Encapsulated salts in velvet worm slime drive its hardening.

Slime expelled by velvet worms entraps prey insects within seconds in a hardened biopolymer network that matches the mechanical strength of industrial polymers. While the mechanic stimuli-responsive nature and building blocks of the polymerization are known, it is still unclear how the velvet worms' slime hardens so fast. Here, we investigated the slime for the first time, not only after, but also before expulsion. Further, we investigated the slime's micro- and nanostructures in-depth. Besides the previously reported protein nanoglobules, carbohydrates, and lipids, we discovered abundant encapsulated phosphate and carbonate salts. We also detected CO2 bubbles during the hardening of the slime. These findings, along with further observations, suggest that the encapsulated salts in expelled slime rapidly dissolve and neutralize in a baking-powder-like reaction, which seems to accelerate the drying of the slime. The proteins' conformation and aggregation are thus influenced by shear stress and the salts' neutralization reaction, increasing the slime's pH and ionic strength. These insights into the drying process of the velvet worm's slime demonstrate how naturally evolved polymerizations can unwind in seconds, and could inspire new polymers that are stimuli-responsive or fast-drying under ambient conditions.

Application of Poly-L-Lysine for Tailoring Graphene Oxide Mediated Contact Formation between Lithium Titanium Oxide LTO Surfaces for Batteries.

When producing stable electrodes, polymeric binders are highly functional materials that are effective in dispersing lithium-based oxides such as Li4Ti5O12 (LTO) and carbon-based materials and establishing the conductivity of the multiphase composites. Nowadays, binders such as polyvinylidene fluoride (PVDF) are used, requiring dedicated recycling strategies due to their low biodegradability and use of toxic solvents to dissolve it. Better structuring of the carbon layers and a low amount of binder could reduce the number of inactive materials in the electrode. In this study, we use computational and experimental methods to explore the use of the poly amino acid poly-L-lysine (PLL) as a novel biodegradable binder that is placed directly between nanostructured LTO and reduced graphene oxide. Density functional theory (DFT) calculations allowed us to determine that the (111) surface is the most stable LTO surface exposed to lysine. We performed Kubo-Greenwood electrical conductivity (KGEC) calculations to determine the electrical conductivity values for the hybrid LTO-lysine-rGO system. We found that the presence of the lysine-based binder at the interface increased the conductivity of the interface by four-fold relative to LTO-rGO in a lysine monolayer configuration, while two-stack lysine molecules resulted in 0.3-fold (in the plane orientation) and 0.26-fold (out of plane orientation) increases. These outcomes suggest that monolayers of lysine would specifically favor the conductivity. Experimentally, the assembly of graphene oxide on poly-L-lysine-TiO2 with sputter-deposited titania as a smooth and hydrophilic model substrate was investigated using a layer-by-layer (LBL) approach to realize the required composite morphology. Characterization techniques such as X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), scanning electron microscopy (SEM) were used to characterize the formed layers. Our experimental results show that thin layers of rGO were assembled on the TiO2 using PLL. Furthermore, the PLL adsorbates decrease the work function difference between the rGO- and the non-rGO-coated surface and increased the specific discharge capacity of the LTO-rGO composite material. Further experimental studies are necessary to determine the influence of the PLL for aspects such as the solid electrolyte interface, dendrite formation, and crack formation.

Influence of Divalent Metal Ions on the Precipitation of the Plasma Protein Fibrinogen.

Fibrinogen nanofibers are very attractive biomaterials to mimic the native blood clot architecture. Previously, we reported the self-assembly of fibrinogen nanofibers in the presence of monovalent salts and have now studied how divalent salts influence fibrinogen precipitation. Although the secondary fibrinogen structure was significantly altered with divalent metal ions, morphological analysis revealed exclusively smooth fibrinogen precipitates. In situ monitoring of the surface roughness facilitated predicting the tendency of various salts to form fibrinogen fibers or smooth films. Analysis of the chemical composition revealed that divalent salts were removed from smooth fibrinogen films upon rinsing while monovalent Na+ species were still present in fibrinogen fibers. Therefore, we assume that the decisive factor controlling the morphology of fibrinogen precipitates is direct ion-protein contact, which requires disruption of the ion-surrounding hydration shells. We conclude that in fibrinogen aggregates, this mechanism is effective only for monovalent ions, whereas divalent ions are limited to indirect fibrinogen adsorption.

Principles of Fibrinogen Fiber Assembly In Vitro.

Fibrinogen nanofibers hold great potential for applications in wound healing and personalized regenerative medicine due to their ability to mimic the native blood clot architecture. Although versatile strategies exist to induce fibrillogenesis of fibrinogen in vitro, little is known about the underlying mechanisms and the associated length scales. Therefore, in this manuscript the current state of research on fibrinogen fibrillogenesis in vitro is reviewed. For the first time, the manifold factors leading to the assembly of fibrinogen molecules into fibers are categorized considering three main groups: substrate interactions, denaturing and non-denaturing buffer conditions. Based on the meta-analysis in the review it is concluded that the assembly of fibrinogen is driven by several mechanisms across different length scales. In these processes, certain buffer conditions, in particular the presence of salts, play a predominant role during fibrinogen self-assembly compared to the surface chemistry of the substrate material. Yet, to tailor fibrous fibrinogen scaffolds with defined structure-function-relationships for future tissue engineering applications, it still needs to be understood which particular role each of these factors plays during fiber assembly. Therefore, the future combination of experimental and simulation studies is proposed to understand the intermolecular interactions of fibrinogen, which induce the assembly of soluble fibrinogen into solid fibers.

Bio-interfactants as double-sided tapes for graphene oxide.

We present a versatile and highly substrate-independent approach for preparing multisandwich layers based on thermally reduced Graphene Oxide (rGO) which gets strongly attached by bio-interfactants using a layer-by-layer (LBL) aqueous dipping and rinsing process. The process allows for the deposition of homogeneous ultra-thin films (∼5.5 nm) in distinct surface topographies, thicknesses and compositions by varying the bio-interfactant layer(s). The layers formed on quartz or other semi conductive material are electrically conductive, flexible, and transparent. The here-developed approach could be applied for the fabrication of wearables, sensors, and antistatic transparent films.

Photoregulating Antifouling and Bioadhesion Functional Coating Surface Based on Spiropyran.

Dynamic regulation of the interactions between specific molecules on functional surfaces and biomolecules, for example, proteins or cells, is critical for biosensor and biomedical devices. Herein, we present a spiropyran (SP)-based light-responsive surface coating, hPG (hyperbranched polyglycerol)-SP, to control the adsorption of proteins and adhesion of cells. In the normal state, the SP groups on the coating surface were in hydrophobic ring-closed form, which promotes the nonspecific protein adsorption and cell adhesion. Under UV irradiation, the grafted SP groups were dynamically isomerized into hydrophilic/zwitterionic merocyanine. Both hydrophilicity and zwitterions support the formation of a hydrated layer and hence the resulting hPG-MC coatings highly resist protein adsorption and cell adhesion. Moreover, the presented hPG also provided a robust bioinert background to suppress the nonspecific protein adsorption and cells adhesion. Therefore, this functionalized coating exhibited a good photoregulated antifouling behavior. Moreover, the detachment of adsorbed proteins and adhered cells from the coating surface was also realized.

High-Antifouling Polymer Brush Coatings on Nonpolar Surfaces via Adsorption-Cross-Linking Strategy.

A new "adsorption-cross-linking" technology is presented to generate a highly dense polymer brush coating on various nonpolar substrates, including the most inert and low-energy surfaces of poly(dimethylsiloxane) and poly(tetrafluoroethylene). This prospective surface modification strategy is based on a tailored bifunctional amphiphilic block copolymer with benzophenone units as the hydrophobic anchor/chemical cross-linker and terminal azide groups for in situ postmodification. The resulting polymer brushes exhibited long-term and ultralow protein adsorption and cell adhesion benefiting from the high density and high hydration ability of polyglycerol blocks. The presented antifouling brushes provided a highly stable and robust bioinert background for biospecific adsorption of desired proteins and bacteria after secondary modification with bioactive ligands, e.g., mannose for selective ConA and Escherichia coli binding.

Bioinspired Universal Monolayer Coatings by Combining Concepts from Blood Protein Adsorption and Mussel Adhesion.

Despite the increasing need for universal polymer coating strategies, only a few approaches have been successfully developed, and most of them are suffering from color, high thickness, or high roughness. In this paper, we present for the first time a universal monolayer coating that is only a few nanometers thick and independent of the composition, size, shape, and structure of the substrate. The coating is based on a bioinspired synthetic amphiphilic block copolymer that combines two concepts from blood protein adsorption and mussel adhesion. This polymer can be rapidly tethered on various substrates including both planar surfaces and nanosystems with high grafting density. The resulting monolayer coatings are, on the one hand, inert to the adsorption of multiple polymer layers and prevent biofouling. On the other hand, they are chemically active for secondary functionalization and provide a new platform for selective material surface modification.

Mussel-inspired dendritic polymers as universal multifunctional coatings.

A rapid and universal approach for multifunctional material coatings was developed based on a mussel-inspired dendritic polymer. This new kind of polymer mimics not only the functional groups of mussel foot proteins (mfps) but also their molecular weight and molecular structure. The large number of catechol and amine groups set the basis for heteromultivalent anchoring and crosslinking. The molecular weight reaches 10 kDa, which is similar to the most adhesive mussel foot protein mfp-5. Also, the dendritic structure exposes its functional groups on the surface like the folded proteins. As a result, a very stable coating can be prepared on virtually any type of material surface within 10 min by a simple dip-coating method, which is as fast as the formation of mussel byssal threads in nature.

Multivalent anchored and crosslinked hyperbranched polyglycerol monolayers as antifouling coating for titanium oxide surfaces.

A set of new catecholic monolayer coatings was developed to improve the antifouling performance of TiO2 surfaces. To solve the problem of the weak charge-transfer interaction between a single catechol anchor and TiO2, multiple catechol groups were combined with hyperbranched polyglycerol (hPG) which is a distinct dendritic scaffold that exposes its multivalent anchor groups on the surface. Thus, multivalent catecholic hPGs can be easily prepared for surface modification. The immobilization of the compounds was monitored by quartz crystal microbalance with dissipation monitoring. Surface properties of the coatings were analyzed by water contact angle, X-ray photoelectron spectroscopy, and atomic force microscopy. The antifouling ability and stability were investigated by protein adsorption and cell adhesion. By increasing the number of catechol groups on the hPG scaffold, the stability and surface coverage could be significantly enhanced. Moreover, the inner-layer crosslinking of the coatings by grafting and initiating vinyl groups clearly improved their long-term stability. As a result, hPG with a catecholic functional degree of 10% (hPG-Cat10) and hPG with both catecholic and vinylic functional degree of 5% (hPG-Cat5-V5) were identified as the best catecholic hPGs to prepare bioinert and stable monolayer coatings on TiO2.

Multivalent anchoring and cross-linking of mussel-inspired antifouling surface coatings.

In this work, we combine nature's amazing bioadhesive catechol with the excellent bioinert synthetic macromolecule hyperbranched polyglycerol (hPG) to prepare antifouling surfaces. hPG can be functionalized by different amounts of catechol groups for multivalent anchoring and cross-linking because of its highly branched architecture. The catecholic hPGs can be immobilized on various surfaces including metal oxides, noble metals, ceramics, and polymers via simple incubation procedures. The effect of the catechol amount on the immobilization, surface morphology, stability, and antifouling performance of the coatings was studied. Both anchoring and cross-linking interactions provided by catechols can enhance the stability of the coatings. When the catechol groups on the hPG are underrepresented, the tethering of the coating is not effective; while an overrepresentation of catechol groups leads to protein adsorption and cell adhesion. Thus, only a well-balanced amount of catechols as optimized and described in this work can supply the coatings with both good stability and antifouling ability.

A universal approach to crosslinked hierarchical polymer multilayers as stable and highly effective antifouling coatings.

Material-independent and bioinert hierarchical polymer multilayer coatings are presented. Chemically active catecholic hyperbranched polyglycerols (hPGs) form a foundation layer on a versatile surface via multivalent anchoring and crosslinking, the activity of which is shielded by the bioinert catecholic hPGs. Mono-catecholic hPGs finally terminate all of the free catechols to build a flexible bioinert top layer. These coatings perfectly prevent protein and cell adhesion.