Table 1 Summary of the materials and processes typically used for the fabrication of flexible and stretchable physical sensing devices
From: Emerging flexible and wearable physical sensing platforms for healthcare and biomedical applications
A | Flexible templates | Young’s modulus (MPa) | Tensile strain (%) | Poisson’s ratio | Processing temperatures (oC) | Ref. |
|---|---|---|---|---|---|---|
Polymeric Substrates | Polyethylene terephthalate (PET) | 2,000–4,100 | <5 | 0.3–0.45 | 70 | |
|  | Polycarbonate (PC) | 2,600–3,000 | <1 | 0.37 | 150 | |
|  | Polyurethane (PU) | 10–50 | >100 | 0.48–0.49999 | 80 | |
|  | Polyethylene naphthalate (PEN) | 5,000–5,500 | <3 | 0.3–0.37 | 120 | |
|  | Polyimide (PI) | 2,500–10,000 | <5 | 0.34–0.48 | 270 | |
Silicone Elastomers | Polydimethylsiloxane (PDMS) | ~ 0.36–0.87 | >200 | 0.49999 | 70–80 | |
|  | EcoFlex | ~ 0.02–0.25 | >300 | 0.49999 | 25 | |
| Â | DragonSkin | 1.11 | >300 | 0.49999 | 25 | |
| Â | Silbione | ~ 0.005 | >250 | 0.49999 | 25 | |
B | Active sensing elements | Structure/form | Â | Size | Sheet resistance | Ref. |
Conductive materials | Metallic nanomaterials (e.g., Ag, Au, Cu, Al, Mn, Zn) | Nanoparticles, nanowires, nanorods |  | 2–400 nm (in diameter) and 200–1000 nm (in length) | 0.015–20  Ω sq−1 | |
|  | Carbon-based nanomaterials (e.g., CNTs, graphene) | Nanoparticles, nanowires, nanotubes, nanofibers |  | 10–2000 nm (in diameter) and 500–5000 nm (in length) | 30–5×106  Ω sq−1 | |
|  | Ionic or metallic liquids (e.g., eGaIn, Galinstan) | Liquid |  | Not applicable | 2.63×10−9–0.025 Ω cm−1 | |
C | Fabrication techniques | Resolution (μm) | Throughput (m min−1) | Limitations |  | Ref. |
Additive processes | Gravure printing | 50–500 | 8–100 | Limited resolution due to alignment |  | |
|  | Screen printing | 30–700 | 0.6–100 | Small selection of inks due to high viscosity requirements Requires hard masks to be replaced regularly |  | |
|  | Inkjet printing | 15–100 | 0.02–5 | Not suitable for roll-to-roll production Coffee-ring effect Limited printing area |  |