Template-Directed Polymerization of Binary Acrylate Monomers on Surface-Activated Lignin Nanoparticles in Toughening of Bio-Latex Films.

Fabricating bio-latex colloids with core-shell nanostructure is an effective method for obtaining films with enhanced mechanical characteristics. Nano-sized lignin is rising as a class of sustainable nanomaterials that can be incorporated into latex colloids. Fundamental knowledge of the correlation between surface chemistry of lignin nanoparticles (LNPs) and integration efficiency in latex colloids and from it thermally processed latex films are scarce. Here, an approach to integrate self-assembled nanospheres of allylated lignin as the surface-activated cores in a seeded free-radical emulsion copolymerization of butyl acrylate and methyl methacrylate is proposed. The interfacial-modulating function on allylated LNPs regulates the emulsion polymerization and it successfully produces a multi-energy dissipative latex film structure containing a lignin-dominated core (16% dry weight basis). At an optimized allyl-terminated surface functionality of 1.04 mmol g-1 , the LNPs-integrated latex film exhibits extremely high toughness value above 57.7 MJ m-3 . With multiple morphological and microstructural characterizations, the well-ordered packing of latex colloids under the nanoconfinement of LNPs in the latex films is revealed. It is concluded that the surface chemistry metrics of colloidal cores in terms of the abundance of polymerization-modulating anchors and their accessibility have a delicate control over the structural evolution of core-shell latex colloids.

Human Dermal Fibroblast Viability and Adhesion on Cellulose Nanomaterial Coatings: Influence of Surface Characteristics.

Biodegradable and renewable materials, such as cellulose nanomaterials, have been studied as a replacement material for traditional plastics in the biomedical field. Furthermore, in chronic wound care, modern wound dressings, hydrogels, and active synthetic extracellular matrices promoting tissue regeneration are developed to guide cell growth and differentiation. Cells are guided not only by chemical cues but also through their interaction with the surrounding substrate and its physicochemical properties. Hence, the current work investigated plant-based cellulose nanomaterials and their surface characteristic effects on human dermal fibroblast (HDF) behavior. Four thin cellulose nanomaterial-based coatings produced from microfibrillar cellulose (MFC), cellulose nanocrystals (CNC), and two TEMPO-oxidized cellulose nanofibers (CNF) with different total surface charge were characterized, and HDF viability and adhesion were evaluated. The highest viability and most stable adhesion were on the anionic CNF coating with a surface charge of 1.14 mmol/g. On MFC and CNC coated surfaces, HDFs sedimented but were unable to anchor to the substrate, leading to low viability.

Heat and mass transfer models to understand the drying mechanisms of a porous substrate.

While drying of paper and paper coatings is expensive, with significant energy requirements, the rate controlling mechanisms are not currently fully understood. Two two-dimensional models are used as a first approximation to predict the heat transfer during hot air drying and to evaluate the role of various parameters on the drying rates of porous coatings. The models help determine the structural limiting factors during the drying process, while applying for the first time the recently known values of coating thermal diffusivity. The results indicate that the thermal conductivity of the coating structure is not the controlling factor, but the drying rate is rather determined by the thermal transfer process at the structure surface. This underlines the need for ensuring an efficient thermal transfer from hot air to coating surface during drying, before considering further measures to increase the thermal conductivity of porous coatings.

Impact of humidity on functionality of on-paper printed electronics.

A multilayer coated paper substrate, combining barrier and printability properties was manufactured utilizing a pilot-scale slide curtain coating technique. The coating structure consists of a thin mineral pigment layer coated on top of a barrier layer. The surface properties, i.e. smoothness and surface porosity, were adjusted by the choice of calendering parameters. The influence of surface properties on the fine line printability and conductivity of inkjet-printed silver lines was studied. Surface roughness played a significant role when printing narrow lines, increasing the risk of defects and discontinuities, whereas for wider lines the influence of surface roughness was less critical. A smooth, calendered surface resulted in finer line definition, i.e. less edge raggedness. Dimensional stability and its influence on substrate surface properties as well as on the functionality of conductive tracks and transistors were studied by exposure to high/low humidity cycles. The barrier layer of the multilayer coated paper reduced the dimensional changes and surface roughness increase caused by humidity and helped maintain the conductivity of the printed tracks. Functionality of a printed transistor during a short, one hour humidity cycle was maintained, but a longer exposure to humidity destroyed the non-encapsulated transistor.

Current progress in functionalization of cellulose nanofibers (CNFs) for active food packaging.

There is a growing interest in utilizing renewable biomass resources to manufacture environmentally friendly active food packaging, against the petroleum-based polymers. Cellulose nanofibers (CNFs) have received significant attention recently due to their sustainability, biodegradability, and widely available sources. CNFs are generally obtained through chemical or physical treatment, wherein the original surface chemistry and interfacial interactions can be changed if the functionalization process is applied. This review focuses on promising and sustainable methods of functionalization to broaden the potential uses of CNFs in active food packaging. Novel aspects, including functionalization before, during and after cellulose isolation, and functionalization during and after material processing are addressed. The CNF-involved structural construction including films, membranes, hydrogels, aerogels, foams, and microcapsules, is illustrated, which enables to explore the correlations between structure and performance in active food packaging. Additionally, the enhancement of CNFs on multiple properties of active food packaging are discussed, in which the interaction between active packaging systems and encapsulated food or the internal environment are highlighted. This review emphasizes novel approaches and emerging trends that have the potential to revolutionize the field, paving the way for advancements in the properties and applications of CNF-involved active food packaging.

ToF-SIMS analysis of UV-switchable TiO2-nanoparticle-coated paper surface.

The chemical composition of a TiO2 nanoparticle coated paper surface was analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS) to study the interconnection between wettability and surface chemistry on the nanoscale. In this work, a superhydrophobic TiO2 surface rich in carboxyl-terminated molecules was created by a liquid flame spray process. The TiO2 nanoparticle coated paper surface can be converted by photocatalytic oxidation into a highly hydrophilic one. Interestingly, the hydrophilic surface can be converted back into a superhydrophobic surface by heat treatment. The results showed that both ultraviolet A (UVA) and oven treatment induce changes in the surface chemistry within a few nanometers of the paper surface. These findings are consistent with those from our previously reported X-ray photoelectron spectroscopy (XPS) analysis, but the ToF-SIMS analysis yields more accurate insight into the surface chemistry.

Nanostructures increase water droplet adhesion on hierarchically rough superhydrophobic surfaces.

Hierarchical roughness is known to effectively reduce the liquid-solid contact area and water droplet adhesion on superhydrophobic surfaces, which can be seen for example in the combination of submicrometer and micrometer scale structures on the lotus leaf. The submicrometer scale fine structures, which are often referred to as nanostructures in the literature, have an important role in the phenomenon of superhydrophobicity and low water droplet adhesion. Although the fine structures are generally termed as nanostructures, their actual dimensions are often at the submicrometer scale of hundreds of nanometers. Here we demonstrate that small nanometric structures can have very different effect on surface wetting compared to the large submicrometer scale structures. Hierarchically rough superhydrophobic TiO(2) nanoparticle surfaces generated by the liquid flame spray (LFS) on board and paper substrates revealed that the nanoscale surface structures have the opposite effect on the droplet adhesion compared to the larger submicrometer and micrometer scale structures. Variation in the hierarchical structure of the nanoparticle surfaces contributed to varying droplet adhesion between the high- and low-adhesive superhydrophobic states. Nanoscale structures did not contribute to superhydrophobicity, and there was no evidence of the formation of the liquid-solid-air composite interface around the nanostructures. Therefore, larger submicrometer and micrometer scale structures were needed to decrease the liquid-solid contact area and to cause the superhydrophobicity. Our study suggests that a drastic wetting transition occurs on superhydrophobic surfaces at the nanometre scale; i.e., the transition between the Cassie-Baxter and Wenzel wetting states will occur as the liquid-solid-air composite interface collapses around nanoscale structures. Consequently, water adheres tightly to the surface by penetrating into the nanostructure. The droplet adhesion mechanism presented in this paper gives valuable insight into a phenomenon of simultaneous superhydrophobicity and high water droplet adhesion and contributes to a more detailed comprehension of superhydrophobicity overall.

Preparation and application of composite phase change materials stabilized by cellulose nanofibril-based foams for thermal energy storage.

The leakage issue and inferior heat conduction of organic phase change materials (PCMs) limit their actual applications. In the present study, cellulose nanofibril (CNF)-based foams were prepared as the porous scaffolds for polyethylene glycol (PEG) and paraffin wax (Pw) to prevent their leakage, and multiwalled carbon nanotubes (CNTs) were incorporated to improve the heat transfer performance. The prepared foams had low density (<67.3 kg/m3) and high porosity (>94.5 %). Selective chemical modifications of nanocellulose foams enhanced their shape-stability and compatibility with PCMs. The highly porous foam structure and favorable compatibility resulted in high PCM loading levels (93.63 % for PEG and 91.77 % for Pw) and negligible PCM leakage (<2 %). CNTs improved the heat transfer performance of PCMs, as evidenced by the improved thermal conductivities and boosted temperature rises during solar heating. Meanwhile, the composite PCMs exhibited improved thermal stability over the control. PEG-based composite PCM exhibited a phase change enthalpy of 143 kJ/kg with a melting temperature of 25.2 °C; Pw-based composite PCM exhibited a phase change enthalpy of 184 kJ/kg with a melting temperature of 53.4 °C. Novel PCM sandwich structures based on these composite PCMs and a thermoelectric generator were designed and displayed promising potential for solar energy harvesting and utilization.

Synthesis of galactoglucomannan-based latex via emulsion polymerization.

This is the first time to report a facile strategy to fabricate galactoglucomannan-based latex with highly transparent, hydrophobic and flexible characteristics by combining etherification with subsequent emulsion polymerization. The allylated galactoglucomannans (A-GGM) and galactoglucomannan-based latexes (GGM-L) were prepared and their chemical structure, substitution degree, molecular weight, conversion rate, particle size and zeta potential were characterized by ATR-FTIR, 1HNMR, quantitative 13CNMR, HP-SEC, HPLC and zeta-sizer nanometer analyzer, respectively. Furthermore, the effects of substitution degree on film surface roughness and homogeneity, water vapor permeability (WVP) and thermal stability were evaluated by AFM, SEM, WVP and TGA, respectively. The optimal GGM-L film exhibited 91.3% transmittance and 0.43% haze, 117° water contact angle, 31.2% elongation at break and 30.9 MPa ultimate tensile stress. The bio-based content of the GGM-L may reach about 99 wt%, which provides a promising avenue for polyolefin-based latex replacement for paper and paperboard applications.

Water-soluble polysaccharides promoting production of redispersible nanocellulose.

To date, the energy-intensive production and high-water content severely limits nanocellulose applications on a large scale off-site. In this study, adding water-soluble polysaccharides (PS) to achieve an integrated process of water-redispersible nanocellulose production was well established. The addition of PS, in particular carboxymethylated-galactoglucomannan (cm-GGM), facilitates fibre fibrillation enabling homogenization at a higher solid content at 1.5 wt% compared with around 0.4 wt% for neat fibre. More importantly, the addition of cm-GGM saved 73 % energy in comparison without PS addition. Good water redispersibility of thus-prepared nanocellulose was validated in viewpoints of size distribution, morphology, viscosity and film properties as compared with neat nanocellulose. The tensile strength and optical transmittance of nanocellulose films increased to 116 MPa and 77 % compared to those without PS addition of 62 MPa and 74 %, respectively. Collectively, this study provides a new avenue for large-volume production of redispersible nanocellulose at a high solid content with less energy-consumption.

Influence of mineral coatings on fibroblast behaviour: The importance of coating formulation and experimental design.

Mineral coatings manipulate surface properties such as roughness, porosity, wettability and surface energy. Properties that are known to determine cell behaviour. Therefore, mineral coatings can potentially be used to manipulate cell fate. This paper studies mineral-cell interactions through coatings in a stacked cell culture platform. Minerals were chosen according to their influence on Human Dermal Fibroblasts (HDFs): calcium carbonate, calcium sulphates, and kaolin. Mineral coatings were formulated with the additives latex, sorbitol, polyvinyl alcohol (PVOH) and TEMPO-oxidised cellulose nanofibrils (CNF-T). The coatings were placed as a bottom or top of the device, for a direct or indirect interaction with HDFs, respectively. Cells were seeded, in various densities, to the bottom of the device; and cell density and confluency were monitored in time. Overall, results show that the coating interaction is influenced at first by the cell seeding density. Scarce cell seeding density limits adaptability to the new environment, while an abundant one encourages confluency in time. In between those densities, coating formulation plays the next major role. Calcium carbonate promoted HDFs growth the most as expected, but the response to the rest of minerals depended on the coating additive. CNF-T encouraged proliferation even for kaolin, a mineral with long-term toxicity to HDFs, while PVOH induced a detrimental effect on HDF growth regardless of the mineral. At last, the placement of the coated layer provided insights on the contact-dependency of each response. This study highlights the importance of the experimental design, including coating formulation, when investigating cellular response to biomaterials.

Cellulose nanofibril/carbon nanotube composite foam-stabilized paraffin phase change material for thermal energy storage and conversion.

The leakage and low thermal conductivity of paraffin phase change material (PCM) must be addressed to achieve a more efficient energy storage process. In this study, cellulose nanofibril (CNF) foams were prepared as the porous support of paraffin to prevent its leakage, and multiwalled carbon nanotubes (CNTs) were incorporated in the foams to improve heat transfer performance. Treatment of CNF with methyltrimethoxysilane improved compatibility between the foams and paraffin. The prepared highly porous (porosity >96%) foams had paraffin absorption capacities exceeding 90%. The form-stable PCM composites displayed negligible paraffin leakage and had a compact structure. The prepared PCM composites had enhanced heat transfer performance, reasonable phase change properties and thermal stabilities. The enthalpy of the SCNF/CNT50-Pw PCM composite decreased by 6% after 100 melting/freezing cycles. Compared with pristine paraffin, the PCM composites exhibited superior form-stabilities and improved thermal properties, which suggested application in a solar-thermal-electricity energy harvesting and conversion system.

Use of cellulose nanofibril (CNF)/silver nanoparticles (AgNPs) composite in salt hydrate phase change material for efficient thermal energy storage.

Salt hydrate phase change materials (PCMs) possess the challenge of supercooling, which must be addressed to allow more efficient energy storage and utilisation. In this work, cellulose nanofibril (CNF), a versatile biopolymer was used to support and disperse silver nanoparticles (AgNPs), and the synthesised CNF/AgNPs composite was used to improve the performance of sodium acetate trihydrate (SAT). Results showed that CNF dispersed the AgNPs uniformly and prevented their aggregation. Through the synergistic effect of 1% CNF/AgNPs and 2% sodium phosphate dibasic dodecahydrate, a low supercooling degree of 1.2 °C was achieved. Moreover, AgNPs were uniformly distributed in the prepared PCM composite. Differential scanning calorimetry results indicated that the prepared PCM@CNF/AgNPs 0.02 composite showed a similar melting point (57.4 °C) and enthalpy (269 kJ/kg), compared to those of pure SAT. Thermogravimetric analysis showed that the PCM composite did not lose all moisture until a heating temperature of 160 °C, showing improved thermal stability. The thermal conductivity of PCM@CNF/AgNPs 0.02 composite was 31.6% higher than that of SAT. The enthalpy of this composite decreased only around 2% after 100 melting/freezing cycles, showing satisfying thermal reliability. This composite can therefore be used to fabricate high-performance TES systems with negligible supercooling and improved thermal properties.

Influence of Substrate in Roll-to-roll Coated Nanographite Electrodes for Metal-free Supercapacitors.

Due to the high electric conductivity and large surface area of nanographites, such as graphene and graphite nanoplatlets, these materials have gained a large interest for use in energy storage devices. However, due to the thin flake geometry, the viscosity of aqueous suspensions containing these materials is high even at low solids contents. This together with the use of high viscosity bio-based binders makes it challenging to coat in a roll-to-roll process with sufficient coating thickness. Electrode materials for commercial energy storage devices are often suspended by organic solvents at high solids contents and coated onto metal foils used as current-collectors. Another interesting approach is to coat the electrode onto the separator, to enable large-scale production of flat cell stacks. Here, we demonstrate an alternative, water-based approach that utilize slot-die coating to coat aqueous nanographite suspension with nanocellulose binder onto the paper separator, and onto the current collector as reference, in aqueous metal-free supercapacitors. The results show that the difference in device equivalent series resistance (ESR) due to interfacial resistance between electrode and current collector was much lower than expected and thus similar or lower compared to other studies with a aqueous supercapacitors. This indicates that electrode coated paper separator substrates could be a promising approach and a possible route for manufacturing of low-cost, environmentally friendly and metal-free energy storage devices.

Stencil Printing-A Novel Manufacturing Platform for Orodispersible Discs.

Stencil printing is a commonly used printing method, but it has not previously been used for production of pharmaceuticals. The aim of this study was to explore whether stencil printing of drug containing polymer inks could be used to manufacture flexible dosage forms with acceptable mass and content uniformity. Formulation development was supported by physicochemical characterization of the inks and final dosage forms. The printing of haloperidol (HAL) discs was performed using a prototype stencil printer. Ink development comprised of investigations of ink rheology in combination with printability assessment. The results show that stencil printing can be used to manufacture HAL doses in the therapeutic treatment range for 6-17 year-old children. The therapeutic HAL dose was achieved for the discs consisting of 16% of hydroxypropyl methylcellulose (HPMC) and 1% of lactic acid (LA). The formulation pH remained above pH 4 and the results imply that the drug was amorphous. Linear dose escalation was achieved by an increase in aperture area of the print pattern, while keeping the stencil thickness fixed. Disintegration times of the orodispersible discs printed with 250 and 500 µm thick stencils were below 30 s. In conclusion, stencil printing shows potential as a manufacturing method of pharmaceuticals.

Fabrication of All-Solid Organic Electrochromic Devices on Absorptive Paper Substrates Utilizing a Simplified Lateral Architecture.

Poly(3,4-ethylenedioxythiophene) doped with the polymer anion poly(styrenesulfonate), PEDOT:PSS, is a common electrochromic material used in the preparation of electrochromic devices (ECDs). In this paper, the PEDOT:PSS doped with a solvent was used both as the electrode and the electrochromic functional layer for fabrication of ECDs on absorptive paper surfaces. The doped PEDOT:PSS dispersion was assessed for the film-forming evenness, sheet resistance and conductivity, and the performance of prepared ECDs for their color contrast and switching dynamics. The ECD performance is discussed in relation to the absorptive characteristics of the substrates. The results indicate that it is feasible to prepare ECDs onto absorptive substrates, despite the partial polymer material imbibition into them. The extent of polymer absorption influences the ECD performance: an increased absorption reduces the color contrast but speeds up the color switching. The electrochemical properties of the used solid electrolyte were found to be crucial for functioning of the ECDs. Insufficient ion transport and associated high resistance led to failure of the devices.

Stacking up: a new approach for cell culture studies.

Traditional cell culture relies mostly on flat plastic surfaces, such as Petri dishes and multiwell plates. These commercial surfaces provide limited flexibility for experimental design. In contrast, cell biology increasingly demands surface customisation, functionalisation, and cell monitoring in order to obtain data that is relevant in vivo. The development of research areas such as microfluidics and electrochemical detection methods greatly promoted the customised design of cell culture platforms. However, the challenges for mass production and material limitations prevent their widespread usage and commercialisation. This article presents a new cell culture platform based on stacks of a transparent flexible printable substrate. The arrangement introduces multi-layered stacks for possible manipulation and access to the cells. The platform is highly compatible with current technologies, such as colorimetric imaging and fluorescence microscopy. In addition, it can potentially integrate, e.g., biomaterials, patterning, microfluidics, electrochemical detection and other techniques to influence, monitor, and assess cell behaviour in a multitude of different settings. More importantly, the platform is a low-cost alternative customisable through functional printing and coating technologies. The device shown in this manuscript represents a prototype for more sophisticated variations that will expand the relevance of in vitro studies in cell biology.

Continuous Processing of Nanocellulose and Polylactic Acid into Multilayer Barrier Coatings.

Recent years have seen an increased interest toward utilizing biobased and biodegradable materials for barrier packaging applications. Most of the abovementioned materials usually have certain shortcomings that discourage their adoption as a preferred material of choice. Nanocellulose falls into such a category. It has excellent barrier against grease, mineral oils, and oxygen but poor tolerance against water vapor, which makes it unsuitable to be used at high humidity. In addition, nanocellulose suspensions' high viscosity and yield stress already at low solid content and poor adhesion to substrates create additional challenges for high-speed processing. Polylactic acid (PLA) is another potential candidate that has reasonably high tolerance against water vapor but rather a poor barrier against oxygen. The current work explores the possibility of combining both these materials into thin multilayer coatings onto a paperboard. A custom-built slot-die was used to coat either microfibrillated cellulose or cellulose nanocrystals onto a pigment-coated baseboard in a continuous process. These were subsequently coated with PLA using a pilot-scale extrusion coater. Low-density polyethylene was used as for reference extrusion coating. Cationic starch precoating and corona treatment improved the adhesion at nanocellulose/baseboard and nanocellulose/PLA interfaces, respectively. The water vapor transmission rate for nanocellulose + PLA coatings remained lower than that of the control PLA coating, even at a high relative humidity of 90% (38 °C). The multilayer coating had 98% lower oxygen transmission rate compared to just the PLA-coated baseboard, and the heptane vapor transmission rate reduced by 99% in comparison to the baseboard. The grease barrier for nanocellulose + PLA coatings increased 5-fold compared to nanocellulose alone and 2-fold compared to PLA alone. This approach of processing nanocellulose and PLA into multiple layers utilizing slot-die and extrusion coating in tandem has the potential to produce a barrier packaging paper that is both 100% biobased and biodegradable.

Human dermal fibroblast proliferation controlled by surface roughness of two-component nanostructured latex polymer coatings.

In this study hierarchically-structured latex polymer coatings and self-supporting films were characterised and their suitability for cell growth studies was tested with Human Dermal Fibroblasts (HDF). Latex can be coated or printed on rigid or flexible substrates thus enabling high-throughput fabrication. Here, coverslip glass substrates were coated with blends of two different aqueous latex dispersions: hydrophobic polystyrene (PS) and hydrophilic carboxylated acrylonitrile butadiene styrene (ABS). The nanostructured morphology and topography of the latex films was controlled by varying the mixing ratio of the components in the latex blend. Thin latex-coatings retain high transparency on glass allowing optical and high resolution imaging of cell growth and morphology. Compared to coverslip glass surfaces and commercial well-plates HDF cell growth was enhanced up to 150-250 % on latex surfaces with specific nanostructure. Growth rates were correlated with selected roughness parameters such as effective surface area (Sq), RMS-roughness (Sdr) and correlation length (Scl37). High-resolution confocal microscopy clearly indicated less actin stress-fibre development in cells on the latex surface compared to coverslip glass. The results show that surface nanotopography can, by itself, passively modulate HDF cell proliferation and cytoskeletal architecture.

The influence of mineral particles on fibroblast behaviour: A comparative study.

Minerals are versatile tools utilised to modify and control the physical-chemical and functional properties of substrates. Those properties include ones directing cell fate; thus, minerals can potentially provide a direct and inexpensive method to manipulate cell behaviour. This paper shows how different minerals influence human dermal fibroblast behaviour depending on their properties. Different calcium carbonates, calcium sulphates, silica, silicates, and titanium dioxide were characterised using TEM, ATR-FTIR, and zeta potential measurements. Mineral-cell interactions were analysed through MTT assay, LDH assay, calcein AM staining, live cell imaging, immunofluorescence staining, western blot, and extra/intracellular calcium measurements. Results show that the interaction of the fibroblasts with the minerals was governed by a shared period of adaptation, followed by increased proliferation, growth inhibition, or increased toxicity. Properties such as size, ion release and chemical composition had a direct influence on the cells leading to cell agglomeration, morphological changes, and the possible formation of protein-mineral complexes. In addition, zeta potential and FTIR measurements of the minerals showed adsorption of the cell culture media onto the particles. This article provides fundamental insight into the mineral-fibroblast interactions, and makes it possible to arrange the minerals according to the time-dependent cellular response.