From: fbignone@alchemy.chem.utoronto.ca (Franco Bignone)
Subject: floating cells
Keywords: cell culture
Organization: University of Toronto Chemistry Department
Date: Wed, 11 Nov 1992 18:44:39 GMT

I have a funny question related to cell growth in colture. Until now I was
unable to find any previous record of this phaenomenon so I am
posting it here in order to see if anybody is able to come up with 
something similar. I would like to say that the phaenomenon is appening.
Particulars about it may be wrong, but is not a problem of knowing if it
is true or not, is there. But at the same time is so funny, and that I
know has never been described before. So I am looking for: the same kind of
observations, or some references. Persons interested can mail me back
directly.

- The phaenomenon is simple: I saw cells in colture that growth, and spread,
  at the interface of liquid and air. SIC!
  
People with experience in cell colture have hard time believing this. But
I was able to repeat the observation several times.

Math and Meth:

- The clone is a clone of partially transformed cells, derived form NIH3T3.
  As a comment .... in general transformed cells are able to survive in very
  bad conditions ... but still.
- The cells start to be visible under the inverted microscope as groups of
  2-6 cells, just after trypsin treatment. Usual trypsin, and usual medium
  -- Difco, DMEM --. The cells look like a small clone after a selection
  procedure .. BUT they are at the top, at the bottom the rest of the cells
  growth happily in a layer, if you go out of focus these cells appear rarely
  at the floating surface. They cannot be cells fixed by some procedure 
  -- formaldehyde or so -- the flasks are plastic. Moreover the clones seems
  to growth to the level of 20-30 cells. At this point the inner part of the 
  round clone become more thick, and eventually the clone stop floating and
  settle at the bottom of the flask. This is more a guess than a demonstration.
  What you see in practice are the clones growing then getting thicker, then 
  after a day no more clones around, and at the bottom you see bumps in the
  monolayer that resemble the groups of cells floating the day before.
- I have tryed several manipulations to improve the results -- more clones
  and bigger, but with scarce success. Only silicon oil sonicated with
  the media and mixed to it was able to increase the phaenomenon, at that
  point the cells doing it are a lot. They also growth directly on the
  silicon.
- The only studies that I was able to find on similar topics are related
  to the study of materials used for dentists or similar, prostesis in
  general. 
  
My guess is that these cells are able to use the surface tension to stay
afloat, what bring them there is very difficult to say. But they seems quite
fine. They seems immersed in water except for the connections to the surface
layer that keep them from going to the bottom of the flask.
I was also thinking that -- being that these cells growth also on the
lateral walls of the flask -- a possibility could be for them to start using
the liquid surface once they run out of plastic space, but this dosen't
seems to be the case, overcowded coltures don't show this phaenomenon more
than normal coltures with less cells.

Anyhow I will wait for replies.

Franco 

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Dr. Franco A. Bignone				    
Dept. of Chemistry, University of Toronto,	   
St. George St., Toronto, Canada M5S1A1.
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