Freeze-thaw-induced cross-linked PVA/chitosan for oxytetracycline-loaded wound dressing: the experimental design and optimization

Abstract

Oxytetracycline is an antibiotic for the treatment of the infections caused by Gram-positive and Gram-negative microorganisms. Among novel formulations applied for damaged skin, hydrogels have shown to be superior as they can provide a moist environment for the wound. The purpose of this study was to prepare and evaluate the hydrogels of oxytetracycline consisted of polyvinyl alcohol (PVA) and chitosan polymers. A study design based on 4 factors and 3 levels was used for the preparation and evaluation of hydrogels formed by freeze-thaw (F-T) cycle using PVA and chitosan as a matrix-based wound dressing system. Furthermore, an experimental design was employed in order to study the effect of independent variables, namely drug amount (X₁, 500-1000 mg), the amount of PVA (X₂, 3.33-7.5%), the amount of chitosan (X₃, 0.5-1%), and F-T cycle (X₄, 3-7 cycles) on the dependent variables, including encapsulation efficiency, swelling index, adsorption of protein onto hydrogel surface, and skin permeation. The interaction of formulation variables had a significant effect on both physicochemical properties and permeation. Hydrogel microbial tests with sequential dilution method in Muller-Hinton broth medium were also carried out. The selected hydrogel (F6) containing 5% PVA, 0.75% chitosan, 1000 mg drug, and 3 F-T cycles was found to have increased encapsulation efficiency, gel strength, and higher skin permeation suitable for faster healing of wounds. Results showed the biological stability of oxytetracycline HCl in the hydrogel formulation with a lower dilution of the pure drug. Thus, oxytetracycline-loaded hydrogel could be a potential candidate to be used as a wound dressing system.

Keywords: Chitosan; Hydrogel; Oxytetracycline; Polyvinyl alcohol; Skin.

Fig. 1

Optical microscopic photograph of oxytetracycline hydrogel.

Fig. 2

Optical microscopic photograph of blank hydrogels.

Fig. 3

Scanning electron microscopy of F6 hydrogel with (A-D) different magnitudes; 2, 5, 20, and 50 μm, respectively.

Fig. 4

Response contour plot showing the effect of (A and B) formulation variables (X2, polyvinyl alcohol; X3, chitosan; and X4, F-T cycles) on drug content and response surface plot showing the effect of (C and D) formulation variables (X1, drug; X3, chitosan; and X4, F-T cycles) on drug content. PVA, polyvinyl alcohol; F-T, freeze-thaw; DC, drug content.

Fig. 5

Differential scanning calorimeteric thermogram of (A) oxytetracycline, (B) polyvinyl alcohol, (C) chitosan, (D) hydrogels of F6, (E) F7, (F) F17, and (G) F21.

Fig. 6

Linear culture of serial dilution tubes of (A₁ and A₂) oxytetracycline powder and (B) F6 hydrogel in minimum inhibitory concentration test. Serial dilutions: 1, 1 μM; 2, 2 μM; 3, 4 μM; 4, 8 μM; 5, 16 μM; 6, 32 μM; 7, 64 μM; 8, 128 μM, 9, 256 μM; 10, 512 μM; 11, 1024 μM; and 12, 2048 μM.

Fig. 7

In vivo study of (A) wound appearance, (B) wound dressing, (C and D) control group (treated without drug), (E and F) blank group (treated with blank hydrogel), and (G and H) drug of group (treated with F6 hydrogel) in rats.

Fig. 8

Histopathological evaluation of the abdominal skin of rat, (A) untreated, (B) treated with blank hydrogel, (C) and treated with oxytetracycline hydrogel (magnification × 10 ).