Interfacial blending in co-axially electrospun polymer core-shell fibers and their interaction with cells via focal adhesion point analysis

Electrospun polymer scaffolds have gained prominence in biomedical applications, including tissue engineering, drug delivery, and wound dressings, due to their customizable properties. As the interplay between cells and materials assumes fundamental significance in biomaterials research, understanding the relationship between fiber properties and cell behaviour is imperative. Nevertheless, altering fiber properties introduces complexity by intertwining mechanical and surface chemistry effects, challenging the differentiation of their individual impacts on cell behaviour. Core-shell fibers present an appealing solution, enabling the control of mechanical properties of scaffolds, flexibility in material and drug selection, efficient encapsulation, strong protection of bioactive drugs against harsh environments, and controlled, prolonged drug release. This study addresses a key challenge in core-shell fiber design related to the blending effect between core and shell polymers. Two types of fibers, PMMA and core-shell PC-PMMA, were electrospun, and thorough analyses confirmed the desired core-shell structure in PC-PMMA fibers. Surface chemistry analysis revealed PC diffusion to the PMMA shell of the core-shell fiber during electrospinning, subsequently prompting an investigation of the fiber's surface potential. Conducting cellular studies on osteoblasts by super-resolution confocal microscopy provided insights into the direct influence of interfacial polymer blending and, consequently, altered fiber surface and mechanical properties on cell focal adhesion points, bridging the gap between material attributes and cell responses in core-shell fibers.

Catalytic reductions of nitroaromatic compounds over heterogeneous catalysts with rhenium sub-nanostructures

Nitroaromatic compounds (NACs) are key contaminants of anthropogenic origin and pose a severe threat to human and animal lives. Although the catalytic activities of Re nanostructures (NSs) are significantly higher than those of other heterogeneous catalysts containing NSs, few studies have been reported on the application of Re-based nanocatalysts for NAC hydrogenation. Accordingly, herein, catalytic reductions of nitrobenzene (NB), 4-nitrophenol (4-NP), 2-nitroaniline (2-NA), 4-nitroaniline (4-NA), and 2,4,6-trinitrophenol (2,4,6-TNP) over new Re-based heterogeneous catalysts were proposed. The catalytic materials were designed to enable effective syntheses and stabilisation of particularly small Re structures over them. Accordingly, catalytic hydrogenations of NACs under mild conditions were significantly enhanced by Re sub-nanostructures (Re-sub-NSs). The highest pseudo-first-order rate constants for NB, 4-NP, 2-NA, 4-NA, and 2,4,6-TNP reductions over the catalyst acquired by stabilising Re using bis(3-aminopropyl)amine (BAPA), which led to Re-sub-NSs with Re concentrations of 16.7 wt%, were 0.210, 0.130, 0.100, 0.180, and 0.090 min-1, respectively.

Mimicking natural electrical environment with cellulose acetate scaffolds enhances collagen formation of osteoblasts

The medical field is continuously seeking new solutions and materials, where cellulose materials due to their high biocompatibility have great potential. Here we investigate the applicability of cellulose acetate (CA) electrospun fibers for bone tissue regeneration. For the first time we show the piezoelectric properties of electrospun CA fibers via high voltage switching spectroscopy piezoresponse force microscopy (HVSS-PFM) tests, which are followed by surface potential studies using Kelvin probe force microscopy (KPFM) and zeta potential measurements. Piezoelectric coefficient for CA fibers of 6.68 ± 1.70 pmV^-1 along with high surface (718 mV) and zeta (-12.2 mV) potentials allowed us to mimic natural electrical environment favoring bone cell attachment and growth. Importantly, the synergy between increased surface potential and highly developed structure of the fibrous scaffold led to the formation of a vast 3D network of collagen produced by osteoblasts only after 7 days of in vitro culture. We clearly show the advantages of CA scaffolds as a bone replacement material, when long-lasting structural support is needed.

Hydrogen Bubble Size Distribution on Nanostructured Ni Surfaces: Electrochemically Active Surface Area Versus Wettability

Emerging manufacturing technologies make it possible to design the morphology of electrocatalysts on the nanoscale in order to improve their efficiency in electrolysis processes. The current work investigates the effects of electrode-attached hydrogen bubbles on the performance of electrodes depending on their surface morphology and wettability. Ni-based electrocatalysts with hydrophilic and hydrophobic nanostructures are manufactured by electrodeposition, and their surface properties are characterized. Despite a considerably larger electrochemically active surface area, electrochemical analysis reveals that the samples with more pronounced hydrophobic properties perform worse at industrially relevant current densities. High-speed imaging shows significantly larger bubble detachment radii with higher hydrophobicity, meaning that the electrode surface area that is blocked by gas is larger than the area gained by nanostructuring. Furthermore, a slight tendency toward bubble size reduction of 7.5% with an increase in the current density is observed in 1 M KOH.

Dendrite Formation on the Poly(methyl methacrylate) Surface Reactively Sputtered with a Cesium Ion Beam

The development of topography plays an important role when low-energy projectiles are used to modify the surface or analyze the properties of various materials. It can be a feature that allows one to create complex structures on the sputtered surface. It can also be a factor that limits depth resolution in ion-based depth profiling methods. In this work, we have studied the evolution of microdendrites on poly(methyl methacrylate) sputtered with a Cs 1 keV ion beam. Detailed analysis of the topography of the sputtered surface shows a sea of pillars with islands of densely packed pillars, which eventually evolve to fully formed dendrites. The development of the dendrites depends on the Cs fluence and temperature. Analysis of the sputtered surface by physicochemical methods shows that the mechanism responsible for the formation of the observed microstructures is reactive ion sputtering. It originates from the chemical reaction between the target material and primary projectile and is combined with mass transport induced by ion sputtering. The importance of chemical reaction for the formation of the described structures is shown directly by comparing the change in the surface morphology under the same dose of a nonreactive 1 keV xenon ion beam.

Effect of poly(tert-butyl methacrylate) stereoregularity on polymer film interactions with peptides, proteins, and bacteria

The impact of polymer stereoregularity on its interactions with peptides, proteins and bacteria strains was studied for three stereoregular forms of poly(tert-butyl methacrylate) (PtBMA): isotactic (iso), atactic (at) and syndiotactic (syn) PtBMA. Principal component analysis of the time-of-flight secondary ion mass spectrometry data recorded for thin polymer films indicated a different orientation of ester groups, which in the case of iso-PtBMA are exposed away from the surface whereas for at-PtBMA and syn-PtBMA these are located deeper within the film. This arrangement of chemical groups modified the interactions of iso-PtBMA with biomolecules when compared to at-PtBMA and syn-PtBMA. For peptides, the affected interactions were explained by the preferential hydrogen bonding and electrostatic interaction between the exposed polar ester groups of iso-PtBMA and positively charged peptides. In turn, for protein adsorption no impact on the amount of adsorbed proteins was observed. However, the polymer stereoregularity influenced the orientation of immunoglobulin G and induced conformational changes in bovine serum albumin structure. Moreover, the impact of polymer stereoregularity occurred equally for their interactions with Gram-positive bacteria (S. aureus), which absorbed preferentially onto iso-PtBMA films as compared to two other stereoregularities.

Surface Potential Driven Water Harvesting from Fog

Access to clean water is a global challenge, and fog collectors are a promising solution. Polycarbonate (PC) fibers have been used in fog collectors but with limited efficiency. In this study, we show that controlling voltage polarity and humidity during the electrospinning of PC fibers improves their surface properties for water collection capability. We experimentally measured the effect of both the surface morphology and the chemistry of PC fiber on their surface potential and mechanical properties in relation to the water collection efficiency from fog. PC fibers produced at high humidity and with negative voltage polarity show a superior water collection rate combined with the highest tensile strength. We proved that electric potential on surface and morphology are crucial, as often designed by nature, for enhancing the water collection capabilities via the single-step production of fibers without any postprocessing needs.

Versailles Project on Advanced Materials and Standards interlaboratory study on intensity calibration for x-ray photoelectron spectroscopy instruments using low-density polyethylene

We report the results of a Versailles Project on Advanced Materials and Standards interlaboratory study on the intensity scale calibration of x-ray photoelectron spectrometers using low-density polyethylene (LDPE) as an alternative material to gold, silver, and copper. An improved set of LDPE reference spectra, corrected for different instrument geometries using a quartz-monochromated Al Kα x-ray source, was developed using data provided by participants in this study. Using these new reference spectra, a transmission function was calculated for each dataset that participants provided. When compared to a similar calibration procedure using the NPL reference spectra for gold, the LDPE intensity calibration method achieves an absolute offset of ∼3.0% and a systematic deviation of ±6.5% on average across all participants. For spectra recorded at high pass energies (≥90 eV), values of absolute offset and systematic deviation are ∼5.8% and ±5.7%, respectively, whereas for spectra collected at lower pass energies (<90 eV), values of absolute offset and systematic deviation are ∼4.9% and ±8.8%, respectively; low pass energy spectra perform worse than the global average, in terms of systematic deviations, due to diminished count rates and signal-to-noise ratio. Differences in absolute offset are attributed to the surface roughness of the LDPE induced by sample preparation. We further assess the usability of LDPE as a secondary reference material and comment on its performance in the presence of issues such as variable dark noise, x-ray warm up times, inaccuracy at low count rates, and underlying spectrometer problems. In response to participant feedback and the results of the study, we provide an updated LDPE intensity calibration protocol to address the issues highlighted in the interlaboratory study. We also comment on the lack of implementation of a consistent and traceable intensity calibration method across the community of x-ray photoelectron spectroscopy (XPS) users and, therefore, propose a route to achieving this with the assistance of instrument manufacturers, metrology laboratories, and experts leading to an international standard for XPS intensity scale calibration.

Cobalt-platinum nanomotors for local gas generation

Bimetallic Co-Pt nanorods exhibit an enhanced capacity for the production of gas from liquid-phase chemicals. Based on the systematic structural and magnetic characterization we discuss potential applications of these hybrid nanostructures for localized fuel generation in microdevices. Experimental proof of the feasibility for controlling the rate of catalytic reaction via external magnetic stimuli is shown. This unique functionality makes these hybrids promising candidates for optimizing the energy conversion rate in microfluidics fuel cells.

Fiber-Based Composite Meshes with Controlled Mechanical and Wetting Properties for Water Harvesting

Water is the basis of life in the world. Unfortunately, resources are shrinking at an alarming rate. The lack of access to water is still the biggest problem in the modern world. The key to solving it is to find new unconventional ways to obtain water from alternative sources. Fog collectors are becoming an increasingly important way of water harvesting as there are places in the world where fog is the only source of water. Our aim is to apply electrospun fiber technology, due to its high surface area, to increase fog collection efficiency. Therefore, composites consisting of hydrophobic and hydrophilic fibers were successfully fabricated using a two-nozzle electrospinning setup. This design enables the realization of optimal meshes for harvesting water from fog. In our studies we focused on combining hydrophobic polystyrene (PS) and hydrophilic polyamide 6 (PA6), surface properties in the produced meshes, without any chemical modifications, on the basis of new hierarchical composites for collecting water. This combination of hydrophobic and hydrophilic materials causes water to condense on the hydrophobic microfibers and to run down on the hydrophilic nanofibers. By adjusting the fraction of PA6 nanofibers, we were able to tune the mechanical properties of PS meshes and importantly increase the efficiency in collecting water. We combined a few characterization methods together with novel image processing protocols for the analysis of fiber fractions in the constructed meshes. The obtained results show a new single-step method to produce meshes with enhanced mechanical properties and water collecting abilities that can be applied in existing fog water collectors. This is a new promising design for fog collectors with nano- and macrofibers which are able to efficiently harvest water, showing great application in comparison to commercially available standard meshes.

Roughness and Fiber Fraction Dominated Wetting of Electrospun Fiber-Based Porous Meshes

Wettability of electrospun fibers is one of the key parameters in the biomedical and filtration industry. Within this comprehensive study of contact angles on three-dimensional (3D) meshes made of electrospun fibers and films, from seven types of polymers, we clearly indicated the importance of roughness analysis. Surface chemistry was analyzed with X-ray photoelectron microscopy (XPS) and it showed no significant difference between fibers and films, confirming that the hydrophobic properties of the surfaces can be enhanced by just roughness without any chemical treatment. The surface geometry was determining factor in wetting contact angle analysis on electrospun meshes. We noted that it was very important how the geometry of electrospun surfaces was validated. The commonly used fiber diameter was not necessarily a convincing parameter unless it was correlated with the surface roughness or fraction of fibers or pores. Importantly, this study provides the guidelines to verify the surface free energy decrease with the fiber fraction for the meshes, to validate the changes in wetting contact angles. Eventually, the analysis suggested that meshes could maintain the entrapped air between fibers, decreasing surface free energies for polymers, which increased the contact angle for liquids with surface tension above the critical Wenzel level to maintain the Cassie-Baxter regime for hydrophobic surfaces.

Between single ion magnets and macromolecules: a polymer/transition metal-based semi-solid solution

The creation of functional magnetic materials for application in high-density memory storage or in the new field of molecular spintronics is a matter of widespread interest among the material research community. Herein, we describe a new approach that combines the qualities of single ion magnets, displaying slow magnetic relaxations, and the merits of polymers, being easy to process and widely used to produce thin films. Basing the idea on cobalt(ii) ions and pyridine-based single ion magnets, a new macromolecular magnetic material was obtained - a polymeric matrix of poly(4-vinylpyridine) (P4VP) cross-linked by a cobalt(ii) salt bound within it, effectively forming a network of single ion magnets, with field-induced magnetic relaxations preserved in both bulk and thin film forms. The binding of cobalt is confirmed by a series of methods, like secondary ion mass spectroscopy or high-resolution X-ray photoelectron spectroscopy. The magnetic relaxation times, up to 5 × 10-6 s, are controllable simply by dilution, making this new material a semi-solid solution. By this approach, a new path is formed to connect molecular magnetism and polymer science, showing that the easy polymer processing can be used in forming self-organizing functional magnetic thin films.

Engineering a Poly(3,4-ethylenedioxythiophene):(Polystyrene Sulfonate) Surface Using Self-Assembling Molecules-A Chemical Library Approach

The surface properties of poly(3,4-ethylenedioxythiophene):(polystyrene sulfonate) (PEDOT:PSS) affect the performance of many organic electronic devices. The work function determines the efficiency of the charge carrier transfer between PEDOT:PSS electrodes and the active layer of the device. The surface free energy affects phase separation in multicomponent blends that are typically used to fabricate active layers of organic light-emitting diodes and photovoltaic devices. Here, we present a method to prepare PEDOT:PSS films with a gradient work function and surface free energy. This modification was achieved by evaporation of trimethoxy(3,3,3-trifluoropropyl)silane in such a way that the degree of surface coverage of the molecules varied in the selected direction. Gradient films were used as electrodes to fabricate two-terminal PEDOT:PSS/poly(3-hexyl thiophene)/Au devices to rapidly screen for the influence of the modification on the performance of the prepared polymer diodes. Gradual changes in the morphology of the solution-cast model poly(3-butyl thiophene)/poly-bromostyrene films followed changes in the surface energy of the substrate.

Temperature-Controlled Three-Stage Switching of Wetting, Morphology, and Protein Adsorption

The novel polymeric coatings of oligoperoxide-graft-poly(4-vinylpyridine-co-oligo(ethylene glycol)ethyl ether methacrylate246) [oligoperoxide-graft-P(4VP-co-OEGMA246)] attached to glass were successfully fabricated. The composition, thickness, morphology, and wettability of resulting coatings were analyzed using X-ray photoelectron spectroscopy, ellipsometry, atomic force microscopy, and contact angle measurements, respectively. In addition, adsorption of the bovine serum albumin was examined with fluorescence microscopy. The thermal response of wettability and morphology of the coatings followed by that of protein adsorption revealed two distinct transitions at 10 and 23 °C. For the first time, three stage switching was observed not only for surface wetting but also for morphology and protein adsorption. Moreover, the influence of the pH on thermo-sensitivity of modified surfaces was shown.

Direct Covalent Biomolecule Immobilization on Plasma-Nanotextured Chemically Stable Substrates

A new method for direct covalent immobilization of protein molecules (including antibodies) on organic polymers with plasma-induced random micronanoscale topography and stable-in-time chemical functionality is presented. This is achieved using a short (1-5 min) plasma etching and simultaneous micronanotexturing process, followed by a fast thermal annealing step, which induces accelerated hydrophobic recovery while preserving important chemical functionality created by the plasma. Surface-bound biomolecules resist harsh washing with sodium dodecyl sulfate and other detergents even at elevated temperatures, losing less than 40% of the biomolecules bound even at the harshest washing conditions. X-ray photoelectron spectroscopy, secondary-ion mass spectrometry, and electron paramagnetic resonance are used to unveil the chemical modification of the plasma-treated and stabilized surfaces. The nanotextured and chemically stabilized surfaces are used as substrates for the development of immunochemical assays for the sensitive detection of C-reactive protein and salmonella lipopolysaccharides through immobilization of the respective analyte-specific antibodies onto them. Such substrates are stable for a period of 1 year with ambient storage.

Effects of polythiophene surface structure on adsorption and conformation of bovine serum albumin: a multivariate and multitechnique study

Protein interactions with surfaces of promising conducting polymers are critical for development of bioapplications. Surfaces of spin-cast and postbaked poly(3-alkylthiophenes), regiorandom P3BT, and regioregular RP3HT are examined prior to and after adsorption of model protein, bovine serum albumin, with time-of-flight secondary ion mass spectrometry, atomic force microscopy, and X-ray photoelectron spectroscopy. The multivariate method of principal component analysis applied to ToF-SIMS data maximizes information on subtle differences in surface chemistry: PCA reveals alkyl side chains and conjugated backbones, exposed for RP3HT and P3BT, respectively. Phase imaging AFM shows semicrystalline microstructure of RP3HT and amorphous morphology of P3BT films. A cellular-like pattern of proteins adsorbed on RP3HT develops with coverage to more uniform overlayer, observed always on P3BT. The amount of adsorbed protein, determined by XPS as a function of BSA concentration (up to 10 mg/mL), is ∼21% lower for RP3HT than P3BT (up to 1.1 mg/m(2)). Although PCA differentiates protein from polythiophene, relative protein surface composition evaluated from ToF-SIMS saturates rather than increases with amount of adsorbed BSA from XPS. This reflects ToF-SIMS sensitivity to outermost layer of proteins, enabling multivariate analysis of protein conformation or orientation. PCA distinguishes between amino acids characteristic for external regions of BSA adsorbed to P3BT and RP3HT. These amino acids are identified for P3BT and RP3HT as hydrophilic and hydrophobic, respectively, by relative hydrophobicity of amino acid side chains. Alternative identification with BSA domains fails, pointing to substrate-induced changes in conformation and degree of denaturation rather than orientation of adsorbed protein.