Saturday, 22 February 2020

Metal Replacement with Polyarylamide (PARA) for Single-Use Surgical Instruments


Today, we discuss an interesting evolving area: the metal replacement of single-use surgical instruments with high performance, semi-aromatic polyamides.

When you listen to the needs of hospitals and small ambulances all over the world, ready-to-use instruments which have optimal mechanical and ergonomic properties are high up on their wish list.

The non-active medical devices supplier Bastos Viegas from Portugal picked up this need in his hands and started a metal replacement program for stainless steel single-use surgical instruments.

The incumbent stainless steel solution fulfills all the mechanical requirements, however weight and cleaning procedures make them in the allover process of handling not attractive.

Requirements of plastic single-use instruments

To replace the stainless steel solution the polymer compound needs to fulfill the following requirements:
- High level of rigidity
- Dimensional stability
- Metal-like strength
- Biocompatibility according to ISO 10993
- Resistance to high-energy gamma radiation without significant change in appearance and physicochemical properties
- Resistance to ethylene oxide (EtO)
- Highly aesthetic surface finish


Material selection

Based on the list of requirements, different materials where analyzed. One material seemed quiet promising for Bastos Viegas from the beginning: the semi-aromatic Polyarylamide (PARA).

This high performance polyamide brings all the aforementioned attributes under one roof. It has a metal-like strength (tensile modulus of 22 GPa at 50% glass loading, room temperature), high dimensional stability, half of the water uptake compared to a normal nylon 6.6. and has the best surface appearance among all polyamides (resin rich surface due to fine crystallization). In addition, its excellent flow ability (similar to PPS) and resistance to high-energy sterilization process made it the ideal candidate for such a replacement.

In the Figure 1 the properties of the selected Ixef® grade GS-1022 are compared to a standard nylon 6.6 and other engineering polymers.
Figure 1: Flexural properties of Polyarylamide (PARA) compared to other high performance and engineering plastics.


In Table 1, a comparison of different property values of PARA, Nylon 6.6, Nylon 6 and PBT is done. This comparison makes the advantages of PARA numerically visible: low water absorption in combination with high modulus values.


Table 1: Specific properties of Polyarylamide (PARA) and comparable others engineering plastics.

So far, we have compared PARA to other Nylon materials or other engineering plastics. Since we want to do a metal replacement, we are interest in the comparison of PARA with other metal die cast materials. This is shown in Table 2. As it can be seen, the tensile strength of PARA is at the same level or in some cases higher than that of the casting metals and its E-modulus although inferior is within the same range. As a result, required performance can be easily attained with significant reduced weight as looking at the respective densities of PARA and the metals.


Table 2: Specific properties of Polyarylamide (PARA) and different die casting metals.

Conclusion

The combination of different property data of PARA explains why PARA is such a good candidate for metal replacement. For instances, this is low moisture uptake, superior strength, stiffness, and highly aesthetic surface finish.

In the future, more and more medical metal applications will be replaced by high performance plastics such as PARA, PEEK and Polysulfones.

Below a selection of the different PARA-based Zillion Black® single-use instruments is shown.

Greetings and till next time,
Herwig Juster

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Literature:
[1] https://www.solvay.com/en/press-release/solvays-ixef-para-enables-zillion-black-single-use-instruments
[2] https://www.solvay.com/en/brands/ixef-para

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