Investigation of Polyaniline and a Functionalised Derivative as Antimicrobial Additives to Create Contamination Resistant Surfaces

Synthesis and characterization of antimicrobial colloidal polyanilines

The potential application of colloidal polyaniline (PANI) as an antimicrobial is limited by challenges related to solubility in common organic solvents, scalability, and antimicrobial potency. To address these limitations, we introduced a functionalized PANI (fPANI) with carboxyl groups through the polymerisation of aniline and 3-aminobenzoic acid in a 1:1 molar ratio. fPANI is more soluble than PANI which was determined using a qualitative study. We further enhanced the solubility and antimicrobial activity of fPANI by incorporating Ag nanoparticles onto the synthesized fPANI colloid via direct addition of 10 mM AgNO3. The improved solubility can be attributed to an approximately 3-fold reduction in size of particles. Mean particle sizes are measured at 1322 nm for fPANI colloid and 473 nm for fPANI-Ag colloid, showing a high dispersion and deagglomeration effect from Ag nanoparticles. Antimicrobial tests demonstrated that fPANI-Ag colloids exhibited superior potency against Gram-positive Staphylococcus aureus, Gram-negative Escherichia coli, and Bacteriophage PhiX 174 when compared to fPANI alone. The minimum bactericidal concentration (MBC) and minimum virucidal concentration (MVC) values were halved for fPANI-Ag compared to fPANI colloid and attributed to the combination of Ag nanoparticles with the fPANI polymer. The antimicrobial fPANI-Ag colloid presented in this study shows promising results, and further exploration into scale-up can be pursued for potential biomedical applications.

Terrien, a metabolite made by Aspergillus terreus, has activity against Cryptococcus neoformans

Antimicrobial compounds, including antibiotics, have been a cornerstone of modern medicine being able to both treat infections and prevent infections in at-risk people, including those who are immune-compromised and those undergoing routine surgical procedures. Their intense use, including in people, animals, and plants, has led to an increase in the incidence of resistant bacteria and fungi, resulting in a desperate need for novel antimicrobial compounds with new mechanisms of action. Many antimicrobial compounds in current use originate from microbial sources, such as penicillin from the fungus Penicillium chrysogenum (renamed by some as P. rubens). Through a collaboration with Aotearoa New Zealand Crown Research Institute Manaaki Whenua-Landcare Research we have access to a collection of thousands of fungal cultures known as the International Collection of Microorganisms from Plants (ICMP). The ICMP contains both known and novel species which have not been extensively tested for their antimicrobial activity. Initial screening of ICMP isolates for activity against Escherichia coli and Staphylococcus aureus directed our interest towards ICMP 477, an isolate of the soil-inhabiting fungus, Aspergillus terreus. In our investigation of the secondary metabolites of A. terreus, through extraction, fractionation, and purification, we isolated nine known natural products. We evaluated the biological activity of selected compounds against various bacteria and fungi and discovered that terrein (1) has potent activity against the important human pathogen Cryptococcus neoformans.

Scalable Hybrid Antibacterial Surfaces: TiO2 Nanoparticles with Black Silicon

With the increase of drug resistance, there is a need for surface coatings that inhibit microbes without antibiotics. Nanostructured photocatalysts, like TiO₂-coated nanotubes, are promising alternatives to antibiotics. Nanostructures rupture the cell wall by impaling the bacteria. Photocatalysts generate reactive oxygen species (ROS) in the presence of light, which oxidize organic matter. The combined effect of photocatalysts and nanostructures is better than the addition of individual components, as nanostructures also enhance the ROS production by trapping light. The synergetic effect is remarkably effective in reducing the growth of bacterial colonies, but scalability still remains a challenge. Conventional techniques like atomic layer deposition (ALD) are excellent for proof of concept but are not scalable to hundreds of square meters, as needed for practical applications. This report demonstrates two scalable and cost-effective techniques for synthesizing photocatalytic nanostructures: spray- and spin-coating TiO₂ nanoparticles. Unlike ALD, spray- and spin-coated TiO₂ nanoparticles do not reduce the roughness of a structured surface, which improves antibacterial performance by 23%. Integration of nanostructures with spray-coated TiO₂ is potentially a low-cost and scalable technology for large-area antibacterial surfaces.

Thermochromic Polymeric Films for Applications in Active Intelligent Packaging-An Overview

The need for passive sensors to monitor changes in temperature has been critical in several packaging related applications. Most of these applications involve the use of bar codes, inks and equipment that involve constant complex electronic manipulation. The objective of this paper is to explore solutions to temperature measurements that not only provide product information but also the condition of the product in real time, specifically shelf-life. The study will explore previously proposed solutions as well as plans for modified approaches that involve the use of smart polymers as temperature sensors.

Revamping squid gladii to biodegradable composites: In situ grafting of polyaniline to β-chitin and their antibacterial activity

The global health concern on wound care is becoming more challenging with the emerging prevalence of inexorable antibiotic resistance. Amidst this crisis, various material innovations have been made to combat this dilemma. Herein, squid pens, which are regarded as discards in the seafood industry, were biorefined into β-chitin-graft-polyaniline (β-chitin-g-PANI) composites for possible wound dressing development. β-chitin was first chemically extracted from gladii, and was then grafted with PANI via in situ chemical oxidative polymerization of various concentrations of aniline, to produce the β-chitin-g-PANI composites. Supporting data from FTIR, UV-Vis, SEM, TGA, and DSC suggest that β-chitin was successfully grafted with PANI. Moreover, improved conductivity and in vitro degradation of the composites were observed as compared to β-chitin and PANI alone, respectively. Zones of inhibition observed from agar diffusion method suggest that the synthesized composites have antibacterial activity against E. coli and S. aureus. The resulting physicochemical and biological properties of integrating conducting PANI to β-chitin substantiated and rendered the β-chitin-g-PANI composites desirable candidates for the development wound care products.

Antimicrobial Properties of the Polyaniline Composites against Pseudomonas aeruginosa and Klebsiella pneumoniae

CuO, TiO2, or SiO2 was decorated on polyaniline (PANI) by a sonochemical method, and their antimicrobial properties were investigated for two common Gram-negative pathogens: Pseudomonas aeruginosa (PA) and Klebsiella pneumoniae (KP). Without PANI, CuO, TiO2, or SiO2 with a concentration of 220 µg/mL exhibited no antimicrobial activities. In contrast, PANI-CuO and PANI-TiO2 (1 mg/mL, each) completely suppressed the PA growth after 6 h of exposure, compared to 12 h for the PANI-SiO2 at the same concentration. The damage caused by PANI-SiO2 to KP was less effective, compared to that of PANI-TiO2 with the eradication time of 12 h versus 6 h, respectively. This bacterium was not affected by PANI-CuO. All the composites bind tightly to the negative groups of bacteria cell walls to compromise their regular activities, leading to the damage of the cell wall envelope and eventual cell lysis.

Antimicrobial Properties of Polyaniline and Polypyrrole Decorated with Zinc-Doped Copper Oxide Microparticles

Polyaniline (PANI) and polypyrrole (PPY) were synthesized by carbon dots (CDs) under UV irradiation and then sonicated together with zinc acetate and copper acetate to form the PANI-Zn@CuO and PPY-Zn@Cu composites. The former consisted of agglomerated spherical particles with diameters of 1–5 µm, whereas the latter displayed irregular stick shapes with similar diameters. The bacterial potency of the composites against Escherichia coli and Staphylococcus aureus was enhanced remarkably with Zn doping in the CuO matrix, designated as Zn_0.11Cu_0.89O, at 0.144 mg/mL. The cell death was mainly attributed to the release of reactive oxygen species (ROS) that would severely damage DNA, proteins, and lipids. Bacteria could adhere to neutral surfaces of the composites by van der Waals attractive forces. The binding event disrupted the native surface charge of bacterial cells to induce cell lysis and result in eventual cell death.

Special Issue: Conductive Polymers: Materials and Applications

Intrinsically conductive polymers (CPs) combine the inherent mechanical properties of organic polymers with charge transport, opto-electronic and redox properties that can be easily tuned up to those typical of semiconductors and metals. The control of the morphology at the nanoscale and the design of CP-based composite materials have expanded their multifunctional character even further. These virtues have been exploited to advantage in opto-electronic devices, energy-conversion and storage systems, sensors and actuators, and more recently in applications related to biomedical and separation science or adsorbents for pollutant removal. The special issue “Conductive Polymers: Materials and Applications” was compiled by gathering contributions that cover the latest advances in the field, with special emphasis upon emerging applications.

Progress in Conductive Polyaniline-Based Nanocomposites for Biomedical Applications: A Review

Inherently conducting polymers (ICPs) are a specific category of synthetic polymers with distinctive electro-optic properties, which involve conjugated chains with alternating single and double bonds. Polyaniline (PANI), as one of the most well-known ICPs, has outstanding potential applications in biomedicine because of its high electrical conductivity and biocompatibility caused by its hydrophilic nature, low-toxicity, good environmental stability, and nanostructured morphology. Some of the limitations in the use of PANI, such as its low processability and degradability, can be overcome by the preparation of its blends and nanocomposites with various (bio)polymers and nanomaterials, respectively. This review describes the state-of-the-art of biological activities and applications of conductive PANI-based nanocomposites in the biomedical fields, such as antimicrobial therapy, drug delivery, biosensors, nerve regeneration, and tissue engineering. The latest progresses in the biomedical applications of PANI-based nanocomposites are reviewed to provide a background for future research.

The antimicrobial action of polyaniline involves production of oxidative stress while functionalisation of polyaniline introduces additional mechanisms

Polyaniline (PANI) and functionalised polyanilines (fPANI) are novel antimicrobial agents whose mechanism of action was investigated. Escherichia coli single gene deletion mutants revealed that the antimicrobial mechanism of PANI likely involves production of hydrogen peroxide while homopolymer poly(3-aminobenzoic acid), P3ABA, used as an example of a fPANI, disrupts metabolic and respiratory machinery, by targeting ATP synthase and causes acid stress. PANI was more active against E. coli in aerobic, compared to anaerobic, conditions, while this was apparent for P3ABA only in rich media. Greater activity in aerobic conditions suggests involvement of reactive oxygen species. P3ABA treatment causes an increase in intracellular free iron, which is linked to perturbation of metabolic enzymes and could promote reactive oxygen species production. Addition of exogenous catalase protected E. coli from PANI antimicrobial action; however, this was not apparent for P3ABA treated cells. The results presented suggest that PANI induces production of hydrogen peroxide, which can promote formation of hydroxyl radicals causing biomolecule damage and potentially cell death. P3ABA is thought to act as an uncoupler by targeting ATP synthase resulting in a futile cycle, which precipitates dysregulation of iron homeostasis, oxidative stress, acid stress, and potentially the fatal loss of proton motive force.