Point-of-care (POC) systems represent a significant innovation in the context of combating epidemics as they facilitate rapid, sensitive, and specific diagnostic screening. However, most existing POC systems are manufactured using petrochemical-derived materials or involve chemical processes that raise significant environmental concerns. In this study, we present a method for encapsulating microfluidic devices using pulverized cellulose microfibril suspensions. Nanopaper with grammages ranging from 5 to 40 g & centerdot;m2 was fabricated using a spray deposition technique integrated with a 6-axis robotic arm. This nanopaper demonstrated effective air barrier properties at grammages of 15 g & centerdot;m-2 or higher. To ensure fluid containment and protection against external contamination, alkyl ketene dimer (AKD) was incorporated, imparting hydrophobic properties. At a loading of 1% (dry weight), this treatment yields a contact angle exceeding 100 degrees for water. Laser etching was employed to structure the encapsulation layer, yielding an operational microfluidic device. Protein labeling of the microfluidic strips, combined with sealing using microfibrillated cellulose (MFC), led to the creation of an operational cellulose-based POC device. The final device is mainly paper-based, with a 10-fold reduction in mass compared to conventional systems.

This review focuses on the additive manufacturing of thermoset polymers incorporating at least one bio-based constituent, whether as a filler or as the thermoset polymer itself. In this work, bio-based thermosets reviewed are mostly epoxy, acrylate, methacrylate and thiol–ene resins. The micro-scale fillers developed in additive manufacturing mainly source from woody biomass, with wood particles but also cellulose powder and lignin. Nano-scale fillers use is also reported with cellulose nano crystals, chitin nano crystals and carbon dots derived from cellulose. Additive manufacturing was chosen as the focus due to its broad range of applications and significant sustainability advantages, including reduced waste, shorter value chains, and easier repairability. Furthermore, the growing demand for bio-based polymers is driven by the anticipated shortage of fossil-based alternatives. This review demonstrates the relevance of this timely topic and highlights the extensive research efforts dedicated to bio-based thermosets and thermosets with bio-based fillers, showcasing a diverse array of innovative approaches explored across 83 studies. Overall, despite significant progress in the development of bio-based thermosets, the dependence on petroleum-derived photoinitiators, together with the limited understanding and control of curing kinetics and rheological behavior of neat and composite precursors, remain major challenges that must be addressed to enable the industrial scale-up of these additive manufacturing materials.

This study investigates printing poly lactic acid (PLA) reinforcement grids on corrugated board boxes as a strategy to enhance their mechanical performance-to-weight ratio, with the objective of decreasing overall material consumption. Four-points bending and compression tests were respectively conducted on plates printed with varying thicknesses and on boxes printed either inside or outside. Stereo digital image correlation (DIC) was employed during compression to monitor panel deflection amplitudes. Increasing the height of printed grids induced an improvement of the bending stiffness-to-weight ratio. While outside-printed boxes showed a 26% BCT increase for a 21% mass increase, inside-printed boxes exhibited a 9% BCT increase but a stable post-BCT behavior, being able to withstand important loads before their ultimate collapse. They exhibited crushing of their panel, contrary to the other box families. Deflection amplitudes measured by DIC were plotted as function of load to further analyze compression behaviors, initial imperfections and buckling loads across the different box families. It revealed that PLA shrinkage during cooling induced initial imperfections, driving printed panels into the post-buckling range, and accelerating their deflection despite their increased bending stiffness. DIC data were used to calibrate an analytical buckling model highlighting the role of initial imperfections in panels deflection evolution.

Point-of-care (POC) devices offer a considerable opportunity to tackle epidemics through rapid, sensitive and specific screening. Microporous nitrocellulose membranes are the most widely used substrate for POC devices due to their high affinity with biological reagents such as proteins and oligonucleotides. However, nitrocellulose has several disadvantages: it is produced through an environmentally unfriendly chemical process, and it is converted with a subtractive process. In addition, nitrocellulose hydrophobicity requires surfactants to increase membrane wettability. The aim of this work is to manufacture a microfluidic paper-based analytical device (µPAD) composite of a microfibrillated cellulose matrix (MFC) embedded with microcrystalline cellulose (MCC) and silicon oxide particles (SiO2) to manage water uptake and fluid flow kinetics within the fluidic strip. Several composite inks were formulated by varying the MFC, MCC and SiO2 mass fractions, and the impact of particle size and mass fraction of the composite on water uptake was compared. An additive manufacturing technique was assessed using a fluid dispenser mounted on a 6-axis robot to manufacture the cellulose-based strips. One key objective was to develop a µPAD as an alternative to nitrocellulose-based POC devices. The µPAD composite was assessed with a migration test in a lateral flow configuration. Promising results were obtained by producing strips with a water capillary rise of 4 cm in 5 min, comparable to the performance of nitrocellulose. Finally, the µPAD strips were spotted with proteins and sealed with MFC in order to produce a functional cellulose-based POC proof of concept.

Nanostructured materials represent promising substrates for biocatalysts immobilization and activation. Cellulose nanocrystals (CNCs), accessible from waste and/or renewable sources, are sustainable and biodegradable, show high specific surface area for anchoring a high number of enzymatic units, and high thermal and mechanical stability. In this work, we present a holistic enzyme‐based approach to functional antibacterial materials by bioconjugation between the lysozyme from chicken egg white and enzymatic cellulose nanocrystals. The neutral CNCs were prepared by endoglucanase hydrolysis from Avicel. We explore the covalent immobilization of lysozyme on the enzymatic CNCs and on their TEMPO oxidized derivatives (TO‐CNCs), comparing immobilization yields, materials properties, and enzymatic activities. The materials were characterized by X‐ray diffractometry (XRD), attenuated total reflectance Fourier Transform infrared spectroscopy (ATR‐FTIR), bicinchoninic acid (BCA) assay, field‐emission scanning electron microscopy (FE‐SEM) and dynamic light scattering (DLS). We demonstrate the higher overall efficiency of the immobilization process carried out on TO‐CNCs, based on the success of covalent bonding and on the stability of the isolated biocojugates.

Cellulose nanocrystals are an important class of bio-based crystalline nanostructures, finding application in several technological fields, including paper and textile coating, biocomposite engineering, biocatalysts immobilization, etc. This study explores enzymatic hydrolysis of Avicel, using endoglucanase from Aspergillus niger, to find an environmentally friendly method to extract cellulose nanocrystals from cellulose sources. Enzymatic hydrolysis has the advantage of reduced energy consumption and higher environmental friendliness compared to acid hydrolysis. In this work, we report for the first time very high nanocrystals yield by combining mechanical pretreatment of the cellulose starting material with a ball miller and endoglucanase hydrolysis, as a result of an extensive optimization of reaction conditions. In particular, a ball milling pretreatment carried out for 50 minutes at 3 Hz, allowed to isolate enzymatic CNCs with 76 % yield and with crystallinity as high as 75 %. The materials were characterized by X-Ray diffractometry, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, dynamic light scattering, zeta potential and field emission scanning electron microscopy (FE-SEM). Their characteristics were compared with the properties of sulfated CNCs, prepared from Avicel by sulfuric acid hydrolysis. Our results are technologically relevant, as they contribute to the accessibility and sustainability of CNCs for a wide range of applications in various industries. Cellulose nanocrystals (N_CNCs) are synthesized in high yield from Avicel by a mild mechano-enzymatic approach. The mechanic pretreatment with a ball miller allows to enhance the endoglucanase hydrolysis efficiency providing nanocrystals with high crystallinity and homogeneous morphology. This work offers good technological solutions for the preparation of CNCs in high yield. image

Abiotic 3D-printed cathodes for biofuel cells were manufactured using chitosan-cellulose nanofibres-iron doped graphene hydrogels and the cold material extrusion (MEX) 3D printing technique. The subsequent pyrolysis under ammoniac flux and in-situ n-doping of 3D cathodes led to the generation of conductive 3D electrodes with macroporosity that can be tuned by adjusting the linera infill in the 3D printing process and enhanced electrochemical activity. In-situ n-doped electrodes with 40

3D cheap, lightweight and robust cellulosic parts can be obtained via extrusion of a cellulosic aqueous paste followed by air-drying. During the air-drying step, an anisotropic shrinkage occurs. The objective of this study is to characterize the macro and mesoscale phenomena occurring during the drying process. We used sub-minute laboratory X-ray microtomography during air-drying tests combined with advanced image analysis including Digital Volume Correlation to reveal the mechanisms that took place at the sample and at the filament scales. This allowed the qualitative and quantitative analysis of the structural and kinematical changes occurring during the air-drying. The macroscopic anisotropic shrinkage of the structure is associated with a decrease of the solid fraction of the cube and a decrease of the volume of the central pore, a decrease of the number and of the volume of the inter-filament and intra-filament pores, a change of the shape and dimensions of the filaments cross section. We observed delamination effects, increase of the number of inter and intra filament pores. These results complete the analysis commonly carried out at the macroscale and are necessary to build a model for the prediction of drying mechanisms of 3D printed part of cellulose and to propose more accurate compensation strategies.

This study aims to develop a green composite based on two biomass-based components via the curing of an oligomeric furfuryl resin coupled with 18-31 wt% cellulose powder. The curing was performed in an atmospheric pressure open air oven. The chemical composition of the used pre-polymer was characterized with Fourier transform infrared and NMR spectroscopy and its curing reaction was followed by differential scanning calorimetry. The final cured composites were characterized to investigate the effect of cellulose addition on their morphology, dimensional stability, and thermo-mechanical performances. The manufactured composite showed good thermal stability up to 200 degrees C with a storage modulus higher than 2 GPa, and a mass loss under 3%. Moreover, the filler improved the composite dimensional stability upon crosslinking by 38% and the mechanical performances with respectively 15% and 40% increase in the Young's and flexural moduli. By the same token, cellulose prevented the typical foaming of poly(furfuryl alcohol) resins crosslinked at high temperature and low pressure. Preliminary tests highlighted the excellent processability of the developed composite, which was used to manufacture a static demonstrator coupling different fabrication techniques, that is, 3D printing (direct ink writing), high temperature compression molding and CNC machining.

The potential of printing stiffeners of polylactic acid (PLA) by fused deposition modelling (FDM) on the panels of folding board boxes was investigated in view of reducing the board weight while maintaining the box resistance to vertical compression. Cyclic loading and unloading compression tests were performed under standard (50% relative humidity [RH]) and humid (85% RH) environmental conditions on boxes printed with different grid patterns. By only adding 7% in weight of PLA to the whole packaging, the performance was improved by 29% under standard conditions and 60% under humid conditions when the inner surface of box panels was printed with an orthogonal‐type grid. A comparison with a higher basis weight folding board suggested that 30% of raw materials could be saved. Results suggested that the grid mainly improved the stiffness of panels and could delay their buckling and thus the box collapse.

Conventional epoxy polymers are obtained from oil-based resources and their structure is formed by permanent covalent crosslinks. Therefore, this class of materials is now considered non environmentally friendly as they are neither renewable nor reprocessable and recyclable. In this study, we prepared a vitrimeric material based on an epoxy-functionalised cardanol cured with a biobased polycarboxylic acid. In the presence of a zinc-containing catalyst, a soft polyester with a Tg = −13 °C was obtained; its reprocessability by a chemical method was demonstrated to be feasible without any relevant change in properties once a second curing cycle was completed. The vitrimeric polyester was then used in combination with cellulose powder for the preparation of a sustainable and biobased composite. The matrix/filler mass fraction was tailored to obtain a composite paste with suitable rheological properties for 3D printing via Liquid Deposition Modelling (LDM). Preliminary printing tests were successful, and the vitrimeric printed parts were then thermally cured retaining the shape. The suitability of the vitrimeric composite for additive manufacturing was thus confirmed: the new material can provide a solution to 3D printing of recyclable thermosetting biobased polymers.

Direct printing of conductive inks at the surface of generic 3D objects using 6 axis robots is attracting an everincreasing interest, however the high precision positioning and the generation of smooth printing trajectories still represent a bottleneck for the manufacturing of 3D electronic circuits. This work presents a new approach for the rapid prototyping of 3D electronics onto generic objects using a 6 axis robot equipped with a piezo jetting printhead and a high speed laser profiler and a six steps protocol composed by the: i) 3D scan of the substrate and mesh smoothing, ii) 2D circuit projection on the planarized mesh and generation of the 3D trajectory, iii) normals alignment of points lying in the 3D trajectory, iv) retrieve of the effective toolhead TCP translation speed along the 3D trajectory with a blank run, v) synchronization of the ink jetting frequency with the effective toolhead speed, vi) generation of the robot code and print. The effect of mesh and normals smoothing and of circuit design on the effective toolhead translation speed was systematically investigated in order to minimize speed fluctuations/heterogeneous ink deposition during printing, the computational load and shape deviation from the pristine 3D substrate. Conductive tracks printed on an ABS dome displayed geometry and line resistance in line with those predicted by a semi-empirical model using the robot nominal speed and silver ink conductivity, thus showing that the robot operated under stable and well controlled conditions during the printing process. The developed process displayed an average duty cycle of ca. 30 min from the 3D scan to the printing of the 3D circuit, thus showing that it could be suitable for the rapid prototyping/benchmarking of 3D electronics on generic objects.

Implantable devices powered by batteries have been used for sixty years. In recent devices, lithium-based batteries are the most widely used power source. However, lithium batteries have many disadvantages in terms of safety, reliability, and longevity and require regular monitoring and substitution. Implantable glucose biofuel cells (BFCs) are increasingly seen as a potential future technology for replacing lithium-based batteries because they do not require surgical replacement after 8-10 years and have a theoretically unlimited lifetime thanks to the continued recovery of glucose and oxygen present in the human body. This paper shows the fabrication of flexible implantable abiotic cathodes, based on a nitrogen/iron-doped graphene catalyst, for glucose/oxygen biofuel cell application. An ink, based on nitrogen-iron doped graphene as the abiotic catalyst and chitosan as a binder, was prepared and coated on a flexible teflonated gas diffusion layer using doctor blade coating. The characterization of the biocathode shows an open potential circuit corresponding to the potential of the abiotic catalyst and a high oxygen reduction current density of up to 66 μA cm-2 under physiological conditions. Those cathodes remain stable for up to two years with a current density loss of only 25%. The flexible abiotic electrode cytotoxicity was evaluated by cell culture experiments showing living cells' high tolerance on the biocathode surface. This work demonstrates that this abiotic catalyst can be a promising alternative for the development of implantable glucose BFCs due to its stability and its cytocompatibility.

Nowadays, composite materials are widely used in different sectors owing to their improved mechanical and functional properties compared to bulk materials and efficient manufacturing processes. Nevertheless, the majority of these materials are still petroleum-based, which is incompatible with the recent environmental awareness. As a result, in the current study, a fully biomass-based composite material was produced employing poly(furfuryl alcohol) (PFA) as a bio-based matrix coupled with cellulose powder as fillers and processing aid agent. The addition of cellulose powder increased the viscosity of the uncured composite paste and conferred it a shear-thinning thixotropic making it suitable for 3D printing using the liquid deposition modeling technique (LDM). After curing, the combination of these raw materials yields a renewable and cost-effective composite for additive manufacturing by the LDM technique with high interlayer and interfilament adhesion, good mechanical performances, and adequate shape fidelity.

In this work, a new ink formulation based on the use of a fully bio-based thermosetting resin as a binder, cellulose powders as rheology modifiers, and carbon nanotubes as conductive fillers was developed, and its potential as a functional material for additive manufacturing by direct ink writing was demonstrated. Electrical and rheological characterization of the nanocomposite at increasing CNT and cellulose concentrations was conducted in order to determine the optimal processing conditions and the printability window for the system. In addition, the resulting nanocomposite was further carbonized to yield a carbon-carbon nanocomposite with a better electrical conductivity. The results of the present study open the possibility of either integrating conductive circuits in a 3D-printed structure, or the printing of a bulk semi-conductive complex structure using a low-cost DIW 3D printing technique and mostly cost-effective renewable raw materials.

This paper presents an off-line programming approach for the automatic generation of trajectories and the printing program for a 6-axis robot in order to print accurate conductive paths on 3D objects using a silver microparticle solvent-based ink. The aim of this study was to develop a semi-predictive model in order to - Adapt the printing parameters of a 6-axis robot arm and a piezo jetting print head to the printing speed and substrate type. - Print 3D electronic circuits matching the targeted geometry and conductivity. For the jetting printing process, 2D patterns printed on substrates with different roughness and wettability were analysed as a function of the print head translation speed and jetting frequency which were used as base variables to develop correlations in order to predict line width, thickness and conductivity. The model was based on the assumption that the behaviour of a single drop impacting the printing substrate is close to that of a train of drops (i.e. lines). Thus, the diameter of individual drops on a specific substrate was used to account for support properties and jetting conditions. The study also proposes a methodology to tune the circuit morphology by adapting the jetting parameters as a function of the trajectory and the speed of the 6-axis robot. As a representative case study, a 3D circuit was printed on a disposable paper cup obtaining an excellent agreement between measured and predicted conductivity values. (C) 2021 CIRP.

The ohmic curing of two silver micro-particle inks was studied. Silver lines of 35 to 75 µm thick were printed on a mixture of polycarbonate and acrylonitrile butadiene styrene (PC+ABS) substrate and on a mineral reinforced Nylon 6 thermoplastic, using a laboratory-made system based on a volumetric dosing dispenser. After 48 h of stabilization in ambient conditions, a current is applied through the printed lines with an imposed intensity value and application time in order to cure the silver inks. Evolutions of the temperature and the resistivity of silver tracks were followed during the process. Printed thermoplastics were characterized at the end of the process in order to check the absence of deformation due to the curing treatment. The study showed that the ohmic curing led to better electrical performances than an oven process with a considerable time saving. Most of the printed line resistivity drop occurred in the first 30 s of the treatment. The ohmic curing induced a local increase of temperature located in the printed line and avoided damaging the substrates, which makes the process compatible with thermal sensitive substrates. Therefore, the ohmic curing is an efficient low-cost process to cure silver micro-particle inks that could be easily implemented at an industrial scale. Graphic abstract