Cooperative crystallization effect in the formation of sonochemically grafted active materials based on polysaccharides
Graphical abstract
Introduction
Active films based on biodegradable polymers and nature-sourced bioactive agents are highly desired since they can be used as advanced eco-compatible and safe packages, patches, covers and coatings for applications in food, pharmacology, agriculture and more [[1], [2], [3]]. However, the incorporation of nature-sourced active agents in the biodegradable polymer matrices is more challenging than the incorporation of synthetic active agents in synthetic polymers, where addition during extrusion [4] bulk polymer modification [5], nanocomposites [6] and surface grafting [7] are regularly applied. Biodegradable polymers are usually less robust than the synthetic ones, while nature-sourced active agents are often more sensitive, sometimes volatile and have limited solubility. Therefore, the approaches that are used with synthetic components are often too vigorous for nature-sourced materials. Specially designed nanotubes [8], nanoemulsions [9] and nanogels [10] were reported to be successfully used for incorporation, protection and controlled release of nature-sourced active agents. For the functionalization of biodegradable polymers blending followed by co-drying processes [11], non-thermal plasma modifications [12] and surface deposition [13] have been utilized. Recently, sonochemical surface deposition technique was reported as a promising method allowing successful adding of active agents to the surfaces of various materials [14,15].
Co-crystallization is a method used in the pharmaceutical applications for enhancing substance solubility and improve its availability and functionality. Co-crystals are usually formed by two or more different molecular entities where the intermolecular interactions are promoted by hydrogen bonding and π- π stacking [16,17]. Co-crystallization was also utilized to improve availability of numerous nature-sourced active agents, such as haloprogin [18], quercetin [19], fumaric acid [20] and more. However, to the best of our knowledge, co-crystallization processes have yet to be thoroughly studied in the regard of sonochemical deposition.
In the current study, we have utilized the sonochemical grafting method for the deposition of natural bioactive agents on biodegradable polysaccharide-based films. Polysaccharides are safe, non-expensive, hypoallergenic materials that are being used in drug delivery, medical devices, agricultural and cosmetic industries. A vast array of applications of polysaccharides was reported as biodegradable active packages capable to extend shelf-life, preserve the quality and provide microbial safety of food products [21,22]. Two polysaccharides with excellent film forming ability, chitosan [23] and carboxymethyl cellulose (CMC) [24] were utilized. Vanillin, a volatile antimicrobial aromatic phenolic aldehyde, capable on preventing yeast, mold and bacterial infections [25,26] and curcumin, the non-volatile water insoluble compound demonstrating antimicrobial, antiviral, antioxidant and anti-inflammatory activity [27] were used as the active agents. These compounds were in situ deposited, separately or as a mixture, in order to examine the option of co-crystallization between the curcumin and vanillin to prolong activity of a volatile vanillin. Spectroscopic, microscopic, morphological, physico-mechanical properties as well as the bioactivity of the new active films were comprehensively studied.
Section snippets
Materials
99.9 % vanillin, 95 % acetic acid and absolute ethanol were supplied by Sigma-Aldrich. Chitosan (100–300 cps, low molecular weight) was purchased from Glentham life sciences. 95 %, curcumin and carboxymethylcellolose sodium salt were supplied by Alfa Aesar. Plate count agar (PCA) was purchased form Merck and potato dextrose agar (PDA) were supplied by Becton, Dickinson and company. Chloramphenicol was supplied by Sigma-Aldrich. Distilled water was used for the preparation of all solutions.
Film preparation
CMC
Formation, characterization and physico-mechanical studies of the active films
CMC and chitosan films were casted from film forming aqueous solutions and then volatile vanillin, non-volatile curcumin, and the mixture of vanillin-curcumin were in situ deposited on the film surfaces from ethanol/aqueous solution using ultrasonic irradiation. The High-Resolution Scanning Electron Microscope (HR-SEM) revealed grafting of active agents on the polymer films surface as a result of the sonication process. The pristine CMC and chitosan films serving as a control exhibited smooth
Conclusions
Biodegradable, active films based on nature-sourced polysaccharides CMC and chitosan were prepared using in situ ultrasonic deposition of vanillin, curcumin and curcumin-vanillin mixture. All the prepared films demonstrated good chemico-physical properties and antimicrobial activity. However, films with a deposited curcumin-vanillin mixture showed superior performance. As was confirmed by HR-SEM and XRD, π−π stacking interactions between the aromatic rings of curcumin and vanillin promote their
CRediT authorship contribution statement
Yevgenia Shebis: Conceptualization, Methodology, Software, Writing - original draft, Investigation, Formal analysis. Vijay Bhooshan Kumar: Methodology, Software, Writing - original draft, Formal analysis. Aharon Gedanken: Conceptualization, Writing - original draft, Supervision, Funding acquisition. Elena Poverenov: Conceptualization, Writing - original draft, Supervision, Investigation, Funding acquisition, Project administration.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The research leading to these results has received funding from the Israeli Ministry of Health Grant No. 3-0000-99611 and contribution from the Agricultural Research Organization, The Volcani Center, Rishon Lezion, Israel.
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