Nanocellulose in biomedicine: Current status and future prospect

Due to remarkable physical properties, especially surface chemistry and excellent biological properties, such as low toxicity, biocompatibility and biodegradability, nanocellulose has gained much attention for its use as biomedical material in the last years. This type of material is widely applied in medical implants, tissue engineering, drug delivery, wound-healing, cardiovascular applications, among others. This paper presents a brief review on the use of nanocellulose in biomedical area. Three different types of nanocellulose, namely cellulose nanocrystals (CNC), cellulose nanofibrils (CNF) and bacterial cellulose (BC) are discussed in terms of their production processes, properties and promising applications, based on the most recent published scientific works. In the same way, possible nanocellulose functional modifications, such as fluorescent modification, with the aim to improve specific properties and behavior are also discussed. Finally, an overview about the future of nanocellulose-based materials in the biomedical field is presented and analyzed.

Nanocellulose is one of the most promising natural polymers to substitute conventional polymers currently employed for tissue engineering applications. The three different types of nanocellulose (cellulose nanocrystals, cellulose nanofibrils, and bacterial cellulose) are presented in this chapter. However, the main focus of discussion is bacterial cellulose (BC) for tissue engineering applications, owing to its meritorious properties such as physical (high purity, permeability, water absorption capacity, and porosity), mechanical (high tensile strength), and biological properties (good biocompatibility and biodegradability). These physical, biological, and mechanical properties of BC are features that enable BC membranes to function as effective temporary wound dressing biomaterial compared with conventional wound dressing materials. BC membranes can easily absorb exudate during wound dressing process and are smoothly removed from a wound surface after recovery. BC used for permanent implantation can remain in the body without causing any toxic or inflammatory reactions due to its good biocompatibility properties. In addition, BC membranes are developed in any shape and size, which enhance their suitability to cover large and difficult areas of the body. Hence, interest in BC biofabricated materials has accelerated steadily as a result of their remarkable potential usage in tissue engineering applications.

Competitive adsorption of cellulose nanofibers at oil-water interface in Pickering emulsion is reported here. Dodecane-in-water emulsions stabilized by either of two types of nanocelluloses, cellulose nanocrystals (CNC) or cellulose nanofibrils (CNF), as well as by their binary mixtures with increasing fractions of CNC, were prepared using particle concentrations of 0.1–0.5 wt% and studied. Despite differences in shape and morphology, both forms of nanofibers produced stable emulsion droplets even at low particle concentrations (0.1 wt%), with CNC producing smaller droplets and emulsions with higher stability. When mixed, an increased fraction of CNC in the mixture reduced the average droplet size, which however applied only for higher contents of oil (30 and 50 wt%) and higher total contents of cellulose particles used under emulsification. The CNC particles controlled the size of emulsion droplets, while the role of CNF contributed to the further surface coverage. When the fraction of CNF in the mixture increased, the capability of CNC particles to readily adsorb at the oil-water interface was reduced by the CNF nanofibrils present in aqueous phase. The stability of emulsions with respect to changes in droplet size and creaming index was influenced more by oil content and total particle concentration than by the fraction of CNC present in the mixture.

Cellulose from sources to nanocellulose and an overview of synthesis and properties of nanocellulose/zinc oxide nanocomposite materials

Plant-derived nanocellulose particles, such as cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs), are becoming increasingly popular for a wide range of applications. In particular, when they are employed as rheology modifiers and/or fillers, a choice between CNFs and CNCs is often not obvious. Here, we present the results of a comparative study on the rheological properties of suspensions and gels of carboxymethylated CNFs and CNCs with the same surface chemistry, surface density of charged groups, and thickness. We demonstrate that, at the same weight concentration, CNF suspensions have much higher viscosity and storage modulus, which is due to their longer length providing many entanglements. However, when comparing at the same nanoparticle concentration relative to C*, the situation is reversed: viscosity and storage modulus of CNCs appear to be much higher. This may be due in particular to the higher rigidity and intrinsic strength of highly crystalline CNCs. The gel points for CNF and CNC suspensions (without crosslinker) were compared for the first time. It was found that in the case of CNFs, the gel point occurs at a 3.5-fold lower concentration compared to that of CNCs. Hydrogels were also obtained by crosslinking negatively charged nanocellulose particles of both types by divalent calcium cations. For the first time, the thermodynamic parameters of the crosslinking of carboxymethylated CNFs by calcium ions were determined. Isothermal titration calorimetry data revealed that, for both CNFs and CNCs, crosslinking is endothermic and driven by increasing entropy, which is most likely due to the release of water molecules surrounding the interacting nanoparticles and Ca2+ ions. The addition of CaCl2 to suspensions of nanocellulose particles leads to an increase in the storage modulus; the increase being much more significant for CNCs. Physically crosslinked hydrogels of both CNFs and CNCs can be reversibly destroyed by increasing the shear rate and then quickly recover up to 85% of their original viscosity when the shear rate decreases. The recovery time for CFC networks is only 6 s, which is much shorter than that of CNC networks. This property is promising for various applications, where nanocellulose suspensions are subjected to high shear forces (e.g., mixing, stirring, extrusion, injection, coating) and then need to regain their original properties when at rest.

Characterization of lipid emulsions during in vitro digestion in the presence of three types of nanocellulose

The recent strategies in preparation of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) were described. CNCs and CNFs are two types of nanocelluloses (NCs), and they possess various superior properties, such as large specific surface area, high tensile strength and stiffness, low density, and low thermal expansion coefficient. Due to various applications in biomedical engineering, food, sensor, packaging, and so on, there are many studies conducted on CNCs and CNFs. In this review, various methods of preparation of CNCs and CNFs are summarized, including mechanical, chemical, and biological methods. The methods of pretreatment of cellulose are described in view of the benefits to fibrillation.

Effect of different types of nanocellulose on the structure and properties of gelatin films

Tailoring structural properties, mechanical behavior and cellular performance of collagen hydrogel through incorporation of cellulose nanofibrils and cellulose nanocrystals: A comparative study

Chapter 3 - Recent trends in isolation of cellulose nanocrystals and nanofibrils from various forest wood and nonwood products and their application

Wound healing requires careful, directed, and effective therapies to prevent infections and accelerate tissue regeneration. In light of these demands, active biomolecules with antibacterial properties and/or healing capacities have been functionalized onto nanostructured polymeric dressings and their synergistic effect examined. In this work, various antibiotics, nanoparticles, and natural extract-derived products that were used in association with electrospun nanocomposites containing cellulose, cellulose acetate and different types of nanocellulose (cellulose nanocrystals, cellulose nanofibrils, and bacterial cellulose) have been reviewed. Renewable, natural-origin compounds are gaining more relevance each day as potential alternatives to synthetic materials, since the former undesirable footprints in biomedicine, the environment, and the ecosystems are reaching concerning levels. Therefore, cellulose and its derivatives have been the object of numerous biomedical studies, in which their biocompatibility, biodegradability, and, most importantly, sustainability and abundance, have been determinant. A complete overview of the recently produced cellulose-containing nanofibrous meshes for wound healing applications was provided. Moreover, the current challenges that are faced by cellulose acetate- and nanocellulose-containing wound dressing formulations, processed by electrospinning, were also enumerated.

The versatility of nanocellulose, modification strategies, and its current progress in wastewater treatment and environmental remediation

High aspect ratio cellulose nanocrystals (CNCs) extracted from tunicate were used to create so-called cryogels from an ice-templating directional freeze-drying process. The structure of the resulting solid foam was investigated at the micro- and nanoscales by scanning electron microscopy and nitrogen adsorption measurements were used to extract the specific surface area. The mechanical properties were probed by compression tests. To highlight the specificities of tunicate CNC-based cryogels, results were compared with the one obtained from two other types of nanocellulose, namely cellulose nanofibrils (CNFs) from wood and CNCs from cotton, which exhibit different dimensions, aspect ratio, flexibility and crystallinity. While CNF- and cotton CNC-based cryogels exhibited a classical morphology characterized by a sheet-like structure, a particular honeycomb organization with individual particles was obtained in the case of tunicate CNC cryogels. The latter cryogels presented a very high specific surface area of about 122 m2 g−1, which is unexpected for foams prepared from a water-based process and much higher than what was obtained for CNF and cotton CNC cryogels (25 and 4 m2 g−1, respectively). High mechanical resistance and stiffness were also obtained with such tunicate CNC cryogels. These results are explained by the high crystallinity, aspect ratio and rigidity of the tunicate CNCs combined with the particular honeycomb architecture of the cryogel.

Influence of nanocellulose on in vitro digestion of whey protein isolate

Nanocellulose, which possesses great physical, chemical, and biological properties, is a natural polymer derived from widely available native cellulose. It has outstanding properties such as high mechanical strength, stiffness, low weight, biocompatibility, and renewability, which are beneficial for the design of advanced drug delivery systems, as either an excipient or a carrier. This review introduces three types of nanocellulose: cellulose nanocrystals, cellulose nanofibers, and bacterial cellulose. Their physical and chemical properties along with their methods of preparation are also compared. Recent studies of nanocellulose for various drug delivery applications are summarized and discussed. Selected nanocellulose studies with significant findings for oral, ocular, intratumoral, topical, and transdermal delivery are also emphasized. Nanocellulose has potential for drug delivery applications due to its high surface area-to-volume ratio and high polymerization, which provide nanocellulose with a high loading and binding capacity for active pharmaceutical ingredients, enabling the control of the drug release.