Nonviral nucleic acid delivery to cells and tissues is considered a standard tool in life science research. However, although an ideal delivery system should have high efficacy and minimal toxicity, existing materials fall short, most of them being either too toxic or little effective. We hypothesized that disulfide cross-linked low-molecular-weight (MW) linear poly(ethylene imine) (MW 1,400 individual experiments to seven commercial transfection reagents in seven different cell lines, we found highly superior transfection efficacies and substantially lower toxicities. This renders reductive degradation a highly promising tool for the design of new transfection materials.

The Diels–Alder (DA) reaction was investigated as a cross-linking mechanism for poly(ethylene glycol) (PEG) based hydrogels. Two complementary macromonomers were synthesized by functionalizing star-shaped PEG with furyl and maleimide groups. Gel formation occurred in water at 37 °C; the gelation time ranged between 171 ± 25 min and 14 ± 1 min depending on the used hydrogel formulation. The complex shear modulus was dependent on the concentration, branching factor and molecular weight of the macromonomers; values between 2821 ± 1479 Pa and 37097 ± 6698 Pa were observed. Hydrogel swelling and degradation were influenced by the same parameters; the degradation time varied between a few days and several weeks. Gel dissolution was found to occur by retro-DA reaction and subsequent hydrolysis of maleimide groups. Calculations of the network mesh size revealed that the prepared hydrogels would be suitable for the controlled release of therapeutic proteins.

The majority of effort in the area of polymeric nanocarriers is aimed at providing controlled drug delivery in vivo. Therefore, it is essential to understand the delicate interplay of polymeric NPs with serum proteins in order to forecast their performance in a biological system. In this study, the interaction of serum proteins with functionalized polymeric colloids as a function of particle charge and hydrophobicity was investigated. Moreover, impact on NP stability and cargo leaching was assessed. The hard protein corona of polymeric NPs with either uncharged methoxy groups (methoxy-NPs), positively charged amine groups (amine-NPs), negatively charged carboxylic acid groups (carboxyl-NPs) or zwitterionic NPs decorated with amine and carboxylic acid groups (zwitterion-NPs) was quantitatively and qualitatively analyzed and correlated with the respective colloidal stability using fluorescence resonance energy transfer. Positively charged amine-NPs displayed an enhanced interaction with serum proteins via electrostatic interactions resulting in a hard corona consisting of diverse protein components. As revealed by FRET and agarose gel electrophoresis, the enhanced adsorption of proteins onto the colloidal surface significantly altered the NP identity and severely impaired the colloidal integrity as the lipophilic cargo was continuously leached out of the hydrophobic NP core. These results highlight the importance of generating a profound knowledge of the bio–nano interface as adherence of biomolecules can severely compromise the performance of a colloidal drug delivery system by changing its identity and integrity.