What do microfiber wipes, van der Waals forces, cell phones and geckos have in common?

While checking into the best ways to clean our cellphones last weekend, we stumbled across a couple of articles on that most adorable of creatures, the gecko. Despite oftentimes heroic and diligent attempts at staying on topic, we disappeared rather rapidly down a rabbit hole of intriguing herpetological pablum, learning that those creatures, so beloved of a certain insurance commercial, are part of the infraorder Gekkota (suborder Scleroglossa) which also includes the perhaps less cute snake-lizard. And geckos are interesting little beasties – some being parthenogenic (females can reproduce without the assistance of a male) and all being polyphyodonts, regrowing their teeth every three to four months. But what really makes them fascinating – and the reason we fell down this particular research rabbit hole – is the geckos’ ability to stick themselves – Mission Impossible-style – to any surface, climbing walls and walking on ceilings without the aid of tiny ropes, slings, or harnesses.

And where does their adhesion come from and how does this relate to cellphones? We’re glad you asked: microhairs.

The foot of a gecko is covered with microscopic hairs called spatulae of around 200 nanometers in width. To give some sense of scale, an average human hair – that ubiquitous measure of all things small – measures a comparatively whopping 100,000 nanometers across.(1) These spatulae form into groups of around 1000 hairs, known as setae, that span approximately 1/10^th the diameter of a stand of hair, and these setae – when arranged in rows – are just about visible to the eye. Each square millimeter of a gecko’s footpad contains approximately 14,000 setae.

So, much like Tolkien’s hobbits, geckos have hairy feet – what of it? Well, where these microhairs become interesting is in the way that they actually form molecular bonds with the surface upon which the gecko finds itself. The hairs are so tiny that they can wedge themselves between the atoms of a surface, providing unparalleled adhesion even when upside down.

Interesting stuff. But again we can almost hear you wondering how on earth this relates to contamination control and cellphones. Bear with us as we explain…

Cellphones. Those indispensible devices that at once keep us connected and also dislocated from our world. Those tantalizing little packages through which we can access the entire sum of human knowledge and wisdom, but which we use to constantly check in with what our friends are doing on Facebook. What did we do before we had them? We’re increasingly obsessed with them, rarely separated from them, and many of us will readily admit that they accompany us even in our most private moments, like in the bathroom. And here’s Uncomfortable Truth #1: Given that we are rarely, if ever, without the things, it’s unsurprising that they get a little…shall we say gross? Most of us will admit that our iPhone or Android (or whichever tech flavor we favor) could use a Close Encounter of the Clorox Kind but few of us actually understand the magnitude of the problem. So let’s put it out there. As Joanna Stern says in an article recently published in the Wall Street Journal, ‘How to Safely Clean Your Dirty, Disgusting Smartphone’:

“That smartphone in your hand? Oh, it just has 10x more germs per square inch than a public toilet seat. OK, the numbers are a bit skewed—toilets tend to be cleaner than you think because they get scrubbed down so often.”(2)

In Stern’s report, an analysis by Charles Gerba, a microbiologist at the University of Arizona, found there to be more than 25,000 germs per square inch of cellphone surface – a computer keyboard hosts only 3000, by comparison. And cleaning those off requires more than a simple rub of the screen with a handkerchief or on the leg of your pants.

But cellphones are expensive and sensitive devices given the complex electronics involved, so what’s the best way to clean them? Stern offers a mixed bag of options, including making your own cleaning solution of 80% water and 20% isopropyl alcohol – IPA – (not terrible advice but we’ll discuss IPA’s effects on oleophobic coatings later) and using a Q-tip (according to other sources, absolutely not recommended). The IPA recipe can be adjusted in favor of a lesser percentage of alcohol (where 80%-20% may be overkill), and to learn more about the optimal concentrations of IPA to water please download our Technical Brief, ‘Pre-Wetted Wipers Optimized for Application-Specific Cleaning.’ In her analysis, Stern does sound a note of caution to those sensitive to the ‘overwhelming smell’ of the volatile organic compounds, admitting that some users may find the fragrance obnoxious. So, given that abrasive, bleach-based, or ammonia-based detergents are off the table as potential cleaners, where does a VOC-sensitive germ-conscious cell user turn?

Remember those gecko feet? Right – let’s take a look at a modest product that makes novel use of interesting physics: the microfiber cloth.

In addition to wedging themselves at an atomic level into the contact surface, geckos’ microscopic hairs leverage Van der Waals forces, named for the Nobel Prize-winning Dutch physicist, Johannes Diderick van der Waals.(3) These physical forces are created through adsorption – the process whereby lots of very weak electrostatic forces create an attraction that holds two surfaces together. And the millions of tiny threads in microfiber cloths – like gecko feet – serve to create an attraction to dust and dirt particles, sucking them up on contact and lodging them deep within the cloth. No chemical cleaners needed.

So assuming that we’re removing germs, dust, and particulate matter from a surface – let’s say, a cellphone – to what extent do microfiber cloths perform better? In short, devoid of harsh chemicals but perhaps spritzed with a little plain water, the materials use a mechanical cleaning process that relies upon the millions of tiny threads to sweep dirt up via the adhesive power of van der Waals forces. Once trapped by the threads, dirt remains captured within the cloth until washing allows the fibers to uncurl and release their payload.(5) The size of the microfiber cloth threads determines its overall performance but given that the majority of cloths have threads in the 3 to 5 microns diameter range, this makes them both antibacterial and antimicrobial. Given that viruses tend to be smaller (around 0.5 microns), microfiber cloths cannot, however, claim the antiviral moniker.

So where could these cloths be used to greatest effect? Within a domestic setting, consumers could certainly benefit from their ease of use and efficiency in cleaning. But when it comes to more sensitive settings, there are potentially both advantages and disadvantages. Let’s take hospital settings as an example. Back in our February article ‘Is IoT Tech the New Foot Soldier in Hand Hygiene Compliance?’we looked at the increasing use of ultra-violet light robots over chemically-based liquid cleaners to sterilize hospital rooms. Although we focused on the robot’s use in sterilizing hardware normally found in such areas – the bed, nightstand, door knobs, remote controls, IV stands, and such – there is something else that commonly finds its way into a hospital room: the cellphone. Whether it belongs to the patient or their visitor, the phone is an important vector of germ transmission – perhaps especially so when it belongs to a guest whose journey to a beloved’s bedside may have involved the use of a public restroom along the way. Indeed, this is a very real problem as an article by Kelly M. Pyrek in Infection Control Today suggests:

“Mobile devices are ubiquitous in society and their infiltration of the healthcare environment poses new challenges for infection prevention and control. Numerous studies have documented that mobile handheld devices are frequently contaminated with healthcare-associated pathogens, but they are seldom cleaned and disinfected due to individuals being unsure of what kind of products and methods to use to decontaminate their electronics.” (6)

So neither patients nor visitors recognize this vector of transmission and, even if they did, they don’t know how to prevent it. As Pyrek continues:

“Educating patients about infection control and stressing individual responsibility of infection control is an important aspect of controlling nosocomial infections. Contaminated mobile phones may act as fomites because most people carry mobile phones along with them to places […] where microorganisms thrive. This study indicates that unreported antibiotic resistant bacterial contaminants of mobile phones of patients may be a matter of great concern. Hence, it is recommended that all patients admitted in hospitals be educated about guidelines of using mobile phones, regular disinfection of their mobile phones, hand hygiene and be advised not to share mobile phones with other people so that role of contaminated mobile phones in the spread of nosocomial infections can be prevented to some extent.”(7)

But if the patient is sensitive to VOCs or industrial cleaners, could microfiber cloths be enough to sanitize these devices? The answer may be yes.

Unlike chemical cleaners, microfiber cloths also have the advantage of being portable, allowing the user to stuff one into a purse or pocket for ease and frequency of use. And if they’re available, they’re more likely to be used. In addition, they offer multiple layers of protection – safeguarding the user and protecting the delicate oleophobic coating already applied to the device screen. The oleophobic coating? Meaning ‘oil resistant’, all capacitive touchscreen devices (cellphones, tablets, touch-sensitive screens) are coated with a specialized polymer that repels oil from greasy fingertips and such.(8) The exact chemical makeup of the polymer changes by manufacturer although – given that most use a specially-toughened product called Gorilla Glass for their screens – the quality of the oleophobic coating is generally normalized. Designed to last for the approximate life-cycle of the device – an all-too-brief two years – the coating is sensitive to breakdown by isopropyl alcohol or harsh cleaners, and the general advice is to avoid them.

Not all microfiber wipes are created equal. If you’d like additional information on the construction of a microfiber wiper, please refer to our Learning Center article ‘I Can See Clearly Now’ (Parts 1 and 2). In these pieces, it’s interesting to note that the same wedge-shaped microdenier fibers used in the construction of eyeglass wipers can also be used for cleanroom microfiber wipers. The major difference is that they are much cleaner. And what about performance? Let’s take a look at some visuals. Below is a series of images that demonstrate the actions of two different wipers used to remove a cellphone fingerprint.

From the second image, it’s quite clear that the greasy print is not entirely removed by using a regular dry knitted cloth. In fact, it looks like all of the grease is still there, but that it’s been redistributed from the lovely fingerprint swirls to a dull smudge. But look at the third image (far right) and you’ll see the results when the same mechanical action is performed using microfiber. Much cleaner, much more effective, no chemicals involved and, best of all perhaps, no increase in effort.

Whichever solution we elect to adopt however, it’s critical that we do actually address the issue. More than ever, we face a crisis of bacterial resistance and good hygiene habits are at the forefront of efforts to defeat the germs. In case you are unconvinced as to the extent of the danger, Caroline Kee, a writer with Buzzfeed, performed an interesting experiment. Swabbing her iPhone, Kee cultured the sample on agar in a petri dish and released the video of her homegrown microbes here. Yikes. It just may be time to reach for that microfiber cloth – we’re sure there’s one around here somewhere…

Are you seeking to reduce your chemical footprint? Would you consider using microfiber? Or are you committed to chemical agents in the on-going battle of the bugs? We’d love to read your comments!

References:

1. http://www.livescience.com/475-nature-velcro-lets-geckos-walk-ceilings.html
2. https://www.wsj.com/articles/how-to-safely-clean-your-dirty-disgusting-smartphone-1487345378
3. http://www.nobelprize.org/nobel_prizes/physics/laureates/1910/waals-bio.html
4. https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm205999.htm
5. http://www.explainthatstuff.com/microfibercloths.html
6. http://www.infectioncontroltoday.com/articles/2017/02/mobile-technology-disinfection-contaminated-devices-pose-threat-to-patients.aspx
7. ibid
8. http://www.phonearena.com/news/Oleophobic-coating–what-it-is-how-to-clean-your-phone-what-to-do-if-the-coating-wears-off_id65974