A research team from the National University of Singapore (NUS) has used 3D printing to produce a novel film that can effectively evaporate sweat from human skin, designed for applications such as underarm pads, insoles, and shoe linings.
The researchers have also demonstrated how the moisture absorbed by the film can be harnessed to power wearable electronic devices such as watches and fitness trackers.
“Sweat is mostly composed of water. When water is evaporated from the skin surface, it lowers the skin temperature and we feel cooler,” explained research team leader Tan Swee Ching, of the NUS Department of Material Science and Engineering. “In our new invention, we created a novel film that is extremely effective in evaporating sweat from our skin and then absorbing the moisture from sweat.
“We also take this one step further – by converting the moisture from sweat into energy that could be used to power small wearable devices.”
3D printing the film
The researchers constructed the film from two hygroscopic chemicals, cobalt chloride and ethanolamine, which can attract and hold water molecules absorbed from their surrounding environment. According to the team, the moisture-absorbing 3D printed film can take in 15 times more moisture at a rate of up to six times faster than comparable conventional materials.
As moisture is absorbed, the film changes color from blue to purple, and then to pink, in order to give an indication of the amount of water absorption that has taken place. When exposed to sunlight, the film can rapidly release the absorbed water and regenerate itself in able to be reused more than a hundred times.
To demonstrate the applications of the film, the researchers integrated it into polytetrafluoroethylene (PTFE) membranes, which are commonly used in clothing, and created an underarm pad, shoe lining, and shoe insole.
“The prototype for the shoe insole was created using 3D printing,” said research team co-leader Professor Ding Jun, also of NUS. “The material used is a mixture of soft polymer and hard polymer, thus providing sufficient support and shock absorption.”
Ching added: “Using the underarm pad, shoe lining, and shoe insole embedded with the moisture-absorbing film, the moisture from sweat evaporation is rapidly taken in, preventing an accumulation of sweat and provides a dry and cool microclimate for personal comfort.”
Powering wearable electronics
Taking their development one step further, the researchers looked for a way to make full use of the sweat harnessed by the film. To do this, they designed and created a wearable energy harvesting device made up of eight electrochemical cells (ECs), within which they used the 3D printed film as an electrolyte.
Upon absorbing moisture, each EC could generate around 0.57 volts of electricity, and in total the device generated enough energy to power a light-emitting diode. According to the team, this proof-of-concept demonstration could pave the way for “significant economic potential” within the fields of functional clothing, footwear, and wearable electronics.
Further details of the study can be found in the paper titled, “Super-hygroscopic film for wearables with dual functions of expediting sweat evaporation and energy harvesting”, in the Nano Energy journal. The paper is co-authored by X. Zhang, J. Yang, R. Borayek, H. Qu, D. Nandakumar, Q. Zhang, J. Ding, and S. Tan.
3D printing wearable technology
3D printing has been involved in the design and creation of wearable technology devices and garments for some time now, and there have been a number of innovative developments in this area in past years, particularly in garments that are able to respond to their environments.
Back in 2015, 3D printing was employed in the creation of a helmet that changes shape in response to the wearer’s brainwaves, the aim of which was to explore the combination of multi-material printing and wearables that respond to neural commands from the brain. A few months later, a couple of MIT designers used FDM to create a 3D printed shoe that changes shape in response to stimuli from the wearer.
More recently, 3D printing has been explored as a potential method to produce electronic wearables, such as watches and fitness trackers.
In 2017, a research group from the National Institute for Interdisciplinary Science and Technology (NIIST) investigated 3D printed flexible electronics for use in remote locations, with the goal of creating a wearable antenna that can be embedded in the jackets of soldiers to communicate health data. Meanwhile, researchers of the Cleaner Electronics Research Group at Brunel University London 3D printed a low cost, flexible battery that could be worked into a wearable silicone band, deemed the first time a flexible supercapacitor had been wholly produced by 3D printing.
Elsewhere, researchers from Sungkyunkwan University have 3D printed wearable medical biosensors for personalized health monitoring, while the Centre for Additive Manufacturing at the University of Nottingham recently made a breakthrough in the study of 3D printing electronics with graphene.
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Featured image shows the shoe insole prototype coated with the novel thin film turns from blue to pink as it absorbs moisture. Image via NUS.
