超临界流体制备组织工程细胞支架工艺基础研究

发布时间：2018-09-18 21:52

【摘要】：细胞支架的制备工艺是组织工程学研究的核心内容。传统细胞支架的制备工艺虽然各有其优势,但存在着有机溶剂残留、制备周期长和孔隙率低等不足。近年来,将超临界流体(简称SCF)技术引入组织工程细胞支架的制备过程已引起研究者广泛关注。利用现有的超临界C02(简称ScCO2)发泡工艺制备细胞支架,虽然没有有机溶剂的残留,但其孔隙率较低、难以控制孔尺寸的范围；利用ScCO2与其他工艺结合制备细胞支架,增加了原工艺的复杂性,使得制备周期延长；利用超临界反溶剂(简称SAS)工艺制备细胞支架,既没有有机溶剂的残留,又可以通过改变工艺参数来控制支架的孔径范围,具有广阔的应用前景。目前对SAS工艺的研究仅停留在实验阶段,主要探讨相关工艺参数对支架性能的影响,缺乏深入系统的理论研究。本论文首先对现有的ScCO2发泡工艺进行改进,采用多次升温和泄压的方法,以典型的无定型类聚合物—PMMA为模型材料,制备了PMMA多孔支架,考察了主要工艺参数对多孔支架性能的影响,并与现有的ScCO2发泡工艺制备的支架进行了比较。结果表明,与现有ScCO2发泡技术制备的PMMA细胞支架相比,在相同温度、压力、泄压时间、不同保压时间的条件下,改进工艺制备的PMMA细胞支架具有孔径范围大、孔隙率高、孔与孔之间连通性好的特点。利用SAS工艺,以PCL、PLLA为模型材料,进行了SAS工艺制备细胞支架的实验研究,确定了聚合物浓度、CO2压力和温度对支架形态、孔径分布的影响规律,得出了实验范围内制备上述材料支架的最佳工艺；为了提高单体PLLA支架的孔隙率与抗压强度,分别以PEG和β-TCP为添加剂,在制备单体PLLA细胞支架的基础上,成功制备了PLLA/PEG和PLLA/β-TCP复合材料支架。结果显示,加入PEG后,可以提高支架的孔隙率,最高可达92%；加入β-TCP后,可以提高支架的抗压强度,最高可达1.76MPa。以Flory-Huggins理论为基础,对SAS工艺的热力学行为进行了研究,建立了适合SAS工艺过程的相平衡热力学模型。利用模型中双节线、旋节线和临界点的计算方法,得到了三元体系相图,分别分析了ScCO2/AC/PCL和ScCO2/CH2C12/PLLA三元体系在制备多孔支架过程中的相行为。结果表明,两种三元体系均在临界点的上方按成核生长机理发生液—液相分离,可制备出具有多孔结构特征的聚合物。随着CO2压力的增加,相互作用参数χ12、χ13均减小,χ23保持不变；随着温度的升高,相互作用参数χ12χ13均增大,X23变化的趋势很小；分相点的计算结果表明,随着压力的增加,非溶剂进入聚合物溶液中的量逐渐增大,而随着温度的升高,非溶剂进入聚合物溶液中的量逐渐减小,两种体系计算结果一致。基于Reuvers模型,建立了适合SAS工艺过程的传质动力学模型,分别针对ScCO2/AC/PCL和ScCO2/CH2C12/PLLA三元体系给出了相关参数的求取方法,模拟了传质过程,得到了三元相图中的传质路径,描述了不同工艺参数对多孔结构的影响趋势。结果表明：两种三元体系在不同工艺条件下各组分体积分数的变化趋势相似,组分间扩散系数随着CO2压力的增加而减小,随着温度的升高而增大：随着聚合物浓度的增加、CO2压力的减小和温度的升高,传质路径逐渐变短,相分离速度逐渐加快,支架的平均孔径呈逐渐减小的趋势。支架平均孔径的最终变化趋势受相平衡热力学和传质动力学两方面因素的影响；两种三元体系中聚合物不同的物理性质、组分间不同的扩散系数造成了两种支架截面孔结构的不同。
[Abstract]:The preparation technology of cell scaffolds is the core of tissue engineering research. Although the traditional preparation technology of cell scaffolds has its own advantages, there are some shortcomings such as residual organic solvents, long preparation cycle and low porosity. ScCO2 foaming process is widely concerned. Although there is no residual organic solvent, its porosity is low and it is difficult to control the range of pore size. ScCO2 combined with other processes to prepare cell scaffolds increases the complexity of the original process and prolongs the preparation cycle. The preparation of cell scaffolds by boundary antisolvent (SAS) process has broad application prospects. There is no residual organic solvent, and the pore size of the scaffolds can be controlled by changing the technological parameters. At present, the research on SAS process is only in the experimental stage, mainly discussing the influence of related technological parameters on the performance of the scaffolds. Theoretical research.
In this paper, the existing ScCO2 foaming process was improved. The typical amorphous polymer-PMMA porous scaffolds were prepared by multiple heating and pressure relief methods. The effects of main process parameters on the properties of the scaffolds were investigated and compared with the scaffolds prepared by the existing ScCO2 foaming process. The results showed that, compared with the existing scaffolds prepared by ScCO2 foaming technology, the improved scaffolds had the characteristics of large pore size, high porosity and good pore-to-pore connectivity under the same temperature, pressure, pressure relief time and different holding time.
Using SAS process and PCL and PLLA as model materials, the SAS process was used to prepare cell scaffolds. The effects of polymer concentration, CO2 pressure and temperature on the morphology and pore size distribution of the scaffolds were determined, and the optimum process for preparing the scaffolds was obtained. The PLLA/PEG and PLLA/beta-TCP composite scaffolds were successfully prepared with PEG and beta-TCP as additives, respectively. The results showed that the porosity of the scaffolds could be increased up to 92% by adding PEG, and the compressive strength of the scaffolds could be increased up to 1.76MPa by adding beta-TCP.
Based on Flory-Huggins theory, the thermodynamic behavior of SAS process was studied, and a phase equilibrium thermodynamic model suitable for SAS process was established. The phase diagrams of ternary system were obtained by calculating the bi-nodal line, spindle line and critical point in the model. ScCO2/AC/PCL and SCCO2/CH2C12/PLLA ternary system were analyzed respectively. The results show that the polymer with porous structure can be prepared by the liquid-liquid phase separation of the two ternary systems above the critical point according to the nucleation growth mechanism. The number 1213 increases and the change trend of X23 is very small. The calculation results of phase separation point show that the amount of non-solvent entering the polymer solution increases with the increase of pressure, but decreases with the increase of temperature, and the results of the two systems are consistent.
Based on the Reuvers model, a mass transfer kinetic model suitable for SAS process was established. The method of calculating the relevant parameters for ScCO2/AC/PCL and SCCO2/CH2C12/PLLA ternary systems was given respectively. The mass transfer process was simulated, the mass transfer path in ternary phase diagram was obtained, and the influence trend of different process parameters on porous structure was described. Ming: The variation trend of volume fraction of each component in the two ternary systems under different process conditions is similar. The diffusion coefficient between components decreases with the increase of CO2 pressure and increases with the increase of temperature. With the increase of polymer concentration, the decrease of CO2 pressure and the increase of temperature, the mass transfer path becomes shorter and the phase separation rate increases. The final variation trend of the average pore size of the scaffolds is affected by two factors, namely, phase equilibrium thermodynamics and mass transfer kinetics. Different physical properties of polymers in two ternary systems and different diffusion coefficients between components result in different pore structures of the two scaffolds.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2012
【分类号】：R318.08

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