Nanocellulose Hydrogels Research Articles

Manufacture of a novel anisotropic bacterial nanocellulose hydrogel membrane by using a rotary drum bioreactor

Since anisotropic hydrogel membranes have great potential in tissue engineering and bioseparation, the aim of this study was to produce an anisotropic BNC hydrogel membrane for the first time with enhanced BNC productivity by using a newly designed 30-L horizontal rotary drum bioreactor. As compared with the traditional tray static cultivation, the BNC hydrogel from the rotary drum bioreactor showed anisotropic morphology, sparser network, lower dry matter content of 0.16 w/w%, thicker fiber diameter, and lower degree of polymerization that was still 1.8 times higher than cotton, and featured with much higher ultraviolet-visible light transmittance, as well as demonstrated anisotropic tensile properties, lower Young’s modulus of 0.23 MPa and compressive modulus of 0.99 kPa. The productivity of dry and wet BNC was enhanced by 1.65 times and 3.73 times, respectively. The proposed technology may not only obtain anisotropic BNC hydrogel membranes with high transparency, but also promote the BNC productivity.

Immobilization of Heparin on Bacterial Nanocellulose Hydrogels Induces Tubulogenesis of Human Endothelial Cells

Models that mimic the angiogenesis initial processes, as adhesion, migration, proliferation and tubulogenesis, are extremely valuable for investigating the action of new anti-cancer drugs. There still is a need for an angiogenesis model that reflects in vivo environment. To address this challenge, we developed a 3D matrix well-defined based on covalently immobilization of heparin (HEP) on bacterial nanocellulose (BNC) hydrogels. Successful immobilization was confirmed by qualitative and quantification analysis. Human umbilical vein endothelial cells (HUVECs) were seeded on bottom and top surfaces of BNC and BNC-HEP hydrogels and cells behavior were analyzed. The bottom surfaces of BNC-HEP hydrogels were able to support cell adhesion and promote proliferation and tubulogenesis formation. Results here presented indicate that the tubulogenesis process could be controlled by physico-chemical properties of the developed hydrogel. The interaction between the bioactive molecule, heparin, and the particular microstructure of BNC induced tubulogenenic behavior of HUVECs in vitro.

Anions reversibly responsive luminescent nanocellulose hydrogels for cancer spheroids culture and release

Artificial stimuli-responsive hydrogels that can mimic natural extracellular matrix for growth and release of cancer spheroids (CSs) have attracted much attention. However, such hydrogels still face a challenge in regulating CSs growth and controlled release as well as keeping CSs integrity. Herein, a new class of ClO−/SCN− reversibly responsive nanocellulose hydrogel with fluorescence on-off reporter is developed. Upon addition of ClO−, the gel network of nanocellulose hydrogel was destructed, accompanying by the fluorescent quenching. Notably, when introducing of SCN−, a red fluorescence filamentous hydrogel was recovered by coordination cross-linking. The hydrogel reforms in a completely reversible process through the regulation of ClO−/SCN−. Benefit from the above response features of the hydrogel, the growth of cancer spheroids (CSs) in the hydrogel and on demand release of CSs from the hydrogel could be easily achieved through ClO−/SCN− regulation. Importantly, the growth and release of CSs can be monitored in real time by fluorescence imaging. Overall, such design strategy based on ClO−/SCN−-responsive fluorescent hydrogels provided a new type of multi-responsive hydrogels as main scaffolds for cancer research and cancer drug screening.

Ageing of aqueous TEMPO-oxidized nanofibrillated cellulose dispersions: a rheological study

The study concerns the development of rheological properties of aqueous TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-oxidized nanofibrillated cellulose (NFC) suspensions prepared from a commercially available TEMPO-NFC powder. Ageing of hydrogels with concentrations from 1 to 3 wt% of TEMPO-NFC was investigated by monitoring shear flow and linear viscoelastic properties after different days from sample preparation. For quantitative representation of the results time dependencies of zero shear viscosity and storage modulus are given. The increase of rheological parameters is described by a sigmoidal mathematical model. By superposition of individual data sets master curves displaying reduced values of the most significant parameters are constructed, showing the effect of ageing kinetics. The reduced storage modulus and zero-shear viscosity values increase for 2 and 3 decades, respectively, before reaching final values. Obtained results are useful for several applications of nanocellulose hydrogels, especially for those, where pumping, mixing, coating or injecting is necessary. For example, in biomedical field, a less viscous suspension can be injected to the spot of interest, where the final gel properties are developed.

Characterization of pulp derived nanocellulose hydrogels using AVAP® technology

Bioinspiration from hierarchical structures found in natural environments has heralded a new age of advanced functional materials. Nanocellulose has received significant attention due to the demand for high-performance materials with tailored mechanical, physical and biological properties. In this study, nanocellulose fibrils, nanocrystals and a novel mixture of fibrils and nanocrystals (blend) were prepared from softwood biomass using the AVAP® biorefinery technology. These materials were characterized using transmission and scanning electron microscopy, and atomic force microscopy. This analysis revealed a nano- and microarchitecture with extensive porosity. Notable differences included the nanocrystals exhibiting a compact packing of nanorods with reduced porosity. The NC blend exhibited porous fibrillar networks with interconnecting compact nanorods. Fourier transform infrared spectroscopy and X-ray diffraction confirmed a pure cellulose I structure. Thermal studies highlighted the excellent stability of all three NC materials with the nanocrystals having the highest decomposition temperature. Surface charge analysis revealed stable colloid suspensions. Rheological studies highlighted a dominance of elasticity in all variants, with the NC blend being more rigid than the NC fibrils and nanocrystals, indicating a double network hydrogel structure. Given these properties, it is thought that these materials show great potential in (bio)nanomaterial applications where careful control of microarchitecture, surface topography and porosity are required.

Nanocellulose as a natural source for groundbreaking applications in materials science: Today’s state

Cellulose is one of the most important natural polymers on earth and its various nanoscale forms provide new opportunities for groundbreaking discoveries in materials science. The current state of nanocellulose research and development, in terms of production and processing (including international market launch), structural details, properties, and innovative applications in life sciences and engineering technology is featured. Nanocelluloses are natural materials with at least one dimension in the nano-scale. They combine important cellulose properties with the features of nanomaterials and open new horizons for materials science and its applications. The field of nanocellulose materials is subdivided into three domains: biotechnologically produced bacterial nanocellulose hydrogels, mechanically delaminated cellulose nanofibers, and hydrolytically extracted cellulose nanocrystals. This review article describes today’s state regarding the production, structural details, physicochemical properties, and innovative applications of these nanocelluloses. Promising technical applications including gels/foams, thickeners/stabilizers as well as reinforcing agents have been proposed and research from last five years indicates new potential for groundbreaking innovations in the areas of cosmetic products, wound dressings, drug carriers, medical implants, tissue engineering, food and composites. The current state of worldwide commercialization and the challenge of reducing nanocellulose production costs are also discussed.

3D printing of nanocellulose hydrogel scaffolds with tunable mechanical strength towards wound healing application.

We present for the first time approaches to 3D-printing of nanocellulose hydrogel scaffolds based on double crosslinking, first by in situ Ca2+ crosslinking and post-printing by chemical crosslinking with 1,4-butanediol diglycidyl ether (BDDE). Scaffolds were successfully printed from 1% nanocellulose hydrogels, with their mechanical strength being tunable in the range of 3 to 8 kPa. Cell tests suggest that the 3D-printed and BDDE-crosslinked nanocellulose hydrogel scaffolds supported fibroblast cells' proliferation, which was improving with increasing rigidity. These 3D-printed scaffolds render nanocellulose a new member of the family of promising support structures for crucial cellular processes during wound healing, regeneration and tissue repair.

Nano-cellulose hydrogel coated flexible titanate-bismuth oxide membrane for trinity synergistic treatment of super-intricate anion/cation/oily-water

Taking into account that oil generally hinders the adsorption performance of adsorbents, the purification of super-intricate wastewater containing abundant toxic cations, anions and oils is full of challenge. Based on the synergistic effects of layered titanate nanofibers (TNFs), oxygen vacancy occupied δ-Bi2O3 and surface carboxyl/hydroxy groups uniformly arranged cellulose, a layer-by-layer assembled nano-cellulose hydrogel coated flexible titanate-bismuth oxide membrane (CH-TBM) was developed for efficiently handling this sewage. The cellulose hydrogel top-layer with a pore size lower than 100 m ensures the oil phase is resisted (oil contact angle > 150°), while the water phase can easily and quickly permeate the membrane (water contact angle ≈ 0°). And, the TNFs-Bi2O3 sub-layer with a pore size larger than 10 m guarantees that the toxic anions/cations in the water are capable of efficiently being removed. The removal capacities of Cs+, I−, Cu2+, SeO42−, Pb2+, SeO32−, Sr2+ and Br− achieve 125.4, 225.9, 136.1, 85.1, 421.1, 204.5, 81.4, and 89.6 g g−1, respectively. Significantly, CH-TBM with controllable shape also shows wide acid and alkali adaptation ranges, good recyclable, and simple post-processing method. Hence, the as-fabricated CH-TBM can be served as an excellent treatment agent for super-complex sewage.

Ion-crosslinked wood-derived nanocellulose hydrogels with tunable antibacterial properties: Candidate materials for advanced wound care applications

Development of advanced dressings with antimicrobial properties for the treatment of infected wounds is an important approach in the fight against evolution of antibiotic resistant bacterial strains. Herein, the effects of ion-crosslinked nanocellulose hydrogels on bacteria commonly found in infected wounds were investigated in vitro. By using divalent calcium or copper ions as crosslinking agents, different antibacterial properties against the bacterial strains Staphylococcus epidermidis and Pseudomonas aeruginosa were obtained. Calcium crosslinked hydrogels were found to retard S. epidermidis growth (up to 266% increase in lag time, 36% increase in doubling time) and inhibited P. aeruginosa biofilm formation, while copper crosslinked hydrogels prevented S. epidermidis growth and were bacteriostatic towards P. aeruginosa (49% increase in lag time, 78% increase in doubling time). The wound dressing candidates furthermore displayed barrier properties towards both S. epidermidis and P. aeruginosa, hence making them interesting for further development of advanced wound dressings with tunable antibacterial properties.

Molecular mobility of nanocellulose hydrogels

The molecular mobility of nanocellulose hydrogels isolated from microcrystalline cellulose is evaluated using the spin probe method, from the correlation time τ (s) and rotational frequency ν = 1/τ(s–1) of stable nitroxyl radicals introduced into the medium under study. In an aqueous gel medium, the EPR spectrum of the probe features an anisotropic triplet of frozen particles over a temperature range of 77 to 265 K. In an aqueous–ethanolic gel solution, the temperature of onset of rotation of the radical is 85 K lower. The rotational correlation time is determined from the parameters of the EPR spectrum recorded in the temperature range of 180–290 K. The resulting Arrhenius temperature dependence logν = f(1/T) is used to evaluate the activation energy of rotation E of the radical and the preexponential factor ν0(s–1), the frequency of rotational vibrations of the particle around the equilibrium position. For the aqueous medium, E = 11.2 kcal/mol; in the presence of ethanol, E = 5.2 kcal/mol; the preexponential factors for the aqueous and aqueous–ethanolic media are ν0 = 7 × 1018 and 6 × 1014 s–1, respectively. The parameters E and ν0 measured in the pure solvents and in the samples containing nanocellulose differ little, which is indicative of a high hydrophobicity of the probe molecule (and hydrogel particles) and of their weak interaction with the environment. The high value (~1018 s–1) of the preexponential factor is explained in terms of the compensation effect of water.

Using in situ nanocellulose-coating technology based on dynamic bacterial cultures for upgrading conventional biomedical materials and reinforcing nanocellulose hydrogels.

Bacterial nanocellulose (BNC) is a microbial nanofibrillar hydrogel with many potential applications. Its use is largely restricted by insufficient strength when in a highly swollen state and by inefficient production using static cultivation. In this study, an in situ nanocellulose-coating technology created a fabric-frame reinforced nanocomposite of BNC hydrogel with superior strength but retained BNC native attributes. By using the proposed technology, production time could be reduced from 10 to 3 days to obtain a desirable hydrogel sheet with approximately the same thickness. This novel technology is easier to scale up and is more suitable for industrial-scale manufacture. The mechanical properties (tensile strength, suture retention strength) and gel characteristics (water holding, absorption and wicking ability) of the fabric-reinforced BNC hydrogel were investigated and compared with those of ordinary BNC hydrogel sheets. The results reveal that the fabric-reinforced BNC hydrogel was equivalent with regard to gel characteristics, and exhibited a qualitative improvement with regard to its mechanical properties. For more advanced applications, coating technology via dynamic bacterial cultures could be used to upgrade conventional biomedical fabrics, i.e. medical cotton gauze or other mesh materials, with nanocellulose. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1077-1084, 2016.

Development of nanocellulose scaffolds with tunable structures to support 3D cell culture

Swollen three-dimensional nanocellulose films and their resultant aerogels were prepared as scaffolds towards tissue engineering application. The nanocellulose hydrogels with various swelling degree (up to 500 times) and the resultant aerogels with desired porosity (porosity up to 99.7% and specific surface area up to 308m2/g) were prepared by tuning the nanocellulose charge density, the swelling media conditions, and the material processing approach. Representative cell-based assays were applied to assess the material biocompatibility and efficacy of the human extracellular matrix (ECM)-mimicking nanocellulose scaffolds. The effects of charge density and porosity of the scaffolds on the biological tests were investigated for the first time. The results reveal that the nanocellulose scaffolds could promote the survival and proliferation of tumor cells, and enhance the transfection of exogenous DNA into the cells. These results suggest the usefulness of the nanocellulose-based matrices in supporting crucial cellular processes during cell growth and proliferation.

Nanocellulose hydrogels: preparation, characterization and cytotoxicity studies toward biomedical applications

Event Abstract Back to Event Nanocellulose hydrogels: preparation, characterization and cytotoxicity studies toward biomedical applications Alex Basu1, Jonas Lindh1, Maria Strömme1 and Natalia Ferraz1 1 Uppsala University, Department of Engineering Sciences, Sweden Nanocellulose (NC) is an emerging biodegradable, recyclable and renewable biopolymer of enormous industrial importance. In recent years, NC has been identified as a promising candidate for biomedical applications[1],[2]. NC based materials are generally regarded as biocompatible, however the interactions with biological systems can be affected by the physicochemical properties and the nano-structure of the studied material[1]. It is therefore of great importance to evaluate the biocompatibility of novel NC based materials as a complement to the physiochemical characterization. In the present work, ion cross-linked hydrogels of NC were prepared to be further evaluated for wound healing applications. Anionic wood-based NC (a-NC) prepared through TEMPO-mediated oxidation as well as cationic wood-based NC (c-NC) modified by EPTMAC condensation were prepared. Through ionic crosslinking with calcium, self-standing hydrogels of two compositions were obtained: the pure a-NC hydrogel and the composite ac-NC hydrogel consisting of a-NC and c-NC fibers. Rheological measurements confirmed successful ionic cross-linking of the gels while water retention tests brought clarity to the distinct water conservation abilities of the two products. SEM micrographs revealed different structures of the materials, where the a-NC hydrogel consisted of nano-scaled fibers while the ac-NC hydrogel presented a mixture of nano-and micro-scaled aggregates. Indirect cytotoxicity tests using the monocyte-like THP-1 cell line and human dermal fibroblasts were performed, revealing that no toxicity was introduced during the preparation of the two NC materials. Thus, the a-NC and ac-NC hydrogels are suitable candidates for further biocompatibility studies directed towards their use in wound healing dressings.

Micromechanical model of biphasic biomaterials with internal adhesion: Application to nanocellulose hydrogel composites

The mechanical properties of hydrated biomaterials are non-recoverable upon unconfined compression if adhesion occurs between the structural components in the material upon fluid loss and apparent plastic behaviour. We explore these micromechanical phenomena by introducing an aggregation force and a critical yield pressure into the constitutive biphasic formulation for transversely isotropic tissues. The underlying hypothesis is that continual fluid pressure build-up during compression temporarily supresses aggregation. Once compression stops and the pressure falls below some critical value, internal aggregation occurs over a time scale comparable to the poroelastic time. We demonstrate this model by predicting the mechanical response of bacterial nanocellulose hydrogel composites, which are promising biomaterials and a structural mimetic for the plant cell wall. Cross-linking of cellulose by xyloglucan creates an extensional resistance and substantially increases the compressive modulus under large compression and densification. In comparison, incorporating non-crosslinking arabinoxylan into the hydrogel has little effect on its mechanics at the strain rates investigated. These results assist in elucidating the mechanical role of these polysaccharides in the complex plant cell wall structure. They also suggest xyloglucan is a suitable candidate to tailor the stiffness of nanocellulose hydrogels in biomaterial design, which includes modulating cell-adhesion in tissue engineering applications. The model and overall approach may be utilised to characterise and design a myriad of biomaterials and mammalian tissues, particularly those with a fibrillar structure. Statement of SignificanceThe mechanical properties of hydrated biomaterials can be non-recoverable upon compression due to increased adhesion occurring between the structural components in the material. Cellulose–hemicellulose composite hydrogels constitute a classical example of this phenomenon, since fibres can freely re-orient and adhere upon fluid loss to produce significant variations in the mechanical response to compression. Here, we model their micromechanics by introducing an aggregation force and a critical yield pressure into the constitutive formulation for transversely isotropic biphasic materials. The resulting model is easy to implement for routine characterization of this type of hydrated biomaterials through unconfined compression testing and produces physically meaningful and reproducible mechanical parameters.

Potential of PVA-doped bacterial nano-cellulose tubular composites for artificial blood vessels.

Bacterial nano-cellulose (BNC) hydrogel has been suggested as a promising biomaterial for artificial blood vessels. However, some properties of BNC do not achieve all of the requirements of a native blood vessel - compliance, for instance. In order to improve the properties of BNC tubes, poly(vinyl alcohol) (PVA) was introduced in the BNC tubes to make composites. Two types of pristine BNC tubes with different inner structures were produced in two bioreactors. A PVA tube and PVA-BNC tubular composites were made for comparison by using a thermally-induced phase separation method. The morphology, water permeability, cytotoxicity, and mechanical properties, including the axial stretch strength, suture retention, burst pressure, and compliance of all the tubes, were evaluated and compared. The results indicated that PVA impregnated into BNC tubes and then significantly improved the properties of BNC, especially the mechanical properties and water permeability. The BNC tube itself played a great role in the performances of the composites as the skeleton base material. The PVA-BNC composite tubes could constitute new biomaterial candidates for vascular grafts.

Metal cation cross-linked nanocellulose hydrogels as tissue engineering substrates.

The use of cellulose materials for biomedical applications is attractive due to their low cost, biocompatibility, and biodegradability. Specific processing of cellulose to yield nanofibrils further improves mechanical properties and suitability as a tissue engineering substrate due to the similarity to the fibrous structure, porosity, and size-scale of the native extracellular matrix. In order to generate the substrate, nanocellulose hydrogels were fabricated from carboxylated cellulose nanofibrils via hydrogelation using metal salts. Hydrogels cross-linked with Ca(2+) and Fe(3+) were investigated as tissue culture substrates for C3H10T1/2 fibroblast cells. Control substrates as well as those with physically adsorbed and covalently attached fibronectin protein were evaluated with X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and enzyme linked immunosorbent assay (ELISA). Significantly more cells were attached to surfaces modified with protein, with the highest number of cells adhered to the calcium cross-linked hydrogels with covalently attached protein.

Nanocellulose aerogel membranes for optimal electrolyte filling in dye solar cells

A new method for depositing electrolyte in dye solar cells (DSCs) is introduced: a nanocellulose hydrogel membrane is screen printed on the counter electrode and further freeze-dried to form a highly porous nanocellulose aerogel, which acts as an absorbing sponge for the liquid electrolyte. When the nanoporous dye-sensitized TiO2 photoelectrode film is pressed against the wetted aerogel, it becomes filled with the electrolyte. The electrolyte flows inside the TiO2 film only about ten micrometers (i.e. the TiO2 film thickness) whereas in the conventional filling method, where the electrolyte is pumped through the cell, it flows about 1000-times longer distance, which is known to cause uneven distribution of the electrolyte components due to a molecular filtering effect. Furthermore, with the new method there is no need for electrolyte filling holes which simplifies significantly the sealing of the cells and eliminates one common pathway for leakage. Photovoltaic analysis showed that addition of the nanocellulose aerogel membrane did not have a statistically significant effect on cell efficiency, diffusion in the electrolyte or charge transfer at the counter electrode. There was, however, a clear difference in the short circuit current density and open circuit voltage between the cells filled with the aerogel method and in the reference cells filled with the conventional method, which appeared to be caused by the differences in the electrolyte filling instead of the nanocellulose itself. Moreover, accelerated aging tests at 1 Sun 40°C for 1000h showed that the nanocellulose cells were as stable as the conventional DSCs. The nanocellulose aerogel membranes thus appear inert with respect to both performance and stability of the cells, which is an important criterion for any electrolyte solidifying filler material.

Biocompatibility evaluation of densified bacterial nanocellulose hydrogel as an implant material for auricular cartilage regeneration.

Bacterial nanocellulose (BNC), synthesized by the bacterium Gluconacetobacter xylinus, is composed of highly hydrated fibrils (99 % water) with high mechanical strength. These exceptional material properties make BNC a novel biomaterial for many potential medical and tissue engineering applications. Recently, BNC with cellulose content of 15 % has been proposed as an implant material for auricular cartilage replacement, since it matches the mechanical requirements of human auricular cartilage. This study investigates the biocompatibility of BNC with increased cellulose content (17 %) to evaluate its response in vitro and in vivo. Cylindrical BNC structures (Ø48 × 20 mm) were produced, purified in a built-in house perfusion system, and compressed to increase the cellulose content in BNC hydrogels. The reduction of endotoxicity of the material was quantified by bacterial endotoxin analysis throughout the purification process. Afterward, the biocompatibility of the purified BNC hydrogels with cellulose content of 17 % was assessed in vitro and in vivo, according to standards set forth in ISO 10993. The endotoxin content in non-purified BNC (2,390 endotoxin units (EU)/ml) was reduced to 0.10 EU/ml after the purification process, level well below the endotoxin threshold set for medical devices. Furthermore, the biocompatibility tests demonstrated that densified BNC hydrogels are non-cytotoxic and cause a minimal foreign body response. In support with our previous findings, this study concludes that BNC with increased cellulose content of 17 % is a promising non-resorbable biomaterial for auricular cartilage tissue engineering, due to its similarity with auricular cartilage in terms of mechanical strength and host tissue response.

Thermoresponsive hybrid hydrogel of oxidized nanocellulose using a polypeptide crosslinker

Thermoresponsive hybrid nanocellulose hydrogels were prepared from a mixture of oxidized nanocellulose and elastin-like polypeptide (ELP). Positively charged ELP was used as a polymeric crosslinker for conjugation with negatively charged nanocellulose. Hydrogel formation was triggered by a simple increase in temperature, and the hydrogel was reversibly returned to the liquid phase by decreasing temperature. Surface potential measurement confirmed the electrostatic properties of oxidized nanocellulose and ELP molecules. The surface morphology of hydrogels was observed by atomic force microscopy and field emission-scanning electron microscopy. Conformational changes in the ELP/nanocellulose hybrid were characterized by circular dichroism. The ELP/nanocellulose hybrid hydrogel was noncytotoxic and suitable for encapsulating cells, indicating its potential for biomedical applications.

Loading of bacterial nanocellulose hydrogels with proteins using a high-speed technique

For the loading of the natural biopolymer bacterial nanocellulose (BNC) with drugs, usually an adsorption method has been described. In the present study, a high-speed loading technique based on vortexing was established for the incorporation of proteins in BNC as drug delivery system. Compared to the conventional technique, vortexing accomplished in 10min the same protein loading capacity as the adsorption method in 24h with comparable protein distribution and protein stability. Vortex loaded BNC demonstrated a retarded protein release with a lower total amount of released protein after 168h compared to the adsorption loaded BNC. This was correlated with a densification of the fiber network as shown by electron microscopy and a reduced water holding capacity. These observations offer the possibility to control the drug release by selection of the preparation technique.