Plant cell wall porosity regulates a number of critical functions in plants, and improved structural and molecular insights are key to understanding factors that influence porosity. Yet, measuring porosity of cell walls in the wet state is not straightforward. Here, simplified hollow core-shell structures were developed with shells composed of cellulose nanofibers (CNFs) and pectin, inspired by the composition of the plant primary cell wall. These structures were examined to evaluate the influence of salinity (sodium chloride) on shell porosity via the permeation of FITC-dextran molecules. Additionally, small angle X-ray scattering, dynamic vapor sorption and electron microscopy imaging were exploited to improve mechanistic understanding. Combined, these techniques covered the sub-nm to micron length scales, and the collective experimental results implicated that sodium chloride only mediates a small increase in pore diameter. The observed increase in FITC-dextran permeability is thus rather due to changes to charge-pairing interactions between the oppositely charged CNF and pectin, and pectin mobility. The approach developed provides a platform on which to enable other plant wall polysaccharides and external stress factors to be systematically investigated.

Fossil-based polymers dominate the packaging industry thanks to their performance and low cost. However, their negative impact on the biosphere demands a paradigm shift in the industry. Nature may provide an alternative in the form of suberin. Suberin is an amorphous polyester present in plants, where it contributes to controlling the water and gas exchange with the environment. The bark is rich in suberin, and it represents a large byproduct of the forestry industry; hence, it is a potential source of renewable monomers for the synthesis of packaging materials. In this study, we demonstrated that unrefined suberin monomers, extracted from birch bark, could be exploited to synthesize a cross-linked polyester film through a standard melt polycondensation and compression molding process. The polyester film resulted in being translucent while blocking UV radiation and having an elastomer-like behavior. The average measured water vapor transmission rate of 2660 g mu m day-1 m-2 was comparable to other polyesters, such as polylactide (1500-2000 g mu m day-1 m-2) and polycaprolactone (2653 g mu m day-1 m-2) at 23 +/- 2 degrees C, with an imposed gradient of 0-50% relative humidity. Finally, the thermal gravimetric analysis showed the absence of any unreacted suberin monomers, and although specific migration tests are required, these suberin-reconstructed polyester films are potential candidates for packaging applications.

Water-soluble polymers are materials rapidly growing in volume and in number of materials and applications. Examples include synthetic plastics such as polyacrylamide, polyacrylic acid, polyethylene glycol, polyethylene oxide and polyvinyl alcohol, with applications ranging from cosmetics and paints to water purification, pharmaceutics and food packaging. Despite their abundance, their environmental concerns (e.g., bioaccumulation, toxicity, and persistence) are still not sufficiently assessed, especially since water soluble plastics are often not biodegradable, due to their chemical structure. This review aims to overview the most important water-soluble and biodegradable polymers, their applications, and their environmental impact. Degradation products from water-insoluble polymers designed for biodegradation can also be water soluble. Most water-soluble plastics are not immediately harmful for humans and the environment, but the degradation products are sometimes more hazardous, e.g. for polyacrylamide. An increased use of water-soluble plastics could also introduce unanticipated environmental hazards. Therefore, excessive use of water-soluble plastics in applications where they can enter the environment should be discouraged. Often the plastics can be omitted or replaced by natural polymers with lower risks. It is recommended to include non-biodegradable water-soluble plastics in regulations for microplastics, to make risk assessments for different water-soluble plastics and to develop labels for flushable materials.

Plant cells represent smart cargo carriers with great socioeconomic potential in oral drug delivery applications. The two exterior barriers, featuring a rigid cell wall and a dense plasma membrane, are unique with complementary structural, mechanical, and chemical properties. Current strategies for producing therapeutic drugs within plant cells for oral delivery are efficient, but largely limited to recombinant pharmaceutical proteins, and involve complex genetic modification of plants. To address this, we engineer plant cell–inspired delivery systems with cellulose nanofiber–based shells and lipid layers through a bottom-up assembly strategy, which offers greater flexibility to encapsulate nonprotein compounds and nanoparticles. Notably, the layered shell structure resists degradation in acidic environments, and two barriers respond differently to external stimuli in simulated gastrointestinal medium, resulting in size-dependent dual-triggered release mechanisms. The cytocompatibility was shown by incubation with Caco-2 cells. Our results open avenues for developing next generation of bioinspired oral delivery systems for multisite-specific gastrointestinal release in a low-cost and sustainable manner.

In nature, colors can originate from pigments or structural effects, with the latter producing brilliant hues through the interference of light with nanoscale structures. This study describes a feasible strategy to achieve structurally colored films based on acetylated lignin nanoparticles. Lignin nanoparticles were prepared by using membrane emulsification and subsequently self-assembled into multilayered films on silicon substrates through an evaporative process. These films exhibit vivid structural colors resulting from thin-film interference, with hues that vary with film thickness. Spectroscopic reflectance measurements and structural analysis reveal a wide range of colors spanning across the visible spectrum. The observed colors are ascribed to interference effects and could be modeled using the transfer matrix method. Furthermore, we demonstrate that increasing relative humidity causes clear color shifts associated with reflectance peak position changes.

The amount of disposable nonwovens used today for different purposes have an impact on the plastic waste streams which is built up from several single-use products. A particular problem comes from nonwoven products with “hidden” plastic (such as cellulose mixed with synthetic fibers and/or plastic binders) where the consumers cannot see or expect plastic. We have here developed a sustainable binder based on natural components; wheat gluten (WG) and a polyelectrolyte complex (PEC) made from chitosan, carboxymethyl cellulose and citric acid which can be used with cellulosic fibers, creating a fully biobased nonwoven product. The binder formed a stable dispersion that improved the mechanical properties of a model nonwoven. With WG added, both the dry and the wet strength of the impregnated nonwoven increased. In dry-state, PEC increased the tensile index with >30 % (from 22.5 to 30 Nm/g), and with WG, with 60 % (to 36 Nm/g). The corresponding increase in the wet strength was 250 % (from 8 to 28 Nm/g) and 300 % (to 32 Nm/g). The increased strength was explained as an enrichment of covalent bonds (ester and amide bonds) established during curing at 170 °C, confirmed by DNP NMR and infrared spectroscopy.

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.

Petrochemical-based plastics are prevalent in the packaging industry. However, given their detrimental impact on the environment, alternatives for future packaging materials are necessary. In this work, the inspiration for creating new types of packaging materials was taken from plant cuticle structures in nature. Potential eco-friendly solutions could be derived from plants. We fabricated cuticle-like materials using molecules found in natural cutins. A cross-linked material was developed through the melt polycondensation of hexadecanedioic acid and glycerol and with the addition of hydroxy-hexadecanoic acid, a noncross-linked terpolyester was obtained. Both compression molding and casting techniques resulted in flexible and transparent/translucent films. Both polyester films showed very low direct UV transmittance, but noticeable total UV transmittance. These semicrystalline materials exhibited water vapor transmission rates that were comparable or superior to other polyesters, such as polylactide and polycaprolactone. An intriguing characteristic was the rough surface exhibited by the copolyester following compression molding, which closely resembled the wax layer structure seen in many natural peels.

The majority of plastics used today are produced from nonrenewable resources, and, depending on the end-of-life management, they may end up in landfills or in nature, giving rise to microplastic pollution. A potential way of minimizing this is to use proteins, preferentially recovered from organic waste and residues, to make plastics. In line with this, we explored here the potential of protein-based bioplastics sourced from single-cell protein (SCP). Films of glycerol-plasticized SCPs (grown by recovering carbon from cheese whey and nitrogen from anaerobic digestate) were produced by compression molding. Electron microscopy revealed a structure of intact cells and the presence of cracks/voids, and the mechanical properties indicated a rather poor cohesion between the cells, despite the high-temperature treatment in the pressing stage. The resulting structure yielded a material that could absorb a sizable amount of both nonpolar (rapid capillary uptake) and polar liquids. The anaerobic biodegradation of the SCP films demonstrated that full biodegradability (100%) and high specific biomethane productions (471 ± 8 mL/gram of volatile solids) could be attained within operating conditions that are typical of anaerobic digestion processes in the treatment of food waste. Overall, this study highlights the potential and also the challenge of using SCP as an alternative bioplastic material in food packaging and edible coatings.