PIPETTE WITH BELLOWS AND USE THEREOF

Abstract: There is disclosed a pipette (40, 40a) and a method of using the pipette in which an active element of the pressurizing means is a bellows (70, 70a) within a piston chamber (50, 50a), operated by a motor (54, 54a). To achieve the advantages of the invention, including ease in manufacturing and the ability of actuate a tip ejector (60), the bellows is mounted so that the outside surface (77, 77a) of the sidewall (74, 74a) of the bellows, together with the piston chamber, defines the air volume operative on a fluid passageway leading to an end (46, 46a) which supports a disposable tip (T).

Description: The invention relates to devices for aspirating and dispensing liquid, such as pipettes. Pipettes and automatic aspirators are constructed preferably with disposable tips or containers, means for mounting the tips or containers, and means for pressurizing or evacuating the contents of the tips or containers. The pressurizing means then comprise a piston chamber, a piston, and means for reciprocating the piston. Most commonly, the piston uses sealing rings that rub against the inside wall of the piston chamber or outside wall of the piston. Because such rings are subject to wear, bellows have been suggested as an alternative since they have a much longer wear capability. Such bellows can be prestressed and simply compressed manually, as shown in U.S. Patent No. 4,296,071, or they can be driven by a motor as shown in U.S. Patent No. 4,041,995, Figure 6 and 8. In either case, some manufacturing difficulties are encountered. In the case of a simple bellows that is of the type shown in U.S. Patent No. 4,041,995, it is difficult to attach the base portion of the bellows to the bottom of the piston chamber, simply because of inaccessibility. A solution would be to assemble the chamber housing in several parts, but it is preferred, e.g., for convenience, to have such a housing be one integral part. One approach to this problem has been to use a flat elastomeric membrane in place of a bellows, for example, as shown in U.S. Pat. No. 4,444,062, since such a membrane can be secured to the top of the piston chamber. As the piston is advanced, Figure 4 of U.S. Patent No. 4,444,062, the membrane (68) is stretched into a cylindrical shape. However, such a design encounters the following disadvantages: the elastomeric membrane tends to crack under the high stress that is delivered, and is therefore short-lived. Furthermore, it provides a non-linear displacement since the cross-sectional shape changes as the piston is advanced. A bellows does not suffer these disadvantages. Thus, such a flat membrane is not a suitable substitute for a bellows. Yet another problem exists with such bellows construction. Many pipettes have a disposable tip ejector comprising a rod extending from the tip mounting surface, back into the end of the piston chamber nearest to the disposable tip. Such rods need to be pushed at the appropriate moment, such as by extending the piston until it contacts the rod. However, when a bellows is disposed in between the piston and the end of the chamber at which such rod is located, excessive power is required to activate the rod. That is, not only must the piston push against the resistance of the rod and tip, but also it must collapse the bellows. For the above reasons, bellows have had limited utility in use as replacement of piston seals, in spite of their advantage in wearing. Therefore, prior to this invention there has been a problem of how to provide a more readily manufacturable bellows design as a piston ring replacement, without interfering with ready operation of tip ejection. A key to the solution to the above problem is to use a bellows that is inverted from the bellows position heretofore used for pressurizing the pipette. More specifically, in accord with one aspect of the invention the above problem is addressed by a pipette comprising a fluid passageway, and means for creating an operative vacuum or a pressure in the passageway different from atmospheric pressure, the means including a piston chamber having an end fluidly connected to said fluid passageway, a piston and a bellows mounted for movement within the chamber, and actuating means for advancing or retracting the piston; characterized in that the bellows comprises an open base portion and a closed top portion, and a preformed generally cylindrical sidewall extending between the base portion and the top portion, the bellows sidewall having an inside surface and an outside surface, the base portion being sealed to the chamber, the top portion being secured to the piston, so that the sidewall outside surface and the piston chamber define the air volume operative on the fluid passageway. In accord with another aspect of the invention, the above problem is addressed by a method of aspirating and dispensing liquid into and from a pipette as described above, the method comprising the steps of: a) inserting the pipette into a source of the liquid; b) creating a partial vacuum within the fluid passageway by collapsing the bellows with the piston, whereby liquid is drawn into the tip; c) moving the pipette relative to the source of liquid and to an object onto which the liquid is to be dispensed; and d) creating a partial pressure within the fluid passageway sufficient to expel at least a portion of the liquid, by moving the piston in a direction that allows the bellows to expand from its collapsed state created in step b). Thus, it is an advantageous feature of the invention that a pipette is provided with a pressurizing means that has the infinite wear characteristics of a bellows, but without the manufacturing problems heretofore required with a bellows. It is another advantageous feature of the invention that a pipette is provided with such a bellows in the pressurizing means, such that the resistance of the bellows does not interfere with the actuation of a tip ejecting rod. The present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a fragmentary elevational view, partly in section, of a pipette utilizing a bellows and piston in a conventional configuration; Figure 2 is an elevational view, partly in section, of a pipette constructed in accordance with the invention; and Figure 3 is a fragmentary elevational view, partly in section, similar to Figure 2 but illustrating an alternate embodiment of the invention. The invention is hereinafter described in connection with a preferred embodiment in which the device is a hand-held pipette, used with a single-sized disposable tip and motor actuation. The invention is useful also in a pipette that is machine-manipulated, and/or is used with more than one-sized tip, as shown for example in U.S. Patent No. 4,593,837 by R. Jakubowicz et al. It is further useful whether the piston of the pipette is actuated by a motor, as shown herein, or by a rod pushed manually against a return spring. It will be readily apparent that a bellows, be it mounted in a manner as provided for in this invention, or unmounted, is simply a special case of a folded membrane, comprising many folds. As used herein, "folded" refers to the presence of at least one fold in the sidewall of the membrane, to distinguish over a taut membrane that is not useful because of the high resistance forces that resist displacement of the membrane when the piston is moved. A conventional pipette construction is illustrated in Figure 1. The pipette 10 has a body 12 and controls 14 at one end. A pipette tip, not shown, is mounted at or adjacent to end 16. A piston 23 in piston chamber 20 generates the partial vacuum and pressure needed to aspirate fluid in, or eject fluid out of the tip. Fluid passageway 18 extends from end 21 of chamber 20 to the pipette end 16. Piston 23 is mounted for movement as driven by motor 24. To replace sealing 0-rings, a bellows 30 is provided, with a base portion 32 sealed to chamber end 21. Top portion 33 of the bellows is connected to piston 23. A generally cylindrical sidewall 34 with multiple folds extends between base portion 32 and top portion 33. The sidewall has an inside surface 35 and an outside surface 37. Most importantly, by this construction it is the inside surface 35 of the sidewall 34 that generates the operative vacuum or pressure that causes air flow within passageway 18 and fluid flow within the pipette tip (not shown). The air volume defined by outside surface 37 and chamber 20 does not affect passageway 18. Instead it is vented via passageway 39, to the atmosphere. It is a characteristic of such a bellows construction that it cannot be readily compressed much below position X. This results in a dead air volume, within the bellows, having a height "h". In accordance with the invention, the pipette is improved, Figure 2, by constructing the pipette so that the bellows is inverted and it is the outside surface of the bellows that defines the air volume that generates the operative vacuum or pressure to cause fluid to flow within the tip. Pipette 40 constructed in such a manner has features similar to those of Figure 1, namely a body 42 in which is contained the pressurizing means as before, and control switches 44 (of conventional construction). At opposite end 46, a conical surface 47 is provided that mounts disposable pipette tips, shown in phantom. A fluid passageway 48 comprises part of end 46, and extends thereto from a piston chamber 50 located internally of body 42. Chamber 50 has generally opposite ends 51 and 52. A piston 53 is mounted for reciprocation within chamber 50, driven by a conventional linear actuator motor 54 via a drive shaft 56. Motor 54 can be, for example, a K92211-P2 motor obtained under the trademark AIRPAX from North American Phillips Company. To eject the disposable tip T after its use is finished, an ejection rod 60 is mounted in body 42. One end 62 of the rod is disposed adjacent surface 47 in contact with a disposable tip. Opposite end 64 is disposed adjacent end 51 of chamber 50 and projects into chamber 50. Rod 60 is slidably mounted to reciprocate parallel to passageway 48, when actuated by piston 53, as is conventional. As noted, an active element of the pressurizing means for the pipette is bellows 70 comprising an open base portion 72, an expandable, generally cylindrical sidewall 74, and a closed top portion 73. Shaft 56 thus extends through base portion 72 inside of the bellows and is secured to piston 53 mounted at top portion 73 of the bellows. Base portion 72 is secured to chamber end 52 that is different from end 51. Thus, it is the outside surface 77, rather than the inside surface 75, that forms the active air volume, with chamber 50, to pressurize or evacuate passageway 48. Passageway 79 vents to the atmosphere. In this construction, the dead air volume is minimized since the bellows, when fully expanded, occupies almost all of the volume of chamber 50. Furthermore, the least force is required by motor 54 to move piston 53 to that fully expanded position, or even beyond, compared to the force expended to completely compress such a bellows. Yet another advantage is that the bellows need not be fully compressed to allow piston 53 to be extended into contact with end 64 of ejection rod 60. Instead, bellows 70 need only be stretched slightly beyond its home position (shown in Figure 2) - a task that presents a minimal load to motor 54 and therefore provides full motor torque for the purpose of tip ejection. Useful materials for bellows 70 include nickel alloy, for example one having a spring constant of less than 1.75 N/cm (1 lb/inch). A vent 79 is provided for venting the interior of bellows 70 to the atmosphere. Alternatively (not shown), bellows can be used as the pressurizing means in a second chamber needed, for example, in constructing a pipette to accept two-differently sized tips. In such a case, shaft 56 can connect to a coupling that pushes or pulls individual drive shafts connected to each of the two pistons and their respective bellows. The motor of the pipette is operated by switches 44 in a conventional fashion, using a circuit board (not shown) that makes connections within body 42. The exact location of the base of the bellows vis-a-vis the motor is not a critical aspect of the invention, as shown in Figure 3. Parts similar to those shown in the previous embodiment bear the same reference numeral, to which the distinguishing suffix "a" has been appended. Thus, as in the embodiment of Figure 2, pipette 40a comprises a motor 54a driving shaft 56a to which is attached piston 53a that moves in piston chamber 50a. Fluid passageway 48a connects end 51a of chamber 50a to end 46a where tip locating surfaces 47a are provided. Bellows 70a is attached to piston 53a at top portion 73a as before. Also, it is the outside surface 77a of wall 74a that defines, together with chamber 50a, the activating air volume for pressurizing and evacuating passageway 48a. However, in this case, base portion 72a of bellows 70a is secured at end 51a of chamber 50a, rather than at a location spaced therefrom. Furthermore, passageway 48a connects to end 51a at an off-center location 80 so as to provide access to the air outside of bellows 70a, rather than inside 70a. Passage 79a vents to the atmosphere. (In this embodiment, tip ejection is preferably achieved by an external ejection system, not shown). Alternatively, if infinite lifetime is not a major concern, the bellows can be replaced (not shown) by an elastomeric membrane that has been preformed with a cylindrical shape that is similar to the bellows. This preformed shape avoids the cracking that occurs when using a flat, stretchable membrane that has to be deformed each time it is used.

Claims: A pipette (40; 40a) comprising a fluid passageway (48; 48a), and means (44, 50, 51, 52, 53, 54, 56, 70, 72, 73, 74, 75, 77; 50a, 51a, 53a, 54a, 56a, 70a, 72a, 73a, 74a, 77a) for creating an operative vacuum or a pressure in said passageway (48; 48a) different from atmospheric pressure, said means (44, 50, 51, 52, 53, 54, 56, 70, 72, 73, 74, 75, 77; 50a, 51a, 53a, 54a, 56a, 70a, 72a, 73a, 74a, 77a) including a piston chamber (50; 50a) having an end (51; 51a) fluidly connected to said fluid passageway (48; 48a), a piston (53; 53a) and a bellows (70, 72, 73, 74, 75, 77; 70a, 72a, 73a, 74a, 77a) mounted for movement within said chamber (50; 50a), and actuating means (54, 56; 54a, 56a) for advancing or retracting the piston (53, 53a); characterized in that said bellows (70, 72, 73, 74, 75, 77; 70a, 72a, 73a, 74a, 77a) comprises an open base portion (72) and a closed top portion (73; 73a), and a preformed generally cylindrical sidewall (74; 74a) extending between said base portion (72) and said top portion (73; 73a), said bellows sidewall (74; 74a) having an inside surface (75; 75a) and an outside surface (77; 77a), said base portion (72) being sealed to said chamber (50; 50a), said top portion (73; 73a) being secured to said piston (53; 53a), so that said sidewall outside surface (77; 77a) and said piston (50; 50a) chamber define the air volume operative on said fluid passageway (48; 48a). A pipette as defined in claim 1, wherein said bellows (70, 72, 73, 74, 75, 77) is sealed to said chamber (50) at an end (52) different from said end (51) fluidly connected to said fluid passageway (48). A pipette as defined in claim 1 or 2, and further including means (46, 47) for supporting a disposable tip (T) about said passageway (48), and means (60, 62, 64) for ejecting a disposable tip (T) off said supporting means (46, 47), said ejecting means (60, 62, 64) including a rod (60) one end (64) of which is mounted in sliding relationship at said end (51) of said chamber (50) fluidly connected to said fluid passageway (48), and in position to be engaged by said piston (53) when said piston (53) is extended completely to said chamber end (51). A method of aspirating and dispensing liquid into and from a pipette as defined in any one of claims 1 to 3, the method comprising the steps of: a) inserting the pipette into a source of the liquid; b) creating a partial vacuum within said fluid passageway by collapsing said bellows with said piston, whereby liquid is drawn into said tip; c) moving the pipette relative to the source of liquid and to an object onto which the liquid is to be dispensed; and d) creating a partial pressure within said fluid passageway sufficient to expel at least a portion of the liquid, by moving said piston in a direction that allows said bellows to expand from its collapsed state created in step b).

Inventors: JAKUBOWICZ, RAYMOND FRANCIS EASTMAN KODAK COMPANY, PORTE, JOHANNES JACOBUS EASTMAN KODAK COMPANY
Applicants: EASTMAN KODAK COMPANY (A NEW JERSEY CORPORATION)
Application year: 1989
Main classification: B01L3
IPC codes: B01L3