Apparatus for forming micropipette of controlled configuration by moving the point of heat application

Abstract: The micropipette puller of this invention includes a pair of gripping jaws (12, 12) that pull a length of glass tubing (T) in opposite directions. The source of heat is a laser and a beam (32) is directed into a beam directing means (34), such as a lens or mirror, to refract or reflect the beam against the glass tubing between the gripping jaws. The mirror or lens may be oscillated at various rates and through selected angles in each direction to move the reflected beam a selected amount and at selected rates along a greater length of the glass tubing.

Description: This invention relates to micropipette pullers of the type shown in my earlier U.S. Patent No. 4,600,424 granted July 15, 1986. Micropipette pullers generally employ a filament comprising a heated metal band or wire to heat the glass tubing to its melting point. The shape of the micropipette is dependent largely upon the shape of the filament and various types of filaments are available for the production of different shapes and lengths of micropipettes. For example, a wide filament is generally used to form a long pipette. The shape of the micropipette is also dependent upon the diameter of the annular filament that encircles the glass tubing. A tight fit of the filament around the tubing will result in a sharp heat gradient between the heated and unheated portions of the glass tubing. This will result in an initial fast taper in the glass as it is pulled out and then, as the glass reduces in diameter and contracts away from the filament, the taper becomes more gradual. If a large diameter annular filament is used, the heat gradient will be more gradual and the result is a micropipette with a more uniform taper from shoulder to tip. The better micropipette pullers are now all computerized so that the variables in the pulling process, such as filament temperature, length of the pull, the strength of the pull and the rate at which the glass is cooled may be programmed into the puller. The only important variable which is not easily changed is the type of heating filament which is being used. Efforts have been made to move the filament during the pulling cycle in order to heat a greater area, but the movement of the filament was slow and very difficult to control in a repeatable manner. It is an object of this invention to provide a micropipette puller with means for moving the point at which heat is applied to the glass tubing. It is a further object of this invention to provide a micropipette puller with means for applying heat to the glass tubing in a controlled and repeatable pattern. It is a further object of this invention to provide a micropipette puller capable of pulling a micropipette of controlled configuration from materials of high melting point, such as quartz. The present invention, in its broadest aspect, is defined in claim 1, where the heating of the glass tubing can be carefully controlled by use of a laser with a beam directing means being capable of directing the beam against the tubing between spaced points at which tension is applied, with the beam directing means being pivotable to cause the directed laser beam to move along the length of the tubing so as to provide carefully controlled heating thereto. In using the apparatus as later described in detail, a tubing of glass, quartz or the like is pulled from both ends, initially by a weight carried on the ends of cables and then by a solenoid. The laser directs a laser beam into a mirror, a lens or other means to direct the laser beam against the glass tubing. The mirror or other beam directing means is oscillated or otherwise moved at a controlled rate and through a predetermined degree of movement to cause the reflected or refracted beam to move along a selected length of the tubing to control the length of the heated tubing. The invention will become further apparent from the description to follow, particularly when read in conjunction with the accompanying drawing, the single Figure of which is a schematic diagram of the apparatus of this invention for pulling a micropipette. Referring now to the drawing with greater particularity, the micropipette puller 10 of this invention includes a pair of gripping jaws 12 on the adjacent ends of puller bars 14. The jaws 12 grip a tubing T of glass, quartz or the like to be pulled into the micropipette as heat is applied to the tubing to melt a portion thereof between the jaws. The puller bars 14 roll along upper and lower roller bearings 16 and 18 and are pulled by cables 20 which extend over upper cable pulleys 22 and then over closely spaced central lower pulleys 24 to suspend a solenoid plunger 28, which is capable of applying a light pull by application of its own weight, and a stronger pull by actuation of the solenoid 26. The source of heat in the micropipette puller 10 is a laser device 30 that projects a generally horizontal beam 32 into a movable mirror 34, positioned to reflect the beam downward at 34 against the glass tubing T. While the laser beam 32 is shown as being reflected by a mirror 34, it is to be understood that other means may be employed to direct the beam. For example, the beam 32 could be directed against the tubing T by refraction through a lens or prism or by fiber optics. In any event, the beam directing means 34 may be oscillated by any suitable means so that the reflected or refracted beam is moved back and forth longitudinally of the tubing T, as indicated by the arrows A-A to heat a length of the tubing T. For example, the mirror or lense 34 may be oscillated by mounting it on the output shaft 38 of a stepping motor 40. It is also contemplated that the beam may be moved by moving the laser device 30 itself. The stepping motor may be controlled by a computer 42 to rotate incrementally in either direction and at various rates to achieve different heating patterns applied to the glass tubing, thereby to control the configuration of the taper and the length of the tip. Each signal from the computer 42 may produce a rotational step from the motor 40 of one degree or less so that the increments of movement of the reflected beam 36 may be closely controlled. For example, the computer can control the stepping motor 40 to heat the tubing T uniformally, or it may vary the movement to concentrate heat at the center for more rapid melting at the mid-point. The computer 42 and stepping motor 40 can control the size of the angle through which the mirror or prism 34 oscillates and it can control the rate of oscillation. Moreover, the movement can be programmed for repeated production. The laser device 30 is not limited by its own melting point as in the case of a filament heater and it can melt materials of high melting point, such as quartz, which resonates at the wave length of a laser beam.

Claims: A micropipette puller comprising: means (12) for gripping a length of glass tubing (T) at spaced points along the length thereof; means (14,20,28,26) for moving said gripping means (12) away from each other so as to apply a pulling force to said length of glass tubing (T); a laser (30) for directing a laser beam (32); a beam directing means (34) disposed to direct said laser beam (32) against said tubing (T) between said spaced points; and means (40,42) for pivoting said beam directing means (34) to cause the directed laser beam (32) to move along the length of said tubing (T). A micropipette puller as claimed in claim 1, including means (42) for controlling the rate at which said beam directing means (34) is pivoted. A micropipette puller as claimed in claim 1 or 2, including means (42) for controlling the angle through which said beam directing means (34) is pivoted. A micropipette puller as claimed in claim 1, 2 or 3, wherein said beam directing means (34) is mounted on the output shaft (38) of an incremental rotary drive (40). A micropipette puller as claimed in claim 1, 2 or 3, wherein said beam directing means (34) is mounted on the output shaft (38) of a bidirectional, incremental drive (40) so that it may be pivoted in both directions and through a selected angle in each direction. A micropipette puller as claimed in any preceding claim, wherein said beam directing means is a mirror (34) to reflect said laser beam (32) against said tubing. A micropipette puller as claimed in any one of claims 1 to 5, wherein said beam directing means is a lens to refract said beam against said tubing (T).

Inventors: FLAMING DALE G, FLAMING, DALE G
Applicants: FLAMING DALE G, FLAMING, DALE G
Application year: 1989
Main classification: C03B23
IPC codes: C03B23, B23K26