change upon incubation in water), which is an important feature for retaining size and mechanical integrity of the gels over time. Moreover, these materials were able to be electrospun into fibers that, upon hydration, formed fibrous hydrogel structures. The nonswellable and tunable mechanical properties of these materials imply great potential for a variety of applications such as personal care, active delivery, and tissue engineering.

We examine connections among polycation composition, DNA-polycation binding thermodynamics, binding strength, and resulting complex properties, for circular and linear DNA and hydrophilic diblock copolymers possessing cationic blocks. Two poly(2-deoxy-2-methacrylamido glucopyranose)-block-poly(N-(2-aminoethyl) methacrylamide) (PMAG-b-PAEMA), with block degrees of polymerization of PMAG56-b-PAEMA30 and PMAG52-b-PAEMA63, are employed. DNA binding behavior of these diblocks is also compared with that of a PAEMA homopolymer, in order to evaluate the role of the hydrophilic, charge-neutral PMAG block. In addition, DNA structure was varied, utilizing both circular and linear DNA with the same contour length. The enthalpy change due to DNA-polycation interactions (ΔH) is observed via isothermal titration calorimetry (ITC) during titrations of DNA with the polycations. With circular DNA, a higher cationic content is found to result in a completion of binding with a smaller amount of polycation, as well as a larger initial ΔH. In contrast to the common understanding that a neutral block simply provides colloidal stability, the PMAG block turns out to significantly impact both the extent of the binding and the size and dispersity of the final complexes. With a lower cationic content, the complex is less compact, but both the size and dispersity are more stable. Changes in circular dichroism spectra of DNA are shown to be correlated with PMAG-to-PAEMA block length ratio. PMAG52-b-PAEMA63 leads to stronger binding with DNA, compared to PMAG56-b-PAEMA30. Better-defined polyplexes and more disruption in the DNA helices are observed when the PMAG-to-PAEMA ratio is lower. All in all, while PMAG itself does not directly interact with DNA, the DNA-polycation binding turns out to be sensitive to the balance between the DNA-PAEMA attraction and PMAG solvation. In addition, it is confirmed that polyelectrolyte complexation is favored both entropically and enthalpically when the ionic strength of the solution is low. While only endothermic interactions occur in the buffered systems, exothermic initial interactions are observed in low-salt, unbuffered cases. Finally, complexes formed with linear DNA show clear bimodal size distributions, distinct from those formed with circular DNA. Collectively, these data provide insights into the controllable parameters in DNA-polycation complexation, which may advance the development of polymeric vehicles for large biomolecules such as nucleic acids.

In this work, isothermal titration calorimetry (ITC) is employed as an affinity agent screening method for the surface-enhanced Raman scattering (SERS) detection of aflatoxin B1 (AFB1). AFB1, a potent carcinogen produced by a fungus that infects crops, is an important target due to the monitoring required based on its FDA regulation. Polymer affinity agents, like those studied here, have the potential to enable separation and detection of relevant small molecules such as pesticides, drugs, and biological toxins, like AFB1, especially when paired with a vibrational spectroscopy technique such as SERS. Herein, seven homopolymers were synthesized to be evaluated as AFB1 affinity agents based on hypothetical hydrogen bonding interactions. Nitrogen-inclusive poly(N-(2-aminoethyl) methacrylamide) (pAEMA) polymers and their oxygen analogs, poly(2-hydroxyethyl methacrylate) (pHEMA) were evaluated. ITC was demonstrated as an effective method for rapid screening among the polymer affinity agents. Chain lengths between seven and 39 repeat units were synthesized to study length-based variance in affinity agent performance. An ITC method was optimized and used for the rapid screening of polymer affinity agents. The results were compared to those generated by SERS. Good agreement between the ITC results and follow-up SERS sensing experiments showcased ITC's screening potential for analytical applications such as separation and detection.

Complexation between plasmid DNA (pDNA) and a set of diblock copolymers, each with one cationic block and one hydrophilic, charge-neutral block, is examined. A range of hydrophilic block structures are explored, whereas the cationic block is fixed as poly( N-(2-aminoethyl) methacrylamide) (PAEMA) with a degree of polymerization of 60 ± 3. The hydrophilic blocks include poly(ethylene glycol) (PEG45), poly(oligo(ethylene glycol) methyl ether methacrylate) (P(OEGMA)51), and poly(2-deoxy-2-methacrylamido glucopyranose) (PMAG52). The numbers represent the degrees of polymerization and are chosen such that the diblock contour lengths are similar (37 ± 2 nm). The three diblock copolymers and a homopolycation control, PAEMA59, are compared with respect to their state of dissolution in aqueous environments, as well as their complexation with pDNA. The diblock copolymers are found to partially aggregate as pH increases above 6, whereas each separate block generally dissolves well over a wide pH range. The hydrophilic block proves to be a critical parameter in determining the structures of pDNA-diblock complexes. When the molar ratio of polycation amines to pDNA phosphates (i.e., N/P) is less than 1, a bulkier hydrophilic block leads to larger resulting complexes. As more polycations are added to the system (N/P > 1.5), colloidal stability becomes an important factor, making more water-soluble systems stabilize at smaller sizes. Further, the charge density effect on the binding thermodynamics is elucidated via calorimetric measurements. P(OEGMA)51- b-PAEMA60 exhibits a greater amount of endothermic pDNA binding per charged amine at higher pH, implying that lower cationic charge density promotes more phosphate pairing per amine on average. Also, the colloidal stability and the circular dichroism spectral evolution of the pDNA-PAEMA59 complexes are dependent on pH, showing noticeable differences between pH = 6.0 vs 7.4. To summarize, controlling the solution pH may be crucial in pDNA-polycation complexation, as it impacts polycation solubility, binding characteristics, and the final complex properties. The findings reported herein should aid researchers in drawing more rigorous structure-function correlations in the field of polymeric gene delivery.