Imperfect cross-linking of xanthan for pH-responsive bio-based composite moist wound dressings by stencil printing

Abstract

The work addresses the use of bio-based and -degradable materials for the production of a moist, adaptive and anti-microbial wound dressing. The dressing is targeted to exhibit a pH-dependent active agent release. Xanthan hydrogel structures are coated on cellulose fabrics via stencil printing and subsequently cross-linked using glyoxal. By alteration of the cross-linker content from 1 to 6% by mass, the hydrogel elasticity can be tuned within a range of 2-16 kPa storage modulus. Increasing initial glyoxal concentrations also result in higher amounts of glyoxal release. Glyoxal, an anti-microbial agent with approval in veterinary medicine, is mostly released upon wound application supporting infection management. As wound simulation, normal saline, as pH 5 and pH 8 buffer solutions, were used. The release profile and magnitude of approx. 65%-90% glyoxal is pH-dependent. Increased release rates of glyoxal are present in pH 8 fluids, which mostly base on faster hydrogel swelling. Higher total glyoxal release is present in pH 5 fluid and normal saline after 3 days. Accordingly, a pH-dependent release profile was encountered. As glyoxal attacks any cell unselectively, it is expected to be effective against antibiotic resistant bacteria. By stencil printing the dressing size can be adjusted to minimize healthy glyoxal tissue exposure.

Keywords: Wound dressing; anti-microbial; bio-based; composite; hydrogel.

Figure 1.

Upper row: Xanthan-cellulose fabric samples containing (a) 0%, (b) 1% and (c) 6% glyoxal by mass. Lower row: (d) Xanthan structures with 6% by mass glyoxal peeled from clear foil for rheometry (e) SEM image of 6% by mass glyoxal sample surface and (f) a cross-section of a dried xanthan layer containing no glyoxal.

Figure 2.

FTIR spectra of a pure cellulose fabric (solid) as prepared samples of increasing glyoxal concentration from bottom to top: 0% (dash-dot-dotted), 1% (dotted), 2% (dash-dotted), 6% (loosely dashed) and 12% wt. (dashed).

Figure 3.

Normalized swelling sample weights of 0% (yellow), 1% (grey) and 6% (red) by mass glyoxal samples for swelling in normal saline (dot-dashed), pH 5 (dotted) and pH 8 (solid) media. Shaded areas represent standard deviations of 3 repetitions.

Figure 4.

(Left axis) bars of storage (petrol) and loss modulus (red) of xanthan hydrogel structures at 10 Hz, 0.3% shear, given a 5% error. (Right axis) theoretical degree of polymerisation (D_p) between cross-links (yellow solid line) as a multiple of the loss factor: 1000*δ (red dots).

Figure 5.

Elution media for all subplots: (grey) normal saline, (red) pH 5 and (yellow) pH 8-buffered media. (a) Glyoxal release of 1% (lower curves) and 6% (upper curves) by mass glyoxal dressings. (b) Share of total glyoxal released (left bar – strong color), as with an additional 1 mol/l HCl wash (right bar – light shade) (c) glyoxylic acid mass release (left) and glycolic acid mass release (right) with given mol ratio to total glyoxal (violet dots).

Figure 6.

Agar diffusion tests after 24 h incubation: (a) 0% glyoxal, (b) 1% glyoxal or (c) 6% glyoxal against S. aureus, (d) 1% (left) and 6% (right) glyoxal against P. aeruginosa, and (e) 1% (left) and 6% (right) glyoxal against E. coli.