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CASE STUDY:  How Two-Shot Molding Solves Medical Design Challenges and Enhanced Performance of a Hemostasis Valve 

The Challenge 

Medical device manufacturers face constant pressure to innovate, improve performance, and control costs. Many OEMs have traditionally molded components (often made from different materials) separately and then joined them together to make a finished component or device. This involves multiple steps, different component molds, and subsequent manual assembly. This multi-stage process increases labor and material costs, slows cycle times, boosts defect rates, and unnecessarily complicates your supply chain and validation activities. Furthermore, many medical device components require a combination of aesthetic, physical and functional properties that cannot be achieved with a single material.  

One manufacturer faced a specific functional challenge with the current design for a hemostasis valve. The first-generation design joined multiple components together in a manual assembly process.  This had some challenges when it came to functionality as well as excessive scrap, and the part did not meet arterial pressure requirements.  In addition, the design had limited tactile “feel” and was more complicated to assemble, boosting the overall cost.

The Solution 

To address the challenges faced by many medical device OEMs, Freudenberg Medical implemented advanced two-shot molding capabilities at facilities in the US and Germany. Two-shot molding, also known as multi-shot, bi-component, 2K or 2C molding, is a sophisticated injection molding process that integrates two or more resins into a unified part. Using this approach commonly involves combining a rigid thermoplastic with a softer thermoplastic elastomer (TPE / TPU) or, in specific applications, a silicone elastomer. Two-shot molding is superior to overmolding techniques which might not support the tight tolerance requirements of many medical device components such as those used in cardiovascular, peripheral vascular and neurovascular devices.  

In manufacturing the hemostasis valve, Freudenberg Medical combined the end cap and gland portion of the valve design into a single bonded Liquid Silicone Rubber (LSR) component using two-shot molding techniques. The valve is produced using two silicones of different shore hardness. Here optimal material selection played a particularly important role, and the resulting hard silicone and softer silicone combination delivered flexibility and was the enabling factor to meet the arterial pressure requirements. The valve’s design, placed within an access catheter, was refined to provide an even more effective seal during minimally invasive surgical procedures, thereby minimizing patients’ blood loss. 

The Benefit 

Two-shot molding offers a compelling solution for medical device manufacturers seeking to optimize product design, reduce costs, and improve overall manufacturing efficiency by getting rid of secondary processes and assembly. Implementing two-shot molding in-house may not make sense for medical device manufacturers due to the high cost of two-shot injection molding machines and complexity of the molds.  However, Freudenberg Medical is able to distribute the investment across many customers and maximize machine output. This results in competitive overall costs and higher quality.  

For this customer, Freudenberg Medical helped redesign their hemostasis valve and increased efficiency by eliminating bonding and material handling and increased the functionality of the part by combining two materials. This resulted in a more tactile, ergonomic design with a robust repeatable process that is scalable.  

A Challenge to Product Developers

Medical device product development teams are tasked with creating a proof-of-concept for a device and two-shot molding is not often considered in early design iterations as it is deemed too expensive for proof of concept.  

When product designers need expert help, Freudenberg engineers can help design components and recommend optimal materials that combine two hard materials, two soft materials, or any combination thereof.  We work with Liquid Silicone Rubber, Thermoplastic Elastomers, Thermoplastic Urethanes, and Thermoplastics.