Nylon resin outperforms expensive alternatives

Edited by the Engineeringtalk editorial team Nov 25, 2003

A German firm has developed novel microtweezers for noninvasive surgery based on a handle and integrated lever moulded with glass-reinforced Zytel nylon resin to ensure easy and safe use.

A German firm, Erbe Elektromedizin, has developed microtweezers for noninvasive surgery, based on a handle and integrated lever moulded with glass-reinforced DuPont Zytel nylon resin to ensure easy and safe use - essential requirements for instruments used in so-called "keyhole surgery".

During noninvasive surgery instruments are introduced into the body through a tiny opening in the skin to access the exact location to be treated.

Erbe's bipolar microtweezers are multipurpose instruments, which can grasp, open and prepare body tissue and administer low-intensity electrical current to accelerate healing of the wound and stop the flow of blood.

The handle's individual parts include the main housing, a cable channel at the back and a holder at the front for a 1.5mm-diameter metal tube, through which the wires for operating the tweezers' jaws pass.

The lever to open the jaws is mounted on the handle.

Instead of the Peek material originally planned for the handle, Erbe and system supplier Pezet, Germany, chose glass-reinforced Zytel.

The heat-stabilised and hydrolysis-resistant grade of nylon 66 was modified, through incorporation of a master batch, to accept laser marking.

Very precise parts can be moulded with the high-performance resin.

Thanks to its dimensional stability, the parts retain their functionality even after multiple sterilisation in an autoclave, with temperatures as high as 134C.

Furthermore, as with all nylons, Zytel also provides long-term resistance to the cleaning agents used in hospitals and medical facilities, such as those used to flush the metal tube.

Achim Brodbeck, Development Engineer at Erbe, comments: "Our in-house tests of this resin confirmed DuPont's recommendation.

In all material points, this Zytel type performed as well as Peek, which is considerably more expensive.

All the parts meet standard requirements for medical equipment, such as EN60601-2-2 (safety of HF-surgical equipment) and EN10993 (biocompatibility)".

"As long as the correct mould temperature, injection speed and injection pressure are strictly adhered to, the parts of Zytel are of very high quality and show no post-shrinkage", reports Jakob Mesam, Head of Design and Development at Pezet.

"In the design stage we made recommendations to Erbe for the optimal gate positions and gave guidance for designing the parts so as to derive maximum advantage from the use of plastics".

"As development progressed, we reviewed part design so as to optimise processing requirements.

Erbe transmitted their 3D files to us, and we used them directly to produce the mould.

As a result of this close co-operation with our customer, we could start production of the nylon parts for fully functional microtweezers following the first mould proofing".