Silver nanoparticles (AgNPs) have been intensively investigated in virtue of their optical and antimicrobial properties, although their applications have been limited due to inherent toxicity and to the need of employing harsh chemical reagents for the synthesis. In this work, ulvan, a sulfated polysaccharide extracted from green algae belonging to Ulva armoricana sp., was for the first time investigated and identified as reducing and stabilizing agent for AgNPs synthesis by using milder conditions than those conventionally adopted by chemical methods. The synthesized AgNPs were thoroughly characterized to highlight the structure and the role exerted by ulvan in their synthesis and stabilization. The formation of AgNPs stabilized by a thick ulvan shell was assessed by UV-vis, XRD, TEM, DLS and zeta potential analyses. The developed Ulvan based AgNps showed an IC50 in the range of 10 μg/ml in Balb/3T3 mouse embryo fibroblasts and antimicrobial activity toward both Gram+and Gram − bacteria.

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In the present work, ulvan, a sulphated polysaccharide of algal origin, was innovatively investigated as stabilizing and emulsifying agent in colloidal formulations containing functional agents for food and cosmetic applications in virtue of its edibility and amphiphilic character. Ulvan was successfully submitted to chemical modification with biocompatible fatty acid moieties to increase the amphiphilic properties of the polysaccharide without compromising its safety profile. Oil in water (O/W) emulsions were developed using the ultrasonication method as an easy and rapid homogenization process. The stability of the obtained formulations was assessed by visual inspection, size distribution and zeta potential analysis. Stable emulsions were obtained by using either native or chemically modified polysaccharide. The most promising formulations based on the use of native ulvan were successfully implemented as clouding and flavouring agents in soft drink beverages and as stabilizing and perfuming agents in body cream milk products. The obtained results may open new perspectives on the exploitation of abundant waste biomasses as sources of biocompatible high value added materials suitable for being applied in critical applications as a safe alternative to synthetic chemicals. In particular ulvan could represent a valuable platform of functional and bioactive compounds with promising properties as stabilizing and emulsifying agents for food and cosmetic applications.

Recurrent microbial infections are a major cause of surgical failure and morbidity. Wound healing strategies based on hydrogels have been proposed to provide at once a barrier against pathogen microbial colonization, as well as a favorable environment for tissue repair. Nevertheless, most biocompatible hydrogel materials are more bacteriostatic than antimicrobial materials, and lack specific action against pathogens. Silver-loaded polymeric nanocomposites have efficient and selective activity against pathogenic organisms exploitable for wound healing. However, the loading of metallic nanostructures into hydrogels represents a major challenge due to the low stability of metal colloids in aqueous environments. In this context, the aim of the present study was the development of highly stable silver nanoparticles (AgNPs) as novel potential antimicrobial agents for hyaluronic acids hydrogels. Two candidate stabilizing agents obtained from natural and renewable sources, namely cellulose nanocrystals and ulvan polysaccharide, were exploited to ensure high stability of the silver colloid. Both stabilizing agents possess inherent bioactivity and biocompatibility, as well as the ability to stabilize metal nanostructures thanks to their supramolecular structures. Silver nitrate reduction through sodium borohydride in presence of the selected stabilizing agents was adopted as a model strategy to achieve AgNPs with narrow size distribution. Optimized AgNPs stabilized with the two investigated polysaccharides demonstrated high stability in phosphate buffer saline solution and strong antimicrobial activity. Loading of the developed AgNPs into photocrosslinked methacrylated hyaluronic acid hydrogels was also investigated for the first time as an effective strategy to develop novel antimicrobial wound dressing materials.