Research On Preparation Of Cell Scaffolds With Well Defined Pore Structure

Tissue engineering is a science which based on the application of principles and methods of engineering and life sciences toward fundamental understanding of structure-function relationships in normal and pathological tissues to create biological substitutes of native tissues to repair or improve the human lesion tissue or organ structure and function. This is a novel technology that obtains new tissues and organs through culturing cells and plays a role of revolutionary change in curing defects and dysfunction of tissues and organs, and which is widely recognized as the most promising treatment in 21st century. Establishing three-dimensional complex of cells and biological materials is the core of tissue engineering, which is the living tissue that has vitality, and the complex can rebuild morphology, structure and function of the lesion tissues. Tissue engineering involves three key factors, they are seeding cells, porous biodegradable scaffolds and cell growth regulatory factors. Porous scaffold is the template of the cell growth in the process of tissue formation, and it not only provide structural support for particular cells, but also guide tissue regeneration and control the characteristics of tissues or organs, so it is an important research field in tissue engineering. Developing ideal scaffold is essential and important in tissue engineering.An ideal scaffold has appropriate pore shape, structure and size, high porosity and good pore connectivity. However, there is no scaffold created with the present techniques meets the standard of ideal scaffold, and the pore structure is variety with different preparation methods. In this paper, a novel technique was developed based on water-soluble flexible microspheres as porogen to improve the traditional solution casting / particle leaching technique to prepare porous PDLLA scaffold. The flexible water-soluble porogen of PVA microspheres were prepared with improved high voltage electrostatic method, and some experimental conditions, such as, voltage, the distance between the electrodes, PVA concentration, injection rate, the number of freeze-thaw cycle, which influenced on the size, appearance, mechanical property of the microspheres, were researched. The novel technique called elastic porogen/pressure filtration technique was tested to create scaffold, and cell scaffolds with well defined pore structure were fabricated with the novel technique. In addition, the macropore size, shape and opening size between macropores of scaffolds were conveniently controlled through adjusting experimental conditions, such as, the diameter of porogen and degree of pressure filtration. The major conclusions of thesis were summarized as below:PVA elastic hydrogel microspheres with size range of 100~1000μm could be fabricated via modified high-voltage electrostatic technique. Those microspheres in spherical shape with smooth surface, good water-solubility and good mechanical properties were one kind of most useful elastic porogens.PDLLA scaffolds with porosity over 90% were prepared, besides, the uniformly distributed pores and regularly as well as fully interconnected channels between pores in scaffolds were obtained. In addition, it was demonstrated that the pore size in scaffold was controlled by porogen size, and the channel dimension was conveniently adjusted by experimental conditions. For instance, pore size of 288.72±19.01(11)μm and 441.69±26.87(14)μm resulted from porogen size of 250~425μm and 425~600μm, respectively, and various pressure degree of filtration resulted in different channel size (282.05±29.03(16)μm, 305.68±10.78(11)μm, and 331.05±22.91(14)μm), while the porogen size of 500~650μm was used with the other experimental conditions kept unchanged. Finally, an assay on remains of PVA in scaffolds was performed, and the low concentration of PVA in scaffold indicated that PVA was removed almost from scaffolds.In conclusion, the scaffolds with well defined pore structure can be formed through this novel technique, and the pore shape and sizes as well as size of channels between pores could be manual controlled conveniently. The pore structure and morphology of scaffolds were satisfied to the requirements of tissue engineering, which suggested that elastic porogen/pressure filtration technique was an ideal cell scaffold forming technique.