Graft them all: synthesis of oppositely charged graft polyelectrolytes and development of underwater adhesives using complex coacervation (MSc Marco Dompe)
Underwater adhesion is technically challenging and hence adhesive technology is rarely applied for bonding in wet conditions, such as in (orthopaedic) medicine. In the aquatic world, several organisms, such as the sandcastle worm, have developed strategies to overcome very similar challenges as faced by adhesive developers. These organisms are able to bond dissimilar materials together under seawater using protein-based adhesives. A key element in the adhesive processing is polyelectrolyte complex formation, so-called complex coacervation. Complex coacervates are particularly suitable for underwater adhesion, because of their fluid-like, yet water immiscible properties and good wettability. After delivery, the adhesive transforms into a solid upon an external trigger.
Inspired by these biological organisms, we are modifying the chemistry of synthetic polyelectrolytes so that additional strengthening mechanisms can be introduced into the material, making it suitable for biomedical applications. In this project, we attach thermoresponsive side chains on a polyelectrolyte backbone in order to produce graft copolymers. By properly tuning the environmental parameters (such as pH, ionic strength, mixing ratio..), complex coacervation is achieved by mixing aqueous solutions of oppositely charged polyelectrolytes: associative phase separation occurs and a polymer-poor (dilute) phase and a polymer-rich (coacervate) phase are obtained. The coacervate phase (in which we are interested in) is a viscous liquid at room temperature but it becomes gel-like when the temperature is increased above a certain threshold, which is few degrees lower than the human body temperature (fig.1). This behaviour makes the modified coacervate an ideal candidate for tissue repair or wound closure: the adhesive is a liquid at room temperature, facilitating the delivery and the wettability inside the human body, but it turns into a load-bearing solid immediately after the application because of the temperature trigger.
In this project, we accurately follow every single step of the material development, starting from the synthesis of the polylectrolyte components to the characterization of the final adhesive using techniques such as NMR, rheology, underwater adhesion (fig.2) and scattering measurements.