01/4 Intelligent tool technology

		Cross Section of Biopsy needle with insulating and active layers applied. Design of stress gauges along the needle length: Deforming the blade by pressing down on the free end, the digital display will show a negative deformation. A deformation in the opposite direction, by pulling the free end upwards, will be shown as a positive deformation.

The knowledge of the exact deformation of metallic instruments (i.e. biopsy needles and Kirchner wires) greatly improves the precision of medical navigation. The knowledge of the forces or deformations of implants (i.e. osteosynthesis plates) opens new possibilities in design of devices and in rehabilitation.

The proposed solution (patent pending by Intelligent Surface Technology - industrial partner of the project) enables the printing of low cost sensors and parts of its signal processing unit on arbitrary formed surfaces. The wide spectrum of sensors includes force-, deformation- and temperature-sensors. For contact-less reading out of the signals on implants, in the same printing step, parts of the signal processing unit like antennas and power receptors can also be printed.

The process of creating the "intelligent or active" biopsy needle relies on a multi-layer surface deposition process (MCP) using a cast molded PDMS master. This is a relatively simple and inexpensive coating/printing process (once mastered).

As shown on the diagram below, there are a number of strain sensors that are printed along the length of the biopsy needle. These strain sensors arrive at the top of the needle. The information is then captured by a small electronic system or "cap". This cap can be connected directly to the active tool used in the navigation system. Feedback to the surgeon is integrated into the software. Optionally, feedback can be provided without a navigation system using a simple LED output attachment.

First demonstrator

A first demonstrator was realized, it shows the application of the technology on the example of a flexible blade. Three strain gauges are printed on both sides of the stainless steel blade.

Deformation of the blade causes a change of the resistivity in the strain gauges. On one side of the blade, the deformation slightly shortens the strain gauge while on the opposite side the corresponding strain gauge is slightly elongated. This small difference of the lengths of a pair of strain gauges is then translated in an electrical signal by the means of a very simple electronic amplification circuit. Finally, this signal is shown on the digital display.

With one pair of strain gauges (top and bottom gauge) a simple bending of the blade can be measured. By cascading multiple pairs of strain gauges on the length of the blade, more complex bending forms can be determined. Extrapolating the signals of the three pairs of strain gauges, the position of the free extremity of the blade can be calculated exactly.

The electronic processing of the present technology demonstrator was deliberately kept extremely simple. The goal of the demonstrator was to validate the technical feasibility of the proposed technology: to sense a deformation and define a value changing proportionally with the elongation.

The basic technology for printing on MCP structures is now controlled by Intelligent Surface. The use of intelligent tools, such as the biopsy needles, has been integrated into the design of a new generation of navigation system (ongoing work).