The European Polysaccharide Network of Excellence (EPNOE) research roadmap 2040: Advanced strategies for exploiting the vast potential of polysaccharides as renewable bioresources

Polysaccharides are among the most abundant bioresources on earth and consequently need to play a pivotal role when addressing existential scientific challenges like climate change and the shift from fossil-based to sustainable biobased materials. The Research Roadmap 2040 of the European Polysaccharide Network of Excellence (EPNOE) provides an expert's view on how future research and development strategies need to evolve to fully exploit the vast potential of polysaccharides as renewable bioresources. It is addressed to academic researchers, companies, as well as policymakers and covers five strategic areas that are of great importance in the context of polysaccharide related research: (I) Materials & Engineering, (II) Food & Nutrition, (III) Biomedical Applications, (IV) Chemistry, Biology & Physics, and (V) Skills & Education. Each section summarizes the state of research, identifies challenges that are currently faced, project achievements and developments that are expected in the upcoming 20 years, and finally provides outlines on how future research activities need to evolve.

4-Axis 3D-Printed Tubular Biomaterials Imitating the Anisotropic Nanofiber Orientation of Porcine Aortae

Many of the peculiar properties of the vasculature are related to the arrangement of anisotropic proteinaceous fibers in vessel walls. Understanding and imitating these arrangements can potentially lead to new therapies for cardiovascular diseases. These can be pre-surgical planning, for which patient-specific ex vivo anatomical models for endograft testing are of interest. Alternatively, therapies can be based on tissue engineering, for which degradable in vitro cell growth substrates are used to culture replacement parts. In both cases, materials are desirable that imitate the biophysical properties of vessels, including their tubular shapes and compliance. This work contributes to these demands by offering methods for the manufacturing of anisotropic 3D-printed nanofibrous tubular structures that have similar biophysical properties as porcine aortae, that are biocompatible, and that allow for controlled nutrient diffusion. Tubes of various sizes with axial, radial, or alternating nanofiber orientation along the blood flow direction are manufactured by a customized method. Blood pressure-resistant, compliant, stable, and cell culture-compatible structures are obtained, that can be degraded in vitro on demand. It is suggested that these healthcare materials can contribute to the next generation of cardiovascular therapies of ex vivo pre-surgical planning or in vitro cell culture.

3D-Printed Collagen-Nanocellulose Hybrid Bioscaffolds with Tailored Properties for Tissue Engineering Applications

Hybrid collagen (Coll) bioscaffolds have emerged as a promising solution for tissue engineering (TE) and regenerative medicine. These innovative bioscaffolds combine the beneficial properties of Coll, an important structural protein of the extracellular matrix, with various other biomaterials to create platforms for long-term cell growth and tissue formation. The integration or cross-linking of Coll with other biomaterials increases mechanical strength and stability and introduces tailored biochemical and physical factors that mimic the natural tissue microenvironment. This work reports on the fabrication of chemically cross-linked hybrid bioscaffolds with enhanced properties from the combination of Coll, nanofibrillated cellulose (NFC), carboxymethylcellulose (CMC), and citric acid (CA). The bioscaffolds were prepared by 3D printing ink containing Coll-NFC-CMC-CA followed by freeze-drying, dehydrothermal treatment, and neutralization. Cross-linking through the formation of ester bonds between the polymers and CA in the bioscaffolds was achieved by exposing the bioscaffolds to elevated temperatures in the dry state. The morphology, pores/porosity, chemical composition, structure, thermal behavior, swelling, degradation, and mechanical properties of the bioscaffolds in the dry and wet states were investigated as a function of Coll concentration. The bioscaffolds showed no cytotoxicity to MG-63 human bone osteosarcoma cells as tested by different assays measuring different end points. Overall, the presented hybrid Coll bioscaffolds offer a unique combination of biocompatibility, stability, and structural support, making them valuable tools for TE.

Cytotoxicity and Antibacterial Efficacy of Betaine- and Choline-Substituted Polymers

Cationic charge has been widely used to increase polymer adsorption and flocculation of dispersions or to provide antimicrobial activity. In this work, cationization of hydroxyethyl cellulose (HEC) and polyvinyl alcohol (PVA) was achieved by covalently coupling betaine hydrochloride and choline chloride to the polymer backbones through carbonyl diimidazole (CDI) activation. Two approaches for activation were investigated. CDI in excess was used to activate the polymers' hydroxyls followed by carbonate formation with choline chloride, or CDI was used to activate betaine hydrochloride, followed by ester formation with the polymers' hydroxyls. The first approach led to a more significant cross-linking of PVA, but not of HEC, and the second approach successfully formed ester bonds. Cationic, nitrogen-bearing materials with varying degrees of substitution were obtained in moderate to high yields. These materials were analyzed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, polyelectrolyte titration, and kaolin flocculation. Their dose-dependent effect on the growth of Staphylococcus aureus and Pseudomonas aeruginosa, and L929 mouse fibroblasts, was investigated. Significant differences were found between the choline- and betaine-containing polymers, and especially, the choline carbonate esters of HEC strongly inhibited the growth of S. aureus in vitro but were also cytotoxic to fibroblasts. Fibroblast cytotoxicity was also observed for betaine esters of PVA but not for those of HEC. The materials could potentially be used as antimicrobial agents for instance by coating surfaces, but more investigations into the interaction between cells and polysaccharides are necessary to clarify why and how bacterial and human cells are inhibited or killed by these derivatives, especially those containing choline.

Morphology and swelling of thin films of dialcohol xylan

Polysaccharides are excellent network formers and are often processed into films from water solutions. Despite being hydrophilic polysaccharides, the typical xylans liberated from wood are sparsely soluble in water. We have previously suggested that an additional piece to the solubilization puzzle is modification of the xylan backbone via oxidative cleavage of the saccharide ring. Here, we demonstrate the influence of the degree of modification, i.e., degree of oxidation (DO) on xylan solubilization and consequent film formation and stability. Oxidized and reduced wood xylans (i.e., dialcohol xylans) with the highest DO (77 %) within the series exhibited the smallest hydrodynamic diameter (d_h) of 60 nm in dimethylsulfoxide (DMSO). We transferred the modified xylans into films credit to their established solubility and then quantified the film water interactions. Dialcohol xylans with intermediate DOs (42 and 63 %) did not form continuous films. The films swelled slightly when subjected to humidity. However, the film with the highest DO demonstrated a significant moisture uptake that depended on the film mass and was not observed with the other modified grades or with unmodified xylan.

3D printing in the planning and teaching of endovascular procedures

BACKGROUND

The introduction of 3D printing in the medical field led to new possibilities in the planning of complex procedures, as well as new ways of training junior physicians. Especially in the field of vascular interventions, 3D printing has a wide range of applications.

METHODOLOGICAL INNOVATIONS

3D-printed models of aortic aneurysms can be used for procedural training of endovascular aortic repair (EVAR), which can help boost the physician's confidence in the procedure, leading to a better outcome for the patient. Furthermore, it allows for a better understanding of complex anatomies and pathologies. In addition to teaching applications, the field of pre-interventional planning benefits greatly from the addition of 3D printing. Especially in the preparation for a complex endovascular aortic repair, prior orientation and test implantation of the stent grafts can further improve outcomes and reduce complications. For both teaching and planning applications, high-quality imaging datasets are required that can be transferred into a digital 3D model and subsequently printed in 3D. Thick slice thickness or suboptimal contrast agent phase can reduce the overall detail of the digital model, possibly concealing crucial anatomical details.

CONCLUSION

Based on the digital 3D model created for 3D printing, another new visualization technique might see future applications in the field of vascular interventions: virtual reality (VR). It enables the physician to quickly visualize a digital 3D model of the patient's anatomy in order to assess possible complications during endovascular repair. Due to the short transfer time from the radiological dataset into the VR, this technique might see use in emergency situations, where there is no time to wait for a printed model.

Unraveling the timescale of the structural photo-response within oriented metal-organic framework films

Fundamental knowledge on the intrinsic timescale of structural transformations in photo-switchable metal-organic framework films is crucial to tune their switching performance and to facilitate their applicability as stimuli-responsive materials. In this work, for the first time, an integrated approach to study and quantify the temporal evolution of structural transformations is demonstrated on an epitaxially oriented DMOF-1-on-MOF film system comprising azobenzene in the DMOF-1 pores (DMOF-1/AB). We employed time-resolved Grazing Incidence Wide-Angle X-Ray Scattering measurements to track the structural response of the DMOF-1/AB film upon altering the length of the azobenzene molecule by photo-isomerization (trans-to-cis, 343 nm; cis-to-trans, 450 nm). Within seconds, the DMOF-1/AB response occurred fully reversible and over several switching cycles by cooperative photo-switching of the oriented DMOF-1/AB crystallites as confirmed further by infrared measurements. Our work thereby suggests a new avenue to elucidate the timescales and photo-switching characteristics in structurally responsive MOF film systems.

Polysaccharide peptide conjugates: Chemistry, properties and applications

The intention of this publication is to give an overview on research related to conjugates of polysaccharides and peptides. Dextran, chitosan, and alginate were selected, to cover four of the most often encountered functional groups known to be present in polysaccharides. These groups are the hydroxyl, the amine, the carboxyl, and the acetal functionality. A collection of the commonly used chemical reactions for conjugation is provided. Conjugation results into distinct properties compared to the parent polysaccharide, and a number of these characteristics are highlighted. This review aims at demonstrating the applicability of said conjugates with a strong emphasis on biomedical applications, drug delivery, biosensing, and tissue engineering. Some suggestions are made for more rigorous chemistries and analytics that could be investigated. Finally, an outlook is given into which direction the field could be developed further. We hope that this survey provides the reader with a comprehensive summary and contributes to the progress of works that aim at synthetically combining two of the main building blocks of life into supramolecular structures with unprecedented biological response.

One-Step Fabrication of Hollow Spherical Cellulose Beads: Application in pH-Responsive Therapeutic Delivery

The path to greater sustainability and the development of polymeric drug delivery systems requires innovative approaches. The adaptation and use of biobased materials for applications such as targeted therapeutic delivery is, therefore, in high demand. A crucial part of this relates to the development of porous and hollow structures that are biocompatible, pH-responsive, deliver active substances, and contribute to pain relief, wound healing, tissue regeneration, and so forth. In this study, we developed a facile single-step and water-based method for the fabrication of hollow spherical cellulose beads for targeted drug release in response to external pH stimuli. Through base-catalyzed deprotection, hydrophobic solid and spherical cellulose acetate beads are transformed into hydrophilic cellulose structures with a hollow interior (wall thickness: 150 μm and inner diameter: 650 μm) by a stepwise increment of temperature and treatment time. Besides the pH-responsive fluid uptake properties, the hollow cellulose structures exhibit a maximum encapsulation efficiency of 20-85% diclofenac (DCF), a nonsteroidal anti-inflammatory drug, used commonly to treat pain and inflammatory diseases. The maximum amount of DCF released in vitro increased from 20 to 100% when the pH of the release medium increased from pH 1.2 to 7.4. As for the DCF release patterns and kinetic models at specific pH values, the release showed a diffusion- and swelling-controlled profile, effortlessly fine-tuned by external environmental pH stimuli. Overall, we show that the modified beads exhibit excellent characteristics for transport across the gastrointestinal tract and enhance the bioavailability of the drug. Their therapeutic efficacy and biocompatibility are also evident from the studies on human fibroblast cells. We anticipate that this platform could support and inspire the development of novel sustainable and effective polysaccharide-based delivery systems.

Solid Phase Peptide Synthesis on Chitosan Thin Films

Stable chitosan thin films can be promising substrates for creating nanometric peptide-bound polyglucosamine layers. Those are of scientific interest since they can have certain structural similarities to bacterial peptidoglycans. Such films were deposited by spin coating from chitosan solutions and modified by acetylation and N-protected amino acids. The masses of deposited materials and their stability in aqueous solutions at different pH values and water interaction were determined with a quartz crystal microbalance with dissipation (QCM-D). The evolution of the surface composition was followed by X-ray photoelectron (XPS) and attenuated total reflectance infrared (ATR-IR) spectroscopy. Morphological changes were measured by atomic force microscopy (AFM), while the surface wettability was monitored by by static water contact angle measurements. The combination of the characterization techniques enabled an insight into the surface chemistry for each treatment step and confirmed the acetylation and coupling of N-protected glycine peptides. The developed procedures are seen as first steps toward preparing thin layers of acetylated chitin, potentially imitating the nanometric peptide substituted glycan layers found in bacterial cell walls.

Rapid Functionalization of Polytetrafluorethylene (PTFE) Surfaces with Nitrogen Functional Groups

The biocompatibility of body implants made from polytetrafluoroethylene (PTFE) is inadequate; therefore, the surface should be grafted with biocompatible molecules. Because PTFE is an inert polymer, the adhesion of the biocompatible film may not be appropriate. Therefore, the PFTE surface should be modified to enable better adhesion, preferably by functionalization with amino groups. A two-step process for functionalization of PTFE surface is described. The first step employs inductively coupled hydrogen plasma in the H-mode and the second ammonia plasma. The evolution of functional groups upon treatment with ammonia plasma in different modes is presented. The surface is saturated with nitrogen groups within a second if ammonia plasma is sustained in the H-mode at the pressure of 35 Pa and forward power of 200 W. The nitrogen-rich surface film persists for several seconds, while prolonged treatment causes etching. The etching is suppressed but not eliminated using pulsed ammonia plasma at 35 Pa and 200 W. Ammonia plasma in the E-mode at the same pressure, but forward power of 25 W, causes more gradual functionalization and etching was not observed even at prolonged treatments up to 100 s. Detailed investigation of the XPS spectra enabled revealing the surface kinetics for all three cases.

Influence of Charge and Heat on the Mechanical Properties of Scaffolds from Ionic Complexation of Chitosan and Carboxymethyl Cellulose

As one of the most abundant, multifunctional biological polymers, polysaccharides are considered promising materials to prepare tissue engineering scaffolds. When properly designed, wetted porous scaffolds can have biomechanics similar to living tissue and provide suitable fluid transport, both of which are key features for in vitro and in vivo tissue growth. They can further mimic the components and function of glycosaminoglycans found in the extracellular matrix of tissues. In this study, we investigate scaffolds formed by charge complexation between anionic carboxymethyl cellulose and cationic protonated chitosan under well-controlled conditions. Freeze-drying and dehydrothermal heat treatment were then used to obtain porous materials with exceptional, unprecendent mechanical properties and dimensional long-term stability in cell growth media. We investigated how complexation conditions, charge ratio, and heat treatment significantly influence the resulting fluid uptake and biomechanics. Surprisingly, materials with high compressive strength, high elastic modulus, and significant shape recovery are obtained under certain conditions. We address this mostly to a balanced charge ratio and the formation of covalent amide bonds between the polymers without the use of additional cross-linkers. The scaffolds promoted clustered cell adhesion and showed no cytotoxic effects as assessed by cell viability assay and live/dead staining with human adipose tissue-derived mesenchymal stem cells. We suggest that similar scaffolds or biomaterials comprising other polysaccharides have a large potential for cartilage tissue engineering and that elucidating the reason for the observed peculiar biomechanics can stimulate further research.

Water-based carbodiimide mediated synthesis of polysaccharide-amino acid conjugates: Deprotection, charge and structural analysis

We report here a one-step aqueous method for the synthesis of isolated and purified polysaccharide-amino acid conjugates. Two different types of amino acid esters: glycine methyl ester and L-tryptophan methyl ester, as model compounds for peptides, were conjugated to the polysaccharide carboxymethylcellulose (CMC) in water using carbodiimide at ambient conditions. Detailed and systematic pH-dependent charge titration and spectroscopy (infrared, nuclear magnetic resonance: ¹H, ¹³C- DEPT 135, ¹H- ¹³C HMBC/HSQC correlation), UV-vis, elemental and ninhydrin analysis provided solid and direct evidence for the successful conjugation of the amino acid esters to the CMC backbone via an amide bond. As the concentration of amino acid esters increased, a conjugation efficiency of 20-80% was achieved. Activated charcoal aided base-catalyzed deprotection of the methyl esters improved the solubility of the conjugates in water. The approach proposed in this work should have the potential to tailor the backbone of polysaccharides containing di- or tri-peptides.

Protein repellent anti-coagulative mixed-charged cellulose derivative coatings

This study describes the formation of cellulose based polyelectrolyte charge complexes on the surface of biodegradable polycaprolactone (PCL) thin films. Anionic sulphated cellulose (CS) and protonated cationic amino cellulose (AC) were used to form these complexes with a layer-by-layer coating technique. Both polyelectrolytes were analyzed by charge titration methods to elucidate their pH-value dependent protonation behavior. A quartz crystal microbalance with dissipation (QCM-D) in combination with X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to follow the growth, stability and water content of up to three AC/CS bi-layers in aqueous environment. This was combined with coagulation studies on one, two and three bilayers of AC/CS, measuring the thrombin formation rate and the total coagulation time of citrated blood plasma with QCM-D. Stable mixed charged bilayers could be prepared on PCL and significantly higher masses of AC than of CS were present in these complexes. Strong hydration due to the presence of ammonium and sulphate substituents on the backbone of cellulose led to a significant BSA repellent character of three bilayers of AC/CS coatings. The total plasma coagulation time was increased in comparison to neat PCL, indicating an anticoagulative nature of the coatings. Surprisingly, a coating solely composed of an AC layer significantly prolonged the total coagulation time on the surfaces although it did not prevent fibrinogen deposition. It is suggested that these cellulose derivative-based coatings can therefore be used to prevent unwanted BSA deposition and fibrin clot formation on PCL to foster its biomedical application.

Comparison of Trimethylsilyl Cellulose-Stabilized Carbonate and Hydroxide Nanoparticles for Deacidification and Strengthening of Cellulose-Based Cultural Heritage

Herein, colloidal dispersions of alkaline nanoparticles (NPs: CaCO₃ and Mg(OH)₂) are stabilized by trimethylsilyl cellulose (TMSC) in hexamethyldisiloxane and employed to treat historical wood pulp paper by an effortless dip-coating technique. Both alkaline NPs exhibit high stability and no size and shape changes upon stabilization with the polymer, as shown by UV-vis spectroscopy and transmission electron microscopy. The long-term effect of NP/TMSC coatings is investigated in detail using accelerated aging. The results from the pH-test and back-titration of coated papers show a complete acid neutralization (pH ∼ 7.4) and introduction of adequate alkaline reserve even after prolonged accelerated aging. Scanning electron microscopy-energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and infrared and water contact angle measurements showed the introduction of a thin and smooth hydrophobic NP/TMSC coating on the paper fibers. Acid-catalyzed desilylation of TMSC was observed by declining C-Si infrared absorbance peaks upon aging. The CaCO₃ coatings are superior to Mg(OH)₂ with respect to a reduced yellowing and lower cellulose degradation upon aging as shown by colorimetric measurements and degree of polymerization analysis. The tensile strength and folding endurance of coated and aged papers are improved to 200-300 and 50-70% as illustrated by tensile strength and double folding endurance measurements.

Affinity of Serum Albumin and Fibrinogen to Cellulose, Its Hydrophobic Derivatives and Blends

This work describes the preparation of spin-coated thin polymer films composed of cellulose (CE), ethyl cellulose (EC), and cellulose acetate (CA) in the form of bi- or mono-component coatings on sensors of a quartz crystal microbalance with dissipation monitoring (QCM-D). Depending on the composition and derivative, hydrophilicity can be varied resulting in materials with different surface properties. The surfaces of mono- and bi-component films were also analyzed by atomic force microscopy (AFM) and large differences in the morphologies were found comprising nano- to micrometer sized pores. Extended protein adsorption studies were performed by a QCM-D with 0.1 and 10 mg mL⁻¹ bovine serum albumin (BSA) and 0.1 and 1 mg mL⁻¹ fibrinogen from bovine plasma in phosphate buffered saline. Analysis of the mass of bound proteins was conducted by applying the Voigt model and a comparison was made with the Sauerbrey wet mass of the proteins for all films. The amount of deposited proteins could be influenced by the composition of the films. It is proposed that the observed effects can be exploited in biomaterial science and that they can be used to extent the applicability of bio-based polymer thin films composed of commercial cellulose derivatives.

Nano- and Micropatterned Polycaprolactone Cellulose Composite Surfaces with Tunable Protein Adsorption, Fibrin Clot Formation, and Endothelial Cellular Response

This work describes the interaction of the human blood plasma proteins albumin, fibrinogen, and γ-globulins with micro- and nanopatterned polymer interfaces. Protein adsorption studies were correlated with the fibrin clotting time of human blood plasma and with the growth of primary human pulmonary artery endothelial cells (hECs) on these patterns. It was observed that blends of polycaprolactone (PCL) and trimethylsilyl-protected cellulose form various thin-film patterns during spin coating, depending on the mass ratio of the polymers in the spinning solutions. Vapor-phase acid-catalyzed deprotection preserves these patterns but yields interfaces that are composed of hydrophilic cellulose domains enclosed by hydrophobic PCL. The blood plasma proteins are repelled by the cellulose domains, allowing for a suggested selective protein deposition on the PCL domains. An inverse proportional correlation is observed between the amount of cellulose present in the films and the mass of irreversibly adsorbed proteins. This results in significantly increased fibrin clotting times and lower masses of deposited clots on cellulose-containing films as revealed by quartz crystal microbalance with dissipation measurements. Cell viability of hECs grown on these surfaces was directly correlated with higher protein adsorption and faster clot formation. The results show that presented patterned polymer composite surfaces allow for a controllable blood plasma protein coagulation and a significant biological response from hECs. It is proposed that this knowledge can be utilized in regenerative medicine, cell cultures, and artificial vascular grafts by a careful choice of polymers and patterns.

UV-Induced reduction of graphene oxide in cellulose nanofibril composites

We report on an effective dry method to reduce graphene oxide (GO) in films of cellulose nanofibrils (CNF) by UV irradiation in the presence of nitrogen gas.

Chitin nanowhisker - Inspired electrospun PVDF membrane for enhanced oil-water separation

The requirement of promoting a revolution in filtration technology has led to growing devotion in advanced functional materials such as electrospun membranes for filtering devices as a solution for providing water at lower energy costs. In this study, electrospun polyvinylidene fluoride membranes were fabricated by reinforcing 0.5 and 1 wt. % of chitin nanowhiskers in order to improve their thermal stability, mechanical properties, pure water flux and oil-water filtration performance for the possible application as filtration membranes. Morphological analysis revealed the porous and fibrous structure of membranes which confirmed by BET surface area analysis. Incorporation of chitin nanowhiskers improved the mechanical properties of the membranes such as elongation at break and tensile strength (specifically at 1 wt. % of chitin nanowhisker) while resulted in substantial enhancement of their thermal properties. Furthermore, polyvinylidene fluoride/chitin nanowhisker membranes showed enhanced oil-water separation ability, while reinforcement of chitin nanowhisker led to increase pure water flux rate, which measured as a crucial point in filtration membranes. The oil-water separation results compared with a commercial polyvinylidene fluoride membrane and the results signified the potential of electrospun polyvinylidene fluoride/chitin nanowhisker to be used for filtration application.

Protein-repellent and antimicrobial nanoparticle coatings from hyaluronic acid and a lysine-derived biocompatible surfactant

Biofilm formation triggered by uncontrolled protein adsorption, on medical devices is the leading cause of catheter-associated urinary tract infections (CAUTI) during implantation. Herein, we report a water-based, green and one-step strategy to functionalize surfaces of silicone catheters, poly(dimethylsiloxane) (PDMS), with antifouling and antimicrobial substances to avoid uncontrolled protein adsorption and microbial attachment. A novel synergetic formulation consisting of an anionic glycosaminoglycan (hyaluronic acid, HA) and a lysine-derived biocompatible cationic surfactant (N^ε-myristoyl-lysine methyl ester, MKM) was prepared, resulting in the formation of nanoparticles (NPs, ca. 100-250 nm). Besides their high stability and long-lasting hydrophilicity in ambient and aqueous environments for 60 days, the nanometric layers (48 ± 3 nm) of HA-MKM NPs on PDMS showed no adsorption of BSA and lysozyme and substantially lower adsorption of fibrinogen as revealed by a quartz crystal microbalance with dissipation (QCM-D). In vitro antimicrobial test with S. aureus, E. coli, P. aeruginosa, P. mirabilis, C. albicans microbes under dynamic conditions revealed that the microbial growth was hampered by 85% compared with unmodified PDMS. Given the multiple functionalities, charges and diverse physiochemical properties of polysaccharide-lysine-based surfactant mixtures, this approach can be easily extended to the development of novel coatings on other silicone-based materials, thereby broadening potential applicability of PDMS-based biomaterials/devices in microfluidics, diagnostic biosensors and others.

Reactive cellulose-based thin films – a concept for multifunctional polysaccharide surfaces

Reactive coatings of hydroxyethyl cellulose furoate in the form of thin films, suitable for the covalent immobilization of functional molecules, were developed and characterized in this work.

Selective immobilization and detection of DNA on biopolymer supports for the design of microarrays

DNA immobilization for the manufacturing of microarrays requires sufficient probe density, low unspecific binding and high interaction efficiency with complementary strands that are detected from solutions. Many of these important parameters are affected by the surface chemistry and the blocking steps conducted during DNA spotting and hybridization. This work describes an alternative method to selectively immobilize probes and to detect DNA on biocompatible, hydrophilic cellulose coated supports with low unspecific binding, high selectivity and appropriate sensitivity. It takes advantage of a relatively selective adsorption of water soluble polysaccharides on a solid cellulose matrix. Single strands of DNA were conjugated to this soluble polysaccharide and subsequently micro-spotted on solid cellulose thin films that were coated on glass and polymer slides. This resulted in adsorptively bound DNA-probes that were used to detect complementary, labelled DNA strands with different lengths and sequences by hybridization. The interaction of the DNA-conjugates with cellulose surfaces and the selectivity of hybridization were investigated by a quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence scanning. The method of non-covalent immobilization of DNA probes on an uncharged, non-reactive, hydrophilic support lowers the unspecific binding and the number of handling steps required to conduct the experiments for the detection of DNA on microarrays. Simultaneously selectivity, hybridization efficiency and detection limits are maintained.

Polysaccharide stabilized nanoparticles for deacidification and strengthening of paper

This paper reports an investigation on the use of a highly stable colloidal organic dispersion consisting of a polysaccharides and alkaline nanoparticles for the simultaneous deacidification and strengthening of historical wood pulp papers.

Photolithographic patterning of cellulose: a versatile dual-tone photoresist for advanced applications

In many areas of science and technology, patterned films and surfaces play a key role in engineering and development of advanced materials. Here, we present a versatile toolbox that provides an easy patterning method for cellulose thin films by means of photolithography and enzymatic digestion. A patterned UV-illumination of trimethylsilyl cellulose thin films containing small amounts of a photo acid generator leads to a desilylation reaction and thus to the formation of cellulose in the irradiated areas. Depending on the conditions of development, either negative and positive type cellulose structures can be obtained, offering lateral resolutions down to the single-digit micro meter range by means of contact photolithography. In order to highlight the potential of this material for advanced patterning techniques, cellulose structures with sub-µm resolution are fabricated by means of two-photon absorption lithography. Moreover, these photochemically structured cellulose thin films are successfully implemented as dielectric layers in prototype organic thin film transistors. Such photopatternable dielectric layers are crucial for the realization of electrical interconnects for demanding organic device architectures.

Triggering protein adsorption on tailored cationic cellulose surfaces

The equipment of cellulose ultrathin films with BSA (bovine serum albumin) via cationization of the surface by tailor-made cationic celluloses is described. In this way, matrices for controlled protein deposition are created, whereas the extent of protein affinity to these surfaces is controlled by the charge density and solubility of the tailored cationic cellulose derivative. In order to understand the impact of the cationic cellulose derivatives on the protein affinity, their interaction capacity with fluorescently labeled BSA is investigated at different concentrations and pH values. The amount of deposited material is quantified using QCM-D (quartz crystal microbalance with dissipation monitoring, wet mass) and MP-SPR (multi-parameter surface plasmon resonance, dry mass), and the mass of coupled water is evaluated by combination of QCM-D and SPR data. It turns out that adsorption can be tuned over a wide range (0.6-3.9 mg dry mass m(-2)) depending on the used conditions for adsorption and the type of employed cationic cellulose. After evaluation of protein adsorption, patterned cellulose thin films have been prepared and the cationic celluloses were adsorbed in a similar fashion as in the QCM-D and SPR experiments. Onto these cationic surfaces, fluorescently labeled BSA in different concentrations is deposited by an automatized spotting apparatus and a correlation between the amount of the deposited protein and the fluorescence intensity is established.

Antifouling coating of cellulose acetate thin films with polysaccharide multilayers

In this investigation, partially deacetylated cellulose acetate (DCA) thin films were prepared and modified with hydrophilic polysaccharides with the layer-by-layer (LbL) technique. As polysaccharides, chitosan (CHI) and carboxymethyl cellulose (CMC) were used. DCA thin films were manufactured by exposing spin coated cellulose acetate to potassium hydroxide solutions for various times. The deacetylation process was monitored by attenuated total reflectance-infrared spectroscopy, film thickness and static water contact angle measurements. A maximum of three bilayers was created from the alternating deposition of CHI and CMC on the DCA films under two different conditions namely constant ionic strengths and varying pH values of the CMC solutions. Precoatings of CMC at pH 2 were used as a base layer. The sequential deposition of CMC and CHI was investigated with a quartz crystal microbalance with dissipation, film thickness, static water contact angle and atomic force microscopy (AFM) measurements. The versatility and applicability of the developed functional coatings was shown by removing the multilayers by rinsing with mixtures containing HCl/NaCl. The developed LbL coatings are used for studying the fouling behavior of bovine serum albumin (BSA).

Preparation of PDMS ultrathin films and patterned surface modification with cellulose

Patterned surface functionalization of PDMS with the biopolymer cellulose via lithographic methods.

Interaction and structure in polyelectrolyte/clay multilayers: a QCM-D study

This study focuses on the investigation of the influence of the ionic strength on the internal structure, film forming behavior, and swelling properties of polyelectrolyte/clay multilayers. Layer-by-layer films were prepared with three different polyelectrolytes [polyethylenimine (PEI), polydiallyldimethylammoniumchloride (pDADMAC), and 2-hydroxy-3-trimethylammonium propyl chloride starch (HPMA starch)] in combination with laponite clay platelets on three different surfaces. All experiments were carried out at two different ionic strengths (30 mM or 500 mM NaCl). The experiments performed with strong polyelectrolytes revealed a higher film thickness and adsorbed masses of clay and polyelectrolyte at 500 mM NaCl. The films containing PEI showed different behavior and were considerably less sensitive to changes in the ionic strength. This was also reflected by the swelling behavior as demonstrated by quartz crystal microbalance with dissipation (QCM-D) measurements. Films comprising PEI showed, in contrast to the other polyelectrolytes, much lower swelling in water leading to more compact and stable films in humid environments which is important for numerous applications of LbL clay coatings.

Interactions of a cationic cellulose derivative with an ultrathin cellulose support

The adsorption behavior of cellulose-4-[N-methylammonium]butyrate chloride (CMABC) on two hydrophilic substrates is studied, namely nanometric cellulose model thin films and silicon dioxide substrates. The adsorption is quantified in dependence of electrolyte concentration and pH value using a quartz crystal microbalance with dissipation (QCM-D). In case of CMABC, at high ionic strengths (25-100 mM NaCl) high adsorption is observed at pH 7 (Δf(3): -15 to -17 Hz) while at lower ionic strengths (1-10 mM) less CMABC (Δf(3): -2 to -12 Hz) is deposited on the cellulose surfaces as indicated by the frequency changes using QCM-D. A change in pH value from 7 to 8 reveals an increase in adsorption. Atomic force microscopy shows that the coating of cellulose thin films with CMABC changes the morphology from a fibrillar to a particle like structure on the surface. The surface wettability with water increases with an increasing amount of CMABC on the surface compared to neat cellulose model films. At lower pH values (3 and 5), CMABC does not adsorb onto the cellulose model thin films. XPS is used to validate the results and to determine the nitrogen content of the surfaces. In addition, adsorption of CMABC onto another hydrophilic and negatively charged substrate, silicon dioxide coated quartz crystals, cannot be detected at different pH values and electrolyte concentrations as proven by QCM-D.

Adsorption of carboxymethyl cellulose on polymer surfaces: evidence of a specific interaction with cellulose

The adsorption of carboxymethyl cellulose (CMC), one of the most important cellulose derivatives, is crucial for many scientific investigations and industrial applications. Especially for surface modifications and functionalization of materials, the polymer is of interest. The adsorption properties of CMC are dependent not only on the solutions state, which can be influenced by the pH, temperature, and electrolyte concentration, but also on the chemical composition of the adsorbents. We therefore performed basic investigation studies on the interaction of CMC with a variety of polymer films. Thin films of cellulose, cellulose acetate, deacetylated cellulose acetate, polyethylene terephthalate, and cyclo olefin polymer were therefore prepared on sensors of a QCM-D (quartz crystal microbalance) and on silicon substrates. The films were characterized with respect to the thickness, wettability, and chemical composition. Subsequently, the interaction and deposition of CMC in a range of pH values without additional electrolyte were measured with the QCM-D method. A comparison of the QCM-D results showed that CMC is favorably deposited on pure cellulose films and deacetylated cellulose acetate at low pH values. Other hydrophilic surfaces such as silicon dioxide or polyvinyl alcohol coated surfaces did not adsorb CMC to a significant extent. Atomic force microcopy confirmed that the morphology of the adsorbed CMC layers differed depending on the substrate. On hydrophobic polymer films, CMC was deposited in the form of larger particles in lower amounts whereas hydrophilic cellulose substrates were to a high extent uniformly covered by adsorbed CMC. The chemical similarity of the CMC backbone seems to favor the irreversible adsorption of CMC when the molecule is almost uncharged at low pH values. A selectivity of the cellulose CMC interaction can therefore be assumed. All CMC treated polymer films exhibited an increased hydrophilicity, which confirmed their modification with the functional molecule.

Creating water vapor barrier coatings from hydrophilic components

The preparation of water vapor barrier coatings composed of polyelectrolyte/clay multilayers using the layer-by-layer technique is reported. The suitability of different synthetic and renewable polyelectrolytes for the preparation of barrier coatings in combination with montmorillonite (MMT) platelets as well as the influence of the ionic strength and the number of bilayers on the coating performance was investigated. Highly hydrophilic and permeable cellulose films were used as substrate for determining the influence of the coatings on the water vapor transmission rate (WVTR). Improved barrier properties were realized by the use of polyethylene imine (PEI) or 2-hydroxy-3-trimethylammonium propyl chloride starch (HPMA starch) in combination with MMT. After the application of only 5 bilayers of PEI and MMT (thickness ∼40 nm) on each side of the cellulose film, the WVTR was significantly reduced. By the deposition of 40 PEI/MMT bilayers, the WVTR transmission rate was reduced by 68%. However, HPMA starch containing coatings led to vapor transmission reduction of up to 32% at the same number of coating steps. A strong correlation between the barrier properties of the coatings and the layer thickness was observed. The barrier properties of the coatings could be increased using higher ionic strengths. These results represent unprecedented water vapor barrier properties for coatings prepared from hydrophilic materials.

Functional polysaccharide conjugates for the preparation of microarrays

A method for the immobilization of functional molecules on cellulose surfaces was developed. The irreversible deposition of the water-soluble polyelectrolyte carboxymethyl cellulose (CMC) on solid cellulose surfaces was used as a basis for this immobilization. CMC was modified using aminofluorescein (AMF) as a model compound for a functional molecule. The carbodiimide mediated coupling efficiency of AMF to CMC was studied in detail, and the functional conjugates were isolated. A quartz crystal microbalance with dissipation was employed to study the immobilization of the functionalized CMC onto cellulose model films in situ. The influence of the carbodiimide concentration, the degree of substitution, and the molecular weight of CMC on the immobilization process was investigated. Atomic force microscopy was used to characterize the changes in the surface morphology of the modified cellulose films. Finally, microspotted arrays of AMF-CMC conjugates were prepared with the knowledge obtained from the basic interaction studies. The successful deposition of AMF-CMC conjugates onto cellulose surfaces was proven by fluorescence microscopy. The conjugation of functional molecules to CMC and the subsequent deposition of these products on cellulose can be seen as a versatile method to immobilize these molecules for applications in the field of microarrays and other sensor surfaces. It offers the possibility to introduce new properties on a variety of cellulosic materials.

Enzymatic digestion of partially and fully regenerated cellulose model films from trimethylsilyl cellulose

Partially and fully regenerated cellulose model films from trimethylsilyl cellulose (TMSC) were prepared by a time dependent regeneration approach. These thin films were characterized with contact angle measurements and attenuated total reflectance infrared spectroscopy (ATR-IR). In order to get further insights into the completeness of the regeneration we studied the interaction of cellulase enzymes from Trichoderma viride with the cellulose films using a quartz crystal microbalance with dissipation (QCM-D). To support the results from the QCM-D experiments capillary zone electrophoresis (CZE) and atomic force microscopy (AFM) were applied. The changes in mass and energy dissipation due to the interaction of the enzymes with the substrates were correlated with the surface wettability and elemental composition of the regenerated films. The highest interaction activity between the films and the enzyme, as well as the highest cellulose degradation, was observed on fully regenerated cellulose films, but some degradation also occurred on pure TMSC films. The enzymatic degradation rate correlated well with the rate of regeneration. It was demonstrated that CZE can be used to support QCM-D data via the detection of enzyme hydrolysis products in the eluates of the QCM-D cells. Glucose release peaked at the same time as the maximum mass loss was detected via QCM-D. It was shown that a combination of QCM-D and CZE together with enzymatic digestion is a reliable method to determine the conversion rate of TMSC to cellulose. In addition QCM-D and AFM revealed that cellulase is irreversibly bound to hydrophobic TMSC surfaces, while pure cellulose is digested almost completely in the course of hydrolysis.