Despite impressive progress on a number of fronts, we think it fair to mention that there are still considerable technical obstacles. The reproducibilty of chemistry occurring at microscopic scales in proximity to solid surfaces, the complexity of effects induced by electric actuation, and the comparative scarceity of clean chemical reactions with limited side-effects are surely three of the features that have limited the rate of progress in this section of PACE. Nonetheless, this area fulfilled its major contribution to PACE and shows great promise for the future.
This work has resulted in several distinct types of achievement:
1. Establishing a high density programmable interface system for evolvable constructive IT: the omega machine.
Highlights were: the integration of the real time optical imaging and parallel electrode actuation loop using FPGA technology, the integration of high density multilevel electrode control with microfluidics, the extensive integrated and portable software system complete with GUI and remote control and interpretative real-time development environment. The platform integrates a robotic interface between multiwell plate technology and continuous flow syringe pump technology, control of a multi-laser parallel confocal microscope system, a microfluidic positioning system, a thermal gradient control system, an integrated custom downstream microcapillary electrophoresis product analysis system, and a high bandwidth digital electrode actuation system. The omega machine was successfully deployed at a commercial partner Protolife after development at the Ruhr University Bochum. A user interface, accessible both to visiting scientists and to lab technicians was developed, underlining the general transferability of this technology between labs.
2. Demonstrating artificial cell component system functionality adapted under microfluidic control.
Online monitorable chemical replication was established at microfluidic scales, and its control through template dosing via electric fields also proved possible. Several existing and two novel chemical replication systems, showing various strengths, were employed. Reversible containment by vesicle and micelle formation, and by gelation were evaluated in the microfluidic context. A screening system for complex phase space, as occur in amphiphile systems, was developed. Metabolism was investigated by resource flow, by photochemical reactions controlling gelation and by pH gradients.
3. Complementation of artificial cell functionality.
Ongoing steady state replication was achieved using the "fan"-reactor. The generalizations of the novel "H"-microreactor, exploiting electrophoretic and electroosmotic flow were shown to support programmable isolation on appropriate time scale for replication containment. In conjunction with reversible in situ gelation, developed both with agarose and at higher resolution with block copolymers, these and other structures also function as an electronic membranes for the differential separation and selective transport of molecules under electric control. This is a primary artificial cell functionality. Programmable spatial control for genetic molecules such as PNA and DNA and for cooperative structures like vesicles was demonstrated. Concentration control, both in defined chambers and in open channels proved possible, and can be used in future to gate bimolecular chemical reactions (through local mass action) and self-assembly processes such as micellization (transition across CMC). Redox reaction and pH control via electrochemistry will provide an important spatially localized programmable tool in future work.
Many paths were explored in the PACE project, and a repertoire of functional subsystems developed that will be of value for the future. Complete integration of an artificial cell has not yet been achieved, but a considerable degree of fine-grained programmability. A major conclusion of this work is that it is advantageous to used mixed phase systems, in particular with localized reversible gelation, rather than single phase aqueous systems. A novel family of genetic containment molecules was identified based on block copolymers that will be employed in a follow on project ECCell to complete an electronic chemical cell, in which reversible gelation replaces vesicle membranes as a selective containment mechanism. Further integration of the chemical subsystems through the omega machine will also be the subject of ongoing work.