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Claire
Sorry this is long but you asked! Much of it is clip and paste but
all worth reading.
I am replying on both points of inquiry. You used the term "stage
heater".
We do not believe in heating the stage when what you really want is
the specimen heated.
Heating of the stage induces "Z" axis drift so we prefer to avoid it!
However you were referring to the Warner DH-35 system that provides
heat from a metal, peripheral source.
There are distinct differences between the two systems.
Briefly,
The warner system uses inexpensive dishes and provides heat that is
radiated peripherally from a heated plate.
The Bioptechs system uses a more costly but technically advanced dish
integrated into a dual priority mode (dynamic temperature and
Imaging) controller.
The Bioptechs system has the capability to transfer heat only to the
cells by means of an electrically conductive, optically transparent
coating on the bottom surface of the dish that transfers heat
directly to the cells by conductivity. These dishes are more
expensive but offer far more utilitarian capability. In a multi user
facility the Bioptechs Delta T system offers the ability to work with
nearly all live specimen types form adherent cells to tissue and
artificial membranes. This is due in part to the variety of
accessories engineered to work with the base system. This includes
condensate free lids with and without perfusion, gas control, second
optical surface conditioning for uniformity of transmitted contrast
images, dead volume control, perfusion, and tissue support
Follow this link http://www.bioptechs.com/thermalimages.html for
thermal images of the Bioptechs Delta T and typical "heated plate"
open dish warmers.
You will see the significant differences in operation. For more
detailed info on our systems cruise through our website.
Although the Bioptechs Delta T system is superior to peripheral
heating, Bioptechs recognizes there are applications where the less
expensive peripheral heat source is appropriate. Therefore, Bioptechs
is happy to take this opportunity to announce a new product that
accommodates standard plastic ware and provides peripheral thermal
support without "Z" axis drift. It is called the DC Stable Z and
priced roughly 1/2 that of existing stage heaters that use generic
dishes. Availability will be announced shortly.
Objective heating:
I have studied this extensively. I am glad to share this with you.
It does not matter what method of heat transfer you use on the
specimen itself. You could use a peripheral heat transfer system
such as the Warner system or, a Bioptechs Delta T,
in either case the instant you have fluid contact between the
coverslip and the objective at room temperature, your cells will
experience a 5 – 7 degree drop.
Here is an example of what happens when a room temperature objective
comes in contact with a 37° C coverslip.
The green dot in the middle of the dish is liquid crystal. It is
green at 37°C, yellow at 36°C, Orange at 35°C and black at 34°C.
http://www.bioptechs.com/movies/product/Obj%20heat%20Sink5.mov
The purpose of an objective heater is not to heat the cells but to
prevent heat that the cells already have from escaping.
Bioptechs developed and patented the first commercial objective
heater at a time other companies would not have anything to do with
objective heating.
Now there are many companies that have decided to jump on the
bandwagon and produce objective heaters.
Here is the straight info on objective heating.
Warming of an objective is not a simple matter of just throwing heat
at it, as some of the copycat companies have done.
A few points to consider:
Heat must be efficiently transferred to the core of the objective.
If the heat is not efficiently transferred, the excess heat will
first radiate out, then, convect upwards. This excess heat can
“cook”, or at least compromise, your cells depending on the
inefficiency of the heat transfer.
All objectives have different thermal profiles.
The thermal profile depends on the relationship between the following
factors:
Cross-sectional distribution of the metal and glass components
The amount of glass and airspace in the objective
The amount of metal to glass surface contact there is in each element
The construction of the objective ( having physical access to an
efficient heat transfer surface)
The proportion of heat that is lost to the nosepiece relative to
heat retained in the retracting barrel of the lens
Given these factors it is clear that some objectives just do not
respond well to direct heating.
The good news is that most objectives can be controlled easily if you
do it right!
When heating an objective heat is distributed in the following manner
1. Radial; the ability for heat to be transferred through the
objective by a contact with an external heat source such as a (heater
band)
2. Longitudinal downward; the progress of heat over time down from
the location of the source of heat to the nosepiece.
3. Longitudinal upward; the propagation of heat to the specimen end
of the objective. This is, of course, what really counts!
Note, there is always an offset to the regulated temperature and the
actual temperature at the specimen plane.
The differences in thermal profiles are apparent through these three
principal vectors. See illustrations http://www.bioptechs.com/
thermalimages.html
You will have to scroll to the bottom of the page to see a fully
equilibrated objective with coverslip in contact with an oiled
objective.
If you were to see this in time lapse you would notice that in the
beginning of the heating process heat absorbed by the objective
travels down toward the nosepiece then it begins migrating and
equilibrating to the top.
In addition to these thermal transfer factors, it should be
appreciated that there are limits as to how much heat is safe to
apply. If the heat is efficiently applied, it takes no more than
about 5 watts of heat to raise the objective temperature from ambient
to 37C in 5 to 10 minutes without damage. Then it takes about 1.3
watts to maintain it, but with constant corrections for changes in
ambient conditions, compensation for heat lost to the nosepiece, and
entropy. The Bioptechs system works within these limits and has
additional safety circuitry to protect the objective if an out of
range temperature is detected.
I wish to caution you about some of the objective heating devices out
there.
Some systems use heat regulation that is based on the temperature of
the heating ring, not the temp of the objective. What good that is I
don't know.
There is one where "The conducting sleeve warms the surrounding air
which in turn gently warms the objective". Ok, so I am supposed to
generate enough heat in the air around a 100 - 200 gm piece of brass
screwed into a nosepiece (read as heat-sink) to warm the objective to
37°C and expect that the excess heat is not going to convect upwards
and "cook" my specimen!
There are also wraparound heating blankets; these things are highly
inefficient at heat transfer to the objective but very efficient at
generating heat that is radiated away from the heater-band.
You might get a laugh out of this one.
They recommend placing the feedback thermistor between the heat
source and the objective so that the temperature regulation is as
invalid as possible. It gets worse! They suggest keeping the
temperature under 150°C. Just wait, it gets worse!!
They also recommend attaching the heater-band by blowing a heat gun
at the objective to tighten a piece of heat shrink tubing!!!
Not to mention the fact that their web site photo shows an objective
with their heater band on the outer sleeve of the objective rather
than the inner metal of the objective where it has a chance of doing
something beneficial. It is no wonder that they have a heater-band
capable of 150°C. That might be what it takes to drive the heat in!
If you would like to try our systems, I would be happy to make them
available to you on a one-week loan.
Dan
On May 25, 2006, at 11:40 AM, Claire Brown wrote:
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I’m looking into temperature control systems for a number of
microscopes and I was looking for some feedback. I have worked with
the stage heaters from Harvard Apparatus/Warner Instruments (DH-35
system) and had very good luck. I was wondering about other options
or companies though. I also have worked with the Bioptics objective
heaters in combination with the stage heater with good luck as well.
I guess before I make a purchase I would like to know of other
alternatives for these things. Also what is the general consensus on
objective heaters for 60-100X? I have always heard you really need
them to avoid the objective from becoming a heat sink, but now I have
seen many people working with just the stage heaters. Any thoughts or
opinions on this?
Also I’m glad my Hg Bulb question generated so much discussion. My
question was answered and I learn a lot more as well.
Sincerely,
Claire
------------------------------------------------------------------------
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Claire M. Brown, PhD
Life Sciences Complex Imaging Facility Director
McGill University
Departments of Biochemistry and Physiology
3655 Promenade Sir William Osler
Montreal, Quebec, H3G 1Y6
Rm 1014
514-398-4400 ext 00795 (Phone)
514-398-7452 (FAX)
[log in to unmask]
Dan Focht
Bioptechs Inc.
V (724)282-7145
F (724)282-0745
www.bioptechs.com
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