Microsystems technology (MST), also called MEMS (micro electro-mechanical systems) in the US is a cross-sectional technology, integrating electronic, mechanical and also optical components into compact systems.
In medicine today, MST-enhanced products are now an everyday reality. Typical examples are MST units in cardiac rhythm management devices or hearing implants. Based on the high density of functional integration and the small space requirements, MST components have become enabler of surgical devices and implants in different clinical areas. These developments have an interdisciplinary background and may find applications in other surgical fields as well, such as urology or gynaecology.
MST-enhanced surgical devices
A good example of MST applications are sensorenhanced laparoscopic instruments such as in the field of tactile sensing. The concept of restoring tactile feedback in laparoscopic surgery has been around for more than a decade, by integrating tactile sensors into the jaws of laparoscopic instruments to allow palpation and mechanical characterisation of tissues during surgery similar to what the surgeon would do with his hand in open surgery.
Our group has developed a tactile polymer sensor array, which is elastic, compliant and can be attached to the tip of a laparoscopic instrument (Figure 1) as a disposable. Using this combined sensor information, the tactile system can indicate the tissue hardness and geometry of the objects grasped, such as lymph nodes or stones inside tubular organs. A visual display in overlay to the endoscopic image on the monitor is used to represent the tactile information.
A randomised controlled pre-clinical trial, in which 10 surgeons were asked to identify hard objects inside a foam model in a laparoscopic trainer, using either a conventional laparoscopic grasper or tactile sensor enhanced grasper, showed that both the objective detection rate, speed of detection and the subjective confidence of correct detection take relevant profit from tactile sensing.
Smart endoscopic capsules and micro-robotics The field of microrobotics for locomotion inside the human body is a very interesting area for the application of MST since high functional integration and miniaturisation, the two main characteristics of MST, are an important advantage in this field. Capsule endoscope is a good example of using MST as an enabling technology for breakthrough innovations in medical devices. The capability of actively controlling the passage of conventional, passive capsule endoscopes through the gastrointestinal system is very restricted.
A technology that might increase the functionality of endoscopic capsules in the future and enable the next level of interaction with the tissue is microrobotics. The VECTOR project (2) supported by the European Commission aims at investigating and developing a miniaturised robotic pill for advanced diagnostics and therapy in the human digestive tract.
The hallmark of the project is the robotic capsule locomotion technology that allows real-time control of the endoscopic device inside the body. The VECTOR capsule has permanent magnetic material embedded into its shell. These inner magnets are attracted by a strong outer permanent magnet, positioned above the abdomen. This outer magnet is attached to a robotic arm, which is guiding the device based on user input via a joy-stick.
Experimental pre-clinical evaluation of the robotic VECTOR capsule has demonstrated the feasibility of active locomotion of wireless capsules.
Implantable MST devices
Telemetric implants are among the most important applications of MST in surgery. MST components implanted into the human body include sensors of various types that measure specific health parameters, such as blood glucose or blood pressure or flow. The signals are then transferred via telemetric coils to read-out devices outside the body.
Our own group has been working within the VECTOR project (2) in the development of an implantable telemetric haemorrhage detection that can be applied for the immediate detection of post-interventional bleeding. A telemetric blood detections system, temporarily implantable into an organ cavity, able to detect the new presence of fresh blood immediately, might be of big help to start therapeutic action without time delay and to avoid significant blood loss.
The implant is an integrated device that comprises several MST components such as an optical sensor system, smart process electronics and miniaturised telemetry systems. The blood is detected by means of transmission spectroscopy. If fresh blood reaches the sensor it sends an alarm to the patient and/or the doctor of the active haemorrhage.
A major role for MST
Nowadays, microsystems technology plays a major role for improving products in the healthcare sector. The clinical interest in the use of MST in surgery is mainly based on the significant potential of MST to enable products that improve disease detection and monitoring, as well as the surgical treatment by means of smart, sensor-enhanced instruments.
1. Schostek S, Binser MJ, Rieber F, Ho CN, Schurr MO, Buess GF. Artificial tactile feedback can significantly improve tissue examination through remote palpation. Surg Endosc. 2010 (in press)