DISPOSABLE DIALYSIS CASSETTE
CROSS-REFERENCE TO RELATED
This application claims priority from provisional patent 5 application Ser. No. 60/144,805, filed Jul. 21, 1999.
STATEMENT REGARDING FEDERALLY
SPONSORED RESEARCH OR DEVELOPMENT
BACKGROUND OF THE INVENTION
The present invention relates to a holder for a dialysis membrane used in osmotic separation. More specifically, the present invention discloses a dialysis support frame.
Dialysis separation is an effective means of separating molecules according to their ability to diffuse through a semi-permeable membrane. The dialysis solution is placed 20 within a dialysis chamber containing one or more walls formed by a semi-permeable membrane. The membrane, by virtue of its composition and porosity, allows molecules equal to or less than a particular molecular weight to pass 2J through and into a dialysis bath in which the chamber is submerged. The driving force behind dialysis separation lies within the osmotic flow created by the concentration differential between the dialysis solution and the dialysis bath.
Although dialysis separation is an effective means of 30 separating molecules of variable sizes, it is cumbersome and generally requires great care to avoid contamination or the loss of a sample. A commonly applied method involves sealing the top and bottom ends of a tubular dialysis mem- 35 brane with clips or collars to form a dialysis chamber. If the ends of the tubing are not carefully sealed, the dialysis chamber will leak and the sample may be lost. In addition, the lack of support for the generally flaccid membrane results in significant difficulty in loading and unloading 40 samples. Because of the nature of the clips and collars used to seal the dialysis chamber, it is often necessary to handle the membrane which may effect the integrity of the membrane thus causing inefficient dialysis separation. 45
Finally, this method does not provide ample space for labeling the chamber to indicate the enclosed sample. Therefore, labeling must be written on the small clamp or collar, or on an object which is inconveniently attached to the tubing with material such as string. 50
U.S. Pat. No. 5,788,075 describes an apparatus containing a floating support ring comprising a central opening surrounded by a downwardly extending tube used to support a dialysis membrane. The walls of the apparatus and the floor 55 of the dialysis membrane converge to create the dialysis chamber. In its operation, the assembled apparatus is suspended over a dialysis bath and the sample loaded into the dialysis chamber.
Although this solution offers advantages, it introduces 60 new problems. First, the sample is open to the air which allows it to be easily contaminated. Secondly, because the vessel is open, it is easy for the sample to spill into the dialysis bath as it floats. Loading and unloading are greatly 65 simplified, but assembly of the device requires some skill by the user.
U.S. Pat. No. 5,503,741, describes a dialysis cassette which embodies a hermetically sealed sample chamber formed by fixing two dialysis membranes to a gasket. The gasket is impermeable to the sample being dialyzed, but is penetrable by a hypodermic needle. Upon assembly, the sealed sample chamber is contained within a rigid housing containing windows exposing the dialysis membranes. In its operation, a hypodermic needle is inserted through the gasket and into the chamber so as to insert or withdraw the dialysis solution. The cassette is then placed within a dialysis bath where dialysis separation occurs.
Unfortunately, this product also has several drawbacks. One such drawback is the fact that the device requires the use of a hypodermic needle to introduce the dialysis solution into the dialysis chamber. The use of a hypodermic needle may be unacceptable when the dialysis cassette is used to separate DNA or RNA fragments as high shear forces are created in the liquid passing through the needle such as may damage larger molecules. The shear forces may also disrupt and inhibit the dialysis of whole mammalian cells, algal cells, protists (i.e., amoebas, water bears, etc.), and colonial organisms.
The dialysis cassette has a further drawback in that it requires greater skill in the loading and unloading of samples, as compared to the methods described above. Furthermore, in view of its construction, the dialysis cassette is likely to carry a greater expense in its use.
What is needed is a simplified device providing minimal risk of contamination or sample loss. This device should allow for the dialysis of delicate samples which include proteins, DNA or RNA.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a simplified disposable dialysis cassette in which a flexible frame supports and exposes a dialysis membrane for simplified filling and handling.
The dialysis cassette embodies a first and second semipermeable dialysis membrane, or tubular dialysis membrane sealed by a flexible frame to form a dialysis chamber having a self-closing channel for the introduction of samples by either a pipette or other dispensing mechanism. The dialysis cassette is assembled by the combination of a first and second flexible polymeric sheet bonded together to form a semi-rigid frame, wherein the bottom end of the dialysis chamber is preferably affixed and sealed within the semirigid frame and the top end of the dialysis chamber is extended within and to the edge of the semi-rigid frame to create a self-closing channel which provides access to a portion of the dialysis chamber exposed by a window formed by central apertures contained within the first and second polymeric sheets. In its use, the frame may be flexed to allow the opening and closing of the self-closing channel for the introduction of a sample into the dialysis chamber.
In a further embodiment of the invention, an instrument guide is affixed within the channel to allow for the easy insertion of a pipette or other dispensing mechanism used to deposit the dialysis sample.
It is an object of the present invention to provide a disposable dialysis cassette which is less bulky, flexible,