Understanding the competition between aggregation and coacervation phenomena in protein/ polysaccharide and polyelectrolyte/polysaccharide systems

International audienceThe complexation of oppositely charged macromolecular species such as proteins, polymers, andcolloids through electrostatic attractions is an associative process found in both natural and syntheticsystems. Depending upon the strength of interaction, the complexation proceeds through either liquid-liquid or liquid-solid phase separation leading to the formation of complex coacervates or a solidprecipitate respectively. Understanding the competition between the mechanisms of liquid-liquid andliquid-solid phase separation as well as identifying parameters leading to one or the other mechanismis essential in the further development of their applications.1The screening of several polymer couples carrying opposite charges (protein-protein, protein-polyelectrolyte, protein-polysaccharide, and polysaccharide-polyelectrolyte) led to a thorough study ontwo specific couples: polyethylene imine (PEI) – alginate (ALG) and lysozyme (LYS) – alginate. Theidea was to study the synthetic counterpart of a positively charged protein, i.e. PEI, in interaction witha negatively charged natural polymer, i.e. alginate. These two couples were studied using classical tools(turbidity, electrophoretic mobility, and optical microscopy (see figure 1). In addition, phase diagramswere built using a homemade droplets-based millifluidic device coupled with image analysis.2-3Preliminary results, by tuning initial conditions such as total concentration, mixing ratio, pH, and ionicstrength clearly showed liquid-liquid phase separation in PEI: ALG mixtures with droplets formationwhile liquid-solid phase separation occurred in LYS: ALG mixtures with aggregates formation. Furtheranalyses will concern the energy of interactions in these two couples using isothermal titrationcalorimetry (ITC) and the small angle X-ray scattering (SAXS)-based structural characterization of theassemblies formed

Microfluidics-assisted generation of stimuli-responsive hydrogels based on alginates incorporated with thermo-responsive and amphiphilic polymers as novel biomaterials

International audienceWe used a droplet-based microfluidics technique to produce monodisperse responsive alginate-block-polyetheramine copolymer microgels. The polyetheramine group (PEA), corresponding to a propylene oxide /ethylene oxide ratio (PO/EO) of 29/6 (Jeffamine (R) M2005), was condensed, via the amine link, to alginates with various mannuronic/guluronic acids ratios and using two alginate:jeffamine mass ratios. The size of the grafted-alginate microgels varied from 60 to 80 mu m depending on the type of alginate used and the degree of substitution. The droplet-based microfluidics technique offered exquisite control of both the dimension and physical chemical properties of the grafted-alginate microgels. These microgels were therefore comparable to isolated grafted-alginate chains in retaining both their amphiphilic and thermo-sensitive properties. Amphiphilicity was demonstrated at the oil-water interface where grafted-alginate microgels were found to decrease interfacial tension by similar to 50%. The thermo-sensitivity of microgels was clearly demonstrated and a 10 to 20% reduction in size between was evidenced on increasing the temperature above the lower critical solution temperature (T-LCST) of Jeffamine. In addition, the reversibility of thermo-sensitivity was demonstrated by studying the oil-water affinity of microgels with temperature after Congo red labeling. Finally, droplet-based microfluidics was found to be a good and promising tool for generating responsive biobased hydrogels for drug delivery applications and potential new colloidal stabilizers for dispersed systems such as Pickering emulsions. (C) 2015 Elsevier B.V. All rights reserved

In Situ Forming, Silanized Hyaluronic Acid Hydrogels with Fine Control Over Mechanical Properties and In Vivo Degradation for Tissue Engineering Applications

International audienceIn situ forming hydrogels that can be injected into tissues in a minimally-invasive fashion are appealing as delivery vehicles for tissue engineering applications. Ideally, these hydrogels should have mechanical properties matching those of the host tissue, and a rate of degradation adapted for neo-tissue formation. Here, the development of in situ forming hyaluronic acid hydrogels based on the pH-triggered condensation of silicon alkoxide precursors into siloxanes is reported. Upon solubilization and pH adjustment, the low-viscosity precursor solutions are easily injectable through fine-gauge needles prior to in situ gelation. Tunable mechanical properties (stiffness from 1 to 40 kPa) and associated tunable degradability (from 4 days to more than 3 weeks in vivo) are obtained by varying the degree of silanization (from 4.3% to 57.7%) and molecular weight (120 and 267 kDa) of the hyaluronic acid component. Following cell encapsulation, high cell viability (> 80%) is obtained for at least 7 days. Finally, the in vivo biocompatibility of silanized hyaluronic acid gels is verified in a subcutaneous mouse model and a relationship between the inflammatory response and the crosslink density is observed. Silanized hyaluronic acid hydrogels constitute a tunable hydrogel platform for material-assisted cell therapies and tissue engineering applications