Carbon Nanotube-Reinforced Poly(4-vinylaniline)/Polyaniline Bilayer-Grafted Bacterial Cellulose for Bioelectronic Applications

Functionalization of Bacterial Cellulose and Related Surfaces Using a Facile Coupling Reaction by Thermoresponsive Catalyst

Recently, bacterial cellulose and related materials attracted significant attention for applications such as leather-like materials, wound healing materials, etc., due to their abundance in pure form and excellent biocompatibility. Chemical modification of bacterial cellulose further helps to improve specific properties for practical utility and economic viability. However, in most cases, chemical modification of cellulose materials involves harsh experimental conditions such as higher temperatures or organic solvents, which may destroy the 3-dimensional network of bacterial cellulose, thereby altering its characteristic properties. Hence, in this work, we have adopted the Suzuki coupling methodology, which is relatively unexplored for chemically modifying cellulose materials. As the Suzuki coupling reaction is tolerable against air and water, modification can be done under mild conditions so that the covalently modified cellulose materials remain intact without destroying their 3-dimensional form. We performed Suzuki coupling reactions on cellulose surfaces using a recently developed thermoresponsive catalyst consisting of poly(N-isopropylacrylamide) (PNIPAM)-tagged N-heterocyclic carbene (NHC)-based palladium(II) complex. The thermoresponsive nature of the catalyst particularly helped to perform reactions in a water medium under mild conditions considering the biological nature of the substrates, where separation of the catalyst can be easily achieved by tuning temperature. The boronic acid derivatives have been chosen to alter the wettability behavior of bacterial cellulose. Bacterial cellulose (BC) obtained from fermentation on a lab scale using a cellulose-producing bacterium called Gluconacetobacter kombuchae (MTCC 6913) under Hestrin-Schramm (HS) medium, or kombucha-derived bacterial cellulose (KBC) obtained from kombucha available in the market or cotton-cellulose (CC) was chosen for the surface functionalization to find the methodology's diversity. Movie files in the Supporting Information and figures in the manuscript demonstrated the utility of the methodology for fluorescent labeling of bacterial cellulose and related materials. Finally, contact angle analysis of the surfaces showed the hydrophobic natures of some functionalized BC-based materials, which are important for the practical use of biomaterials in wet climatic conditions.

Bacterial cellulose: A promising biopolymer with interesting properties and applications

The ever-increasing demands for materials with desirable properties led to the development of materials that impose unfavorable influences on the environment and the ecosystem. Developing a low-cost, durable, and eco-friendly functional material with biological origins has become necessary to avoid these consequences. Bacterial cellulose generated by bacteria dispenses excellent structural and functional properties and satisfies these requirements. BC and BC-derived materials are essential in developing pure and environmentally safe functional materials. This review offers a detailed understanding of the biosynthesis of BC, properties, various functionalization methods, and applicability in biomedical, water treatment, food storage, energy conversion, and energy storage applications.

Bacterial cellulose as a potential biopolymer in biomedical applications: a state-of-the-art review

Throughout history, natural biomaterials have benefited society. Nevertheless, in recent years, tailoring natural materials for diverse biomedical applications accompanied with sustainability has become the focus. With the progress in the field of materials science, novel approaches for the production, processing, and functionalization of biomaterials to obtain specific architectures have become achievable. This review highlights an immensely adaptable natural biomaterial, bacterial cellulose (BC). BC is an emerging sustainable biopolymer with immense potential in the biomedical field due to its unique physical properties such as flexibility, high porosity, good water holding capacity, and small size; chemical properties such as high crystallinity, foldability, high purity, high polymerization degree, and easy modification; and biological characteristics such as biodegradability, biocompatibility, excellent biological affinity, and non-biotoxicity. The structure of BC consists of glucose monomer units polymerized via cellulose synthase in β-1-4 glucan chains, creating BC nano fibrillar bundles with a uniaxial orientation. BC-based composites have been extensively investigated for diverse biomedical applications due to their similarity to the extracellular matrix structure. The recent progress in nanotechnology allows the further modification of BC, producing novel BC-based biomaterials for various applications. In this review, we strengthen the existing knowledge on the production of BC and BC composites and their unique properties, and highlight the most recent advances, focusing mainly on the delivery of active pharmaceutical compounds, tissue engineering, and wound healing. Further, we endeavor to present the challenges and prospects for BC-associated composites for their application in the biomedical field.

Cellulose-Based Flexible Functional Materials for Emerging Intelligent Electronics

There is currently enormous and growing demand for flexible electronics for personalized mobile equipment, human-machine interface units, wearable medical-healthcare systems, and bionic intelligent robots. Cellulose is a well-known natural biopolymer that has multiple advantages including low cost, renewability, easy processability, and biodegradability, as well as appealing mechanical performance, dielectricity, piezoelectricity, and convertibility. Because of its multiple merits, cellulose is frequently used as a substrate, binder, dielectric layer, gel electrolyte, and derived carbon material for flexible electronic devices. Leveraging the advantages of cellulose to design advanced functional materials will have a significant impact on portable intelligent electronics. Herein, the unique molecular structure and nanostructures (nanocrystals, nanofibers, nanosheets, etc.) of cellulose are briefly introduced, the structure-property-application relationships of cellulosic materials summarized, and the processing technologies for fabricating cellulose-based flexible electronics considered. The focus then turns to the recent advances of cellulose-based functional materials toward emerging intelligent electronic devices including flexible sensors, optoelectronic devices, field-effect transistors, nanogenerators, electrochemical energy storage devices, biomimetic electronic skins, and biological detection devices. Finally, an outlook of the potential challenges and future prospects for developing cellulose-based wearable devices and bioelectronic systems is presented.

A review of functionalised bacterial cellulose for targeted biomedical fields

Bacterial cellulose (BC), which can be produced by microorganisms, is an ideal biomaterial especially for tissue engineering and drug delivery systems thanks to its properties of high purity, biocompatibility, high mechanical strength, high crystallinity, 3 D nanofiber structure, porosity and high-water holding capacity. Therefore, wide ranges of researches have been done on the BC production process and its structural and physical modifications to make it more suitable for certain targeted biomedical applications thoroughly. BC's properties such as mechanical strength, pore diameter and porosity can be tuned in situ or ex situ processes by using various polymer and compounds. Besides, different organic or inorganic compounds that support cell attachment, proliferation and differentiation or provide functions such as antimicrobial effectiveness can be gained to its structure for targeted application. These processes not only increase the usage options of BC but also provide success for mimicking the natural tissue microenvironment, especially in tissue engineering applications. In this review article, the studies on optimisation of BC production in the last decade and the BC modification and functionalisation studies conducted for the three main perspectives as tissue engineering, drug delivery and wound dressing with diverse approaches are summarized.

Electrically conductive biocompatible composite aerogel based on nanofibrillated template of bacterial cellulose/polyaniline/nano-clay

Bacterial cellulose (BC) aerogel owing to its porous and 3D structure, poses a suitable matrix for embedding nanomaterials and polymers. Herein, BC composites comprising nano-clay/polyaniline (PANI) were synthesized via a two-step procedure. Clay nanoplatelets were dispersed in the BC membrane to form a nanofibrillated template for aniline in-situ polymerization leading to formation of a double interconnected network of electrically conductive path within the aerogel. Deposition of PANI particles on BC/clay nanocomposite was confirmed by FTIR, XRD, FESEM, and EDX techniques. The surface electrical conductivity of 0.49 S/cm was obtained for the composite aerogel comprising 5 wt% nano-clay which is 16 folds higher than that of the sample without nano-clay. Thermal stability and storage modulus of the aerogels was improved by inclusion of PANI and nano-clay. Synergistic effect of clay and polyaniline on biocompatibility and cell adhesion was obtained with no mutagenic or carcinogenic effects. The developed electrically conductive composite aerogels can be utilized as suitable scaffolds for tissue engineering applications demanding a good balance of flexibility, dimensional and thermal stability and biocompatibility.

Induced neural stem cell differentiation on a drawn fiber scaffold-toward peripheral nerve regeneration

To achieve regeneration of long sections of damaged nerves, restoration methods such as direct suturing or autologous grafting can be inefficient. Solutions involving biohybrid implants, where neural stem cells are grown in vitro on an active support before implantation, have attracted attention. Using such an approach, combined with recent advancements in microfabrication technology, the chemical and physical environment of cells can be tailored in order to control their behaviors. Herein, a neural stem cell polycarbonate fiber scaffold, fabricated by 3D printing and thermal drawing, is presented. The combined effect of surface microstructure and chemical functionalization using poly-L-ornithine (PLO) and double-walled carbon nanotubes (DWCNTs) on the biocompatibility of the scaffold, induced differentiation of the neural stem cells (NSCs) and channeling of the neural cells was investigated. Upon treatment of the fiber scaffold with a suspension of DWCNTs in PLO (0.039 g l^-1) and without recombinants a high degree of differentiation of NSCs into neuronal cells was confirmed by using nestin, galactocerebroside and doublecortin immunoassays. These findings illuminate the potential use of this biohybrid approach for the realization of future nerve regenerative implants.

Poly(4-vinylaniline)/Polyaniline Bilayer-Functionalized Bacterial Cellulose for Flexible Electrochemical Biosensors

A bacterial cellulose (BC) nanofibril network is modified with an electrically conductive polyvinylaniline/polyaniline (PVAN/PANI) bilayer for construction of potential electrochemical biosensors. This is accomplished through surface-initiated atom transfer radical polymerization of 4-vinylaniline, followed by in situ chemical oxidative polymerization of aniline. A uniform coverage of the BC nanofiber with 1D supramolecular PANI nanostructures is confirmed by Fourier transform infrared, X-ray diffractogram, and CHN elemental analysis. Cyclic voltammograms evince the switching in the electrochemical behavior of BC/PVAN/PANI nanocomposites from the redox peaks at 0.74 V, in the positive scan and at -0.70 V, in the reverse scan, (at 100 mV·s^-1 scan rate). From these redox peaks, PANI is the emeraldine form with the maximal electrical performance recorded, showing charge-transfer resistance as low as 21 Ω and capacitance as high as 39 μF. The voltage-sensible nanocomposites can interact with neural stem cells isolated from the subventricular zone (SVZ) of the brain, through stimulation and characterization of differentiated SVZ cells into specialized and mature neurons with long neurites measuring up to 115 ± 24 μm length after 7 days of culture without visible signs of cytotoxic effects. The findings pave the path to the new effective nanobiosensor technologies for nerve regenerative medicine, which demands both electroactivity and biocompatibility.