Biobased Nanomaterials─The Role of Interfacial Interactions for Advanced Materials.

This review presents recent advances regarding biomass-based nanomaterials, focusing on their surface interactions. Plant biomass-based nanoparticles, like nanocellulose and lignin from industry side streams, hold great potential for the development of lightweight, functional, biodegradable, or recyclable material solutions for a sustainable circular bioeconomy. However, to obtain optimal properties of the nanoparticles and materials made thereof, it is crucial to control the interactions both during particle production and in applications. Herein we focus on the current understanding of these interactions. Solvent interactions during particle formation and production, as well as interactions with water, polymers, cells and other components in applications, are addressed. We concentrate on cellulose and lignin nanomaterials and their combination. We demonstrate how the surface chemistry of the nanomaterials affects these interactions and how excellent performance is only achieved when the interactions are controlled. We furthermore introduce suitable methods for probing interactions with nanomaterials, describe their advantages and challenges, and introduce some less commonly used methods and discuss their possible applications to gain a deeper understanding of the interfacial chemistry of biobased nanomaterials. Finally, some gaps in current understanding and interesting emerging research lines are identified.

Affinity of Keratin Peptides for Cellulose and Lignin: A Fundamental Study toward Advanced Bio-Based Materials.

Keratin is a potential raw material to meet the growing demand for bio-based materials with special properties. Keratin can be obtained from feathers, a by-product from the poultry industry. One approach for keratin valorization is to use the protein to improve the properties of already existing cellulose and lignin-based materials to meet the requirements for replacing fossil-based plastics. To ensure a successful combination of keratin with lignocellulosic building blocks, keratin must have an affinity to these substrates. Hence, we used quartz crystal microbalance with a dissipation monitoring (QCM-D) technique to get a detailed understanding of the adsorption of keratin peptides onto lignocellulosic substrates and how the morphology of the substrate, pH, ionic strength, and keratin properties affected the adsorption. Keratin was fractionated from feathers with a scalable and environmentally friendly deep eutectic solvent process. The keratin fraction used in the adsorption studies consisted of different sized keratin peptides (about 1-4 kDa), which had adopted a random coil conformation as observed by circular dichroism (CD). Measuring keratin adsorption to different lignocellulosic substrates by QCM-D revealed a significant affinity of keratin peptides for lignin, both as smooth films and in the form of nanoparticles but only a weak interaction between cellulose and keratin. Systematic evaluation of the effect of surface, media, and protein properties enabled us to obtain a deeper understanding of the driving force for adsorption. Both the structure and size of the keratin peptides appeared to play an important role in its adsorption. The keratin-lignin combination is an attractive option for advanced material applications. For improved adsorption on cellulose, modifications of either keratin or cellulose would be required.

Microalgae Chlorella vulgaris and kraft lignin stabilized cellulosic wet foams for camouflage.

Plants, animals, and humans use camouflage to blend in with their surroundings. The camouflage is achieved with different combinations of colors, patterns, and morphologies. In stealth applications, the simplest camouflage uses textiles colored similarly to the environment to create an illusion. However, often, visible light range camouflage is not enough since the multispectral detection technologies of today are readily utilized for identification. Foams can be created with a straightforward fabricating process, and lightweight material exhibits good thermal insulation properties, providing stealth in the infrared light region. Herein, we produce cellulosic wet foams from surfactant and bleached pulp or cellulose nanofibrils. The visible light camouflage is created with green microalgae, Chlorella vulgaris, and brown kraft lignin, which also stabilized the foams. The thermal and spectral camouflage performance of foams was influenced by the cellulose content as well as the stability and water content of foams. Overall, these results give insight into how stability impacts the thermal and spectral properties of wet foams and provide a solid base for further material development to improve camouflage performance. While there is plenty of data on dry foams, the functional behavior of wet foams is currently not well known. Our method, using plant-based components can be exploited in a variety of other applications where simplicity and scalability are important.

Well-Defined Lignin Model Films from Colloidal Lignin Particles.

The transformation of a molecularly complex and irregularly shaped lignin into a nanoscale spherical architecture is anticipated to play a pivotal role in the promotion of lignin valorization. From the standpoint of using colloidal lignin particles (CLPs) as building blocks for a diverse range of applications, it has become essential to study their interactions with soluble compounds of varied origin. However, the lack of model films with well-defined surface properties similar to those of CLPs has hindered fundamental studies using surface-sensitive techniques. Here, we report well-defined and stable thin films prepared from CLPs and demonstrate their suitability for investigation of surface phenomena. Direct adsorption on substrates coated with a cationic anchoring polymer resulted in uniform distribution of CLPs as shown with atomic force microscopy (AFM). Quartz crystal microbalance with dissipation monitoring (QCM-D) experiments revealed higher adsorbed mass of cationic lignin onto the CLP-coated substrate in comparison to the film prepared from dissolved lignin, suggesting preferential adsorption via the carboxylic acid enriched surfaces of CLPs. QCM-D further enabled detection of small changes such as particle swelling or partial dissolution not detectable via bulk methods such as light scattering. The CLP thin films remained stable until pH 8 and displayed only a low degree of swelling. Increasing the pH to 10 led to some instability, but their spherical geometry remained intact until complete dissolution was observed at pH 12. Particles prepared from aqueous acetone or aqueous tetrahydrofuran solution followed similar trends regarding adsorption, pH stability, and wetting, although the particle size affected the magnitude of adsorption. Overall, our results present a practical way to prepare well-defined CLP thin films that will be useful not only for fundamental studies but also as a platform for testing stability and interactions of lignin nanoparticles with materials of technical and biomedical relevance.

Three-Dimensional Printed Cell Culture Model Based on Spherical Colloidal Lignin Particles and Cellulose Nanofibril-Alginate Hydrogel.

Three-dimensional (3D) printing has been an emerging technique to fabricate precise scaffolds for biomedical applications. Cellulose nanofibril (CNF) hydrogels have attracted considerable attention as a material for 3D printing because of their shear-thinning properties. Combining cellulose nanofibril hydrogels with alginate is an effective method to enable cross-linking of the printed scaffolds in the presence of Ca2+ ions. In this work, spherical colloidal lignin particles (CLPs, also known as spherical lignin nanoparticles) were used to prepare CNF-alginate-CLP nanocomposite scaffolds. High-resolution images obtained by atomic force microscopy (AFM) showed that CLPs were homogeneously mixed with the CNF hydrogel. CLPs brought antioxidant properties to the CNF-alginate-CLP scaffolds in a concentration-dependent manner and increased the viscosity of the hydrogels at a low shear rate, which correspondingly provide better shape fidelity and printing resolution to the scaffolds. Interestingly, the CLPs did not affect the viscosity at high shear rates, showing that the shear thinning behavior typical for CNF hydrogels was retained, enabling easy printing. The CNF-alginate-CLP scaffolds demonstrated shape stability after printing, cross-linking, and storage in Dulbecco's phosphate buffer solution (DPBS +) containing Ca2+ and Mg2+ ions, up to 7 days. The 3D-printed scaffolds showed relative rehydration ratio values above 80% after freeze-drying, demonstrating a high water-retaining capability. Cell viability tests using hepatocellular carcinoma cell line HepG2 showed no negative effect of CLPs on cell proliferation. Fluorescence microscopy indicated that HepG2 cells grew not only on the surfaces but also inside the porous scaffolds. Overall, our results demonstrate that nanocomposite CNF-alginate-CLP scaffolds have high potential in soft-tissue engineering and regenerative-medicine applications.

Preparation and Characterization of Dentin Phosphophoryn-Derived Peptide-Functionalized Lignin Nanoparticles for Enhanced Cellular Uptake.

The surface modification of nanoparticles (NPs) using different ligands is a common strategy to increase NP-cell interactions. Here, dentin phosphophoryn-derived peptide (DSS) lignin nanoparticles (LNPs) are prepared and characterized, the cellular internalization of the DSS-functionalized LNPs (LNPs-DSS) into three different cancer cell lines is evaluated, and their efficacy with the widely used iRGD peptide is compared. It is shown that controlled extent of carboxylation of lignin improves the stability at physiological conditions of LNPs formed upon solvent exchange. Functionalization with DSS and iRGD peptides maintains the spherical morphology and moderate polydispersity of LNPs. The LNPs exhibit good cytocompatibility when cultured with PC3-MM2, MDA-MB-231, and A549 in the conventional 2D model and in the 3D cell spheroid morphology. Importantly, the 3D cell models reveal augmented internalization of peptide-functionalized LNPs and improve antiproliferative effects when the LNPs are loaded with a cytotoxic compound. Overall, LNPs-DSS show equal or even superior cellular internalization than the LNPs-iRGD, suggesting that DSS can also be used to enhance the cellular uptake of NPs into different types of cells, and release different cargos intracellularly.

Strong, Ductile, and Waterproof Cellulose Nanofibril Composite Films with Colloidal Lignin Particles.

Brittleness has hindered commercialization of cellulose nanofibril (CNF) films. The use of synthetic polymers and plasticizers is a known detour that impairs biodegradability and carbon footprint of the product. Herein, we utilize a variety of softwood Kraft lignin morphologies to obtain strong and ductile CNF nanocomposite films. An optimum 10 wt % content of colloidal lignin particles (CLPs) produced films with nearly double the toughness compared to a CNF film without lignin. CLPs rendered the films waterproof, provided antioxidant activity and UV-shielding with better visible light transmittance than obtained with irregular lignin aggregates. We conclude based on electron microscopy, dynamic water sorption analysis, and tp-DSC that homogeneously distributed CLPs act as ball bearing lubricating and stress transferring agents in the CNF matrix. Overall, our results open new avenues for the utilization of lignin nanoparticles in biopolymer composites equipped with versatile functionalities for applications in food packaging, water purification, and biomedicine.

Aggregation response of triglyceride hydrolysis products in cyclohexane and triolein.

Here, we examine the aggregation response of a series of triglyceride-based biosurfactants in cyclohexane and triglyceride solvents via all-atom molecular dynamics simulations and supporting experiments. The surfactant aggregation follows in all systems, with only minor deviations, a multiple equilibrium, i.e. open association, model. Monoglyceride aggregation in cyclohexane exhibits a critical micellization concentration, cmc, showing a cmc can exist even in a system following open association. However, the cmc is associated with a change in balance with oligomeric and larger aggregates in the solution, not an onset of aggregate formation. It is demonstrated that reverse micelles can form in the absence of water stabilized by intersurfactant hydrogen bonds alone, and that the polarity and hydrogen bonding capability of triolein systematically reduces surfactant aggregation in comparison to cyclohexane. A comparison between CHARMM27 and CHARMM36 simulation models reveals that while trends are preserved, the models differ in quantitative prediction. Finally, consolidation of the general aggregation response trends predicted by the modelling are obtained via 7,7,8,8-tetracyanoquinodimethane dye (TCNQ) solubilization experiments on the corresponding model plant oil systems. The findings provide guidelines for predicting and controlling surfactant aggregation response in organic solvents via tuning the solvent polarity and hydrogen bonding ability, and a critical assessment of simulation and aggregation models for surfactant systems in organic solvents.

Emulsion Stabilization with Functionalized Cellulose Nanoparticles Fabricated Using Deep Eutectic Solvents.

In this experiment, the influence of the morphology and surface characteristics of cellulosic nanoparticles (i.e., cellulose nanocrystals [CNCs] and cellulose nanofibers [CNFs]) on oil-in-water (o/w) emulsion stabilization was studied using non-modified or functionalized nanoparticles obtained following deep eutectic solvent (DES) pre-treatments. The effect of the oil-to-water ratio (5, 10, and 20 wt.-% (weight percent) of oil), the type of nanoparticle, and the concentration of the particles (0.05⁻0.2 wt.-%) on the oil-droplet size (using laser diffractometry), o/w emulsion stability (via analytical centrifugation), and stabilization mechanisms (using field emission scanning electron microscopy with the model compound-i.e., polymerized styrene in water emulsions) were examined. All the cellulosic nanoparticles studied decreased the oil droplet size in emulsion (sizes varied from 22.5 µm to 8.9 µm, depending on the nanoparticle used). Efficient o/w emulsion stabilization against coalescence and an oil droplet-stabilizing web-like structure were obtained only, however, with surface-functionalized CNFs, which had a moderate hydrophilicity level. CNFs without surface functionalization did not prevent either the coalescence or the creaming of emulsions, probably due to the natural hydrophobicity of the nanoparticles and their instability in water. Moderately hydrophilic CNCs, on the other hand, distributed evenly and displayed good interaction with both dispersion phases. The rigid structure of CNCs meant, however, that voluminous web structures were not formed on the surface of oil droplets; they formed in flat, uniform layers instead. Consequently, emulsion stability was lower with CNCs, when compared with surface-functionalized CNFs. Tunable cellulose nanoparticles can be used in several applications such as in enhanced marine oil response.

Adsorption of Proteins on Colloidal Lignin Particles for Advanced Biomaterials.

Coating of colloidal lignin particles (CLPs), or lignin nanoparticles (LNPs), with proteins was evaluated in order to establish a safe, self-assembly mediated modification technique to tune their surface chemistry. Gelatin and poly- l-lysine formed the most pronounced protein corona on the CLP surface, as determined by dynamic light scattering (DLS) and zeta potential measurements. Spherical morphology of individual protein coated CLPs was confirmed by transmission electron (TEM) and atomic force (AFM) microscopy. A mechanistic adsorption study with several random coiled and globular model proteins was carried out using quartz crystal microbalance with dissipation monitoring (QCM-D). The three-dimensional (3D) protein fold structure and certain amino acid interactions were decisive for the protein adsorption on the lignin surface. The main driving forces for protein adsorption were electrostatic, hydrophobic, and van der Waals interactions, and hydrogen bonding. The relative contributions of these interactions were highly dependent on the ionic strength of the surrounding medium. Capillary electrophoresis (CE) and Fourier transform infrared spectroscopy (FTIR) provided further evidence of the adsorption-enhancing role of specific amino acid residues such as serine and proline. These results have high impact on the utilization of lignin as colloidal particles in biomedicine and biodegradable materials, as the protein corona enables tailoring of the CLP surface chemistry for intended applications.

Correlation between cellulose thin film supramolecular structures and interactions with water.

Water interactions of ultra-thin films of wood-derived polysaccharides were investigated by using surface sensitive methods, Quartz Crystal Microbalance with Dissipation (QCM-D) and Atomic Force Microscopy (AFM). These approaches allow systematic molecular level detection and reveal information on the inherent behaviour of biobased materials with nanosensitivity. The influence of structural features of cellulose films i.e. crystallinity, surface roughness and porosity on water interactions was clarified. Cellulose films were prepared using spin-coating and Langmuir-Schaefer deposition to obtain thin films of equal thickness, identical cellulose origin, simultaneously with different supramolecular structures. The uptake/release of water molecules and swelling were characterized using QCM-D, and the structural features of the films were evaluated by AFM. More crystalline cellulose film possessed nanoporosity and as a consequence higher accessible surface area (more binding sites for water) and thus, it was capable of binding more water molecules in humid air and when immersed in water when compared to amorphous cellulose film. Due to the ordered structure, more crystalline cellulose film remained rigid and elastic although the water binding ability was more pronounced compared to amorphous film. The lower amount of bound water induced softening of the amorphous cellulose film and the elastic layer became viscoelastic at high humidity. Finally, cellulose thin films were modified by adsorbing a layer of 1-butyloxy-2-hydroxypropyl xylan, and the effect on moisture uptake was investigated. It was found that the supramolecular structure of the cellulose substrate has an effect not only on the adsorbed amount of xylan derivative but also on the water interactions of the material.

Supracolloidal multivalent interactions and wrapping of dendronized glycopolymers on native cellulose nanocrystals.

Cellulose nanocrystals (CNCs) are high aspect ratio colloidal rods with nanoscale dimensions, attracting considerable interest recently due to their high mechanical properties, chirality, sustainability, and availability. In order to exploit them for advanced functions in new materials, novel supracolloidal concepts are needed to manipulate their self-assemblies. We report on exploring multivalent interactions to CNC surface and show that dendronized polymers (DenPols) with maltose-based sugar groups on the periphery of lysine dendrons and poly(ethylene-alt-maleimide) polymer backbone interact with CNCs. The interactions can be manipulated by the dendron generation suggesting multivalent interactions. The complexation of the third generation DenPol (G3) with CNCs allows aqueous colloidal stability and shows wrapping around CNCs, as directly visualized by cryo high-resolution transmission electron microscopy and electron tomography. More generally, as the dimensions of G3 are in the colloidal range due to their ~6 nm lateral size and mesoscale length, the concept also suggests supracolloidal multivalent interactions between other colloidal objects mediated by sugar-functionalized dendrons giving rise to novel colloidal level assemblies.

A cartilage-inspired lubrication system.

Articular cartilage is an example of a highly efficacious water-based, natural lubrication system that is optimized to provide low friction and wear protection at both low and high loads and sliding velocities. One of the secrets of cartilage's superior tribology comes from a unique, multimodal lubrication strategy consisting of both a fluid pressurization mediated lubrication mechanism and a boundary lubrication mechanism supported by surface bound macromolecules. Using a reconstituted network of highly interconnected cellulose fibers and simple modification through the immobilization of polyelectrolytes, we have recreated many of the mechanical and chemical properties of cartilage and the cartilage lubrication system to produce a purely synthetic material system that exhibits some of the same lubrication mechanisms, time dependent friction response, and high wear resistance as natural cartilage tissue. Friction and wear studies demonstrate how the properties of the cellulose fiber network can be used to control and optimize the lubrication and wear resistance of the material surfaces and highlight what key features of cartilage should be duplicated in order to produce a cartilage-mimetic lubrication system.

Chitosan hydrogels enriched with bioactive phloroglucinol for controlled drug diffusion and potential wound healing.

We report a facile strategy to prepare chitosan (CS) hydrogels that eliminates the need for chemical crosslinking for advanced biomedical therapies. This approach gives controlled properties to the hydrogels by incorporating a natural bioactive phenolic compound, phloroglucinol (PG), into their microstructure. The adsorption of PG onto CS chains enhanced the hydrogels' antioxidant activity by up to 25 % and resulted in a denser, more entangled structure, reducing the pore size by 59 µm while maintaining porosity above 94 %. This allowed us to finely adjust pore size and swelling capacity. These structural properties make these hydrogels well-suited for wound healing dressings, promoting fibroblast proliferation and exhibiting excellent hemocompatibility. Furthermore, to ensure the versatility of these hydrogels, herein, we demonstrate their potential as drug delivery systems, particularly for dermal infections. The drug release can be controlled by a combination of drug diffusion through the swollen hydrogel and relaxation of the CS chains. In summary, our hydrogels leverage the synergistic effects of CS's antibacterial and antifungal properties with PG's antimicrobial and anti-inflammatory attributes, positioning them as promising candidates for biomedical and pharmaceutical applications, more specifically in advanced wound healing therapies with local drug delivery.

Insights into spheroids formation in cellulose nanofibrils and Matrigel hydrogels using AFM-based techniques.

The recent FDA decision to eliminate animal testing requirements emphasises the role of cell models, such as spheroids, as regulatory test alternatives for investigations of cellular behaviour, drug responses, and disease modelling. The influence of environment on spheroid formation are incompletely understood, leading to uncertainty in matrix selection for scaffold-based 3D culture. This study uses atomic force microscopy-based techniques to quantify cell adhesion to Matrigel and cellulose nanofibrils (CNF), and cell-cell adhesion forces, and their role in spheroid formation of hepatocellular carcinoma (HepG2) and induced pluripotent stem cells (iPS(IMR90)-4). Results showed different cell behaviour in CNF and Matrigel cultures. Both cell lines formed compact spheroids in CNF but loose cell aggregates in Matrigel. Interestingly, the type of cell adhesion protein, and not the bond strength, appeared to be a key factor in the formation of compact spheroids. The gene expression of E- and N-cadherins, proteins on cell membrane responsible for cell-cell interactions, was increased in CNF culture, leading to formation of compact spheroids while Matrigel culture induced integrin-laminin binding and downregulated E-cadherin expression, resulting in looser cell aggregates. These findings enhance our understanding of cell-biomaterial interactions in 3D cultures and offer insights for improved 3D cell models, culture biomaterials, and applications in drug research.

Bioactive Fiber Foam Films from Cellulose and Willow Bark Extract with Improved Water Tolerance.

Cellulose-based materials are gaining increasing attention in the packaging industry as sustainable packaging material alternatives. Lignocellulosic polymers with high quantities of surface hydroxyls are inherently hydrophilic and hygroscopic, making them moisture-sensitive, which has been retarding the utilization of cellulosic materials in applications requiring high moisture resistance. Herein, we produced lightweight all-cellulose fiber foam films with improved water tolerance. The fiber foams were modified with willow bark extract (WBE) and alkyl ketene dimer (AKD). AKD improved the water stability, while the addition of WBE was found to improve the dry strength of the fiber foam films and bring additional functionalities, that is, antioxidant and ultraviolet protection properties, to the material. Additionally, WBE and AKD showed a synergistic effect in improving the hydrophobicity and water tolerance of the fiber foam films. Nuclear magnetic resonance (NMR) spectroscopy indicated that the interactions among WBE, cellulose, and AKD were physical, with no formation of covalent bonds. The findings of this study broaden the possibilities to utilize cellulose-based materials in high-value active packaging applications, for instance, for pharmaceutical and healthcare products or as water-resistant coatings for textiles, besides bulk packaging materials.

Tuning the water interactions of cellulose nanofibril hydrogels using willow bark extract.

Cellulose nanofibrils (CNFs) are increasingly used as precursors for foams, films and composites, where water interactions are of great importance. In this study, we used willow bark extract (WBE), an underrated natural source of bioactive phenolic compounds, as a plant-based modifier for CNF hydrogels, without compromising their mechanical properties. We found that the introduction of WBE into both native, mechanically fibrillated CNFs and TEMPO-oxidized CNFs increased considerably the storage modulus of the hydrogels and reduced their swelling ratio in water up to 5-7 times. A detailed chemical analysis revealed that WBE is composed of several phenolic compounds in addition to potassium salts. Whereas the salt ions reduced the repulsion between fibrils and created denser CNF networks, the phenolic compounds - which adsorbed readily on the cellulose surfaces - played an important role in assisting the flowability of the hydrogels at high shear strains by reducing the flocculation tendency, often observed in pure and salt-containing CNFs, and contributed to the structural integrity of the CNF network in aqueous environment. Surprisingly, the willow bark extract exhibited hemolysis activity, which highlights the importance of more thorough investigations of biocompatibility of natural materials. WBE shows great potential for managing the water interactions of CNF-based products.

In Situ Adsorption of Red Onion (Allium cepa) Natural Dye on Cellulose Model Films and Fabrics Exploiting Chitosan as a Natural Mordant.

Synthetic dyes and chemicals create an enormous impact on environmental pollution both in textile manufacturing and after the product's lifetime. Biobased plant-derived colorants and mordants have great potential for the development of more sustainable textile dyeing processes. Colorants isolated from biomass residues are renewable, biodegradable, and usually less harmful than their synthetic counterparts. Interestingly, they may also bring additional functions to the materials. However, the extraction and purification of the biocolorants from biomass as well as their dyeing efficiency and color fastness properties require a more thorough examination. Here, we extracted red onion (Allium cepa) skins to obtain polyphenolic flavonoids and anthocyanins as biocolorants, characterized the chemical composition of the mixture, and used a quartz crystal microbalance and thin films of cellulose nanofibrils to study the adsorption kinetics of dyes onto cellulose substrates in situ. The effect of different mordants on the adsorption behavior was also investigated. Comparison of these results with conventional dyeing experiments of textiles enabled us to determine the interaction mechanism of the dyes with substrates and mordants. Chitosan showed high potential as a biobased mordant based both on its ability to facilitate fast adsorption of polyphenols to cellulose and its ability to retain the purple color of the red onion dye (ROD) in comparison to the metal mordants FeSO4 and alum. The ROD also showed excellent UV-shielding efficiency at low concentrations, suggesting that biocolorants, due to their more complex composition compared to synthetic ones, can have multiple actions in addition to providing aesthetics.

Toward Corneal Limbus In Vitro Model: Regulation of hPSC-LSC Phenotype by Matrix Stiffness and Topography During Cell Differentiation Process.

A functional limbal epithelial stem cells (LSC) niche is a vital element in the regular renewal of the corneal epithelium by LSCs and maintenance of good vision. However, little is known about its unique structure and mechanical properties on LSC regulation, creating a significant gap in development of LSC-based therapies. Herein, the effect of mechanical and architectural elements of the niche on human pluripotent derived LSCs (hPSC-LSC) phenotype and growth is investigated in vitro. Specifically, three formulations of polyacrylamide gels with different controlled stiffnesses are used for culture and characterization of hPSC-LSCs from different stages of differentiation. In addition, limbal mimicking topography in polydimethylsiloxane is utilized for culturing hPSC-LSCs at early time point of differentiation. For comparison, the expression of selected key proteins of the corneal cells is analyzed in their native environment through whole mount staining of human donor corneas. The results suggest that mechanical response and substrate preference of the cells is highly dependent on their developmental stage. In addition, data indicate that cells may carry possible mechanical memory from previous culture matrix, both highlighting the importance of mechanical design of a functional in vitro limbus model.

Functional and anionic cellulose-interacting polymers by selective chemo-enzymatic carboxylation of galactose-containing polysaccharides.

Carboxylated, anionic polysaccharides were selectively prepared using a combination of enzymatic and chemical reactions. The galactose-containing polysaccharides studied were spruce galactoglucomannan, guar galactomannan, and tamarind galactoxyloglucan. The galactosyl units of the polysaccharides were first oxidized with galactose oxidase (EC 1.1.3.9) and then selectively carboxylated, resulting in the galacturonic acid derivatives with good conversion and yield. The degrees of oxidation (DO) of the products were determined by gas chromatography-mass spectrometry (GC-MS). A novel feasible electrospray ionization-mass spectrometry (ESI-MS) method was also developed for the determination of DO. The solution properties and charge densities of the products were investigated. The interaction of the products with cellulose was studied by two methods, bulk sorption onto bleached birch kraft pulp and adsorption onto nanocellulose ultrathin films by quartz crystal microbalance with dissipation (QCM-D). To study the effect of the location of the carboxylic acid groups on the physicochemical properties, polysaccharides were also oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated reaction producing polyuronic acids. The chemo-enzymatically oxidized galacturonic polysaccharides with an unmodified backbone had a better ability to interact with cellulose than the TEMPO-oxidized products. The selectively carboxylated polysaccharides can be further exploited, as such, or in the targeted functionalization of cellulose surfaces.