Targeted Synthesis of the Type-A Particle Substructure from Enzymatically Produced Eumelanin.

Eumelanin exhibits a defined supramolecular buildup that is deprived of at least three distinct particle species. To enable the full potential of its promising material properties, access to all particle types is crucial. In this work, the first protocol for the synthesis of the intermediate type-A particles in pure and stable dispersion form is described. It is found that aggregation of type-A particles into the larger type-B variant can be inhibited by a strict pH control during the synthesis. The exact influence of pH on the supramolecular buildup is investigated via a combination of time-resolved light scattering, electron microscopy, and UV-vis spectroscopy. It is observed that a rapid buildup of type-B particles occurs without pH control and is generally dominant at lower pH values. At pH values above 6.2 however, type-A particles are gained, and no further aggregation occurs. Even more, lowering the pH of such a stable type-A dispersion at a later stage lifts the inhibition and again leads to the formation of larger particle species. The results confirm that it is easily possible to halt the aggregation of eumelanin substructures and to access them in the form of a stable dispersion. Moreover, a profound additional understanding of the supramolecular buildup is gained by the in-depth investigation of the pH influence.

Self-Assembled Fibrinogen Hydro- and Aerogels with Fibrin-like 3D Structures.

The natural blood protein fibrinogen is a highly potent precursor for the production of various biomaterials due to its supreme biocompatibility and cell interaction. To gain actual materials from fibrinogen, the protein needs to undergo fibrillogenesis, which is mostly triggered via enzymatic processing to fibrin, electrospinning, or drying processes. All of those techniques, however, strongly limit the available structures or the applicability of the material. To overcome the current issues of fibrin(ogen) as material, we herein present a highly feasible, quick, and inexpensive technique for self-assembly of fibrinogen in solution into defined, nanofibrous three-dimensional (3D) patterns. Upon interaction with specific anions in controlled environments, stable and flexible hydrogel-like structures are formed without any further processing. Moreover, the material can be converted into highly porous and elastic aerogels by lyophilization. Both of these material classes have never been described before from native fibrinogen. The observed phenomenon also represents the first enzyme-free process of fibrillogenesis from fibrinogen with significant yield in solution. The produced hydrogels and aerogels were investigated via electron microscopy, IR spectroscopy, and fluorescence spectroscopy, which also confirms the native state of the protein. Additionally, their mechanical properties were compared with actual fibrin and unstructured fibrinogen. The structural features show a striking analogy to actual fibrin, both as hydro- and aerogel. This renders the new material a highly promising alternative for fibrin in biomaterial applications. A much faster initiation of fiber formation, exclusion of possible thrombin residuals, and low-cost reagents are great advantages.

Superstructure-Dependent Loading of DNA Origami Nanostructures with a Groove-Binding Drug.

DNA origami nanostructures are regarded as powerful and versatile vehicles for targeted drug delivery. So far, DNA origami-based drug delivery strategies mostly use intercalation of the therapeutic molecules between the base pairs of the DNA origami's double helices for drug loading. The binding of nonintercalating drugs to DNA origami nanostructures, however, is less studied. Therefore, in this work, we investigate the interaction of the drug methylene blue (MB) with different DNA origami nanostructures under conditions that result in minor groove binding. We observe a noticeable effect of DNA origami superstructure on the binding affinity of MB. In particular, non-B topologies as for instance found in designs using the square lattice with 10.67 bp/turn may result in reduced binding affinity because groove binding efficiency depends on groove dimensions. Also, mechanically flexible DNA origami shapes that are prone to structural fluctuations may exhibit reduced groove binding, even though they are based on the honeycomb lattice with 10.5 bp/turn. This can be attributed to the induction of transient over- and underwound DNA topologies by thermal fluctuations. These issues should thus be considered when designing DNA origami nanostructures for drug delivery applications that employ groove-binding drugs.