Cryostructuring of Polymeric Systems: 67 Properties and Microstructure of Poly(Vinyl Alcohol) Cryogels Formed in the Presence of Phenol or Bis-Phenols Introduced into the Aqueous Polymeric Solutions Prior to Their Freeze-Thaw Processing

Abstract

Poly(vinyl alcohol) (PVA) physical cryogels that contained the additives of o-, m-, and p-bis-phenols or phenol were prepared, and their physico-chemical characteristics and macroporous morphology and the solute release dynamics were evaluated. These phenolic additives caused changes in the viscosity of initial PVA solutions before their freeze-thaw processing and facilitated the growth in the rigidity of the resultant cryogels, while their heat endurance decreased. The magnitude of the effects depended on the interposition of phenolic hydroxyls in the molecules of the used additives and was stipulated by their H-bonding with PVA OH-groups. Subsequent rinsing of such "primary" cryogels with pure water led to the lowering of their rigidity. The average size of macropores inside these heterophase gels also depended on the additive type. It was found also that the release of phenolic substances from the additive-containing cryogels occurred via virtually a free diffusion mechanism; therefore, drug delivery systems such as PVA cryogels loaded with either pyrocatechol, resorcinol, hydroquinone, or phenol, upon the in vitro agar diffusion tests, exhibited antibacterial activity typical of these phenols. The promising biomedical potential of the studied nanocomposite gel materials is supposed.

Keywords: antimicrobial activity; drug release; phenols; physico-chemical properties; poly(vinyl alcohol) cryogel.

Figure 1

Chemical structures of pyrocatechol (a), resorcinol (b), hydroquinone (c), and phenol (d).

Figure 2

Flow curves for the 100 g/L aqueous PVA solutions without (1) and with the additives of pyrocatechol (a), resorcinol (b), hydroquinone (c), and phenol (d) in concentrations of 0.036 mol/L (2), 0.100 mol/L (3), and 0.180 mol/L (4).

Figure 3

The values of the Young’s compression modulus (E) of PVACGs as dependent on the molar concentration of pyrocatechol (a), resorcinol (b), hydroquinone (c), and phenol (d) in the 100 g/L aqueous PVA feed solutions.

Figure 4

Fusion temperature values (T_f) of PVACGs as dependent on the molar concentration of pyrocatechol (a), resorcinol (b), hydroquinone (c), and phenol (d) in the 100 g/L aqueous PVA feed solutions.

Figure 5

The values of the Young’s compression modulus (E) of the “primary” PVA cryogels formed at −20 °C (white columns) and the respective “secondary” PVACGs (grey columns) as dependent on the molar concentration of pyrocatechol (a), resorcinol (b), hydroquinone (c), and phenol (d) in the 100 g/L aqueous PVA feed solutions.

Figure 6

Environmental SEM images of microstructure of the “secondary” PVACGs derived from the “primary” cryogels that contained additives of pyrocatechol (a), resorcinol (b), hydroquinone (c), and phenol (d); the microstructure (e) of the “secondary” cryogel derived from the additive-free “primary” PVACG is given for the sake of comparison (scale bars—10 μm for all cases).

Figure 7

Kinetic profiles of the release of phenolic additives (pyrocatechol (a), resorcinol (b), hydroquinone (c), and phenol (d)) from the respective “primary” PVACGs.

Figure 7

Kinetic profiles of the release of phenolic additives (pyrocatechol (a), resorcinol (b), hydroquinone (c), and phenol (d)) from the respective “primary” PVACGs.

Figure 8

Growth inhibition zones formed around the PVA cryogels that contained 0.18 mol/L of pyrocatechol (a,f), resorcinol (b,g), hydroquinone (c,h), and phenol (d,i) or were additive-free (e,j) after sample incubation for 24 h onto the lawns of S. aureus (a–e) and E. coli (f–j) bacterial cells.