Carboxyl chitosan

The PFTBA core solution preparation was carried out in accordance with previous investigations [33 (link)]. Briefly, 190 ​mg of egg yolk lecithin (Sigma, USA) was dissolved in 1 ​mL of Tyrode's solution (Sigma, USA), and mixed via ultrasonic shaker twice at 4 ​°C for 15 ​s. Subsequently, 1 ​mL of PFTBA stock solution was introduced, followed by sonic concussion 10 times under the same parameters. In control groups (without PFTBA), PBS (Gibco, USA) was introduced instead. Finally, carboxyl-chitosan (Sigma, USA) was introduced to the above emulsion to form a gelatinized core solution. Varying concentrations of carboxyl chitosan (5% w/v, 7.5% w/v, 10% w/v, 12.5% w/v, 15% w/v; 20% w/v, Sigma, USA) were used to form the optimal structure. In addition, to prepare the shell solution, 20% w/v polycaprolactone (PCL, Sigma, USA) particles were dissolved in methanol-chloroform solution, in a 1:4 v/v ratio. To observe the electrospinning process, Rhodamine B (1 ​mg/mL, Sigma, USA) was mixed with the shell material, fluorescein isothiocyanate (FITC; 2 ​mg/mL, YEASEN, China) with the core material, and the core-shell structure was fluorescently labeled during the electrospinning process.