Cytocompatibility of Wood-Derived Cellulose Nanofibril Hydrogels with Different Surface Chemistry

Preparation and Characterization of Softwood and Hardwood Nanofibril Hydrogels: Toward Wound Dressing Applications

Hydrogels of cellulose nanofibrils (CNFs) are promising wound dressing candidates due to their biocompatibility, high water absorption, and transparency. Herein, two different commercially available wood species, softwood and hardwood, were subjected to TEMPO-mediated oxidation to proceed with delignification and oxidation in a one-pot process, and thereafter, nanofibrils were isolated using a high-pressure microfluidizer. Furthermore, transparent nanofibril hydrogel networks were prepared by vacuum filtration. Nanofibril properties and network performance correlated with oxidation were investigated and compared with commercially available TEMPO-oxidized pulp nanofibrils and their networks. Softwood nanofibril hydrogel networks exhibited the best mechanical properties, and in vitro toxicological risk assessment showed no detrimental effect for any of the studied hydrogels on human fibroblast or keratinocyte cells. This study demonstrates a straightforward processing route for direct oxidation of different wood species to obtain nanofibril hydrogels for potential use as wound dressings, with softwood having the most potential.

Polysaccharides and Structural Proteins as Components in Three-Dimensional Scaffolds for Breast Cancer Tissue Models: A Review

Breast cancer is the most common cancer among women, and even though treatments are available, efficiency varies with the patients. In vitro 2D models are commonly used to develop new treatments. However, 2D models overestimate drug efficiency, which increases the failure rate in later phase III clinical trials. New model systems that allow extensive and efficient drug screening are thus required. Three-dimensional printed hydrogels containing active components for cancer cell growth are interesting candidates for the preparation of next generation cancer cell models. Macromolecules, obtained from marine- and land-based resources, can form biopolymers (polysaccharides such as alginate, chitosan, hyaluronic acid, and cellulose) and bioactive components (structural proteins such as collagen, gelatin, and silk fibroin) in hydrogels with adequate physical properties in terms of porosity, rheology, and mechanical strength. Hence, in this study attention is given to biofabrication methods and to the modification with biological macromolecules to become bioactive and, thus, optimize 3D printed structures that better mimic the cancer cell microenvironment. Ink formulations combining polysaccharides for tuning the mechanical properties and bioactive polymers for controlling cell adhesion is key to optimizing the growth of the cancer cells.

Responses of Rat Mesenchymal Stromal Cells to Nanocellulose with Different Functional Groups

Cellulose nanofibrils (CNFs) are multiscale hydrophilic biocompatible polysaccharide materials derived from wood and plants. TEMPO-mediated oxidation of CNFs (TO-CNF) turns some of the primary hydroxyl groups to carboxylate and aldehyde groups. Unlike carboxylic functional groups, there is little or no information about the biological role of the aldehyde groups on the surface of wood-based CNFs. In this work, we replaced the aldehyde groups in the TO-CNF samples with carboxyl groups by another oxidation treatment (TO-O-CNF) or with primary alcohols with terminal hydroxyl groups by a reduction reaction (TO-R-CNF). Rat mesenchymal stem/stromal cells (MSCs) derived from bone marrow were seeded on polystyrene tissue culture plates (TCP) coated with CNFs with and without aldehyde groups. TCP and TCP coated with bacterial nanocellulose (BNC) were used as control groups. Protein adsorption measurements demonstrated that more proteins were adsorbed from cell culture media on all CNF surfaces compared to BNC. Live/dead and lactate dehydrogenase assays confirmed that all nanocellulose biomaterials supported excellent cell viability. Interestingly, TO-R-CNF samples, which have no aldehyde groups, showed better cell spreading than BNC and comparable results to TCP. Unlike TO-O-CNF surfaces, which have no aldehyde groups either, TO-R-CNF stimulated cells, in osteogenic medium, to have higher alkaline phosphatase activity and to form more biomineralization than TCP and TO-CNF groups. These findings indicate that the presence of aldehyde groups (280 ± 14 μmol/g) on the surface of TEMPO-oxidized CNFs might have little or no effect on attachment, proliferation, and osteogenic differentiation of MSCs.

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.

Hydrogels from TEMPO-Oxidized Nanofibrillated Cellulose Support In Vitro Cultivation of Encapsulated Human Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are the most prominent type of adult stem cells for clinical applications. Three-dimensional (3D) cultivation of MSCs in biomimetic hydrogels provides a more physiologically relevant cultivation microenvironment for in vitro testing and modeling, thus overcoming the limitations of traditional planar cultivation methods. Cellulose nanofibers are an excellent candidate biomaterial for synthesis of hydrogels for this application, due to their biocompatibility, tunable properties, availability, and low cost. Herein, we demonstrate the capacity of hydrogels prepared from 2,2,6,6-tetramethylpiperidine-1-oxyl -oxidized and subsequently individualized cellulose-nanofibrils to support physiologically relevant 3D in vitro cultivation of human MSCs at low solid contents (0.2-0.5 wt %). Our results show that MSCs can spread, proliferate, and migrate inside the cellulose hydrogels, while the metabolic activity and proliferative capacity of the cells as well as their morphological characteristics benefit more in the lower bulk cellulose concentration hydrogels.

Gene-Expression Analysis of Human Fibroblasts Affected by 3D-Printed Carboxylated Nanocellulose Constructs

Three-dimensional (3D) printing has emerged as a highly valuable tool to manufacture porous constructs. This has major advantages in, for example, tissue engineering, in which 3D scaffolds provide a microenvironment with adequate porosity for cell growth and migration as a simulation of tissue regeneration. In this study, we assessed the suitability of three cellulose nanofibrils (CNF) that were obtained through 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO)-mediated oxidation. The CNFs were obtained by applying three levels of carboxylation, i.e., 2.5, 3.8, and 6.0 mmol sodium hypochlorite (NaClO) per gram of cellulose. The CNFs exhibited different nanofibrillation levels, affecting the corresponding viscosity and 3D printability of the CNF gels (0.6 wt%). The scaffolds were manufactured by micro-extrusion and the nanomechanical properties were assessed with nanoindentation. Importantly, fibroblasts were grown on the scaffolds and the expression levels of the marker genes, which are relevant for wound healing and proliferation, were assessed in order to reveal the effect of the 3D-scaffold microenvironment of the cells.

Nanocelluloses - Nanotoxicology, Safety Aspects and 3D Bioprinting

Nanocelluloses have good rheological properties that facilitate the extrusion of nanocellulose gels in micro-extrusion systems. It is considered a highly relevant characteristic that makes it possible to use nanocellulose as an ink component for 3D bioprinting purposes. The nanocelluloses assessed in this book chapter include wood nanocellulose (WNC), bacterial nanocellulose (BNC), and tunicate nanocellulose (TNC), which are often assumed to be non-toxic. Depending on various chemical and mechanical processes, both cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) can be obtained from the three mentioned nanocelluloses (WNC, BNC, and TNC). Pre/post-treatment processes (chemical and mechanical) cause modifications regarding surface chemistry and nano-morphology. Hence, it is essential to understand whether physicochemical properties may affect the toxicological profile of nanocelluloses. In this book chapter, we provide an overview of nanotoxicology and safety aspects associated with nanocelluloses. Relevant regulatory requirements are considered. We also discuss hazard assessment strategies based on tiered approaches for safety testing, which can be applied in the early stages of the innovation process. Ensuring the safe development of nanocellulose-based 3D bioprinting products will enable full market use of these sustainable resources throughout their life cycle.

Efficient removal of U(VI) in acidic environment with spent coffee grounds derived hydrogel

In this study, humic-like substances (HLSs) was extracted from spent coffee grounds (SCGs), and it together with poly acrylic acid (PAA), was used for the first time to synthesize hydrogel material, namely HLSs/PAA gel, by one-step radical polymerization. Its maximum theoretical sorption capacity toward U(VI) at pH 3.00 was 661.01 mg/g, and it could decrease the concentration of U(VI) in acidic actual groundwater from 0.2537 to 0.0003 mg/L, showing that the gel had excellent U(VI) removal efficiency in acidic environment. The SEM characterization of HLSs/PAA gel showed that its macroporous network structure maintained well after the sorption process, indicating that the gel had excellent acid-resistant property. Moreover, the gel exhibited excellent anti-interference performance in the interfering ions effect experiment. The gel integrates the merits of excellent U(VI) sorption properties, stability and anti-interference performance in acidic environment, and has promising application prospects in the remediation of acidic uranium wastewater.

Bioactive Hydrogels: Design and Characterization of Cellulose-Derived Injectable Composites

Cellulose represents a low cost, abundant, and renewable polysaccharide with great versatility; it has a hierarchical structure composed of nanofibers with high aspect ratio (3–4 nm wide, hundreds of μm long). TEMPO-mediated oxidation represents one of the most diffused methods to obtain cellulose nanofibers (CNFs): It is possible to obtain physically crosslinked hydrogels by means of divalent cation addition. The presence of inorganic components, such as calcium phosphates (CaP), can improve not only their mechanical properties but also the bioactivity of the gels. The aim of this work is to design and characterize a TEMPO-oxidized cellulose nanofibers (TOCNFs) injectable hydrogel embedded with inorganic particles, CaP and CaP-GO, for bone tissue regeneration. Inorganic particles act as physical crosslinkers, as proven by rheological characterization, which reported an increase in mechanical properties. The average load value registered in injection tests was in the range of 1.5–4.4 N, far below 30 N, considered a reasonable injection force upper limit. Samples were stable for up to 28 days and both CaP and CaP-GO accelerate mineralization as suggested by SEM and XRD analysis. No cytotoxic effects were shown on SAOS-2 cells cultured with eluates. This work demonstrated that the physicochemical properties of TOCNFs-based dispersions could be enhanced and modulated through the addition of the inorganic phases, maintaining the injectability and bioactivity of the hydrogels.

3D Printed Nanocellulose Scaffolds as a Cancer Cell Culture Model System

Current conventional cancer drug screening models based on two-dimensional (2D) cell culture have several flaws and there is a large need of more in vivo mimicking preclinical drug screening platforms. The microenvironment is crucial for the cells to adapt relevant in vivo characteristics and here we introduce a new cell culture system based on three-dimensional (3D) printed scaffolds using cellulose nanofibrils (CNF) pre-treated with 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO) as the structural material component. Breast cancer cell lines, MCF7 and MDA-MB-231, were cultured in 3D TEMPO-CNF scaffolds and were shown by scanning electron microscopy (SEM) and histochemistry to grow in multiple layers as a heterogenous cell population with different morphologies, contrasting 2D cultured mono-layered cells with a morphologically homogenous cell population. Gene expression analysis demonstrated that 3D TEMPO-CNF scaffolds induced elevation of the stemness marker CD44 and the migration markers VIM and SNAI1 in MCF7 cells relative to 2D control. T47D cells confirmed the increased level of the stemness marker CD44 and migration marker VIM which was further supported by increased capacity of holoclone formation for 3D cultured cells. Therefore, TEMPO-CNF was shown to represent a promising material for 3D cell culture model systems for cancer cell applications such as drug screening.

Characterization and Antibacterial Properties of Autoclaved Carboxylated Wood Nanocellulose

Cellulose nanofibrils (CNFs) were obtained by applying a chemical pretreatment consisting of autoclaving the pulp fibers in sodium hydroxide, combined with 2,2,6,6-tetramethylpiperidinyl-1-oxyl-mediated oxidation. Three levels of sodium hypochlorite were applied (2.5, 3.8, and 6.0 mmol/g) to obtain CNF qualities (CNF_2.5, CNF_3.8, and CNF_6.0) with varying content of carboxyl groups, that is, 1036, 1285, and 1593 μmol/g cellulose. The cytotoxicity and skin irritation potential (indirect tests) of the CNFs were determined according to standardized in vitro testing for medical devices. We here demonstrate that autoclaving (121 °C, 20 min), which was used to sterilize the gels, caused a modification of the CNF characteristics. This was confirmed by a reduction in the viscosity of the gels, a morphological change of the nanofibrils, by an increase of the ultraviolet-visible absorbance maxima at 250 nm, reduction of the absolute zeta potential, and by an increase in aldehyde content and reducing sugars after autoclaving. Fourier-transform infrared spectroscopy and wide-angle X-ray scattering complemented an extensive characterization of the CNF gels, before and after autoclaving. The antibacterial properties of autoclaved carboxylated CNFs were demonstrated in vitro (bacterial survival and swimming assays) on Pseudomonas aeruginosa and Staphylococcus aureus. Importantly, a mouse in vivo surgical-site infection model on S. aureus revealed that CNF_3.8 showed pronounced antibacterial effect and performed as good as the antiseptic Prontosan wound gel.

Bioinspired tissue-compliant hydrogels with multifunctions for synergistic surgery-photothermal therapy

Operation therapy is a common treatment for many cancers, but malignant tumors likely recur and metastasize after surgery, resulting in treatment failure. In this study, we aimed at synthesizing a multifunctional hydrogel patch that features multifunctions for synergistic surgery-photothermal therapy. Our polydopamine nanoparticle (PDA NP)-crosslinked poly(acrylamide-co-N-(3-aminopropyl)methacrylamide) hydrogels undergo several dynamic interactions (e.g., hydrogen bonds, π-π interactions, and imine bonds), which confer high stretchability (∼3430%) and adhesive strength to porcine skin (∼75 kPa) that mimics soft wound tissues. Furthermore, PDA NP incorporation into the hydrogel matrix endows it with photothermal responsivity under 808 nm irradiation. As a proof of concept, our hydrogel system was used to ablate residual tumors in 4T1 tumor-bearing mice models after surgery via photothermal therapy. We find that synergistic operation-photothermal therapy effectively eradicates solid tumors and prevents cancer recurrence in mice. We envision that our work provides an effective synergistic strategy for cancer treatment and offers great potential for clinical applications.

Cellulose Nanofibers for Encapsulation and Pluripotency Preservation in the Early Development of Embryonic Stem Cells

Materials for three-dimensional cultures aim to reproduce the function of the extracellular matrix, enabling cell adhesion and growth by remodeling the environment. However, embryonic stem cells (ESCs) must develop in environments that prevent adhesion and preserve their pluripotency. In this study, we used cellulose nanofiber hydrogels to mimic the developing conditions required for ESCs. These plant-based hydrogels are simultaneously biocompatible and exogenous to mammalian cells, preventing remodeling and attachment. The storage modulus of these hydrogels could be fine-tuned by varying the degree of oxidation to enable selective degradation. The ESCs proliferated in the artificial environment, forming increasingly large embryoid bodies for 15 days. Unlike traditional cultures in which ESCs begin differentiating upon the removal of the chemical inhibition, the expression of pluripotency markers in the ESC population remained high for the entire two weeks. Cellulase from Trichoderma reesei was used to retrieve the ESC cultures selectively. The proposed unique system is a prospective model with which to study the early development of embryonic cells, as well as a nonchemical method of preserving undifferentiated populations of ESCs.

Cellulose Mesh with Charged Nanocellulose Coatings as a Promising Carrier of Skin and Stem Cells for Regenerative Applications

Engineering artificial skin constructs is an ongoing challenge. An ideal material for hosting skin cells is still to be discovered. A promising candidate is low-cost cellulose, which is commonly fabricated in the form of a mesh and is applied as a wound dressing. Unfortunately, the structure and the topography of current cellulose meshes are not optimal for cell growth. To enhance the surface structure and the physicochemical properties of a commercially available mesh, we coated the mesh with wood-derived cellulose nanofibrils (CNFs). Three different types of mesh coatings are proposed in this study as a skin cell carrier: positively charged cationic cellulose nanofibrils (cCNFs), negatively charged anionic cellulose nanofibrils (aCNFs), and a combination of these two materials (c+aCNFs). These cell carriers were seeded with normal human dermal fibroblasts (NHDFs) or with human adipose-derived stem cells (ADSCs) to investigate cell adhesion, spreading, morphology, and proliferation. The negatively charged aCNF coating significantly improved the proliferation of both cell types. The positively charged cCNF coating significantly enhanced the adhesion of ADSCs only. The number of NHDFs was similar on the cCNF coatings and on the noncoated pristine cellulose mesh. However, the three-dimensional (3D) structure of the cCNF coating promoted cell survival. The c+aCNF construct proved to combine benefits from both types of CNFs, which means that the c+aCNF cell carrier is a promising candidate for further application in skin tissue engineering.

Nanocellulose in biomedical and biosensing applications: A review

Cellulose is abundant in the nature and nanocellulose (NC) in particular is regarded as a credible green substrate to be used in bio nanocomposites for various applications. NC exhibits excellent mechanical reinforcement properties comparable to conventionally used materials due to its high specific surface area and tunable surface chemistry. Additionally, low toxicity, biodegradability and biocompatibility of NC deem it a promising material for use in different biomedical applications. In this review, we highlight the biomedical applications of NC based hydrogels and aerogels/nanocomposites and advancements of their employment in the areas of wound dressing, drug delivery, tissue engineering, scaffolds and biomedical implants. This review also explores the recent use of NC in making biosensors for the detection of cholesterol, various enzymes and diseases, heavy metal ions in human sweat and urine, and for general health monitoring.

Recent Advances in Porous 3D Cellulose Aerogels for Tissue Engineering Applications: A Review

Current approaches in developing porous 3D scaffolds face various challenges, such as failure of mimicking extracellular matrix (ECM) native building blocks, non-sustainable scaffold fabrication techniques, and lack of functionality. Polysaccharides and proteins are sustainable, inexpensive, biodegradable, and biocompatible, with structural similarities to the ECM. As a result, 3D-structured cellulose (e.g., cellulose nanofibrils, nanocrystals and bacterial nanocellulose)-based aerogels with high porosity and interconnected pores are ideal materials for biomedical applications. Such 3D scaffolds can be prepared using a green, scalable, and cost-effective freeze-drying technique. The physicochemical, mechanical, and biological characteristics of the cellulose can be improved by incorporation of proteins and other polysaccharides. This review will focus on recent developments related to the cellulose-based 3D aerogels prepared by sustainable freeze-drying methods for tissue engineering applications. We will also provide an overview of the scaffold development criteria; parameters that influenced the aerogel production by freeze-drying; and in vitro and in vivo studies of the cellulose-based porous 3D aerogel scaffolds. These efforts could potentially help to expand the role of cellulose-based 3D scaffolds as next-generation biomaterials.

DLP 3D Printing Meets Lignocellulosic Biopolymers: Carboxymethyl Cellulose Inks for 3D Biocompatible Hydrogels

The development of new bio-based inks is a stringent request for the expansion of additive manufacturing towards the development of 3D-printed biocompatible hydrogels. Herein, methacrylated carboxymethyl cellulose (M-CMC) is investigated as a bio-based photocurable ink for digital light processing (DLP) 3D printing. CMC is chemically modified using methacrylic anhydride. Successful methacrylation is confirmed by ¹H NMR and FTIR spectroscopy. Aqueous formulations based on M-CMC/lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) photoinitiator and M-CMC/Dulbecco’s Modified Eagle Medium (DMEM)/LAP show high photoreactivity upon UV irradiation as confirmed by photorheology and FTIR. The same formulations can be easily 3D-printed through a DLP apparatus to produce 3D shaped hydrogels with excellent swelling ability and mechanical properties. Envisaging the application of the hydrogels in the biomedical field, cytotoxicity is also evaluated. The light-induced printing of cellulose-based hydrogels represents a significant step forward in the production of new DLP inks suitable for biomedical applications.

Biological responses to physicochemical properties of biomaterial surface

Biomedical scientists use chemistry-driven processes found in nature as an inspiration to design biomaterials as promising diagnostic tools, therapeutic solutions, or tissue substitutes. While substantial consideration is devoted to the design and validation of biomaterials, the nature of their interactions with the surrounding biological microenvironment is commonly neglected. This gap of knowledge could be owing to our poor understanding of biochemical signaling pathways, lack of reliable techniques for designing biomaterials with optimal physicochemical properties, and/or poor stability of biomaterial properties after implantation. The success of host responses to biomaterials, known as biocompatibility, depends on chemical principles as the root of both cell signaling pathways in the body and how the biomaterial surface is designed. Most of the current review papers have discussed chemical engineering and biological principles of designing biomaterials as separate topics, which has resulted in neglecting the main role of chemistry in this field. In this review, we discuss biocompatibility in the context of chemistry, what it is and how to assess it, while describing contributions from both biochemical cues and biomaterials as well as the means of harmonizing them. We address both biochemical signal-transduction pathways and engineering principles of designing a biomaterial with an emphasis on its surface physicochemistry. As we aim to show the role of chemistry in the crosstalk between the surface physicochemical properties and body responses, we concisely highlight the main biochemical signal-transduction pathways involved in the biocompatibility complex. Finally, we discuss the progress and challenges associated with the current strategies used for improving the chemical and physical interactions between cells and biomaterial surface.

Blending Gelatin and Cellulose Nanofibrils: Biocomposites with Tunable Degradability and Mechanical Behavior

Many studies show how biomaterial properties like stiffness, mechanical stimulation and surface topography can influence cellular functions and direct stem cell differentiation. In this work, two different natural materials, gelatin (Gel) and cellulose nanofibrils (CNFs), were combined to design suitable 3D porous biocomposites for soft-tissue engineering. Gel was selected for its well-assessed high biomimicry that it shares with collagen, from which it derives, while the CNFs were chosen as structural reinforcement because of their exceptional mechanical properties and biocompatibility. Three different compositions of Gel and CNFs, i.e., with weight ratios of 75:25, 50:50 and 25:75, were studied. The biocomposites were morphologically characterized and their total- and macro- porosity assessed, proving their suitability for cell colonization. In general, the pores were larger and more isotropic in the biocomposites compared to the pure materials. The influence of freeze-casting and dehydrothermal treatment (DHT) on mechanical properties, the absorption ability and the shape retention were evaluated. Higher content of CNFs gave higher swelling, and this was attributed to the pore structure. Cross-linking between CNFs and Gel using DHT was confirmed. The Young’s modulus increased significantly by adding the CNFs to Gel with a linear relationship with respect to the CNF amounts. Finally, the biocomposites were characterized in vitro by testing cell colonization and growth through a quantitative cell viability analysis performed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Additionally, the cell viability analysis was performed by the means of a Live/Dead test with Human mesenchymal stem cells (hMSCs). All the biocomposites had higher cytocompatibility compared to the pure materials, Gel and CNFs.

Production and Mechanical Characterisation of TEMPO-Oxidised Cellulose Nanofibrils/β-Cyclodextrin Films and Cryogels

Wood-based TEMPO-oxidised cellulose nanofibrils (toCNF) are promising materials for biomedical applications. Cyclodextrins have ability to form inclusion complexes with hydrophobic molecules and are considered as a method to bring new functionalities to these materials. Water sorption and mechanical properties are also key properties for biomedical applications such as drug delivery and tissue engineering. In this work, we report the modification with β-cyclodextrin (βCD) of toCNF samples with different carboxyl contents viz. 756 ± 4 µmol/g and 1048 ± 32 µmol/g. The modification was carried out at neutral and acidic pH (2.5) to study the effect of dissociation of the carboxylic acid group. Films processed by casting/evaporation at 40 °C and cryogels processed by freeze-drying were prepared from βCD modified toCNF suspensions and compared with reference samples of unmodified toCNF. The impact of modification on water sorption and mechanical properties was assessed. It was shown that the water sorption behaviour for films is driven by adsorption, with a clear impact of the chemical makeup of the fibres (charge content, pH, and adsorption of cyclodextrin). Modified toCNF cryogels (acidic pH and addition of cyclodextrins) displayed lower mechanical properties linked to the modification of the cell wall porosity structure. Esterification between βCD and toCNF under acidic conditions was performed by freeze-drying, and such cryogels exhibited a lower decrease in mechanical properties in the swollen state. These results are promising for the development of scaffold and films with controlled mechanical properties and added value due to the ability of cyclodextrin to form an inclusion complex with active principle ingredient (API) or growth factor (GF) for biomedical applications.

TEMPO-Nanocellulose/Ca2+ Hydrogels: Ibuprofen Drug Diffusion and In Vitro Cytocompatibility

Stable hydrogels with tunable rheological properties were prepared by adding Ca2+ ions to aqueous dispersions of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-oxidized and ultra-sonicated cellulose nanofibers (TOUS-CNFs). The gelation occurred by interaction among polyvalent cations and the carboxylic units introduced on TOUS-CNFs during the oxidation process. Both dynamic viscosity values and pseudoplastic rheological behaviour increased by increasing the Ca2+ concentration, confirming the cross-linking action of the bivalent cation. The hydrogels were proved to be suitable controlled release systems by measuring the diffusion coefficient of a drug model (ibuprofen, IB) by high-resolution magic angle spinning (HR-MAS) nuclear magnetic resonance (NMR) spectroscopy. IB was used both as free molecule and as a 1:1 pre-formed complex with β-cyclodextrin (IB/β-CD), showing in this latter case a lower diffusion coefficient. Finally, the cytocompatibility of the TOUS-CNFs/Ca2+ hydrogels was demonstrated in vitro by indirect and direct tests conducted on a L929 murine fibroblast cell line, achieving a percentage number of viable cells after 7 days higher than 70%.

Rice husk derived double network hydrogel as efficient adsorbent for Pb(II), Cu(II) and Cd(II) removal in individual and multicomponent systems

In this study, lignin extracted from rice husk was used to synthesis double network hydrogel adsorbent, named RH-CTS/PAM gel. RH-CTS/PAM gel exhibited macroporous structure and high buried water content, which gave rise to the exceptional adsorption performance. As results, in individual systems, the equilibrium time of Pb(II), Cu(II) and Cd(II) with initial concentration of 200 mg/L could be reached within 10 min, with the theoretical maximum adsorption capacity of 374.32, 196.68 and 268.98 mg/g, respectively. The adsorption rate and capacity of Pb(II), Cu(II) and Cd(II) in multicomponent systems were lower than that of individual systems. However, in a few cases of ternary system, higher adsorption rate and capacity was observed compare to binary systems. Adsorption mechanism indicated that both oxygen-containing and nitrogen-containing functional groups played a dominant role during the adsorption process, and mainly through chemical interaction along with a small amount of physical interaction.

Generation of Cost-Effective Paper-Based Tissue Models through Matrix-Assisted Sacrificial 3D Printing

Due to the combined advantages of cellulose and nanoscale (diameter 20-60 nm), bacterial cellulose possesses a series of attractive features including its natural origin, moderate biosynthesis process, good biocompatibility, and cost-effectiveness. Moreover, bacterial cellulose nanofibers can be conveniently processed into three-dimensional (3D) intertwined structures and form stable paper devices after simple drying. These advantages make it suitable as the material for construction of organ-on-a-chip devices using matrix-assisted sacrificial 3D printing. We successfully fabricated various microchannel structures embedded in the bulk bacterial cellulose hydrogels and retained their integrity after the drying process. Interestingly, these paper-based devices containing hollow microchannels could be rehydrated and populated with relevant cells to form vascularized tissue models. As a proof-of-concept demonstration, we seeded human umbilical vein endothelial cells (HUVECs) into the microchannels to obtain the vasculature and inoculated the MCF-7 cells onto the surrounding matrix of the paper device to build a 3D paper-based vascularized breast tumor model. The results showed that the microchannels were perfusable, and both HUVECs and MCF-7 cells exhibited favorable proliferation behaviors. This study may provide a new strategy for constructing simple and low-cost in vitro tissue models, which may find potential applications in drug screening and personalized medicine.

Development & Characterization of Fluorescently Tagged Nanocellulose for Nanotoxicological Studies

The rapid adoption of nanocellulose-based engineered nanomaterials (CNM) by many industries generates environmental health and safety (EHS) concerns. This work presents the development of fluorescently tagged CNM which can be used to study their interactions with biological systems. Specifically, cellulose nano-fibrils and cellulose nano-crystals with covalently attached fluorescein isothiocyanate (FITC) molecules on their surface were synthesized. The fluorescence of the FITC-tagged materials was assessed along with potential FITC detachment under pH conditions encountered in the human gastrointestinal tract, in intracellular compartments, and in cell culture media. Finally, the potential cytotoxicity due to the presence of FITC molecules on the surface of CNM was assessed using a cellular gut epithelium model. The results showed that neither FITC-CNF nor FITC-CNC were cytotoxic and that they have a comparable bioactivity to their untagged counterparts, rendering them suitable for biological studies.

Surface Engineered Biomimetic Inks Based on UV Cross-Linkable Wood Biopolymers for 3D Printing

Owing to their superior mechanical strength and structure similarity to the extracellular matrix, nanocelluloses as a class of emerging biomaterials have attracted great attention in three-dimensional (3D) bioprinting to fabricate various tissue mimics. Yet, when printing complex geometries, the desired ink performance in terms of shape fidelity and object resolution demands a wide catalogue of tunability on the material property. This paper describes surface engineered biomimetic inks based on cellulose nanofibrils (CNFs) and cross-linkable hemicellulose derivatives for UV-aided extrusion printing, being inspired by the biomimetic aspect of intrinsic affinity of heteropolysaccharides to cellulose in providing the ultrastrong but flexible plant cell wall structure. A facile aqueous-based approach was established for the synthesis of a series of UV cross-linkable galactoglucomannan methacrylates (GGMMAs) with tunable substitution degrees. The rapid gelation window of the formulated inks facilitates the utilization of these wood-based biopolymers as the feeding ink for extrusion-based 3D printing. Most importantly, a wide and tunable spectrum ranging from 2.5 to 22.5 kPa of different hydrogels with different mechanical properties could be achieved by varying the substitution degree in GGMMA and the compositional ratio between GGMMA and CNFs. Used as the seeding matrices in the cultures of human dermal fibroblasts and pancreatic tumor cells, the scaffolds printed with the CNF/GGMMA inks showed great cytocompatibility as well as supported the matrix adhesion and proliferative behaviors of the studied cell lines. As a new family of 3D printing feedstock materials, the CNF/GGMMA ink will broaden the map of bioinks, which potentially meets the requirements for a variety of in vitro cell-matrix and cell-cell interaction studies in the context of tissue engineering, cancer cell research, and high-throughput drug screening.

Three-Dimensional Stable Alginate-Nanocellulose Gels for Biomedical Applications: Towards Tunable Mechanical Properties and Cell Growing

Hydrogels have been studied as promising materials in different biomedical applications such as cell culture in tissue engineering or in wound healing. In this work, we synthesized different nanocellulose-alginate hydrogels containing cellulose nanocrystals, TEMPO-oxidized cellulose nanocrystals (CNCTs), cellulose nanofibers or TEMPO-oxidized cellulose nanofibers (CNFTs). The hydrogels were freeze-dried and named as gels. The nanocelluloses and the gels were characterized by different techniques such as Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMTA), while the biological features were characterized by cytotoxicity and cell growth assays. The addition of CNCTs or CNFTs in alginate gels contributed to the formation of porous structure (diameter of pores in the range between 40 and 150 μm). TEMPO-oxidized cellulose nanofibers have proven to play a crucial role in improving the dimensional stability of the samples when compared to the pure alginate gels, mainly after a thermal post-treatment of these gels containing 50 wt % of CNFT, which significantly increased the Ca2+ crosslinking density in the gel structure. The morphological characteristics, the mechanical properties, and the non-cytotoxic behavior of the CNFT-alginate gels improved bioadhesion, growth, and proliferation of the cells onto the gels. Thus, the alginate-nanocellulose gels might find applications in tissue engineering field, as for instance, in tissue repair or wound healing applications.

Inflammatory responses and tissue reactions to wood-Based nanocellulose scaffolds

Two wood-derived cellulose nanofibril (CNF) porous scaffolds were prepared by TEMPO-oxidation and carboxymethylation. The effects of these scaffolds on the production of inflammatory cytokines by human macrophage-like cells (U937) was profiled in vitro after 1 and 3 days and in subcutaneous tissues of rats after 4 and 30 days, using PCR and Multiplex arrays. Tissue culture plates (TCP) and gelatin scaffolds served as controls in vitro and in vivo respectively. After 3 days in vitro, there was no significant difference between the effects of CNF scaffolds and TCP on the production of chemokines/growth factors and pro-inflammatory cytokines. At day 4 in vivo there was significantly higher gene expression of the anti-inflammatory IL-1Ra in the CNF scaffolds than the gelatin scaffold. Production of IL-1β, IL-6, MCP-1, MIP-1α CXCL-1 and M-CSF was significantly less than in the gelatin, demonstrating an early mild inflammatory response. At day 30, both CNF scaffolds significantly stimulated the production of the anti-inflammatory cytokine IL-10. Unlike gelatin, neither CNF scaffold had degraded 180 days post-implantation. The slow degradation of CNF scaffolds resulted in a foreign body reaction, with high production of IL-1β, IL-2, TNF-α, IFN-ϒ, MCP-1, MIP-1α, M-CSF, VEGF cytokines and expression of MMP-9 gene. The surface chemistry of the CNF scaffolds elicited a modest effect on cytokine production and did not shift the inflammatory profile in vitro or in vivo. The decisive role in development of the foreign body reaction was the slow degradation of the CNF scaffolds.

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.

Polymeric 3D scaffolds for tissue regeneration: Evaluation of biopolymer nanocomposite reinforced with cellulose nanofibrils

Biopolymers such as gelatin (Gel) and cellulose nanofibrils (CNF) have many of the essential requirements for being used as scaffolding materials in tissue regeneration; biocompatibility, surface chemistry, ability to generate homogeneous hydrogels and 3D structures with suitable pore size and interconnection, which allows cell colonization and proliferation. The purpose of this study was to investigate whether the mechanical behaviour of the Gel matrix can be improved by means of functionalization with cellulose nanofibrils and proper cross-linking treatments. Blending processes were developed to achieve a polymer nanocomposite incorporating the best features of both biopolymers: biomimicry of the Gel and structural reinforcement by the CNF. The designed 3D structures underline interconnected porosity achieved by freeze-drying process, improved mechanical properties and chemical stability that are tailored by CNF addition and different cross-linking approaches. In vitro evaluations reveal the preservation of the biocompatibility of Gel and its good interaction with cells by promoting cell colonization and proliferation. The results support the addition of cellulose nanofibrils to improve the mechanical behaviour of 3D porous structures suitable as scaffolding for tissue regeneration.