Polyurethane-Nanolignin Composite Foam Coated with Propolis as a Platform for Wound Dressing: Synthesis and Characterization

Abstract

This piece of research explores porous nanocomposite polyurethane (PU) foam synthesis, containing nanolignin (NL), coated with natural antimicrobial propolis for wound dressing. PU foam was synthesized using polyethylene glycol, glycerol, NL, and 1, 6-diisocyanato-hexane (NCO/OH ratio: 1.2) and water as blowing agent. The resultant foam was immersed in ethanolic extract of propolis (EEP). PU, NL-PU, and PU-NL/EEP foams were characterized from mechanical, morphological, and chemical perspectives. NL Incorporation into PU increased mechanical strength, while EEP coating showed lower strength than PU-NL/EEP. Morphological investigations confirmed an open-celled structure with a pore diameter of 150-200 μm, a density of nearly 0.2 g/cm^3,, and porosity greater than 85%, which led to significantly high water absorption (267% for PU-NL/EEP). The hydrophilic nature of foams, measured by the contact angle, proved to be increased by NL addition and EEP coating. PU and PU-NL did not show important antibacterial features, while EEP coating resulted in a significant antibacterial efficiency. All foams revealed high biocompatibility toward L929 fibroblasts, with the highest cell viability and cell attachment for PU-NL/EEP. In vivo wound healing using Wistar rats' full-thickness skin wound model confirmed that PU-NL/EEP exhibited an essentially higher wound healing efficacy compared with other foams. Hence, PU-NL/EEP foam could be a promising wound dressing candidate.

Keywords: nanolignin; polyurethane foam; propolis; wound dressing.

Figure 1

Particle Size Distribution of NL.

Figure 2

The FTIR spectra of NL, PU-NL, EEP, and PU-NL/EEP.

Figure 3

SEM images of PU-NL (A–F) and PU-NL/EEP (G–I) samples. The red arrows are displaying the propolis at the surface of the foam’s pore walls.

Figure 4

Contact angle images of the samples: (A) PU, (B) PU-NL, and (C) PU-NL/EEP.

Figure 5

(A) The PU, PU-NL, PU-NL/EEP, and PU-NL/WEP films’ antibacterial activity against Staphylococcus aureus and Escherichia coli strains according to the zone of inhibition test. (B) Biocompatibility of the PU, PU-NL, PU-NL/EEP films with L929 skin normal fibroblast after different incubation times according to MTT assay analyzes.

Figure 6

SEM images of the PU-Nl/EEP surface at the (A) 1st and (B) 7th days after L929 cells seeding. The red arrows indicate the L929 cells. (C) SEM images with higher magnification. Yellow arrows indicate L929 cells expanded podocytes.

Figure 7

(A) Macroscopic appearances of the wounds at the 1st and 10th days post-operation at the PU, PU-NL, and PU-NL/EEP groups. (B) Histograms of the wound closure progression of the PU, PU-NL, and PU-NL/EEP groups. The data are expressed as mean ± standard deviation, (n = 8, *: p < 0.05, ns: not significant). (C) H&E stained sections of skin specimens from the wound site of the PU, PU-NL, and PU-NL/EEP groups. Two-head arrows indicated by a and b letters indicate the epidermis and dermis layers, respectively. Also, the green and blue arrows indicate the keratin layer and sebaceous gland, respectively.