2.2.2. Electrospinning and Electrospraying of PLA Fibers and SiO2 Microparticles

The tailor-made pilot equipment utilized for the formation of the bilayers consisted of two single needle injectors, one for electrospinning (PLA) and one for electrospraying (SiO2), which sequentially deposited fibers and microparticles onto the PET film using an AC controlled proprietary Fluidnatek® LE500 pilot line from Bioinicia S.L. (Valencia, Spain, see Figure 1). The roll containing the PET films was moving over the roll-to-roll system in continuous at a speed of 1 mm/s. Initially, for optimization purposes, the PET films were only coated with an electrospun layer of PLA fibers. To this end, the PET films were first placed on the continuous roll-to-roll collector and the PLA solution was then pumped in one of the injectors at a flow-rate of 20 mL/h through a needle with an inner diameter of 0.8 mm and a distance to the collector of 15 cm. The electrical voltages of the dual polarizers were set at 17 kV and –4 kV using a high-voltage supply unit in which the spinneret filled with the polymer solution was connected to the positive terminal of the power supply and the collector was to the negative electrode (ground). Optimal deposition was found when the collector was placed at a distance of 12 cm. The process was carried out in the air conditioning (AC) system—controlled environmental chamber set at 23 ◦C and 40% relative humidity (RH).

Once the PLA deposition was optimized (PET/PLA films), the second injector for electrospraying was incorporated into the system to obtain a sequential electrospinning of PLA fibers, followed by the electrospraying of SiO2 microparticles (PET/PLA/SiO2 films). The process was carried out in identical conditions that those applied during electrospinning with the exemption that the SiO2 solution was pumped at different flow-rates, from 20 to 50 mL/h, through the needle. In addition, for achieving a homogenous electrospraying deposition, the tip-to-collector distance was reduced to 10 cm for the SiO2 deposition. Once optimization of both jets was achieved, the roll-to roll system worked in a manner where non-coated PET films went through the injector area for both depositions, continuously moving until reaching the roll collector in which a roll containing coated-PET films was obtained.

**Figure 1.** (**A**) Co-continuous electrospinning/electrospraying proprietary setup for the coating of the polyethylene terephthalate (PET) film by polylactide (PLA) fibers and silica (SiO2) microparticles including an amplified image of the injector. (**B**) The roll containing the non-coated PET moving continuously from the area of the injector (for the deposition of fibers and microparticles) to the end of the roll collector, where it was collected in a coil-like manner.
