The ability to synthesize laser-induced graphene (LIG) on cellulosic materials such as paper opens the door to a wide range of potential applications, from consumer electronics to biomonitoring. In this work, strain and bending sensors fabricated by irradiation of regular filter paper with a CO2 laser are presented. A systematic study of the influence of the different process parameters on the conversion of cellulose fibers into LIG is undertaken, by analyzing the resulting morphology, structure, conductivity, and surface chemistry. The obtained material is characterized by porous electrically conductive weblike structures with sheet resistances reaching as low as 32 Ω sq–1. The functionality of both strain (gauge factor of ≈42) and bending sensors is demonstrated for different sensing configurations, emphasizing the versatility and potential of this material for low-cost, sustainable, and environmentally friendly mechanical sensing.

Laser irradiation to induce networks of graphene‐based structures toward cost‐effective, flexible device fabrication is a highly pursued area, with applications in various polymeric substrates. This work reports the application of this approach toward commonly available, eco‐friendly, low‐cost substrates, namely, chromatographic and office papers. Through an appropriate chemical treatment with sodium tetraborate as a fire‐retardant agent, photothermal conversion to porous laser‐induced graphene (LIG) on paper is achieved. Raman peaks are identified, with I2D/IG and ID/IG peak ratios of 0.616 ± 0.095 and 1.281 ± 0.173, showing the formation of multilayered graphenic material, exhibiting sheet resistances as low as 56.0 Ω sq–1. Coplanar, LIG‐based, three‐electrode systems (working, counter and reference electrodes) are produced and characterized, showing high current Faradaic oxidation and reduction peaks, translating in high electrochemical active area, doubling the geometric area. Good electron transfer kinetics performed exclusively with on‐chip measurements are reached, with k0 values as high as 7.15 × 10–4 cm s–1. Proof‐of‐concept, amperometric, enzymatic glucose biosensors are developed, exhibiting good analytical performance in physiologically relevant glucose levels, with results pointing to the applicability of paper‐based LIG toward efficient, disposable electrochemical sensor development, increasing their sustainability and accessibility, while simplifying their production and reducing their cost.

Since the discovery of laser-induced graphene (LIG), significant advances have been made to obtain green LIG (gLIG) from abundant, eco-friendly, natural, and organic renewable bio-based carbon sources. Recently, some sustainable and cost-effective electronic devices have been designed with gLIG, resulting in diverse solutions to the environmental impact caused by electronic waste (e-waste). However, there are still several challenges that must be addressed regarding the widespread market implementation of gLIG-based products, from synthesis to practical applications. In this review, we focus on sustainable precursor sources, their conversion mechanisms, physical and chemical properties and applications, along with the challenges related to its implementation, showing the future opportunities and perspectives related to this promising new material. Various systems based on gLIG for energy storage, electrocatalysis, water treatment, and sensors have been reported in the literature. Additionally, gLIG has been proposed for ink formulation or incorporation into polymer matrices, to further expand its use to non-carbon-based substrates or applications for which pristine LIG cannot be directly used. In this way, it is possible to apply gLIG on diverse substrates, aiming at emerging wearable and edible electronics. Thus, this review will bring an overview of gLIG developments, in accordance with the European Green Deal, the United Nations Sustainable Development Goals and the new era of internet-of-things, which demands cost-effective electronic components based on the principles of energy efficiency and sustainable production methods.

A new strategy for the surface modification of bacterial cellulose (BC) through the combination of oxygen plasma deposition and silanization with trichloromethyl silane (TCMS) is described. The combined use of the two techniques modifies both the surface roughness and energy and therefore maximizes the obtained hydrophobic effect. These modified membranes were characterized by Scanning Electron Microscopy (SEM), water contact angle measurements, Fourier-transform infrared spectroscopy (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS), and its cytotoxic potential was investigated using both indirect and direct contact in vitro studies. The obtained results suggest an effective conjugation of TCMS to the surface of BC, leading to a highly hydrophobic surface, with a water contact angle of approximately 1308. It is also demonstrated that this is a stable and durable surface modification strategy, since BC remained hydrophobic even after 6 months, in dry conditions or after being submerged in distilled water for about a month. Importantly, this surface modification revealed no short-term cytotoxic effects on L929 and hDNFs cells. Altogether, these data indicate the successful development of a surface modification method that can be applied to BC, enabling the production of a biodegradable and hydrophobic platform that can be applied to different areas of research and industry.

Laser-induced graphene (LIG) is as a promising material for flexible microsupercapacitors (MSCs) due to its simple and cost-effective processing. However, LIG-MSC research and production has been centered on non-sustainable polymeric substrates, such as polyimide. In this work, it is presented a cost-effective, reproducible, and robust approach for the preparation of LIG structures via a one-step laser direct writing on chromatography paper. The developed strategy relies on soaking the paper in a 0.1 M sodium tetraborate solution (borax) prior to the laser processing. Borax acts as a fire-retardant agent, thus allowing the laser processing of sensitive substrates that other way would be easily destroyed under the high-energy beam. LIG on paper exhibiting low sheet resistance (30 Ω sq−1) and improved electrode/electrolyte interface was obtained by the proposed method. When used as microsupercapacitor electrodes, this laser-induced graphene resulted in specific capacitances of 4.6 mF cm−2 (0.015 mA cm−2). Furthermore, the devices exhibit excellent cycling stability (> 10,000 cycles at 0.5 mA cm−2) and good mechanical properties. By connecting the devices in series and parallel, it was also possible to control the voltage and energy delivered by the system. Thus, paper-based LIG-MSC can be used as energy storage devices for flexible, low-cost, and portable electronics. Additionally, due to their flexible design and architecture, they can be easily adapted to other circuits and applications with different power requirements. Graphical Abstract

The demand for smart, wearable devices has been dictating our daily life with the evolution of integrated miniaturized electronics. With technological innovations, comes the impactful human footprint left on the planet's ecosystems. Therefore, it is necessary to explore renewable materials and sustainable methodologies for industrial processes. Here, an eco-friendly approach to producing flexible electrodes based on single-step direct laser writing (DLW) is reported. A 1.06 µm wavelength fiber laser was used for the first time to produce porous 3D laser-induced graphene (LIG) on an agglomerated cork substrate. The obtained material exhibits the typical Raman spectra, along with an exceptionally low sheet resistance between 7.5-10 ohm sq-1. LIG on cork high electrical conductivity and the friendliness of the used production method, makes it an interesting material for future technological applications. To show its applicability, the production of planar micro-supercapacitors (MSCs) was demonstrated, as a proof of concept. Electrochemical performance studies demonstrate that LIG interdigitated electrodes, using PVA-H2SO4 electrolyte, achieve an area capacitance of 1.35 mF cm-2 (103.63 mF cm-3) at 5 mV s-1 and 1.43 mF cm-2 (109.62 mF cm-3) at 0.1 mA cm-2. In addition, devices tested under bending conditions exhibit a capacitance of 2.20 mF cm-2 (169.22 mF cm-3) at 0.1 mA cm-2. Here, showing that these electrodes can be implemented in energy storage devices, also successfully demonstrating LIG promising application on innovative, green, and self-sustaining platforms.

Poly(hydroxyalkanoates) (PHAs) with differing material properties, namely, the homopolymer poly(3-hydroxybutyrate), P(3HB), the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate), P(3HB-co-3HV), with a 3HV content of 25 wt.% and a medium chain length PHA, and mcl-PHA, mainly composed of 3-hydroxydecanoate, were studied as scaffolding material for cell culture. P(3HB) and P(3HB-co-3HV) were individually spun into fibers, as well as blends of the mcl-PHA with each of the scl-PHAs. An overall biopolymer concentration of 4 wt.% was used to prepare the electrospinning solutions, using chloroform as the solvent. A stable electrospinning process and good quality fibers were obtained for a solution flow rate of 0.5 mL h−1, a needle tip collector distance of 20 cm and a voltage of 12 kV for P(3HB) and P(3HB-co-3HV) solutions, while for the mcl-PHA the distance was increased to 25 cm and the voltage to 15 kV. The scaffolds’ hydrophilicity was significantly increased under exposure to oxygen plasma as a surface treatment. Complete wetting was obtained for the oxygen plasma treated scaffolds and the water uptake degree increased in all treated scaffolds. The biopolymers crystallinity was not affected by the electrospinning process, while their treatment with oxygen plasma decreased their crystalline fraction. Human dermal fibroblasts were able to adhere and proliferate within the electrospun PHA-based scaffolds. The P(3HB-co-3HV): mcl-PHA oxygen plasma treated scaffold highlighted the most promising results with a cell adhesion rate of 40 ± 8%, compared to 14 ± 4% for the commercial oxygen plasma treated polystyrene scaffold AlvetexTM. Scaffolds based on P(3HB-co-3HV): mcl-PHA blends produced by electrospinning and submitted to oxygen plasma exposure are therefore promising biomaterials for the development of scaffolds for tissue engineering.

Komagataeibacter xylinus strains DSM 2004 and DSM 46604 were evaluated for their ability to grow and produce bacterial cellulose (BC) upon cultivation on terephthalic acid (TA) and ethylene glycol (EG), which are monomers of the petrochemical-derived plastic polyethylene terephthalate (PET). Both strains were able to utilize TA, EG, and their mixtures for BC synthesis, with different performances. K. xylinus DSM 2004 achieved higher BC production from TA (0.81 ± 0.01 g/L), EG (0.64 ± 0.02 g/L), and TA + EG mixtures (0.6 ± 0.1 g/L) than strain DSM 46604. The latter was unable to utilize EG as the sole carbon source and reached a BC production of 0.16 ± 0.01 g/L and 0.23 ± 0.1 g/L from TA alone or TA + EG mixtures, respectively. Further supplementing the media with glucose enhanced BC production by both strains. During cultivation on media containing TA and EG, rapid pH drop due to metabolization of EG into acidic compounds led to some precipitation of TA that was impregnated into the BC pellicles. An adaptation of the downstream procedure involving BC dissolution in NaOH was used for the recovery of pure BC. The different medium composition tested, as well as the downstream procedure, impacted the BC pellicles’ physical properties. Although no variation in terms of the chemical structure were observed, differences in crystallinity degree and microstructure of the produced BC were observed. The BC produced by K. xylinus DSM 2004 had a higher crystallinity (19–64%) than that of the strain DSM 46604 (17–53%). Moreover, the scanning electron microscopy analysis showed a higher fiber diameter for K. xylinus DSM 2004 BC (46–56 nm) than for K. xylinus DSM 46604 (37–49 nm). Dissolution of BC in NaOH did not influence the chemical structure; however, it led to BC conversion from type I to type II, as well as a decrease in crystallinity. These results demonstrate that PET monomers, TA and EG, can be upcycled into a value-added product, BC, presenting an approach that will contribute to lessening the environmental burden caused by plastic disposal in the environment.