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论文范文
1. Introduction In recent years, porous cellulose beads (CBs) derived from regenerated cellulose are receiving intense research interest for their potential biomedical and biotechnological applications such as chromatography system [1], immobilization of enzymes [2], and drug delivery system [3]. CBs are potentially cost-effective drug delivery carriers due to their high porosity and high specific surface area, favourable drug loadings, and release profiles under specific conditions [4]. Importantly, CBs are nontoxic, biocompatible, cheap, and possess excellent thermal and mechanical properties [5, 6]. In the pharmaceutical field, CBs constitute the main component in the formulation of drug pellets using the extrusion-spheronization method [7]. CBs are prepared by mechanically shaping the wet hydrolyzed cellulose fibre fragments into spherical particles through spheronization and then loaded with model drugs such as isosorbide dinitrate, terodiline, and N-actyl-L-cysteine for subsequent drug release studies [8, 9]. However, the main disadvantages of the extrusion-spheronization method were difficulties in controlling the size and porous structure of CBs formed which could lead to burst release instead of sustained release of drug components from the delivery system. The drug release time could be increased by loading CBs with paracetamol containing lipophilic release modifiers using the absorption method [10]. Different hydrophilic and hydrophobic model drugs such as anhydrous theophylline, riboflavin 5′-phosphate sodium, and lidocaine hydrochloride monohydrate had been incorporated into spherical CBs by the immersion method for studying their drug release profiles [3]. In addition, the effects of functionalized cellulose matrix and types of drugs on their release profiles from CBs were investigated [11, 12]. The preparation of CBs with spherical shape and mean diameter within the range of micrometer to millimeter were reported by several researchers via three main steps: dissolution of cellulose, shaping of the cellulose solution, and solidifying or precipitate the solution in a coagulation bath to form beads [13, 14]. However, due to insolubility of cellulose fibres in water and most organic solvents, all these CBs preparation approaches required the use of derivatizing solvents and toxic chemicals such as carbon disulfide and epichlorohydrin, which could have adverse environmental impacts [15, 16]. In our previous study, we had reported a green chemistry approach for the fabrication of porous CBs from regenerated cellulose of paper wastes using nonderivatizing and environmental friendly ionic liquid as the reaction medium, and water as the antisolvent [17]. Herein, we reported the fabrication of CBs with controllable mean sizes and highly porous microstructure by varying experimental conditions including the use of extrusion syringe needle with different nozzle diameters, and different cellulose bead drying conditions. Curcumin was being used as a model drug for investigating the loading capacity and efficiency of curcumin onto CBs. The release kinetic profiles of curcumin-loaded CBs were studied in aqueous media at different pH values by simulating digestive juices (pH = 1.23) and intestinal fluids (pH = 6.40). Experimental data were subsequently being fitted to both zero and first-order kinetic equations, as well as to several empirical kinetic models for the elucidation of drug release mechanisms under specific conditions. 
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