Biological transport processes for microhydraulic actuation

Plants have the ability to develop large mechanical force from chemical energy available with bio-fuels. The energy released by the cleavage of a terminal phosphate ion during the hydrolysis of bio-fuel assists the transport of ions and fluids in cellular homeostasis. Materials that develop pressure and hence strain similar to plants for an external stimuli are classified as Nastic materials. This paper discusses the concept of using biological ion transporters for fabricating an actuator that generates strain by moving fluid through a membrane into an enclosed cavity. Fluid transport through ion transporters reconstituted on a bilayer lipid membrane (BLM) is demonstrated. The BLM was formed from 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-l-serine] (sodium salt) (POPS) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) [Avanti Polar Lipids, AL] lipids. The biological ion transporter used for demonstration was a H+-suc co-transporter (AtSUT4) extracted from Arabidopsis thaliana and expressed in yeast. Transporter proteins (AtSUT4) were supplied to us in frozen condition suspended in a pH 7.0 medium after purification. The BLM was reconstituted with AtSUT4 was CaCo2 membrane in a transport assay cup and a pH gradient is applied to the reconstituted membrane. Due to the selectivity of the transporter, fluid transport was observed from the bottom chamber into the cup in the presence of sucrose in the bottom chamber. Fluid flux was observed to be dependent on the concentration of sucrose in the bottom chamber. The experimental results were used for simulating the deformation in the cover plate for a representative actuator configuration. The model predicts transport of fluid starting from the hydrolysis reaction of adenosine tri-phosphate (ATP). The resulting pH gradient from the hydrolysis reaction was used as inputs for the Nernst–Plank electrodiffusion equation to predict the fluid flux. The deformation in the material of the cover plate was estimated by coupling the electro-diffusion equations with a hyperelastic model.