2.2. Preparation of PLLA nanofibers and CS
The PLLA was dissolved in DCM and DMF with a mass ratio of 1.8: 93.29: 4.91, then was electrospun by electrospun equipment. Electrospun equipment kept fixed parameters: 30 ml syringe; 19 G needle; 30 cm distance between the needle and the collector; 17 kV voltage; 5 ml/h feeding speed; 2 h collection [18].
CS was obtained by the following method. First, a candle was lit and a glass plate was placed above the candle flame. Then, the black CS gradually adhered to the glass plate and lasted for 3 minutes. Finally, the glass plate was removed and cooled, and the CS was gained by scraping off the coating on the glass plate.