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

51– 53

 

Polycarbonate (PC)

2,600–3,000

<1

0.37

150

53

 

Polyurethane (PU)

10–50

>100

0.48–0.49999

80

54, 55

 

Polyethylene naphthalate (PEN)

5,000–5,500

<3

0.3–0.37

120

52, 53, 87

 

Polyimide (PI)

2,500–10,000

<5

0.34–0.48

270

53, 86

Silicone Elastomers

Polydimethylsiloxane (PDMS)

~ 0.36–0.87

>200

0.49999

70–80

53

 

EcoFlex

~ 0.02–0.25

>300

0.49999

25

53

 

DragonSkin

1.11

>300

0.49999

25

56

 

Silbione

~ 0.005

>250

0.49999

25

56– 58

B

Active sensing elements

Structure/form

 

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

53

 

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

53, 62– 65

 

Ionic or metallic liquids (e.g., eGaIn, Galinstan)

Liquid

 

Not applicable

2.63×10−9–0.025 Ω cm−1

84, 85

C

Fabrication techniques

Resolution (μm)

Throughput (m min−1)

Limitations

 

Ref.

Additive processes

Gravure printing

50–500

8–100

Limited resolution due to alignment

 

53

 

Screen printing

30–700

0.6–100

Small selection of inks due to high viscosity requirements

Requires hard masks to be replaced regularly

 

53

 

Inkjet printing

15–100

0.02–5

Not suitable for roll-to-roll production Coffee-ring effect Limited printing area

 

53