Poly(vinyl alcohol)-tannic Acid Cryogel Matrix as Antioxidant and Antibacterial Material

Abstract

The biocompatible, viscoelastic properties of poly(vinyl alcohol) (PVA) in combination with the antimicrobial and antioxidant natural polyphenolic, tannic acid (TA), and the natural flavonoid and antioxidant curcumin (Cur), were used in the preparation of PVA:TA and PVA:TA:Cur cryogel composites using cryotropic gelation to combine the individually beneficial properties. The effect of TA content on the antioxidant and antimicrobial activities of PVA:TA cryogel composites and the antioxidant activities of PVA:TA:Cur cryogel composites was determined using Trolox equivalent antioxidant capacity (TEAC) and total phenol content (TPC) assays, and were compared. The PVA:TA:Cur cryogel composite showed the highest antioxidant activity, with a TEAC value of 2.10 ± 0.24 and a TPC value of 293 ± 12.00. The antibacterial capacity of the PVA:TA and PVA:TA:Cur 1:1:0.1 cryogel composites was examined against two different species of bacteria, E. coli and S. aureus. It was found that the minimum inhibition concentration (MIC) value of the PVA:TA:Cur 1:1:0.1 cryogel composites varied between 5 and 10 mg/mL based on the type of microorganism, and the minimum bactericidal concentration (MBC) value was 20 mg/mL irrespective of the type of microorganism. Furthermore, the hemocompatibility of the PVA:TA cryogel composites was evaluated by examining their hemolytic and coagulation behaviors. PVA:TA 1:1 cryogels with a value of 95.7% revealed the highest blood clotting index value amongst all of the synthesized cryogels, signifying the potential for blood contacting applications. The release of TA and Cur from the cryogel composites was quantified at different pH conditions, i.e., 1.0, 7.4, and 9.0, and additionally in ethanol (EtOH) and an ethanol-water (EtOH:Wat) mixture. The solution released from the PVA:TA cryogels in PBS was tested for inhibition capability against α-glucosidase (E.C. 3.2.1.20). Concentration-dependent enzyme inhibition was observed, and 70 µL of 83 µg/mL PVA:TA (1:1) cryogel in PBS inhibited α-glucosidase enzyme solution of 0.03 unit/mL in 70 µL by 81.75 ± 0.96%.

Keywords: antibacterial; antioxidant; cryogel; phenolic compound; polyvinyl alcohol.

Figure 1

(a) Schematic representation, and (b) digital camera images of PVA cryogel, PVA-TA cryogel composites, and PVA-TA-Cur cryogel composites, and (c) their SEM images.

Figure 2

(a) FTIR spectra and (b) TG thermograms of pure TA, pure Cur, PVA cryogel, PVA:TA, and PVA:TA:Cur cryogel composites.

Figure 3

TA release profiles from PVA:TA cryogel composites at (a) pH 1.0, (b) pH 7.4, and (c) pH 9.0.

Figure 4

TA and Cur release profiles from PVA:TA:Cur 1:1:0.1 cryogel composites, (a) TA release profiles in EtOH and EtOH:Wat by UV-Vis spectroscopy, and (b) Cur release profiles in EtOH and EtOH:Wat by fluorescence spectroscopy. Digital camera images of these cryogels under (c) 366 nm UV light, and (d) daylight.

Figure 5

Hemocompatibility of PVA cryogel, PVA:TA, and PVA:TA:Cur cryogel composites according to (a) hemolysis assay and (b) blood coagulation assay.

Figure 6

Bacterial growth number (log colony forming unit ((CFU)/mL)) in nutrient broth in the presence of PVA:TA:Cur 1:1:0.1 cryogel composites for (a) Gram-negative E. coli and (b) Gram-positive S. aureus.

Figure 7

The α-glucosidase inhibitory activity of (a) TA, (b) PVA:TA cryogel composites at pH 7.4 PBS (different concentrations; 333, 167, 83, 42, and 21 μg/mL). (c) The α-glucosidase inhibitory activity of PVA:TA cryogel composites at pH 7.4 (at 333 µg/mL concentration).