Cellulose-Based Gels

Structure-properties relationships of defined CNF single-networks crosslinked by telechelic PEGs

The high structural anisotropy and colloidal stability of cellulose nanofibrils' enable the creation of self-standing fibrillar hydrogel networks at very low solid contents. Adding methacrylate moieties on the surface of TEMPO oxidized CNFs allows the formation of more robust covalently crosslinked networks by free radical polymerization of acrylic monomers, exploiting the mechanical properties of these networks more efficiently. This technique yields strong and elastic networks but with an undefined network structure. In this work, we use acrylate-capped telechelic polymers derived from the step-growth polymerization of PEG diacrylate and dithiothreitol to crosslink methacrylated TEMPO-oxidized cellulose nanofibrils (MATO CNF). This combination resulted in flexible and strong hydrogels, as observed through rheological studies, compression and tensile loading. The structure and mechanical properties of these hydrogel networks were found to depend on the dimensions of the CNFs and polymer crosslinkers. The structure of the networks and the role of individual components were evaluated with SAXS (Small-Angle X-ray Scattering) and photo-rheology. A thorough understanding of hybrid CNF/polymer networks and how to best exploit the capacity of these networks enable further advancement of cellulose-based materials for applications in packaging, soft robotics, and biomedical engineering.

Nanocellulose-based hydrogels as versatile materials with interesting functional properties for tissue engineering applications

Tissue engineering has emerged as a remarkable field aiming to restore or replace damaged tissues through the use of biomimetic constructs. Among the diverse materials investigated for this purpose, nanocellulose-based hydrogels have garnered attention due to their intriguing biocompatibility, tunable mechanical properties, and sustainability. Over the past few years, numerous research works have been published focusing on the successful use of nanocellulose-based hydrogels as artificial extracellular matrices for regenerating various types of tissues. The review emphasizes the importance of tissue engineering, highlighting hydrogels as biomimetic scaffolds, and specifically focuses on the role of nanocellulose in composites that mimic the structures, properties, and functions of the native extracellular matrix for regenerating damaged tissues. It also summarizes the types of nanocellulose, as well as their structural, mechanical, and biological properties, and their contributions to enhancing the properties and characteristics of functional hydrogels for tissue engineering of skin, bone, cartilage, heart, nerves and blood vessels. Additionally, recent advancements in the application of nanocellulose-based hydrogels for tissue engineering have been evaluated and documented. The review also addresses the challenges encountered in their fabrication while exploring the potential future prospects of these hydrogel matrices for biomedical applications.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.

Natural Polymer-Based Hydrogels: From Polymer to Biomedical Applications

Hydrogels prepared from natural polymer have attracted extensive attention in biomedical fields such as drug delivery, wound healing, and regenerative medicine due to their good biocompatibility, degradability, and flexibility. This review outlines the commonly used natural polymer in hydrogel preparation, including cellulose, chitosan, collagen/gelatin, alginate, hyaluronic acid, starch, guar gum, agarose, and dextran. The polymeric structure and process/synthesis of natural polymers are illustrated, and natural polymer-based hydrogels including the hydrogel formation and properties are elaborated. Subsequently, the biomedical applications of hydrogels based on natural polymer in drug delivery, tissue regeneration, wound healing, and other biomedical fields are summarized. Finally, the future perspectives of natural polymers and hydrogels based on them are discussed. For natural polymers, novel technologies such as enzymatic and biological methods have been developed to improve their structural properties, and the development of new natural-based polymers or natural polymer derivatives with high performance is still very important and challenging. For natural polymer-based hydrogels, novel hydrogel materials, like double-network hydrogel, multifunctional composite hydrogels, and hydrogel microrobots have been designed to meet the advanced requirements in biomedical applications, and new strategies such as dual-cross-linking, microfluidic chip, micropatterning, and 3D/4D bioprinting have been explored to fabricate advanced hydrogel materials with designed properties for biomedical applications. Overall, natural polymeric hydrogels have attracted increasing interest in biomedical applications, and the development of novel natural polymer-based materials and new strategies/methods for hydrogel fabrication are highly desirable and still challenging.

Tailoring the Swelling-Shrinkable Behavior of Hydrogels for Biomedical Applications

Hydrogels with tailor-made swelling-shrinkable properties have aroused considerable interest in numerous biomedical domains. For example, as swelling is a key issue for blood and wound extrudates absorption, the transference of nutrients and metabolites, as well as drug diffusion and release, hydrogels with high swelling capacity have been widely applicated in full-thickness skin wound healing and tissue regeneration, and drug delivery. Nevertheless, in the fields of tissue adhesives and internal soft-tissue wound healing, and bioelectronics, non-swelling hydrogels play very important functions owing to their stable macroscopic dimension and physical performance in physiological environment. Moreover, the negative swelling behavior (i.e., shrinkage) of hydrogels can be exploited to drive noninvasive wound closure, and achieve resolution enhancement of hydrogel scaffolds. In addition, it can help push out the entrapped drugs, thus promote drug release. However, there still has not been a general review of the constructions and biomedical applications of hydrogels from the viewpoint of swelling-shrinkable properties. Therefore, this review summarizes the tactics employed so far in tailoring the swelling-shrinkable properties of hydrogels and their biomedical applications. And a relatively comprehensive understanding of the current progress and future challenge of the hydrogels with different swelling-shrinkable features is provided for potential clinical translations.

Shape-recovering nanocellulose networks: Preparation, characterization and modeling

Development of strong cellulose nanofibril (CNF) networks for advanced applications, such as in the biomedical field, is of high importance owing to the biocompatible nature and plant-based origin of cellulose nanofibrils. Nevertheless, lack of mechanical strength and complex synthesis methods hinder the application of these materials in areas where both toughness and manufacturing simplicity are required. In this work, we introduce a facile method for the synthesis of a low solid content (< 2 wt%), covalently crosslinked CNF hydrogel where Poly (N-isopropylacrylamide) (NIPAM) chains are utilized as crosslinks between the nanofibrils. The resulting networks have the capability to fully recover the shape in which they were formed after various drying and rewetting cycles. Characterization of the hydrogel and its constitutive components was performed using X-ray scattering, rheological investigations and uniaxial testing in compression. Influence of covalent crosslinks was compared with networks crosslinked by the addition of CaCl₂. Among other things the results show that the mechanical properties of the hydrogels can be tuned by controlling the ionic strength of the surrounding medium. Finally, a mathematical model was developed based on the experimental results, which describes and predicts to a decent degree the large-deformation, elastoplastic behavior, and fracture of these networks.

Lipid nanoparticles strategies to modify pharmacokinetics of central nervous system targeting drugs: Crossing or circumventing the blood-brain barrier (BBB) to manage neurological disorders

The main limitation to the success of central nervous system (CNS) therapies lies in the difficulty for drugs to cross the blood-brain barrier (BBB) and reach the brain. Regarding its structure and enzymatic complexity, crossing the BBB is a challenge, although several alternatives have been identified. For instance, the use of drugs encapsulated in lipid nanoparticles has been described as one of the most efficient approaches to bypass the BBB, as they allow the passage of drugs through this barrier, improving brain bioavailability. In particular, solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) have been a focus of research related to drug delivery to the brain. These systems provide protection of lipophilic drugs, improved delivery and bioavailability, having a major impact on treatments outcomes. In addition, the use of lipid nanoparticles administered via routes that transport drugs directly into the brain seems a promising solution to avoid the difficulties in crossing the BBB. For instance, the nose-to-brain route has gained considerable interest, as it has shown efficacy in 3D human nasal models and in animal models. This review addresses the state of the art on the use of lipid nanoparticles to modify the pharmacokinetics of drugs employed in the management of neurological disorders. A description of the structural components of the BBB, the role of the neurovascular unit and limitations for drugs to entry into the CNS is first addressed, along with the developments to increase drug delivery to the brain, with a special focus on lipid nanoparticles. In addition, the obstacle of BBB complexity in the creation of new effective drugs for the treatment of the most prevalent neurological disorders is also addressed. Finally, the proposed strategies for lipid nanoparticles to reach the CNS, crossing or circumventing the BBB, are described. Although promising results have been reported, especially with the nose-to-brain route, they are still ongoing to assess its real efficacy in vivo in the management of neurological disorders.

A Comprehensive Review of Cross-Linked Gels as Vehicles for Drug Delivery to Treat Central Nervous System Disorders

Gels are attractive candidates for drug delivery because they are easily producible while offering sustained and/or controlled drug release through various mechanisms by releasing the therapeutic agent at the site of action or absorption. Gels can be classified based on various characteristics including the nature of solvents used during preparation and the method of cross-linking. The development of novel gel systems for local or systemic drug delivery in a sustained, controlled, and targetable manner has been at the epitome of recent advances in drug delivery systems. Cross-linked gels can be modified by altering their polymer composition and content for pharmaceutical and biomedical applications. These modifications have resulted in the development of stimuli-responsive and functionalized dosage forms that offer many advantages for effective dosing of drugs for Central Nervous System (CNS) conditions. In this review, the literature concerning recent advances in cross-linked gels for drug delivery to the CNS are explored. Injectable and non-injectable formulations intended for the treatment of diseases of the CNS together with the impact of recent advances in cross-linked gels on studies involving CNS drug delivery are discussed.

Plant Polysaccharides in Engineered Pharmaceutical Gels

Hydrogels are a great ally in the pharmaceutical and biomedical areas. They have a three-dimensional polymeric structure that allows the swelling of aqueous fluids, acting as an absorbent, or encapsulating bioactive agents for controlled drug release. Interestingly, plants are a source of biogels, specifically polysaccharides, composed of sugar monomers. The crosslinking of these polymeric chains forms an architecture similar to the extracellular matrix, enhancing the biocompatibility of such materials. Moreover, the rich hydroxyl monomers promote a hydrophilic behavior for these plant-derived polysaccharide gels, enabling their biodegradability and antimicrobial effects. From an economic point of view, such biogels help the circular economy, as a green material can be obtained with a low cost of production. As regards the bio aspect, it is astonishingly attractive since the raw materials (polysaccharides from plants-cellulose, hemicelluloses, lignin, inulin, pectin, starch, guar, and cashew gums, etc.) might be produced sustainably. Such properties make viable the applications of these biogels in contact with the human body, especially incorporating drugs for controlled release. In this context, this review describes some sources of plant-derived polysaccharide gels, their biological function, main methods for extraction, remarkable applications, and properties in the health field.

Advances in Cellulose-Based Hydrogels for Biomedical Engineering: A Review Summary

In recent years, hydrogel-based research in biomedical engineering has attracted more attention. Cellulose-based hydrogels have become a research hotspot in the field of functional materials because of their outstanding characteristics such as excellent flexibility, stimulus-response, biocompatibility, and degradability. In addition, cellulose-based hydrogel materials exhibit excellent mechanical properties and designable functions through different preparation methods and structure designs, demonstrating huge development potential. In this review, we have systematically summarized sources and types of cellulose and the formation mechanism of the hydrogel. We have reviewed and discussed the recent progress in the development of cellulose-based hydrogels and introduced their applications such as ionic conduction, thermal insulation, and drug delivery. Also, we analyzed and highlighted the trends and opportunities for the further development of cellulose-based hydrogels as emerging materials in the future.

Confronting the Challenge of Cellulose Molecular Weight Measurement: An Accurate, Rapid, and Universal Method with Ionic Liquid as an Additive

Molecular weight parameters are the key fundamental information of polymer materials, but the accurate characterization of the molecular weight of cellulose is extremely difficult due to its strong hydrogen bonding network. Herein, we demonstrated two new methods to accurately and rapidly measure the molecular weight parameters of cellulose by using 1-butyl-3-methylimidazolium acetate (BmimAc) ionic liquid (IL) as an additive. Cellulose is rapidly dissolved in BmimAc/DMSO (1:1, w/w) at room temperature at first. Then, DMAc is added to dilute the solution, and finally, the molecular weight and molecular weight distribution of cellulose samples are measured by the gel permeation chromatography (GPC) method with BmimAc/DMSO/DMAc (1:1:18, w/w) as the mobile phase. Such a simple method is suitable to all kinds of cellulose samples and exhibits an extremely high analytical efficiency which is 50 times higher than the previous GPC methods. In addition, a viscosity method that is available for industrial application was proposed by using the BmimAc/DMSO/DMAc (1:1:8, w/w) system with low viscosity. The relationship between the intrinsic viscosity of the cellulose/BmimAc/DMSO/DMAc solution and the molecular weight of cellulose is well established and is applicable to cellulose samples of M_w = 4.5 × 10⁴ to 1.8 × 10⁶, which is the widest applicable range among the reported viscosity methods. Overall, two new methods based on the use of BmimAc as an additive have many advantages, such as wide applicable range, simple preparation process, mild dissolution condition, no degradation or aggregation of cellulose, high accuracy, fast detection, and low IL consumption, overcoming the existing problems in the traditional methods. It is expected to be used as a standard procedure to characterize the molecular weight of cellulose in academia and industries.

Rheological and tribological properties of low-temperature greases based on cellulose acetate butyrate gel

A new approach to produce biodegradable low-temperature greases, based on cellulose acetate butyrate (CAB) that dissolves in the medium of acetyl tributyl citrate (ATBC) at high temperatures and produces a gel during cooling because of phase separation, is proposed. Rheological properties of CAB solutions and gels in a wide temperature range from -80 °C to 160 °C were investigated with characterization of their viscoelasticity and viscoplasticity that arise because of the sol-gel transition of CAB/ATBC systems at 55 °C. CAB gelation reduces the wear coefficient tenfold when using ATBC as a lubricant but leads to a noticeable increase in the friction coefficient. To improve tribological properties of gel greases, additives of various solid particles were used: hexagonal boron nitride, graphite, and polytetrafluoroethylene (PTFE). The introduction of 10% to 30% additives in a gel grease containing 10% CAB has shown the preference of PTFE at a concentration of 10% for improving grease tribological characteristics.

Load-bearing hydrogels ionically reinforced through competitive ligand exchanges

Fast advances in soft robotics and tissue engineering demand for new soft materials whose mechanical properties can be interchangeably and locally varied, thereby enabling, for example, the design of soft joints within an integral material. Inspired by nature, we introduce a competitive ligand-mediated approach to selectively and interchangeably reinforce metal-coordinated hydrogels. This is achieved by reinforcing carboxylate-containing hydrogels with Fe³⁺ ions. Key to achieving a homogeneous, predictable reinforcement of the hydrogels is the presence of weak complexation agents that delay the formation of metal-complexes within the hydrogels, thereby allowing a homogeneous distribution of the metal ions. The resulting metal-reinforced hydrogels show a compressive modulus of up to 2.5 MPa, while being able to withstand pressures as high as 0.6 MPa without appreciable damage. Competitive ligand exchanges offer an additional advantage: they enable non-linear compositional changes that, for example, allow the formation of joints within these hydrogels. These features open up new possibilities to extend the field of use of metal reinforced hydrogels to load-bearing applications that are omnipresent for example in soft robots and actuators.

Effect of Cellulose Nanocrystal Addition on the Physicochemical Properties of Hydroxypropyl Guar-Based Intelligent Films

As an important functional material in food industry, intelligent packaging films can bring great convenience for consumers in the field of food preservation and freshness detection. Herein, we fabricated pH-sensing films employing hydroxypropyl guar (HPG), 1-butyl-3-methylimidazolium chloride (BmimCl), and anthocyanin (Anth). Besides, the effects of adding cellulose nanocrystals (CNC) into the composite films upon the films’ structures and physicochemical properties are elucidated. The addition of CNC promoted more compact film structures. Moreover, CNC dramatically improved several properties of the pH-sensing films, including the distinguishability of their color changes, sensitivity to pH, permeability to oxygen and water vapor, solvent resistance, durability, and low-temperature resistance. These results expand the application range of pH-sensing films containing CNC in the fields of food freshness detection and intelligent packaging.

Room-Temperature Self-Standing Cellulose-Based Hydrogel Electrolytes for Electrochemical Devices

The trend of research towards more sustainable materials is pushing the application of biopolymers in a variety of unexplored fields. In this regard, hydrogels are attracting significant attention as electrolytes for flexible electrochemical devices thanks to their combination of ionic conductivity and mechanical properties. In this context, we present the use of cellulose-based hydrogels as aqueous electrolytes for electrochemical devices. These materials were obtained by crosslinking of hydroxyethyl cellulose (HEC) with divinyl sulfone (DVS) in the presence of carboxymethyl cellulose (CMC), creating a semi-IPN structure. The reaction was confirmed by NMR and FTIR. The small-amplitude oscillatory shear (SAOS) technique revealed that the rheological properties could be conveniently varied by simply changing the gel composition. Additionally, the hydrogels presented high ionic conductivity in the range of mS cm⁻¹. The ease of synthesis and processing of the hydrogels allowed the assembly of an all-in-one electrochromic device (ECD) with high transmittance variation, improved switching time and good color efficiency. On the other hand, the swelling ability of the hydrogels permits the tuning of the electrolyte to improve the performance of a printed Zinc/MnO₂ primary battery. The results prove the potential of cellulose-based hydrogels as electrolytes for more sustainable electrochemical devices.

Directionally-Grown Carboxymethyl Cellulose/Reduced Graphene Oxide Aerogel with Excellent Structure Stability and Adsorption Capacity

A novel three-dimensional carboxymethyl cellulose (CMC)/reduced graphene oxide (rGO) composite aerogel crosslinked by poly (methyl vinyl ether-co-maleic acid)/poly (ethylene glycol) system via a directional freezing technique exhibits high structure stability while simultaneously maintaining its excellent adsorption capacity to remove organic dyes from liquid. A series of crosslinked aerogels with different amounts of GO were investigated for their adsorption capacity of methylene blue (MB), which were found to be superb adsorbents, and the maximum adsorption capacity reached 520.67 mg/g with the incorporation of rGO. The adsorption kinetics and isotherm studies revealed that the adsorption process followed the pseudo-second-order model and the Langmuir adsorption model, and the adsorption was a spontaneous process. Furthermore, the crosslinked aerogel can be easily recycled after washing with dilute HCl solution, which could retain over 97% of the adsorption capacity after recycling five times. These excellent properties endow the crosslinked CMC/rGO aerogel’s potential in wastewater treatment and environment protection.

3D Printing of Gelled and Cross-Linked Cellulose Solutions, an Exploration of Printing Parameters and Gel Behaviour

In recent years, 3D printing has enabled the fabrication of complex designs, with low-cost customization and an ever-increasing range of materials. Yet, these abilities have also created an enormous challenge in optimizing a large number of process parameters, especially in the 3D printing of swellable, non-toxic, biocompatible and biodegradable materials, so-called bio-ink materials. In this work, a cellulose gel, made out of aqueous solutions of cellulose, sodium hydroxide and urea, was used to demonstrate the formation of a shear thinning bio-ink material necessary for an extrusion-based 3D printing. After analysing the shear thinning behaviour of the cellulose gel by rheometry a Design of Experiments (DoE) was applied to optimize the 3D bioprinter settings for printing the cellulose gel. The optimum print settings were then used to print a human ear shape, without a need for support material. The results clearly indicate that the found settings allow the printing of more complex parts with high-fidelity. This confirms the capability of the applied method to 3D print a newly developed bio-ink material.