A Review on the Role and Performance of Cellulose Nanomaterials in Sensors

Tailoring pore structure in nanocellulose cryogels: Enhancing thermal and electromagnetic interference shielding properties

Engineering porosity levels in hierarchical cryogels presents an exciting opportunity for advancing electromagnetic interference (EMI) shielding materials. This study introduces a feasible approach to tailoring micro-scale morphology in cellulose nanofiber (CNF)-based cryogels by simply adjusting the freeze-templating temperature, resulting in tunable porosity and enhanced performance characteristics. By varying the freeze-templating temperature, we successfully controlled pore size (ranging from 31 to 178 μm), which influenced the mechanical strength (decreasing from 59 to 14 kPa). To explore the effect of micro-scale porosity on the EMI shielding performance, we rendered the CNF cryogels conductivity upon integrating poly(3,4-ethylenedioxythiophene) (PEDOT) with the cryogels framework via chemical vapor polymerization. Our results demonstrate that the larger pore sizes promoted an absorption-dominant EMI shielding mechanism, with an average absorbance (A) of 0.59 across the X-band frequency range. A specific EMI shielding effectiveness (SSE/t) of 4801.25 dB cm2 g-1 was achieved for samples with larger porosities, highlighting the decent performance of these engineered cryogels. Our findings reveal a straightforward yet effective strategy for optimizing porosity to achieve appreciable shielding effectiveness, contributing to the advancement of sustainable, high-performance EMI shielding solutions.

Tailoring cellulose: from extraction and chemical modification to advanced industrial applications

Cellulose is a natural polymer with excellent physicochemical properties that can be extracted from various plant sources and has widespread applications across multiple industries. Due to its biodegradability, renewability, and mechanical strength, cellulose has gained significant attention in fields such as pharmaceuticals, food packaging, sensors, water treatment, and textiles. However, its inherent limitations, such as poor solubility, low electrical conductivity, and limited functionality, hinder its application in advanced technologies. To overcome these challenges, chemical modifications have been extensively explored to enhance its structural properties and broaden its utility in specialized applications. This review explores the modifications applied to cellulose with a focus on targeted advanced industries. Emphasis is placed on identifying the limitations of cellulose in each industry and highlighting the most recent techniques available for modifying its properties to meet specific requirements. Finally, this review discusses the challenges associated with cellulose processing and the high costs of extraction while providing insights into future research directions and potential advancements in cellulose-based technologies.

Emerging trends in cellulose and lignin-based nanomaterials for water treatment

Several industrial and agricultural practices contribute significantly to water contamination. These activities release several amount of pollutants, including pesticides, heavy metals, and organic compounds, into water sources, posing health risks and causing environmental damage. Industries such as mining, textiles, and pharmaceuticals discharge harmful toxins, further polluting water. Processes like ball-milling, adsorption, filtration, and flocculation are commonly used for wastewater treatment. Recent advancements have focused on the study of green nanomaterials (NMs), particularly cellulose-based and lignin-based NMs, due to their various properties, biodegradability, and low toxicity. This review covers the fabrication methods, modification techniques, and applications of cellulose-based and lignin-based NMs, such as cellulose nanofibers, nanocrystals, lignin-based aerogels, and hydrogels for wastewater treatment. The unique properties of lignin and cellulose, including their high surface area, functionalization, and biocompatibility, make them suitable for water purification. The paper also discusses a SWOT analysis, which will be useful for future researchers, highlighting both opportunities and challenges in this area. This paper aims to provide valuable insights into ongoing research and development in cellulose and lignin-based nanomaterials for next-generation water treatment solutions.

Flame-retardant bamboo fiber-based films for high-performance fire sensors

Natural polymers play a non-negligible role in the development of green and sustainable sensors. However, their poor flame retardancy and deficient thermal stability inevitably restrict their application in sensors for monitoring the fire full-process. In this work, a facile and eco-friendly method for the large-scale preparation of flexible films composed of bamboo fiber (BF), carboxymethyl cellulose (CC), and graphene (GN) by solution casting was put forward. Iron ions and phytic acid (PA) self-assemble on its surface, eventually resulting in a film (referred to as BCGP) that exhibits high strength and high flame retardancy. Specifically, the strength of the film reaches 3.92 MPa, and reliable strength still be ensured even after long-term soaking. Furthermore, the limiting oxygen index of the film is as high as 33 %, the vertical burning test attains the V-0 level. As a sensor, the film promptly triggers an alarm within 3.6 s of contact with flames, and its response remains sensitive even after repeated scorching. The temperature response encompasses a wide range of 50 to 200 °C, and the gauge factor is as high as 1572.

Microfibrillated cellulose-based colorimetric sensor strips for detecting total iron in water

Microfibrillated cellulose (MFC), a sustainable material derived from biomass, stands out as an environmentally friendly alternative for developing chemical sensors owing to its advantageous properties including high porosity, surface area, and available surface functional groups. Herein, we propose a simple and low-cost strategy for developing cellulose-based strips for the colorimetric detection of total iron in water. The strips were prepared by functionalizing MFC casting membranes with 1-(2-Thiazolylazo)-2-naphthol (TAN), which was characterized by structural and morphological techniques. The sensing ability of the MFC@TAN strips towards total iron was evaluated under distinct reaction times by digital image colorimetry. Under optimal conditions, the strips yielded limits of detections of 0.08 and 0.09 mg L-1 using the Blue (5 min) and Red (30 min) channels, respectively. Additionally, the sensor enabled total iron detection in tap water in the concentration range of 0.08-0.70 mg L-1, showing no significant difference against the standard method. When compared to commercial papers, the MFC@TAN strips showed enhanced sensing performance owing to their more porous and interpenetrating structure, which benefited the TAN immobilization and reaction with Fe2+. Our cellulose-based sensor strips offer a compelling combination of simplicity in manufacturing and cost-effectiveness, highlighting their potential for routine water analysis.

Cellulose-based Conductive Materials for Bioelectronics

The growing demand for electronic devices has led to excessive stress on Earth's resources, necessitating effective waste management and the search for renewable materials with minimal environmental impact. Bioelectronics, designed to interface with the human body, have traditionally been made from inorganic materials, such as metals, which, while having suitable electrical conductivity, differ significantly in chemical and mechanical properties from biological tissues. This can cause issues such as unreliable signal collection and inflammatory responses. Recently, natural biopolymers such as cellulose, chitosan, and silk have been explored for flexible devices, given their chemical uniqueness, shape flexibility, ease of processing, mechanical strength, and biodegradability. Cellulose is the most abundant natural biopolymer, has been widely used across industries, and can be transformed into electronically conductive carbon materials. This review focuses on the advancements in cellulose-based conductive materials for bioelectronics, detailing their chemical properties, methods to enhance conductivity, and forms used in bioelectronic applications. It highlights the compatibility of cellulose with biological tissues, emphasizing its potential in developing wearable sensors, supercapacitors, and other healthcare-related devices. The review also addresses current challenges in this field and suggests future research directions to overcome these obstacles and fully realize the potential of cellulose-based bioelectronics.

Citrus wastes as sustainable materials for active and intelligent food packaging: Current advances

Citrus fruits are one of the most popular crops in the world, and around one quarter of them are subjected to industrial processes, aiming at the production of different food products. Citrus processing generates large amounts of waste, including peels, pulp, and seeds. These materials are rich sources of polymers (e.g., pectin, cellulose, hemicellulose, lignin), phenolic compounds, and essential oils. At the same time, the development of food packaging materials using citrus waste is a highly sought strategy for food preservation, and meets the principles of circular economy. This review surveys current advances in the development of active and intelligent food packaging produced using one or more citrus waste components (polymers, phenolics extracts, and essential oils). It highlights the contribution and effects of each of these components on the properties of the developed packaging, as well as emphasizes the current state and challenges for developing citrus-based packaging. Most of the reported investigations employed citrus pectin as a base polymer to produce packaging films through the casting technique. Likewise, most of them focused on developing active materials, and fewer studies have explored the preparation of citrus waste-based intelligent materials. All studies characterized the materials developed, but only a few actually applied them to food matrices. This review is expected to encourage novel investigations that contribute to food preservation and to reduce the environmental impacts caused by discarded citrus byproducts.

Robust and ultra-thin nanocellulose/MXene composite film and its performance in efficient electricity-generation and sensing

The conversion of mechanical energy into electrical energy by triboelectric nanogenerators (TENG) has attracted attention in recent years, particularly in the field of wearable sensor. In this work, TEMPO-oxidized cellulose nanofibers (TOCNF) with carboxylate groups were compounded with MXene to serve as both the negative friction layer and the electrode in assembling a TENG with nylon. The synergistic effect between TOCNF and MXene was analyzed to disclose its influence on the performance of the as-prepared TENG. The MXene/TOCNF composite film, containing 50 wt% MXene, exhibited the best performance among all specimens, and the assembled TENG demonstrated excellent performance with an open-circuit voltage of 210 V, a short-circuit current of 0.84 μA, and a transferred charge of 8.6 nC. The excellent output performance might be attributed to the presence of carboxylate and F-containing groups in the composite film. This flexible TENG also functioned as a self-powered sensor, generating sensitive and stable signals in response to human motion and writing. This work verifies the simultaneous use of robust and flexible nanocellulose/MXene composite films as both the friction layer and electrode, which could spur the development of TENGs using sustainable and abundant cellulosic materials.

Cellulose-Based Electrochemical Sensors

Among the most promising areas of research, cellulose-based electrochemical sensors stand out for their intrinsic properties such as abundance, biocompatibility, and versatility. This review is concerned with the integration and application of cellulose-derived materials in electrochemical sensors, pointing out improvements in sensitivity, selectivity, stability, and functionality for a wide variety of applications. The most relevant developments on cellulose-based sensors have been concentrated on nanocellulose composite synthesis, advanced cellulose modification, and the successful embedding in wearable technologies, medical diagnostics, and environmental monitoring. Considering these, it is worth mentioning that significant challenges still need to be overcome regarding the scalability of production, selectivity improvement, and long-term stability under real operational conditions. Future research efforts will concern the union of cellulose-based sensors with the Internet of Things (IoT) and artificial intelligence (AI) toward wiser and more sustainable health and environmental solutions. Correspondingly, this work puts cellulose in the front line among the most perspective materials for enabling the development of eco-friendly and high-performance sensing technologies.

Visual detection of uric acid in serum through catalytic oxidation by a novel cellulose membrane biosensor with schiff base immobilized uricase

Uric acid (UA) serves as an important biochemical marker of various diseases, making the development of a novel method for its rapid and straightforward visual detection highly valuable. In this study, a uricase-based cellulose membrane biosensor (UCMB) was constructed by immobilizing uricase via a Schiff base reaction and nitroblue tetrazolium chloride (NBT) through adsorption. The UCMB detects UA through a mechanism in which uricase catalyzes the oxidation of UA, generation O2-· radicals that subsequently oxidize NBT to formazan, producing a distinctive color change from yellow to purple. The UCMB demonstrated successful visual detection of UA within 15 min, allowing for rapid naked-eye analysis. Additionally, the biosensor quantitatively detected UA over a broad linear range from 0 to 1000 μM, with a low detection limit of 3.88 μM. Most notably, the UCMB has accurately measured UA in human serum samples, comparable to the results from a commercial UA meter. These findings suggest that the UCMB can serve as a simple and reliable tool for early diagnosis of UA-related diseases.

Fabrication of flame-retardant and water-resistant nanopapers through electrostatic complexation of phosphorylated cellulose nanofibers and chitin nanocrystals

Biogenic, sustainable two-dimensional architectures, such as films and nanopapers, have garnered considerable interest because of their low carbon footprint, biodegradability, advanced optical/mechanical characteristics, and diverse potential applications. Here, bio-based nanopapers with tailored characteristics were engineered by the electrostatic complexation of oppositely charged colloidal phosphorylated cellulose nanofibers (P-CNFs) and deacetylated chitin nanocrystals (ChNCs). The electrostatic interaction between anionic P-CNFs and cationic ChNCs enhanced the stretchability and water stability of the nanopapers. Correspondingly, they exhibited a wet tensile strength of 17.7 MPa after 24 h of water immersion. Furthermore, the nanopapers exhibited good thermal stability and excellent self-extinguishing behavior, triggered by both phosphorous and nitrogen. These features make the nanopapers sustainable and promising structures for application in advanced fields, such as optoelectronics.

Robust Metal Oxide Adhesion Layers for Cellulose Nanofiber-Based QCM Sensors

Here, we demonstrate the significant role of robust metal oxide adhesion layers on the cellulose nanofiber (CNF)-based quartz crystal microbalance (QCM) humidity sensor characteristics including sensitivity and stability. In this study, we deposited various metal oxide films (NiO, TiO2, ZnO, and WO3) onto QCM Au electrodes as adhesion layers before drop-casting CNF dispersion water. These metal oxide adhesion layers significantly enhanced the stability of CNF films on QCM sensors even in a high-humidity environment where a conventional adhesion layer (polyethylenimine) for CNF could not maintain stable adhesion. There was a significant difference between different metal oxide layers in the QCM data for humidity sensing. We found a negative correlation between the QCM sensitivity and the water wettability of metal oxide surfaces. Morphology analysis of the deposited CNF films revealed that the center-concentrated CNF microstructures on the metal oxide adhesion layers rigorously explained the observed negative correlation between the sensitivity and the wettability of metal oxide surfaces. This trend was further confirmed by gradually changing the hydrophobicity of the NiO adhesion surfaces. Thus, the proposed strategy using robust metal oxide adhesion layers will be a foundation for further development of various CNF-based QCM gas sensors.

Customising Sustainable Bio-Based Polyelectrolytes: Introduction of Charged and Hydrophobic Groups in Cellulose

Cellulose has been widely explored as a sustainable alternative to synthetic polymers in industrial applications, thanks to its advantageous properties. The introduction of chemical modifications on cellulose structure, focusing on cationic and hydrophobic modifications, can enhance its functionality and expand the range of applications. In the present work, cationization was carried out through a two-step process involving sodium periodate oxidation followed by a reaction with the Girard T reagent, yielding a degree of substitution for cationic groups (DScationic) between 0.3 and 1.8. Hydrophobic modification was achieved via esterification with fatty acids derived from commercial plant oils, using an enzyme-assisted, environmentally friendly method. Lipase-catalysed hydrolysis, optimised at 0.25% enzyme concentration and with a 1 h reaction time, produced an 84% yield of fatty acids, confirmed by FTIR and NMR analyses. The degree of substitution for hydrophobic groups (DShydrophobic) ranged from 0.09 to 0.66. The molecular weight (MW) of the modified cellulose derivatives varied from 1.8 to 141 kDa. This dual modification strategy enables the creation of cellulose-based polymers with controlled electrostatic and hydrophobic characteristics, customisable for specific industrial applications. Our approach presents a sustainable and flexible solution for developing cellulose derivatives tailored to diverse industrial needs.

High-Value Utilization of Cellulose: Intriguing and Important Effects of Hydrogen Bonding Interactions─A Mini-Review

Cellulose has been widely used in papermaking, textile, and chemical industries due to its diverse sources, environmental friendliness, and renewability. Recently, much more attention has been paid to converting cellulose into high-value-added products. Therefore, the extraction of nanocellulose, the dissolution of cellulose, and their applications are some of the most important research topics currently. However, cellulose's dense hydrogen bond network poses challenges for efficient extraction and dissolution, limiting its potential for functional material development. This review discusses the mechanisms of hydrogen bond disruption and weak interactions during nanocellulose extraction and cellulose dissolution. Key challenges and future research directions are highlighted, emphasizing developing efficient, ecofriendly, and cost-effective methods. Additionally, this review provides theoretical insights for constructing high-performance cellulose-based materials.

Synthesis, functionalization, and commercial application of cellulose-based nanomaterials

In recent times, cellulose, an abundant and renewable biopolymer, has attracted considerable interest due to its potential applications in nanotechnology. This review explores the latest developments in cellulose-based nanomaterial synthesis, functionalization, and commercial applications. Beginning with an overview of the diverse sources of cellulose and the methods employed for its isolation and purification, the review delves into the various techniques used for the synthesis of cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs), highlighting their unique properties and potential applications. Furthermore, the functionalization strategies employed to enhance the properties and tailor the functionalities of cellulose-based nanomaterials were discussed. The review also provides insights into the emerging commercial applications of cellulose-based nanomaterials across diverse sectors, including packaging, biomedical engineering, textiles, and environmental remediation. Finally, challenges and prospects for the widespread adoption of cellulose-based nanomaterials are outlined, emphasizing the need for further research and development to unlock their full potential in sustainable and innovative applications.

Strain-Temperature Dual Sensor Based on Deep Learning Strategy for Human-Computer Interaction Systems

Thermoelectric (TE) hydrogels, mimicking human skin, possessing temperature and strain sensing capabilities, are well-suited for human-machine interaction interfaces and wearable devices. In this study, a TE hydrogel with high toughness and temperature responsiveness was created using the Hofmeister effect and TE current effect, achieved through the cross-linking of PVA/PAA/carboxymethyl cellulose triple networks. The Hofmeister effect, facilitated by Na+ and SO42- ions coordination, notably increased the hydrogel's tensile strength (800 kPa). Introduction of Fe2+/Fe3+ as redox pairs conferred a high Seebeck coefficient (2.3 mV K-1), thereby enhancing temperature responsiveness. Using this dual-responsive sensor, successful demonstration of a feedback mechanism combining deep learning with a robotic hand was accomplished (with a recognition accuracy of 95.30%), alongside temperature warnings at various levels. It is expected to replace manual work through the control of the manipulator in some high-temperature and high-risk scenarios, thereby improving the safety factor, underscoring the vast potential of TE hydrogel sensors in motion monitoring and human-machine interaction applications.

Development of cellulose/ZnO based bioplastics with enhanced gas barrier, UV-shielding effect and antibacterial activity

Development of renewable and biodegradable plastics with good properties, such as the gas barrier, UV-shielding, solvent resistance, and antibacterial activity, remains a challenge. Herein, cellulose/ZnO based bioplastics were fabricated by dissolving cellulose carbamate in an aqueous solution of NaOH/Zn(OH)42-, followed by coagulation in aqueous Na2SO4 solution, and subsequent hot-pressing. The carbamate groups detached from cellulose, and ZnO which transformed from cosolvent to nanofiller was uniformly immobilized in the cellulose matrix during the dissolution/regeneration process. The appropriate addition of ZnO (below 10.67 wt%) not only improved the mechanical properties but also enhanced the water and oxygen barrier properties of the material. Additionally, our cellulose/ZnO based bioplastic demonstrated excellent UV-blocking capabilities, increased water contact angle, and enhanced antibacterial activity against S. aureus and E. coli, deriving from the incorporation of ZnO nanoparticles. Furthermore, the material exhibited resistance to organic solvents such as acetone, THF, and toluene. Indeed, the herein developed cellulose/ZnO based bioplastic presents a promising candidate to replace petrochemical plastics in various applications, such as plastic toys, anti-UV guardrails, window shades, and oil storage containers, offering a combination of favorable mechanical, gas barrier, UV-blocking, antibacterial, and solvent-resistant properties.

Piezoelectric dressings for advanced wound healing

The treatment of chronic refractory wounds poses significant challenges and threats to both human society and the economy. Existing research studies demonstrate that electrical stimulation fosters cell proliferation and migration and promotes the production of cytokines that expedites the wound healing process. Presently, clinical settings utilize electrical stimulation devices for wound treatment, but these devices often present issues such as limited portability and the necessity for frequent recharging. A cutting-edge wound dressing employing the piezoelectric effect could transform mechanical energy into electrical energy, thereby providing continuous electrical stimulation and accelerating wound healing, effectively addressing these concerns. This review primarily reviews the selection of piezoelectric materials and their application in wound dressing design, offering a succinct overview of these materials and their underlying mechanisms. This study also provides a perspective on the current limitations of piezoelectric wound dressings and the future development of multifunctional dressings harnessing the piezoelectric effect.

Biotechnological innovations in nanocellulose production from waste biomass with a focus on pineapple waste

New materials' synthesis and utilization have shown many critical challenges in healthcare and other industrial sectors as most of these materials are directly or indirectly developed from fossil fuel resources. Environmental regulations and sustainability concepts have promoted the use of natural compounds with unique structures and properties that can be biodegradable, biocompatible, and eco-friendly. In this context, nanocellulose (NC) utility in different sectors and industries is reported due to their unique properties including biocompatibility and antimicrobial characteristics. The bacterial nanocellulose (BNC)-based materials have been synthesized by bacterial cells and extracted from plant waste materials including pineapple plant waste biomass. These materials have been utilized in the form of nanofibers and nanocrystals. These materials are found to have excellent surface properties, low density, and good transparency, and are rich in hydroxyl groups for their modifications to other useful products. These materials are well utilized in different sectors including biomedical or health care centres, nanocomposite materials, supercapacitors, and polymer matrix production. This review explores different approaches for NC production from pineapple waste residues using biotechnological interventions, approaches for their modification, and wider applications in different sectors. Recent technological developments in NC production by enzymatic treatment are critically discussed. The utilization of pineapple waste-derived NC from a bioeconomic perspective is summarized in the paper. The chemical composition and properties of nanocellulose extracted from pineapple waste may have unique characteristics compared to other sources. Pineapple waste for nanocellulose production aligns with the principles of sustainability, waste reduction, and innovation, making it a promising and novel approach in the field of nanocellulose materials.

Exploring the potential of cellulose autofluorescence for optical detection of tannin in red wines

The growing demand for opto-electronic devices within an automated landscape has opened up new opportunities for harnessing sustainable cellulose materials for sensors technology. Cellulose, a versatile material, enables its combination with other materials, but in most of these applications, cellulose is typically employed as support or substrate, while its inherent autofluorescence remains largely underexplored for sensors. In light of this context, this study delves into the autofluorescence characteristics of pristine cellulose nanocrystals extracted from wood via enzymatic route for optical sensors tailored to detect tannins. By fine-tuning the experimental setup, photoluminescence (PL) emission bands were scrutinized across three distinct spectral regions, namely 300-400 nm, 400-500 nm and 550-700 nm. The proposed mechanism reveals the occurrence of dynamic fluorescence quenching, which enabled the selective monitoring of tannins in red wines across a dynamic range spanning from 10 to 1060 μg mL-1. This sensing platform provided a limit of detection (LoD) of 6.1 μg mL-1. Notably, the sensing platform's efficacy was validated with remarkable recovery rates of 99.7 % and 95.3 % when subjected to testing with cabernet sauvignon and tannat wines. These findings emphasize the sensing platform's potential for monitoring tannic acids in beverages and food products.

Cellulose-Based Conductive Materials for Energy and Sensing Applications

Cellulose-based conductive materials (CCMs) have emerged as a promising class of materials with various applications in energy and sensing. This review provides a comprehensive overview of the synthesis methods and properties of CCMs and their applications in batteries, supercapacitors, chemical sensors, biosensors, and mechanical sensors. Derived from renewable resources, cellulose serves as a scaffold for integrating conductive additives such as carbon nanotubes (CNTs), graphene, metal particles, metal-organic frameworks (MOFs), carbides and nitrides of transition metals (MXene), and conductive polymers. This combination results in materials with excellent electrical conductivity while retaining the eco-friendliness and biocompatibility of cellulose. In the field of energy storage, CCMs show great potential for batteries and supercapacitors due to their high surface area, excellent mechanical strength, tunable chemistry, and high porosity. Their flexibility makes them ideal for wearable and flexible electronics, contributing to advances in portable energy storage and electronic integration into various substrates. In addition, CCMs play a key role in sensing applications. Their biocompatibility allows for the development of implantable biosensors and biodegradable environmental sensors to meet the growing demand for health and environmental monitoring. Looking to the future, this review emphasizes the need for scalable synthetic methods, improved mechanical and thermal properties, and exploration of novel cellulose sources and modifications. Continued innovation in CCMs promises to revolutionize sustainable energy storage and sensing technologies, providing environmentally friendly solutions to pressing global challenges.

Dental delivery systems of antimicrobial drugs using chitosan, alginate, dextran, cellulose and other polysaccharides: A review

Dental caries, periodontal disease, and endodontic disease are major public health concerns worldwide due to their impact on individuals' quality of life. The present problem of dental disorders is the removal of the infection caused by numerous microbes, particularly, bacteria (both aerobes and anaerobes). The most effective method for treating and managing dental diseases appears to be the use of antibiotics or other antimicrobials, which are incorporated in some drug delivery systems. However, due to their insufficient bioavailability, poor availability for gastrointestinal absorption, and pharmacokinetics after administration via the oral route, many pharmaceutical medicines or natural bioactive substances have limited efficacy. During past few decades, a range of polysaccharide-based systems have been widely investigated for dental dug delivery. The polysaccharide-based carrier materials made of chitosan, alginate, dextran, cellulose and other polysaccharides have recently been spotlighted on the recent advancements in preventing, treating and managing dental diseases. The objective of the current review article is to present a brief comprehensive overview of the recent advancements in polysaccharide-based dental drug delivery systems for the delivery of different antimicrobial drugs.

Cellulose acylation in homogeneous and heterogeneous media: Optimization of reactions conditions

The dependence of the DS on the acid anhydride/anhydroglucose unit ((RCO)₂O/AGU) molar ratio was correlated using second-order polynomials. The regression coefficients of the (RCO)₂O/AGU terms showed that increasing the length of the RCO group of the anhydride led to lower values of DS. For acylation under heterogeneous reaction conditions, the following were employed: acid anhydrides and butyryl chloride as acylating agents; iodine as a catalyst; N,N-dimethylformamide (DMF) as a solvent, pyridine, and triethylamine as solvents and catalysts. For acylation using acetic anhydride plus iodine, the values of DS correlate with reaction time by a second-order polynomial. Due to its role as a polar solvent and a nucleophilic catalyst, pyridine was the most effective base catalyst, independent of the acylating agent (butyric anhydride and butyryl chloride).

Light and pH dual-responsive spiropyran-based cellulose nanocrystals

Reversibly light and pH dual-responsive spiropyran-based cellulose nanocrystals (SP-CNCs) is synthesized by the attachment of carboxyl-containing spiropyran (SP-COOH) onto cellulose nanocrystals (CNCs). The resulting structure and properties of SP-CNCs are examined by Fourier transform infrared spectroscopy (FT-IR), elemental analysis, transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic laser light scattering (DSL), ζ-potential measurements and ultraviolet-visible (UV-Vis) light absorption spectroscopy. SP-CNCs exhibit excellent photochromic and photoswitching properties. Spiropyran moieties on SP-CNCs can be switched between open-ring merocyanine (MC) and closed ring spiropyran (SP) forms under UV/Vis irradiation, leading to color changes. Moreover, SP-CNCs display improved photoresponsiveness, photoreversibility, fatigue resistance, and stability in DMSO than in H₂O. We further investigate the pH-responsive behavior of SP-CNCs in H₂O. SP-CNCs aqueous solution display different colors at different pH values, which can be directly observed by naked eye, indicating that SP-CNCs can function as a visual pH sensor. These results suggest that light and pH dual-responsive SP-CNCs possess great potential for applications in reversible data storage, sensing, optical switching and light-controlled nanomaterials.

Bio-Graphene Sensors for Monitoring Moisture Levels in Wood and Ambient Environment

Wood is an inherently hygroscopic material which tends to absorb moisture from its surrounding. Moisture in wood is a determining factor for the quality of wood being employed in construction, since it causes weakening, deformation, rotting, and ultimately leading to failure of the structures resulting in costs to the economy, the environment, and to the safety of residents. Therefore, monitoring moisture in wood during the construction phase and after construction is vital for the future of smart and sustainable buildings. Employing bio-based materials for the construction of electronics is one way to mitigate the environmental impact of such electronics. Herein, a bio-graphene sensor for monitoring the moisture inside and around wooden surfaces is fabricated using laser-induced graphitization of a lignin-based ink precursor. The bio-graphene sensors are used to measure humidity in the range of 10% up to 90% at 25 °C. Using laser induced graphitization, conductor resistivity of 18.6 Ω sq-1 is obtained for spruce wood and 57.1 Ω sq-1 for pine wood. The sensitivity of sensors fabricated on spruce and pine wood is 2.6 and 0.74 MΩ per % RH. Surface morphology and degree of graphitization are investigated using scanning electron microscopy, Raman spectroscopy, and thermogravimetric analysis methods.

Detection of gases and organic vapors by cellulose-based sensors

The growing interest in the development of cost-effective, straightforward, and rapid analytical systems has found cellulose-based materials, including cellulose derivatives, cellulose-based gels, nanocellulosic materials, and the corresponding (nano)cellulose-based composites, to be valuable platforms for sensor development. The present work presents recent advances in the development of cellulose-based sensors for the determination of volatile analytes and derivatives of analytical relevance. In particular, strategies described in the literature for the fabrication and modification of cellulose-based substrates with responsive materials are summarized. In addition, selected contributions reported in the field of paper-based volatile sensors are discussed, with a particular emphasis on quick response (QR) code paper-based platforms, intelligent films for food freshness monitoring, and sensor arrays for volatile discrimination purposes. Furthermore, analytical strategies devised for the determination of ionic species by in situ generation of volatile derivatives in both paper-based analytical devices (PADs) and microfluidic PADs will also be described.

Paper-Based Humidity Sensors as Promising Flexible Devices: State of the Art: Part 1. General Consideration

In the first part of the review article "General considerations" we give information about conventional flexible platforms and consider the advantages and disadvantages of paper when used in humidity sensors, both as a substrate and as a humidity-sensitive material. This consideration shows that paper, especially nanopaper, is a very promising material for the development of low-cost flexible humidity sensors suitable for a wide range of applications. Various humidity-sensitive materials suitable for use in paper-based sensors are analyzed and the humidity-sensitive characteristics of paper and other humidity-sensitive materials are compared. Various configurations of humidity sensors that can be developed on the basis of paper are considered, and a description of the mechanisms of their operation is given. Next, we discuss the manufacturing features of paper-based humidity sensors. The main attention is paid to the consideration of such problems as patterning and electrode formation. It is shown that printing technologies are the most suitable for mass production of paper-based flexible humidity sensors. At the same time, these technologies are effective both in the formation of a humidity-sensitive layer and in the manufacture of electrodes.

Nanocellulose-based sensors in medical/clinical applications: The state-of-the-art review

In recent years, the considerable importance of healthcare and the indispensable appeal of curative issues, particularly the diagnosis of diseases, have propelled the invention of sensing platforms. With the development of nanotechnology, the integration of nanomaterials in such platforms has been much focused on, boosting their functionality in many fields. In this direction, there has been rapid growth in the utilisation of nanocellulose in sensors with medical applications. Indeed, this natural nanomaterial benefits from striking features, such as biocompatibility, cytocompatibility and low toxicity, as well as unprecedented physical and chemical properties. In this review, different classifications of nanocellulose-based sensors (biosensors, chemical and physical sensors), alongside some subcategories manufactured for health monitoring, stand out. Moreover, the types of nanocellulose and their roles in such sensors are discussed.

Antibody Immobilization on Sulfated Cellulose Nanocrystals

Exploiting cellulose nanocrystals' high aspect ratio and tailorable surface for immunological biosensors has been hindered by the relatively limited research on using commonly available sulfated cellulose nanocrystals (CNCs) for antibody immobilization and by the low hydrolytic stability of dried assemblies produced from sulfated CNCs. Herein, we report a reaction scheme that enables both hydrolytic stability and antibody immobilization through 3-aminopropyl-triethoxysilane and glutaric anhydride chemistry. Immobilization was demonstrated using three model antibodies used in the detection of the cancer biomarkers: alpha-fetoprotein, prostate-specific antigen, and carcinoembryonic antigen. Thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy provided evidence of CNC modification. Quartz crystal microbalance with dissipation monitoring was used to monitor binding during each step of the immobilization scheme as well as binding of the corresponding antigens. The general reaction scheme was tested using both aqueous CNC dispersions and CNC films. Film modification is slightly simpler as it avoids centrifugation and washing steps. However, modifying the dispersed CNCs provides access to their entire surface area and results in a greater capacity for antigen binding.

Biobased Nanomaterials─The Role of Interfacial Interactions for Advanced Materials

This review presents recent advances regarding biomass-based nanomaterials, focusing on their surface interactions. Plant biomass-based nanoparticles, like nanocellulose and lignin from industry side streams, hold great potential for the development of lightweight, functional, biodegradable, or recyclable material solutions for a sustainable circular bioeconomy. However, to obtain optimal properties of the nanoparticles and materials made thereof, it is crucial to control the interactions both during particle production and in applications. Herein we focus on the current understanding of these interactions. Solvent interactions during particle formation and production, as well as interactions with water, polymers, cells and other components in applications, are addressed. We concentrate on cellulose and lignin nanomaterials and their combination. We demonstrate how the surface chemistry of the nanomaterials affects these interactions and how excellent performance is only achieved when the interactions are controlled. We furthermore introduce suitable methods for probing interactions with nanomaterials, describe their advantages and challenges, and introduce some less commonly used methods and discuss their possible applications to gain a deeper understanding of the interfacial chemistry of biobased nanomaterials. Finally, some gaps in current understanding and interesting emerging research lines are identified.

Versatile Assembly of Metal-Phenolic Network Foams Enabled by Tannin-Cellulose Nanofibers

Metal-phenolic network (MPN) foams are prepared using colloidal suspensions of tannin-containing cellulose nanofibers (CNFs) that are ice-templated and thawed in ethanolic media in the presence of metal nitrates. The MPN facilitates the formation of solid foams by air drying, given the strength and self-supporting nature of the obtained tannin-cellulose nanohybrid structures. The porous characteristics and (dry and wet) compression strength of the foams are rationalized by the development of secondary, cohesive metal-phenolic layers combined with a hydrogen bonding network involving the CNF. The shrinkage of the MPN foams is as low as 6% for samples prepared with 2.5-10% tannic acid (or condensed tannin at 2.5%) with respect to CNF content. The strength of the MPN foams reaches a maximum at 10% tannic acid (using Fe^(III) ions), equivalent to a compressive strength 70% higher than that produced with tannin-free CNF foams. Overall, a straightforward framework is introduced to synthesize MPN foams whose physical and mechanical properties are tailored by the presence of tannins as well as the metal ion species that enable the metal-phenolic networking. Depending on the metal ion, the foams are amenable to modification according to the desired application.

Application of cellulose nanocrystals in water treatment membranes: A review

Nanomaterials have brought great changes to human society, and development has gradually shifted the focus to environmentally friendly applications. Cellulose nanocrystals (CNCs) are new one-dimensional nanomaterials that exhibit environmental friendliness and ensure the biological safety of water environment. CNCs have excellent physical and chemical properties, such as simple preparation process, nanoscale size, high specific surface area, high mechanical strength, good biocompatibility, high hydrophilicity and antifouling ability. Because of these characteristics, CNCs are widely used in ultrafiltration membranes, nanofiltration membranes and reverse osmosis membranes to solve the problems hindering development of membrane technology, such as insufficient interception and separation efficiency, low mechanical strength and poor antifouling performance. This review summarizes recent developments and uses of CNCs in water treatment membranes and discusses the challenges and development prospects of CNCs materials from the perspectives of ecological safety and human health by comparing them with traditional one-dimensional nanomaterials.

Natural Piezoelectric Biomaterials: A Biocompatible and Sustainable Building Block for Biomedical Devices

The piezoelectric effect has been widely observed in biological systems, and its applications in biomedical field are emerging. Recent advances of wearable and implantable biomedical devices bring promise as well as requirements for the piezoelectric materials building blocks. Owing to their biocompatibility, biosafety, and environmental sustainability, natural piezoelectric biomaterials are known as a promising candidate in this emerging field, with a potential to replace conventional piezoelectric ceramics and synthetic polymers. Herein, we provide a thorough review of recent progresses of research on five major types of piezoelectric biomaterials including amino acids, peptides, proteins, viruses, and polysaccharides. Our discussion focuses on their structure- and phase-related piezoelectric properties and fabrication strategies to achieve desired piezoelectric phases. We compare and analyze their piezoelectric performance and further introduce and comment on the approaches to improve their piezoelectric property. Representative biomedical applications of this group of functional biomaterials including energy harvesting, sensing, and tissue engineering are also discussed. We envision that molecular-level understanding of the piezoelectric effect, piezoelectric response improvement, and large-scale manufacturing are three main challenges as well as research and development opportunities in this promising interdisciplinary field.

Coimmobilized enzymes as versatile biocatalytic tools for biomass valorization and remediation of environmental contaminants - A review

Due to stringent regulatory norms, waste processing faces confrontations and challenges in adapting technology for effective management through a convenient and economical system. At the global level, attempts are underway to achieve a green and sustainable treatment for the valorization of lignocellulosic biomass as well as organic contaminants in wastewater. Enzymatic treatment in the environmental aspect thrived on being the promising rapid strategy that appeased the aforementioned predicament. On that account, coimmobilization of various enzymes on single support enhances the catalytic activity ensuing operational stability with industrial applications. This review pivoted towards the coimmobilization of enzymes on diverse supports and their applications in biomass conversion to industrial value-added products and removal of contaminants in wastewater. The limelight of this study chronicles the unique breakthroughs in biotechnology for the production of reusable biocatalysts, which inculcating various enzymes towards the scope of environment application.

The Frontiers of Functionalized Nanocellulose-Based Composites and Their Application as Chemical Sensors

Chemical sensors are a rapidly developing technology that has received much attention in diverse industries such as military, medicine, environmental surveillance, automotive power and mobility, food manufacturing, infrastructure construction, product packaging and many more. The mass production of low-cost devices and components for use as chemical sensors is a major driving force for improvements in each of these industries. Recently, studies have found that using renewable and eco-friendly materials would be advantageous for both manufacturers and consumers. Thus, nanotechnology has led to the investigation of nanocellulose, an emerging and desirable bio-material for use as a chemical sensor. The inherent properties of nanocellulose, its high tensile strength, large specific surface area and good porous structure have many advantages in its use as a composite material for chemical sensors, intended to decrease response time by minimizing barriers to mass transport between an analyte and the immobilized indicator in the sensor. Besides which, the piezoelectric effect from aligned fibers in nanocellulose composites is beneficial for application in chemical sensors. Therefore, this review presents a discussion on recent progress and achievements made in the area of nanocellulose composites for chemical sensing applications. Important aspects regarding the preparation of nanocellulose composites using different functionalization with other compounds are also critically discussed in this review.

Iridium-Functionalized Cellulose Microcrystals as a Novel Luminescent Biomaterial for Biocomposites

Microcrystalline cellulose (MCC) is an emerging material with outstanding properties in many scientific and industrial fields, in particular as an additive in composite materials. Its surface modification allows for the fine-tuning of its properties and the exploitation of these materials in a plethora of applications. In this paper, we present the covalent linkage of a luminescent Ir-complex onto the surface of MCC, representing the first incorporation of an organometallic luminescent probe in this biomaterial. This goal has been achieved with an easy and sustainable procedure, which employs a Bronsted-acid ionic liquid as a catalyst for the esterification reaction of -OH cellulose surface groups. The obtained luminescent cellulose microcrystals display high and stable emissions with the incorporation of only a small amount of iridium (III). Incorporation of MCC-Ir in dry and wet matrices, such as films and gels, has been also demonstrated, showing the maintenance of the luminescent properties even in possible final manufacturers.

Advances in Cellulose-Based Hydrogels for Biomedical Engineering: A Review Summary

In recent years, hydrogel-based research in biomedical engineering has attracted more attention. Cellulose-based hydrogels have become a research hotspot in the field of functional materials because of their outstanding characteristics such as excellent flexibility, stimulus-response, biocompatibility, and degradability. In addition, cellulose-based hydrogel materials exhibit excellent mechanical properties and designable functions through different preparation methods and structure designs, demonstrating huge development potential. In this review, we have systematically summarized sources and types of cellulose and the formation mechanism of the hydrogel. We have reviewed and discussed the recent progress in the development of cellulose-based hydrogels and introduced their applications such as ionic conduction, thermal insulation, and drug delivery. Also, we analyzed and highlighted the trends and opportunities for the further development of cellulose-based hydrogels as emerging materials in the future.

Poly(3-hydroxybutyrate) Nanocomposites with Cellulose Nanocrystals

Poly(3-hydroxybutyrate) (PHB) is one of the most promising substitutes for the petroleum-based polymers used in the packaging and biomedical fields due to its biodegradability, biocompatibility, good stiffness, and strength, along with its good gas-barrier properties. One route to overcome some of the PHB's weaknesses, such as its slow crystallization, brittleness, modest thermal stability, and low melt strength is the addition of cellulose nanocrystals (CNCs) and the production of PHB/CNCs nanocomposites. Choosing the adequate processing technology for the fabrication of the PHB/CNCs nanocomposites and a suitable surface treatment for the CNCs are key factors in obtaining a good interfacial adhesion, superior thermal stability, and mechanical performances for the resulting nanocomposites. The information provided in this review related to the preparation routes, thermal, mechanical, and barrier properties of the PHB/CNCs nanocomposites may represent a starting point in finding new strategies to reduce the manufacturing costs or to design better technological solutions for the production of these materials at industrial scale. It is outlined in this review that the use of low-value biomass resources in the obtaining of both PHB and CNCs might be a safe track for a circular and bio-based economy. Undoubtedly, the PHB/CNCs nanocomposites will be an important part of a greener future in terms of successful replacement of the conventional plastic materials in many engineering and biomedical applications.

Mechanically Robust and Elastic Graphene/Aramid Nanofiber/Polyaniline Nanotube Aerogels for Pressure Sensors

The preparation of graphene-based aerogels with excellent mechanical strength, elasticity, and compressibility is still a challenge. Herein, we demonstrate a robust, elastic, and lightweight graphene/aramid nanofiber/polyaniline nanotube (rGO/ANF/PANIT) aerogel that is prepared by mixing graphene oxide (GO), ANF, and PANIT dispersions, followed by thermal treatment at 90 °C, freeze-drying, and a low-temperature annealing process. The PANIT bonds the graphene sheets tightly, benefitting the formation of composite gels. The ANF tightly interconnects the graphene sheets and further reinforces the composite network framework significantly, hence endowing rGO/ANF/PANIT composite aerogels with robust mechanical property. The prepared aerogels present a low density of ∼12 mg cm^-3, high conductivity, good resilience, and high compressibility. The rGO/ANF/PANIT aerogels as pressure sensors exhibit a high sensitivity of 1.73 kPa^-1, low detection limit (40 Pa), wide detection range, and excellent compressive cycle stability, highlighting the promising applications in pressure-sensitive electrical devices, including medical health detection, wearable electronics, and intelligent packaging fields.

Perspective about Cellulose-Based Pressure and Strain Sensors for Human Motion Detection

High-performance wearable sensors, especially resistive pressure and strain sensors, have shown to be promising approaches for the next generation of health monitoring. Besides being skin-friendly and biocompatible, the required features for such types of sensors are lightweight, flexible, and stretchable. Cellulose-based materials in their different forms, such as air-porous materials and hydrogels, can have advantageous properties to these sensors. For example, cellulosic sensors can present superior mechanical properties which lead to improved sensor performance. Here, recent advances in cellulose-based pressure and strain sensors for human motion detection are reviewed. The methodologies and materials for obtaining such devices and the highlights of pressure and strain sensor features are also described. Finally, the feasibility and the prospects of the field are discussed.

Detection of Human Neutrophil Elastase by Fluorescent Peptide Sensors Conjugated to TEMPO-Oxidized Nanofibrillated Cellulose

Peptide-cellulose conjugates designed for use as optical protease sensors have gained interest for point-of-care (POC) detection. Elevated serine protease levels are often found in patients with chronic illnesses, necessitating optimal biosensor design for POC assessment. Nanocellulose provides a platform for protease sensors as a transducer surface, and the employment of nanocellulose in this capacity combines its biocompatibility and high specific surface area properties to confer sensitive detection of dilute biomarkers. However, a basic understanding of the spatiotemporal relationships of the transducer surface and sensor disposition is needed to improve protease sensor design and development. Here, we examine a tripeptide, fluorogenic elastase biosensor attached to TEMPO-oxidized nanofibrillated cellulose via a polyethylene glycol linker. The synthetic conjugate was found to be active in the presence of human neutrophil elastase at levels comparable to other cellulose-based biosensors. Computational models examined the relationship of the sensor molecule to the transducer surface. The results illustrate differences in two crystallite transducer surfaces ((110) vs. (1-10)) and reveal preferred orientations of the sensor. Finally, a determination of the relative (110) vs. (1-10) orientations of crystals extracted from cotton demonstrates a preference for the (1-10) conformer. This model study potentiates the HNE sensor results for enhanced sensor activity design.