Abstract
In-vivo sensors yield valuable medical information by measuring directly on the living tissue of a patient. These devices can be surface or implant devices. Electrical activity in the body, from organs or muscles can be measured using surface electrodes. For short term internal devices, catheters are used. These include cardiac catheter (in blood vessels) and bladder catheters. Due to the size and shape of the catheters, silicon devices provided an excellent solution for sensors. Since many cardiac catheters are disposable, the high volume has led to lower prices of the silicon sensors. Many catheters use a single sensor, but silicon offers the opportunity to have multi sensors in a single catheter, while maintaining small size. The cardiac catheter is usually inserted for a maximum of 72 h. Some devices may be used for a short-to-medium period to monitor parameters after an operation or injury (1–4 weeks). Increasingly, sensing, and actuating, devices are being applied to longer term implants for monitoring a range of parameters for chronic conditions. Devices for longer term implantation presented additional challenges due to the harshness of the environment and the stricter regulations for biocompatibility and safety. This paper will examine the three main areas of application for in-vivo devices: surface devices and short/medium-term and long-term implants. The issues of biocompatibility and safety will be discussed.
Highlights
The importance of in-vivo measurements is that these are performed directly on the living tissue, either as surface or internal devices
This device was developed by Intelligent Medical Implants AG (IMI) in Switzerland [74]
Microsystems have played a major role in medical development
Summary
The importance of in-vivo measurements is that these are performed directly on the living tissue, either as surface or internal devices. Examples of in-vivo devices include false teeth made from shells by the Mayan people around 600 AD These devices along with bone implants were not intended to measure, but to restore function and/or support the hard tissue during recovery. Still widely used today, are electrodes for electrical measurements of the heart electrocardiogram (ECG) [3,4]. These early devices were simple electrodes, but many developments have been made by integrating electronics into the electrodes to improve the signal-to-noise ratio (SNR) [5,6,7]. Examples here were pressure sensors and balloon catheters for the treatment of stenosis or aneurysm These techniques are still widely used today [11,12]. These different approaches, applications and devices will be discussed in the sections below
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