Table 1 The forms, electrical conductivity, advantages and disadvantages of different materials

Platinum-gold alloy [46]

Discs

Gold 4.52 × 10⁷ S/m

Platinum 9.6 × 10⁶ S/m

High mechanical strength, long-term stability, good biocompatibility and good corrosion resistance

Expensive, cell death caused by ion release

Magnesium (Mg) alloys [48]

Discs

≈2 × 10⁷ S/m

High strength, fracture resistance, good electrical conductivity

Poor biocompatibility; cell death caused by high ion release, and change of local pH

Polypyrrole [57]

Coating

10²~ 10³ S/cm

Good compatibility and support cell adhesion and growth

Rigid, insoluble and poorly processable

Polyaniline [58]

Film

5~ 10 S/cm

Good environmental stability, low cost, good biocompatibility

Poor mechanical properties and complicated manufacturing methods

Graphene [55]

Coating

10⁶ ~ 10⁸ S/m

Good mechanical properties, easy bio-functionalization and drug loading

Moderate toxicity

Carbon nanotubes [52, 53]

Doping with other materials

1.8 × 10⁷ S/m

High mechanical resilience, good support for active materials, high chemical stability, elasticity

Poor biocompatibility, poor dispersion, insoluble and toxic to the cells