Precision Dispenser Provides Nontoxic Adhesive to Wearable Sensor Technology
Ensuring the long-term reliability and performance of wearable sensors hinges on robust manufacturing processes.
Anthony Buzzerio, Venkat Nandivada, Rohit Ramnath
Cool Stuff
Dec 9, 2025
From smart watches to fitness trackers to smart clothing, the growing field of wearable technology relies heavily on miniaturized sensors capable of providing accurate and continuous physiological data. This is especially true in the medical field where all types of demanding conditions including physical stress, thermal fluctuations, and exposure to bodily fluids can create a harsh environment. One of the keys to operational superiority includes biocompatible adhesives for encapsulating these delicate sensor components.
Here we’ll examine the selection and implementation of a non-cytotoxic adhesive chosen for its ability to encapsulate sensors from harsh environmental factors such as humidity, dust, and mechanical impact. We’ll also explore the automated dispensing equipment used to achieve the accuracy and consistency required for production. To ensure that the manufacturing process was optimized, Nordson EFD partnered with specialty adhesive manufacturer Master Bond.
The product selected for this encapsulation process needed to meet several key requirements to ensure its effectiveness and compatibility with the wearable sensor, including a low-viscosity epoxy with capillary flow characteristics for precise dispensing, the material needed to be curable below 80oC to protect heat-sensitive electronic components from damage, and it needed to be a non-cytotoxic encapsulant to ensure safe use when used against a human body. Finally, the dispensing process had to be automated and capable of dispensing approximately 3cc of the material per sensor consistently.
Material Solution
Master Bond’s EP21LSCL-2Med, a two-component epoxy adhesive, met the overall application requirements. The product has an ISO 10993-5 non-cytotoxicity rating, which qualifies for wearable sensors. EP21LSCL-2Med was specifically engineered for low-temperature heat curing, which was instrumental in protecting the integrity of the sensitive electronics within the device. Important was the adhesive’s low mixed viscosity—measured at 500–1000 cps at room temperature—making it highly suitable for capillary action, which ensured that intricate spaces were properly filled with no voids.
The Master Bond EP21LSCL-2Med has a working life of 6-8 hours. The working life of a fluid is the amount of time before the epoxy becomes too thick to be applied. An additional consideration for fluid dispensing technology selection was that once the Master Bond compound was thawed to room temperature from the -40° C freezer in the manufacturing process, it could not be re-frozen. This fact informed the dispense solution selection for the application.
The material was packaged in pre-mixed and frozen syringes (stored at -40oC until use), delivered in 3cc Nordson EFD syringes, making the process highly efficient and reducing waste. Operators could simply thaw and load the syringes into Nordson's dispensing system, streamlining the workflow and minimizing handling errors.
Dispensing and Packaging
Nordson EFD offers several fluid dispensing solutions for effectively encapsulating wearable electronics. The company’s broad selection of fluid dispense solutions enables manufacturers to choose the right technology for their unique application needs.
To meet the requirement for the material to flow easily around the sensor components and fill the intricate spaces without leaving voids in the application, a fluid dispenser, valve, automation, cartridge, and tip technologies were required. To maximize the usage within the Master Bond EP21LSCL-2Med’s working life, Nordson EFD engineers recommended using the Ultimus V high precision dispensers, which provided a benchtop fluid dispensing control for the manual or automated application of fluids.
As the viscosity of the epoxy changes, the full electronic press regulation feature keeps the critical fluid dispensing processes consistent from start to finish. The Ultimus V fluid dispensing solution shot size stays consistent regardless of changes in viscosity of the epoxy. This solution also offered electronic control of the dispensing time, air pressure, and vacuum. Once programmed the air pressure automatically adjusts as the fluid gets thicker.
If larger volume is required (30cc or more), an xQR41V Series needle valve can be an alternative to avoid full-to-empty variation issues. The design of the xQR41V allows for quick fluid change-over and easy cleaning of wetted parts at the end of the shift. The needle valve features a patented quick release clasp, enabling fast and easy servicing in the field. In addition, the low level of fluids retained in the fluid body reduces fluid waste, and the reduced form factor of the solution increases production capacity.
After benchtop testing was successful, in order to meet the longer time requirement for automated dispensing, Nordson EFD advised that the customer use the EV Series of tabletop automated dispensing systems for easy integration into the manufacturing operations.
The consistent application of the fluid was maintained by using Nordson EFD for general purpose orange or red stainless-steel tips. The orange tip is 23 gauge and has an inner diameter of 0.33 mm/0.013-in. This tip is most optimal when the material is applied manually. The red tip is 25 gauge and has an inner diameter of 0.25 mm/0.010-in, which is more suited for automated processes. Nordson EFD uses a laboratory-focused approach to recommending fluid dispensing technologies—evaluating fluids, substrates, application goals, and production needs to provide a consultative approach to selecting the right solution.
Minimizing Air Bubbles for Pre-mixed and Frozen Packaging
One of the most common challenges in dispensing epoxy adhesives is the presence of air bubbles. To address this, Master Bond implemented rigorous degassing protocols during the packaging process. After mixing the two components of the EP21LSCL-2Med, the formulation underwent centrifugation at 2000–3000 rpm for 1–2 minutes. This critical step effectively removed entrapped air and reduced the risk of voids during application. Using a centrifuge system like the ProcessMate 5000 Universal Centrifuge is a proven way to ensure no air pockets exist after thawing the epoxy used in this application. This approach only eliminated the need for on-site mixing, a process prone to variability and contamination, but also dramatically improved production uptime and consistency.
The collaborative application of Master Bond’s innovative pre-mixed and frozen epoxy alongside Nordson’s best-in-class dispensing technology proved instrumental in the customer's success in manufacturing their wearable sensor solution.
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About the authors: Anthony Buzzerio is the Application/Systems Engineer II at Nordson EFD; Venkat Nandivada is the Manager of Technical Support, Master Bond; and Rohit Ramnath is the Senior Product Engineer at Master Bond.