The cooling of blends in water supports durable, thermo-responsive, and porous gelatin-polyphenolic tannin assemblies with antimicrobial activities

Abstract

We applied an amino-functionalized polyphenolic tannin derivative (TN), commercially called Tanfloc, to stabilize gelatin (GE) chains and provide physical assemblies. Zeta potential measurements showed that the TN presents an isoelectric point of 4.45. Hydrolyzed tannins comprise the TN structure, supporting negative Zeta potentials at pHs higher than 4.45. Aqueous GE (1.0, 2.0, 3.0, and 4.0 % wt/vol) and polyphenolic tannin derivative (TN, 4.6 g⋅L―1) mixtures in distilled water (pH 5.5, at 50 °C) provided physical assemblies after cooling at 4 °C. The thermosensitive hydrogels often showed gelation temperatures between 41 and 45 °C. A durable, porous, and organized structure with solid-liquid phase transition (gelation) higher than 60 °C was obtained at 4.0 % wt/vol GE and 50/50 GE/TN volume ratio at GE + TN equal to 134.0 mg. Viscoelastic materials were created by blending GE (4.0 % wt/vol) and TN (4.6 g⋅L―1) aliquots at GE/TN volume ratios equal to 90/10 vol/vol (assembly 4-90/10 at GE + TN equal to 212.3 mg) and 50/50 vol/vol (assembly 4/50/50 at GE + TN = 134.0 mg). A pure GE material showed the highest porosity (89 %). The TN presence reduced the material porosity to 65 % (assembly 4-90/10) and 63 % (assembly 4-50/50). The assembly 4-90/10 showed aqueous instability because the polymer blend had no enough TN to stabilize the GE chains. However, the assembly 4-90/10 had antimicrobial activities against Escherichia coli (E. coli) with minimal inhibitory and minimum bactericidal concentrations of 500 μg⋅ mL―1. The disk diffusion method showed that the assembly 4-90/10 provided an inhibition halo of 11 mm toward E. coli after 24 h of exposure at pH 6.0. GE/TN assemblies can provide physical hydrogels for biomedical applications (wound dressings).