Thin Polymer Layer Research Articles

Characterization of Thin Polymer Layer Prepared from Liposomes and Polyelectrolytes for TGF-β3 Release in Tissue Engineering.

Implant-integrated drug delivery systems that enable the release of biologically active factors can be part of an in situ tissue engineering approach to restore biological function. Implants can be functionalized with drug-loaded nanoparticles through a layer-by-layer assembly. Such coatings can release biologically active levels of growth factors. Sustained release is desired for many in vivo applications. The layer-by-layer technique also allows for the addition of extra layers, which can serve as "barriers" to delay the release. Electrospun Polycaprolactone (PCL) fiber mats are modified with a Chitosan (CS) grafted with PCL sidechains (CS-g-PCL24) and coated with transforming growth factor beta 3 (TGF-β3) loaded Chitosan/tripolyphosphate nanoparticles as a drug delivery system. Additional layers including polystyrene sulfonate, alginate, carboxymethyl cellulose, and liposomes (phosphatidylcholine) are applied. Streaming potential and X-ray photoelectron spectroscopy (XPS) measurements indicated a strong interpenetration of the chitosan and polyanion layers, while liposomes formed separate layers, which are more promising for sustained release. All samples release TGF-β3 at different cumulative levels without altering release kinetics. Variations in layer structure, interpenetration, and stability depending on the chitosan used are observed, which ultimately has minimal impact on the release kinetics. Polyelectrolyte layers strongly interpenetrated the active layers and therefore do not act as effective diffusion barriers, while the liposome layer, though separated, lacked sufficient stability.

Incorporation of Chromium Nanostructures into PVC Interlayer to Improve Electrical Features of Au/n-Si Schottky Diodes

Abstract This work comprehensively examined the effects of polyvinyl chloride (PVC) polymer and polyvinyl chloride-chromium (PVC:Cr) thin layers on the electronic characteristics of Au/n-Si (D0) sample. To achieve this, the configurations Au/PVC/n-Si (D1) and Au/PVC:Cr/n-Si (D2) were created. A detailed description of the PVC:Cr nanocomposite synthesis process was given. The Cr nanoparticles and PVC:Cr nanocomposite were analyzed using energy-dispersive X-ray (EDX) spectroscopy and field emission scanning electron microscopy (FE-SEM) to determine the purity and surface morphology. Following the structural analysis, current-voltage (I-V) measurements were taken at a wide voltage range (±3 V), and several methodologies were applied to obtain and compare the major electronic variables of the created Schottky diodes. Experimental results show that PVC:Cr nanocomposite reduced ideality factor (n), surface states density (Nss), and series resistance (Rs) while increasing barrier height (BH) of the electric potential, shunt resistance (Rsh), and rectification rate (RR). It was found that the D2 sample's RR was 89 times greater than the D0 sample's. Furthermore, the surface state density (Nss) depending on the energy was determined using the n(V) and ΦB0(V) functions. Based on the ln(IR)-VR0.5 profile in the reverse bias region, a Schottky emission (SE) transport mechanism was found to be effective for the D0 structure. On the other hand, the indicates that D1 and D2 structures exhibited the Poole-Frenkel emission (PFE) type.

Toward Sustainable 3D-Printed Sensor: Green Fabrication of CNT-Enhanced PLA Nanocomposite via Solution Casting.

The current study explores, for the first time, an eco-friendly solution casting method using a green solvent, ethyl acetate, to prepare feedstock/filaments from polylactic acid (PLA) biopolymer reinforced with carbon nanotubes (CNTs), followed by 3D printing and surface activation for biosensing applications. Comprehensive measurements of thermal, electrical, rheological, microstructural, and mechanical properties of developed feedstock and 3D-printed parts were performed and analyzed. Herein, adding 2 wt.% CNTs to the PLA matrix marked the electrical percolation, achieving conductivity of 8.3 × 10-3 S.m-1, thanks to the uniform distribution of CNTs within the PLA matrix facilitated by the solution casting method. Rheological assessments paralleled these findings; the addition of 2 wt.% CNTs transitioned the nanocomposite from liquid-like to a solid-like behavior with a percolated network structure, significantly elevating rheological properties compared to the composite with 1 wt.% CNTs. Mechanical evaluations of the printed samples revealed improvement in tensile strength and modulus compared to virgin PLA by a uniform distribution of 2 wt.% CNTs into PLA, with an increase of 14.5% and 10.3%, respectively. To further enhance the electrical conductivity and sensing capabilities of the developed samples, an electrochemical surface activation treatment was applied to as-printed nanocomposite samples. The field-emission scanning electron microscopy (FE-SEM) analysis confirmed that this surface activation effectively exposed the CNTs to the surface of 3D-printed parts by removing a thin layer of polymer from the surface, thereby optimizing the composite's electroconductivity performance. The findings of this study underscore the potential of the proposed eco-friendly method in developing advanced 3D-printed bio-nanocomposites based on carbon nanotubes and biopolymers, using a green solution casting and cost-effective material extrusion 3D-printing method, for electrochemical-sensing applications.

Epithelial Folding Through Local Degradation of an Elastic Basement Membrane Plate

AbstractEpithelia are polarized layers of cells that line the outer and inner surfaces of organs. At the basal side, the epithelial cell layer is supported by a basement membrane, which is a thin polymeric layer of self‐assembled extracellular matrix (ECM) that tightly adheres to the basal cell surface. Proper shaping of epithelial layers is an important prerequisite for the development of healthy organs during the morphogenesis of an organism. Experimental evidence suggests that local degradation of the basement membrane is one of the mechanisms that can drive epithelial folding. However, how folding emerges in the absence of tissue growth remains elusive. Here, we present a coarse‐grained plate theory model of the basement membrane that assumes force balance between i) cell‐transduced active forces and ii) deformation‐induced elastic forces. We verify key assumptions of this model through experiments in the Drosophila wing disc epithelium and demonstrate that the model can explain the emergence of outward epithelial folds upon local plate degradation. The model accounts for local degradation of the basement membrane as a mechanism for the generation of epithelial folds in the absence of epithelial growth.

Impact of Surface Modification of Hemp Fibers Using a Coupling Agent in Solvent on the Properties of Polyethylene Composites

This study investigates the grafting of a coupling agent, maleic anhydride-grafted polyethylene (MAPE), onto hemp fibers in a 1,2,4-trichlorobenzene (TCB) solution, followed by an evaluation of the morphological, rheological, and mechanical properties of the resulting polyethylene composites containing 30% hemp. The SEM analysis revealed that a thin layer of MAPE formed on the surface of the modified fibers. This was further confirmed by the appearance of a MAPE degradation peak at 448°C, observed in the modified fibers but absent in the unmodified counterparts. Composites made with unmodified hemp fibers (UT30) showed a significant increase in modulus but not in tensile strength. In contrast, the modification of hemp in solution significantly enhanced the tensile strength of the composites (UTE3S) without significantly affecting the modulus. Increasing the amount of coupling agent (in UTE6S and UTE9S) reinforced this trend, indicating that the thin polymer layer on the surface of the modified hemp fibers notably improved interfacial bonding, with minimal impact on the tensile modulus of the composites.

Reusable and non-invasive TiO2-based photodynamic transdermal patch (RPT) for treating MDR-negative bacteria strain and promote wound healing through a synergistic approach of ROS-induced RNS

Wound healing is delayed due to the infection and biofilm formation of antibiotic-resistant species of gram-negative bacteria especially Pseudomonas aeruginosa and Escherichia coli. Antibacterial photodynamic therapy provides an efficient therapeutic strategy for overcoming drug resistance by producing reactive oxygen species (ROS) and reactive nitrogen species (RNS). Here, we have designed a low-cost light emitting diode (LED) based reusable and non-invasive titanium dioxide nanoparticles patch which is sandwiched between the thin polymer layers. The light-induced pore formation in the polymeric film due to the free radical, in turn, passes through the system and kills the bacteria rather than nanoparticles entering the system resulting in the reusability nature of the patch. The patch's in vitro antibacterial and antibiofilm activity and their mechanism (synergic ROS-induced RNS) were studied. In addition, the reusable antibacterial properties, biocompatibility and wound-healing properties of the patch were also successfully elucidated.

Tunable Assembly of Photocatalytic Colloidal Coatings for Antibacterial Applications.

In this study, evaporation-induced size segregation and interparticle interactions are harnessed to tune the microstructure of photocatalytic colloidal coatings containing TiO2 nanoparticles and polymer particles. This enabled the fabrication of a library of five distinct microstructures: TiO2-on-top stratification, a thin top layer of polymer or TiO2, homogeneous films of raspberry particles, and a sandwich structure. The photocatalytic and antibacterial activities of the coatings were evaluated by testing the viability of Methicillin-resistant Staphylococcus aureus (MRSA) bacteria using the ISO-27447 protocol, showing a strong correlation with the microstructure. UVA irradiation for 4 h induces a reduction in MRSA viability in all coating systems, ranging from 0.6 to 1.1 log. Films with TiO2-enriched top surfaces exhibit better resistance to prolonged exposure to disinfection and bacterial testing. The remaining systems, nonetheless, present higher antibacterial activity because of a larger number of pores and coating defects that enhance light and water accessibility for the generation and transport of reactive oxygen species. This work establishes design rules for photocatalytic coatings based on the interplay between performance and film architecture, offering valuable insights for several applications, including antibacterial surfaces, self-cleaning/antifogging applications, and water purification.

Investigating the spall phenomena in glass filler embedded epoxy composites using laser-induced stress wave

Recently, Singh and Kitey (Experimental Mechanics, 60(7), 2020) used laser-induced stress pulse in conjugation with Michelson's interferometer to measure the spall strength of thin polymer layers. In this investigation, the method is expanded to measure the spall strength of spherical and slender glass filler-reinforced epoxy composites. A filler-reinforced epoxy layer of ∼150 μm was deposited onto a glass substrate, and a short-duration and high-magnitude stress pulse developed at the back surface of the substrate. A complex interaction between the mode-converted main compressive wave and slow-moving secondary tensile wave generated a greater magnification tensile area near the layer's free surface, causing a spall. The composite layers experienced a strain rate of ∼107/s, with the secondary wave not distinct from the interferometric data due to filler-induced multiple mode conversions. An equation correlating strain rate, impedance, and fracture toughness with spall strength was used to ascertain the composite layers' spall strength. The findings showed that stiff reinforcements improve epoxy spall strength, with milled fiber composites exhibiting greater spall strength than spherical particle cases, as corroborated by optical micrographs showing fiber-bridging across the spalled zone. The spall strength of epoxy composites with 10 % milled fibers was nearly 2.5 times greater than pure epoxy.

Experimental investigation of tribological performance of PTFE-derived solid lubricants in sliding building bearings

Friction pendulum systems (FPS) and sliding bearings are widely used in bridges and buildings for seismic isolation. As their engineering applications increase, there is a growing need to understand the overall tribological performance of sliding-type bearings under severe earthquake conditions. Solid lubricants are the thin layers of polymer installed between the bearing sliding interfaces, and predominate the tribological performance of bearings. Despite advances in material science, few studies have investigated the tribological performance of bearings under seismic action. This study aimed to address this issue by conducting 48 tests with different pressure (15–50 MPa) and peak velocity (4–200 mm/s) levels using three commercially available solid lubricant formulas derived from polytetrafluoroethylene (PTFE). All lubricants exhibited a decrease in the friction coefficient as the pressure level increased. The friction coefficient increased with the peak velocity before 100 mm/s, and remained approximately constant thereafter. The surface wearing mechanism of filler-modified lubricants was different to that of unfilled PTFE. The wearing profile of lubricants was mostly pressure-insensitive and velocity-sensitive. The experimental results demonstrate the significant effect of the pressure and peak velocity on the friction coefficients and wear of bearing lubricants, and provide valuable insights for the design of future solid lubricants in FPS and other sliding bearings for aseismic applications.

Impact of Buried Interface Texture on Compositional Stratification and Ion Migration in Perovskite Solar Cells

AbstractDespite the striking increase in the power conversion efficiency (PCE) of lead‐based perovskite solar cells (PSCs), their poor operational stability impedes their commercialization. Among the various factors that influence device stability, ion migration has been identified as a key driver of degradation. In this work, the focus is on studying ion migration‐induced degradation in inverted architecture PSCs, which employ either a thin polymer layer or a self‐assembled monolayer (SAM) for hole extraction. It is demonstrated that the difference in texture imposed by the use of these hole transport layers (HTL) is an important and thus far inconspicuous factor that impacts ion migration, and consequently device stability. By investigating the buried interface in detail, it is revealed that its texture has a strong impact on the vertical compositional stratification in the perovskite active layer. By monitoring bias‐induced ion migration in devices with different hole extraction layers, it is demonstrated that the smooth polymer‐based HTL results in a higher degree of ion migration than the rough SAM HTL, corresponding to a stronger degradation in the former. These results further indicate that the use of SAMs for hole extraction is a promising strategy to suppress ion migration and improve device efficiency.

Observations and impact of char layer formation and loss for engineered timber

The char layer plays a critical role in the fire behaviour of engineered timber. Several chemical and physical processes can reduce char layer thickness and integrity. A series of experiments studied 12 cross-laminated timber (CLT) columns (130 × 790 × 125 mm WxHxD) exposed to combined thermal (20 kW/m2 or 50 kW/m2) and mechanical loading (39 kN, eccentric). Char loss from the surface lamella was observed and the impact of this on the thermal response of the timber studied. In all cases, unprotected CLT exhibited fall-off of charred pieces. Cracking, shrinkage and movement of char contributed significantly to the exposure of underlying timber sections to external heating. There was no direct correlation between char fall-off and the measured glue line temperature in this configuration. To enable comparison between CLT with and without char fall-off, a thin layer of glass fibre-reinforced polymer was added to the exposed surface of six samples which prevented all char fall-off. Retention of the char layer significantly decreased temperatures beneath the char layer, loss of section and burning duration compared to samples with char fall-off.

Pilot-scale study of membrane-coated cathodes: Achieving high cathodic efficiency and outstanding stability in chlorate electrolysis

Sodium chlorate (NaClO3) is primarily used for producing chlorine dioxide, an environmentally friendly bleaching agent for pulp. Currently, dichromate is used as an electrolyte additive in the chlorate process where it has several functions, but due to health and environmental risks associated with chromate, there is a need for a less toxic alternative. In the present study, we prepared a membrane-coated cathode as a substitute for chromium(VI), to keep a high current efficiency in chlorate electrolysis. This electrode employed an industrially relevant electrode with active catalysts as the substrate and a thin layer of ion exchange polymer as the coating. The coating effectively blocked anions such as ClO− and ClO3− from reaching the cathode, thereby suppressing cathodic side reactions. We conducted a series of electrochemical characterizations on the membrane-coated cathodes with varying coating thickness and tested them in a pilot-scale setup for efficiency and stability under industrial testing conditions.

Surface-Functionalized Microgels as Artificial Antigen-Presenting Cells to Regulate Expansion of T Cells.

Artificial antigen-presenting cells (aAPCs) are currently used to manufacture T cells for adoptive therapy in cancer treatment, but a readily tunable and modular system can enable both rapid T cell expansion and control over T cell phenotype. Here, it is shown that microgels with tailored surface biochemical properties can serve as aAPCs to mediate T cell activation and expansion. Surface functionalization of microgels is achieved via layer-by-layer coating using oppositely charged polymers, forming a thin but dense polymer layer on the surface. This facile and versatile approach is compatible with a variety of coating polymers and allows efficient and flexible surface-specific conjugation of defined peptides or proteins. The authors demonstrate that tethering appropriate stimulatory ligands on the microgel surface efficiently activates T cells for polyclonal and antigen-specific expansion. The expansion, phenotype, and functional outcome of primary mouse and human T cells can be regulated by modulating the concentration, ratio, and distribution of stimulatory ligands presented on microgel surfaces as well as the stiffness and viscoelasticity of the microgels.

Assessing the hydromechanical control of plant growth.

Multicellular organisms grow and acquire their shapes through the differential expansion and deformation of their cells. Recent research has addressed the role of cell and tissue mechanical properties in these processes. In plants, it is believed that growth rate is a function of the mechanical stress exerted on the cell wall, the thin polymeric layer surrounding cells, involving an effective viscosity. Nevertheless, recent studies have questioned this view, suggesting that cell wall elasticity sets the growth rate or that uptake of water is limiting for plant growth. To assess these issues, we developed a microfluidic device to quantify the growth rates, elastic properties and hydraulic conductivity of individual Marchantia polymorpha plants in a controlled environment with a high throughput. We characterized the effect of osmotic treatment and abscisic acid on growth and hydromechanical properties. Overall, the instantaneous growth rate of individuals is correlated with both bulk elastic modulus and hydraulic conductivity. Our results are consistent with a framework in which the growth rate is determined primarily by the elasticity of the wall and its remodelling, and secondarily by hydraulic conductivity. Accordingly, the coupling between the chemistry of the cell wall and the hydromechanics of the cell appears as key to set growth patterns during morphogenesis.

Improved ammonia sensitivity and broadband photodetection by using PBTTT-C14/WS2-QDs nano-heterojunction based thin film transistor

An ambient temperature broadband photo-detector and ammonia (NH3) gas sensor devices are developed with PBTTT-C14/WS2-QDs heterojunction thin film. This composite thin film of PBTTT-C14 conjugate polymer and hydrothermally synthesized WS2-QDs have been deposited by high yield and cost-effective ‘floating film transfer method’ (FTM), which works as a channel (p-type) of the thin film transistor (TFT). To determine the NH3 sensing behavior of the TFT, different concentrations of analyte (0.5–20 ppm) have been exposed on the channel of the TFT, which shows the response of ∼ 50 % at 10 ppm ammonia concentration that is significantly higher than PBTTT-C14 only TFT. This improvement is made possible by the NH3-responsive depleted layer of polymer/QDs heterojunction, which varies widely in the presence of ammonia. As a consequence, the ON/OFF ratio, carrier mobility and threshold voltage (Vth) of the device changes in a wider range. Besides, this TFT based gas sensor is also highly selective to the other interfering gases. In addition to NH3 gas sensitivity, This TFT also shows very high photosensitivity under white light illumination that enhances ‘ON’ and ‘OFF’ current of the device by ∼ 2.2 and 70 times, respectively under one sun white light illumination, whereas Vth of the device is shifted by ∼ 22 V. Besides, the device shows quite fast response/ recovery time under NH3 gas exposure and light illumination.

Functional Polymer Thin Films for Establishing an Effective Electrode Interface in Sulfide‐Based Solid‐State Batteries

AbstractSulfide solid electrolytes (SSEs) have garnered significant attention for their high ionic conductivity in the development of all‐solid‐state batteries (ASSBs). However, SSEs face challenges due to poor chemical and electrochemical stability, leading to SE decomposition at the anode, which in turn increases internal resistance and reduces cycle performance. Herein, to address this issue, thin polymer layers are applied to prevent direct contact between the SSE and anode using the initiated chemical vapor deposition process. This method facilitates the uniform coating of eight types of polymers with polar functionalities on indium (In) anodes. Half‐cell tests and X‐ray photoelectron spectroscopy analysis reveals that poly(acrylic acid) and poly((perfluorohexyl)ethyl acrylate), containing ─COOH and C─F bonds respectively, effectively stabilized the In/SSE interface. In full cells assembled with polymer‐coated In and LiNi0.8Co0.1Mn0.1O2 (NCM811), capacity retention show remarkable improvement, achieving 64.8% for In@pAA and 50.7% for In@pC6FA after 100 cycles, compared to 29.0% for bare In. This study provides insights into the interaction between polar bonds in polymers and SSEs, potentially bridging a significant knowledge gap resulting from the significant lack of research investigating the relationship between polymers, one of the primary materials commonly used in ASSBs.

Fast Processing Affects the Relaxation of Polymers: The Slow Arrhenius Process Can Probe Stress at the Molecular Level.

Polymer materials are commonly processed at rates higher than those at which their molecules spontaneously reach equilibrium conditions. The resulting nonequilibrium conformations might significantly affect the mechanical behavior and the shelf time of the final products. To understand how processing-properties relations work, we investigated the impact of spin coating, an archetypical method to fabricate thin polymer layers. By using a geometry in which nonequilibrium conformations are frozen over sufficiently long experimental times, we could identify how molecular relaxation is affected by fast preparation methods. We find that while the (α-)segmental relaxation is not affected by the rate at which films are processed, the intensity of the slow Arrhenius process (SAP), a relaxation mechanism active both above and below the glass transition, can be used as a probe of the degree of mechanical stress experienced by the material.

Biodegradable polymer composite containing ground corn stalk modified with polydopamine

AbstractModifying plant fibers before their incorporation into the polymer matrix is a crucial factor that influences the characteristics of the resulting composites. This article reports on a study that investigated how modifying ground corn stalks impacted certain properties of a biodegradable polymer composite. The composite was made up of a mixture of polylactide and polycaprolactone in a ratio of 70:30, and the filler was modified using dopamine hydrochloride to create a thin polymer layer of polydopamine on the surface of the particles. The study evaluated the structural, mechanical, thermal, and thermomechanical properties of composites that contained 30%, 40%, or 50% of the filler by weight. Additionally, the tests to determine how well the composites would compost in an industrial setting were conducted. The results of the study showed that modifying the filler particles had a positive impact on most of the properties tested, including tensile strength, flexural strength, Young's modulus, storage modulus, and impact strength. Interestingly, despite concerns about the antibacterial properties of polydopamine, the composting tests revealed that the modification of the filler particles did not have any negative effects on the industrial composting process.

Electrochemical Sensing of Vitamin C Using Graphene/Poly-Thionine Composite Film Modified Electrode

Background: Gastric irritation and kidney problems occur due to excess ascorbic acid content, whereas the lack of ascorbic acid in the human body leads to poor wound healing, muscle degeneration, and anemia. Objectives: Herein, we report the development of an electrochemical sensor for the detection of ascorbic acid using poly-thionine/ graphene (P-Th/Gr) modified glassy carbon electrode (GCE) in 0.1 M phosphate buffer solution (PBS) (pH 7.4). Electrostatically fused graphene affixed with poly-thionine was successfully illustrated for effective voltammetric sensing of ascorbic acid. Methodology: FE-SEM indicated the blended edge of a 2D graphene sheet with a deposited thin layer of polymer, which confirmed the formation of a poly-thionine/graphene composite. The cyclic voltammetry (CV) technique was utilized for the electrochemical assay of ascorbic acid (AsA, Vitamin C). Results: With the increased concentrations of AsA, the oxidation peak current of ascorbic acid increased at 0.0 V, and the overpotential showed a decrease compared to bare GCE. The effect of scan rate on cyclic voltammograms was recorded with 500 μM of ascorbic acid from 10 mV/s to 250 mV/s, which indicated that AsA oxidation is a diffusion-controlled process on poly-thionine/ graphene-modified electrode. Conclusion: It was concluded that a poly-thionine/graphene composite-based sensor could be useful for the determination of ascorbic acid in various biological samples.

Efficient Approach for Direct Robust Surface Grafting of Polyethyleneimine onto a Polyester Surface during Moulding.

This paper uses a very effective way for surface modification of thermoplastic polymers during moulding. It is based on a grafting reaction between a thin layer of a functional polymer, deposited on a substrate in advance, and a polymer melt. In this paper, a glycol-modified polyethylene terephthalate (PETG) that was brought in contact with a polyethyleneimine layer during fused filament fabrication is investigated. The focus of this paper is the investigation of the reaction product. Grafting was realised by the formation of stable amide bonds by amidation of ester groups in the main chain of a PETG. XPS investigations revealed that the conversion of amino groups was very high, the distribution was even, and the quantity of amino groups per polyester surface area was still very high. The surface properties of the produced polyester part were mainly characterised by polyethyleneimine. The grafting was able to resist several cycles of extraction in alkaline solutions. The stability was only limited by saponification of the polyester. The degree of surface modification was dependent on the molar mass of polyethyleneimine. This could be rationalised, because grafting only occurred with the one polyethyleneimine molecule that is in close vicinity to the polyester surface when both components come in contact. Fused deposition modelling was chosen as the model process with control over each processing step. However, any other moulding process may be applied, particularly injection moulding for mass production.