Method for depositing a flattened droplet on a surface and apparatus therefor, and a pump therefor

Abstract

A method and apparatus therefor for depositing a flattened droplet on a partially absorbent surface comprising the steps of providing a narrow bore transfer tube having a proximal end and a distal end and containing a microvolume of liquid, the proximal end connected to a pneumatic system adapted for issuing an outgoing flow of displacement gas into the tube and drawing an incoming flow of displacement gas therefrom; and issuing an outgoing flow of displacement gas for slowly discharging substantially the entire microvolume of liquid as a droplet on the surface and controllably blowing one or more bubbles into the droplet towards the end of its discharge for flattening the droplet on the surface. A pump ( 31 ) comprising a housing ( 33 ) having a bore ( 34 ) with an internal peripheral surface ( 36 ), and a stationary annular sealing member ( 48 ) integrally formed therewith at a first end ( 37 ) of a pair of opposite ends ( 37 and 38 ); a slide rod ( 39 ) disposed in the bore and having an external peripheral surface ( 41 ) and a displaceable annular sealing member ( 49 ) integrally formed therewith; the sealing members sealing the peripheral surfaces to define a vented displacement volume ( 51 ) therebetween whose volume is proportional to an annular cross section area between the peripheral surfaces and a distance between the sealing members; and the slide rod being slidably reciprocable between first and second positions respectively toward and away from the stationary sealing member whereupon the displaceable sealing member moves to reduce the volume to issue an outgoing flow of displacement gas from the displacement volume on a downstroke of the slide rod from its second position to its first position and the displaceable sealing member moves to increase the volume to draw an incoming flow of displacement gas into the displacement volume on an upstroke of the slide rod from its first position to its position.

1 . A method for depositing a flattened droplet on a partially absorbent surface comprising the steps of: 
 (a) providing a narrow bore transfer tube having a proximal end and a distal end and containing a microvolume of liquid, the proximal end connected to a pneumatic system adapted for issuing an outgoing flow of displacement gas into the tube and drawing an incoming flow of displacement gas therefrom; and    (b) issuing an outgoing flow of displacement gas for slowly discharging substantially the entire microvolume of liquid as a droplet on the surface and controllably blowing one or more bubbles into the droplet towards the end of its discharge for flattening the droplet on the surface.    
     
     
         2 . The method of  claim 1  wherein step (a) includes: 
 (a1) preventing capillary forces to draw liquid into the transfer tube upon the insertion of its distal end into a vessel containing liquid;  
 (a2) inserting the transfer tube's distal end into the vessel;  
 (a3) drawing an incoming flow of displacement gas from the transfer tube such that a microvolume of liquid is drawn thereinto; and  
 (a4) removing the transfer tube's distal end from the liquid.  
 
     
     
         3 . The method of  claim 2  wherein step (a1) includes issuing an outgoing flow of displacement gas into the transfer tube.  
     
     
         4 . The method of  claim 3  further comprising the step of: 
 (a5) drawing the microvolume of liquid into the transfer tube away from its distal end; and  
 (a6) neutralizing the inward displacement by a brief outgoing flow of displacement gas into the transfer tube.  
 
     
     
         5 . The method according to any one of claims  1 - 4  further comprising the step of: 
 (c) providing additional outflow of displacement gas while displacing the transfer tube away from the droplet so separate the droplet from its distal end.  
 
     
     
         6 . The method according to any one of claims  1 - 5  wherein the microvolume of liquid is a culture medium containing embryo(s) which are urged against the surface by the droplet's prevailing surface tension.  
     
     
         7 . Apparatus for depositing a flattened droplet on a partially absorbent surface, the apparatus for use with a narrow bore transfer tube having a proximal end and a distal end and a vessel of liquid, the apparatus comprising: 
 (a) a pneumatic system connected to the transfer tube's proximal end and adapted for issuing an outgoing flow of displacement gas into said transfer tube and drawing an incoming flow of displacement gas thereinto from said transfer tube; and    (b) a control mechanism for controlling said pneumatic system in different operational modes including: 
 an user controlled suction mode for drawing an incoming flow of displacement gas from said transfer tube whereby a microvolume of liquid is drawn thereinto prior to the removal of said distal end from the vessel; and  
 an user initiated automated delivery mode for issuing an outgoing flow of displacement gas into said transfer tube for slowly discharging substantially the entire microvolume of liquid as a droplet on the surface and controllably blowing one or more bubbles into the droplet towards the end of its discharge for flattening the droplet on the surface.  
   
     
     
         8 . Apparatus according to  claim 7  wherein said control mechanism includes an automatic pre-suction mode for issuing an outgoing flow of displacement gas.  
     
     
         9 . Apparatus according to  claim 7  or  8  wherein separate units house a suction control unit for controlling said user controlled suction mode and a transfer control unit for controlling said user initiated automatic delivery mode.  
     
     
         10 . A pump comprising a housing having a bore with an internal peripheral surface, and a stationary annular sealing member integrally formed therewith at a first end of a pair of opposite ends; a slide rod disposed in said bore and having an external peripheral surface and a displaceable annular sealing member integrally formed therewith; said sealing members sealing said peripheral surfaces to define a vented displacement volume therebetween whose volume is proportional to an annular cross section area between said peripheral surfaces and a distance between said sealing members; and said slide rod being slidably reciprocable between first and second positions respectively toward and away from said stationary sealing member whereupon said displaceable sealing member moves to reduce said volume to issue an outgoing flow of displacement gas from said displacement volume on a downstroke of said slide rod from said second position to said first position and said displaceable sealing member moves to increase said volume to draw an incoming flow of displacement gas into said displacement volume on an upstroke of said slide rod from said first position to said second position.  
     
     
         11 . The pump according to  claim 10  wherein both said bore and said slide rod are of right cylindrical shape and said cross section area is defined by π(a 2 -b 2 ) where a and b are the radii of said internal peripheral surface and said external peripheral surface, respectively.  
     
     
         12 . The pump according to either  claim 10  or  11  wherein said cross section area has an area of about 4-10 mm 2 .  
     
     
         13 . The pump according to any one of claims  10 - 12  wherein said displacement volume can be incrementally changed in the order of 0.1-0.4 μl.