Intracorporeal MSTEnhanced Devices

Intracorporeal but not implantable medical and surgical devices use MST components to provide additional qualities and functions that cannot be realized with standard technology. A good example of this class of MST applications is sensor-enhanced surgical instruments. The concept of restoring tactile feedback in laparoscopic surgery has been around for more than a decade. Several attempts have been made to integrate tactile sensors into the jaws of laparoscopic instruments to allow palpation and mechanical characterization of tissues during surgery, such as the surgeon would do with his or her hand in open surgery [22]. In the past, some attempts to create tactile sensors have failed, partly related to complex technologies that could not be efficiently applied in this small market segment.

Since tactile sensing in laparoscopic surgery is still an attractive proposition from a medical standpoint, new attempts are being made to realize such instruments on a more cost-friendly technology basis.

One of these is a program carried out by our own institution to develop a polymer sensor array, which is elastic, compliant and can be attached to the tip of a laparoscopic instrument as a disposable. This sensor (Fig. 11.4) is composed of a conductive and a resistive layer of polymer separated by a perforated layer.

Through exerting external pressure, the resistive coupling between the elastic conductive membranes is changed, indicating the force across the sensor array. The current forceps prototype (Fig. 11.5) has an array with 32 sensory elements. The force exerted on each element is visualized on a display. Experimental evaluation of the tactile forceps has shown that objects of different size and hardness can be well different shaded from their neighboring structures.

Fig. 11.3 Telemetric three-channel ECG system. Source: Fraunhofer Institute Photonic Microsystems, Dresden, Germany
Fig. 11.4 A polymer microsensor for tactile laparoscopic instruments (schematic drawing)

In animal experiments (Fig. 11.6) objects simulating lymph nodes at the mesenteric root could be localized and differentiated using the instrument.

Further research will be required to optimize the sensitivity and the applicability of tactile sensor arrays for laparoscopic surgery.

Another example of intracorporeal MST applications is advanced optical diagnostic systems for microscopic analysis of tissues in situ [7]. The concept of con-focal laser scanning microscopy is widely known in the histological examination of tissues samples. Using the miniaturization potential of MST, laser scanning microscopes can be scaled down to a level that they can be used via an endoscope directly inside the human body, e.g., for in situ analysis of lesions suspicious for cancer [8]. Figure 11.7 shows a prototype two axes microscanner with two miniature mirrors etched from silicon, compared with the size of a regular 10-mm laparoscope. The two electrostatically driven mirrors pivot and scan the laser beam across the tissue surface at video speed.

The resulting fluorescence can be enhanced by local tissue staining techniques. Figure 11.8 compares histological images obtained by this fluorescence laser scanning microscopy technique with conventional he-matoxylin and eosin (HE)-stained histology.

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