U.S. patent application number 10/344597 was filed with the patent office on 2004-10-14 for method of forming a fluid tight seal.
Invention is credited to Dodgson, John Robert, Shaw, John Edward Andrew.
Application Number | 20040201174 10/344597 |
Document ID | / |
Family ID | 9891431 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040201174 |
Kind Code |
A1 |
Dodgson, John Robert ; et
al. |
October 14, 2004 |
Method of forming a fluid tight seal
Abstract
A method of forming a fluid tight seal between a first fluid
pathway and a second fluid pathway a volume is defined between an
outer surface of the first fluid pathway and an inner surface of
the second fluid pathway. The surfaces are maintained in a given
orientation and distance with respect, one to another, so as to
achieve a desired capillaric property therebetween. A quantity of
sealant is delivered to a junction region of said surfaces. The
sealant is caused or permitted to flow into the defined volume, so
as to achieve capillary balance. Only substantially sufficient
sealant is delivered to fill the volume. The sealant is then caused
or permitted to cure or set.
Inventors: |
Dodgson, John Robert;
(Surrey, GB) ; Shaw, John Edward Andrew;
(Middlesex, GB) |
Correspondence
Address: |
Martin Fleit
Fleit Kain Gibbons Gutman Bongini & Bianco
Suite 404
601 Brickell Key Drive
Miami
FL
33131
US
|
Family ID: |
9891431 |
Appl. No.: |
10/344597 |
Filed: |
April 2, 2004 |
PCT Filed: |
May 14, 2001 |
PCT NO: |
PCT/GB01/02084 |
Current U.S.
Class: |
277/316 |
Current CPC
Class: |
F15C 5/00 20130101; B29C
66/1122 20130101; B29C 66/324 20130101; B29C 65/483 20130101; B29L
2031/756 20130101; F16K 99/0017 20130101; B29C 66/322 20130101;
F16L 13/11 20130101; B29C 65/4845 20130101; F16K 99/0001 20130101;
F16K 99/0061 20130101; B29C 66/5221 20130101; B29C 65/548 20130101;
F16K 99/0057 20130101 |
Class at
Publication: |
277/316 |
International
Class: |
E04B 001/682 |
Foreign Application Data
Date |
Code |
Application Number |
May 12, 2000 |
GB |
0011428.0 |
Claims
1. A method of forming a fluid tight seal between a first fluid
pathway and a second fluid pathway comprising the steps of:
defining a volume between an outer surface of the first fluid
pathway and an inner surface of the second fluid pathway;
maintaining said surfaces in a given orientation and distance with
respect, one to another, so as to achieve a desired capillaric
property therebetween; delivering a quantity of sealant to a
junction region of said surfaces; causing or permitting the sealant
to flow into said volume, so as to achieve capillary balance
whereby only substantially sufficient sealant is delivered to fill
the volume; and causing or permitting the sealant to cure or
set.
2. A method according to claim 1 wherein the first fluid pathway is
a capillary tube.
3. A method according to claim 2 wherein the second fluid pathway
is disposed within a micro-fluidic device.
4. A method according to claim 2 wherein the sealant is delivered
to the junction region by way of a further capillary tube.
5. A method according to claim 4 wherein the capillarity of the
further capillary tube is greater than the capillarity of the
second fluid pathway.
6. A method according to claim 1 wherein the sealant is delivered
to the junction region by way of a sealant application
reservoir.
7. A method according to claim 6 wherein the second fluid pathway
has a stepped profile so as to form the sealant application
reservoir.
8. A method according to claim 6 wherein the sealant application
reservoir is formed by a further fluid pathway defined in the
device.
9. A method according to claim 8 wherein the sealant application
reservoir has a tapered profile.
10. A method according to claim 6 wherein the capillarity of the
application reservoir is less than the capillarity of the
volume.
11. A method according to claim 6 wherein the capillarity of the
application reservoir is greater than the capillarity of the second
fluid pathway.
12. A method according to claim 6 wherein the volume of the
application reservoir is greater than the volume of the volume.
13. A method according to claim 4 wherein the capillarity of the
volume is greater than the capillarity of the further capillary
tube.
14. A method according to claim 8 including a further pathway for
receiving excess sealant.
15. A method according to claim 14 wherein the second fluid pathway
has a capillary stop defined therein.
16. A method of forming a fluid tight seal between a first
substrate and a second substrate comprising the steps of:
maintaining said substrates in a given orientation and distance
with respect, one to another, so as to define a volume therebetween
which has a desired capillaric property; delivering a quantity of
sealant to a junction region of said substrates; causing or
permitting the sealant to flow into said volume, so as to achieve
capillary balance whereby only substantially sufficient sealant is
delivered to fill the volume; and causing or permitting the sealant
to cure or set.
17. A method according to claim 16 wherein the first substrate has
a first recess formed therein which, when the first substrate is
joined to the second substrate, forms a channel.
18. A method according to claim 16 wherein the second substrate has
a second recess formed therein which, when the first substrate is
joined to the second substrate, forms a channel.
19. A method according to claim 16 wherein the first substrate has
a stepped cross-section so as to define a reservoir with the second
substrate.
20. A method according to claim 16 wherein the second substrate has
a stepped cross-section so as to define a reservoir with the first
substrate.
21. A method according to claim 16 wherein a portion of the first
substrate is of a higher capillarity than surrounding portions
thereof in order to form a capillary stop.
22. A method according to claim 16 wherein a portion of the second
substrate is of a higher capillarity than surrounding portions
thereof in order to form a capillary stop.
23. A method according to claim 21 wherein the high capillarity
portion of one of the first and second substrates is adjacent the
channel.
24. A method according to claim 16 wherein the first and second
substrates are part of a micro-fluidic device.
25. A micro-fluidic device assembled using the method claimed in
claim 1.
26. A micro-fluidic device assembled using the method claimed in
claim 16.
27. (canceled)
22. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of forming a fluid
tight seal and a device so formed.
BACKGROUND ART
[0002] A rapid means of forming a reliable and permanent fluid
tight seal between a micro-fluidic chip and external fluidic
circuitry is sought. FIG. 1 illustrates how this may be achieved. A
micro-fluidic device (10) has an inlet channel (12) into which a
capillary (14) is inserted in order to make fluidic connection to
the channel (12). The inlet channel (12) communicates with a
channel (20) which leads into the device. In the prior art, sealant
(16) is applied to the exterior of the device (10) at the opening
of the inlet channel (12), and flows by capillary action into the
seal space (18) between the capillary and the channel walls.
Ideally the flow ceases when the meniscus of the sealant reaches
the end of the seal space, forming a surface (17). However, in
practice, as the dimensions involved are so small, a relatively
large volume of sealant tends to be deposited at the opening of the
inlet channel (12). This forms a surface (19), whose precise shape
depends on the wetting properties of the sealant to the outside of
device (10) and the capillary (14), but will be generally gently
curved owing to the volume of material it contains. Capillary
action tends to draw the sealant past the end of the capillary (14)
into channel (20) and/or the interior of the capillary, forming
menisci at positions (21) and (23). This problem arises from lack
of control of capillary action at the area of application of the
sealant (16). Thus the flow of sealant needs to be controlled.
[0003] A method of connecting a capillary to a micro-fluidic chip
is described in U.S. Pat. No. 5,890,745 (Kovacs). A capillary is
inserted into a channel whose diameter is only very slightly larger
than the capillary. Sealing of the capillary in the channel is
achieved either by close fit alone, by a compressive plastic
component mounted on the chip, or by contraction of the capillary
at low temperature before insertion into the channel. In a
preferred embodiment, adhesive is used to hold the capillary in
place. However, no means are provided to control the flow of this
sealant, and so the success of this method is likely to depend
critically on maintaining close tolerance between the capillary and
the channel. Also, the method will be awkward to implement for
multi-way connections.
[0004] U.S. Pat. No. 5,985,086 (Peall) discloses a method of
sealing an optical fibre into a v-groove etched in a silicon wafer
by means of adhesive wicked from reservoirs remote from the fibre,
to a region where it contacts the fibre and effects a seal. The
specification is clear in that a measured amount of adhesive is
applied, and that the reservoir and the wicking channels are
designed to convey the sealant to the sealing site, rather than to
control the amount that is applied. As such, the operation still
needs careful control and therefore is open to error.
[0005] Our earlier UK patent application (GB9625491.7) describes a
method of using capillary connections inserted into inlet channels
formed in the end surface of a chip. Various means were described
of sealing the capillaries into the chip, including flowing sealant
into the space between the capillary and the inlet channel
(referred to herein as the "seal space"). In order to prevent
excess sealant entering and flowing past the end of the capillary,
control over the flow or location of the sealant is necessary. Our
earlier patent application described methods involving active
control by an operator, for instance application of closely
measured amounts of sealant, or observation to determine when
sufficient amounts of sealant had been applied. Also described was
the use of blocking methods, such as a removable insert inside the
capillary or application of ultra-violet light to stop the flow of
a UV-curable adhesive at the end of the capillary. These methods
were suitable for handling of one capillary at a time, and are
potentially overly time consuming for multi-way connections. The
present invention overcomes these drawbacks and provides a method
of applying the correct amount of sealant without accurate
pre-measurement of the amount or monitoring by the operator.
[0006] An aim of the invention is to provide a method of forming a
fluid tight seal which allows the amount of sealant to be carefully
controlled. Another aim of the invention is to provide a method of
forming a fluid tight seal that is suitable for forming multi-way
connections between components.
DISCLOSURE OF INVENTION
[0007] According to a first aspect of the invention there is
provided a method of forming a fluid tight seal between a first
fluid pathway and a second fluid pathway comprising the steps of:
defining a volume between an outer surface of the first pathway and
an inner surface of the second pathway; maintaining said surfaces
in a given orientation and distance with respect, one to another,
so as to achieve a desired capillaric property therebetween;
delivering a quantity of sealant to a junction region of said
surfaces; causing or permitting the sealant to flow into said
volume, so as to achieve capillary balance whereby only
substantially sufficient sealant is delivered to fill the volume;
and causing or permitting the sealant to cure or set.
[0008] Preferably the first fluid pathway is a capillary tube. The
second fluid pathway is preferably disposed within a micro-fluidic
device, and is known as the inlet channel. The inlet channel may be
of any cross-section, but is advantageously close in size and shape
to the capillary tube.
[0009] The device may have a rectangular cross-section having first
and second major (i.e., upper and lower) surfaces. However, the
device may be of any other suitable shape. The inlet channel
preferably extends from a side surface of the device into the
device, parallel to the upper and lower surfaces. However, the
inlet channel could equally well be formed so that it extends from
the upper (or lower) surface of the chip so that it is
perpendicular to this surface.
[0010] The sealant may be delivered to the junction by way of a
further capillary tube, or applicator. The applicator may be used
to meter a volume of sealant as well as its delivery. To this end,
the applicator might have variable capillarity along its length,
for example a capillary break at a certain point, which means that
a controlled volume of sealant can be filled into it by capillary
action and the allowed to flow out into the seal space. Such a
capillary break might be formed by a sudden widening of the
applicator tube (the sealant is taken to wet the applicator), or by
a change in the inner surface of the applicator so as to change the
angle of contact. Alternatively, more than one capillary break
might be used to control flow of the adhesive under pressure: a
narrowing of the applicator might increase its capillarity to the
point where the seal space will no longer fill spontaneously. A
pressure increase applied to the applicator might then urge the
sealant past the capillary break and fill the seal space. Such an
arrangement might be used for sequential filling of a number of
seal spaces from a series of slugs of sealant and air in the
applicator tube. As a further alternative, a sponge applicator
might be used to deliver an accurately metered amount of
sealant.
[0011] Preferably the capillarity of the applicator is greater than
the capillarity of the second fluid pathway, and the capillarity of
the volume (or seal space) is greater than the capillarity of the
applicator.
[0012] In an alternative aspect of the invention, the sealant may
be delivered to the junction region by way of an application
reservoir. The application reservoir may be formed by the second
fluid pathway having a stepped profile so that the volume of the
second fluid pathway is larger towards the edge of the device. The
reservoir and inlet channel again might be of any appropriate cross
section, but advantageously are close in size and shape to the
first fluid pathway. Preferably the volume of the application
reservoir (whatever its shape) is greater than the volume of the
seal space.
[0013] Alternatively, the application reservoir may be formed by a
further fluid pathway defined in the device. This further fluid
pathway is preferably defined in one of the major surfaces of the
device so that it is substantially perpendicular to the second
fluid pathway. The reservoir might have parallel sides, a stepped
profile, or a tapering profile. The stepped or tapering reservoir
has the advantages that a larger opening (or port) into the device
is provided so that it is more easily filled, but that the smaller
dimensions needed to achieve the capillary control of filling are
provided further within the structure. Initially also the capillary
force opposing wicking is small, and so the seal space fills
quickly. As the level of sealant in the port lowers, the minimum
dimension in the reservoir profile decreases and so the opposing
force increases, slowing the wicking of the sealant in to the inlet
channel.
[0014] Preferably the capillarity of the application reservoir is
less than the capillarity of the volume. The capillarity of the
application reservoir is preferably greater than the capillarity of
the second pathway.
[0015] Obviously the concept of a stepped or tapering reservoir
might also be applied to the capillary inlet arrangement where the
reservoir is formed by the shape of the second fluid pathway.
[0016] A variation of the previous embodiment of the invention uses
the principle of a plurality of narrow pathways through which, or
past which, the sealant has to flow in order to reach the seal
space. The region of the reservoir communicating with the seal
space can be made to have a number of parallel narrow flow channels
that together can sustain a significant flow rate, but individually
have a high degree of capillarity. This might be achieved, for
example, by using a porous filter in the lower portion of the
reservoir.
[0017] Once flow has been established through the porous filter
from the reservoir (the flow being driven by capillarity in the
seal space), it will continue until the meniscus of the sealant
reaches the porous filter, where a number of individual much
smaller menisci will form, each with large capillarity, so stopping
the flow. This is particularly advantageous when there is a
tendency for the sealant to wick on beyond the end of the capillary
into the channel, despite the overall capillarity of the channel
being lower than that of the reservoir. This is likely to happen if
the channel cross-sections have sharp angle corners, for example,
square, semicircular or triangular channels. The porous filter
might be fabricated from a filter membrane or a micro fabricated
stature, for example micro-fabricated mesh.
[0018] The function will be the same if the sealant does not
actually flow through the structure, but rather that the meniscus
of the sealant encounters a series of narrow channels as is
retreats towards the end of the reservoir. The overall effect is to
introduce a region of higher capillarity than the seal space in
between the reservoir and the seal space which is more effective
than that of the outer end of the seal space in stopping the
flow.
[0019] The reservoir may also be used as a metering device for the
amount of sealant applied. The amount of sealant applied relies on
the rate of exit of sealant from the reservoir being lower than the
rate at which it is applied to the reservoir. The use of balance of
capillarity to stop the process means that the precise amount of
sealant applied is immaterial. However, a further embodiment of the
invention may be provided to control the rate at which the sealant
leaves the reservoir, or to halt it altogether until the reservoir
has been filled, and then to allow it to start. Such control can be
provided by means of a capillary stop or impedance at the end of
the reservoir between the reservoir and seal space. An increase in
the minimum dimension of the seal space near the end of the
reservoir would provide a stop, and a constriction in the seal
space would provide a limitation through viscosity of the rate of
outflow.
[0020] Activation past the capillary stop night be by for example a
positive pressure pulse applied to the reservoir inlet, a negative
pressure pulse applied to a port to reduce the pressure inside the
seal space, or a temperature change to change the degree of wetting
of the reservoir or the surface of the seal space, to expand the
sealant past the stop or to expand a gas bubble included in the
sealant in the reservoir for this purpose.
[0021] The methods of the invention may also include a further
pathway (known as an overflow or run-off channel) for receiving
excess sealant.
[0022] According to another aspect of the invention there is
provided a method of forming a fluid tight seal between a first
substrate (or component) and a second substrate (or component)
comprising the steps of maintaining said substrates in a given
orientation and distance with respect, one to another, so as to
define a volume therebetween which has a desired capillaric
property; delivering a quantity of sealant to a junction region of
said substrates; causing or permitting the sealant to flow into
said volume, so as to achieve capillary balance whereby only
substantially sufficient sealant is delivered to fill the volume;
and causing or permitting the sealant to cure or set.
[0023] A micro-fluidic chip may be formed from a first component
and a second component. The first and/or second components may have
a first recess formed therein which, when the first component is
joined to the second component, forms a channel. The first and
second components are joined by adhesive which is introduced into
the seal space (i.e., volume) between the components from a
reservoir at the edge of the device. The reservoir is formed simply
by a recess in the first and/or second components. The reservoir
may be formed by the first and/or second component having a stepped
cross-section. The reservoir may be at edge of the device, or
formed in one of the major surfaces of the device.
BRIEF DESCRIPTION OF DRAWINGS
[0024] A number of embodiments of the invention will now be
described with reference to the Figures, where:
[0025] FIG. 1 shows a method of forming a fluid tight seal,
according to the prior art;
[0026] FIG. 2 shows a cross-sectional view of a first embodiment of
the invention;
[0027] FIG. 3 shows a cross-sectional view of a second embodiment
of the invention;
[0028] FIG. 4 shows a cross-sectional view of a third embodiment of
the invention;
[0029] FIGS. 5a to 5d show the connection of a capillary to a
micro-fluidic device which is formed using an embodiment of the
invention;
[0030] FIGS. 6a to 6f shows various views of another embodiment of
the invention;
[0031] FIG. 7 shows a cross-sectional view of a further embodiment
of the invention; and
[0032] FIG. 8 shows a plan view of a micro-fluidic chip having a
metering device.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0033] A first embodiment of the invention is shown in FIG. 2, and
is a system which comprises an applicator with appropriately
designed capillary properties. The Figure shows a micro-fluidic
chip (10) which has a rectangular cross-section, the upper and
lower surfaces of the chip being longer than the side surfaces. The
chip (10) has an inlet channel (12) formed therein which extends
from a side surface of the chip into the chip, parallel to the
upper and lower surfaces. The inlet channel (12) communicates with
a channel (20) which leads further into the chip (10). The inlet
channel (12) is shaped and dimensioned to receive a capillary tube
(14). The diameter of the inlet channel (12) is larger than that of
the capillary tube (14) so that a space (18) (the seal space) is
left between the inlet channel and the capillary tube. The diameter
of the channel (20) is smaller than the diameter of the capillary
tube (14) so that the capillary tube is prevented from passing into
the channel (20).
[0034] To form a fluid tight seal between the capillary (14) and
the inlet channel (12), an applicator (22) filed with sealant (16)
is brought into contact with the end of the inlet channel. Sealant
(16) is allowed to flow out of the applicator (22) and into the
seal space (18). The applicator (22) is a capillary tube in its
simplest form, and has a capillary action which tends to retain
sealant (16) within it. However, the seal space (18) is designed to
have a greater capillarity than the applicator (22), so that
sealant (16) will be drawn out of the applicator and into the seal
space.
[0035] The capillarity of the applicator is also chosen to be
greater than that of the inlet channel (12) (or channel (20), if
the end of the capillary (14) is in contact with channel (20) and
this is of narrower minimum dimension than inlet channel (12)), so
that when the sealant (16) reaches the end of the seal space (18),
there is a net force opposing its continuing progress. In other
words, the meniscus inside the applicator (22) controls the force
which is opposing the filling force, rather than an uncontrolled
capillary force from the ill-defined meniscus (19) which is shown
in FIG. 1. In FIG. 2, residual menisci (11) are shown around the
interface between the end of the applicator (22) and the side
surface of the chip device (10). Capillary action tends to retain
sealant (16) inside the applicator (22), and thus will ensure that
the residual menisci (11) have lower capillarity than other parts
of the system.
[0036] A second embodiment of the invention is shown in FIG. 3. As
in the first embodiment of the invention, there is shown a
micro-fluidic chip (10) which has an inlet channel (12) formed
therein. The inlet channel is designed to accept a fluid connection
capillary (14), and communicates with a channel (20) which leads
into the chip (10). In this embodiment of the invention, the inlet
channel (12) has a stepped profile so that its radius, r.sub.R, in
the region where the inlet channel leads out of the chip (10) is
larger than its radius, r.sub.C, towards the inner region of the
chip (10), thereby forming an application reservoir (24). The
radius of the channel (20) is the same as the radius r.sub.C of the
inner region of the inlet channel (12).
[0037] To form a fluid tight seal between the capillary tube (14)
and the micro-fluidic chip (10), sealant (16) is introduced into
the application reservoir (24). The capillarity of the application
reservoir (24) is designed to be less than that of the seal space
(18), but greater than that of the channel (20). In this way, the
capillarity of the application reservoir (24), the seal space (18),
and the channel (20) control the application of the sealant. For
circularly symmetric channels (12,20), with an application
reservoir (24) and capillary (14) made of identical materials and
hence contact angles, the condition for the movement of sealant
(16) to be controlled via differences in capillarity is as follows:
(r.sub.c-r.sub.t)<(r.sub.R-r.sub.t)<r.sub.j<r.sub.c, where
r.sub.c is the diameter of the channel (20) and the inner region of
the inlet channel (12), r.sub.t and r.sub.j are the outer radius
and inner radius of the capillary (14), and r.sub.R is the diameter
of the application reservoir (24).
[0038] The condition for channels of other cross sections and for
differing contact angles will (all other parameters being equal)
depend on the order of the minimum dimension in the system. In
other words, the diameter of the seal space (18) is less than the
diameter of the application reservoir (24), which is less than the
diameter of the channels (12,20) beyond the capillary (14) and the
internal dimension of the capillary (14). The condition for the
size of the reservoir (24) is that its volume must be greater than
the volume of the seal space (18), and that the reservoir (24) can
be filled by an operator before the seal space (18) has filled
substantially. The preferred condition of operation is that the
operator can fill the reservoir (24), and the opposing force of the
menisci (17) and (25) will draw the sealant to the ends of the
capillary (14), where it will stop.
[0039] A single reservoir (24) and a single inlet channel (12) are
shown in FIG. 3. However, the same principle can be applied to a
number of channels and capillaries with a common reservoir (24),
provided that the volume of the reservoir is adequate for them all,
and that the minimum dimension of the reservoir maintains
capillarity greater than that of the channel (20). A preferable
arrangement for the reservoir is a rectangular shape with a height
close to that of the capillaries, with the capillaries and inlet
channels arranged side-by-side.
[0040] A third embodiment of the invention is shown in FIG. 4,
where the application reservoir (24) is formed in the upper surface
of the micro-fluidic chip (10). As in the aforedescribed
embodiments of the invention the chip (10) has an inlet channel
(12) formed therein which receives a capillary tube (14). The
application reservoir (24) leads to a parallel sided channel (34)
which in turn leads to the inlet channel (12). In order to form a
fluid tight seal between the chip (10) and the capillary (14),
sealant (16) is introduced into the application reservoir (24). The
sealant passes into die parallel sided channel (34) to the seal
space (18) between the inlet channel (12) and the capillary
(14).
[0041] As shown in FIG. 4, the application reservoir has a tapered
profile. This is advantageous as a larger opening into the chip
(10) is provided which is more easily filled with sealant (16), and
the smaller dimensions needed to achieve capillary control of the
sealant are provided at the base of the reservoir (24), leading
into the inlet channel (12). In addition, the capillary force
opposing wicking of the sealant into the seal space (18) is small
and so the seal space fills quickly. The parallel sided channel
(34) provides a region of constant high capillarity near the end of
the filling process, and so gives better control over the stopping
point of the sealant
[0042] As the level of sealant in the application reservoir (24)
decreases, the force opposing the movement of the sealant
increases, thereby slowing the wicking of the sealant into the
inlet channel (12). At its base, the application reservoir (24) has
a diameter such that its capillarity lies between that of the seal
space (18) and that of the channel (20) beyond the seal space,
thereby stopping the wicking of the sealant into the channel.
[0043] The aforedescribed embodiments of the invention describe the
concept of sealing a capillary tube (14) to a fluidic inlet channel
(12) of a micro-fluidic chip (10). This concept can also be applied
to the introduction of sealant into any other space, for example
the region between two components which are to be joined to form a
device. This gives an advantageous way of controlling the ingress
of adhesive between two flat components of a micro-fabricated
device.
[0044] Frequently, micro-fluidic devices are fabricated in more
than one part, with details on one fare which define channels or
other features, this face then being joined to another face to
close the features. The faces are held together by various means,
one of which is the ingress of liquid adhesive to the space between
the faces, this ingress driven by the capillarity of the space. In
the prior art devices, it is difficult to control the ingress of
adhesive closely--the amount which is taken into the space depends
on the stopping of the flow when the meniscus reaches a defined
boundary between the faces where the capillarity suddenly drops.
This may occur by increase of the minimum dimension of the space,
as happens at the boundary of an open channel feature, or by a
change in the contact angle at one or both of the faces, as might
be achieved by a change in the surface nature or the bulk nature of
the materials making up the faces. This may not be sufficient in
some cases, and there is a danger that the channels will fill and
blocks.
[0045] A fourth embodiment of the invention is shown in FIG. 5a.
This Figure shows a cross-section through part of a micro-fluidic
chip (10) formed from a first component (40) and a second component
(42). The first component (40) has a first recess (44) formed
therein which, when the first component (40) is joined to the
second component (42), forms a channel. The first (40) and second
(42) components are joined by adhesive (16) which is introduced
into the seal space (46) between the components (40,42) from a
reservoir (48) at the edge of the device. The reservoir (48) is
formed simply by a recess (50) in the first component (40).
[0046] The position of the adhesive (16) after capillary action has
reached equilibrium is determined by the minimum dimensions of the
pathways at the positions of the adhesive menisci (52) and (54),
and the amount of adhesive applied. The amount of adhesive applied
is determined by the volume of the reservoir (48), which is larger
than the volume of adhesive (16) intended to be wicked into the
seal space (46). The reservoir (48) is designed to fill quickly
relative to the movement of adhesive (16) out of the reservoir into
the seal space (46). To this end, the reservoir (48) may have
features formed within it to speed the ingress of adhesive and to
render wall effects less important, giving a more uniform front to
the adhesive as it enters the seal space. Grooves in one or more
walls of the reservoir (48) are an example of such a feature.
[0047] FIG. 5b shows an alternative arrangement which is
advantageous when the adhesive (16) has a significant viscosity.
The seal space (46) is provided with features which act to ease the
flow of adhesive (16) through it, optionally directing the flow
preferentially into certain regions, while ensuring that it comes
to a capillary stop where it is required to. The closer the spacing
between the components (40,42), i.e., the narrower is seal space
(46), the more marked will be the capillary stop when the adhesive
reaches the channel (44). However, if the adhesive is viscous, a
narrow space will fill only slowly from a remote reservoir. Seal
space (46) is therefore provided with regions (56) of lower
capillarity and concomitant lower viscous impedance, and regions
(58) of higher capillarity next to the channels (44) where a good
seal and a defined capillary stop are required. Regions (56) might
be channels which act to direct flow of adhesive (16) from the
reservoir (48) to areas where it is required. Alternatively,
regions (56) might be larger so as to form an open sealing area
rather than a narrow channel; the sealing area might be subdivided
by ribs or similar structures to form adjoining areas which fill in
a pre-ordered manner from one or more reservoirs. The capillary
stop is still provided by the balance of capillarity at the
interior meniscus (52) and the exterior meniscus (54).
[0048] An example of an application of this embodiment of the
invention is shown in FIG. 5c and FIG. 5d. FIG. 5c shows a
capillary (80) connected to a plug component (82). The capillary is
inserted into a channel (84) formed in the plug component (82)
leaving a short length (88) of capillary protruding from the end of
the plug. Sealant (16) is then wicked into the seal space (86)
between the plug (82) and the capillary (80), and subsequently
hardened. The end length (88) of the capillary is then removed to
form a plug assembly (90). Typically the sealant (16) will form a
reproducible meniscus around the capillary (80) and so the profile
of the surface (89) which is formed when the end length (88), of
the capillary (80) is removed will be predictable, and can be
accommodated into the design of the opening in the device that
receives it. Alternatively the surface (89) of the plug component
might easily be ground or polished to be largely flat.
[0049] The plug assembly (90) so formed is then connected to a
micro-fluidic device (10), as shown in FIG. 5d. The device (10) has
an opening (or socket) formed to be a close fit to the plug
assembly (90). A seal space is formed between the surfaces (94) and
(96) of the socket and plug respectively. This seal space is filled
with sealant in the controlled manner of the invention. The
surfaces form a reservoir (98) with a known capillarity which is
designed to be intermediate between the capillarity of the space
(100) between the end of the plug and the recess near the channel
(93) in the device. In this way the correct amount of sealant is
drawn into the seal space. Optional projections (104) might be
provided on the base of the plug to control the capillarity of the
space (100). Also projections or surface profiling might be
provided on one or both of the surfaces (94, 96) to control the
movement of sealant (16) in the space between them. In this way, a
reliable permanent attachment is made between the capillary (80)
and the device (10).
[0050] While the connection of a single capillary to a device has
been described, a similar connection might use multiple capillaries
in any practical geometric arrangement. The capillaries would be
attached first to the plug, and then the whole multi-way plug
sealed in one process into the device port. Devices might be
connected together by ready-formed plug-to-plug multi-way capillary
`cables`. The means of sealing a capillary into a ready formed
component as in FIG. 5c might be applied to a socket component
also, allowing the seal structure and method in FIG. 5d to join two
capillary `cables` end-to-end.
[0051] In situations where overfilling of a reservoir might occur,
it is advantageous to provide run-off channels to accommodate
excess sealant. FIG. 6a shows a cross sectional view, and FIGS. 6b,
6c and 6d plan views, of another embodiment of the invention which
incorporates this idea In FIGS. 6a to 6d, there is shown a device
(10) formed of components (40) and (42), which define a reservoir
(48) for sealant (16). The device also has a second channel (60)
which communicates with the reservoir (48), and has a vent (62) at
its other end. The reservoir (48) leads to a channel or seal space
(46) into which sealant is to be moved by capillary action. Sealant
(16) is applied to the inlet of the reservoir (48) and wicks into
the reservoir, and then into channel (60).
[0052] In the case that the reservoir (48) opens to the edge of the
device (10), the sealant will tend to form a meniscus (66) which
protrudes from the reservoir and from the edge of the device, as
shown in FIG. 6b. This is shown by way of example only, and it is
likely in preferable embodiments that sealant will be dispensed
into a specifically provided receiving area into which the
reservoir (48) opens. As the sealant moves into the reservoir (48)
under capillary action, it encounters the start of the channel or
seal space (46) which has a greater capillarity than the reservoir,
and moves quickly into this, the driving force being the difference
in capillarity at the seal space meniscus (68) and that at the
reservoir meniscus (66). The minimum dimension of channel (60) is
smaller than that of the reservoir (48), so when the sealant in the
reservoir is emptied into the seal space, the greater capillarity
in channel (60) means that that a portion of sealant is left in
situ. The system provides a competition between tide rate of flow
into the seal space and that into the side channel, so acting to
meter the amount that flows into the seal space.
[0053] Preferably the system includes a capillary break, which is
shown in FIG. 6a as a narrowing of the channel (72). Once the slug
of sealant (16) in the reservoir (48) has been separated into two
by detachment of the main flow from the excess in the channel (60),
the capillary break will act to halt the main flow of sealant into
the seal space at the break as shown in FIG. 6d. This allows an
accurate amount of sealant to enter the seal space.
[0054] An embodiment preferred for some applications is shown in
cross-section in FIG. 6e, and in plan view in FIG. 6f. Here, the
overflow channel (60) is provided at the start of the seal space.
The greater capillarity of the seal space means that that will fill
first. Excess sealant is then drawn into the overflow channel (60).
The vent channel (62) might be designed to end up filled with
sealant, or a capillary stop might be provided to halt the flow at
the end of the channel (60). In this and previous embodiments, the
vent channel (62) might be as shown, or might exit through another
face of the device (10).
[0055] FIG. 7 shows an alternative embodiment of the invention,
suitable for use in sealing capillary connections in place, in
which a runoff channel (30) is provided As before, when sealant is
placed in the port (24) it wicks into both the seal space (18) and
into channel (30). The processes will compete, and the dimensions
of channel (30), port (24) and the seal space (18) are chosen so
that the effect of channel (30) is to lower the level of sealant in
the port to below the junction of the port and channel (30) in a
time less than that taken for sealant to reach the end of the seal
space, preferably much less. In this manner, the amount of sealant
which will fill the seal space is set approximately by the
dimensions of the lower part of the port, the excess sealant being
taken up by the ran-off channel (30). Correct choice of the
dimensions of the channels will make this a close
approximation.
[0056] A metering device can be incorporated in the surface of the
micro-fluidic chip (10) as in FIG. 8, allowing an accurate amount
sealant (16) to be metered from an unmeasured dispensing process,
and then injected by transient pressure past a capillary stop into
the seal space (18). The metering apparatus (150) is formed in the
surface of a substrate (152). An application recess (154)
communicates with a metering channel (156) and one or more overflow
channels (158). The channel (156) has at its other end a capillary
stop (114), past which a channel leads to a capillary fill port
(160). Capillarities in the design are such that the capillarity of
the capillary stop (114)<application recess (154)<that of the
overflow channel (158)<the metering channel (156)<the
capillary fill port (160). This means that when liquid is applied
to recess (154), it flows preferentially into channel (156) until
it reaches the capillary stop, with meniscus position (124), then
into overflow channel(s) (158), leaving a meniscus that may lie
within the region of the application recess as shown in FIG. 8, or
may be at the ends of the channels where they open into the recess.
This leaves a metered amount of liquid in channel (156) and the
remainder in channel(s) (158). Application of positive pressure to
the application recess, for example by pressing a semi gas-tight
cover placed over the recess, then moves the meniscus (124) past
the capillary stop; allowing channel (12) to empty into the port
(160), and moving the meniscus(es) (162) further into the overflow
channels. Thereby a metered amount of material is introduced to
port (160).
[0057] In summary, the present invention controls capillary forces
at or near the point of application of the sealant to reduce or
prevent the tendency of a meniscus to flow beyond a desired
stopping point This can be achieved in three ways, all within the
scope of the invention. The sealing system can be designed to
control the movement using opposing capillary forces, filling from
a reservoir of lesser capillarity than the space between the
capillary and the channel wall, but greater capillarity than the
channel beyond the end of the capillary; the seal space might fill
in competition with a second space, the capillarity of the second
space being less than that of the seal space but greater than that
of the channel beyond the capillary, or the amount of sealant
needed might be metered by a capillary fill structure before it is
introduced to the seal space. By each of these methods the sealing
process is made either less dependent, or completely independent of
the amount of sealant initially applied, and is self-terminating,
i.e., no observation or control of the process by an operator is
needed. This makes the seal process much easier and more reliable
and no longer is the quality of the seal dependent upon the volume
of sealant supplied because this volume is self-regulating.
[0058] An advantage of the invention is that it provides a means of
accurately controlling the movement of and the amount of adhesive
introduced into a micro-fluidic device, formed from more than one
component fixed together, under the influence of capillary
action.
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