Research For The Open-cell Structure Control And Mechanical Properties Of Microcellular Foamed PCL/PEO Blends

In this paper,PCL/PEO blend polymer was prepared by twin-screw extrusion molding,and the PCL porous scaffold was fabricated by supercritical carbon dioxide batch foaming.The microstructure and mechanical properties of cells were characterized by PCL/PEO soft and hard phase blending system.The open-cell foaming mechanism of PCL/PEO blend polymer was studied in depth.Based on supercritical carbon dioxide foaming technology and polymer leaching technology,a small-diameter three-dimensional porous tubular scaffold meeting the requirements of use was prepared.The main research is as follows:The PCL/PEO blend polymer was prepared by melt blending using a biodegradable PCL and a water-soluble PEO material through a co-rotating twin-screw extruder.In the PCL/PEO blend system,the PEO was filtered off with deionized water and the blend was frozen and brittle.The morphology of the cross section was observed by SEM.The PCL/PEO blend showed "dispersion-continuous" phase morphology structure depending on the composition.First,observing the DSC curve of the PCL/PEO blend found that there were two distinct melting peaks（60℃ and 63 ℃）,indicating that PCL/PEO is an incompatible blend.Secondly,the thermal properties analysis and rheological properties of the blends of different soft and hard phase systems were carried out.Finally,the mechanical properties of the blended materials were simply tested.After comprehensive analysis,two distinct phase morphological blends of PCL70 and PCL50 were selected to be studied as porous scaffolds.Combined with supercritical carbon dioxide foaming technology and polymer leaching technology,two different incompatible PCL/PEO polymer blends were foamed to prepare PCL porous scaffolds with high open pore content.The effects of different phase morphology on the cell structure of porous scaffolds were systematically studied.Batch foaming was carried out under different soaking time,temperature and pressure.The foaming process was optimized according to the cell morphology and mechanical properties.PCL/PEO blend was found that the optimal foaming process window is CO₂ soaking time 1.5 h,foaming temperature 45℃,and saturation pressure 2000 psi（13.5 MPa）.After foaming,PEO was filtered out.It was found that all the samples had improved internal cell interconnectivity and porosity,and both are more than 85%,meeting the requirements of a larger number of tissue engineering scaffolds.At the same time,the open-cell mechanism of different blends was qualitatively analyzed and quantitatively analyzed.It can be seen from the analysis that the two-phase incompatible blending system can effectively improve the open cell content inside the blend of "sea-island"structure.Polymer leaching provides a significant increase in the interconnectivity of the internal cells of the"co-continuous," phase morphology blend.A small-diameter three-dimensional PCL porous tubular scaffold was prepared by supercritical carbon dioxide batch foaming technology.Based on a self-made foaming mold,a small-diameter porous tubular scaffold having an outer diameter of 5 mm and an inner diameter of 4 mm and a porosity of about 76%was prepared under the limited conditions using an optimum process.The morphology of the cell structure of the tubular scaffold was analyzed.The average pore size of the PCL70 tubular scaffold was 30μm～40μm,and the average pore size of the PCL50 tubular scaffold was 18μm～25μm.A series of mechanical properties tests,such as axial uniaxial stretching,radial uniaxial stretching and radial cyclic stretching,were carried out.It was found that the mechanical properties of the PCL70 scaffold were more in line with the requirements of the tissue engineering scaffold.The radial tensile results show that the nonlinear region of the PCL70 scaffold reaches about 20%,the axial tensile strength is greater than that of the PCL50 scaffold,and the residual strain generated during the cyclic stretching process should be changed little and the elastic recovery ability is stronger.The surface opening problem of the three-dimensional porous tubular scaffold was studied by PEO surface coating and ultrasonic vibration technique.Due to the temperature gradient in the restricted foaming process,the foamed material forms a dense"cortex",which makes the surface difficult to open.In this paper,through the secondary treatment of the blended material,the surface of the porous scaffold material was opened,that is,the surface of the tubular scaffold was treated by PEO surface coating and ultrasonic vibration,and the tubular scaffold with surface opening was successfully fabricated.The scaffold was observed that the open pore size of the surface is approximately 10μm.Through some tentative experiments,it is found that the size of the surface pore size can be regulated,so it is proposed to establish a universal surface opening method by optimizing the process.