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Medical Device Adhesives – The Myths and Mysteries

Many myths surround the term ‘medical device adhesive’, including myths about FDA approval, or that the existence of an FDA device master file on an adhesive denotes or implies bio-compatibility.

Simply put, medical device adhesives are ‘adhesives that are marketed to medical device manufacturers’. Unlike food grade adhesives, medical device adhesives contain no special approval or blessing from the FDA. Often, bio-compatibility testing is performed on the adhesive as a marketing tool to increase the buyer’s trust in the product. Types of biocompatibility testing include cytotoxicity, USP Class VI, and IS010993.  Even then, the assessment does not replace the testing required of the device manufacturer by the FDA. Device manufacturers are required to prove that the device they manufacture is bio-compatible and effective.

The logic path is this:

•    Adhesives are tested for bio-compatibility after they are cured;
•    Lack of proper curing can affect bio-compatibility;
•    Curing occurs within the device manufacturer’s assembly process.
Therefore:
•    Bio-compatibility can only be determined on the finished medical device.

In addtion, FDA master files are simply repositories of information that the FDA may require, and which manufacturers of medical device components may be unwilling to provide directly to the manufacturer of the medical device itself.  So having a file number does not even indicate that the FDA has read the contents, or even made a decision on them.

So if medical device adhesives are not FDA approved, what is the big mystery?
We know that “adhesives that are marketed to medical device manufacturers” doesn’t give you an overload of information. But it does drive home the point that they are not sanctioned by any governing authority. So, what are they? …Generally, the term ‘medical device adhesives’ refers to those adhesives used on medical devices that come into contact with the body, body fluids or delivery systems. As such, the adhesives are designed to bond the plastics and other materials common to the industry. So a UV curable adhesive used to bond an oxygen mask together is likely considered a medical device adhesive. But the epoxy, threadlockers and, structural acrylics used in the manufacture of an x-ray machine are not considered medical device adhesive. However, if you use the same epoxy used in the x-ray machine to bond a needle into the hub of a hypodermic needle…well, now there is a medical device adhesive!

So, choose the adhesive that meets your requirements, regardless of whether it is termed a medical device adhesive or not. The following provides a starting point for choosing an adhesive technology:

Technology Biocompatibility Sterilization Applications
Anaerobic Generally not used in fluid path Threadlocking, retaining, sealing, gasketing of metals only
Cyanoacrylates Most will pass the majority of tests OK for EtO & Gamma but will degrade with repetitive autoclave cycles Bonding various plastics and metals, generally not suitable for glass
UV acrylates Most will pass the majority of tests OK for EtO & Gamma but will degrade with repetitive autoclave cycles Excellent on plastics, glass, metals and ceramics
Epoxy Most will pass the majority of tests OK for EtO & Gamma and will perform better in autoclave cycles than others Some adhesion to some plastics. Generally used to lock needles into plastic hubs or bond metals.
Urethane Varies OK for EtO & Gamma but test for repetitive autoclave cycles Commonly used for potting hollow fibers
Structural Acrylics Generally not used in fluid path. Compatibility will depend on complete cure. OK for EtO & Gamma but test for repetitive autoclave cycles Structural adhesives, primarily for equipment as opposed to disposable devices