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- Ruan, Chang-Qing
(author)
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Functionalization, Characterization and Applications of Oxidized Nanocellulose Derivatives
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Cellulose, a sustainable raw material derived from nature, can be used for various applications following its functionalization and oxidation. Nanocellulose, inheriting the properties of cellulose, can offer new properties due to nanoscale effects, in terms of high specific surface area and porosity. The oxidation of cellulose can provide more active sites on the cellulose chains, improving its functionalization and broadening applications. Two kinds of oxidation and their corresponding applications are described in this thesis: periodate oxidation and Oxone® oxidation.2,3-dialdehyde cellulose (DAC) beads were prepared from Cladophora nanocellulose via periodate oxidation, and were further modified with amines via reductive amination. Several diamines were selected as possible crosslinkers to produce porous DAC beads, which showed higher porosity, stability in alkaline solution and enhanced thermal stability.After functionalization of DAC beads with L-cysteine (DAC-LC), thiol, amine and carboxyl groups were introduced into the DAC beads, endowing the DAC-LC beads with high adsorption capacity for palladium. The synthesized DAC-LC beads were characterized with SEM, FTIR, XPS, TGA, BET and XRD and the palladium adsorption process was investigated.Chitosan was employed as a crosslinker in functionalization of DAC beads (DAC-CS). The conditions for the synthesis of DAC-CS beads were screened and verifying the stability of the beads in alkaline solution. The DAC-CS beads produced were investigated using SEM, FTIR, XPS, TGA and BET, and the adsorption and desorption capacity of Congo red was studied, indicating DAC-CS beads have potential as sorbent.Oxone oxidation of cellulose is a novel one-pot oxidation method in which mainly the hydroxyl groups on C6 are oxidized to produce carboxylic acid groups on the cellulose chains. To increase the efficiency of Oxone oxidation, several reaction parameters were studied. Cellulose pulp and Cladophora nanocellulose were chosen as prototypes to investigate the effects of oxidation, and the physicochemical properties of the oxidized products were characterized. Cellulose pulp, pretreated with Oxone oxidation, was disintegrated by homogenization to prepare cellulose nanofibers (CNF). The effect of pretreatment on the preparation of CNF was studied, and the results indicated that Oxone oxidation was efficient in the production of CNF.
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| 3. |
- Sultan, Sahar, 1987-
(author)
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Nanocellulose based 3D printed hydrogel scaffolds for cartilage and bone regeneration : Tuning of composition, pore structure and functions
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Biobased-materials with customized scaffolds have played a prominent role in the success of tissue engineering (TE). Cellulose nanomaterials (CNM) isolated from the abundant biopolymer, cellulose, is explored in this thesis for TE engineering due to its versatile properties such as biocompatibility, high specific strength, surface functionality and water retention capacity. Hydrogel formation capability of CNM at low concentrations (1–2 wt%) and shear thinning behavior has facilitated its use in 3-dimensional (3D) printing as a fabrication technique for 2-dimensional (2D) and 3D scaffolds. This technique offers 3D scaffolds with tailored, controlled and complex geometries having precise micro and macro scaled structures. The current work focuses on CNM-based 3D printed hydrogel scaffolds with tuned composition and pore structure for cartilage and bone regeneration. Design of CNM hydrogel formulations with suitable rheological properties, hydrogel inks capable of ex-situ crosslinking, print resolution during printing due to swelling and mechanical and dimensional stability of the printed scaffolds in moist environment are key challenges that were addressed.Inspired by the hierarchical and gradient nature of natural tissues 3D printed hydrogel scaffolds with gradient pore structure and composition are reported for the first time with focus on cellulose nanocrystals (CNC) and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-oxidized cellulose nanofibers (TOCNF) based hydrogel ink printing for advanced and functional scaffolds.CNC-based hydrogel ink was used to 3D print uniform and gradient porous cubic scaffolds for cartilage regeneration. This work highlighted the importance of nozzle movement to obtain high resolution scaffolds with higher z-axis. The anisotropic rigid CNC aligned themselves along the printing direction due to the shear induced orientation that was quantified between 61–76%. To obtain adequate mechanical properties (0.20–0.45 MPa) suitable for cartilage regeneration, the hydrogel ink solid content was increased almost two-fold (5.4 wt% to 9.9 wt%) while exhibiting and mimicking the viscoelasticity of natural cartilage tissues. To improve the bioactivity of the CNC-based 3D printed scaffolds, a surface treatment through dopamine coating was performed. This coating enhanced the hydrophilicity and capability of 3D printed scaffolds to bind bioactive molecules such as fibroblast growth factor (FGF-18) for soft TE scaffolds.Surface functionality of TOCNF was utilized to fabricate functional hybrid scaffolds (CelloZIF-8) through one-pot in- situ synthesis of Metal-Organic frameworks (MOFs) with varied ZIF-8 loadings (30.8–70.7%). The inherent porosity of the ZIF-8 was used for loading and stimuli-responsive (pH-dependent) releasing of drug molecule such as curcumin. The developed CelloMOF system was extended to other MOFs (MIL-100) and drugs (methylene blue). The shear thinning property of TOCNF was reserved after MOFs hybridization and was used to 3D print porous scaffolds with excellent shape fidelity. In Cello-Apatite, TOCNF was also used as template for in-situ synthesis of hydroxyapatite (HAP) where the HAP loading was 67 wt% to mimic the bone composition. In an attempt to address both cartilage and bone regeneration, a biphasic osteochondral 3D printed hydrogel scaffold has been introduced with tuned composition, pore structure and mechanical properties.The work presents a sustainable, cost effective and scalable approach for TE using biobased and toxic free water-based formulations using low temperature processes that are extendable to other biomaterials as well as to other applications, such as water treatment.
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