Several bonding characteristics determine how well an adhesive performs in diagnostic applications, especially under stress or over time.  

• Peel strength: Measures how well the adhesive resists separation from surfaces—important for maintaining bond integrity during handling or testing.  
• Tack: Indicates initial stickiness, which helps with fast and accurate placement during assembly.  
• Shear resistance: Ensures the adhesive can withstand lateral forces without shifting or failing.  
• Long-term stability: Critical for maintaining performance over time, especially in devices with extended shelf life or prolonged use.  
• Cohesive strength: Ability of the adhesive to remain intact (not split), minimizing residue transfer to bonded surfaces. 
• Fluid/chemical resistance: Ability to resist swelling, softening, or leaching when exposed to samples, buffers, and assay reagents. 

These properties help ensure reliable bonding under various conditions in diagnostic applications.  

Surface energy is a measure of how readily a solid surface can be wetted by a liquid (and, by extension, how easily an adhesive can spread to make intimate contact). High surface energy materials (e.g., metals or glass) typically wet and bond more readily, while low surface energy (LSE) plastics (e.g., polyethylene, polypropylene) are harder to wet and therefore harder to bond without surface treatment or specialized adhesives. 

In microfluidic devices, surface energy (often discussed via water contact angle) helps predict how liquids will interact with channel walls and can influence capillary‑driven flow behavior. 

Measurement methods: 

• Contact angle: A droplet’s angle on the surface—lower angles indicate higher surface energy.  
• Dyne pens or solutions: Apply liquids of known surface tension; if the liquid wets out, it indicates the surface energy is at/above that dyne level. 

Bond failure or leakage may result from: 

• Inconsistent adhesive thickness affecting channel sealing. 
• Poor alignment between bonded layers. 
• Incompatible surface energies between substrates. 
• Mechanical stress during handling or testing. 

Bonding materials can influence assay results by: 

• Altering channel dimensions or spacing. 
• Introducing variability if registration shifts. 
• Allowing leaks or air intrusion that disrupt fluid movement. 

Trade‑offs may include: 

• Higher bond strength increasing the risk of channel deformation. 
• Softer materials improving conformity but reducing structural support. 
• Thicker adhesives improving sealing while affecting channel geometry. 

Manufacturing tolerances can impact bonding by: 

• Causing variation in bond line thickness. 
• Affecting repeatability across devices. 
• Increasing the risk of misalignment in multilayer builds. 

Bonding performance should be validated: 

• Before finalizing channel and layer geometry. 
• Prior to scaling manufacturing processes. 
• Whenever materials or substrates change.