Synthesis and Bioactivity of Cellulose Derivatives

Anticoagulation activity of sulfated carboxymethyl cellulose/Azadirachta indica leaf powder-based bio-composite

Polymeric bio-composites synthesized via a green approach using natural herbs have fascinating anticoagulant activity due to their eco-friendly and non-toxic behavior towards various physical and chemical actions. Herein, we introduce a simple and eco-friendly approach for the fabrication of a new hybrid type of bio-composite based on sulfated carboxymethyl cellulose (S-CMC) and Azadirachta indica leaf powder (S-CMC/NLP). First, a non-toxic sulfating agent called N(SO3Na)3 was used to modify carboxymethyl cellulose into S-CMC. With an ion exchange capacity of 0.25 meq. g-1, the level of sulfation (%) of S-CMC (modified polysaccharide) was measured to be 12.01%. Three types of S-CMC/NLP bio-composites were developed by varying the concentration of NLP. FE-SEM, EDX, and XRD were used to characterize the structural features of S-CMC/NLP bio-composites. FTIR spectroscopy indicated that the S-CMC/NLP bio-composite possesses COO-, -OH and SO3- groups, suggesting the structural similarity to heparin. In addition, the anticoagulant effect of the S-CMC/NLP bio-composite was investigated using PT and APTT assays. The APTT investigation confirmed that following the intrinsic pathway of the coagulation system, 2-NLP/S-CMC bio-composite dose-dependently (0.045-0.28 mg mL-1) prolonged the time of blood coagulation compared to control (pure plasma). The S-CMC/NLP bio-composite showed its potential as a new, safe, and effective candidate for anticoagulant activity.

Recent Progress on Cellulose-Based Ionic Compounds for Biomaterials

Glycans play important roles in all major kingdoms of organisms, such as archea, bacteria, fungi, plants, and animals. Cellulose, the most abundant polysaccharide on the Earth, plays a predominant role for mechanical stability in plants, and finds a plethora of applications by humans. Beyond traditional use, biomedical application of cellulose becomes feasible with advances of soluble cellulose derivatives with diverse functional moieties along the backbone and modified nanocellulose with versatile functional groups on the surface due to the native features of cellulose as both cellulose chains and supramolecular ordered domains as extractable nanocellulose. With the focus on ionic cellulose-based compounds involving both these groups primarily for biomedical applications, a brief introduction about glycoscience and especially native biologically active glycosaminoglycans with specific biomedical application areas on humans is given, which inspires further development of bioactive compounds from glycans. Then, both polymeric cellulose derivatives and nanocellulose-based compounds synthesized as versatile biomaterials for a large variety of biomedical applications, such as for wound dressings, controlled release, encapsulation of cells and enzymes, and tissue engineering, are separately described, regarding the diverse routes of synthesis and the established and suggested applications for these highly interesting materials.

Hydrogels Based on Oxidized Cellulose Sulfates and Carboxymethyl Chitosan: Studies on Intrinsic Gel Properties, Stability, and Biocompatibility

Cellulose and chitosan are excellent components for the fabrication of bioactive scaffolds, as they are biocompatible and abundantly available. Their derivatives Ocarboxymethyl chitosan (CMChi) and oxidized cellulose sulfate (oxCS) can form in situ gelling, bioactive hydrogels, due to the formation of imine bonds for crosslinking. Here the influence of the degrees of sulfation (DS), oxidation (DO), and the molecular weight of oxCS on intrinsic and rheological properties of such hydrogels and their ability to support the survival and growth of human-adipose-derived stem cells (hADSC) is investigated. It is found that the pH of the hydrogels is generally slightly acidic, while their network density and E-modulus are found to be dependent on the DS and DO, which makes the properties of hydrogels tunable. Extensive studies show that hydrogels can be stable for up to 14 days and that their stability is largely dependent on the DO, molecular weight, and the components mixing ratio. Cytotoxicity studies of the hydrogel with hADSCs show biocompatible gels in dependence on the molecular weight and degree of oxidation with viable cells up to 14 days. These findings can help to develop specifically tailored hydrogels for tissue engineering applications to replace different types of connective tissue.

Human-based fibrillar nanocomposite hydrogels as bioinstructive matrices to tune stem cell behavior

The extracellular matrix (ECM)-biomimetic fibrillar structure of platelet lysate (PL) gels along with their enriched milieu of biomolecules has drawn significant interest in regenerative medicine applications. However, PL-based gels have poor structural stability, which severely limits their performance as a bioinstructive biomaterial. Here, rod-shaped cellulose nanocrystals (CNC) are used as a novel approach to modulate the physical and biochemical microenvironment of PL gels enabling their effective use as injectable human-based cell scaffolds with a level of biomimicry that is difficult to recreate with synthetic biomaterials. The incorporation of CNC (0 to 0.61 wt%) into the PL fibrillar network during the coagulation cascade leads to decreased fiber branching, increased interfiber porosity (from 66 to 83%) and modulates fiber (from 1.4 ± 0.7 to 27 ± 12 kPa) and bulk hydrogel (from 18 ± 4 to 1256 ± 82 Pa) mechanical properties. As a result of these physicochemical alterations, nanocomposite PL hydrogels resist the typical extensive clot retraction (from 76 ± 1 to 24 ± 3 at day 7) and show favored retention of PL bioactive molecules. The feedback of these cues on the fate of human adipose-derived stem cells is evaluated, showing how it can be explored to modulate the commitment of encapsulated stem cells toward different genetic phenotypes without the need for additional external biological stimuli. These fibrillar nanocomposite hydrogels allow therefore the exploration of the outstanding biological properties of human-based PL as an efficient engineered ECM which can be tailored to trigger specific regenerative pathways in minimal invasive strategies.

Preparation of carboxymethyl cellulose sulfates and its application as anticoagulant and wound dressing

Tissue engineering is aiming to build an artificial environment or biological scaffold material that imitates the living environment of cells in the body. In this work, carboxymethyl cellulose sulfates were prepared by reacting carboxymethyl cellulose with N(SO3Na)3 which was synthesized by sodium bisulfite and sodium nitrite in aqueous solution. The reaction conditions affected the degree of substitution (DS) were measured by the barium sulfate nephelometry method. And the anticoagulant activity of carboxymethyl cellulose sulfates with different DS, concentration and molecular weights were investigated by the activated partial thromboplastin time (APTT), thrombin time (TT) and prothrombin time (PT). In addition, the effect of carboxymethyl cellulose sulfates on wound healing had been evaluated by the rate of wound healing and the histological examinations. The results indicated that the introduction of sulfate groups into the carboxymethyl cellulose sulfates improved its anticoagulant activity, and the wound dressings treated with carboxymethyl cellulose sulfates obviously promoted wound healing.

Modulation of osteogenic activity of BMP-2 by cellulose and chitosan derivatives

Polysaccharides with structure and potential bioactivity similar to heparin were synthesized based on cellulose which was regioselectively sulfated, carboxylated or carboxymethylated, and chitosan that was sulfated only. Osteogenic activity of these derivatives was studied in cooperation with BMP-2 using C2C12 myoblast cells as a model system measuring alkaline phosphatase (ALP) activity and the expression of the genes Osterix, Noggin and Runx-2. It was found that highly sulfated chitosan showed the strongest osteogenic activity of all polysaccharides, but only at lower concentrations, while higher concentrations were inhibitory. By contrast, cellulose with a low or intermediate degree of sulfation showed increasing ALP activity and expression of Osterix and Noggin with rising concentrations. Lower sulfated cellulose with a high degree of carboxylation was less osteogenic, but had a positive effect on cell viability, while carboxymethylated cellulose had almost no osteogenic activity. The results indicate that regioselectively sulfated as well as carboxylated cellulose and chitosan possess an osteogenic activity, which makes them interesting candidates for application in tissue engineering of bone.

Regioselective esterification and etherification of cellulose: a review

Deep understanding of the structure-property relationships of polysaccharide derivatives depends on the ability to control the position of the substituents around the monosaccharide ring and along the chain. Equally important is the ability to analyze position of substitution. Historically, both synthetic control and analysis of regiochemistry have been very difficult for cellulose derivatives, as for most other polysaccharide derivatives. With the advent of cellulose solvents that are suitable for chemical transformations, it has become possible to carry out cellulose derivatization under conditions sufficiently mild to permit increasingly complete regiochemical control, particularly with regard to the position of the substituents around the anhydroglucose ring. In addition, new techniques for forming cellulose and its derivatives from monomers, either by enzyme-catalyzed processes or chemical polymerization, permit us to address new frontiers in regiochemical control. We review these exciting developments in regiocontrolled synthesis of cellulose derivatives and their implications for in-depth structure-property studies.