Considerations for Selecting an Adhesive for Medical Device Applications

MatWeb Featured Article
By Robert Michaels
Vice President, Master Bond, Inc.

Picking the right adhesive almost always entails a balancing act as engineers attempt to find products that meet conflicting end-use and manufacturability requirements including:

• Resistance of aggressive sterilization methods
• Difficultly meeting application requirements— such as high bond strength, thermal performance and chemical resistance
• Burden of picking materials that are biocompatible

Difficulties may arise when choosing materials and adhesives that not only work together as a system but also minimize performance and manufacturability trade-offs. Finding the medical adhesive that can do it all may not be easy, but taking the following points into consideration is a great start:

1. Biocompatible Adhesives

• One common misconception about medical adhesives involves their biocompatibility
  • There is no specific requirement of using biocompatible adhesives – engineers have the freedom to select and combine materials as they please, as long as the finished device passes the required FDA specifications
• The most widely accepted test standard in North America is United States Pharmacopeia (USP) Class VI while a related European standard is ISO 10993
  • Intended to evaluate the suitability of polymeric materials for direct and indirect patient contact – however passing USP Class VI testing doesn’t guarantee that a device will gain FDA approval
  • USP Class VI testing represents a valuable tool and serves as an excellent guideline for identifying products suitable for medical applications

2. Sterilization and Use

• Many polymeric materials, including various standard adhesives, have the potential to degrade under repeated exposure to many popular sterilization methods
• Disposable versus Reusable Devices:
  • Disposable devices
    • Typically bulk sterilized a single time using ETO, gamma or other forms of radiation which generally do not pose a degradation problem for medical adhesives at that level of exposure
  • Reusable devices
    • Mostly endure multiple cycles of sterilization or exposure to aggressive chemicals that can potentially degrade the adhesive – this greatly limits options of suitable medical compounds

3. Importance of Manufacturability

• Designing for use versus designing for assembly
  • Adhesives that offer the best resistance to repeated sterilization might not always be the fastest or easiest to use on the shop floor
  • Based on the severity of the operating conditions there may be potential trade-offs in the manufacturing of the medical device
  • Keep in mind that the addition of heat during the curing process typically helps optimize mechanical and physical properties

4. Adhesive Consideration Early in the Process

• There are many more bonding options available when materials and adhesives are evaluated as a system early in the design process
  • Engineers need to remember that the substrates play a critical role in both the selection of the adhesive and eventual performance of the device

5. Technical Support

• With every new material comes new questions about biocompatibility, sterilization resistance, bonding performance and ease of assembly
  • The best way to stay current is to stay in touch with your adhesive supplier