# Breakthrough Assembly of a Silk Fibroin Composite for Application in Resistive Pressure Sensing

## TL;DR

This paper presents a sustainable, biocompatible composite made from silk fibroin and conductive polymers for use in pressure sensors.

## Contribution

A novel method for creating highly porous, electrically conductive 3D structures using natural and synthetic polymers for resistive pressure sensing.

## Key findings

- The composite with 1% v/v PVA content showed the best balance of elasticity, resilience, and shape recovery.
- The sensor exhibited sensitivity comparable to other hybrid silk fibroin composites.
- The material demonstrated swift response times and good current recovery during repeated compression cycles in wet conditions.

## Abstract

Driven by the dictates of sustainability, we have designed,
realized,
and optimized a method for easy development of biocompatible, highly
porous, and electrically conductive 3D structures from the combination
of natural and synthetic polymers for pressure sensing applications.
In particular, a foaming method followed by a fast freezing step,
both performed on blends made of silk fibroin (SF) aqueous solution,
PEDOT:PSS electrically conductive polymer, and water-soluble PVA,
has allowed the fabrication of conductive electrosponges, intrinsically
integrating the structural and electrical counterparts of a resistive
pressure sensor in a single “green” material. An exhaustive
analysis of their structural (with FTIR), morphological (with μ-CT),
and mechanical (by means of stress–strain measurements) properties
has been performed, of which the latter was coupled with the electrical
characterization of the electrosponges while undergoing compression–decompression
cycles. PVA addition has been recognized as crucial for conferring
to the material the right compromise among elasticity, recovery attitude,
and resilience/durability to the proposed constructs. The fabricated
electrosponges show a promising combination of mechanical and electrical
properties, with the former induced by both the highly porous structure
of the foamed/frozen compound and the elasticity enhancement induced
by PVA, whose concentration influences the electrosponge resilience
and recovery attitude. Based on the results from the material characterization,
the composite with 1% v/v PVA content has shown the best compromise
among elasticity, resilience, and shape recovery. The related sensor
shows a sensitivity comparable to other hybrid SF composites (10–3 kPa/mA vs 10–3–10–2 kPa/decade), an applied stress magnitude-dependent swiftness (from
hundreds of milliseconds to few seconds), and an exhaustive current
recovery on numerous repeated compression–decompression cycles
in wet conditions.