Construction, Structure And Properties Of Biomedical Materials Based On Cellulose

In the21st century, science and technology have moved toward renewable raw materials, as well as more environmentally friendly and sustainable resources and processes. As the most abundant natural polymers on earth, cellulose is widely used to yield biomaterials such as wound dressing, dialysis membrane, scaffold, drug carrier and so on. In our laboratory, a environmental friendly, low-cost cellulose solvent (alkali/urea aqueous solution) has been exploited, which can rapidly dissolve cellulose at low temperature, and cellulose materials has been successfully fabricated. In the present work, aiming to the biomaterial application, a series of regenerated cellulose materials including films, hydrogels, microspheres and sponges were successfully prepared by dissolving cellulose in alkali/urea aqueous solution. Their structure and properties were studied, and their application prospects in bioanalysis, cell culture and drug delivery were also evaluated.The innovations of this dissertation are as follows:(1) a series of cellulose/gelatin films were successfully prepared via NaOH/urea aqueous solution. The composite films combined the advantages of two natural polymer, possessing good mechanical properties, optical transmittance and biocompatibility, which could be used as cell culture substrates;(2) a series of cellulose/collagen hydrolysate films were successfully prepared. Strong hydrogen-bonding interactions existed between cellulose and collagen hydrolysate. Genipin as crosslinker further improved the mechanical properties and biocompatibility of composite films;(3) for the first time cellulose hydrogel was used to fabricate microfluidic device. Cellulose hydrogel possessed good mechanical properties, microstructure replication ability and cytocompatiblity. The soluble factors could generated stable concentration gradients in hydrogels, which enabled the microfluidic device to mimic cell microenvironment;(4) regenerated cellulose microspheres with narrow size distribution as drug carriers were successfully fabricated by microfluidic technology, which was a green, efficient and easy process;(5) cellulose and cellulose/gelatin sponges were prepared by low temperature dissolution technology. The cellulose-based sponges possessed good mechanical properties, water retention ability, biocompatibility, grow factor release capability, which could be used as wound dressing or scaffold in tissue engineering.The main contents and conclusions in this dissertation can be divided into the following parts:Cellulose and gelatin were two abundant resources from plant and animal. In this work, a series of cellulose/gelatin (C/G) films were prepared in NaOH/urea aqueous solution via a simple, low cost and green pathway. To overcome the disadvantages of the protein material (brittleness and poor water resistance), gelatin was combined with cellulose to construct cellulose/gelatin composite films. The strong interaction between hydroxyl group of cellulose and amino groups of gelatin led to the improvement of the water resistance of gelatin. The results revealed that good compatibility existed between cellulose and gelatin in the composite films. The composite film exhibited the best mechanical properties when the content of protein was less than22.3%. The mechanical properties and the water resistance of the crosslinked films were further improved by cross-linking with glutaraldehyde. Furthermore, the films exhibited good biocompatibility, and supported cell adhesion and growth, by proliferation of COS7cells on the surface of the C/G films.A series of cellulose/collagen hydrolysate (RC/CH) films were prepared in NaOH/urea aqueous solution via a simple, low-cost and green pathway. CH was combined with cellulose to construct RC/CH composite materials, leading to great improvement of the water resistance of CH. Strong hydrogen bonding existed between the hydroxyl groups of cellulose and amino groups of collagen hydrolysate. Genipin as a safe crosslinker further improved the mechanical properties and water resistance of the RC/CH films in the wet state. The composite films possessed excellent optical transmittance, revealing good miscibility of cellulose and collagen hydrolysate. Moreover, the RC/CH films exhibited good biocompatibility and supported cell adhesion and growth by cell culture and MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cytotoxicity tests owing to the addition of collagen hydrolysate.For the first time, we demonstrated that the cross-linked cellulose (RCC) hydrogel could be used as the bulk material for microchip. The cellulose hydrogel was prepared by crosslinking cellulose with epichlorohydrin (ECH). Collagen as a key extracellular matrix (ECM) component for promoting cell cultivation was cross-linked in the cellulose hydrogel network to obtain cellulose-collagen (RCC/C) hybrid hydrogels. The experimental results revealed that cellulose-based hydrogel microchips with well-defined2D or3D microstructures possessed excellent structure replication ability, good mechanical properties, and cytocompatibility for cell culture as well as excellent dimension stability at elevated temperature. The hydrogel as a transparent microchip material had no influences on the fluorescence behaviors of FITC-dextran and Rhodamine-dextran, leading to the good conjunction with fluorescent detection and imaging. Moreover, collagen could be immobilized in the RCC/C hydrogel scaffold for the promoting cell growth and the generating stable chemical concentration gradients, leading to the superior cytocompatibility. This work provided new hydrogel materials in the microfluidic technology area that mimicking a3D cell culture microenvironment for cell-based tissue engineering and drug screening.In this work, cellulose microspheres with narrow size distribution were successfully fabricated by using microfluidic technology, based on the generation of cellulose droplets in microfluidic device. Cellulose droplets formed at cross-junction of mirochannels by the shear stress from liquid-paraffin as continuous phase. These cellulose droplets then solidified in a coagulation agent consisted of alcohol and castor oil to form cellulose microspheres. The diameters of cellulose microspheres with narrow size distributions varied from170-420μm by adjusting the flow rate ratio of water to oil, and the polymey disperse index was3%-6%. High cellulose concentration led to a dense structure of microspheres and low swelling ratio in water. Furthermore, the adsorption and controlled release capabilities of cellulose microspheres on doxorubicin hydrochloride (DOX) were studied. The drug encapsulation efficiency of microspheres was up to80%, which could be improved by increasing the weight of microspheres. Microspheres made from the cellulose solution with high concentration could have higher drug encapsulation efficiency and ideal release capabilities. The cellulose microspheres with narrow size distribution have many potential applications in pharmaceutical area. This work provided a new approach for microspheres derived from natural polymers.The novel cellulose/gelatin (RC/G) sponges were prepared by crosslinking and freeze-dried method. Cellulose (RC) and RC/C sponges have interconnected porous structure. Gelatin was combined to cellulose pores walls by hydrogen-bonding interaction. The addition of gelatin further improved the water retention abilities and mechanical properties of sponges. The cytocompatibility of the scaffolds were evaluated by in vitro rat fibroblast cells adhesion and proliferation tests. MTT cytotoxicity tests further clarified the safety of RC and RC/G sponges. Basic fibroblast growth factor (bFGF) release experiment results indicated that the cellulose-based sponges possessed bFGF release capabilities, and the additon of gelatin generated a stable, controlled long-term delivery for bFGF. Therefore, these results suggested that these novel RC/G sponges have the potential as wound dressings or scaffolds in tissue engineering.In this work, a series of regenerated cellulose materials were constructed via a novel, green and efficient process for rapid dissolution, by using the simplest and cheapest alkali/urea aqueous solution as solvent for the biomaterials application. These basic researches provided valuable information for construction and development of biopolymers with different properties from renewable resource. Therefore, this dissertation exhibited great scientific significance and prospects of applications, and it well accorded with the target of our country and have the great importance for a sustainable development.