Medical-grade adhesives are adhesives used for bonding medical devices. Many types of medical devices today rely on adhesives for assembly. The modern medical device manufacturing industry demands maximum reliability and performance in end products under numerous challenging conditions.
Medical device manufacturers often require extensive testing and verification to determine the adhesive's performance when deciding on adhesives. This also requires that medical adhesives possess specific properties to meet the economic and high-volume manufacturing requirements of the medical device market. Virtually all medical devices or diagnostic equipment may utilize medical-grade adhesives.
The most common medical adhesive applications fall into three categories:
1. Disposables (such as syringes, catheters, and oxygenators);
2. Reusable devices (such as surgical instruments and diagnostic equipment);
3. Implantable devices (such as pacemakers).
Medical adhesive materials must not only meet common industry standards (heat resistance, aging resistance, strength, etc.) required by other industries, but also must pass toxicity testing or antibacterial testing.
Standards and Regulations:
Medical devices impact human health, and in the medical device manufacturing sector, there's a heightened focus on adhesive selection criteria and the requirements for optimal bonding performance. The selection of adhesives for medical applications follows the same process as for other applications, with criteria including: determining the specific bonding substrate, strength requirements, load type, impact resistance, high-temperature resistance, low fluid resistance, and processing requirements.
However, many medical devices also require at least two other important criteria: sterilization resistance and low toxicity.
As a result, the medical device industry has established several key standards and regulations.
1. Toxicity and Biocompatibility
Adhesives used in medical devices need to be tested for their effects on cells (cytotoxicity), blood components (hemolysis), adjacent tissues, and overall biological systems. Several types of biocompatibility testing currently exist.
Adhesive suppliers generally test for toxicological properties and biocompatibility according to the following established guidelines:
1) United States Pharmacopeia (USP) Class VI
2) International Organization for Standardization (ISO)-10993
These standards were originally developed to test plastics used in medical devices for suitability for contact with body fluids, and they are now also applied to medical adhesives. Generally, products are tested by independent laboratories, and the results are provided to the device or adhesive manufacturer in the form of a standard certification. Successful testing indicates that the cured product is non-toxic and biocompatible.
2. Sterilization Resistance
Another important requirement for medical adhesives is sterilization resistance. Most disposable and reusable medical devices require sterilization before use.
Some products (such as endoscopes and surgical instruments) may require multiple sterilization cycles, and adhesives must withstand these processes without compromising their primary functionality.
3. Medical Device Assembly Methods
Assembly methods used in medical device manufacturing include solvent welding, ultrasonic welding, vibration welding, and bonding. Adhesive bonding has gained widespread acceptance in the medical device manufacturing industry because it doesn't pose the same health and safety concerns as solvent welding. It also doesn't require the expensive equipment investment of ultrasonic or vibration welding.
Medical adhesives are highly valued in the medical device assembly industry because they offer the following properties:
1) excellent gap-filling properties;
2) compatibility with thermoset and thermoplastic substrates, non-polymer substrates, and other diverse substrates;
3) adjustable flexibility or rigidity;
4) uniform stress distribution across the bond;
5) ability to create a hermetic seal between two substrates.
Key physical and chemical properties of adhesives
Working time: The maximum time interval between mixing the adhesive and mating the parts to be bonded.
Initial cure time: The time required to reach removable strength, which allows for handling of the bonded parts, including removal from the fixture.
Full cure time: The time required for the adhesive to achieve its final mechanical properties after mixing.
Shelf life: The time it takes for the adhesive to maintain its working properties and specified strength under certain conditions.
Storage time: Bond strength: The stress required to cause failure at the interface between the adhesive and the adherend or at its adjacent locations under the action of an external force.
Shear strength: Shear strength is the shear force per unit surface area that the bonded part can withstand at failure. It is expressed in MPa (N/mm²).
Uneven pull-off strength: The maximum load a joint can withstand when subjected to an uneven pull-off force. Because the load is concentrated at two or one edge of the adhesive layer, it is expressed per unit length rather than per unit length. Force per unit area, expressed in kN/m
Tensile Strength
Tensile strength, also known as uniform pull strength or normal tensile strength, refers to the tensile force per unit area when the adhesive fails. It is expressed in MPa (N/mm²).
Peel Strength
Peel strength is the maximum load per unit width that can be sustained when the adhesive is separated under specified peeling conditions. It is expressed in kN/m.
Common Adhesive Testing Items
1. Physical Properties
General Properties: Thickness; Viscosity; Water Resistance
Mechanical Tests: Tensile Properties;
Peel Strength; Tensile Shear Strength; Compression Shear Strength; Horizontal and Vertical Adhesion
Flammability: Horizontal Burning; Vertical Burning; Glow-Wire Burning
Electrical Properties: Surface and Volume Resistivity of Insulating Materials; Surface Resistivity of Antistatic Materials; Dielectric Strength, Breakdown Voltage; Withstand Voltage
2. Aging Tests
Rapid UV Aging; Xenon Lamp Aging; Temperature and Humidity Aging; Salt Spray Aging Appearance and performance evaluation after aging
3. Component Analysis
Qualitative analysis of principal components; Qualitative analysis of all components; Quantitative analysis of all components; Ash content
4. Reliability
Temperature and humidity cycle; Temperature shock; Water and dust resistance; Vibration testing
