1. Field of the Invention
The present invention relates to static diffusion cells useful in automated and manual diffusion sampling systems as well as assay methods that utilize diffusion sampling systems that include one or more diffusion cells according to the present invention. In particular, the present invention provides a static diffusion cell that includes a single chambered receptor compartment, which design reduces or eliminates the disadvantages associated with diffusion cells having multi-chambered receptor compartments and allows for improved sampling systems and assay methods.
2. Description of the Related Art
In vitro membrane diffusion systems with automated sampling are widely available for flow-through diffusion cells. However, applicants are presently aware of only two commercial systems that provide both static diffusion cells and automated sampling. Hanson Research Corp. of Chatsworth, Calif., sells the Hanson MicroettePlus™ Transdermal Diffusion System, and Logan Instruments Corp. of Somerset, Vt., sells the Logan System-902 and Logan System-912 Automated Transdermal Sampling Systems. Logan also sells an upgraded system that includes a cell design similar to the 902-system and an XYZ robot for automatic sampling. Although, the diffusion systems available from Hanson Research and Logan Instruments exhibit differences in design, the systems available from both companies includes a large amount of small diameter tubing and pumps (peristaltic or syringe) that move fluids through multiple compartments within the systems.
As illustrated in
As illustrated in
The designs of the systems described above can make cell set-up, handling, and cleaning difficult and can lead to inaccurate experimental data. In particular, the relatively extensive use of tubing in the systems available from Logan Instruments Corp. and Hanson Research Corp. introduces several potential problems. For example, the tubing can clog or leak, and the use of tubing can result in variable or inaccurate calculations of cell volume. Perhaps even more problematic is binding of media constituents, such as the material to be assayed, to the tubing or leaching of chemicals from the tubing into the receptor medium. Both the binding of materials from the receptor medium to the tubing and the leaching of materials from the tubing into the receptor medium can lead to an inaccurate assay of the amount or type of materials that diffuse through the diffusion membrane and into the receptor medium.
Further, systems designed according to those available from Logan Instruments Corp. and Hanson Research Corp. permit the accumulation of air bubbles under the diffusion membrane even after receptor medium has been degassed. Accumulation of air bubbles under the diffusion membrane causes a reduction in the area of the diffusion membrane in contact with the receptor medium, thereby reducing the effective diffusion area. Such a reduction in diffusion area can, in turn, result in inaccurate experimental data. However, removing air bubbles from the systems available from Logan Instruments Corp. and Hanson Research Corp. system is tedious at set-up and very difficult or even unattainable once a diffusion experiment has started. Accordingly, when these systems are used, they typically require supervision to ensure that air bubbles do not accumulate under the diffusion membrane, which supervision defeats, at least in part, the purpose of having an automated sampling process.
In one aspect, the present invention is directed to a new design for a diffusion cell that can be used in conjunction with automated or manual sampling systems. In particular, the present invention provides a diffusion cell that integrates a diffusion chamber, sampling chamber, and bubble trap into a single receptor compartment. The cell design of the present invention allows for a diffusion cell that is completely free of tubing.
In another aspect, the present invention includes a diffusion sampling system that incorporates one or more diffusion cells according to the present invention.
In yet another aspect, the present invention an assay method that utilizes a diffusion sampling system according to the present invention.
In one aspect, the present invention is directed to a new design for a diffusion cell that can be used in conjunction with automated or manual sampling systems. In particular, the present invention provides a diffusion cell that integrates a diffusion chamber, sampling chamber, and bubble trap into a single receptor compartment. The cell design of the present invention allows for a diffusion cell that is completely free of tubing. Moreover, the design of a diffusion cell according to the present invention eliminates the need for a pump for circulating the fluid within various chambers.
It is believed that the design of the diffusion cell of the present invention has several advantages over diffusion cell designs that include multiple compartments, wherein the receptor medium flows into the different compartments through tubing that places the compartments in fluid communication. For example, relative to systems requiring the interconnection of multiple compartments via lengths of tubing, the diffusion cells of the present invention can be easily removed and replaced within a diffusion apparatus, which eases experimental set-up and cleaning. Moreover, in diffusion systems including multiple chambers interconnected by tubing, calculation of the cell volume includes assessment of the receptor fluid within the tubing, which makes an accurate determination of cell volume difficult. In contrast, because diffusion cells of the present invention include a single-chambered receptor compartment, diffusion cells of the present invention allow easier and more accurate determination of cell volume. The absence of tubing in a diffusion cell according to the present invention also eliminates potential tube leaks and clogs as well as the problems that result from binding of receptor medium materials to tube walls or leaching of chemicals from the tubing into the receptor medium. Diffusion cells designed according to the present invention are also ease the tasks of replenishing receptor medium and maintaining the receptor medium at a constant volume within the diffusion cell.
Further, unlike existing sampling systems (e.g., the Hanson and the Logan systems described earlier), the diffusion cell design of the present invention allows for relatively easy removal of bubbles appearing under the surface of the diffusion membrane during the course of the experiment. In preferred embodiments, the static diffusion cell of the present invention is designed to automatically reduce the possibility of accumulation of air bubbles at the surface of the diffusion membrane exposed to the receptor compartment.
Each embodiment of the diffusion cell of the present invention illustrated herein is shown without a water jacket. Existing diffusion cells are often designed to include a water jacket, which serves to control the temperature of the diffusion cell by circulating water of a desired temperature around at least a portion of the receptor compartment. Though the diffusion cell of the present invention can be designed to include a water jacket, if desired, presently preferred embodiments do not include such a feature. Eliminating the water jacket further simplifies the design of the diffusion cell, and, in particular, eliminates the need for the tubing and fixtures to support such a temperature regulating system. In addition, control of the temperature within the diffusion cells of the present invention can be achieved through alternative means. For example, temperature control of a diffusion cell according to the present invention can be achieved by positioning the diffusion cell within a mounting block that is regulated to a desired temperature and is designed to accommodate one or more diffusion cells.
A first embodiment of the diffusion cell of the present invention is illustrated in
In order to ensure the diffusion membrane is properly held in place between the donor and receptor compartments, the diffusion membrane may be positioned over or disposed between a device or component that reinforces the diffusion membrane and allows the diffusion membrane to be securely held in place without undesired damage to the membrane. As is illustrated in
A test material is deposited in the donor compartment in contact with the top surface of the diffusion membrane. The test material includes one or more constituents, such as one or more drugs, to be tested for permeability or flux across the diffusion membrane. Though in preferred embodiments the diffusion cell of the present invention is used to evaluate the flux of one or more drugs contained in a test material across the diffusion membrane, diffusion cells according to the present invention are not so limited in use. A diffusion cell according to the present invention can be used to evaluate the permeability or flux of virtually any desired substance across a chosen diffusion membrane. The test material, therefore, can include a wide range of substances or formulations. For example, the test material may simply be a desired amount of a particular compound at a chosen purity. Alternatively, the test material may include a formulation of two or more materials, such as a liquid formulation (e.g., a solution, suspension, emulsion, etc.) or a lotion, cream, gel, or other semi-solid formulation. Even further, the test material may include a drug delivery device, such as a transdermal therapeutic device, designed to delivery a chosen substance, such as one or more therapeutic agents.
The receptor compartment of a diffusion cell of the present invention may be designed according to any desired size or shape. However, the geometry of the receptor compartment is preferably designed for efficient stirring of the receptor medium. The receptor compartment typically includes a magnetic stir bar or other suitable means to ensure proper stirring of the receptor medium throughout the diffusion cell, which reduces the possibility of forming stagnant diffusion layers near the diffusion membrane. A receptor compartment of a diffusion cell according to the present invention also includes a first outlet and a second outlet.
The first outlet may be formed to any size and shape that allows positioning of the diffusion membrane over the first opening. For example, where the receptor compartment is designed to accommodate a 5-30 ml volume of receptor medium, the first opening is preferably sized from about 0.7 to about 5 cm2. However, the size and shape of the first opening can be varied, as desired, to allow the use of differently sized diffusion membranes and to suit any particular test conditions. As can be seen in
The second outlet of the receptor compartment serves as a sampling arm and a bubble trap. The second outlet may be sized and shaped according to any desired configuration providing a suitable sampling arm. Typically, the opening of the second outlet will be smaller than that of first outlet. The second outlet includes a cap or a seal having a septum that can be penetrated by a sampling needle. Typically the opening of the second outlet will be circular in shape and will be about 0.5 cm in diameter. In preferred embodiments, the second outlet is sized and shaped so that HPLC vial caps with a septum can be used to cap the second outlet.
The sampling arm formed at the second outlet also serves as a bubble trap, allowing the removal of bubbles that form under the diffusion membrane. Depending on the design of the diffusion cell of the present invention, bubbles are removed either by tilting the cell and forcing the bubbles from under the diffusion membrane and into the sampling arm, or the diffusion cell may be designed such that bubbles forming within the cell automatically migrate into the sampling arm formed by the second outlet. If large bubbles accumulate in the sampling arm and the total receptor medium level decreases, more receptor medium can be easily added through the sampling arm to keep the total receptor medium level constant.
The donor compartment of a diffusion cell according to the present invention is positioned over the first opening of the receptor compartment and can be sized and shaped as desired to meet any experimental need. The donor compartment is designed to contain the test material. A cap or seal, such as a screw cap, septum, or the like, may be provided over the donor compartment and may be necessary where the test material is a liquid or low viscosity or where evaporation or contamination of the test material are to be reduced or eliminated. As is indicated above, the donor compartment can be associated with the receptor compartment using any suitable mechanism. For example, the donor compartment may be clamped to the receptor compartment or, alternatively, the donor compartment may be associated with the receptor compartment using a threaded connection, a male-female connection, a snap-fit connection or by a friction or interference fit. Therefore, the design of one or more components forming the donor compartment can be adapted to facilitate association of the donor compartment with the receptor compartment according to any desired mechanism. In each embodiment, the mechanism for associating the donor compartment with the receptor compartment maintains the donor compartment in close contacting relationship with the diffusion membrane or the first opening of the receptor compartment. Though the means for associating the donor compartment with the receptor compartment may form an adequate seal between the two compartments and the diffusion membrane, one or more additional sealing elements, such as one or more O-rings or gaskets, may be used where the diffusion membrane, donor compartment, or receptor compartment interface with one or more other components of the diffusion cell.
As shown in
In a particularly preferred embodiment, the diffusion cell of the present invention is not only designed with receptor compartment having a top surface that inclines upward toward the second opening, but the diffusion cell also includes a channel connecting the first and second outlets. The channel can simply be a depression formed in the top surface of the receptor compartment that extends between the first and second outlets. An illustration of such a channel is provided in
The volume of receptor medium contained within a diffusion cell according to the present invention must be considered when designing a diffusion study. Commonly, receptor compartment volumes for diffusion cells range from about 5-30 ml. However, diffusion cells having virtually any desired volume of receptor media can be designed. When it is anticipated that the material to be assayed from the receptor media exhibits a low permeability or flux across the diffusion membrane, relatively small volumes of receptor medium are desirable and may be necessary so that the concentration of the material to be assayed within the receptor medium can be above the limit of detection for the assay method used within a reasonable amount of time. However, when it is anticipated that the material to be assayed from the receptor media exhibits a high permeability or flux across the diffusion membrane, a relatively large volumes of receptor media are desirable and may be necessary to maintain sink conditions in the receptor compartment throughout the diffusion study. Therefore, the volume of the receptor compartment can be varied to provide any particular volume of receptor medium useful for a chosen diffusion study.
To better facilitate tailoring the volume of the receptor compartment to a chosen diffusion study, the diffusion cell of the present invention can be designed having separable top and bottom sections (shown in
Where the diffusion cell of the present invention is designed with separable top and bottom sections, the two sections of the diffusion cell can be associated using any suitable means. In a preferred embodiment (illustrated in
It should be understood that top and bottom sections of a diffusion cell of the present invention might also be associated using any other suitable mechanism. For example, the top and bottom sections of a diffusion cell according to the present invention can be associated using a clamp. Alternatively, the top and bottom sections of a diffusion cell of the present invention can be associated using, for example, a threaded connection, a male-female connection or a snap-fit connection. The design of the top and bottom sections of a diffusion cell of the present invention is flexible and can be altered to accommodate the use of virtually any suitable connection mechanism.
The various different components of diffusion cells of the present invention can be fabricated using materials well known in the art. However, in preferred embodiments, at least a portion of the receptor compartment is formed of a glass material. Where the diffusion cell according to the present invention includes a top and bottom section, it is preferable to form the top section of TEFLON® and the bottom section of glass. However, any other materials that are suitable for application in a diffusion cell of the present invention may also be used. For example, instead of TEFLON®, the top section of a diffusion cell of the present invention can be formed of a metal or metal alloy, a polymer material or glass. Moreover, instead of glass, the bottom section of a diffusion cell of the present invention can be formed of a metal or metal alloy or a polymer material. A material is suitable for use in the fabrication of a diffusion cell of the present invention provided it is capable of withstanding exposure to the anticipated test conditions without physical failure and without contaminating the receptor media or retaining undesirable amounts of the material to be assayed.
The diffusion cells of the present invention can be used to conduct a variety of assays used in the art. For example, diffusion cells of the present invention can be used to test various drug dosage forms, including transdermal dosage forms, oral dosage forms, ocular dosage forms such as transdermal or transmucosal patches, tablets, semi-solid dosage forms, gel formulations, pastes, ointments, emulsions, suspension, drops and the like.
Diffusion cells according to the present invention can also be used for mechanistic studies, e.g. transport studies through epithelia that focus on various parameters, such as vehicle effect, ionic strength, markers and the like. The diffusion cells of the present invention can also be used for non-passive diffusion assessments that involve active transport mechanisms, which include iontophoresis, sonophoresis, and the like.
The diffusion cells of the present invention can be used to form a diffusion sampling system. A diffusion sampling system of the present invention includes one or more diffusion cells according to the present invention positioned within a mounting apparatus, such as a mounting block, that allows for stirring of the receptor media in the diffusion cells and serves to maintain the diffusion cells at a desired temperature. Where a mounting block is used, the mounting block is preferably formed of a conductive metal, such as an aluminum alloy or stainless steel, that can be maintained at a substantially uniform temperature throughout the mounting block and allows the use of magnetic stir bars within the receptor compartment. The diffusion cells included in a diffusion sampling system of the present invention are positioned within the mounting apparatus such that sampling ports of each diffusion cell are readily accessible. In preferred embodiments, the diffusion cells include a keying feature that require the diffusion cells to be positioned within the mounting apparatus such that the sample ports are aligned in a configuration that facilitates easy sampling. Once positioned within the mounting apparatus, the diffusion cells can be sampled manually or automatically.
Where automatic sampling of multiple diffusion cells is desired, the diffusion sampling system of the present invention can include, for example, a robot with multidirectional flexibility, such as an XYZ. XYZ robots are often used in high throughput screening applications and are capable of controlled, programmable movements in all directions along the XYZ axes. XYZ robots can also be provided with sampling heads that allow the simultaneous sampling of several cells (generally up to 6 to 12 cells simultaneously). Depending on the positioning of the diffusion cells in the mounting apparatus, different robot sampling heads can be used. Examples of two designs for the blocks and the matching sampling heads are shown in
The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. All such variations and modifications are considered to be within the scope and spirit of the present invention.
Pursuant to the provisions of 35 U.S.C. § 119(e), this application claims the benefit of the filing date of provisional patent application Ser. No. 60/458,905, filed Mar. 28, 2003, for “Static Diffusion Cell for Diffusion Sampling Systems.”
Number | Date | Country | |
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60458905 | Mar 2003 | US |