Porous polyimide membranes prepared by wet phase inversion for use in low dielectric applications

Basic amino acid-mediated cationic amphiphilic surfaces for antimicrobial pH monitoring sensor with wound healing effects

BACKGROUND

The wound healing process is a complex cascade of physiological events, which are vulnerable to both our body status and external factors and whose impairment could lead to chronic wounds or wound healing impediments. Conventional wound healing materials are widely used in clinical management, however, they do not usually prevent wounds from being infected by bacteria or viruses. Therefore, simultaneous wound status monitoring and prevention of microbial infection are required to promote healing in clinical wound management.

METHODS

Basic amino acid-modified surfaces were fabricated in a water-based process via a peptide coupling reaction. Specimens were analyzed and characterized by X-ray photoelectron spectroscopy, Kelvin probe force microscopy, atomic force microscopy, contact angle, and molecular electrostatic potential via Gaussian 09. Antimicrobial and biofilm inhibition tests were conducted on Escherichia coli and Staphylococcus epidermidis. Biocompatibility was determined through cytotoxicity tests on human epithelial keratinocytes and human dermal fibroblasts. Wound healing efficacy was confirmed by mouse wound healing and cell staining tests. Workability of the pH sensor on basic amino acid-modified surfaces was evaluated on normal human skin and Staphylococcus epidermidis suspension, and in vivo conditions.

RESULTS

Basic amino acids (lysine and arginine) have pH-dependent zwitterionic functional groups. The basic amino acid-modified surfaces had antifouling and antimicrobial properties similar to those of cationic antimicrobial peptides because zwitterionic functional groups have intrinsic cationic amphiphilic characteristics. Compared with untreated polyimide and modified anionic acid (leucine), basic amino acid-modified polyimide surfaces displayed excellent bactericidal, antifouling (reduction ~ 99.6%) and biofilm inhibition performance. The basic amino acid-modified polyimide surfaces also exhibited wound healing efficacy and excellent biocompatibility, confirmed by cytotoxicity and ICR mouse wound healing tests. The basic amino acid-modified surface-based pH monitoring sensor was workable (sensitivity 20 mV pH-1) under various pH and bacterial contamination conditions.

CONCLUSION

Here, we developed a biocompatible and pH-monitorable wound healing dressing with antimicrobial activity via basic amino acid-mediated surface modification, creating cationic amphiphilic surfaces. Basic amino acid-modified polyimide is promising for monitoring wounds, protecting them from microbial infection, and promoting their healing. Our findings are expected to contribute to wound management and could be expanded to various wearable healthcare devices for clinical, biomedical, and healthcare applications.

The multicomponent synergistic effect of a hierarchical Li0.485La0.505TiO3 solid-state electrolyte for dendrite-free lithium-metal batteries

Development of a composite electrolyte with high ionic conductivity, excellent electrochemical stability and preeminent mechanical strength is beneficial for suppressing Li-dendrite penetration and unstable interfacial reactions in solid-state Li-metal batteries. Herein, a novel composite electrolyte material comprising perovskite Li_0.485La_0.505TiO₃ (LLTO), poly(ethylene oxide) (PEO), and a barium titanate (BTO)-polyimide (PI) composite matrix has been successfully fabricated. Benefiting from the well-defined ion channels, the resulting BTO-PI@LLTO-PEO-FEC-LiTFSI (BP@LPFL) exhibits excellent cycling stability, low interfacial resistance, enhanced mechanical strength, and high ionic conductivity. Particularly, BP@LPFL possesses an excellent ionic conductivity of 3.0 × 10^-4 S cm^-1 at room temperature and achieves a wide electrochemical window of 5.2 V (vs. Li⁺/Li). For Li-LiFePO₄ batteries, such an ingenious structure yields a discharge capacity of 124 mA h g^-1 at 0.1 C after 200 cycles at room temperature and delivers a discharge capacity of 165 mA h g^-1 at 0.1 C after 110 cycles at 60 °C. Additionally, the symmetric Li cell remains stable after 700 h at a current density of 0.5 mA cm^-2. Furthermore, ex situ X-ray photoelectron spectroscopy and ex situ scanning electron microscopy were used to verify the interface evolution. Besides, a flexible full battery is fabricated, which exhibits impressive performance. These properties presented here provide support for BP@LPFL as a feasible candidate electrolyte for solid-state lithium batteries.

Amino acid-mediated negatively charged surface improve antifouling and tribological characteristics for medical applications

To prevent infections associated with biomedical catheters, various antimicrobial coatings have been investigated. However, those materials do not provide consistent antibacterial effects or biocompatibility, generally, due to degradation of the coating materials, in vivo. Additionally, biomedical catheters must have low surface friction to reduce tribological damage. In this study, we developed an antifouling surface composed of biocompatible amino acids (leucine, taurine, and aspartic acid) on polyimide, via modification using a series of facile immersion steps with waterborne reactions. The naturally derived amino acid could be formed highly biostable amide bonds on the polyimide surface like peptides. The amino acid-modified surface formed a water layer with antifouling performance through the hydrophilic properties of amino acids. Amino acid-mediated modification reduced adhesion up to 84.45% and 94.81% against Escherichia coli and Staphylococcus epidermidis, respectively, and exhibited an excellent prevention to adhesion against the proteins, albumin and fibrinogen. Evaluation of the surface friction of the catheter revealed a dramatic reduction in the tribological force after amino acid modification on polyimide that of 0.81 N to aspartic acid of 0.44 N. These results clearly demonstrate a reduced occurrence of infections, thrombi and tribological damage following the relatively facile surface modification of catheters. The proposed modification method can be used in a continuous manufacturing process via using the same time of modification steps for the easy producing the product. Moreover, the method uses biocompatible naturally derived materials and can be applied to medical equipment that requires biocompatibility and biofunctionality with polyimide surfaces.

Dielectric properties of calamansi (Citrus microcarpa) under high-temperature treatment

High-temperature treatment of fruit is a developing way of decreasing nutrient loss and preventing decay. Its effect on calamansi (Citrus microcarpa) has not yet been reported. This study aims to study the effects of high-temperature treatment via dielectric properties. The results show that high-temperature treatment of calamansi suppresses the dielectric constant between 200 MHz and 20 GHz and alters loss factor between 200 MHz and 10 GHz. Storage at room temperature can affect loss factor between 4.5 and 10 GHz. These results may indicate that the dehydration process first affects the loss factor from 4.5 to 10 GHz, and then from 200 MHz to 4.5 GHz. This study may be favorable for evaluating calamansi's quality during storage and transportation. Moreover, the loss factor under 10 GHz is promising as an index for monitoring the water deficit and for assessing the adopted pre-treatment on calamansi. PRACTICAL APPLICATION: The quality inspector can use nondestructive examination ways to measure the dielectric property for evaluating Citrus microcarpa's quality and storage time after harvest. Moreover, the adopted pre-treatment may be speculated.

Mass-Synthesized Solution-Processable Polyimide Gate Dielectrics for Electrically Stable Operating OFETs and Integrated Circuits

Polyimides (PIs) are widely utilized polymeric materials for high-temperature plastics, adhesives, dielectrics, nonlinear optical materials, flexible hard-coating films, and substrates for flexible electronics. PIs can be facilely mass-produced through factory methods, so the industrial application value is limitless. Herein, we synthesized a typical poly(amic acid) (PAA) precursor-based solution through an industrialized reactor for mass production and applied the prepared solution to form thin films of PI using thermal imidization. The deposited PI thin films were successfully applied as gate dielectrics for organic field-effect transistors (OFETs). The PI layers showed suitable characteristics for dielectrics, such as a smooth surface, low leakage current density, uniform dielectric constant (k) values regardless of frequency, and compatibility with organic semiconductors. Utilizing this PI layer, we were able to fabricate electrically stable operated OFETs, which exhibited a threshold voltage shift lower than 1 V under bias-stress conditions and a field-effect mobility of 4.29 cm² V^-1 s^-1. Moreover, integrated logic gates were manufactured using these well-operated OFETs and displayed suitable operation behavior.

Polyimide-Derived Carbon-Coated Li4Ti5O12 as High-Rate Anode Materials for Lithium Ion Batteries

Carbon-coated Li₄Ti₅O₁₂ (LTO) has been prepared using polyimide (PI) as a carbon source via the thermal imidization of polyamic acid (PAA) followed by a carbonization process. In this study, the PI with different structures based on pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) moieties have been synthesized. The effect of the PI structure on the electrochemical performance of the carbon-coated LTO has been investigated. The results indicate that the molecular arrangement of PI can be improved when the rigid p-PDA units are introduced into the PI backbone. The carbons derived from the p-PDA-based PI show a more regular graphite structure with fewer defects and higher conductivity. As a result, the carbon-coated LTO exhibits a better rate performance with a discharge capacity of 137.5 mAh/g at 20 C, which is almost 1.5 times larger than that of bare LTO (94.4 mAh/g).

Ammonia Storage in Hydrogen Bond-Rich Microporous Polymers

The fascinating structural flexibility of porous polymers is highly attractive because it can result in optimized materials with specific host-guest interactions. Nevertheless, the fundamental mechanisms responsible for controlling the weak interactions of these hydrogen bond-rich networks-essential for developing smart task-specific materials used in recognition, capture, and sequestration processes-remain unexplored. Herein, by systematically comparing performance changes between poly(amic acid) (PAA)- and polycyclic imide (PI)-based porous polymers before and after NH₃ adsorption, the role of hydrogen bonds in conformational lability and responsiveness toward guest molecules is highlighted. By combining thermal gravimetric analysis with neutron spectroscopy supported by DFT calculations, we demonstrate that PAA's chemical and physical stability is enhanced by the presence of stronger host-guest interactions. This observation also emphasizes the idea that efficient adsorption relies on having a high number of sites, upon which gas molecules can adsorb with greater affinity via strong hydrogen bonding interactions.

Influence of Coagulation Bath Temperature on the Structure and Dielectric Properties of Porous Polyimide Films in Different Solvent Systems

In this work, the effect of coagulation bath temperature in different solvent systems [1,4-butyrolactone (GBL)/N,N-dimethylacetamide (DMAC)] on the structure and dielectric properties of polyimide (PI) films was investigated for the first time. The solubility parameter was introduced to explain the formation process of porous PI films. The results showed that the changed tendency of the dielectric constant versus temperature is opposite for the single-solvent system and cosolvent system. For a single DMAC and GBL solvent, the dielectric constants of the films decreased with increasing temperature. In contrast, the dielectric constants increased with the increase in temperature for the GBL/DMAC cosolvent system. Moreover, the measured porosities were applied to estimate the dielectric constants of the PI films. This showed that the porosity increased with increasing temperature for a single-solvent system, while it decreased for a cosolvent system. Scanning electron microscopy images suggested that the variation trends are derived from the different influences of the temperature on the structure and morphology. Thus, this study reveals the effect of coagulation bath temperature on the structure and dielectric properties of porous PI films and provides the guidance for the design and optimization of architectures for high-performance porous films.

Fabrication of Nanostructured Polyamic Acid Membranes for Antimicrobially Enhanced Water Purification

Water scarcity and quality challenges facing the world can be alleviated by Point-of-Use filtration devices (POU). The use of filtration membranes in POU devices has been limited largely because of membrane fouling, which occurs when suspended solids, microbes, and organic materials are deposited on the surface of filtration membranes significantly decreasing the membrane lifespan, thereby increasing operation costs. There is need therefore to develop filtration membranes that are devoid of these challenges. In this work, nanotechnology was used to fabricate nanostructured polyamic acid (nPAA) membranes, which can be used for microbial decontamination of water. The PAA was used as support and reducing agent to introduce silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) with antimicrobial properties. The nPAA membranes were fabricated via thermal and wet phase inversion technique and then tested against Escherichia coli and Staphylococcus aureus following standard tests. The resulting nanoparticles exhibited excellent dispersibility and stability as indicated by the color change of the solution and increments of optical density at 415 nm for AgNPs and 520 nm for AuNPs. The wet phase inversion process used produced highly porous, strong, and flexible nPAA membranes, which showed well-dispersed spherical AuNPs and AgNPs whose rough average size was found to be 35 nm and 25 nm, respectively. The AgNPs demonstrated inhibition for both gram positive E. coli and gram negative S. aureus, with a better inhibitory activity against S. aureus. A synergistic enhancement of AgNPs antimicrobial activity upon AuNPs addition was demonstrated. The nPAA membranes can thus be used to remove microbials from water and can hence be used in water purification.

Facile Synthesis of Robust and Pore-Size-Tunable Nanoporous Covalent Framework Membrane by Simultaneous Gelation and Phase Separation of Covalent Network/Poly(methyl methacrylate) Mixture

We report a facile route toward the preparation of organic-solvent-resistant and three-dimensionally continuous nanoporous covalent framework membrane. The membrane was prepared from the blend of linear poly(methyl methacrylate) and the cross-linked polyurea-based organic network, followed by selective removal of the linear polymer part. The pore morphologies, porosity, and solvent permeation properties of the membrane could be simply modified by the initial composition of the poly(methyl methacrylate) added to a sol of the organic network. The pore was three-dimensionally continuous with pore size ranging from 5 nm to tens of nanometers. Despite the broad pore size distribution, ultrafiltration of sub-10 nm solutes was realized with a molecular size cutoff near 5 nm thanks to the bicontinuous pore structure of the membrane. The nanoporous structure exhibited long-term resistance to organic solvents as well as thermal stability and mechanical strength. The separation performance remained unchanged in organic-rich medium for a prolonged time. Our strategy provides a synthetic route to a structurally robust, three-dimensionally continuous nanoporous polymeric membrane for potential application that necessitates the use of organic solvent.

Silsesquioxane polymer as a potential scaffold for laryngeal reconstruction

Cancer, disease and trauma to the larynx and their treatment can lead to permanent loss of structures critical to voice, breathing and swallowing. Engineered partial or total laryngeal replacements would need to match the ambitious specifications of replicating functionality, outer biocompatibility, and permissiveness for an inner mucosal lining. Here we present porous polyhedral oligomeric silsesquioxane-poly(carbonate urea) urethane (POSS-PCUU) as a potential scaffold for engineering laryngeal tissue. Specifically, we employ a precipitation and porogen leaching technique for manufacturing the polymer. The polymer is chemically consistent across all sample types and produces a foam-like scaffold with two distinct topographies and an internal structure composed of nano- and micro-pores. While the highly porous internal structure of the scaffold contributes to the complex tensile behaviour of the polymer, the surface of the scaffold remains largely non-porous. The low number of pores minimise access for cells, although primary fibroblasts and epithelial cells do attach and proliferate on the polymer surface. Our data show that with a change in manufacturing protocol to produce porous polymer surfaces, POSS-PCUU may be a potential candidate for overcoming some of the limitations associated with laryngeal reconstruction and regeneration.

Honeycomb-Patterned Polyimide Film as a Versatile Coating for High-Performance Dielectric Material

A honeycomb-patterned porous film was conveniently prepared by means of the microemulsion method and then used as an effective coating for improving the dielectric properties and water resistance of polyimide (PI) film while maintaining its mechanical properties. The dielectric properties could be regulated by tuning the structure of the porous film through controlling its formation conditions. When suitable conditions were used, the prepared composite PI film exhibited a significant reduction of 28.3 % in its dielectric constant and 9.48-54.99 % in dielectric loss accompanied by an extremely low water uptake of 0.62 % relative to the 2.47 % of flat PI film. The composite PI film also displayed excellent durability under moist conditions, as the dielectric constant was still below 2.4 after exposure to 75 % relative humidity for more than 12 h. This provides a novel method to improve and control the dielectric properties of materials. It also suggests that this film is a suitable candidate for coating dielectric materials in high-humidity environments.

Micron-Sized Pored Membranes Based on Polyvinylidene Difluoride Hexafluoropropylene Prepared by Phase Inversion Techniques

In this study, micron-sized pored membranes, based on the co-polymer polyvinylidene difluoride hexafluoropropylene (PVdF-HFP) were prepared via phase inversion techniques. The aim of the approach was to find less harmful and less toxic solvents to fabricate such films. Therefore, the Hansen solubility approach was used to identify safer and less toxic organic solvents for the phase inversion process, relative to present solvent mixtures, based on acetone, dimethyl formamide, dimethyl acetamide or methanol. With this approach, it was possible to identify cyclopentanone, ethylene glycol and benzyl alcohol as suitable solvents for the membrane preparation process. Physicochemical and mechanical properties were analyzed and compared, which revealed a uniform membrane structure through the cross section. Differences were observed at the top surface, in dependence of both preparation approaches, which are described in detail.

A Microporous Amic Acid Polymer for Enhanced Ammonia Capture

Amic acids, consisting of carboxylic acids and amides, are often utilized as intermediates that can further undergo a dehydration-cyclization step to yield polymeric cyclic imides. Compared with imide-based materials, the presence of Brønsted acidic groups and multiple hydrogen-bond donors and acceptors in materials incorporating amic acids opens up the possibility for a variety of host-guest interactions. Here we report a facile and catalyst-free synthesis of a Brønsted acidic porous poly(amic acid) (PAA) and present its NH₃ uptake properties using gas adsorption and breakthrough measurements. Simple addition of water as a cosolvent to a mixture of tetrakis(4-aminophenyl)methane and pyromellitic anhydride resulted in the formation of PAA in almost quantitative yield. Further mechanistic studies with model compounds revealed the importance of additive water to generate amic acid species selectively without forming cyclic imides at high temperatures. Gas adsorption isotherms and breakthrough curves obtained under dry and humid conditions demonstrate the enhanced NH₃ uptake in the case of PAA compared with the related polycyclic imide at both low and high pressures. Furthermore, the results of adsorption/desorption cycling experiments provide insights into the strength of the interaction between ammonia and the polymers.

Morphology and properties of porous polyimide films prepared through thermally induced phase separation

Porous polyimide (PI) synthesized from 4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-diaminodiphenyl ether (ODA) monomers is a promising material with an ultralow-dielectric constant.

Biodegradable injectable in situ implants and microparticles for sustained release of montelukast: in vitro release, pharmacokinetics, and stability

The objective of this study was to investigate the sustained release of a hydrophilic drug, montelukast (MK), from two biodegradable polymeric drug delivery systems, in situ implant (ISI) and in situ microparticles (ISM). N-Methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), triacetin, and ethyl acetate were selected as solvents. The release of 10% (w/v) MK from both systems containing poly-lactic-co-glycolic acid (PLGA) as the biodegradable polymer was compared. Upon contact with the aqueous medium, the PLGA in ISI and ISM systems solidified resulting in implants and microparticles, respectively. The in vitro drug release from the ISI system showed marked difference from miscible solvents (NMP and DMSO) than the partially miscible ones (triacetin and ethyl acetate), and the drug release decreased with increased PLGA concentration. In the ISM system, the initial in vitro drug release decreased with decreased ratio of polymer phase to external oil phase. In vivo studies in rats showed that ISM had slower drug release than the drug release from ISI. Also, the ISM system when compared to ISI system had significantly reduced initial burst effect. In vitro as well as the in vivo studies for both ISI and ISM systems showed sustained release of MK. The ISM system is suitable for sustained release of MK over 4-week period with a lower initial burst compared to the ISI system. Stability studies of the ISI and ISM formulations showed that MK is stable in the formulations stored at 4°C for more than 2 years.