U.S. patent application number 09/811970 was filed with the patent office on 2001-11-29 for mechanical interlock for filters.
Invention is credited to Foley, Brian, Groves, James, Zermani, Thomas.
Application Number | 20010045389 09/811970 |
Document ID | / |
Family ID | 22724510 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010045389 |
Kind Code |
A1 |
Zermani, Thomas ; et
al. |
November 29, 2001 |
Mechanical interlock for filters
Abstract
The present invention provides a mechanical lock for securing
one or more filters within a filtration device and methods for
producing the mechanical lock. The use of an interference fit punch
causes a portion of the inner surface of the wall to be skived and
rolled along the wall until it reaches the desired location where
it forms a mechanical crimp to retain the one or more filters
within the device. In one embodiment, the inner surface has an
inwardly taper. In the other, it has straight walls or outwardly
tapered walls. The use of a gasket such as an O-ring on top of the
filter before the wall is skived provides a liquid tight seal.
Inventors: |
Zermani, Thomas; (Peabody,
MA) ; Groves, James; (Annisquam, MA) ; Foley,
Brian; (Westford, MA) |
Correspondence
Address: |
MILLIPORE COPORATION
80 ASHBY RD
BEDFORD
MA
01730
US
|
Family ID: |
22724510 |
Appl. No.: |
09/811970 |
Filed: |
March 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60196221 |
Apr 10, 2000 |
|
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|
Current U.S.
Class: |
210/495 ;
29/896.62 |
Current CPC
Class: |
Y10T 83/8825 20150401;
B01L 2300/0829 20130101; Y10S 264/48 20130101; B01D 29/05 20130101;
Y10T 29/49604 20150115; B01D 2201/40 20130101; B01D 2201/34
20130101; B01D 29/012 20130101; B01L 3/50255 20130101; B01D 29/52
20130101; B01L 2200/12 20130101; B01D 29/012 20130101; B01D 29/05
20130101; B01D 29/52 20130101 |
Class at
Publication: |
210/495 ;
29/896.62 |
International
Class: |
B01D 029/05 |
Claims
1. A filtration device comprising at least one well, one or more
pieces of filter, a filter retention device within the depth of the
well and a mechanical interlock, said interlock being formed from
at least a portion of an inner wall of the well and wherein the
interlock remains attached to and as a portion of the inner
wall.
2. The device of claim 1 wherein at least a portion of the inner
wall is tapered inwardly as it progresses from the top of the well
toward the bottom of the well.
3. The device of claim 1 wherein at least a portion of the inner
wall is tapered inwardly as it progresses from the top of the well
toward the bottom of the well and wherein the taper is from about 0
degrees toward the vertical center line of the well to about 20
degrees toward the vertical center line of the well.
4. The device of claim 1 wherein at least a portion of the inner
wall is tapered inwardly as it progress from the top of the well
toward the bottom of the well and wherein the taper is about 7
degrees toward the vertical center line of the well.
5. The device of claim 1 wherein at least a portion of the inner
wall is tapered outwardly as it progresses from the top of the well
toward the bottom of the well and wherein the taper is from about 0
degrees toward the vertical center line of the well to about -20
degrees toward the vertical center line of the well.
6. The device of claim 1 wherein at least a portion of the inner
wall is tapered outwardly as it progress from the top of the well
toward the bottom of the well and wherein the taper is about -7
degrees toward the vertical center line of the well.
7. The device of claim 1 wherein the filter retention device is
selected from the group consisting of underdrains, shelves, rims,
lattice supports, undercuts and combinations thereof.
8. The device of claim 1 wherein the filter retention device is an
underdrain.
9. The device of claim 1 wherein the device is made from a single
molded plastic piece and the filter retention device is an
integrally formed underdrain containing one or more openings.
10. The device of claim 1 wherein the one or more pieces of filter
are made from a material selected from the group consisting of
glass, polymer, metal, paper and ceramic.
11. The device of claim 1 wherein the one or more pieces of filter
are made from a polymeric material selected from the group
consisting of nitrocellulose, cellulose acetate, polysulphones,
polyethersulphones, polyarylsulphones, polyvinylidene fluoride,
polyolefins, nylons, polyamides, PTFE resin, thermoplastic
fluorinated polymers and polycarbonates.
12. The device of claim 1 wherein the device is made of a material
selected from the group consisting of styrene acrylonitriles,
polyolefins, polycarbonates, styrene homopolymers and copolymers,
PTFE resins, blends of polyolefins with small amounts of PTFE
resins, ABS, acrylic resins, methacrylic resins and copolymers of
either, BAREX.RTM. resin, nylons, epoxies, polyurethanes and
reinforced resins.
13. The device of claim 1 wherein the mechanical interlock is one
or more skives.
14. The device of claim 1 wherein the mechanical interlock is one
or more skives formed continuously from a portion of the wall.
15. The device of claim 1 wherein the mechanical interlock is one
or more crimps formed continuously from a portion of the wall.
16. The device of claim 1 wherein the device has a number of wells
selected from the group consisting of 96, 384 and 1536.
17. A method for securing a filter within a filtration device,
comprising selecting a filtration device with one or more wells,
each well having an inner wall, one or more filters retained within
each well of the device and skiving a portion of the inner wall to
form a mechanical interlock that forms an interference fit with the
filter and fixes the one or more filters to the device.
18. The method of claim 17 wherein the portion of the wall is
skived by a punch having a diameter greater than that of the inner
diameter of the inner wall of the well above and adjacent the
filter.
19. The method of claim 17 wherein the portion of the wall is
skived by a punch having a diameter greater than that of the inner
diameter of the inner wall of the well above and adjacent the
filter and at least one cutting surface to form the mechanical
interlock.
20. The method of claim 17 wherein the portion of the wall is
skived by a punch having a diameter greater than that of the inner
diameter of the inner wall of the well above and adjacent the
filter and at least two cutting surfaces to form the mechanical
interlock.
21. The method of claim 17 wherein the portion of the wall has an
outward taper as it progresses from a top of the well toward the
filter in the well and inner wall is skived by a expandable punch
that upon expansion has a diameter greater than that of the inner
diameter of the inner wall of the well above and adjacent the
filter and the punch forms at least one cutting surface to form the
mechanical interlock.
22. The method of claim 17 wherein the inner wall of the well is
heated either before or during the skiving.
23. The method of claim 17 wherein the inner wall of the well is
heated during the skiving.
Description
BACKGROUND OF THE INVENTION
[0001] The MULTISCREEN.RTM. Harvest Plate is a 96-well plate
designed and optimized for cell harvesting applications. The plate
is a single molded device having 96 distinct and separate wells
into which is inserted a glass fiber mat filter which is used for
retaining cells or other selected items. The plate has been well
received, as its individual wells were specifically designed to
have no cross talk between the wells.
[0002] The glass fiber disc was stuffed into each well such that
the disc had an interference fit with the sides and /or bottom of
the well. Lab tests of the plate were very successful, so the
product was launched.
[0003] Unfortunately, the plate was not robust for all
applications. It was learned that the plates are handled quite
roughly, for example typically being loaded haphazardly into liquid
filled drums. Many of the discs became dislodged as they were only
held in by an interference fit.
[0004] Any dislodgment was unacceptable, so a means for securing
the glass fiber disc had to be determined. Yet, the filter disc had
to be secured without adding another molding step to minimize the
cost and avoid the cross talk issue. As no other
single-molded-plate was available on the market, no multiple-molded
plate sold in the prior art offered a solution.
[0005] In two piece multiple well plates, e.g. those having a
separate underdrain plate and a mating open welled top plate, the
same means for securing the filter in the well has been used. When
that has been found to be insufficient, other means such as
ultrasonically welding the filter to one of the two components or
using an O-ring above the filter have been tried. While these
methods have worked to some degree they are slow, costly and time
consuming.
[0006] Accordingly, it was desirable to provide a multiple well
plate, whether a single molded design or a two piece design, that
had its filtration material secured therein such that it did not
come dislodged during usage.
[0007] In addition, it would be desirable to provide a process for
making such plates.
SUMMARY OF THE INVENTION
[0008] This invention provides a mechanical interlock for securing
the filter inside a receptacle designed to receive such filter.
Specifically, the interlock is material from the inner wall of the
device formed in such a manner that the material prevents the
filter from moving but also remains fixed to the wall of the
device. Preferably, the wall of the device is skived in a manner
that the material of the device wall is peeled therefrom, without
breaking off, until it is in contact with the filter to be fixed
therein. The interlock prevents the filter, typically in the form
of a disc, from moving and since a portion of the interlock remains
fixed to the wall of the device, the result is a sturdy
mechanically fixed filter within a device.
[0009] The inner wall of the device may be straight, outwardly
tapered or inwardly tapered (the taper being defined relative to
the central vertical axis of the well of the device as defined from
the top (open portion) of the device toward the bottom). In all of
them, an interference fit punch causes a portion of the inner
surface of the wall to be skived and rolled along the wall until it
reaches the desired location where it forms a mechanical crimp to
retain a filter within the device.
[0010] This invention also provides methods of skiving wall devices
for the purpose of securing a filter therein.
BRIEF DESCRIPTION OF THE DRAWING
[0011] FIG. 1 illustrates a cross-section of a well of the present
invention prior to formation of the mechanical interlock.
[0012] FIG. 2 illustrates a cross-section of a well of the present
invention after formation of the mechanical interlock.
[0013] FIG. 3 illustrates a cross-section of a well of an
alternative embodiment of the present invention after formation of
the mechanical interlock.
[0014] FIG. 4 illustrates a cross-section of a well of the present
invention during the formation of the mechanical interlock.
[0015] FIGS. 5 a, b and c show alternative mechanical interlock
forming device designs in cross-sectional view.
[0016] FIG. 6 is a photograph of a prior art well.
[0017] FIG. 7 is a photograph of a prior art well.
[0018] FIG. 8 is a photograph of a well of the present invention
after formation of the mechanical interlock.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0019] FIG. 1 provides a cross section of the interior of a device
such as a well in a multiple well plate of the present invention
prior to the formation of the mechanical interlock of the present
invention. It shows the device 1 having one or more wells 2. Each
well has an open top 3 and a closed bottom formed as an underdrain
4 in this example. The underdrain has one or more holes 5 which
allow liquid to pass through under some type of driving force
(positive pressure, vacuum or centrifugation). A filter 6 is shown
as being in position against the underdrain 4. The filter, as shown
has a diameter larger than the diameter of the well adjacent the
underdrain 4 so that a portion 7 of the filter 6 is folded up along
the sides of the well 2. This is the interference fit configuration
of the devices of the prior art. While the embodiment shows the
portion 7 extending up the wall to create an interference fit, it
is not necessary although preferred in this invention. One can use
filters having substantially the same diameter, dimension and
cross-sectional configuration of the well area adjacent the
underdrain 4. Alternatively, it may be smaller. In all embodiments,
the size of the filter should be sufficient to ensure that a good
mechanical interlock is formed.
[0020] FIG. 1 shows a well with an inwardly tapered diameter, e.g.
the top inner diameter of the well is larger than the inner
diameter of the well adjacent the underdrain 4. All or just a
portion of the inner wall of the well may be inwardly tapered.
Whether all or just some is tapered depends upon a number of
factors and desires. In one embodiment, the entire length of the
inner wall is tapered. In another, only that portion of the well
between the top of the well and the location of the filter is
tapered. In a further embodiment, a portion of the well adjacent to
the top of the well is not tapered and the portion directly above
the filter support device is inwardly tapered. In another
embodiment of the present invention, the wall or a portion of it
may taper outwardly. In a further embodiment the wall of the well
is straight (substantially vertical or substantially perpendicular
to the plane of the filter). All of these are possible and useful.
In any embodiment, the well needs to provide a sufficient amount of
inner wall to form the mechanical interlock or skive necessary to
hold the filter in place.
[0021] FIG. 2 shows the device of FIG. 1 after formation of the
mechanical interlock. As can be seen a portion of the inner wall 11
has been skived and rolled on top of the filter 12 to form a
mechanical interlock 13 against the filter 12 in the well 14. Also
as shown in FIG. 2, the outer portion 15 of the filter 12 which had
extended up along the inner wall 11 of the well 14 has been
compressed and retained under the interlock 13.
[0022] FIG. 3 shows an alternative embodiment of the present
invention. This embodiment may be used where either the membrane is
not resilient and therefore tends to compress under pressure and
not rebound and/or where one desires not only to have a mechanical
interlock but also a liquid tight seal formed. In this embodiment,
shown after formation of the interlock 20, the filter 21 is
retained against the bottom of the well 22, in this example the
bottom being an underdrain 23 having one or more holes 24 for fluid
to pass through. A gasket 25, in this embodiment, an O-ring, is
placed on top of the filter 21 before the formation of the
mechanical interlock 20 and is retained by interlock 20 along with
the filter 21.
[0023] As described in the embodiment of FIG. 1, the well wall may
have a pitch or taper for the skiving device to come in contact
therewith and form the skive that seals the filter in place. The
pitch of well wall prior to skiving is 7 degrees. Other angles may
be used as well. Typically an angle on an inwardly tapering wall is
of from about 0 degrees to about 20 degrees, preferably from about
0 to about 10 degrees. As stated above all of the wall may be
tapered, only a portion may be tapered or distinct portions may
have different tapers.
[0024] In those embodiments using an outward taper the angle may be
from about 0 degrees to about -20 degree, preferably from about 0
to about -10 degrees. As stated above, all of the wall may be
tapered, only a portion may be tapered or distinct portions may
have different tapers.
[0025] The cross-section of the well of the device may be any of
those commonly used today such as round, oval, square and square
with rounded comers. The cross-section is only a consideration when
designing the proper skiving tool cross-section so that it fits
within the well and forms the desired mechanical interlock. The
diameter of the well may be whatever is used on single well or
multiple welled devices. Typically, 96 well devices have wells with
a crossectional diameter of about 0.23 inch (5.8 mm) to about 0.252
inch (6.4 mm). 384 welled devices have diameters of about 0.138
inch (3.5 mm) and 1564 welled devices have wells with diameters of
about 0.067 inch (1.7 mm).
[0026] The material used to create the mechanical interlock, that
is the skive, may be a styrene acrylonitrile polymer (SAN), but
other materials are contemplated, such as polyolefins including
polyethylene and polypropylene, polycarbonates, other styrene
homopolymers and copolymers, PTFE resins, blends of polyolefins
with small amounts of PTFE resins to reduce protein binding, ABS,
acrylic resins, methacrylic resins and copolymers of either,
BAREX.RTM. resin, nylons, epoxies polyurethanes and reinforced
resins such as glass filled epoxy resins, and other such materials
commonly used to make such devices, with or without fillers,
pigments, etc. as may be desired or required by the intended end
use of the device.
[0027] The filter may be a glass fiber mat, or it may be any other
material used to make membranes, such as a polymer, metal, ceramic
or paper. Suitable membranes may be microfilters, ultrafilters or
nanofilters, depending on the size of the material to be retained.
Polymeric filters can be made of materials selected from the group
consisting of nitrocellulose, cellulose acetate, polysulphones
including polyethersulphone and polyarylsulphones, polyvinylidene
fluoride, polyolefins such as ultrahigh molecular weight
polyethylene, low density polyethylene and polypropylene, nylon and
other polyamides, PTFE, thermoplastic fluorinated polymers such as
poly (TFE-co-PFAVE), e.g. PFA, polycarbonates or particle filled
membranes such as EMPORE.RTM. membranes available from 3M of
Minneapolis, Minn. Chromatography papers, cellulosic structures
containing chromatography media, ligands, a chemical treatment
rendering them charged (positive or negative) or other such
selective binding functionalities may also be used and are
available from a variety of sources such as Whatman. Metal filters
can be made of stainless steel, nickel or chromium such as th SF
stainless steel filter or the NF nickel filter available from
Millipore Corporation of Bedford, Mass.
[0028] All of these filters are well known in the art, may be
symmetrical or asymmetrical or a combination of the two, composite
(cast on to a separate preformed membrane support layer), may be in
the form of mats, flat sheets, made as meshes or woven and
non-wovens and are commercially available from a variety of sources
including Durapore.RTM. membranes and Express.RTM. membranes
available from Millipore Corporation of Bedford, Massachusetts.
[0029] The underdrain as shown in FIG. 1 is integral with the plate
of the present invention, so it is what the filter rests upon prior
to the formation of the mechanical interlock. Other arrangements
such as partial shelves, rims, lattice supports, undercuts and the
like may be used to support the filter in place until the skive
locks it to the underdrain or other such support.
[0030] It is contemplated that the present invention would be
useful for mechanically locking multiple layers of filters into a
filtration device, such as a pre-filter and a filter, thereby
lengthening the life of the device while eliminating the need for
expensive welding equipment such as ultrasonic welders or the use
of adhesives such as epoxies or thermal bonding technology.
Alternatively multiple filters could be locked sequentially into a
well separated by the height of the mechanical interlock formed
between each layer of filter. These may have simple open spaces
between the layers of filter or the spaces may be filled with
chromatography media, absorptive materials and the like.
[0031] The plate may be a single molded plate having an integral
underdrain formed in it as shown in FIG. 1 or it may be a two piece
plate comprised of a lower underdrain portion and an upper open
welled portion that is aligned with the underdrains of the lower
plate portion. These plates can be secured together by adhesives,
ultrasonic or vibration welding or mechanical devices such as
clamps, screws, rivets, rubber bands, snap fits, etc.
[0032] The skiving device of the present invention is preferably
produced by a punch pin made of M2 HSS (high speed steel), hardened
to Rockwell C 61-63. Metal is preferred as it makes a clean skive
and has a long lasting edge that is capable of being resharpened
after extensive use. Alternatively, ceramic or glass punches and
other materials harder than the material being skived and which are
capable of forming the mechanical interlock of the present
invention may be used if desired.
[0033] FIG. 4 shows the device of the skiving device 30, in this
example the pin, as it enters the well 31. As can be seen the
skiving device 30 encounters at least a portion of the inner wall
surface 32 above the location of the filter 33 and begins to form a
continuous roll 34 of wall material that stays attached to the wall
after completion of the skiving and which mechanically interlocks
the filter 33 in place within the well 31.
[0034] The depth to which the skiving device travels can be varied
by varying the thickness of the stripper plate spacer and its shims
on the press used to exert the force on the pin. The length of the
skive is controlled by the wall configuration (tapered or not), the
punch design and the amount of material needed to form the skive or
interlock.
[0035] As such, the height of the skive is pre-determined and it
can be controlled to a great degree of specificity, such that it is
envisioned that the present invention would be useful for higher
density well formats, such as 384 or 1536 wells per plate. The use
of multiple skiving devices at the same time in two or more wells
is also possible and preferred as it reduces the number of steps
required to make the present invention in a multi-well format. The
use of an equal number of skiving devices to the number of wells
each aligned with each other is preferred. This is particularly
possible with multiple well plates as the wells are typically
uniformly aligned and arranged. This allows one to set up one
master jig with an alignment pin that matches the plate wells to
the jig and allows for repeatedly accurate mechanical interlocks to
be formed in all wells.
[0036] FIGS. 5a-5c show some, but not all of the punch pin designs
that can be used to form the mechanical interlock or crimp of the
present invention. FIG. 5a shows a punch 36 with a relatively flat
cutting surface 37 which forms a skive around the entire perimeter
of the inner wall of the well. FIG. 5b shows an alternative design
wherein the bottom center portion 38 of the skiving device 39 is
recessed. FIG. 5c shows a skiving device 40 in which a series of
cutters 41 are formed in the device 40 so that one creates a series
of small mechanical interlocks rather than one continuous
interlock. In those applications where the diameter at bottom of
the well is larger than at the top, expandable dies may be used or
smaller diameter dies, applied at an angle to a lower portion of
the well wall may be used.
[0037] In a further embodiment of the present invention can use
mild heat applied to the inner wall of the device to soften the
material and make it flow as a continuous piece in forming the
interlock. Such heat can be applied by preheating the device in an
oven or by the use of heat lamps or heating rods placed within the
wells or by applying heat, such as through a resistance heater, to
the skiving device which then transfers that heat to the inner wall
of the device. The temperature selected can be from about above
room temperature to about a temperature close to or above the
softening point of the material from which it is made. Preferably,
it should not be to a temperature at or above the melting point of
the well material or a temperature at which the material distorts
or degrades.
EXAMPLE
[0038] A multi-well device according to the present invention was
made by taking a standard multiwell plate, a MULTISCREEN.RTM.
harvester plate available from Millipore Corporation of Bedford
Mass., which had 96 wells, each having an inward taper of 7 degrees
toward the vertical center line of the wells. The wells had an
integral underdrain on which one or more pieces of filtration
filter could be laid. The wells had a top inner diameter of 0.250
inch (6.35 mm) and an inner diameter of 0.2338 inch (5.94 mm)
adjacent the underdrain. Each well had a depth of 0.125 inch (3.17
mm). The plate was made of a mixture of styrene acrylonitrile
polymer (SAN) with titanium dioxide as a colorant. A glass mat
filter was used in each well. Each piece of filter had a diameter
of 0.300 inch (7.62 mm) and was set by hand into each well on the
upper surface of the underdrain such that a portion of the mat
extended upwardly along the inner surface of the well. (as shown in
FIG. 1)
[0039] A punch pin made of M2 HSS (high speed steel), hardened to
Rockwell C 61-63 having a diameter of 0.2420 inch (6.15 mm) was
used in each well to form the skive.
[0040] The punch traveled a portion of the way into the well before
encountering the inner wall surface (approximately 0.049 inch (1.24
mm)). Once encountered, the punch skived a portion of the wall in a
continuous, rolling collar until it reached a point adjacent the
location of the filter.
[0041] A dye from a felt tipped pen (red) was applied to the inner
surface of the wells before the skiving took place merely to
enhance the visualization of the process and its effect. In
practice, a dye is not required. Microphotographs were taken and
showed that the plastic of the inner wall had in fact been skived
and formed a mechanical retention device for the filter in the
well.
[0042] FIG. 6 is a photograph of a prior art well that has not been
stained. Note the filter is located therein and the lack of any
skive or permanent retention means.
[0043] FIG. 7 is a photograph of a prior art well that has been
stained with the same dye described above for illustration purposes
only. It is provided to contrast with FIG. 8. In FIG. 7, there is
no band of clear material.
[0044] FIG. 8 is a photograph of a skived well of the present
invention that was stained prior to skiving as described above.
Note the clear band 51 represents a portion of the wall that was
skived as well as the crimp or mechanical interlock 52 that is
formed in overlapping the filter 53.
[0045] The present invention while primarily discussed in
relationship to multiple well devices can also be of benefit in
single well devices such as CENTRICON.RTM. centrifugal devices
available form Millipore Corporation of Bedford, Mass. and other
such devices where the filter is retained within some type of well
or opening that provides a wall that can be skived to form the
mechanical interlock. It is meant by the above specification and
the attached claims to cover all such embodiments and obvious
extensions of the present invention.
* * * * *