CORDIS - EU research results

Getting right anaesthetic needle technology through novel forming and coating processes

Final Report Summary - GRANT (Getting right anaesthetic needle technology through novel forming and coating processes)

The overall aim of the GRANT project was to develop novel high-added value anaesthetic needles which entailed low energy supply of neuro-stimulation needles, first closed circuit bipolar needle system, properly focused needle tip electric field, increased haptic navigation safety of needles, higher needle stability for reduced risk of needle break.

In order to achieve the above mentioned operational targets the following technical objectives had to be met:
1. Bipolar coating: a) develop the first three layer compound consistent of the insulating layer on metal tube, the electro-conducting layer on insulating layer and the insulating and minimal-friction layer on electro-conducting layer, b) withstanding skin friction forces of 2N, c) furthermore this compound had to fulfil the following demands: breakdown voltage of the insulating layer of 300 volts, a dielectric strength of over 4 Mvolt/cm and electric conductivity of electro-conducting layer of 0.2/ohm
2. Needle forming process: to develop a new medical needle forming process for reduced needle tips in order to reduce needle break risk significantly by introducing a cold rolling process for metal tube diameters below 1 mm. This includes the challenges of small diameters never tried for rolling, single step cold rolling process and following tempering in order not to reduce the needle stability, as well as rolling of two needles at a time to reduce production costs.

There were five product performance objectives:
- to achieve a coating yield of over 50 % friction stable coated needles;
- to create a focused electric field at the needle tip by developing and manufacturing coating masks for the needle tips during coating;
- to create a bipolar wiring for the needle system to be used on a neuro-stimulator;
- to achieve a needle forming yield of over 60 % stable needles with reduced tips;
- to reduce the production costs of the current needle forming process by 12 %.

Finally, the enabling innovation related objectives were the following:
- 1. formulate the project results into a protectable form and apply for patent protection on:
a) the first biocompatible and strongly adhesive electro-conducting coating, covered with an insulating coating;
b) the first non-biocompatible but strongly adhesive electro-conducting coating, covered with an insulating coating for electronic applications;
c) the first working bipolar needle for neurostimulation;
d) the novel spinal/epidural needle system and associated procedure of making the same by month 18 of the project;
2. transfer knowledge from the research and technological development (RTD) performers to the SME participants through four technology transfer events;
3. broadcast the benefits of the developed technology and knowledge beyond the consortium to potential medical user communities and specifically:
a) 5 workshops at highly recommended hospitals;
b) contribution to 3 specialised congresses and conferences;
c) presentations at 3 medical devices trade shows;
d) paper and software information material would be created for further distribution of the new system.

The following surface analysis tools defined during the early work packages were used for the testing of the bipolar needle: surface energy, adhesion, electrical resistivity, impedance, film thickness and friction. Following the coating of the bipolar needle electrical conductivity tests were conducted. This involved the development of the electrode connectors, which allow the cables to be attached to the coated needle.

In order to obtain the best connection four connection method were considered:
- a metal-clip in combination with an adhesive or soldering process;
- direct adhesion of the wires onto the surface of the needles using either chemical bonding or soldering techniques;
- the use of a shrinkable tubing to form a mechanical fixation to the needle;
- crimping of a metal clip around the needle to form a mechanical contact between the components.

From the designs generated during a drawing and a rolling machine were manufactured. These machines together with Medilecs knowledge of tub forming were used to generate sample needles. In total two types of spinal needles were made from a ISO5832-7 grade stainless steel. These consisted of a parallel needle with a pencil point tip and a tapered needle which had a reduced section for approximately 15 mm from the tip.

Metallurgical analysis was performed on the needles in the region of the reduced sections scanning electron microscopy (SEM) analysis showed a uniform grain size with no evidence of re-crystallisation associated with the work hardening region of the needle. The results of the metallurgical analysis showed that the deformation process did not affect the microstructure of the needle. This would suggest that the deformation process was performed in a controlled manner, thus preventing work hardening and or over heating of the material during the forming operation.