Adhesive strength is a key parameter in the performance of medical adhesives, which are used to secure devices and dressings to the skin. These systems must maintain reliable contact over time, across a wide range of conditions and patient types.
Measuring adhesive strength is essential to ensure the correct balance between secure fixation and safe removal. If adhesion strength is too low, devices may fail or become dislodged. If it is too high, removal can cause pain, skin damage, or medical adhesive-related skin injury (MARSI), where the adhesive bond exceeds the strength of the skin itself.
Adhesive strength test methods such as tensile, shear, and peel measurements are used to quantify this performance and support the development of adhesives that are both effective and skin compatible.
Adhesive Strength Meaning
Adhesive strength refers to the strength of the bond between adhesive coating and substrate interface. Cohesive strength is another component which refers to the internal strength of the adhesive and its ability to hold itself together under stress.
Surface Energy & Adhesive Selection
Another factor to consider when creating an effective bond with adhesives is substrate surface energy. Surface energy describes the excess interaction energy that exists at the surface of a given substrate and depends on their chemical make-up.
A high surface energy (HSE) means a strong molecular attraction, therefore easier to bond. Examples of HSE surfaces include Copper, Nylon, Polyester, Aluminium, Zinc, ABS, Tin, Stainless Steel, Polycarbonate, Acrylic, Epoxy Paint, Lead, PVC Rigid, Glass Porcelain
A low surface energy (LSE) means a weak molecular attraction, therefore harder to bond. Examples of LSE surfaces include Powder Coated Paints, EVA, Acetal, PVA, Polyethylene, Polypropylene.
When selecting an adhesive, the bonding surface and its surface energy is a vital consideration. With regards to liquid adhesives, ‘wetting out’ needs to occur for optimum adhesion; this is where the adhesive spreads over the surface to maximise the attractive forces between the adhesive and the surface.
Over the years, the range of adhesives that have become available has increased dramatically, with some being specifically created for LSE surfaces. This means there are now more opportunities for manufacturers to use alternative adhesives to the usual, traditional methods of bonding.
How to Measure Adhesive Strength
Adhesive strength measurement is calculated using three tests; a tensile strength test, shear strength test, and peel strength test which all determine the effectiveness of an adhesive and its ability to bond to certain substrates.
Tensile Strength
Tensile strength is measured by stretching apart two sample substrates that are bonded with the adhesive. The point at which the adhesive breaks indicates the peak tension force it can withstand; this amount is then divided by its cross sectional area and the total figure is its tensile strength. This measurement is most commonly used in structural adhesives and bonded assemblies as it refers to the adhesive’s ability to resist loads under stress without failure.
Shear Strength
Shear strength is measured by pulling two sample substrates that are bonded with the adhesive in a sliding motion and in opposite directions. The peak shear force that is sustained before failure is then divided by its cross-sectional area resulting in the shear strength of the adhesive. This measurement represents the adhesive’s ability to resist forces that can potentially cause their internal adhesive layers sliding under load.
Peel Strength
Peel strength is measured by pulling back two sample substrates that are bonded with the adhesive, commonly peeled at 90° and 180° angles and at a constant rate. It is normally reported as force per unit width (N/25mm) as peel loading acts linearly along the bond line, concentrating stress at the peeling edge. This measurement is used to identify the adhesive’s resistance to localised stresses.
Adhesive Tack
Adhesive tack measures the initial adhesion level at the point of application. This is especially important for wearables and wound dressings which must stay in place immediately, even during movement. In pressure sensitive adhesives (PSAs), adhesion often builds over several house and may take up to 24 hours to reach its final level. Tack is commonly assessed using loop tack, probe tack or rolling ball tests.
What Adhesive Strength Means for Different Applications
Adhesive strength requirements vary depending on the application, substrate, wear duration, and patient condition. The key is balancing adhesion, cohesion, and biocompatibility.
Wound Dressings
Adhesives must provide sufficient tack and peel strength for secure fixation while enabling low-trauma removal. Excessive adhesion can cause skin stripping, irritation, increased TEWL, and pain – particularly in fragile skin. As a result, wound dressings are typically designed with moderate, controlled adhesion, with silicone adhesives commonly used to minimise skin damage.
Wearable Medical Devices
Wearables require higher peel and shear strength to remain secure during movement, moisture exposure, and extended wear. However, long-term use can impact skin barrier function and reduce adhesion over time. Adhesives must therefore balance durability with skin compatibility and low sensitisation.
Long-Term & Repeated Use
Repeated application (e.g. ostomy care or continuous monitoring) increases the risk of skin damage, MARSI, and sensitisation. Adhesives in these applications must maintain consistent performance across cycles while enabling gentle removal and compatibility with varying skin conditions.
Fixation Applications
For devices such as catheters and sensors, adhesives must deliver high mechanical reliability, with strong shear and peel resistance to prevent displacement. At the same time, they must allow controlled removal to minimise skin trauma.
Why is Adhesion Strength Testing Important?
Adhesion strength testing is important for quality control purposes. This is not just for meeting customer specifications, but for adhering to industry standards too. Different industries and applications have various adhesive strength requirements, so it is vital to test according to those parameters.
Adhesion failures are economically costly and risk reputations; adhesive bond strength analysis can avoid these pitfalls along with other testing and prototyping during the design process. Identifying adhesive capabilities and the impact of variations on its performance is a significant part of the manufacturing process and one that needs meticulous attention to detail, especially medical adhesives.
At BDK, we provide comprehensive project management which consists of design, materials, prototyping and development, process validation and production. During our prototyping and development stage, we undertake adhesive strength testing to provide a solution that meets your specification.
Contact us today to find out more information and to discuss your project with BDK.