Smart biomaterial could differentiate motions as artificial skin

Next time you watch a superhero movie where new skin grows by itself or a device is implanted within the body, take note because scientists are inching closer day by day.

Yes, you read that right!

In real life, ‘Artificial skin’ research is driven by clinical applications for wounding, burning and skin cancer. Although a vast amount of investigation is already devoted to development, most of the tested substances are artificial non-biodegradable polymers. Moreover, these already developed materials usually lack high enough air/water permeability which is necessary to mimic biological skin. To bridge this gap, scientists from National University of Singapore and Xiamen University in China developed artificial skin using silk fibroin (SF), which is a naturally-occurring protein.

Development of these SF-based materials for artificial skin is still at the early phase due to low mechanical stability, elasticity and significantly low response to the external environment.

Here, researchers tried to address the issues by using electrostatic spinning followed by treating with glycerol and silver (Ag) to fabricate the SF-based materials (Figure 1).

Figure 1: Processing of silkworm cocoons to form SF film followed by incorporating silver (Ag) nanofibers within. Adapted from ref. 1 with permission from John Wiley and Sons, copyright 2019.
Figure 2: Conductivity of the SF films was maintained after bending and twisting (top) and also resistance was unaffected after stretching (bottom). Adapted from ref. 1 with permission from John Wiley and Sons, copyright 2019.

Firstly, silk cocoons were cut into small pieces and dissolved in aqueous solution. They were then fabricated on a glass slide to obtain transparent films that were treated with glycerol to increased robustness. To further enhance mechanical and optoelectronic properties, Ag nanofibers were incorporated within these materials. They were able to fabricate these AgNFs/SF conductive materials in large area. These conductive films were also proved to be strong and resistant to bending, twisting and stretching (Figure 2).

These materials were then attached to elbow and larynx to monitor movements at different scales. Small scale movements such as coughing, drinking, pronouncing or swallowing could be tracked when these materials are inserted on the neck. The ultrahigh sensitivity of the sensors is evident from the sharp change in the measured capacitance with the neck movements (Figure 3). During eating, different processes such as chewing, swallowing and stopping can be monitored very effectively which implies the higher sensitivity of the material (Figure 3d). Similarly, large scale movements were also monitored when these sensors were laminated on the elbow for gesture control.

Figure 3: Movement of the muscles could be effectively captured using the sensors. Adapted from ref. 1 with permission from John Wiley and Sons, copyright 2019.

Biocompatibility and biodegradability of the materials were tested by fabricating them on the skin for different days. These nanodevices were intact even after 6 days, and no allergic reaction was visible on the skin (Figure 4). Most importantly, they could be disintegrated using non-hazardous reagents, which is often not the case for similar types of materials. By immersing the devices within a biodegradable enzyme – named papain – for 24 hours, they could be fragmented and ruptured.

Figure 4: Biocompatibility of the materials was examined showing no allergic reaction even after 6 days. Adapted from ref. 1 with permission from John Wiley and Sons, copyright 2019.

There are other potential applications for these materials; for example, monitoring the coughing of a patient or language teaching, to monitor the movement of the throat when pronouncing a new word.

As fascinating as it sounds, artificial skin-based research is still at its infancy and lots of work needs to be done before it can fully function as its biological original. However, these small baby steps will hopefully one day cumulate, and we will be able to acknowledge the development of artificial body parts.

  1. C. Hou, Z. Xu, W. Qiu, R. Wu, Y. Wang, Q. Xu, X. Y. Liu and W. Guo, Small 2019, 15, 1805084.

(cover image by Kevin Craft, Stanford School of Engineering).


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