## 4 Bionanosystems
### Bionanosystems for Ulvan  
The production of bionanosystems based on ulvan must consider the specific properties of this polymer in water solutions. Negative groups can be present on the macromolecular structure due to the presence of carboxylate and sulphate groups. In good agreement, [PERSON] et al. [162] noticed an aggregating tendency of ulvan in dilute aqueous solutions in the presence of 0.1 M NaCl. In addition, in the presence of divalent cations, such as Ca\({}^{2+}\), ulvan has gelling properties in a pH range of 7.5 to 8.0 [163]. In addition, the negative groups can be exploited to prepare specific nanostructured systems, with the aim of improving specific functional properties of ulvan or combining it with other functional agents. For example, ulvan was used to produce antimicrobial biofilms of silver for food packaging [164]. In the food industry, nisin is a biopreservative with antimicrobial properties against Gram-positive bacteria and the nisin-loaded ulvan particles were more stable and thus, ulvan was used as a carrier for the small nisin molecule [165]. The latter has the tendency of generating positive ions in water solution due to the presence of basic -NH-moieties, hence the regulation of pH during the preparation of the particles was pivotal. Ulvan (obtained from _U. lactuca_) was modified as a carrier system to deliver water-insoluble metabolites. The produced nanogels were based on ulvan acetate self-organized in aqueous solution, increasing the solubility of the yellow pigment curcumin extracted from _Curcuna longa_ rhizomes [166]. Curcumin is hydrophobic in nature, so it has poor solubility in water or hydrophilic solutions, but it is an important natural polyphenol with notably anti-inflammatory and other biological properties [167]. It contains -OH groups that may develop interactions with similar groups in the polysaccharide. The acetylated polysaccharide ulvan was efficiently converted to nanogels to deliver curcumin in aqueous medium [166]. Drug delivery was also exploited to form nanostructures combining the anionic characteristic of ulvan (from _U. rigida_) and the lysozyme, the ubiquitous positive charged enzyme at neutral pH. Synergistic properties were verified most probably attributed to the nanoscale and the complexes displayed higher antibacterial activity against _Staphylococcus aureus_ when compared with the enzyme or the polymer alone [67]. Application in the synthesis of hydrogels and bioactive membranes for biomedical application was also demonstrated [72]. Exploiting the tissue engineered bioactive bioreenewable scaffolds, complexes of ulvan and chitosan were designed, i.e., mixtures of positively and negatively charged polyelectrolytes blended at the molecular level [168]. Polyelectrolyte membranes are new generation of biomaterials composed of the natural polymers and can include ulvan as well as ulvan/chitosan membranes to stimulate the attachment and proliferation of specialized cells such as osteoblasts [168]. These matrices are similar to green avenues for scaffold and membrane developments and the future for macroalgae with high impact in biomedical applications. Although many experiments have been conducted on formulations involving chitin/ chitosan nanoparticles with the combination of RA, few studies proposed the incorporation of ulvan in preparations containing a matrix of chitin or chitosan. In the preparations it is important to mention the detailed structural analysis of chitosan since defined chitosan are important to their bioactivities [169] and the same for ulvan, resulting in the second generation of highly defined active molecules. Nanoparticles of chitosan-ulvan (from _U. olnoi_) were obtained and presented immunostimulant activity inducing an oxidative burst in fish macrophage [170]. The nanoparticles could be potentially used as nanocaries in feed additives or vaccine vehicles in aquaculture considering that the high molecular weight ulvan polymer was more active and the low molecular weight loose the immune-stimulatory activity in vitro [170].