Method for securing a microsieve to a support member

A method is provided for securing a metallic microsieve which comprises; PA0 (a) inserting a metallic microsieve within the well of a frame-like support member, at least a portion of the upper edge of the well being fabricated from a fusible material and the height of the well wall being greater than the thickness of the microsieve; PA0 (b) directing a laser beam against a point on the upper edge of the well to melt fusible material in contact with the laser beam; PA0 (c) permitting the laser-molten fusible material to travel down the wall of the well and contact the edge of the microsieve; and, PA0 (d) permitting the laser-molten fusible material in contact with the edge of the microsieve solidify thereby forming a retaining member which secures the microsieve to the support member.

BACKGROUND OF THE INVENTION 
This invention relates to a method for securing an extremely thin metal 
structure possessing a grid-like array of minute, closely spaced, 
precisely dimensioned apertures to a support member or carrier and the 
resulting supported microsieve. 
Such an apertured metal structure, hereinafter referred to as a 
"microsieve", is especially useful in sorting and sieving objects of only 
a few microns in size. One such microsieve, designated a "cell carrier", 
is described in Spanish Pat. No. 522,207, granted June 1, 1984, and in 
commonly assigned, copending U.S. patent application Ser. No. 550,233, 
filed Nov. 8, 1983, the disclosure of which is incorporated by reference 
herein, for classifying biological cells by size. The cell carrier is 
prepared employing a modified photofabrication technique of the type used 
in the manufacture of transmission electron microscope grids. The cell 
carrier is on the order of only a few microns in thickness and possesses a 
numerically dense pattern of minute apertures. Even with the exercise of 
great care, the very delicate nature of the cell carrier makes it 
difficult to manipulate, for example, to insert it in a holder of the type 
shown in aforesaid U.S. patent application Ser. No. 550,233, without 
causing it appreciable damage, frequently in the form of a structural 
deflection or deformation which renders it useless for its intended use. 
Laser-welding is a known technique for selectively fusing adjacent surfaces 
of the same, e.g., thermoplastic, material. Reference may be had in this 
respect to the disclosures of U.S. Pat. Nos. 3,974,016; 4,029,535; 
4,069,080; 4,224,096; and, 4,461,947. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method and means for 
securing a metallic microsieve to a fusible support member. 
It is another object of the invention to provide a laser procedure for 
securing a metallic microsieve to a fusible support member. 
It is still a further object of the invention to provide a metal microsieve 
which is secured within a well defined within a support means with a 
precise planar disposition of the microsieve within the well. 
These and other objects of the invention are readily achieved by the method 
for securing a metallic microsieve to a support member which comprises: 
(a) inserting a metallic microsieve within the well of a frame-like support 
member, at least a part of the upper edge of the well being fabricated 
from a fusible material and the height of the well wall being greater than 
the thickness of the microsieve; 
(b) directing a laser beam against a point on the upper edge of the well to 
melt fusible material in contact with the laser beam; 
(c) permitting the laser-molten fusible material to flow down the wall of 
the well and contact the edge of the microsieve; and, 
(d) permitting the laser-molten fusible material in contact with the edge 
of the microsieve to solidify thereby forming a retaining member which 
secures the microsieve to the support. 
Employing the foregoing method, it is possible to securely mount a very 
delicate metallic microsieve within its holder without disturbing the 
planar disposition of the microsieve and without subjecting the microsieve 
to any appreciable damage which would interfere with or even destroy its 
proper functioning.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIGS. 1(a) and 1(b), a representative section 1 of a known type 
of microsieve which is adapted for use as a biological cell carrier 
possesses numerous closely spaced apertures 2 arranged in a matrix-like 
pattern of rows and columns along axes X and Y, respectively. This 
arrangement makes it possible to unambiguously identify the position of 
any one aperture in terms of its X and Y coordinates in the plane of the 
carrier. The number of apertures is selected with the number of biological 
cells to be carried in mind. For example, with 100 apertures per row and 
column, there will be provided a total of 10,000 apertures to carry up to 
10,000 cells. Microsieve 1 can be round, square, rectangular, etc., in 
configuration and can be fabricated from any suitable material, for 
example, a metal such as copper, gold, nickel, silver, etc., or metal 
alloy. The shape of apertures 2 enables biological cells of preselected 
dimensions to be effectively held to the microsieve by applying means, 
such as a pressure difference between the upper and the bottom side of the 
carrier, or electromagnetic forces. To first separate a particular group 
of cells from cells of other groups, microsieve 1 is chosen to have 
apertures of sizes so that when the matter, for example, blood, containing 
the various cell groups is placed thereon most, if not all, of the 
apertures become occupied by cells of the group of interest with each 
aperture containing one such cell. Thus, the apertures can be sized to 
receive, say, lymphocytes of which there are two principal sizes, namely, 
those of 7 microns and those of 10-15 microns, with the former being the 
cells of particular interest. To capture and retain the smaller size 
lymphocytes at the upper surface or side 1t of microsieve 1, apertures 2 
will have a cross-sectional diameter of about 6 micrometers. In this way, 
a lymphocyte from the desired population of cells can easily enter an 
aperture but once it has occupied the aperture, it cannot pass out of the 
bottom 1b of the microsieve. 
The dimensions of microsieve 1 are necessarily very fine, both the width 
and depth of apertures 2 being on the order of only a few microns. 
Consequently, the microsieve is extremely delicate and vulnerable to 
damage employing conventional tools/equipment to place it in, and secure 
it to, its associated holder. 
The present invention is illustrated in the side elevational views of FIGS. 
2(a), (b) and (c) illustrating the various steps of the method. 
As shown in FIG. 2(a), microsieve 10 is inserted in the well 20 of a 
frame-like support member 30 fabricated in its entirety from a 
thermoplastic material such as polyethylene, polypropylene, polystyrene, 
polycarbonate, polyacrylate, etc. Well 20 is defined by a central bore 40 
possessing a shoulder 50 and a wall 60. The width, or height, of 
microsieve 10 is somewhat less than the height of wall 60. In FIG. 2(b), a 
laser beam is directed against the upper edge 70 of the wall 60 of support 
member 30 causing a portion of said support member to melt and flow under 
the influence of gravity upon a peripheral edge 80 of microsieve 10 to 
form a bead-like retaining member 90 when cooled to the solidifying 
temperature of the polymeric substance and which secures microsieve 10 to 
support member 30 as shown in FIG. 2(c). 
While support member 30 can be entirely fabricated from a material which 
fuses under the laser beam directed thereon, it is, of course, within the 
scope of the invention to provide a section of material applied to, or as 
part of, support member 30 which alone possesses this fusible quality. 
It is also within the scope of this invention to continuously rotate the 
laser beam, or, preferably, the support member, so that a continuous bead 
of molten material flows upon the upper circumferential edge of the 
microsieve forming a correspondingly continuous retaining member. Two or 
more laser beams spaced equidistant from each other can be directed upon 
upper edge 70 of well 60 in this embodiment of the invention. Where a 
plurality of laser beams are employed, either they or the support member 
can be sequentially rotated to different sites along upper edge 70 with 
the result that a number of equidistant individual retaining members will 
be formed. 
In a preferred embodiment of the invention, microsieve 10 is inserted in 
the well 20 of support member 30 by a manipulating device which employs a 
vacuum to retain a single microsieve 10 to itself until positioned 
immediately over said well whereupon release of the vacuum permits the 
microsieve to gently fall in place.