Importance of Adhesives
Why Are Adhesives Even a Big Deal in Medical Devices?
Adhesives used in medical devices generally fall into two main categories — and understanding the difference is key to choosing the right material for the job.
First, there are structural adhesives used within the medical device itself. These adhesives hold internal components together, seal housings, and ensure that the device stays intact throughout its lifespan. For example, they might be used to bond plastic casings in a diagnostic cartridge, or to seal the layers in a multi-layer blood filtration unit. These adhesives are all about durability, precision, and long-term reliability — often under sterilization or chemical exposure.
Then, you have skin-contact adhesives, which are used to attach a device to a person or even to another device. Think of the adhesive on a wearable heart monitor, a diabetes patch, or even a simple wound dressing. These adhesives need to strike a careful balance: they must adhere well to skin (which isn’t exactly a uniform or predictable surface), stay put during movement or sweat, and come off without causing irritation.
Both types serve critical roles, but they’re designed with very different performance requirements. Choosing the wrong one — or underestimating what the adhesive has to endure — can lead to device failure, patient discomfort, or even health risks.
Tough-to-Bond Materials: A Real Engineering Hurdle
Many medical devices are made from materials that are notoriously difficult to bond — like silicones, polyolefins, and TPEs (thermoplastic elastomers). These materials have low surface energy, which makes it hard for adhesives to form a strong bond without special treatment.
Take silicone tubing, for instance. It’s commonly used for its flexibility and biocompatibility, but getting an adhesive to stick reliably? That’s a major challenge — especially if you want to avoid primers, abrasion, or other surface prep that can complicate manufacturing.
Here’s the thing: we’re not chemical engineers by trade, and we don’t pretend to be. But what sets us apart is our ability to work closely with adhesive manufacturers — companies like 3M, among others — who bring deep technical expertise and access to a wide portfolio of adhesive solutions. That collaboration allows us to quickly explore multiple paths, test options in real time, and zero in on the best adhesive for a specific material and application — without wasting cycles on trial and error.
This kind of partnership means we’re not limited to one way of thinking. We can compare off-the-shelf and custom solutions side-by-side, validate performance with real-world prototypes, and move faster from problem to solution — even when the materials are notoriously stubborn.
In short, bonding to tough substrates is always a challenge, but it’s a challenge we know how to navigate — with the right partners and a problem-solving mindset.
Why Are Adhesives Even a Big Deal in Medical Devices?
Adhesives used in medical devices generally fall into two categories.
Structural adhesives are used within the device to bond materials like plastics, metals, or elastomers. Think of assembling a handheld diagnostic device, bonding lenses in an endoscope, or sealing housings in catheters. These adhesives are designed to provide long-term, durable bonds under mechanical stress, sterilization, and environmental exposure.
Skin-contact adhesives are applied directly to the patient, such as the adhesive layer in a wearable ECG monitor, a wound dressing, or an insulin patch. These need to be gentle on skin, maintain adhesion during movement or perspiration, and remove cleanly without causing irritation.
In this guide, we’re focusing primarily on structural adhesives, since they’re integral to the integrity and performance of the device itself. However, we always keep skin-contact adhesives in mind during our risk mitigation planning — especially when devices involve patient interaction. Understanding how skin-contact adhesives behave can help us anticipate issues like unintentional skin contact, residue transfer, or accidental exposure during use.
Having working knowledge of both types doesn’t just help — it often gives us a more complete picture of potential injury risks, particularly in edge cases or during device misuse. We’ve found that knowing how both adhesive types function allows us to build safer, more thoughtful designs that consider the full lifecycle of the device — and the people using it.
So, while the focus is on structural adhesives, it’s never in isolation. The most effective solutions always come from looking at the big picture.
Sterilization Resistance: Holding Up Under Pressure
Medical devices often undergo sterilization — and it’s not a gentle process. Whether it’s heat, gas, or radiation, each method presents its own challenge to adhesive performance. If the adhesive can’t withstand these conditions, the entire device can be compromised.
Some of the most common sterilization methods include:
Autoclaving This method uses steam at high pressure and temperatures reaching 121–134°C (250–273°F). It’s effective, but also incredibly harsh on adhesives. Prolonged exposure to high heat and moisture can soften certain adhesives, causing them to revert to a malleable state. Under pressure, this softening can lead to unwanted shifting, seal failures, or bond line deformation — particularly in devices with tight mechanical tolerances.
Ethylene Oxide (EtO) A lower-temperature method often used for heat-sensitive materials. EtO is generally more forgiving on adhesives, but requires long aeration times to remove chemical residues, which could potentially interact with certain adhesive chemistries.
Gamma Irradiation Gamma rays are highly penetrating and effective at sterilization, but they come with trade-offs. Gamma irradiation can significantly alter adhesives by causing both physical and chemical changes. These include:
The effects can go either way. In some cases, cross-linking at optimal doses can actually improve adhesive performance. In others, gamma can trigger degradation, chain scission, or even blackening of the adhesive. The specific impact depends on the adhesive chemistry and irradiation dose — which is why materials used in gamma-sterilized devices must be selected and tested with great care.
Electron Beam (E-Beam) Similar to gamma but with lower penetration depth and more localized energy transfer. The effects on adhesives are often comparable to gamma but can be somewhat easier to control.
Adhesives used in medical devices need to maintain not only their bond strength, but also their dimensional stability and chemical integrity after sterilization. Any weakening, softening, or leaching can result in compromised devices or failed validation testing.
So, when selecting an adhesive, understanding how it behaves under real sterilization conditions — not just lab tests — is critical. The wrong adhesive can pass early tests but degrade over time, especially after repeated sterilization cycles.
Methods of Assembly: What Adhesives Add to the Equation
When it comes to building medical devices, manufacturers use a range of assembly methods — from ultrasonic welding and mechanical fastening to laser welding and, of course, adhesive bonding. Each approach has its pros and cons, but adhesives bring their own unique set of considerations that often fly under the radar during early design stages.
Adhesive bonding can simplify certain aspects of design — like joining dissimilar materials, creating seals, or distributing stress evenly across a joint — but it can also introduce complexity into the assembly process itself.
Glue Adds More Than Just Stick
Unlike snap-fits or welds that provide near-instant bonding, adhesives usually require time, heat, pressure, or even UV light to cure. These steps may seem small, but they add layers of process control that need to be tightly managed in production:
Curing Time Some adhesives require hours to fully cure, which can affect takt time on the assembly line. Skipping or rushing this step can lead to bond failure — something that may not show up until the product is already in the field.
Baking or Heat Exposure Certain adhesives need to be baked at elevated temperatures (e.g., 60–120°C) to reach their final cured state. This may require adding ovens to your production line and rethinking your component materials to withstand heat.
Precise Application Control Applying too much or too little adhesive can affect bond strength, device function, and aesthetic quality. Controlling bead size, placement, and volume becomes a critical quality parameter — especially in small or sensitive assemblies.
Fixture or Clamping During Cure Adhesives often require parts to be held in place for a specific duration to ensure alignment and bonding integrity. This may call for custom fixtures or jigs, which adds time and tooling costs.
Why This Matters
It’s easy to underestimate how adhesive selection ripples out across your entire assembly process. Many engineers overlook the additional steps adhesives may introduce, assuming the glue is just “apply and forget.” In reality, adhesives often tighten your process window, requiring greater control over time, temperature, and pressure than some other joining methods.
For example, a medical diagnostic device using a two-part epoxy might require:
A pre-mix step with a limited pot life
A precise assembly window before the material begins to gel
A multi-hour room-temperature cure
A post-bake to reach full mechanical properties
That’s four new steps — each with its own quality control points — layered into your manufacturing flow. Miss one, and you may be facing adhesive failures that are hard to diagnose and even harder to fix after the fact.
Key Takeaway
Adhesives can enable design flexibility and improve device performance, but they demand discipline in manufacturing. When used correctly, they’re an asset. When mismanaged, they’re a liability. The key is recognizing upfront how adhesive use fits into your broader assembly strategy — and building your processes accordingly.
Testing Glued Surfaces: It’s More Than Just Pulling Until It Breaks
Once the adhesive is selected and applied, you’re not done — not even close. Verifying a glued joint’s performance requires more than a simple pull test. In fact, adhesive testing is often one of the most underestimated yet mission-critical stages in medical device development. If testing doesn’t reflect how the product will be used (or misused), you might be setting yourself up for hidden failures — the kind that only appear after clinical use or, worse, post-market.
It’s Not Just the Force — It’s How and Where It’s Applied
Let’s say you’re bonding a strain relief boot to a cable in a wearable device. It passes a straight-line pull test on the bench with flying colors. Great. But in the real world? That cable might be tugged sideways, bent repeatedly, or even snagged and yanked abruptly at an angle. That kind of real-world loading introduces peel and torsional stresses — and adhesives typically don’t handle those as well as pure tensile loads.
This is a classic case where test setup can mislead you — and it's exactly why understanding force direction and stress types is critical in adhesive applications.
Types of Stress Modes to Consider
Each mode stresses the adhesive and the bonded materials differently:
Tensile: Straight pulling apart; often used in lab tests, but not the most common real-world force.
Shear: Sliding layers past each other; common in housings and panel bonding.
Peel: One edge is lifted or peeled away — adhesives are most vulnerable in this mode.
Torsional: Twisting the bonded parts; especially relevant in cylindrical or cable-based designs.
Flexural/Bending: Happens frequently in flexible or wearable devices where repeated motion is expected.
This Is Where DoE Becomes Critical
Understanding how glued joints perform across these different stress modes — under a variety of temperatures, humidity levels, and load angles — is where a Design of Experiments (DoE) becomes essential.
With adhesives, performance isn’t driven by one factor. It’s the interaction of multiple variables — adhesive type, surface prep, bond area, cure time, environmental exposure, and applied load — that determines real-world success or failure.
A well-structured DoE allows you to:
Identify which variables have the greatest impact on bond strength and durability.
Simulate edge-case scenarios (like angled pulls or variable cure times).
Reduce surprises in validation and scale-up.
Avoid over-testing unimportant variables, while zeroing in on what actually matters.
Establish safe processing windows — crucial for manufacturing repeatability.
If you're seeing intermittent failures or unexplained variation in adhesive performance, that's a red flag. A DoE can help untangle those problems before they show up in verification or field use
Design Tip: Longer, Flatter Joints = Stronger Joints
One of the simplest ways to improve joint strength — regardless of adhesive type — is to maximize the bond area and optimize joint geometry.
📌 Key Design Insight: Long, flat bonded surfaces help distribute stress more evenly and reduce concentration points. Short or point-contact joints often fail early — especially under peel or shear loads.
If you’re relying on a small dab of adhesive or bonding around curved or uneven surfaces, consider revisiting the design. Extending the bond line length, adding more overlap, or flattening mating surfaces can all dramatically improve strength and consistency.
Bottom Line
Glued joints don’t just need strong adhesives — they need smart testing, informed by real-world use and stress scenarios. Lab tests that don’t account for pull angles, environmental exposure, or mechanical fatigue can paint a false picture of reliability.
This is where good design meets good engineering process: robust testing methods, realistic failure modes, and data-backed DoEs are what turn a “working prototype” into a validated, field-ready product.
Design it flat. Test it thoroughly. Trust the data — not assumptions.
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