Harvesting electricity from human hair.

Electrical conductivity of human hair is a debatable issue among hair experts and scientists. There are unsubstantiated claims that hair conducts electricity. However, hair experts provided ample evidence that hair is an insulator. Although wet hair exhibited drastic reduction in resistivity; scientists regarded hair as a proton semiconductor at the best. Here, we demonstrate that hair filaments generate electricity on absorbing water vapor between 50 degrees and 80 degrees C. This electricity can operate low power electronic systems. Essentially, we are exposing the hydrated hair polymer to a high temperature (50 degrees-80 degrees C). It has long been speculated that when certain biopolymers are simultaneously hydrated and exposed to high temperature, they exhibit significant proton hopping at a specific temperature regime. This happens due to rapid movement of water molecules on the polymer surface. This lead us to speculate that the observed flow of current is partly ionic and partly due to "proton hopping" in the hydrated nano spaces of hair filament. Such proton hopping is exceptionally high when the hydrated hair polymer is exposed to a temperature between 50 degrees and 80 degrees C. Differential scanning calorimetry data further corroborated the results and indicated that indeed at this temperature range, there is an enormous movement of water molecules on the hair polymer surface. This enormously rapid movement of water molecules lead to the "making and breaking" of innumerable hydrogen bonds and thus resulting in hopping of the protons. What is challenging is "how to tap these hopping protons to obtain useful electricity?" We achieved this by placing a bundle of hair between two different electrodes having different electro negativities, and exposing it to water vapor (water + heat). The two different electrodes offered directionality to the hopping protons and the existing ions and thus resulting in the generation of useful current. Further, by continuously hydrating the polymer with water vapor, we prolonged the process. If this interesting aspect of polymer is exploited further and fine tuned, then it will open new avenues for development of sophisticated polymer-based systems, which could be used to harvest electricity from waste heat.

The role of photo-electric properties of silk cocoon membrane in pupal metamorphosis: A natural solar cell.

Silkworm metamorphosis is governed by the intrinsic and extrinsic factors. One key intrinsic factor is the temporal electrical firing of the neuro-secretory cells of the dormant pupae residing inside the silk cocoon membrane (SCM). Extrinsic factors are environmental like temperature, humidity and light. The firing pattern of the cells is a function of the environmental factors that eventually controls the pupal development. How does the nervous organization of the dormant pupae sense the environment even while enclosed inside the cocoon shell? We propose that the SCM does this by capturing the incident light and converting it to electricity in addition to translating the variation in temperature and humidity as an electrical signal. The light to electricity conversion is more pronounced with ultraviolet (UV) frequency. We discovered that a UV sensitive fluorescent quercetin derivative that is present on the SCM and pupal body surface is responsible for generating the observed photo current. Based on these results, we propose an equivalent circuit model of the SCM where an overall electrical output transfers the weather information to pupae, directing its growth. We further discuss the implication of this electrical energy conversion and its utility for consumable electricity.

Electricity from the silk cocoon membrane.

Silk cocoon membrane (SCM) is an insect engineered structure. We studied the electrical properties of mulberry (Bombyx mori) and non-mulberry (Tussar, Antheraea mylitta) SCM. When dry, SCM behaves like an insulator. On absorbing moisture, it generates electrical current, which is modulated by temperature. The current flowing across the SCM is possibly ionic and protonic in nature. We exploited the electrical properties of SCM to develop simple energy harvesting devices, which could operate low power electronic systems. Based on our findings, we propose that the temperature and humidity dependent electrical properties of the SCM could find applications in battery technology, bio-sensor, humidity sensor, steam engines and waste heat management.