
Necessity is the mother of invention
Case Study: Mask Rejuvenation System During COVID-19
Oct 4, 2024in: automation, COVID19
In response to the COVID-19 pandemic and the global shortage of personal protective equipment (PPE), we collaborated with Open Source Medical Supplies to develop a number of emergency methods and techniques. One of them is a way to prolong the usable life of N95 masks in shortage situations. This system was designed to be simple, cost-effective, and adaptable to available resources, making it accessible to those in critical need.
The core of the method involves using a microcontroller, such as an ESP01, alongside a basic inductive circuit to generate a 110kHz square wave with a 25V peak-to-peak output (While a simpler 555 timer circuit could have been employed to drive the transducers, and was successfully tested later, we opted for ESP01 microcontrollers due to a surplus at the time). This drives multiple piezoelectric ultrasonic transducers. The N95 mask to be regenerated is placed inside a sealed plastic container (e.g., a Tupperware box) filled with a small amount of hydrogen peroxide, which serves as the disinfecting agent. Depending on availability, the hydrogen peroxide concentration can range from 3% to 20%, making this system flexible in emergency situations.
To prolong the chemical life of the hydrogen peroxide, the entire setup is operated in a dark environment. The mask itself is suspended inside the box by its ear strings and rotated via a geared TT motor powered by the same supply as the microcontroller. This ensures even exposure to the disinfecting mist. The piezoelectric transducers, mounted at an angle on 3D-printed supports, leverage capillary action to draw hydrogen peroxide upwards and then mist it uniformly across the mask, effectively disinfecting it.
The system allows for manual replacement of masks every 15-30 minutes, alongside replenishing the hydrogen peroxide as needed. Given the variability in hydrogen peroxide concentration, the design can accommodate non-medical-grade supplies, such as hydrogen peroxide typically used for hair dye.
According to Kenney, et al, exposure to hydrogen peroxide has less than a 1% effect on the filtration efficiency of n95 masks. Further study is necessary to recommend this equipment outside of emergency measures, but during supply shortages, it is much better than no mask.
Stay safe out there.