Controlling pore-size in 3D polymeric skeins produced by wet electrospinning

In this thesis, it is aimed to produce 3-dimensional (3D) polycaprolactone (PCL) scaffolds by wet electrospinning method with adjustable density and pore diameters. These scaffolds having adjustable pore diameters will facilitate the infiltration of surface-dependent cells, providing a favorable environment for 3D tissue formation. The pore diameters of 3D PCL structures were adjusted by varying temperature of the coagulation bath and the electric field rotation speed at constant temperature thanks to the conductive patterns underneath the bath. Two coagulation baths were designed to control the bath temperature (R1) and both bath temperature and electric field strength (R2) for the production of 3D structures. 3D structures are made of PCL with a molecular weight of 80000 g/mol. A mixture of dichloromethane (DCM) and N,N-dimethylformamide (DMF) (50:50, 65:35) was used as solvent for the PCL. Production of the 3D structures was carried out at constant time, temperature, flow rate and voltage values. The parameters affecting the wet electrospinning process were optimized and 3D structures with fiber diameters of 3.33±0.71 µm were produced. The temperature of the R1 temperature-controlled coagulation bath while using a 50:50 solution was 25 °C, 3D structures were obtained with a fiber yarn diameter of 0.21±0.03 cm, geometric factor of 1.83±0.20 cm, and average pore diameter of 24.9±3.5 µm. The temperature of R1 was gradually reduced and the fiber yarn diameter of 3D structures increased to 0.62±0.07 cm, geometric factor to 2.85±0.09 cm, average pore diameters to 85.5±5.6 µm at 7 °C. Similarly, the temperature of the R1 temperature-controlled coagulation bath using a 65:35 solution was measured fiber yarn diameter of 0.23±0.02 cm, geometric factor of 2.16±0.57 cm, pore diameter of 37.2±6.1 µm at 25 °C. The fiber yarn diameter, geometric factor and average pore size values were obtained with the same polymer solution at the lowest despicable temperature (5 °C) in the R1 bath, were 0.36±0.04 cm, 3.22±0.28 µm and 111.5±14.7 µm, respectively. The total porosity of this sample obtained from X-ray microtomography (µ-CT) is 87.22%. In the temperature-controlled coagulation bath R2, where the electric field strength is increased, the fiber yarn diameters, geometric factors and mean pore diameters of the 3D structures increased as the temperature decreased, as well as the R1, and the pore diameters and volumes of the 3D structures were changed by changing the electric field rotation at constant coagulation bath temperatures. The highest fiber yarn diameter obtained at a bath temperature of 5 °C was 0.45±0.02 cm, geometric factor was 2.54±0.22 cm, average pore size diameter was 128.29±57.67 µm. The total porosity of the 25 °C bath samples produced under the same conditions during µ-CT scanning was 70.35%, while the average porosity of 5 °C samples was found to be 83.22±2.92%. The data obtained from 3D PCL structures in the studies carried out within the scope of the thesis show that it is feasible to produce tissue scaffold with adjustable pore sizes in accordance with the needs by changing the temperature and electric field rotation in the designed temperature-controlled coagulation baths. 3D structures with exchangeable pore size distribution can be used in many areas such as tissue scaffold, acoustic materials, filtration media and battery technologies.