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I'm a physician doing benchtop experimentation. Background: Tissue is known to coagulate at 43 degrees celsius (CEM 43 thermal tissue damage index).

I'm seeking to find/build a temperature controlled heating device to induce various thermal injuries in explanted (ex vivo) tissue. I'll be measuring those changes at the surface level of the tissue using a fiberoptic temperature probe.

Specifically, I need the device to accurately generate heat (40-80 deg Celsius w/ increments of 1 degree celsius). Any ideas? I've explored modifying a soldering iron and heating up metal in water bath to specific temps.

Thanks in advance!

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  • \$\begingroup\$ Have you checked hot plates? Maybe that inside a box do reduce drafts? You could then use an array of sensors to determine temperature across many points inside of it and adjust insulation/airflow inside it to a uniformity you think is enough. p.s.: or a sous-vide device. \$\endgroup\$ – Wesley Lee Nov 30 '16 at 2:02
  • \$\begingroup\$ How fast do you expect to move from one temperature to another? How much accuracy do you actually require? And do you know the difference between accuracy and precision? And do you need repeatability between instruments (if your system breaks down and you buy another one, will you have a way of renormalizing the data from earlier datasets to newly generated ones, for example?) Can you accept overshoot? If so, how much? \$\endgroup\$ – jonk Nov 30 '16 at 2:27
  • \$\begingroup\$ Do you happen to have a denaturing gradient electrophoresis temperature control unit to hand? \$\endgroup\$ – Andrew Morton Nov 30 '16 at 20:36
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The temperature control is a well-trodden path. You need to have a sensor of adequate accuracy and a heater of appropriate power level and a temperature controller. I would suggest purchasing a Pt100 sensor (100 ohm platinum RTD), a cartridge heater and a commercial PID temperature controller.

Have a block of aluminum fabricated with cross holes for the sensor and the heater. Bury the sensor inside the block so the tip is many hole diameters in. You could use copper too, but the machinist will be less enthusiastic about the deep holes in copper. The idea is to make the plate thick enough and thermally conductive enough that it is effectively isothermal to the degree that you care.

The heater does not have to be very powerful for this application, maybe 100W.

For the best accuracy you will want to keep air currents off the surface of the plate, so a cover would be a good idea. Insulate the bottom of the plate and use stand-offs so that even if the heater stays on at 100% it cannot cause a fire.

This should cost maybe a few hundred dollars, more or less, depending on quality of control, sensor accuracy etc. and you should be able to hold the temperature steady to within a couple tenths of a Kelvin.

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  • \$\begingroup\$ Given the medical application and what I know about temperature experimentation on cells (one of my instruments was used to heat brain cells while also observing their temp, in a closed loop control system), I'd be worried about overshoot and just how quickly this experimentation needs to move from one step change to the next one. \$\endgroup\$ – jonk Nov 30 '16 at 2:17
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    \$\begingroup\$ @jonk That's why I would recommend a commercial temperature controller which will use a modified algorithm to minimize over/under shoot and will be self-tuning for the PID parameters. \$\endgroup\$ – Spehro Pefhany Nov 30 '16 at 2:21
  • \$\begingroup\$ The "accuracy" requirement may also suggest a commercial approach, selecting products that can trace themselves back to NIST standards in some way and can be re-calibrated periodically, as well. An ice bath is cheap, but only goes so far. And more than one point of calibration may be needed, anyway. \$\endgroup\$ – jonk Nov 30 '16 at 2:24
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Might I suggest that you could buy a 3D printer heated bed (usually 200 mm - 300 mm square and put a Borosilicate glass cover on it. These items are readily available online and might allow you to build a relatively cheap unit. The heated beds using a PCB layout actually have quite even heating over the surface, and are designed to reach 100 degC or more.
You can find lot's of information on the groups for RepRap: http://reprap.org/wiki/Heated_bed

Here's the RepRap wiki on temperature PIDs for both the extruders and hotbeds: http://reprap.org/wiki/PID_Tuning
I doubt that these are really accurate enough for you application, but if you search for "PID controller brewing" on Amazon or Ebay you will find a slew of controllers which might meet your needs at reasonable low cost and requiring minimal interfacing.

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  • \$\begingroup\$ 3D printer beds are heated, but are not temperature controlled -- there is no requirement that the bed hit, or stay at, any specific temperature. \$\endgroup\$ – user39382 Nov 30 '16 at 6:23
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    \$\begingroup\$ 3D printer beds ARE usually (in fact I've never seen one that is not) temperature controlled since they are driven with a PWM power source. The temperature controls available may not be what the OP needs to set 40 degC, but no matter the solution he uses he will need a PID controller for it. I simply suggested an easy way (without extensive engineering) to create a platform. \$\endgroup\$ – Jack Creasey Nov 30 '16 at 17:32
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    \$\begingroup\$ @JackCreasey is right.. the one I have can be programmed to various temperatures with 1°C resolution. Accuracy and stability are probably no great shakes. \$\endgroup\$ – Spehro Pefhany Nov 30 '16 at 21:21

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