**4. Materials and Methods**

### *4.1. Cell Culture and Reagents*

The murine melanoma B16-F10 cell line was all obtained from the Type Culture Collection of the Chinese Academy of Sciences (Shanghai, China). The B16-F10 cells were cultured in RPMI-1640 supplemented with 10% (*v*/*v*) heat-inactivated FBS and 1% (*v*/*v*) penicillin–streptomycin. HUVECs were obtained from the Procells company (Shanghai, China) and cultured in Ham's F-12K supplemented with 100μg/mL Heparin, 50μg/mL ECGs, 10% (*v*/*v*) heat-inactivated FBS, and 1% (*v*/*v*) penicillin-streptomycin solution. Cells were cultured at 37 ◦C in a humidified atmosphere containing 5% CO2. Cells were maintained at subconfluency, and the culture medium was changed every other day. The B16-F10 cells used were between 3 and 30 passages.

PSS was provided by Chia Tai Haier Pharmaceutical Co., Ltd. (Qingdao, China). Heparin (201 U/mg) was obtained from Wanbang Pharmaceuticals Company (Xuzhou, China). All proteins were purchased from Sino Biological (Beijing, China). All antibodies were purchased from Cell Signaling Technology (Cell Signaling Technology Inc., MA, USA). Matrigel was purchased from Corning Company (Tewksbury, MA, USA). All other chemicals and solvents were of analytical grade and purchased from Sinopharm Group Co. Ltd. (Beijing, China)

### *4.2. The Binding Kinetics of Propylene Glycol Alginate Sodium Sulfate and Fibroblast Growth Factor 2*

The kinetics and specificity of the binding between PSS derivatives and FGF2 and VEGF165 proteins were determined by a PlexArray ®HT SPR system (Plexera Inc., Seattle, DC, USA). Briefly, PSS (1–5 mM) were immobilized on Graft-to-PCL sensor chips by UV crosslinking for 15 min, according to an established protocol. The mobile phase was FGF2 or VEGF165 solution (dissolved in PBS), and the concentrations used were 125, 250, and 500 nM. The data obtained were analyzed and fitted by PLEXERA SPR DAM to obtain the equilibrium dissociation constant (KD).
