Conductive bacterial cellulose by in situ laccase polymerization of aniline

Conductive bacterial cellulose: From drug delivery to flexible electronics

Bacterial cellulose (BC) is a chemically pure, non-toxic, and non-pyrogenic natural polymer with high mechanical strength and a complex fibrillar porous structure. Due to these unique biological and physical properties, BC has been amply used in the food industry and, to a somewhat lesser extent, in medicine and cosmetology. To expand its application the BC structure can be modified. This review presented some recent developments in electrically conductive BC-based composites. The as-synthesized BC is an excellent dielectric. Conductive polymers, graphene oxide, nanoparticles and other materials are used to provide it with conductive properties. Conductive bacterial cellulose (CBC) is currently investigated in numerous areas including electrically conductive scaffolds for tissue regeneration, implantable and wearable biointerfaces, flexible batteries, sensors, EMI shielding composites. However, there are several issues to be addressed before CBC composites can enter the market, namely, composite mechanical strength reduction, porosity decrease, change in chemical characteristics. Some of them can be addressed both at the stage of synthesis, biologically, or by adding (nano)materials with the required properties to the BC structure. We propose several solutions to meet the challenges and suggest some promising BC applications.

Transparent, conductive and superhydrophobic cellulose films for flexible electrode application

Cellulose has shown encouraging properties in many applications, such as energy storage, optical instrument and catalysis. In particular, cellulose films have shown potential applications in flexible transparent devices and are expected to replace indium-tin oxide (ITO). However, cellulose is highly hydrophilic and electrically insulating, which limits its scope of application. In this study, the conductivity (R _s = 40.3 Ω sq^-1), transparency (81.4%) and superhydrophobicity (static contact angle = 153.2°, sliding angle = 4.1°) of cellulose film (CTSC-P) are reported. First, before suction filtration to prepare the film, cellulose was oxidized to improve dispersibility and mechanical strength. Then, the obtained film was hydrophobically modified by grafting long-chain silanes on the surface, followed by electrospinning and electroless plating. In general, the design is an ingenious way to manufacture transparent, conductive, and super-hydrophobic films in the future, and is transformed into a flexible electronic technically feasible device.

Synthesis-property-performance relationships of multifunctional bacterial cellulose composites fermented in situ alkali lignin medium

This work demonstrates a unique approach of utilizing alkali lignin (AL), as smart additive to in situ BC fermentation in which it concurrently acts as promoter to microbial growth as well as reinforcing filler for fabrication of multifunctional composites. Traditionally, BC fermentation is accompanied by inhibitor formation with sudden drop in pH leading to low yield and biomass growth. AL due to its antioxidant nature prevents formation of gluconic acid as byproduct, at ∼0.25 wt.% AL based on inhibitory byproduct kinetics. Interestingly, AL self-assembles to form primary and secondary structures in BC pores, resulting in simultaneous improvement in thermal stability as well as toughness. The BC/AL films show strong UV-blocking capacity with prolonged radical scavenging activity and preventing browning of freshly cut apples making it suitable as food packaging. Therefore, present work opens up new avenues for fabrication of high-performance BC-based composites through selection of smart materials which can simultaneously improve BC bioprocessing.

Carboxymethyl Cellulose (CMC) as a Template for Laccase-Assisted Oxidation of Aniline

Polyaniline (PANi) is a conducting polymer which has been subject of intensive research on the exploitation of new products and applications. The main aim of the work is the development of a conductive bacterial cellulose (BC)-based material by enzymatic-assisted polymerization of aniline. For this, we study the role of carboxymethyl cellulose (CMC) as a template for the in situ polymerization of aniline. Bacterial cellulose was used as the supporting material for the entrapment of CMC and for the in situ oxidation reactions. The amount of CMC entrapped inside BC was optimized as well as the conditions for laccase-assisted oxidation of aniline. The new oligomers were evaluated by spectrometric techniques, namely 1H NMR and MALDI-TOF, and the functionalized BC surfaces were analyzed by thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), and reflectance spectrophotometry. The conductivity of the developed materials was evaluated using the four-probe methodology. The oligomers obtained after reaction in the presence of CMC as template display a similar structure as when the reaction is conducted only in BC. Though, after oxidation in the presence of this template, the amount of oligomers entrapped inside BC/CMC is considerably higher conferring to the material greater electrical conductivity and coloration. The use of CMC as a template for aniline oxidation on BC seems to be a promising and cheap strategy to improve the yield of functionalization and increment the properties of the materials, namely electrical conductivity and coloration.

Poly(Vinyl Alcohol)-Based Nanofibrous Electrospun Scaffolds for Tissue Engineering Applications

Tissue engineering (TE) holds an enormous potential to develop functional scaffolds resembling the structural organization of native tissues, to improve or replace biological functions and prevent organ transplantation. Amongst the many scaffolding techniques, electrospinning has gained widespread interest because of its outstanding features that enable the production of non-woven fibrous structures with a dimensional organization similar to the extracellular matrix. Various polymers can be electrospun in the form of three-dimensional scaffolds. However, very few are successfully processed using environmentally friendly solvents; poly(vinyl alcohol) (PVA) is one of those. PVA has been investigated for TE scaffolding production due to its excellent biocompatibility, biodegradability, chemo-thermal stability, mechanical performance and, most importantly, because of its ability to be dissolved in aqueous solutions. Here, a complete overview of the applications and recent advances in PVA-based electrospun nanofibrous scaffolds fabrication is provided. The most important achievements in bone, cartilage, skin, vascular, neural and corneal biomedicine, using PVA as a base substrate, are highlighted. Additionally, general concepts concerning the electrospinning technique, the stability of PVA when processed, and crosslinking alternatives to glutaraldehyde are as well reviewed.

Bacterial Nanocellulose Nitrates

Bacterial nanocellulose (BNC) whose biosynthesis fully conforms to green chemistry principles arouses much interest of specialists in technical chemistry and materials science because of its specific properties, such as nanostructure, purity, thermal stability, reactivity, high crystallinity, etc. The functionalization of the BNC surface remains a priority research area of polymers. The present study was aimed at scaled production of an enlarged BNC sample and at synthesizing cellulose nitrate (CN) therefrom. Cyclic biosynthesis of BNC was run in a semisynthetic glucose medium of 10-72 L in volume by using the Medusomyces gisevii Sa-12 symbiont. The most representative BNC sample weighing 6800 g and having an α-cellulose content of 99% and a polymerization degree of 4000 was nitrated. The nitration of freeze-dried BNC was performed with sulfuric-nitric mixed acid. BNC was examined by scanning electron microscopy (SEM) and infrared spectroscopy (IR), and CN was explored to a fuller extent by SEM, IR, thermogravimetric analysis/differential scanning analysis (TGA/DTA) and 13C nuclear magnetic resonance (NMR) spectroscopy. The three-cycle biosynthesis of BNC with an increasing volume of the nutrient medium from 10 to 72 L was successfully scaled up in nonsterile conditions to afford 9432 g of BNC gel-films. CNs with a nitrogen content of 10.96% and a viscosity of 916 cP were synthesized. It was found by the SEM technique that the CN preserved the 3D reticulate structure of initial BNC fibers a marginal thickening of the nanofibers themselves. Different analytical techniques reliably proved the resultant nitration product to be CN. When dissolved in acetone, the CN was found to form a clear high-viscosity organogel whose further studies will broaden application fields of the modified BNC.

Effect of Additives on the in situ Laccase-Catalyzed Polymerization of Aniline Onto Bacterial Cellulose

Laccase-mediated systems are a green route to accelerate the oxidation of aniline and obtain polyaniline with conductive properties. The synthesis of green polyaniline (emeraldine salt) was herein improved by the inclusion of additives like sodium bis (2-ethyl hexyl) sulfosuccinate (AOT) and potassium hexacyanoferrate (II) (KHCF) in the medium. The aniline polymerization was confirmed by the detection of the absorption band typical of emeraldine salt at 420 nm, typical of the semiquinoid radical cation, and of the polaron absorption band at 700-800 nm, corresponding to the distinctive signal of doped or partial doped aniline. The oligomers and/or polymers obtained were characterized by spectrometry techniques, namely ¹H NMR and MALDI-TOF, and the bacterial cellulose (BC) conductivity was assessed by means of a four-point probe electrical conductivity technique. The best polymerization results were obtained with 5 mM AOT, 10 mM KHCF, and 25 U/mL of laccase. The synergistic effect between both additives in the presence of a catalyst leads to obtaining BC samples coated with green polyaniline with promising electric conductive properties.