The number of applications for hemp continues to grow, and it is quickly becoming the plant that can quite literally do anything. From food to medicine to industrial applications, hemp is making its way into all industries. Most recently, researchers in Turkey and the U.S. have proposed yet another use for hemp —analytical testing.
Moving away from tree fiber paper to hemp fiber paper reduces water consumption and price point. It could also make the physician components of microfluidics more robust for remote or challenging fieldwork. Thanks to extensive testing results, researchers have determined hemp-based papers are a suitable alternative to the convention tree-based options.
What Are Microfluidic Paper-Based Analytical Devices (µPADs)?
The fundamentals of any µPAD product is a cellulose (plant-based) substrate for analytics. µPADs incorporate the hydrophilic nature of paper with specialized hydrophobic barriers to channel fluid samples into specific areas for a readable reaction.
In layperson terms, this means water quickly absorbs into and through paper (imagine a drop of water on a piece of newsprint) but can be controlled with specialized treatment of the same paper (imagine using wax to protect areas of the paper from water penetration).
Since 2007, µPADs have become an aspect of medical diagnosis, pharmaceutical analysis, clinical research, forensic investigations, environmental monitoring, and more. Part of the appeal for these paper-based testing devices is their extreme simplicity.
Testing with µPADs doesn't require any complicated laboratory equipment or technical facilities. µPADs are also convenient, portable, and comparatively affordable compared with other methods of testing. Under most circumstances, results develop instantaneously and don't require lab technicians or lengthy delays.
Different types of paper have different characteristics (like flow rate, porosity, and particle retention) that lend themselves to various applications. Common grades of paper for the production of these microfluidics tests are Whatman Grade 1 and Grade 4 filters. However, a new study published in Micromachines is exploring the potential of hemp-based microfluidics.
Why Test Hemp Paper As a Vehicle for µPADs?
There is a high annual yield with hemp cultivation, and nearly all aspects of the plant are either valuable, compostable, or reusable. On an acre-to-acre comparison, hemp plants produce four times the amount of fiber pulp (the foundation of paper production) than trees.
According to the National Hemp Association, hemp paper is remarkably more robust than traditional wood-based papers. Hemp-based µPADs could theoretically stand up to harsher environmental conditions, rougher handling, and remote work better than Whatman's graded wood-based paper.
Could Hemp-Based Paper Become the Standard for µPADs?
Mikail Temirel, Sajjad Rahmani Dabbagh, and Savas Tasoglu tested hemp-based paper compared to conventional µPADs (Whatman Grade 1 and 4) to determine whether it is a suitable alternative.
The research team used several approaches to assess the properties of hemp-based papers, including desktop pen plotter and commercial markers to create hydrophobic barriers. They also sought to determine the smallest and thinnest water-resistant patterns possible on hemp paper and examined several liquids' wicking speed and fluid distance.
Finally, they put hemp-based µPADs to the test by using them to test the potassium levels of artificial urine. An almost ironic final test, considering fake urine is often used among cannabis users to pass drug tests.
The team determined that, for certain applications, hemp is a viable alternative for microfluidics. For example, it was comparable to Whatman samples for low-viscosity fluids (like urine). They also concluded no measurable differences between wicking distances among all samples tested.
To counter the slow wicking speed of hemp-based µPADs on very viscous liquids, the researchers suggest increasing the pore density of the hemp paper (for example, using origami, adhesives, or high-resolution patterning).
Does Hemp Have a Future in Microfluidics?
Given the results of this 2021 study, it seems highly plausible that hemp-based µPADs will eventually become commonplace in certain sectors. Wherever µPADs are employed for analytical testing, hemp fiber may very well begin to replace tree fiber devices.
However, the researchers behind this publication note many details still need investigation. Future research would need to examine machine-learning methods to quantify hemp-based tests more accurately, as well as to solve specific issues like the paper's slow-wicking speeds. Still, this study serves as a starting point for more experimentation into hemp-based microfluidics.