In the last few years, hybrid lipid-copolymer assemblies have attracted increasing attention as possible two-dimensional (2D) membrane platforms, combining the biorelevance of the lipid building ...blocks with the stability and chemical tunability of copolymers. The relevance of these systems varies from fundamental studies on biological membrane-related phenomena to the construction of 2D complex devices for material science and biosensor technology. Both the fundamental understanding and the application of hybrid lipid-copolymer-supported bilayers require thorough physicochemical comprehension and structural control. Herein, we report a comprehensive physicochemical and structural characterization of hybrid monolayers at the air/water interface and of solid-supported hybrid membranes constituted by 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and the block copolymer poly(butadiene-b-ethyleneoxide) (PBD-b-PEO). Hybrid lipid-copolymer supported bilayers (HSLBs) with variable copolymer contents were prepared through spontaneous rupture and fusion of hybrid vesicles onto a hydrophilic substrate. The properties of the thin films and the parent vesicles were probed through dynamic light scattering (DLS), differential scanning calorimetry (DSC), optical ellipsometry, quartz crystal microbalance with dissipation monitoring (QCM-D), and confocal scanning laser microscopy (CSLM). Stable, hybrid lipid/copolymer systems were obtained for a copolymer content of 10–65 mol %. In particular, DSC and CSLM show lateral phase separation in these hybrid systems. These results improve our fundamental understanding of HSLBs, which is necessary for future applications of hybrid systems as biomimetic membranes or as drug delivery systems, with additional properties with respect to phospholipid liposomes.
Abstract This study explores the coating of photocatalytic nanoparticles with antimicrobial peptides (AMPs) for boosted antimicrobial effects, and how such effects depend on AMP properties. For this, ...TiO 2 nanoparticles are coated with the AMP KYE21 or its hydrophobically enhanced variant WWWKYE21. Mirroring effects of free peptides, coated nanoparticles displayed higher binding and UV‐induced degradation for bacteria‐like than for mammalian‐like membranes. In addition, they degraded bacterial lipopolysaccharides (LPS). WWWKYE21‐coated nanoparticles displayed higher binding to LPS and bacteria‐like membranes and photocatalytic degradation, although saturation effects are found at high nanoparticle binding. Neutron reflectometry showed that binding of peptide‐coated nanoparticles to bacteria‐like membranes resulted in partial lipid removal in the absence of UV, but that UV illumination caused additional degradation, featuring increases in the hydration of headgroup and acyl chain regions. For LPS, UV induced removal of its outer O‐antigen region. Analogous to findings in model systems, antimicrobial effects of peptide‐coated nanoparticles against Escherichia coli bacteria on illumination are pronounced, while toxicity against human monocytes remained low. Altogether, results show that AMP coating boosts the antimicrobial effects of photocatalytic nanoparticles without causing cell toxicity. From a broader perspective, the study points to the potential of nanoarchitectonic combination of component properties for the design of composite NP properties.
Interactions between soft interfaces govern the behavior of emulsions and foams and crucially influence the functions of biological entities like membranes. To understand the character of these ...interactions, detailed insight into the interfaces’ structural response in terms of molecular arrangements and conformations is often essential. This requires the realization of controlled interaction conditions and surface-sensitive techniques capable of resolving the structure of buried interfaces. Here, we present a new approach to determine the distance-dependent structure of interacting soft interfaces by neutron reflectometry. A solid/water interface and a water/oil interface are functionalized independently and initially macroscopically separated. They are then brought into contact and structurally characterized under interacting conditions. The nanometric distance between the two interfaces can be varied via the exertion of osmotic pressures. Our first experiments on lipid-anchored polymer brushes interacting across water with solid-grafted polyelectrolyte brushes and with bare silicon surfaces reveal qualitatively different interaction scenarios depending on the chemical composition of the two involved interfaces.
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Cholesterol has been shown to affect the extent of coronavirus binding and fusion to cellular membranes. The severity of Covid-19 infection is also known to be correlated with lipid ...disorders. Furthermore, the levels of both serum cholesterol and high-density lipoprotein (HDL) decrease with Covid-19 severity, with normal levels resuming once the infection has passed. Here we demonstrate that the SARS-CoV-2 spike (S) protein interferes with the function of lipoproteins, and that this is dependent on cholesterol. In particular, the ability of HDL to exchange lipids from model cellular membranes is altered when co-incubated with the spike protein. Additionally, the S protein removes lipids and cholesterol from model membranes. We propose that the S protein affects HDL function by removing lipids from it and remodelling its composition/structure.
Interfacial adsorption of monoclonal antibodies (mAbs) can cause structural deformation and induce undesired aggregation and precipitation. Nonionic surfactants are often added to reduce interfacial ...adsorption of mAbs which may occur during manufacturing, storage, and/or administration. As mAbs are commonly manufactured into ready-to-use syringes coated with silicone oil to improve lubrication, it is important to understand how an mAb, nonionic surfactant, and silicone oil interact at the oil/water interface. In this work, we have coated a polydimethylsiloxane (PDMS) nanofilm onto an optically flat silicon substrate to facilitate the measurements of adsorption of a model mAb, COE-3, and a commercial nonionic surfactant, polysorbate 80 (PS-80), at the siliconized PDMS/water interface using spectroscopic ellipsometry and neutron reflection. Compared to the uncoated SiO2 surface (mimicking glass), COE-3 adsorption to the PDMS surface was substantially reduced, and the adsorbed layer was characterized by the dense but thin inner layer of 16 Å and an outer diffuse layer of 20 Å, indicating structural deformation. When PS-80 was exposed to the pre-adsorbed COE-3 surface, it removed 60 wt % of COE-3 and formed a co-adsorbed layer with a similar total thickness of 36 Å. When PS-80 was injected first or as a mixture with COE-3, it completely prevented COE-3 adsorption. These findings reveal the hydrophobic nature of the PDMS surface and confirm the inhibitory role of the nonionic surfactant in preventing COE-3 adsorption at the PDMS/water interface.
Surface treatment by adhesive polymers is a promising solution to immobilize and study bacteria cells through microscopic assays and, for example, control their growth or determine their ...susceptibility to antibiotic treatment. The stability of such functional films in wet conditions is crucial, as the film degradation would compromise a persistent use of the coated devices. In this work, low roughness chitosan thin films of degrees of acetylation (DA) ranging from 0.5 % to 49 % were chemically grafted onto silicon and glass substrates and we have demonstrated how the physicochemical properties of the surfaces and the bacterial response were DA-dependent. A fully deacetylated chitosan film presented an anhydrous crystalline structure while the hydrated crystalline allomorph was the preferred structure at higher DA. Moreover, their hydrophilicity increased at higher DA, leading to higher film swelling. Low DA chitosan-grafted substrate favored bacterial growth away from the surface and could be envisioned as bacteriostatic surfaces. Contrarily, an optimum of Escherichia coli adhesion was found for substrates modified with chitosan of DA = 35 %: these surfaces are adapted for the study of bacterial growth and antibiotic testing, with the possibility of reusing the substrates without affecting the grafted film – ideal for limiting single-use devices.
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•Thin films of chitosans (DA from 0 % to 55 %) were grafted on flat substrates.•Water-temperature treatment granted both grafting and crosslinking of the films.•Low DA chitosan films swelled 3 times more at low pH than at high pH.•High DA chitosan films swelled almost independently of pH.•Escherichia coli adhered and grew preferably on chitosan thin films of DA 35 %.
The combination of polyelectrolyte multilayers (PEMs) and end-grafted brushes represents a valuable approach to the design of complex organic composite materials with tailored responsive properties. ...This article addresses the correlation between the swelling properties of composites and their internal structure. Here, we present composites of end-grafted 2-(methacryloyloxy)ethyl-trimethylammonium chloride (PMETAC) brushes covered with poly(sodium styrenesulfonate) (PSS) and poly(diallyldimethylammonium) chloride (PDADMAC) PEMs and characterize them under various relative humidities. Ellipsometry and neutron reflectometry are carried out to monitor the swelling behavior and the internal structure, respectively, of the composites, giving evidence of a significant mutual influence of the two components. The reflectivity data reveal a deep penetration of the PEMs’ polyelectrolyte chains into the underlying brush but also a significant humidity dependence of their spatial distribution, indicating considerable mobility within the brush. In contrast to a compact bare brush, for composites a pronounced stretching of the brush after PEM adsorption is observed. The water uptake of the brush is reduced. A PEM on top of a brush is less influenced by the latter one. Swelling gradually reduces the brush/PEM interpenetration, while water accumulates in the interfacial region between the brush and PEM so that these two compartments get increasingly separated with increasing humidity. The swelling process is largely reversible, which demonstrates the potential applicability of these composites as chemical gas or moisture sensors.
Photocatalytic nanoparticles offer antimicrobial effects under illumination due to the formation of reactive oxygen species (ROS), capable of degrading bacterial membranes. ROS may, however, also ...degrade human cell membranes and trigger toxicity. Since antimicrobial peptides (AMPs) may display excellent selectivity between human cells and bacteria, these may offer opportunities to effectively "target" nanoparticles to bacterial membranes for increased selectivity. Investigating this, photocatalytic TiO
nanoparticles (NPs) are coated with the AMP LL-37, and ROS generation is found by C
-BODIPY to be essentially unaffected after AMP coating. Furthermore, peptide-coated TiO
NPs retain their positive ζ-potential also after 1-2 h of UV illumination, showing peptide degradation to be sufficiently limited to allow peptide-mediated targeting. In line with this, quartz crystal microbalance measurements show peptide coating to promote membrane binding of TiO
NPs, particularly so for bacteria-like anionic and cholesterol-void membranes. As a result, membrane degradation during illumination is strongly promoted for such membranes, but not so for mammalian-like membranes. The mechanisms of these effects are elucidated by neutron reflectometry. Analogously, LL-37 coating promoted membrane rupture by TiO
NPs for Gram-negative and Gram-positive bacteria, but not for human monocytes. These findings demonstrate that AMP coating may selectively boost the antimicrobial effects of photocatalytic NPs.
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The exposure of biological membranes to reactive oxygen species (ROS) plays an important role in many pathological conditions such as inflammation, infection, or sepsis. ROS also ...modulate signaling processes and produce markers for damaged tissue. Lipid peroxidation, mainly affecting polyunsaturated phospholipids, results in a complex mixture of oxidized products, which may dramatically alter membrane properties. Here, we have employed a set of biophysical and surface-chemical techniques, including neutron and X-ray scattering, to study the structural, compositional, and stability changes due to oxidative stress on phospholipid bilayers composed of lipids with different degrees of polyunsaturation. In doing so, we obtained real-time information about bilayer degradation under in situ UV exposure using neutron reflectometry. We present a set of interrelated physicochemical effects, including gradual increases in area per molecule, head group and acyl chain hydration, as well as bilayer thinning, lateral phase separation, and defect formation leading to content loss upon membrane oxidation. Such effects were observed to depend on the presence of polyunsaturated phospholipids in the lipid membrane, suggesting that these may also play a role in the complex oxidation processes occurring in cells.
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