2.2.3. Sacrificial Core Electrospinning

PA66 pellets were suspended in different organic solvents at various concentrations (see Table 1) and stirred continuously until completely dissolved. The solution was electrospun at ambient temperature (20–22 ◦C) in a low humidity environment (25 ± 5% RH – relative humidity, controlled by purging the chamber with nitrogen gas). The sacrificial core electrospinning setup included a high-voltage power supply, a digital syringe pump and a specialized collecting unit, composed of the sacrificial core and printed framework connected to a DC (direct current) motor and placed directly in front of a grounded metal plate (Figure 1c). The entire setup was enclosed inside a custom-made plastic chamber with fume extraction and safety interlocks. To reduce variability in fiber diameter and packing density, the DC motor was run at a constant speed during the fabrication of all capsules. Systematic optimization was performed by varying the processing parameters, as detailed in Table 1.


**Table 1.** Details of electrospinning parameters varied during optimization.

#### *2.3. Characterization Studies*

The morphological features of the electrospun PA66 materials were imaged and analyzed using SEM (Evo LS15, Carl Zeiss, Oberkochen, Germany). For this purpose, the samples were air dried in a chemical fume hood. They were then mounted on the specimen holder with double adhesive electro-conductive carbon tape, sputter-coated with platinum for 90 seconds under argon gas in a coating unit (Polaron range SC7620, Quorum Technologies Ltd, East Sussex, UK), and imaged. Fiber diameter was calculated manually by analyzing the images using Image J software (NIH, Bethesda, MD, USA).

Changes to the chemistry of PA66 after electrospinning were tracked using Attenuated Total Reflection-Fourier-transform infrared spectroscopy (ATR-FTIR, Tensor 37, Bruker, Billerica, MA, USA). For each measurement, 16 scans were recorded with a resolution of 1 cm−<sup>1</sup> and wave numbers ranging from 800 to 4000 cm−1. During the measurements, the instrument was continuously purged with nitrogen using blow-off from a liquid nitrogen tank to eliminate the spectral contributions of atmospheric water vapor.

The thermal properties of PA66 before and after electrospinning were analyzed by simultaneous thermogravimetry/differential thermal analysis (TG/DTA, Diamond, PerkinElmer, Waltham, MA, USA). In each measurement, the sample was heated from 40 to 600 ◦C at a rate of 10 ◦C/min. During the measurements, the instrument was continuously purged with nitrogen gas at a rate of 20 mL/min to eliminate the spectral alterations due to the presence of ambient air.
