The nanowatt-level power density of current biobased piezoelectric energy harvesters restricts their applicative potential for the efficient conversion of biomechanical energy. A high-performing, fully renewable piezoelectric device incorporating green piezo-active Rochelle salt in a laser-drilled wood template is demonstrated to form ordered crystal pillar arrays by melt crystallization. Investigating the effect of different crystal pillar configurations on the piezoelectric response, a shearing design (45 degrees-oriented pillars) shows potential of up to 30 V and a current of 4 mu A - corresponding to a 10-fold power increase compared to single-crystalline Rochelle salt. A concept of direct laser graphitization on the crystal surfaces are demonstrated using a fully renewable ink to create electrodes of low resistance (36 Omega sq-1). The entire device can be disassembled, fully recycled, and reused. This nanogenerator outperforms state-of-the-art biobased ones and competes with conventional lead-based devices in power generation while showing a significantly lower environmental footprint, as indicated by life-cycle assessment.

The inherent colloidal dispersity (due to length, aspect ratio, surface charge heterogeneity) of CNCs, when produced using the typical traditional sulfuric acid hydrolysis route, presents a great challenge when interpreting colloidal properties and linking the CNC film nanostructure to the helicoidal self-assembly mechanism during drying. Indeed, further improvement of this CNC preparation route is required to yield films with better control over the CNC pitch and optical properties. Here we present a modified CNC-preparation protocol, by fractionating and harvesting CNCs with different average surface charges, rod lengths, aspect ratios, already during the centrifugation steps after hydrolysis. This enables faster CNC fractionation, because it is performed in a high ionic strength aqueous medium. By comparing dry films from the three CNC fractions, discrepancies in the CNC self-assembly and structural colors were clearly observed. Conclusively, we demonstrate a fast protocol to harvest different populations of CNCs, that enable tailored refinement of structural colors in CNC films.

Polymer coating to substrates alters surface chemistry and imparts bulk material functionalities with a minute thickness, even in nanoscale. Specific surface modification of a substate usually requires an active substrate that, e.g., undergoes a chemical reaction with the modifying species. Here, we present a generic method for surface modification, namely, solid-state adsorption, occurring purely by entropic strive. Formed by heating above the melting point or glass transition and subsequent rinsing of the excess polymer, the emerging ultrathin (<10 nm) layers are known in fundamental polymer physics but have never been utilized as building blocks for materials and they have never been explored on soft matter substrates. We show with model surfaces as well as bulk substrates, how solid-state adsorption of common polymers, such as polystyrene and poly(lactic acid), can be applied on soft, cellulose-based substrates. Our study showcases the versatility of solid-state adsorption across various polymer/substrate systems. Specifically, we achieve proof-of-concept hydrophobization on flexible cellulosic substrates, maintaining irreversible and miniscule adsorption yet with nearly 100% coverage without compromising the bulk material properties. The method can be considered generic for all polymers whose Tg and Tm are below those of the to-be-coated adsorbed layer, and whose integrity can withstand the solvent leaching conditions. Its full potential has broad implications for diverse materials systems where surface coatings play an important role, such as packaging, foldable electronics, or membrane technology.

Interactions between dry cellulose were studied using model systems, cellulose beads, and cellulose films, usingcustom-built contact adhesion testing equipment. Depending on the configuration of the substrates in contact,Polydimethylsiloxane (PDMS) film, cellulose films spin-coated either on PDMS or glass, the interaction showsthree distinct processes. Firstly, molecular interlocking is formed between cellulose and cellulose when there is asoft PDMS thin film backing the cellulose film. Secondly, without backing, no initial attraction force between thesurfaces is observed. Thirdly, a significant force increase, ΔF, is observed during the retraction process for cel­lulose on glass, and there is a maximum in ΔF when the retraction rate is increased. This is due to the kinetics of acontacting process occurring in the interaction zone between the surfaces caused by an interdigitation of a finefibrillar structure at the nano-scale, whereas, for the spin-coated cellulose surfaces on the PDMS backing, there isa more direct adhesive failure. The results have generated understanding of the interaction between cellulose-rich materials, which helps design new, advanced cellulose-based materials. The results also show thecomplexity of the interaction between these surfaces and that earlier mechanisms, based on macroscopic materialtesting, are simply not adequate for molecular tailoring.

Cellulose has shown great potential in the development of green triboelectric nanogenerators. Particularly, regenerated cellulose (R-cellulose) has shown remarkably high output power density but the structural features and key parameters that explain such superior performance remain unexplored. In this work, wood cellulose fibers were dissolved in a LiOH(aq)-based solvent to produce a series of R-cellulose films. Regeneration in different alcohols (from methanol to n-pentanol) was performed and the films’ structural features and triboelectric performance were assessed. Nonsolvents of increased hydrophobicity led to R-cellulose films with a more pronounced (1–10) diffraction peak. An open-circuit voltage (VOC) of up to ca. 260 V and a short-circuit current (ISC) of up to ca. 150 µA were measured for R-cellulose against polytetrafluoroethylene (as negative counter-layer). However, R-cellulose showed an increased VOC of 175% (from 88.1 V) against polydimethylsiloxane when increasing the alcohol hydrocarbon chain length from methanol to n-pentanol. The corresponding ISC and output power also increased by 76% (from 89.9 µA) and by 382% (from 8.8 W m–2), respectively. The higher R-cellulose hydrophilicity, combined with soft counter-tribolayer that follow the surface structures increasing the effective contact area, are the leading reasons for a superior triboelectric performance.

Three-dimensional (3D) tumor spheroids are regarded as promising models for utilization as preclinical assessments of chemo-sensitivity. However, the creation of these tumor spheroids presents challenges, given that not all tumor cell lines are able to form consistent and regular spheroids. In this context, we have developed a novel layer-by-layer coating of cellulose nanofibril–polyelectrolyte bilayers for the generation of spheroids. This technique builds bilayers of cellulose nanofibrils and polyelectrolytes and is used here to coat two distinct 96-well plate types: nontreated/non-sterilized and Nunclon Delta. In this work, we optimized the protocol aimed at generating and characterizing spheroids on difficult-to-grow pancreatic tumor cell lines. Here, diverse parameters were explored, encompassing the bilayer count (five and ten) and multiple cell-seeding concentrations (10, 100, 200, 500, and 1000 cells per well), using four pancreatic tumor cell lines—KPCT, PANC-1, MiaPaCa-2, and CFPAC-I. The evaluation includes the quantification (number of spheroids, size, and morphology) and proliferation of the produced spheroids, as well as an assessment of their viability. Notably, our findings reveal a significant influence from both the number of bilayers and the plate type used on the successful formation of spheroids. The novel and simple layer-by-layer-based coating method has the potential to offer the large-scale production of spheroids across a spectrum of tumor cell lines.

New sustainable materialsproduced by green processing routes arerequired in order to meet the concepts of circular economy. The replacementof insulating materials comprising flammable synthetic polymers bybio-based materials represents a potential opportunity to achievethis task. In this paper, low-density and flame-retardant (FR) porousfiber networks are prepared by assembling Layer-by-Layer (LbL)-functionalizedcellulose fibers by means of freeze-drying. The LbL coating, encompassingchitosan and sodium hexametaphosphate, enables the formation of aself-sustained porous structure by enhancing fiber-fiber interactionsduring the freeze-drying process. Fiber networks prepared from 3 Bi-Layer(BL)-coated fibers contain 80% wt of cellulose and can easily self-extinguishthe flame during flammability tests in vertical configuration whiledisplaying extremely low combustion rates in forced combustion tests.Smoke release is 1 order of magnitude lower than that of commerciallyavailable polyurethane foams. Such high FR efficiency is ascribedto the homogeneity of the deposited assembly, which produces a protectiveexoskeleton at the air/cellulose interface. The results reported inthis paper represent an excellent opportunity for the developmentof fire-safe materials, encompassing natural components where sustainabilityand performance are maximized.

The capacity of cells to adhere to, exert forces upon and migrate through their surrounding environment governs tissue regeneration and cancer metastasis. The role of the physical contractile forces that cells exert in this process, and the underlying molecular mechanisms are not fully understood. We, therefore, aimed to clarify if the extracellular forces that cells exert on their environment and/or the intracellular forces that deform the cell nucleus, and the link between these forces, are defective in transformed and invasive fibroblasts, and to indicate the underlying molecular mechanism of control. Confocal, Epifluorescence and Traction force microscopy, followed by computational analysis, showed an increased maximum contractile force that cells apply on their environment and a decreased intracellular force on the cell nucleus in the invasive fibroblasts, as compared to normal control cells. Loss of HDAC6 activity by tubacin-treatment and siRNA-mediated HDAC6 knockdown also reversed the reduced size and more circular shape and defective migration of the transformed and invasive cells to normal. However, only tubacin-mediated, and not siRNA knockdown reversed the increased force of the invasive cells on their surrounding environment to normal, with no effects on nuclear forces. We observed that the forces on the environment and the nucleus were weakly positively correlated, with the exception of HDAC6 siRNA-treated cells, in which the correlation was weakly negative. The transformed and invasive fibroblasts showed an increased number and smaller cell-matrix adhesions than control, and neither tubacin-treatment, nor HDAC6 knockdown reversed this phenotype to normal, but instead increased it further. This highlights the possibility that the control of contractile force requires separate functions of HDAC6, than the control of cell adhesions, spreading and shape. These data are consistent with the possibility that defective force-transduction from the extracellular environment to the nucleus contributes to metastasis, via a mechanism that depends upon HDAC6. To our knowledge, our findings present the first correlation between the cellular forces that deforms the surrounding environment and the nucleus in fibroblasts, and it expands our understanding of how cells generate contractile forces that contribute to cell invasion and metastasis.

Despite extensive research on biobased and fiber-basedmaterials, fundamental questions regarding the molecular processesgoverning fiber−fiber interactions remain unanswered. In this study, weintroduce a method to examine and clarify molecular interactions withinfiber−fiber joints using precisely characterized model materials, i.e.,regenerated cellulose gel beads with nanometer-smooth surfaces. Byphysically modifying these materials and drying them together to createmodel joints, we can investigate the mechanisms responsible for joiningcellulose surfaces and how this affects adhesion in both dry and wet statesthrough precise separation measurements. The findings reveal a subtlebalance in the joint formation, influencing the development ofnanometer-sized structures at the contact zone and likely inducingbuilt-in stresses in the interphase. This research illustrates how model materials can be tailored to control interactions betweencellulose-rich surfaces, laying the groundwork for future high-resolution studies aimed at creating stiff, ductile, and/or tough jointsbetween cellulose surfaces and to allow for the design of high-performance biobased materials.