Optically Driven PH Gradient Generator Based on Self-Assembled Proton Pumps for Activating Hydrogel Microactuators

This dissertation presents a new approach for developing a biologically inspired photo-electro-chemo-mechanical microactuator by exploiting the ion pumping characteristics of bacteriorhodopsin (bR) proton pumps and the pH sensitivity of smart hydrogels. The ultimate goal of this project is to prove the viability of integrating bR monolayer into novel actuation applications using molecular level architectures. To accomplish this, the bR proton pumps are molecularly labelled, organized, and directionally immobilized on Au-coated substrate, and then integrated with pH sensitive hydrogel. When responding to an incident light beams, the internal proton pumping mechanism is mathematically modeled for quantifying the processing of the photonic energy into electro-chemical potential. Experimental and theoretical findings indicate that the photo-electric response of the dry bR is attributed to charge displacement and recombination; whereas, the response of the aqueous bR measured is a real proton pumping mechanism. The photo-electric properties, light source conditions all have influence on the observed photo-electric response characteristics. The presented technology is proven both experimentally and analytically through simulation. Experiments are conducted using acrylic acid (AA) monomer linked to 2-hydroxyethyl methacrylate (HEMA) monomer and the developed bR monolayer forming this hybrid microactuator. The light detecting part of the actuator is the bR monolayer. In this part the incident light beams are processed in the bR proton pumps through their photo-cycle to transport protons from the cytoplasmic side to the extracellular side of the bR protein. The bR monolayer is fabricated with molecular level recognition, labelling, and adsorption leading to a novel architecture able to transport protons through a porous substrate. Once protons are transported from one side to the other side of the membrane, the concentration of the hydrogen ions is changed. The change in the hydrogen ions concentration is expected theoretically and has been proved by monitoring pH changes in the ionic solution as pH gives direct indication on the hydrogen ions concentration. The change in the pH is exploited by integrating the light detecting part of the actuator to the pH-sensitive hydrogel which acts as the actuator shell that receives the pH changes and treat it as an input signal and then process it to undergo in an electric phase transition that leads to volume transition and associated mechanical work. The generated mechanical work is exploited in microactuation techniques with interest in microfluidic valves to control the flow in the microchannels. Based on the presented work the bR monolayer shows great potential for becoming a viable biomaterial for use in optical sensing and actuation. Many industrial and biomedical applications may benefit from the presented advances in generating higher performance micro-systems

Ionic Polymer Microactuator Activated by Photoresponsive Organic Proton Pumps

An ionic polymer microactuator driven by an organic photoelectric proton pump transducer is described in this paper. The light responsive transducer is fabricated by using molecular self-assembly to immobilize oriented bacteriorhodopsin purple membrane (PM) patches on a bio-functionalized porous anodic alumina (PAA) substrate. When exposed to visible light, the PM proton pumps produce a unidirectional flow of ions through the structure’s nano-pores and alter the pH of the working solution in a microfluidic device. The change in pH is sufficient to generate an osmotic pressure difference across a hydroxyethyl methacrylate-acrylic acid (HEMA-AA) actuator shell and induce volume expansion or contraction. Experiments show that the transducer can generate an ionic gradient of 2.5 μM and ionic potential of 25 mV, producing a pH increase of 0.42 in the working solution. The ΔpH is sufficient to increase the volume of the HEMA-AA microactuator by 80%. The volumetric transformation of the hydrogel can be used as a valve to close a fluid transport micro-channel or apply minute force to a mechanically flexible microcantilever beam

Ionic Polymer Microactuator Activated by Photoresponsive Organic Proton Pumps

An ionic polymer microactuator driven by an organic photoelectric proton pump transducer is described in this paper. The light responsive transducer is fabricated by using molecular self-assembly to immobilize oriented bacteriorhodopsin purple membrane (PM) patches on a bio-functionalized porous anodic alumina (PAA) substrate. When exposed to visible light, the PM proton pumps produce a unidirectional flow of ions through the structure’s nano-pores and alter the pH of the working solution in a microfluidic device. The change in pH is sufficient to generate an osmotic pressure difference across a hydroxyethyl methacrylate-acrylic acid (HEMA-AA) actuator shell and induce volume expansion or contraction. Experiments show that the transducer can generate an ionic gradient of 2.5 μM and ionic potential of 25 mV, producing a pH increase of 0.42 in the working solution. The ΔpH is sufficient to increase the volume of the HEMA-AA microactuator by 80%. The volumetric transformation of the hydrogel can be used as a valve to close a fluid transport micro-channel or apply minute force to a mechanically flexible microcantilever beam