Fabrication And Regulation Of Calcium Alginate Membranes With Gradient Pore Microstructure

In recent years, with the increasingly development of biological functional materials used in tissue engineering, researches on the influence of vitro cells culture caused by scaffold microstructure and distribution gradually increased, which brought out the fabrication of functionally bionics materials. Thus the designing and fabrication of porous scaffold which have controllable pore size became more and more important. Alginate has a lot of good characteristics, such as non-toxic, excellent in biological compatibility, biodegradable, now it has been widely used in the field of tissue engineering. In this study, taking full advantage of the excellent chemical, physical and biological properties of alginate, porous scaffolds were fabricated using freeze drying technique. This research focused on the control of pore size of the porous materials and the fabrication of scaffolds with gradient pore size distribution.The alginate engineering scaffolds prepared by freeze drying technique are soft, porous and flexible, with open sheet pore structure. Uniform pore distribution and pore size can be found in the porous scaffolds fabricated under uniform pre-cooled condition and pore size of the porous scaffold can be regulated by adjusting the parameter of thermal density(?/D) of the container(from 89?m to 320?m). Porous scaffold with pore size gradient in the longitudinal section can be prepared using several methods, such as creating temperature gradient in the pre-cooled condition, changing ?/D of convection heated surface of the container, different heat conduction direction, different solution quantity and different pre freezing temperature. Pore size varied from 15?m to 450?m. And the basic properties of the prepared materials varied with the change of pore size and distribution. We can choose the proper method to fabricate the scaffolds we needed.By changing the solution component and the content of every component, the pore of scaffolds prepared can be adjusted to the predesigned size(from 80?m to 146?m). So does changing the addition content of nano cellulose, polyvinyl alcohol or pectin(from 67?m to 140?m). The porosity, water absorption test and tensile properties also can be influence by changing those parameters.By adjusting the freezing temperature gradient, the initial freezing temperature and the freezing time, gradient scaffolds with different pore size and distribution can be fabricated. The experimental results showed that, with the same freezing temperature and freezing time, enlarging the freezing temperature gradient can greatly change the pore distribution of the scaffolds. Alginate solution pre-cooled under proper freezing gradient, pore size constantly changed from small ones to big ones. While under enlarged freezing temperature gradient, pore size changed abruptly. The best solution is to realizing the constant variation of temperature. The initial freezing temperature and freezing time mainly affect the pore size and the difference between the smallest pores and the biggest. We can prepare the predesigned scaffold using this method. The smallest pores prepared in the experiment changed from 9?m-25?m, while the biggest ones varied from 51?m-154?m.The other basic properties of the scaffolds were excellent. The scaffold with pore size varied from 20?m to 100?m, prosity above 89%, Wa above 2400%,Wm above 95%, SA/V above 0.014?m-1 and breaking strength above 0.036 MPa was expected to be used in medical fields such as skin tissue engineering.