POWERING THE BODY

Why bodies are a tough place

small · safe · soft

Devices on or in the body must be tiny, safe, and often flexible. Body fluids are salty water, so electrolytes must be compatible, and any leak or toxic material is unacceptable. At the millimeter scale, a battery stores very little.

Size, safety, and softness all come first.

WEARABLES

Power that moves with you

Smart textiles Woven and fiber supercapacitors from Part 4 power sensors in clothing

Skin patches Thin, stretchable films that follow the skin's motion

Fitness trackers Bursts for radios and displays between slow recharges

Wearable harvesters Motion, heat, or light harvesters paired with a small supercapacitor

Flexibility and safe electrolytes matter as much as capacity.

IMPLANTS

Inside the body: the constraints

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Safe materials

Biocompatible, non-toxic materials, with nothing that can leak into tissue

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Neutral electrolyte

Saline-like or gel electrolytes, not strong acids or bases

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Long life

Replacing an implant means surgery, so long cycle life is valuable

The durability that suits grids suits implants too.

BODY-FRIENDLY ELECTROLYTES

Working in physiological fluid

Saline and PBS About 0.15 M salt water: safe, but only moderately conductive

Voltage window Aqueous limits of roughly 1 V apply, as in Part 5

Inert carbons Glassy carbon and similar carbons resist corrosion and biofouling in saline

Sterilization Materials must survive it, and the seal must stay intact

Testing Biocompatibility and leakage checks come before any approval

Physiological fluids trade voltage for safety.

HOW THEY RECHARGE

Pairing with a power source

Wireless power Inductive coupling charges a small buffer through the skin

Motion and heat Harvesters turn body movement or body heat into a trickle

Biofuel cells Enzymes and fuels like glucose make small currents

Pulsed loads Stimulation or sensing bursts draw on the supercapacitor's fast output

The supercapacitor turns weak, steady input into strong, brief output.

UNIT 41 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered flexible, body-safe power, and how wearables and implants recharge.