Effects of Osmolyte Concentrations on Complex Coacervate Systems

Vaccine delivery has never been more important than it is now. Current vaccine delivery methods require significant refrigeration to keep a vaccine stable, making it difficult to vaccinate in locations that have minimal resources for deep freezing. Ideally, a vaccine should be able to be stored at room temperature. Complex coacervation can potentially increase vaccine stability at greater temperatures by encapsulating vaccine material and mimicking the microenvironment of that material. Coacervation is a liquid-liquid phase separation that occurs from the electrostatic complexation of charged polymers and the release of counterions resulting in significant gains of entropy. This phenomenon has been used to encapsulate biological materials, create films, and much more. Research on complex coacervation generally studies the coacervate phase behavior as a function of salt concentration. The addition of salts can suppress the interaction between polyions to inhibit counterions from releasing, lowering the entropic gains and eventually disfavoring phase separation. In a biological context, this would release the material contained within a coacervate, with a potential application being vaccine delivery technology. However, certain biological materials are denatured by the presence of such a sufficiently large salt concentration and injecting humans with such concentrations of salt can be highly irritating. These factors discourage salt usage in applications like vaccine delivery. We hypothesize the use of biofriendly osmolytes can help or even replace salt as a means of disassembling a coacervate. The osmotic materials that are of particular interest include sugars and amino acids, materials which already have uses in stabilizing vaccines. These possibly charge-neutral osmolytes have the potential to modulate coacervate phase behavior by altering the osmotic pressure balance in the system. We will measure the critical concentrations of osmolytes to understand their effect on phase behavior. Measured critical concentrations of these osmolytes can prove useful for future coacervate research that requires controlled biological material release, such as vaccine research.