Poly(L -lactic acid) [molecular weight (Mw) = 50 kDa, Mw/Mn = 1.61] was prepared via bulk ring-opening polymerization of L -lactide using stannous chloride as an initiator (Jinan Daigang Co., Jinan, China). Dichloromethane and trichloromethane were purchased from the Chinese Medicine Group Chemical Reagent Corporation. Dextran (average Mw = 64,000–76,000 Da) and polyethylene glycol (PEG6000) were purchased from Sigma (St. Louis, MO, United States). All other chemicals and solutions were obtained from Guoyao Corporation (Shanghai, China).
Electrospun fabrication was performed as described previously (Cui et al., 2009 (link)). A high-voltage (15 kV) direct current was applied to fabricate the PLLA fibrous membrane. The polymeric solution was fed into the needle tip using a syringe pump at an injection rate of 3.0 mL/h. A grounded aluminum foil was used to collect the fibrous membranes. A 15-cm distance was left between the spray head and the collecting device. The first layer was sprayed with ethylalcohol and vacuum-dried for 1 day before collecting the second layer on the same foil. The second layer was sprayed with ethylalcohol and dried under the same conditions as those used for the first layer.
Electrospun fabrication was performed as described previously (Cui et al., 2009 (link)). A high-voltage (15 kV) direct current was applied to fabricate the PLLA fibrous membrane. The polymeric solution was fed into the needle tip using a syringe pump at an injection rate of 3.0 mL/h. A grounded aluminum foil was used to collect the fibrous membranes. A 15-cm distance was left between the spray head and the collecting device. The first layer was sprayed with ethylalcohol and vacuum-dried for 1 day before collecting the second layer on the same foil. The second layer was sprayed with ethylalcohol and dried under the same conditions as those used for the first layer.