Surfactant activity is generally associated with small molecules rather than biological macromolecules like proteins. Only a few proteins have good intrinsic surfactant activity, an example being the natural surfactant ranaspumin 2 (Rsn2) from the foam nests of the túngara frog. In solution, Rsn2 has a hydrophobic core and hydrophilic exterior, but when Rsn2 comes in contact with an air-water interface, it changes conformation to expose its hydrophobic core to interact with the air and present a hydrophilic face to the water. The unique combination of biocompatibility along with surface activity offers the possibility of developing biomedical applications based on Rsn2. Some of the possible applications, including cell patterning, functionalising scaffolds and stabilising droplets, have been explored in the work described in this thesis.
The ability of Rsn2 to coat hydrophobic surfaces persistently, rendering them wettable and the nature of coating and interaction with the surfaces were investigated. This formed the basis for the development of a method to coat a range of hydrophobic polymers, which are commonly used for biomedical applications. These Rsn2 coated surfaces were tested for their capability to control cell adhesion on surfaces which usually do not support cell adhesion. Rsn2 coating was demonstrated to promote, and thus allowed the spatial control over, cell adhesion on otherwise non-cell compatible surfaces.
The potential of Rsn2 to be used as a protein fusion partner for the production of further functionalised cell engineering substrates was explored by constructing five different integrin binding sequence (IBS)-Rsn2 conjugates. Specific IBS-Rsn2 proteins proved successful in increasing the adhesion and biomineralising potential of osteoblasts isolated from neonatal rats.
In addition, Rsn2's ability to stabilise microscopic oil droplets were investigated. Rsn2 stabilised oil droplets were stable for more than six months.
Thus, the surfactant properties of Rsn2 can be used for many potential biomedical applications
