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Specialty thermoplastic elastomer compounds for medical applications.

The versatility of thermoplastic elastomers (TPEs), which can be processed as thermoplastics and function as elastomers, provides many benefits to medical related applications. Among various material technologies, TPE compounds based on styrenic block copolymers (SBCs) constitute an important category.

In contrast to conventional elastomers or silicones, SBC-based TPEs are manufactured through physical blending of components like polymers, plasticizers, fillers, pigments and additives. All raw materials can be strictly selected to guarantee maximal purity. Since no chemical reactions are involved in the process, no reactive residues, breakdown by-products or other extractables are left in the finished TPE compounds. For medical device manufacturers, their products can be fabricated using TPEs using traditional thermoplastic processes, including extrusion, injection molding and two-component overmolding. As a result, the manufacturers can achieve high production speed, ultimate product quality and low overall costs.

Kraiburg TPE has offered SBC-based TPE compounds with a low product liability risk for medical applications since the late 1990s. In response to increasing customer demands for high-quality, high-safety materials in the medical and pharmaceutical industry, and building on our experience accumulated with TPE materials for medical applications, Kraiburg has recently launched a new product line, Thermolast M. These new products guarantee a maximum of quality, safety and reliability in combination with a unique service package that supports various medical applications. Achieving superb bonding to HDPE, PP, PC, ABS and PC/ABS substrates, the new medical TPE grades eliminate any concerns associated with materials potentially detaching themselves from pharmaceutical packaging and entering the bloodstream. In this article, we present technical results related to the new Thermolast M TPE materials of all six distinct series that are specifically tailored to address requirements for different medical and pharmaceutical applications.

Safety, quality and reliability

It is Kraiburg TPE's goal that the new Thermolast M materials meet the very high standards for safety, quality and reliability. An optimal production standard has been set up with a company-owned, high-purity production system.

To eliminate any possible cross-contamination from raw materials or products, a separate system is allocated for handling only input materials approved for medical use. Similarly, a production line has been dedicated solely for the production of Thermolast M products. These procedures and arrangements ensure that optimal purity and consistency are achieved with our medical TPE grades. It is also guaranteed that the medical TPEs will be delivered in exactly the same form for an extended period of at least two years.

Due to factors beyond our control in raw material feedstock supply, modifications to our Thermolast M TPEs may become necessary at times. In such cases, raw material availability is guaranteed from our suppliers such that the affected customers will be informed of changes at least two years in advance.

Medical approvals

TPE compounds for medical applications are typically required to meet medical technology standards. For all the compounds in the Thermolast M portfolio, comprehensive medical approvals have been achieved according to USP Class VI, USP Class 6.6.1, ISO 10993-4, ISO 10993-5, ISO 10993-10, ISO 10993-11, as well as Drug Master Files. Extractable studies were performed for selected compounds, especially those for applications with contact to pharmaceutical media. Table 1 lists the medical approval status for all six medical TPE series in Thermolast M.

Sterilization

Thermolast M materials are designed to be sterilizable by gamma radiation, EtO and autoclaving with superheated steam at temperatures up to 134[degrees]C. For example, the mechanical properties of TM7MED, a 70 durometer A material in the MT series, held up very well in various sterilization tests. As demonstrated in figure 1, the material displayed little change in tear resistance after various exposures to gamma irradiation. The tensile strength of TM7MED decreased only slightly in a series of aggressive steam autoclaving sterilization tests (figure 2). Table 2 summarizes sterilizability with gamma radiation, autoclaving and EtO for all our medical grades.

Adhesion

Common thermoplastics for medical related applications include HDPE, PP, PC, ABS and PC/ABS resins. Thermolast M materials have been tested and have exhibited excellent bonding to all these hard substrates. Figure 3 is the Renault adhesion test profile for TM7MED. The peel force reached an average of 15.8 N/mm for this grade. The excellent adhesion of the MT/CO series on more polar substrates, such as PC, ABS, PC/ ABS, PETG, etc., is exemplified by the Renault peel profile of TMSADT on PC, as shown in figure 4. The adhesion levels achieved by Thermolast M grades effectively meet the requirements for many overmolding parts with various hard polymers (table 3).

General properties

Table 4 provides the general properties and application highlights of all six series in the Thermolast M product line. Each series contains grades with similar properties for the same application areas, but with a suitable hardness range to satisfy specific customer needs. Most of the medical grades are translucent for easy identification of contaminations by foreign substances. Another advantage of this translucent color is their outstanding colorability. With excellent compression set and a wide hardness range, the MT series provides general purpose materials for applications from gaskets to soft touch components. MT/RS products are suitable for resealable membranes and infusion stoppers. The MT/HE series gives very good candidates for drip chambers, Luer locks, etc., due to their high elasticity. With excellent adhesion on polar substrates, the MT/CO series can be used for gaskets and soft touch pieces. Good low friction properties qualify the MT/LF series for various applications that require this feature. The MT/HD series offers further choices for certain situations where optimal cycle time is preferred.

Thermolast M compounds are generally safe for applications with indirect contact to bodily fluids and/or blood. In addition, these materials are usable for applications with direct blood contact when a risk assessment completed by the Kraiburg TPE medical team deems them suitable.

Summary

Kraiburg TPE has significantly expanded its product portfolio with the addition of a new family of SBC-based TPE compounds focused specifically on the needs of the medical and healthcare markets. Combining the processing benefits of two-component molding, and the product design flexibility of thermoplastics with performance attributes typically associated with rubber or silicone materials, Kraiburg's Thermolast M compounds are also backed by a 24-month supply guarantee, along with required USE ISO and Drug Master File listings for added security to OEMs or manufacturers of medical devices. Achieving superb bonding to HDPE, PP, ABS and PC/ABS substrates eliminates any concerns associated with materials in diaphragms, seals or valves potentially detaching themselves from pharmaceuticals packaging and entering the bloodstream. Additionally, the compounds are suitable for gamma sterilization and enable autoclaving with superheated steam at temperatures of up to 134[degrees]C. Thermolast M compounds are generally safe for applications with indirect contact to bodily fluids and/or blood. In addition, these materials are usable for applications with direct blood contact when a risk assessment completed by the Kraiburg TPE medical team deems it suitable for them.

by John Chiao and Kenneth Sienkowski, Kraiburg TPE

Table 1--Thermolast M--medical approval status

Series            MT     MT/RS     MT/HE     MT/CO     MT/LF     MT/HD

IS0           [check]   [check]   [check]   [check]   [check]   [check]
10993-4

IS0           [check]   [check]   [check]   [check]   [check]   [check]
10993-5

ISO           [check]   [check]   [check]   [check]   [check]   [check]
10993-10

ISO           [check]   [check]   [check]   [check]   [check]   [check]
10993-11

USP Class     [check]   [check]   [check]   [check]   [check]   [check]
VI

LISP Class    [check]   [check]   [check]   [check]   [check]   [check]
6.6.1

DMF           [check]   [check]   [check]   [check]   [check]   [check]

Extractable       --        --        --        --        --        --
study

Table 2--Thermolast M--sterilization

Series           MT     MTIRS     MTIHE     MTICO     MTILF     MTIHD

Gamma        [check]   [check]   [check]   [check]   [check]   [check]
(2 x 35
kGy)

Hot steam    [check]   [check]   [check]   [check]   [check]
(135
[degrees]
C)

EtO          [check]   [check]   [check]   [check]   [check]   [check]

Table 3--Thermolast M--adhesion to
common polymers

Series          MT     MTIRS     MT1HE     MTICO     MTlLF     MT1HD

PP, HDPE    [check]   [check]   [check]       --    [check]   [check]

PC, ABS,        --        --        --    [check]       --        --
PC/ABS

Table 4--general properties and application highlights of Thermolast M

Series                      MT               MTIRS            MTIHE
Hardness                 30-90               30.45            55.45
                   durometer A         durometer A      durometer D
Color              Translucent         Translucent      Translucent
Colorability       Possible by         Possible by      Possible by
                      Kraiburg            Kraiburg         Kraiburg
Highlights           Excellent           Excellent             High
               compression set       resealability       elasticity
Application      Gaskets, soft       RS membranes,   Drip chambers,
examples                 touch   infusion stoppers       Luer locks

Series                 MT/CO          MTILF           MTIHD
Hardness               30-70          30-70           30-70
                 durometer A    durometer A     durometer A
Color            Translucent    Translucent         Natural
Colorability     Possible by    Possible by     Possible by
                    Kraiburg       Kraiburg        Kraiburg
Highlights         Excellent   Low friction      Cycle time
                    adhesion                      optimized
Application    Gaskets, soft     Blood tube   Gaskets, soft
examples               touch       closures           touch
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Author:Chiao, John; Sienkowski, Kenneth
Publication:Rubber World
Date:Jun 1, 2013
Words:1414
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