# Electrospun Porous PDLLA Fiber Membrane Coated with nHA
## 3 Results and Discussion  
### Porous PDLLA Fibers and nHA Particles Features  
The morphology of porous PDLLA fibers could be affected by electrospun ambient humidity. At a humidity of 50%, the as-spun PDLLA fibers are smooth and featureless as shown in Figure 1A. Increasing the humidity to 65% caused a visible difference in the surface morphology of the fibers. Figure 1B shows that the fibers surface contains a relatively small number of uniform, oval pores randomly distributed on the surface of the fibers. The most dramatic difference was observed when the fibers were electrospun under the highest achievable humidity of 80%. Figure 1C shows that at this increased humidity the pores are abundant on the surface of fibers, leaving little space between adjacent pores. The average pore size is in the order of 100 nm in width and 400 nm in length, with the long axis being oriented along the fiber's axis. The possible mechanism for pore formation is phase separation. A nonsolvent vapor causes phase separation of the polymer solution. In this case, electrospun ambient water is the nonsolvent, which induces the phase separation of the homogeneous mixture of PDLLA and DCM [28]. Therefore, the number of pores and their diameter on the surface of PDLLA fibers increases with increasing ambient humidity. The elongation of the pores along the fiber's axis was the result of a uniaxial extension of the jet in the electric field [29]. Furthermore, Figure 1 shows that humidity also influences the diameter of the as-spun PDLLA fibers in this experiment. As the electrospun ambient humidity increases, the mean diameter of fibers increases from 0.8 to 1.2 \(\upmu\)m.  
Further investigations into the environment temperature effects on the surface features of electrospun PDLLA fibers allowed for a more comprehensive look at the role of humidity in the electrospinning process. The PDLLA fibers electrospun at 15 \({}^{\circ}\)C showed smooth surface morphology (Figure 2A). Increasing the environment temperature to 20 \({}^{\circ}\)C, the as-spun fiber's surface contains a relatively small number of uniform, oval pores randomly distributed on the surface of the PDLLA fibers (Figure 2B). Figure 2C shows that the pores obtained at 25 \({}^{\circ}\)C were uniform in shape and were slightly larger than those obtained at other temperatures. Thermodynamic instability is another driving force behind phase separation. Increasing the ambient temperature could accelerate the volatilization of DCM. During the electrospinning process, a more rapid evaporation of the solvent as the jet was being projected from the needle causes lowering of the temperature on the fibers [30]. Pore formation begins when the temperature reaches the bimodal temperature and continues to grow until the crystallization temperature is reached [31]. These situations were encountered, thus making phase separation a likely contributing mechanism of pore formation [28]. Obviously, the humidity and environment temperature have a large effect on the morphology of the fibers' surface. In follow-up experiments, the  
Figure 1: SEM of PDLLA fibers electrospun with different humidity at 25 \({}^{\circ}\)C. (**A**) 50%; (**B**) 65%; (**C**) 80%.  
best electrospinning environmental conditions (25 \({}^{\circ}\)C and 80% humidity) to fabricate porous PDLLA fibers with good morphology was used. The mean diameter of porous fiber is around 1.2 \(\upmu\)m.  
The XRD patterns of nHA particles are shown in Figure 3. Based on Figure 3a, the characteristic diffraction peak at 26 of 25.9\({}^{\circ}\), 31.8\({}^{\circ}\), 32.2\({}^{\circ}\) and 32.9\({}^{\circ}\), which are assigned to [0 0 2], [2 1 1], [1 1 2] and [3 0 0] lattice planes of nHA, indicates the XRD standard card of HA JCPDS:09-0432 (Figure 3b). It was confirmed that nHA particles were successfully prepared.