Hybrid protein membranes: Snatch contaminants from water and strike gold

Industrial development, energy production and mining have led to dramatically increased levels of environmental pollutants such as heavy metal ions, metal cyanides and nuclear waste. Current technologies for purifying contaminated waters are typically expensive and ion specific, and there is therefore a significant need for new approaches. Here, we report inexpensive hybrid membranes made from protein amyloid fibrils and activated porous carbon that can be used to remove heavy metal ions and radioactive waste from water. During filtration, the concentration of heavy metal ions drops by three to five orders of magnitude per passage and the process can be repeated numerous times. Notably, their efficiency remains unaltered when filtering several ions simultaneously. The performance of the membrane is enabled by the ability of the amyloids to selectively absorb heavy metal pollutants from solutions. We also show that our membranes can be used to recycle valuable heavy metal contaminants by thermally reducing ions trapped in saturated membranes, leading to the creation of elemental metal nanoparticles and films. Please click Additional Files below to see the full abstract

Multifunctional nano‐biointerfaces: cytocompatible antimicrobial nanocarriers from stabilizer‐free cubosomes

The rational design of alternative antimicrobial materials with reduced toxicity toward mammalian cells is highly desired due to the growing occurrence of bacteria resistant to conventional antibiotics. A promising approach is the design of lipid‐based antimicrobial nanocarriers. However, most of the commonly used polymer‐stabilized nanocarriers are cytotoxic. Herein, the design of a novel, stabilizer‐free nanocarrier for the human cathelicidin derived antimicrobial peptide LL‐37 that is cytocompatible and promotes cell proliferation for improved wound healing is reported. The nanocarrier is formed through the spontaneous integration of LL‐37 into novel, stabilizer‐free glycerol mono‐oleate (GMO)‐based cubosomes. Transformations in the internal structure of the cubosomes from Pn3m to Im3m‐type and eventually their transition into small vesicles and spherical micelles are demonstrated upon the encapsulation of LL‐37 into their internal bicontinuous cubic structure using small angle X‐ray scattering, cryogenic transmission electron microscopy, and light scattering techniques. Additional in vitro biological assays show the antimicrobial activity of the stabilizer‐free nano‐objects on a variety of bacteria strains, their cytocompatibility, and cell‐ proliferation enhancing effect. The results outline a promising strategy for the comprehensive design of antimicrobial, cytocompatible lipid nanocarriers for the protection and delivery of bioactive molecules with potential for application as advanced wound healing materials

Interaction of cylindrical polymer brushes in dilute and semi-dilute solution

We present a systematic study of flexible cylindrical brush-shaped macromolecules in a good solvent by small-angle neutron scattering (SANS), static light scattering (SLS), and by dynamic light scattering (DLS) in dilute and semi-dilute solution. The SLS and SANS data extrapolated to infinite dilution lead to the shape of the polymer that can be modeled in terms of a worm-like chain with a contour length of 380 nm and a persistence length of 17.5 nm. SANS data taken at higher polymer concentration were evaluated by using the polymer reference interaction site model (PRISM). We find that the persistence length reduce from 17.5 nm at infinite dilution to 5.3 nm at the highest concentration (volume fraction 0.038). This is comparable with the decrease of the persistence length in semi-dilute concentration predicted theoretically for polyelectrolytes. This finding reveals a softening of stiffness of the polymer brushes caused by their mutual interaction

Arsenic removal from Peruvian drinking water using milk protein nanofibril–carbon filters: a field study

The tap water quality in Peru fails to meet the World Health Organization (WHO) drinking water standards; consequently, the local population in Peru has been exposed over the last few years to harmful arsenic levels through water consumption. A field study was conducted in Peru between 2019 and 2020 using granular adsorbers and hybrid membranes based on the technology using milk protein nanofibril–carbon hybrid materials previously introduced in the literature by us (S. Bolisetty and R. Mezzenga, Nat. Nanotechnol., 2016, 11, 365). The performance was analyzed across 28 households as well as 3 community-based water treatment plants in some of the Peruvian arsenic burdened regions, covering a range of groundwater arsenic concentrations between 11 μg L−1 and 1.1 mg L−1. Three different kinds of filtration units were installed including the combined granular media and hybrid membrane (type I), hybrid membrane alone (type II), and granular media (type III), to determine the effectiveness of different filtration setups for arsenic removal in different regions. The arsenic removal by household filtration units and community filtration units shows a removal efficiency exceeding 99% at various initial arsenic concentrations for a duration up to nine months. In addition, it is shown that an aqueous NaOH solution can be used to regenerate the adsorbent, extending its operational lifetime and the overall capacity for As removal. High purification efficiency, very low cost, safety, little to no energy requirement, possibility of regeneration and simplicity of operation make this technology suitable for arsenic removal from drinking water in a broad range of urban and rural areas.ISSN:2053-1400ISSN:2053-141

Amyloid hybrid membranes for removal of clinical and nuclear radioactive wastewater

Nuclear medicine uses various radioactive compounds for the administration into patients to diagnose and treat diseases, which generates large amounts of radioactively contaminated water. Currently, radioactively contaminated hospital wastewater has to be stored until the contained radionuclides have sufficiently decayed because cost-effective and efficient removal technologies are not available. Similar considerations apply in the nuclear power industry, with, however, decay times of the radionuclides several orders of magnitude higher. Previously, we reported hybrid membranes composed of amyloid fibrils produced from cheap and readily available proteins and activated carbon, which efficiently removed heavy metal ions and radioactive compounds from water. Here, we show that these membranes are highly efficient in the adsorption & removal of diverse, clinically relevant radioactive compounds from hospital wastewater by single-step filtration. The radionuclides technetium (Tc-99m), iodine (I-123) and gallium (Ga-68) can be removed from water with efficiencies above 99.8% in one single step. We also demonstrate the purification of a real clinical wastewater sample from a Swiss hospital containing iodine (I-131) and lutetium (Lu-177). With the use of single-photon emission computed tomography (SPECT) and positron emission tomography (PET), we were able to visualize the accumulation of the radioactive compounds within the membrane and demonstrate its outstanding performance. By converting large volumes of radioactive wastewater into low volumes of solid radioactive waste, the present technology emerges as a possible game-changer in the treatment of nuclear wastewater.ISSN:2053-1400ISSN:2053-141

Elasticity in Physically Cross-Linked Amyloid Fibril Networks

ISSN:0031-9007ISSN:1079-711

Gelation, phase behavior, and dynamics of β-Lactoglobulin amyloid fibrils at varying concentrations and ionic strengths

We have investigated the thermodynamic and dynamic behavior of multistranded β-lactoglobulin protein fibrils in water, by combining static, dynamic, and depolarized dynamic light scattering (SLS, DLS, DDLS), small angle neutron scattering (SANS), rheology, and cryogenic transmission electron microscopy (cryo-TEM). We focus on the region of the phase diagram at which ionic strength and concentration changes induce transitions in gelation and lyotropic liquid crystalline behavior. An increase in ionic strength, induced by NaCl salt, progressively causes the phase transitions from nematic (N) to gel (G) phases; a further increase causes the transition to a translucent phase and to a macroscopic phase separation, respectively. An increase in fibril concentration induces first a phase transition from an isotropic (I) to a nematic phase (N); a further increase induces the formation of a gel phase. The protein gel strength is investigated by rheology measurements. SANS and osmotic compressibility calculated by SLS measurements clearly capture the main features of the IN transition of β-lactoglobulin protein fibrils. The form and structure factors measured by scattering experiments are analyzed by the polymer reference interaction site model (PRISM). Dynamics of the protein fibrils at different concentrations, measured by polarized and depolarized dynamic light scattering, show both individual and collective diffusion after the isotropic–nematic transition. Above this transition, cryo-TEM images further demonstrate the alignment of the protein fibrils, which is quantified by a 2D order parameter. This work discusses comprehensively, both experimentally and theoretically, the thermodynamics and dynamic features of β-lactoglobulin amyloid fibrils in a vast region of the concentration–ionic strength phase diagram

Controlled aggregation of peptide-DNA hybrids into amyloid-like fibrils

We report on the fibril genesis under controlled aggregation conditions of a series of peptide–DNA hybrids composed of short peptide fragments, namely diphenylalanine (FF), ditryptophan (WW) and the amyloid β peptide motif (16–21) (KLVFFA), K stands for lysine, L for leucine, V for valine and A for alanine. The copolymers based on KLVFFA and WW form long fibers by nucleation dependent polymerization, very similar to amyloid fibril formation. At low concentrations and ambient temperature, they form spherical structures, which under controlled aggregation conditions such as increased temperature, concentration and incubation time assemble into long β-sheeted fibers, as evidenced by wide angle X-ray scattering. This mechanism is driven by π–π stacking supported by intermolecular electrostatic interactions and/or weak hydrogen bonding in an aprotic solvent such as an aqueous solution of dimethylsulfoxide (DMSO). In pure water, solely WW–DNA assembles into fibers owing to strong π–π stacking of the aromatic dipeptide stabilized by intermolecular hydrogen bonding. Overall, this study supports the mechanism of structure formation of peptide–DNA conjugates under controlled aggregation conditions