Highly elastic conductive polymeric MEMS.

Polymeric structures with integrated, functional microelectrical mechanical systems (MEMS) elements are increasingly important in various applications such as biomedical systems or wearable smart devices. These applications require highly flexible and elastic polymers with good conductivity, which can be embedded into a matrix that undergoes large deformations. Conductive polydimethylsiloxane (PDMS) is a suitable candidate but is still challenging to fabricate. Conductivity is achieved by filling a nonconductive PDMS matrix with conductive particles. In this work, we present an approach that uses new mixing techniques to fabricate conductive PDMS with different fillers such as carbon black, silver particles, and multiwalled carbon nanotubes. Additionally, the electrical properties of all three composites are examined under continuous mechanical stress. Furthermore, we present a novel, low-cost, simple three-step molding process that transfers a micro patterned silicon master into a polystyrene (PS) polytetrafluoroethylene (PTFE) replica with improved release features. This PS/PTFE mold is used for subsequent structuring of conductive PDMS with high accuracy. The non sticking characteristics enable the fabrication of delicate structures using a very soft PDMS, which is usually hard to release from conventional molds. Moreover, the process can also be applied to polyurethanes and various other material combinations.

Design of an implantable active microport system for patient specific drug release.

We present a novel concept of an implantable active microport based on micro technology that incorporates a high-resolution volumetric dosing unit and a drug reservoir into the space of a conventional subcutaneous port. The controlled release of small drug volumes from such an "active microport" is crucial e.g. for innovative methods in cancer treatment or pain therapy. Our microport system delivers a flow rate in the range of 10-1,000 mul/h and enables a patient-specific release profile. The core of our device is a two-stage piezoelectric micropump. It features a backpressure-independent volumetric dosing capability i.e. a stable flow rate is ensured up to a backpressure of 30 kPa. The stroke volume and hence the resolution of the mircopump is voltage controlled and can be preset between 10 and 200 nl. A miniaturized high-performance electronic control unit enables freely programmable dosing profiles. This electronic circuit is optimized for both energy consumption and weight which are both essential for a portable device. The data of an implemented pressure sensor are used to permanently monitor the dosing process and to detect a potential catheter occlusion. A polyurethane soft lithography process is introduced for the fabrication of the prototype. Therewith, a compact multilayer system has been developed which measures only 50 x 35 x 25 mm(3).