UV-curing Of Cellulose Nanofibers And Its Controllable Preparation Of Tissue Engineering Scaffolds

Cellulose is the most abundant and renewable biodegradable polymer material in nature. And cellulose nanofibers(CNFs) produced from the raw cellulose materials not only has good biodegradability, biocompatibility and nontoxicity, but also has a unique nanostructure, which has potential application prospect in biological medicine, tissue engineering and other fields. Film forming, freeze drying, spray drying and surface coating are often used in the application process of CNFs, but these methods are slow and with low efficiency. Therefore, it’s a great challenge to controllable prepare three dimensional structure materials with specific geometric structures and internal pore structures, which can be adapt to the special requirements for the scaffolds during cell culture. And it is also one of the difficult problems of the research and development for biological materials with CNFs. TEMPO/NaBr/NaClO mediated oxidation system was applied to treat eucalyptus pulp under alkaline conditions at room temperature. The oxidation efficiency of cellulose was improved by increasing the concentration of oxidation system and adjusting the time TEMPO solutions mixed with cellulose. Combined with high-pressure homogenization or ultrasonic treatment, CNFs was quickly and efficient prepared. A kind of UV-curing resin with good biocompatibility(a kind of acrylate resin, shortened to CR) was mixed with CNFs in order to establish the CNFs/CR UV-curing system. The properties of UV-curable hydrogel scaffolds and the relationship between external geometric structures and mechanical behaviors of the scaffolds were discussed to investigate the process of UV-curing. In addition, CNFs aerogel scaffolds were controllable prepared combined UV-curing with freeze drying. The structure morphology and mechanical properties of the CNFs aerogel scaffolds were characterized and the factors of CNFs addition and CR proportion were discussed. Furthermore, NIH 3T3 cells from mouse fibroblast were seeded and cultured on the aerogel scaffolds, cell viability was detected by Confocal Laser Scanning Microscopy(CLSM). The results are showed as follows: 1. TEMPO oxidized cellulose(TOC) with different carboxyl content can be prepared by adjusting the dosage of oxidant NaClO in the TEMPO/ NaBr/ NaClO oxidation system. When the mixing time of TEMPO solutions with cellulose was controlled on 0.5h, the carboxyl content of TOC significantly increased while the degree of polymerization(DP) only slightly decreased. Besides, the difference of carboxyl content and DP of TOC was slightly when the pulp concentration of the oxidation system was increased from 1% to 2%, but the yield of TOC were all over 90%, the preparation efficiency nearly doubled increased. 2. High pressure homogenization and ultrasonic mechanical treatment had no significant effect on the chemical structures of TOC, and also didn’t change the structure of cellulose I type. But the crystalline structure of cellulose was obviously destroyed by the mechanical treatment. CNFs with uniform size can be fast and efficient prepared by adjusting the carboxyl content of cellulose, homogeneous concentration, homogeneous time and ultrasonic processing time in the process of high pressure homogenization and ultrasonic treatment. 3. CNFs acted as additive components in CNFs/CR UV-curing system, didn’t participate in the crosslinking reaction. CNFs/CR hydrogel scaffolds with uniform shape and controllable morphology can be prepared by the UV-curing system. The mechanical strength of the scaffolds was provided by the crosslinking of CR components, and can be adjusted and controlled by the addition of CNFs. 4. CNFs/CR hydrogel scaffolds with controllable external geometric structures and porous size were prepared by CNFs/CR UV-curing system. And the clarity and precision of the prepared scaffolds decreased with the decreasing of geometric structure size. The rigidity and toughness of CNFs/CR hydrogel scaffolds was influenced by the addition of CNFs. With the increasing of CNFs, the rigidity slightly decreased but toughness significantly increased. Moreover, hydrogel scaffolds with geometric structures prepared by UV-curing has special Poisson’s ratio and exhibited special deformation behavior under tensile or compressive force. Poisson’s ratio of the scaffolds was not affected by the materials in the elastic stage, and was only associated with the geometric structure of the scaffolds. 5. CNFs aerogel scaffolds were rapid prepared combined UV-curing with freeze drying. And CNFs played an important role on the internal structures of the aerogel scaffold. With the addition of CNFs, the CNFs/CR scaffolds formed a connected three-dimensional porous structure with pore size of 50~200 m and connected through small pores with 10~20 m. The compressive modulus of the scaffolds was within 1~3MPa, which was in the same order of magnitude with the elastic modulus of cartilage. CLSM results showed that, the cells were attached and well grown in the scaffolds with three dimensional distribution, and showing a good cell viability.