Parts retain function even after multiple sterilizations in an autoclave and exposure to the cleaning agents used in hospitals and medical facilities.
The German firm of ERBE Elektromedizin GmbH has developed microtweezers for non-invasive surgery, whose handle and working parts are moulded of glass-reinforced DuPont™ Zytel® to ensure easy and safe use.
This is an essential requirement for instruments used in non-invasive surgery. With this operating technique, familiarly known as ‘keyhole surgery’, instruments are introduced into the body through a tiny opening in the skin to access the exact location to be treated. The technique’s benefits include smaller operation scars and more rapid healing; often, ambulant treatment suffices where earlier methods would necessitate a stay in hospital.
ERBE’s bipolar microtweezer is a multi-purpose instrument: it can grasp, open and prepare the 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 1.5-mm diameter metal tube; the wires which move the tweezer jaws pass through this tube. The lever to operate the wires is mounted on the handle. The jaws automatically close when the instrument is not in use.
Materials Selected and Why
Instead of the PEEK material, which was originally planned for the handle, ERBE and system supplier PEZET chose Zytel® 70G30HSL. This glass-reinforced, heat-stabilised, hydrolysis-resistant grade of nylon 66 was modified through incorporation of a masterbatch to accept laser-marking.
Very precise parts can be molded from this high-performance resin. Thanksto its dimensional stability, the parts retain their functionality even after multiple sterilizations in an autoclave with superheated steam at 134°C. Like all nylons, this type also offers 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 the requirements of the standards for medical equipment, such as EN 60601-2-2 (safety of HF-surgical equipment) and EN 10993 (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 to us the 3D files, which they had created, and we used them directly to produce the mould. As a result of this close co-operation with our customer, we could start regular production of the nylon parts for fully working microtweezers after the first mould proving.”
ERBE Elektromedizin GmbH, located at Tübingen, near Stuttgart, researches, develops and manufactures equipment and accessories for medical use. The company has subsidiaries in Europe and USA, and representative offices in China and Russia, and employs about 450.
PEZET AG, established in 1973, has about 150 employees at its works at Haigerloch. The company co-operates closely with OEMs to design, develop and produce systems for use in precision, electrical and other types of engineering, in pneumatics and medical equipment. The company’s core competencies are in plastics and assembly technology. It also has a highly skilled mould-making shop and print shop.