Several studies have been reported on the development of controllable catheters in the biomedical field. Electronic conductive polymers (ECP) actuators appeared to be among the most suitable systems thank to their biocompatibility, low operating potential (± 2V) with a reasonable deformation (2%)[1–3]. Electroactive catheters, especially in neurosurgery, should have two levels of properties: strong deformations tip in order to reach, for example the aneurysms and sweep the total volume of the pouch, and sufficient rigid middle part for getting forward in the tortuous vessels network. We designed an electroactive catheter, constituted of two parts with different deformation ability and modulus. The high deformations tip can be obtained with a weak modulus actuator. On the other hand, the second part needs to possess high modulus where small deformations are sufficient. In this work, interpenetrating polymer networks (IPN) will be used as the structural material of the catheter. The IPN architecture allows the synthesis of actuators containing the ions necessary for the redox process and thus avoiding any interference of the position control due to the exchange with the ions from the physiological medium. In addition, the fact that the catheter can be synthesized in a customized way allows modulating its mechanical properties. By introducing a rigid polystyrene network into a specific part of the actuator, it is possible to locally increase the rigidity of the device while keeping reasonable deformation. First, we will describe the synthesis and the characterization of a beam shape actuators with different local stiffnesses. Then, the first steps for the elaboration of tubular actuator will be presented.
Trilayer actuators enable large mechanical amplification, but at the expense of force. Thicker trilayers can generate more force, but displacement drops. Ideally of course a combination of high force and large displacement is desirable. In this work we explore the stacking of trilayers driven by conducting polymers in order to combine large force and reasonable deflection. Trilayer actuators operating in air are simulated using the finite element method. Force generated and the maximum beam deflection of individual and multiple stacked trilayers are studied in terms of the interface condition of the neighboring layers and the length of the auxiliary trilayer. The best performance is obtained when trilayers are able to slide with respect to each other so forces can add without impeding displacement. This case will require low friction and uniformity among the trilayers. Bonding of stacked trilayers along their entire length increases force, but dramatically reduces displacement. An alternative which leads to moderate displacements with increased force is the use of a long and a short trilayer that are bonded.
A polyurethane hydrogel based touch sensor with high transparency and conformability is demonstrated. Polyurethane hydrogels swollen with various electrolytes were compressed at a pressure of 30 kPa, simulating a fingertap on a conventional touch screen device. Unlike ionic polymer metal composite and conducting polymer trilayer sensors, where electrodes render the sensors opaque and relatively rigid, the electrodes used in this work are metal wires or strips, separated from each other by regions of transparent film, enabling transparency and compliance. The voltages and currents observed when the perturbation is above one electrode are on the order of 10-2 V and 10-7 A, relative to a second electrode that is approximately 1 cm away. The sign of voltage and current signals detected from perturbations made between electrodes is determined by relative proximity to each electrode, and the magnitude appears to decrease with increasing distance from the electrodes. These observations suggest that it may be possible to discriminate the location of touch based on signals transmitted to the edges of an ionically conductive film. A model to describe the inhomogeneous ionic distribution and predict the resultant voltage and current is presented to qualitatively explain the sensing, based on the Donnan potential.
Polypyrrole-based actuators are of interest due to their biocompatibility, low operation voltage and relatively high strain and force. Modeling and simulation are very important to predict the behaviour of each actuator. To develop an accurate model, we need to know the electro-chemo-mechanical specifications of the Polypyrrole. In this paper, the non-linear time-variant model of Polypyrrole film is derived and proposed using a combination of an RC transmission line model and a state space representation. The model incorporates the potential dependent ionic conductivity. A function of ionic conductivity of Polypyrrole vs. local charge is proposed and implemented in the non-linear model. Matching of the measured and simulated electrical response suggests that ionic conductivity of Polypyrrole decreases significantly at negative potential vs. silver/silver chloride and leads to reduced current in the cyclic voltammetry (CV) tests. The next stage is to relate the distributed charging of the polymer to actuation via the strain to charge ratio. Further work is also needed to identify ionic and electronic conductivities as well as capacitance as a function of oxidation state so that a fully predictive model can be created.