Bioactive Films from Willow Bark Extract and Nanocellulose Double Network Hydrogels

Abstract

In nature, the protection of sensitive components from external threats relies on the combination of physical barriers and bioactive secondary metabolites. Polyphenols and phenols are active molecules that protect organisms from physical and chemical threats such as UV irradiation and oxidative stress. The utilization of biopolymers and natural bioactive phenolic components as protective coating layers in packaging solutions would enable easier recyclability of materials and greener production process compared with the current plastic-based products. Herein, we produce a fully wood-based double network material with tunable bioactive and optical properties consisting of nanocellulose and willow bark extract. Willow bark extract, embedded in nanocellulose, was cross-linked into a polymeric nanoparticle network using either UV irradiation or enzymatic means. Based on rheological analysis, atomic force microscopy, antioxidant activity, and transmittance measurements, the cross-linking resulted in a double network gel with enhanced rheological properties that could be casted into optically active films with good antioxidant properties and tunable oxygen barrier properties. The purely biobased, sustainably produced, bioactive material described here broadens the utilization perspectives for wood-based biomass, especially wood-bark extractives. This material has potential in applications where biodegradability, UV shielding, and antioxidant properties of hydrogels or thin films are needed, for example in medical, pharmaceutical, food, and feed applications, but also as a functional barrier coating in packaging materials as the hydrogel properties are transferred to the casted and dried films.

Inspired by nature: Fiber networks functionalized with tannic acid and condensed tannin-rich extracts of Norway spruce bark show antimicrobial efficacy

“…This study provides baseline knowledge and proof-of-concept for the further development of antimicrobial, biobased functional coatings, and protective materials by valorizing the side streams of forestry Frontiers in Bioengineering and Biotechnology frontiersin.org industries, focusing on the condensed tannin-rich extract of Norway spruce bark as a case study. Similar value-added phenolics can also be obtained from other wood species or plant biomasses, such as willows, as shown in our earlier study (Tienaho et al, 2021) and those by (Lohtander et al, 2020;Lohtander et al, 2021) Broad-acting antimicrobial materials may be created by impregnating antimicrobial compound(s) to different materials or binding those compounds as a covalent coating on a material(s) to prevent viral transmission by or through the handled materials (Kaczmarek, 2020). Research exists on the use of tannic acid in different materials (Halim et al, 2018;Ferreira Leite et al, 2021;Ulu et al, 2021), but to the best of our knowledge, no studies have been conducted on utilizing the condensed tannin-rich extract of Norway spruce to produce broadly acting antimicrobial tissue and paper materials (i.e., evidence against both virus and bacteria).…”

“…This study provides baseline knowledge and proof-of-concept for the further development of antimicrobial, biobased functional coatings, and protective materials by valorizing the side streams of forestry industries, focusing on the condensed tannin-rich extract of Norway spruce bark as a case study. Similar value-added phenolics can also be obtained from other wood species or plant biomasses, such as willows, as shown in our earlier study ( Tienaho et al, 2021 ) and those by ( Lohtander et al, 2020 ; Lohtander et al, 2021 )…”

Bioactive Fiber Foam Films from Cellulose and Willow Bark Extract with Improved Water Tolerance

“…The role of sorbitol in foams was to bring flexibility, while the CMC was hypothesized to stabilize foams further by hindering the drainage of water. Based on previous work, the laccase enzyme was also tested to improve WBE network formation . The viscosity of foam systems, including CNF, CMC, sorbitol, MC, and WBE, before foaming was measured using a Brookfield Viscometer RVDV-III Ultra (Brookfield AMETEK Inc., USA) with a spindle size of 06 and a speed of 50 rpm.…”

“…Willow bark extract (WBE) was added to the system to bring bioactive properties in the resulting fiber foam films. WBE is an aqueous solution of polyphenols and monosugars, which increase the viscosity of the CNF hydrogels . Therefore, it was hypothesized that the WBE would influence the mechanical properties of the dry foam as well.…”

“…We present a novel approach that utilizes the synergistic effect of AKD and polyphenol-rich WBE for creating lightweight, self-standing, cellulose-based fiber foam films with improved hydrophobicity. The concept of functionalizing cellulose-based films by WBE has been presented earlier. , The novelty of this work lies in creating a self-standing foam structure from a high-consistency CNF with bioactive functionalities. The foam structure enables the use of less material compared to dense films, and the high solids content of the CNF grade utilized here allows the formation of stable wet foams.…”