The efficacy of chitosan (CS) to be used as drug delivery carrier has previously been reported. However, limited work has been pursued to produce stable and mucoadhesive CS electrosprayed particles for oral drug delivery, which is the aim of this study. Various CS types with different molecular weight (MW), degree of deacetylation (DD), and degree of polymerization (DP) were assessed. In addition, the effect of the solvent composition was also investigated. Results showed that stable CS electrosprayed particles can be produced by dissolving 3% w/v of low MW CS in mixtures of aqueous acetic acid and ethanol (50/50% v/v). The stable CS particles displayed diameters of approximately 1 μm as determined by dynamic light scattering. The zeta potential of these particles was found to be approximately 40 mV confirming the mucoadhesion properties of these CS electrosprayed particles and its potential to be used as drug delivery carrier.

We examined the interaction between chitosan-based nanocapsules (NC), with average hydrodynamic diameter ∼114-155nm, polydispersity ∼0.127, and ζ-potential ∼+50mV, and an E. coli bacterial quorum sensing reporter strain. Dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) allowed full characterization and assessment of the absolute concentration of NC per unit volume in suspension. By centrifugation, DLS, and NTA, we determined experimentally a "stoichiometric" ratio of ∼80 NC/bacterium. By SEM it was possible to image the aggregation between NC and bacteria. Moreover, we developed a custom in silico platform to simulate the behavior of particles with diameters of 150nm and ζ-potential of +50mV on the bacterial surface. We computed the detailed force interactions between NC-NC and NC-bacteria and found that a maximum number of 145 particles might interact at the bacterial surface. Additionally, we found that the "stoichiometric" ratio of NC and bacteria has a strong influence on the bacterial behavior and influences the quorum sensing response, particularly due to the aggregation driven by NC.

Novel hybrid hydrogels were formed by adding chitosan (Ch) to phospholipids (P) self-assembled particles in lactic acid. The effect of the phospholipid concentration on the hydrogel properties was investigated and was observed to affect the rate of hydrogel formation and viscoelastic properties. A lower concentration of phospholipids (0.5% wt/v) in the mixture, facilitates faster network formation as observed by Dynamic Light Scattering, with lower elastic modulus than the hydrogels formed with higher phospholipid content. The nano-porous structure of Ch/P hydrogels, with a diameter of 260±20 nm, as observed by cryo-scanning electron microscopy, facilitated the penetration of water and swelling. Cell studies revealed suitable biocompatibility of the Ch/P hydrogels that can be used within life sciences applications.

Quorum sensing (QS) explains a type of bacterial cell-cell communication mediated by exocellular compounds that act as autoinducers (AIs). As such, QS can be considered the most primordial form of language. QS has profound implications for the control of many important traits ( e.g. biofilm formation, secretion of virulence factors, etc.). Conceptually, the QS response can be split into its “listening” and “speaking” components, i.e. the power to sense AI levels vs. the ability to synthesize and release these molecules. By explaining the cell-density dependence of QS behavior as the consequence of the system’s arrival to a threshold AI concentration, models of QS have traditionally assumed a salient role for the “QS speaking” module during bacterial cell-to-cell communication. In this paper, we have provided evidence that challenges this AI-centered view of QS and establishes LuxR-like activators at the center of QS. Our observation that highly coordinated, cell-density dependent responses can occur in the absence of AI production, implies that the ability to launch such responses is engrained within the “QS listening” module. Our data indicates that once a critical threshold of intracellular activator monomers in complex with AI is reached, a highly orchestrated QS response ensues. While displaying a clear cell-density dependence, such response does not strictly require the sensing of population levels by individual cells. We additionally show, both in vivo and in silico , that despite their synchronous nature, QS responses do not require that all the cells in the population participate in the response. Central to our analysis was the discovery that percolation theory (PT) can be used to mathematically describe QS responses. While groundbreaking, our results are in agreement with and integrate the latest conclusions reached in the field. We explain for the first time, the cell-density-dependent synchronicity of QS responses as the function of a single protein, the LuxR-like activator, capable of coordinating the temporal response of a population of cells in the absence of cell-to-cell communication. Being QS the most primordial form of speech, our results have important implications for the evolution of language in its ancient chemical form. Abbreviations: 3D three dimensional a _c wthreshold intracellular concentration of activator molecules AHL acyl-homoserine lactone AHL _fisch N-(3-oxohexanoyl)-L-homoserine lactone AHL _viol N-hexanoyl-DL-homoserine-lactone AI autoinducer a.u arbitrary units BMB bromophenol blue CA trans-cinnamaldehyde Fl fluorescence intensity FI/OD600 density-normalized fluorescence intensity GFP green fluorescent protein M _w molecular weight PT percolation theory QS quorum sensing t _c percolation critical time wt wild type

Genipin is increasingly used as a crosslinking agent for chitosans due to its low cytotoxicity as a naturally occurring extract of the plant Gardenia jasminoides. Genipin reacts with the primary amino groups of chitosan to form blue hydrogels. We studied the gelation kinetics of different chitosans varying in their properties (molar mass 34 000-213 000 g mol-1, degree of acetylation 9-20%) and genipin in detail. We found that critical sol-gel transition times obtained from dynamic light scattering were in good agreement with the results obtained by small deformation oscillatory rheometry and microviscosimetry at high concentrations of chitosan. However, at below critical concentrations, we found a second regime of gelation that followed the same Ross-Murphy's gelation kinetics. The macroscopic appearance of these samples was a suspension of weak gel-like particles that were sensitive to mechanical forces. We believe that the material is a mesoscopic gel, as described for other polymers. To the best of our knowledge, this is the first time that this phenomenon has been described for the gelling system of chitosan and genipin.