Piezo-Based Energy Harvesting May Repel Tooth Decay

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I’ve always been interested in small-scale energy harvesting projects. After all, it seems like the almost ideal “something for nearly nothing” arrangement. Get a suitable transducer, power-management IC (PMIC), an energy storage component (rechargeable battery or supercapacitor) and you’re all set when you need to power a remote node, an IoT device, or other low-power devices. Of course, there are also large-scale harvesting such as wind, solar, or geothermal power, but those projects are at a very different scale, while small-scale harvesting seems more personal and non-intrusive.

What’s a suitable power range to consider when harvesting using vibration, RF, solar/light, thermal, or other ambient sources? It’s always tricky to make generalizations, but a recent article in Sensor Technology, “Energy Harvesting Can Enable 1 Trillion Battery-Free Sensors in the IoT,” seemed to offer a good start via an interesting graphic, Figure 1.

Fig 1: This is one perspective of the energy harvesting sweet spot for IoT edge devices/battery life extension impact. (Image source: EnABLES, the European Infrastructure Powering the Internet of Things, via Tech Briefs)

The article also said “There is a sweet spot, from around one microwatt to a few hundred microwatts, where there is the ‘double impact’ of significantly less drain on the existing power source and increased viability for using ambient energies from reasonably sized harvesters. This can significantly increase battery life, in some cases even leading to complete power autonomy.” There’s one thing that we inherently assume when we talk about energy harvesting: that it always involves energy capture, conversion to electrical energy, storage, and final use as current flow and thus power. 

But that doesn’t have to be the case, as it is possible to have a small-scale wind unit directly power a mechanical linkage and then drive a small pump, for example, but that non-electronic approach is often a challenge. However, unconventional harvesting thinking can lead to some fascinating potential solutions to problems that are far removed from electronics. 

Consider a research effort at the University of Pennsylvania Dental School that uses discs embedded with nanoparticles of barium titanate (BTO) and the piezoelectric effect to generate charge and energy via chewing, but with a very unusual “load.” They created smart dental implants, Figure 2, and exposed them to Streptococcus mutans, a primary component of the bacterial biofilm responsible for tooth decay (commonly called dental plaque). They found that the discs spurred resistance to biofilm formation, and discs with higher concentrations of BTO were better at preventing biofilms from binding.

Fig 2: A smart dental implant could improve upon present-day devices by employing electric charges created by piezoelectric nanoparticles. (Image source: University of Pennsylvania)

Qualitatively, the material generated an enhanced negative charge on the surface that repelled the negatively charged cell walls of bacteria, Figure 3. They demonstrated potent antibiofilm properties against plaque while retaining their piezoelectric and mechanical behaviors. This antiadhesive effect led to an approximately 10-fold reduction in colony-forming units in an in vitro lab set-up. They also corroborated the reduced adhesion between BTO-nanocomposites and the direct cell-to-surface binding force data using atomic force microscopy (AFM).

Fig 3: The development of the piezoelectric charge-generating discs and their ability to place bacteria-shedding charges on the surface of a tooth presents the possibility of dental implants which inhibit plaque adhesion and subsequent decay. (Image source: University of Pennsylvania)

Details of this unconventional use of piezoelectric-based energy harvesting are in their formal paper published in ACS Publications with the somewhat obfuscating title “Bimodal Nanocomposite Platform with Antibiofilm and Self-Powering Functionalities for Biomedical Applications,” which surprisingly never uses the obvious terms “harvesting” or “piezoelectric.” There’s also supporting information that details how the BTO discs were fabricated, the underlying chemistry and surface-energy physics of the films, as well as additional results.

Have you assumed energy harvesting to be a good solution to your power project issue at first, but found it was not viable when all the real-world issues were listed or quantified? Have you seen any viable or interesting energy-harvesting situations that did not need to supply current or drive electronic circuitry?

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