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POLYmer microACTuators for biomedicine

Final Report Summary - POLYACT (POLYmer microACTuators for biomedicine)

Within the areas of cell biology, biomedicine and minimal invasive surgery, there is a need for soft, flexible and dextrous biocompatible manipulators for handling biological objects, such as single cells and tissues. Present day technologies are based on simple suction using micropipettes for grasping objects. The micropipettes lack the possibility of accurate force control, nor are they soft and compliant and may thus cause damage to the cells or tissue. Other micromanipulators use conventional electric motors however the further miniaturization of electrical motors and their associated gear boxes and/or push/pull wires has reached its limits. Therefore there is an urgent need for new technologies for micromanipulation of soft biological matter.
Our aim is to develop soft, flexible micromanipulators such as micro- tweezers for the handling and manipulation of biological species such as cells and surgical tools for minimal invasive surgery. This ambitious objective will be accomplished by developing novel patterning and microfabrication methods for polymer microactuators and integrate these microactuators into easy to use manipulation tools. We aim to produce tools with minimal dimensions of 100 µm to 1 mm in size, which is 1-2 orders of magnitude smaller than existing technology.
The main objective of this proposed project is to fabricate micro-sized PPy based actuators that can be individually controlled and integrate these in devices with a small footprint and minimum electric power requirement. We focus on developing these microactuators for applications within micromanipulation of cells and surgical tools for minimal invasive surgery. However, the developed technology can be used in many other application areas such robotic devices, optical shutters and diaphragms. One attribute of these actuators is that they require a small electric power, as low as 20-30 mW, and low potentials (~1-2 V). This allows the creation of autonomous micromanipulation tools with the power source on board.
We have developed, fabricated and evaluated two generations and two new fabrication methods to produce soft flexible microactuators In the first generation fabricated individually controlled PVDF thin film based milli-actuators. For this we developed a novel bottom-up fabrication approach. These PVDF thin film milli-actuators were able to work in air and in an electrolyte solution However, it showed that these actuators did not fully exploit the actuation capabilities of polypyrrole because the solid polymer electrolyte (SPE) layer (the thin film PVDF) does not exhibit a high enough ionic conductivity. The bending was not enough to achieve a gripping motion needed. Therefore, instead of downsizing these actuators to the micrometer-domain, we redesigned the actuator layout and focused on exchanging the PVDF SPE with other materials exhibiting high ionic conductivities. A variety of materials has been investigated and evaluated. It showed that ionic materials based on interpenetrating polymer network (IPN) were excellent candidates to produce individually controlled actuators using the bottom-up fabrication approach. Changing the SPE layer also meant that the developed metal patterning on these materials is not possible since it delaminates from the SPE layer due to the swelling of the material. So we developed a second patterning method to achieve high electronic conducting polymer layers to replace the metal layers. The method is based on a vapour phase polymerisation of a conducting polymer which is pattern by micro-contact printed or drop-on-demand printed oxidant layers. After the initial patterned layer of first conducting polymer layer, as second functional conducting polymer layer is electrochemically synthesised. This allowed the patterning of complex actuator devices for micromanipulation The deflection however was not as large as for similar non-patterned trilayer actuators thus limiting the gripping functionality of the produced devices.
We have developed two generations of soft, flexible polymer microactuators based on conducting polymer for micromanipulation of soft objects. The first generation is based on a PDVF membrane and Au/PPy individually controllable actuators. The second generation is based on an IPN layer with PEDOT/PPy individually controllable actuators.
We have developed a novel patterning process to pattern highly conductive conducting polymer electrodes. This allows the fabrication of all polymer, patterned microfabricated actuators as demonstrated by the second generation devices developed.
The newly developed soft microactuators may be used in soft microrobotic applications in biomedicine. New surgical technologies are currently developed that employ robotic manipulators, like the DaVinci surgical robot systems. However, these still use traditional, metal based rigid manipulators. Our developed soft microactuators might replace those, resulting in manipulators that are better adapted to interact with the soft tissue in the human body and thus cause less risk of surgery induced trauma. In addition the soft micromanipulators could be used in handling cells and tissues in cultures. Soft manipulators better match the texture and consistency of biological objects.