Science

My co-worker has a formlabs printer, it seems pretty decent... The Z
direction sounds good, but I imagine it could be obviated by the use
of a spin-coater. They say their minimum feature size if 300microns...
I was thinking about this recently actually and ran into the
laserShark galvanometer controller. I think the main thing that would
need to change for great microfluidics with this type of setup is
really just the per-bit voltage-interval... i.e. if the DAC on the
galvanometer controller is 16-bits spanning the form1 build dimensions
of "125 × 125 × 165 mm"... then the range of millimeters spanned needs
decreased. If it's a linear decrease, then if I wanted a max
microfluidic X/Y dimension of 30mm, that's 125/30==4.166 then
300/4.166==72 microns resolution. Maybe their DAC is not enough bits,
or maybe this technique is not optimal, I don't know. It could simply
be that the long path that the beam passes takes, leaving the laser,
bouncing off the galvos, is just too much from a beam divergence
standpoint. To get a small spot size with such focal distances, I
think the laser would need a pretty big beam expander before lensing
onto the first galvo.

On Sat, Feb 28, 2015 at 3:52 PM, Otto Heringer <ottowheringer@gmail.com> wrote:
> I always wanted to print a mold for PDMS microfluidic chips using a "form 1"
> 3D printer (that one who got funded on kickstarter). They say that it have
> 10 microns of resolution on Z axis.
>
> When I was about to try it on a local FAB Lab, the printer got broke! If it
> was worked out, I would suggest to consider a 3D printer for the molds.
>
> I think its about time for people go for digital fabrication methods on
> microfluidics.
>
> Em 27/02/2015 21:17, <scocioba@gmail.com> escreveu:
>
>> This is true, only issue there was when using a syringe to pull from chip
>> to chip, the line would sputter and induce air pockets on top of very swift
>> changes in fluid flow once it gets past the bottleneck that is the chip.
>> There is a lot of resistance since the channel features are so small that
>> manual pull is to quick. Need a syringe pump in reverse that pulls slowly.
>>
>> Like filling a syringe quickly with liquid through a very small needle, it
>> bucks back until the liquid meets the top of the plunger (vacuum until
>> pressure equalizes) so either way fine, non-manual control would be ideal.
>> Backpressure is too high for standard cheap-o eBay peristaltic pumps in
>> either direction. Basically its analogous to electronic theory...small
>> channel, high resistance. Syringe acts as a voltage source trying to pull
>> more than the channel can deliver so its either slow or the channels (or
>> chip) fails structurally.
>>
>> For the few moments when the pdms is perfectly bonded via coronal arch
>> discharge and everything is aligned properly, I did get some plant
>> protoplasts stuck in a T junction for a while while flowing media through.
>> Its possible, just really really finicky.
>>
>> On my laundry list of experiments to run, I'd like to do some data
>> gathering on the characteristics of shrinky dink plastic sheets,
>> temperature, shrink rate (~63%), etc to see if its a viable material for
>> making multiple fairly-identical chips. Basically a datasheet characterizing
>> the material within the scope of microfluidics. May prove useful to people
>> trying to start working with microfluidics.
>>
>> Sebastian S. Cocioba
>> CEO & Founder
>> New York Botanics, LLC
>> Plant Biotech R&D
>> ________________________________
>> From: John Griessen
>> Sent: ‎2/‎27/‎2015 6:46 PM
>> To: diybio@googlegroups.com
>> Subject: Re: [DIYbio] Re: At home fabrication of micron scale
>> microfluidics
>>
>> On 02/27/2015 05:29 PM, Simon Quellen Field wrote:
>> > The alternative that suggests itself is to pull the liquid from one
>> > block to another using a relative vacuum. Now the liquid wants
>> > to go only where you want it to go.
>>
>> because vacuum makes contact seals seal harder, and pressure makes them
>> leak.
>>
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I always wanted to print a mold for PDMS microfluidic chips using a "form 1" 3D printer (that one who got funded on kickstarter). They say that it have 10 microns of resolution on Z axis.

When I was about to try it on a local FAB Lab, the printer got broke! If it was worked out, I would suggest to consider a 3D printer for the molds.

I think its about time for people go for digital fabrication methods on microfluidics.

The two terms xs and x are temperature based terms relating temperature to how much the air can absorb.... Something like that.

On 02/28/2015 03:57 AM, Nathan McCorkle wrote:
> perhaps hone the
>>calculation to get rid of my 'mollier diagram; guesstimation issues?

I did not see temperature in the model, so it seems odd to miss that...

or is it there as a worst case constant somewhere at about 40 deg C?

As evaporation happens from a capillary, the exposed water surface will shrink back into
the capillary and cause evap slow down more because it is in a well where there will be no breeze.

That part seems to become a diffusion calculation that will vary as depth of the "well".

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There was also this answer, which gives a formula if you know the
energy of your heat source:
http://physics.stackexchange.com/questions/91810/how-do-i-predict-volume-loss-due-to-evaporation-when-boiling-water

On Sat, Feb 28, 2015 at 1:51 AM, Nathan McCorkle <nmz787@gmail.com> wrote:
> On Fri, Feb 27, 2015 at 10:08 PM, Mac Cowell <mac@diybio.org> wrote:
>> The capillary design is not as complicated as you make it sound, Cathal. I
>> think evaporation is marginal in open 10 uL tubes, so they don't need to be
>> closed,
>
>
> hmm, this comment really interested me, since I've previously done
> some experiments where I watched evaporation over a few days using a
> nice mettler lab scale with a serial port on it for data collection.
>
> I tried finding out how to calculate for evaporation losses, and found
> an empirical equation for things like swimming pools.
>
> TLDR; the calculation I did (which could be wrong) shows about 2 to 15
> nanoliters PER HOUR of evaporation for a 100 micron diameter capillary
> with no air movement from 25 to ~65 C (but if you're really
> interested, please try to verify this number on your own... and let us
> know). However, if you increase the diameter from 100 microns to 1mm,
> the evaporation seems to be more like 200nL/H to 1.5uL/H (1500nL/H).
>
>
> This is where I got the equation:
> http://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html
>
> which says:
>
> gs = Θ A (xs - x) / 3600
>
> or
>
> gh = Θ A (xs - x)
>
> where
>
> gs = amount of evaporated water per second (kg/s)
>
> gh = amount of evaporated water per hour (kg/h)
>
> Θ = (25 + 19 v) = evaporation coefficient (kg/m2h)
>
> v = velocity of air above the water surface (m/s)
>
> A = water surface area (m2)
>
> xs = humidity ratio in saturated air at the same temperature as the
> water surface (kg/kg) (kg H2O in kg Dry Air)
>
> x = humidity ratio in the air (kg/kg) (kg H2O in kg Dry Air)
>
>
> What I ended up plugging in for numbers, to get my nanoliter values:
> http://www.wolframalpha.com/input/?i=%2825*%28+pi*%2850+%2F1000000%29%5E2%29*%280.02-0.0098%29%29+kilograms+water+to+microliters
>
>
> used this page to try getting some values to plug in for [xs]
> http://www.engineeringtoolbox.com/humidity-ratio-air-d_686.html
>
> Used this hard-to-figure-out chart to try some other values for a
> higher temperature (variable [x]):
> http://www.engineeringtoolbox.com/psychrometric-chart-mollier-d_27.html
>
>
>
>
>
> Can someone verify or disprove the numbers, or perhaps hone the
> calculation to get rid of my 'mollier diagram; guesstimation issues?



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On Fri, Feb 27, 2015 at 10:08 PM, Mac Cowell <mac@diybio.org> wrote:
> The capillary design is not as complicated as you make it sound, Cathal. I
> think evaporation is marginal in open 10 uL tubes, so they don't need to be
> closed,


hmm, this comment really interested me, since I've previously done
some experiments where I watched evaporation over a few days using a
nice mettler lab scale with a serial port on it for data collection.

I tried finding out how to calculate for evaporation losses, and found
an empirical equation for things like swimming pools.

TLDR; the calculation I did (which could be wrong) shows about 2 to 15
nanoliters PER HOUR of evaporation for a 100 micron diameter capillary
with no air movement from 25 to ~65 C (but if you're really
interested, please try to verify this number on your own... and let us
know). However, if you increase the diameter from 100 microns to 1mm,
the evaporation seems to be more like 200nL/H to 1.5uL/H (1500nL/H).


This is where I got the equation:
http://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html

which says:

gs = Θ A (xs - x) / 3600

or

gh = Θ A (xs - x)

where

gs = amount of evaporated water per second (kg/s)

gh = amount of evaporated water per hour (kg/h)

Θ = (25 + 19 v) = evaporation coefficient (kg/m2h)

v = velocity of air above the water surface (m/s)

A = water surface area (m2)

xs = humidity ratio in saturated air at the same temperature as the
water surface (kg/kg) (kg H2O in kg Dry Air)

x = humidity ratio in the air (kg/kg) (kg H2O in kg Dry Air)


What I ended up plugging in for numbers, to get my nanoliter values:
http://www.wolframalpha.com/input/?i=%2825*%28+pi*%2850+%2F1000000%29%5E2%29*%280.02-0.0098%29%29+kilograms+water+to+microliters


used this page to try getting some values to plug in for [xs]
http://www.engineeringtoolbox.com/humidity-ratio-air-d_686.html

Used this hard-to-figure-out chart to try some other values for a
higher temperature (variable [x]):
http://www.engineeringtoolbox.com/psychrometric-chart-mollier-d_27.html





Can someone verify or disprove the numbers, or perhaps hone the
calculation to get rid of my 'mollier diagram; guesstimation issues?

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On 02/27/2015 05:29 PM, Simon Quellen Field wrote:
> The alternative that suggests itself is to pull the liquid from one block to another using a relative vacuum. Now the liquid wants
> to go only where you want it to go.

because vacuum makes contact seals seal harder, and pressure makes them leak.

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On Fri, Feb 27, 2015 at 8:59 AM, <scocioba@gmail.com> wrote:
> Would this beat shrinky dink microfluidics? I've managed to make features
> using shrink sheets printed using a standard toner printer and pdms at
> around 100-150um

That was my first thought.... the scale is quite large when you start
thinking of doing cellular operations that are anything more than an
incubation chamber.

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On 02/27/2015 05:33 AM, Cathal Garvey wrote:
> h, nice idea! I wonder if even plastic capillaries at that scale are conductive enough to work, I could see it being possible to
> make "pinch-off" capillaries that you fill (by capillary action? :)) and pinch, then lay on your micro-cycler
+1

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On 02/27/2015 02:35 AM, Mac Cowell wrote:
> But the thermocycler is so simple in this case. Peltier, sawtooth heat sink with 5-10 ridges, mosfet for switching power, embedded
> thermocouple, microcontroller, and 5-10 glass capillaries, one per sample

Would work fine with forced air heat and cool also. What is a good way to seal ends of capillaries so
they stay pure, yet are easy to unload? Maybe some high melting point wax, (above PCR temps)? Hot glue plastic?

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On 02/27/2015 02:29 AM, Mac Cowell wrote:
> It would be interesting to explore a hybrid design combining dynamic conductive heating in the tube block with constant radiative
> heating from a lamp or hot air flow positioned at just the right distance, instead of a heated lid in constant contact with the
> cap. Can the radiative heat source be set up to always add +20C to the exposed cap and 5-10 C to the reaction mixture?


Sure, and with a little fan to help cool. It will be tough to make them always add +20C passively, but it is
easy to use the micro and feedback loop to control it actively.

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