Highly stretchable gamma-irradiated poly (vinyl alcohol)/Tannic acid composite hydrogels with superior transparency and antibacterial activity

Abstract

The development of facile and cost-effective strategies for hydrogels with multifunctionality is of great scientific interest. In this work, a series of poly (vinyl alcohol)/tannic acid (PVA/TA) composite hydrogels were facilely prepared by gamma radiation of a PVA solution and subsequent soaking treatment in TA solutions. The chemical composition, transparency, microstructure, mechanical property and antibacterial activity of the resulting composite hydrogels were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), UV-Vis spectroscopy, SEM, tensile measurements and an antibacterial test, respectively. The introduction of TA into the gamma radiation-induced chemically cross-linked networks of PVA hydrogels via the soaking treatment, which forms the second physically cross-linked networks, endows the PVA hydrogels with improved mechanical performance. The tensile strength, toughness and elongation at break of the composite hydrogel were increased by 1500 % (from 18 kPa to 254 kPa), 3600 % (from 8.5 kJ m −3 to 315 kJ m −3 ) and 360 % (from 87 to 403 %), respectively. Meanwhile, high transparency of the neat irradiated PVA hydrogels was maintained in the obtained composite hydrogels (transmittance over 60 % at 660 nm). The strong hydrogen bonding interaction between PVA and TA within the networks serves as sacrificial bonds and suppresses the crystallinity of the PVA hydrogels. In addition, the composite hydrogels also possess superior antibacterial activity against both gram-negative and gram-positive bacteria. This work provided a simple approach for the construction of multifunctional hydrogels on large-scale preparation, thus would hopefully promote their applications in biomedicine, wound dressings and soft devices.

Influence of chemical nature of citric and malic acids on reaction time of the crosslinking of polyvinyl alcohol hydrogels

“…For hydrogels composed of PVOH/AC and -AM, as shown in Table 4, the melting point Tm of -AC, -AC1, -AC2, -AC3 and -AM, -AM1, -AM2, -AM3 are 161.52 °C to 164.37 °C and from 160.55°C to 163.74°C respectively, and all Tm points were shifted to a lower temperature as the concentration of organic acids increased, with similar behaviour for the -AC/-AM groups. This behaviour was also observed in a study by Yang et al [10] with the incorporation of tannic acid.…”

“…Samples sealed in an aluminium pan were heated from 25 to 220°C at a heating rate of 10°C/min rate and were kept at 220°C heating isothermal for 1 min. The degree of crystallinity of the PVOH was calculated from the integration of the endothermic peak of the DSC curves using equation 3, following a method applied by Yang et al [10] with the use of the TA Universal Analysis® software.…”

“…Where: ΔHc is the thermodynamic enthalpy of hydrogels and ΔHc is the thermodynamic enthalpy of fusion of 100% crystalline PVOH (136.8 J g −1 ) [10].…”

“…PVOH hydrogels were Soxhlet extracted in water reflux for 24 hours following the method described by Yang et al [10] . The sol-gel ratio was calculated using the equations:…”

“…Yang et al [10] studied the incorporation of tannic acid (TA) in PVOH-based hydrogels by FTIR, the results showed a band shift from 3408 cm −1 to 3373 cm −1 , which is attributed to the stretching bands of -OH, indicating that the intermolecular interactions between PVOH and TA via hydrogen bonds are formed, being characterized by the intermolecular types presented above and observed in the analysed spectra of -AM and its variations. Also, Zhang et al [17] when evaluating the behaviour of AM and AT acids, observed that the zeta potential increased slightly at the beginning of the titration and then decreased, while in the AT series, thus the surface energy decreased continuously, showing a strong influence of the interaction of hydrogen bonding in AM and showing a greater interaction with hydroxyl groups (-OH), presented under the chemical change in the polymeric chains of poly(2-vinyl pyridine).…”