Scheme 1. Schematic of the preparation process of the functionalized γ-PGA compound.

Fig. 1. Characterization of the functionalized γ-PGA compound. (A) 1H NMR spectra of ELA, γ-PGA and γ-PGA-ELA. The solvents used were CDCl3, D2O and CD4O, respectively. (B) FTIR spectra of γ-PGA, ELA and γ-PGA-ELA. (C) TGA curves of γ-PGA-ELA and γ-PGA.

Fig. 2. Solubility of the functionalized γ-PGA compound and characterization of the γ-PGA-ELA coating. (A) Digital pictures of the functionalized γ-PGA compound dissolved in different solvents. (B) Schematic illustration of the formation of the γ-PGA-ELA coating and digital pictures of different substrates stained with crystal violet; uncoated substrates were treated with the same process as for coated substrates. (C) Water contact angles of untreated PP and PP coated with γ-PGA, ELA, and γ-PGA-ELA. γ-PGA and ELA are water-soluble, and the corresponding coatings could be washed away easily and leave the hydrophobic PP. (D) FTIR spectra of untreated PP film and γ-PGA-ELA coated PP film.

Fig. 3. Antibacterial performances of the functionalized γ-PGA compound coated films. (A) Inhibition zone assay of γ-PGA-ELA coated films at different concentrations. (B) Agar plate colony counting assay: the photographs represent the growth of bacteria on agar plates after co-cultured with samples for 24 h. (C) Representative SEM images of S. aureus adhered to the surface of the uncoated and coated films at different magnifications. (D) Representative CLSM images of S. aureus attachment to the surface of the uncoated and coated films.

Fig. 4. Antibacterial activity of the lumen of γ-PGA-ELA coated catheters compared with that of uncoated catheters. S. aureus was selected for the representative bacteria. The catheters were filled with S. aureus solution (1 × 106 CFU mL-1) and cultured at 37 °C for 3 h. For static flow catheter test: (A) OD600 values of the inoculant diluted with fresh LB medium tested at different time. (B) Plates for bacterial count of the S. aureus bacterial suspension diluted with PBS after incubated at 37 °C for 24 h. For dynamic flow catheter test: (C) Photographs represent the growth of bacteria on agar plates of coated catheters and uncoated catheters from different parts of the catheters after 24 h flow of LB. (D) Agar plate colony counting results of the bacteria adhered to the lumen of catheters from front end, middle and tail end, respectively. (E) SEM images of the bacteria adherent on the lumen of the catheters with a total length of 2 m and an inner diameter of 1 mm at both endings and the middle part of the catheters (the yellow arrows indicate the dead bacteria).

Fig. 5. Antibacterial activity PE blended with γ-PGA-ELA. (A) Comparison of antibacterial activities of PE blended with different proportions of γ-PGA-ELA. The photographs represent the number of bacteria growing on the surface of the corresponding membranes after 24 h incubation. (B) Comparison of antibacterial activities of PE blended with 10 % (w/w) γ-PGA-ELA and ELA. The photographs represent the number of bacteria growing on the surface of the corresponding membranes after 24 h incubation.

Fig. 6. Biocompatibility assays of the γ-PGA-ELA coated films with different concentrations. (A) Results of CCK-8 cytotoxicity assay of coated films and control groups against L929 murine fibroblasts cells. (B) Results of hemolysis assay of coated films and control groups against mouse red blood cells.

Fig. 7. Results of the histocompatibility assay of coated catheters compared with uncoated catheters based on a sterile subcutaneous implant model. (A) Representative image of the tissue compatibility in visually (5 days) chosen from 5 different samples. (B) Results of H&E staining assay.

Fig. 8. Antibacterial activity of the coated catheters compared with unmodified catheters in vivo based on a subcutaneous implant model. (A) Representative image of the inflammatory reaction in visually (5 days), chosen from 5 different catheters. (B) Digital photographs and statistical counting of the colonies bred on the agar plates of the implants after a five-day inoculation in the back of the mouse. (C) Results of H&E staining assay of the subcutaneous tissue at the implants.