Feedback Controlled Bilayer Heating Within the Regulated Attachment Method

Abstract

Synthetic lipid bilayers provide a cell-inspired environment for studying the functions of biomolecules. The regulated attachment method (RAM) is one method for forming liquid-supported lipid bilayers — known as droplet interface bilayers (DIBs) — that form at the interface of lipid-encased aqueous volumes in oil. While RAM allows for independent control of the aqueous phases on both sides of the membrane and provides a convenient way to control the size of the bilayer, previous studies utilizing this technique have been performed exclusively at room temperature. The goal of this research is to incorporate proportional-integral (PI) feedback control of temperature within the flexible RAM substrate with initial efforts focused on heating above room temperature. The proposed system includes a resistive etched-foil heating element and wire-type thermocouples for point-wise temperature measurement in standard RAM substrates. Open loop heating tests are used to map the magnitudes of steady state temperature distributions within the substrate and characterize the dynamic heating response. These tests show that a first-order heating model accurately describes transient temperature responses to heater power inputs. A one-probe configuration is found to provide measurements that are within <1°C of temperature measured at the bilayer region. The optimized probe configuration is used in PI feedback control, where the closed loop system is found to track the desired temperature to within +/−0.3°C. Experiments of temperature control with aqueous lipid droplets present permit electrical measurements of bilayer area without increasing background noise. Using this platform, we study the effect of temperature on the stability and size of a diphytanoyl phosphatidylcholine (DPhPC) lipid bilayer, and we observe that increasing the temperature of the bilayer from room temperature to 30°C results in a 30% decrease in the area of the membrane.