Until recently, mainstream skin treatment patches have been passive, in other words, without an electric power source. They function by protecting wounds or delivering medication through diffusion. Recently, a lot of research has taken place around the world towards active skin treatment products. Many of the new skin treatment products or prototypes use a button battery to increase functionality. However, the usage of the button battery also carries certain challenges: 1) the devices are usually not flexible for curved skin or 2) they may contain an extra electronic box, which takes away user-friendliness and comfort.

At the same time, the demand for easily portable and effective health patches is fast growing amidst a growing, health-conscious population and increasing subhealth problems & chronic diseases. IDTechEx market research has predicted that the market value of active skin patches will exceed 300 M USD in a few years powered by a thin film battery. ResearchAndMarkets.com also predicts a size of USD 1.2 billion global market of anti-biofilm wound dressing (patches) by 2028. Despite so, making devices easier to use is a big challenge. The paper battery technology brings a solution. 

The paper battery technology brings one innovative product: a skin patch based on Enfucell printed paper battery technology. The paper battery is a thin and flexible power source with a voltage of 1.5 V or 3.0 V. It is based on Zn-MnO2 chemistry and is manufactured by printing and laminating it in a specific shape. In general, the paper battery is intended to power a variety of printed electronic applications such as smart sensor cards, cosmetics masks, intelligent packaging etc. Due to the flexible nature of paper batteries, it has become possible to create and bring many new valuable products to market by enabling many flexible and hybrid electronics applications. Flexibility is also the key feature to address the curvature of human skin for a skin patch. 

Enfucell has developed many devices and application products by using the paper battery as a power source. These applications belong mainly to two categories: 

  • Devices that have a measurement function and wireless communication (Fig. 1.a-b). 

One case is where it is used to power the RFID sensor label such as RFID temperature tags. The tag can be used as a temperature monitor of a goods during logistics & its shelf life. Food, bioproducts and medical products are immediate application targets with huge potential given increasing health safety regulatory requirement and accelerated growth in international e-commerce market.

  • Microcurrent patches that consist of electrodes and a power source (Fig. 1. c-e). These applications will be described in more detail below, especially in Fig. 1. d-e.  

Typically, a discrete battery is utilized in an electronic device. This traditional approach may appear bulky. The idea behind the paper battery research was to create a power source that well suits the needs of the ever-growing world of thin and flexible devices. 

A thin paper battery was developed for this purpose using screen-printing. The technique allows a high degree of customization according to the voltage, capacity and power requirements. Its layered flexible structure consists of sealing materials, a separator layer, current collectors, and active anode and cathode layers (Fig. 2.).  

Devices with such a battery can be manufactured in a roll-to-roll (R2R) printing process, using plastic foils, functional inks, and adhesives. In many cases, these printed electronics products can be used for the same purposes as the bulky traditional electronics mentioned earlier, but in a more delicate way. 

Ideally, the battery is printed directly on the same substrate together with the electronic circuitry. Such an integrated structure was found to improve production yield and product reliability. Furthermore, the screen-printing technique enables efficient production of such integrated devices in modern R2R production lines. It also provides for a unique shape, more suitable and conformable on human skin. 

The paper battery has its roots in traditional dry cells (Leclanché cells) but it is not limited to this chemistry. One benefit of this chemistry is that it is considered safe in air transport. Another important factor is that such devices are very safe during use due to its lower voltage (such as 1.5 or 3.0 V) and a very small corresponding current in less than one milli-ampere. It will not generate any risks of explosion and burning even when there is a short circuit due that the paper battery has a much “large” internal resistance compared to the button battery. The last advantage is that paper battery is considered as environment-friendly product, which is very important in the modern society, especially as it is used as disposable device.   

The skin care patch was one of the first application areas for the paper battery. Such a patch includes electrodes, medical grade adhesive, hydrogel, and an embedded paper battery. 

There are two types of the skin care patches based on the paper battery technology. One is used together with a lotion or medicament. The other works without additional active substances. 

In the first case a substance like therapeutic lotion or medicament is applied onto the electrodes. When the patch is attached to the skin, a closed circuit is formed, and a small electric current drives the active ingredients through the skin. This method is called iontophoresis and has been used for a long time in cosmetics industry. The level of the micro-ampere current applied on each person mainly depends on the skin property of the person and the treatment time. This method is more intensive, deeper, and the effect is more enduring than treatment with the said substance alone. A corresponding patch was developed for that purpose (Fig. 2.d). 

In the second case, no additional substance is used. A microcurrent is generated as soon as the patch is applied onto the skin. Microcurrent treatment is known to be effective in relieving neuropathic pain & improving blood circulation and waste’s metabolic rate. It enhances naturally occuring bioelectrical processes by stimulating the nervous system and muscles. 

A microcurrent electrotherapy patch consists of a printed paper battery, two or more electrodes, and a skin-friendly adhesive layer (Fig. 2.e). The size and shape of the product is tailored in line with the intended position in the body. The patch is flexible, effective, hygienic, and safe to use. It is disposable and has minimal impact on the environment.  It is a natural, drug-free, and non-invasive method for persons who aim to reduce the use of medication. 

One target group of this new patch is adults suffering from regular headache. Apart from headaches, the electrotherapy principle can be applied to other pain cases, e.g. on a knee or in the back, or even pain in the breast triggered by mammary gland proliferation. 

The patch has been tested on human beings and the preliminary results show an efficiency above 80% in treatment of migraine or other types of headaches, toothaches and arthritis. Recently, one skin patch prototype was preliminarily approved by a Shanghai Hospital. They found it helpful to reduce pain generated by mammary nodules. Further research will follow in order to get a medical device certification for it. 

Moreover, there is evidence that microcurrent promotes wound healing. It reduces infection by inhibiting bacteria growth and killing the bacteria in and around wounds. The microcurrent patches can offer an efficient treatment for ulcers, a typical symptom of diabetes. A battery-assisted patch offers a cordless and convenient option for the end-users. 

The iontophoresis and electrotherapy principles are not new, Paper battery simply amplifies their impact and brings cost competitiveness through mass-printing.

To sum up, active skin patch is a good example of many of what the paper battery technology could enable in various industries, amid growing scenarios brought by portable low-power IoT applications in daily life. 

References

  1. Iontophoresis https://en.wikipedia.org/wiki/Iontophoresis
  2. Electrotherapy https://en.wikipedia.org/wiki/Electrotherapy
  3. IdTechEx https://www.idtechex.com/