Trying to heat a wire to around 94F for a few seconds using Pi3 and Nichrome
You must define Power and load resistance for a given surface area.


TBD:  Pd [mW], Area[mm2]
unknowns : Rjc, Rca  for thermal resistance of junction, j of heat source, case,c or the human interfaces and ambient, a,  temperatures.


Summary Proposal


ARM Cortex GPIO ports use ~25Ω drivers for RdsOn using datasheet \$R=\frac{V_{OL}}{I_{OL}}\$
Using 1/8W carbon film , CF18, resistors , I calculated thermal resistance as 0.68 °C/mW 


this is the case temperature rise above ambient
thus for 10°C rise , only Pd = 15mW is required
NiChr wire would be useful to trace pattern from track 
but must be pulsed current from a MOSFET  !!





How to generate 15mW power in a resistor , I leave up to you.


But as an initial test, I would 74ALVCxx gates @3.3V into 700Ω using CF18


Proof:  \$ V^2/W = R=  3.3^2/15mW = 726Ω \$ then subtract 25Ω driver and choose 700 Ω 
then record time to rise 10'C
to speed up time, use 25Ω load which causes Voh=Vcc/2 and pulse at 14% duty cycle for same Pd in resistor
then compare response times.



Record measurements faithfully in logbook.
    1: https://i.stack.imgur.com/26J0a.png