U.S. patent application number 15/546270 was filed with the patent office on 2018-01-11 for method for thermally drawing nanocomposite-enabled multifunctional fibers.
This patent application is currently assigned to THE REGENTS OF THE UNIVERSITY OF CALIFORNIA. The applicant listed for this patent is THE REGENTS OF THE UNIVERSITY OF CALIFORNIA. Invention is credited to Injoo Hwang, Xiaochun Li, Jingzhou Zhao.
Application Number | 20180010266 15/546270 |
Document ID | / |
Family ID | 56544185 |
Filed Date | 2018-01-11 |
United States Patent
Application |
20180010266 |
Kind Code |
A1 |
Li; Xiaochun ; et
al. |
January 11, 2018 |
METHOD FOR THERMALLY DRAWING NANOCOMPOSITE-ENABLED MULTIFUNCTIONAL
FIBERS
Abstract
A method of thermally drawing fibers containing continuous
crystalline metal nanowires therein includes forming a preform
comprising an inner core and an outer cladding, wherein at least
one of the core and cladding has nanoelements dispersed therein.
The preform is drawn through a heated zone to form a reduced size
fiber. A second preform is then created from a plurality of fibers
created from the reduced size fiber. The second preform is then
drawn through the heated zone to form an elongated fiber containing
continuous crystalline metallic nanowires therein having a maximum
cross-sectional dimension of less than 100 nm. Optionally, a third
or additional preforms are created from fibers made from the
previous thermal drawing operation that are then drawn through the
heated zone to form a fiber containing even smaller crystalline
metal continuous nanowires therein. In some embodiments, only a
single pass through the heated zone may be needed.
Inventors: |
Li; Xiaochun; (Manhattan
Beach, CA) ; Zhao; Jingzhou; (Los Angeles, CA)
; Hwang; Injoo; (Los Angeles, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THE REGENTS OF THE UNIVERSITY OF CALIFORNIA |
Oakland |
CA |
US |
|
|
Assignee: |
THE REGENTS OF THE UNIVERSITY OF
CALIFORNIA
Oakland
CA
|
Family ID: |
56544185 |
Appl. No.: |
15/546270 |
Filed: |
January 21, 2016 |
PCT Filed: |
January 21, 2016 |
PCT NO: |
PCT/US16/14262 |
371 Date: |
July 25, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62110363 |
Jan 30, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D02G 3/367 20130101;
B21C 3/08 20130101; D06M 11/42 20130101; D06M 11/83 20130101; B21C
37/047 20130101 |
International
Class: |
D02G 3/36 20060101
D02G003/36; D06M 11/83 20060101 D06M011/83; D06M 11/42 20060101
D06M011/42 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND
DEVELOPMENT
[0002] This invention was made with Government support under award
number 1449395, awarded by the National Science Foundation. The
Government has certain rights in the invention.
Claims
1. A method of thermally drawing fibers containing continuous
crystalline metal nanowires therein comprising: a) forming a
preform comprising an inner core comprising the crystalline metal
and an outer cladding, wherein at least one of the core and
cladding having nanoelements dispersed therein; b) drawing the
preform through a heated zone to form a reduced size fiber; c)
forming a second preform created from a plurality of fibers from
the reduced size fiber of (b); and d) drawing the second preform of
(c) through the heated zone to form another reduced sized fiber
having a continuous length exceeding one meter and containing
crystalline metal nanowires therein having a diameter less than 100
nm.
2. The method of claim 1, wherein the nanoelements comprise
nanoparticles, nanowires, nanoplates, nanoflakes, or
nanowhiskers.
3. The method of claim 1, further comprising forming a third
preform created from a plurality of fibers of (d) and drawing the
third preform through the heated zone to form another reduced sized
fiber having a continuous length exceeding 1 meter and containing
crystalline metal nanowires therein having a diameter less than 100
nm.
4. The method of claim 3, further comprising forming one or more
additional preforms created from a plurality of fibers formed by
the third preform and drawing the one or more additional preforms
through the heated zone to form another reduced sized fiber having
a continuous length exceeding 1 meter and containing crystalline
metal nanowires therein having a diameter less than 100 nm.
5. The method of claim 1, wherein the nanoelements have a diameter
or major cross-sectional dimension within the range of 1 to 100
nm.
6. The method of claim 1, wherein the nanoelements comprises a
metal or ceramic.
7. (canceled)
8. The method of claim 1, wherein the core comprises one of gold,
platinum, or silver.
9. The method of claim 1, wherein the cladding comprises a polymer
or glass.
10. (canceled)
11. The method of claim 1, further comprising sintering the reduced
sized fiber having metal nanowires therein.
12. The method of claim 1, further comprising cutting the fiber,
wherein the cut fiber has a distal end and a proximal end and the
diameter of the distal end is << the diameter of the proximal
end.
13. A method of thermally drawing a fiber containing crystalline
metal nanowires therein comprising: forming a preform comprising an
inner core having a plurality of individual metal wires surrounded
by an outer cladding, wherein at least one of the inner core and
cladding comprise nanoelements dispersed therein; and drawing the
preform through a heated zone to form a reduced size fiber having a
length of at least one meter and containing a plurality of
continuous crystalline metal nanowires therein having a maximum
cross-sectional dimension less than 100 nm.
14. The method of claim 13, wherein the nanoelements comprise one
or more of nanoparticles, nanowires, nanoplates, nanoflakes, or
nanowhiskers.
15. The method of claim 13, wherein the nanoelements have a
diameter or major cross-sectional dimension within the range of 1
to 100 nm.
16. The method of claim 13, wherein the nanoelements comprises a
metal or ceramic.
17. (canceled)
18. The method of claim 13, wherein the core comprises one of gold,
platinum, or silver.
19. The method of claim 13, wherein the cladding comprises a
polymer or glass.
20. (canceled)
21. A nanoelectrode array comprising: a fiber having a distal end
and a proximal end, the fiber having a plurality of crystalline
metal nanowires each with a maximum cross-sectional dimension less
than 100 nm embedded therein and terminating at a plurality of
exposed electrodes at the distal end of the fiber, wherein the
distal end of the fiber has a diameter that is << than a
diameter of the proximal end of the fiber.
22. The nanoelectrode array of claim 21, further comprising a
circuit interface device coupled to the proximal end of the
fiber.
23. The nanoelectrode array of claim 21, wherein the distal end of
the fiber is disposed in a well, channel, or reservoir of a
microfluidic device.
24. The nanoelectrode array of claim 21, wherein the composition of
the metal nanowires changes along the length thereof with the
exposed electrodes comprising a first metal and a proximal portion
that is located proximally with respect to the exposed electrodes
comprises a second, different metal.
25. (canceled)
Description
RELATED APPLICATION
[0001] This Application claims priority to U.S. Provisional Patent
Application No. 62/110,363 filed on Jan. 30, 2015, which is hereby
incorporated by reference in its entirety. Priority is claimed
pursuant to 35 U.S.C. .sctn.119 and any other applicable
statute.
TECHNICAL FIELD
[0003] The technical field generally relates to methods and devices
used in the thermal drawing of fibers having nanoparticles
contained in the core, cladding, or both.
BACKGROUND OF THE INVENTION
[0004] Long fibers with embedded functionalities have great
potentials for numerous applications. Ongoing research on
ultra-long functional fibers include, for example, microstructured
photonic crystal fibers, optical micro/nano fibers, electronics in
fibers, fiber-based metamaterials, fibers as a novel platform for
sensing devices, studying chemical reactions, multi-material
functional fibers, and more recently fibers as a platform for
fabrication of nanowires and nanoparticles. The trend of combining
a multitude of functionalities into a single long fiber demands the
incorporation of a multiplicity of solid materials each with
disparate physical properties. Significant progress has been made
along this direction by thermal drawing of macroscopic
multi-materials preforms. Materials that have distinctively
different electrical and optical properties are integrated into a
single fiber by means of a preform-based thermal drawing technique.
Various electronic and optoelectronic devices have been realized in
kilometer long fibers. Large-scale fabrics woven from such fibers
have also been demonstrated. The capability of this technique
towards scalable nanofabrication has been explored, however, with
mixed success.
[0005] There exists a strong demand for low-cost and scalable
manufacturing methods and techniques of these fibers having
continuous nanowires contained therein. For example, such nanowires
may be made from generally inert metals such as gold (Au), silver
(Ag), and platinum (Pt) and used in short-haul electrical
interconnect bundles and front-end sensing/recording
multi-electrode arrays. Additional existing and emerging
applications include, for instance, high resolution
semiconductor/thin-film resistivity probes, electrical cellular
phenotyping, neural/cardiac electrical signal recording, etc.,
representing a large global commercial market. Despite the huge
potential economic and technological impact that high-volume
production of fibers with continuous metallic nanowires will bring
about, there has been little success for their reliable and
scalable manufacturing; mostly due to the fluid instability induced
by the low viscosity of molten metals and its large interfacial
energy with the cladding.
[0006] Thermal drawing is a very promising approach to realize
volume and low-cost nano-production of fibers with nanowires
without harnessing costly lithography. However, there are
significant scientific and manufacturing barriers that must be
overcome. A successful thermal drawing of fibers from a macro
preform made of multi-materials is fundamentally limited by at
least the following constraints: (1) the viscosity of the most
viscous constituent material (i.e. the cladding) should fall
between 10.sup.3.5 and 10.sup.7 Poise at the drawing temperature in
order for the process to be controllable. Amorphous materials, such
as glass and polymers, are typically used as the support (cladding)
to contain other core materials for cross-sectional stability; (2)
the softening or melting temperature of the core material(s) should
be lower than or overlap with the drawing temperature. If a
crystalline material is to be drawn, low vapor pressure is desired
and its boiling should be avoided; (3) chemical reactions between
the cladding and core materials should be avoided unless
intentionally designed (e.g., for in-fiber synthesis purposes); (4)
it is desired that cladding and core materials exhibit good
adhesion/wetting with each other during and after drawing to avoid
cracks, bubbles and fluid instability of the core material(s); and
(5) the cladding and core materials should have relatively
compatible thermal expansion coefficients in the temperature range
up to the drawing temperature.
[0007] These constraints pose severe challenges to find suitable
material combinations for multifunctional polymers or glass fibers
drawn with metal nanowires. At present, most crystalline metal
nanowires or even micro-wires are beyond the capability of current
manufacturing techniques, due to the fluid instability induced by a
low viscosity of molten metals and the large interfacial energy
with the cladding materials.
[0008] Fibers with metal microwires are routinely produced by
thermal drawing. The softening temperature of the cladding
determines the types of metals that can be drawn within. Low
melting temperature metals such as tin (Sn), bismuth (Bi), indium
(In), and their respective alloys have been thermally drawn in
polymer cladding (e.g., polyethersulphone (PES), polysulfone (PSU),
and polyethylenimine (PEI) at which the softening temperature is
below 300.degree. C.). The resulting metal fibers with rectangular
or circular cross sections have critical dimensions ranging from
tens to hundreds of micrometers; they are not in the nanometer
range. Fibers with metal microwires are also thermally drawn along
with other functional materials (usually semiconductors or
conductive polymers) and serve as conductive electrodes in
multi-material functional fibers, which are in turn utilized as,
for example, 1D photodetectors, thermal sensors, piezoelectric
transducers, chemical sensors, and capacitors. The smallest
diameter reported for metal-based wires that can be reliably drawn
into infinitely long arrays is around 4 .mu.m and is achieved from
a low melting temperature Sn.sub.0.95Ag.sub.0.05 alloy with PES
cladding. See Yaman et al., Arrays of indefinitely long uniform
nanowires and nanotubes, Nature Materials, vol. 10, pp. 494-501
(2011). Beads, discontinuities, and structural deformation were
observed upon further size reduction. Others have demonstrated that
thermally drawn functional fibers embedding in wires with diameter
approaching 1 .mu.m. See Tuniz et al., Fabricating Metamaterials
Using the Fiber Drawing Method, Journal of Visualized Experiments,
vol. 68, 2012.
[0009] Higher melting temperature metals such as Au, copper (Cu),
zinc (Zn), and their respective alloys require cladding materials
with higher softening temperatures. Pyrex glass (with softening
point .about.800.degree. C.) and fused silica (with softening point
.about.1700.degree. C.) are the materials of choice in this regime,
though not excluding their usage to draw metals with low melting
temperature. In fact, larger sized, metal microwire fabrication by
thermal drawing in a glass cladding, known as the Taylor-wire
process, has been in practice for decades. However, similar to the
case with polymer cladding, manufacturing reliability suffers as
the diameter of metal wire approaches less than 1 .mu.m. Au
microwires of 4 .mu.m diameter have been fabricated over a length
of several centimeters and this continuous length shrank to
.about.20 .mu.m as their diameter reduced to 260 nm. See Tyagi et
al., Plasmon Resonances on Gold Nanowires Directly Drawn in A
Step-index fiber, Optics Letters, vol. 35, pp. 2573-2575 (2010).
Pb--Sn alloys and Bi nanowires (drawn in glass cladding) with
diameter down to 50 nm were reported with a length reaching 1 m
with no experimental evidence provided to support their continuity
over the claimed 1 m drawn length. See Badinter et al., Exceptional
Integration of Metal or Semimetal Nanowires in Human-hair-like
Glass Fiber, Materials Letters, vol. 64, pp. 1902-1904 (2010).
Similarly, fabrication of discontinuous Cu.sub.0.93P.sub.0.07 with
a diameter of 500 nm has been reported using Pyrex glass cladding.
See Zhang et al., Mass-Productions of Vertically Aligned Extremely
Long Metallic Micro/Nanowires using Fiber Drawing
Nanomanufacturing, Advanced Materials, vol. 20, pp. 1310-1314
(2008). On the other hand, and again being consistent with that of
using polymer cladding, thermally drawn continuous Cu microwire of
4 .mu.m in diameter has been demonstrated which enables single mode
visible light guidance by metallic reflection in a photonic crystal
fiber See Hou et al., Metallic Mode Confinement in Microstructured
Fibres, Optics Express, vol. 16, pp. 5983-5990 (2008).
[0010] Fiber drawing via laser-based heat source pulling of short
pieces of Pt microwires has been used to fabricate quartz-sealed Pt
nanowires. The resultant fibers were tapered down to 10 nm in
diameter yet with a length of only 5 mm. See Percival et al.,
Laser-pulled Ultralong Platinum and Gold Nanowires, RSC Adv., vol.
4, pp. 10491-10498 (2014). Since such tapering method is confined
to a narrow (length) region of wires, it is hard to extend it to
pull wires that are tens of centimeters long. Alternatively, a
polyol process, which is the synthesis of metal-containing
compounds in ethylene glycol, was used to fabricate Ag nanowires
with length up to 230 .mu.m and diameter of 60-90 nm. See Araki et
al., Low Haze Transparent Electrodes and Highly Conducting Air
Dried Films with Ultra-long Silver Nanowires Synthesized by
One-step Polyol Method, Nano Research, vol. 7, pp. 236-245 (2014)
and Jiu et al., Facile Synthesis of Very-long Silver Nanowires for
Transparent Electrodes, J. Mater. Chem. A, vol. 2, pp. 6326-6330
(2014). Polyvinylpyrrolidone (PVP) and ethylene glycol (EG) were
used as the capping and reducing agent, respectively, which also
mandated a few more steps in manufacturing.
[0011] From the above-described literature citations, despite the
fact that reliable drawing of indefinitely long amorphous
semiconductor and polymer nanowires has been achieved, it is clear
that there exists a fundamental size limit to the diameter of
thermally drawn crystalline metal wires below which the metal wires
become inherently unstable and extremely difficult to control, if
not impossible, by current manufacturing techniques. Capillary
fluid instability poses severe challenges for scale-up
manufacturing processes. It is clear that there exists a
fundamental size limit to the diameter of thermally drawn metal
wires below which the metal wires become inherently unstable and
extremely difficult to control, if not impossible, by current
manufacturing techniques. There is a great and unmet need to break
the fundamental limits and technical barriers to enable a reliable
way to manufacture nanometer sized (diameter from tens to hundreds
of nanometers) crystalline metal wires with a continuous
length.
SUMMARY
[0012] In one aspect of the invention, a method of thermally
drawing fibers containing continuous crystalline metal nanowires
therein includes the steps of: (a) forming a preform comprising an
inner core comprising the crystalline metal and an outer cladding,
wherein at least one of the core and cladding having dispersed
therein nanoelements; (b) drawing the preform through a heated zone
to form a reduced size fiber; (c) forming a second preform created
from a plurality of fibers from the reduced size fiber of (b); and
(d)drawing the second preform of (c) through the heated zone to
form another reduced sized fiber having a continuous length
exceeding one meter and containing crystalline metal nanowires
therein having a diameter less than 100 nm. In alternative
embodiments, this last process may be repeated one or more times to
further reduce the size of the crystalline metal nanowires.
[0013] In another aspect of the invention, a method of thermally
drawing a fiber containing crystalline metal nanowires therein
includes forming a preform comprising an inner core having a
plurality of individual metal wires surrounded by an outer
cladding, wherein at least one of the inner core and cladding
comprise nanoelements dispersed therein. The preform is then drawn
through a heated zone (e.g., a furnace) to form a reduced size
fiber having a length of at least one meter and containing a
plurality of continuous crystalline metal nanowires therein having
a maximum cross-sectional dimension less than 100 nm.
[0014] In another embodiment, a nanoelectrode array includes a
fiber having a distal end and a proximal end, the fiber having a
plurality of crystalline metal nanowires each with a maximum
cross-sectional dimension less than 100 nm embedded therein and
terminating at a plurality of exposed electrodes at the distal end
of the fiber, wherein the distal end of the fiber has a diameter
that is << than a diameter of the proximal end of the
fiber.
[0015] In another embodiment, an article of manufacture includes a
fiber having a distal end and a proximal end, the fiber having a
plurality of crystalline metal nanowires embedded therein, each
nanowire having a maximum cross-sectional dimension less than 100
nm, wherein the fiber has a length exceeding 1 meter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIGS. 1A and 1B illustrate a flowchart illustrating one
illustrative method of thermally drawing fibers containing
continuous nanowires.
[0017] FIG. 1C illustrates a cross sectional view of a fiber
containing continuous crystalline metal nanowires therein.
[0018] FIG. 2 illustrates another flow chart illustrating a thermal
drawing process for creating a fiber according to one
embodiment.
[0019] FIG. 3 illustrates one exemplary method of creating a
nanocomposite core using accumulative roll bonding (ARB).
[0020] FIG. 4 illustrates a fiber embedded with crystalline metal
nanowires used for cell-based assays.
[0021] FIG. 5 illustrates an electrode-embedded fiber cell-based
assay platform.
[0022] FIG. 6A illustrates a schematic illustration of a preform
made from a Sn--Si nanocomposite core and polyethersulphone
(PES).
[0023] FIG. 6B illustrates a photograph of an experimentally drawn
tapered fiber within nanowires made from the Sn--Si
nanocomposite.
[0024] FIG. 6C illustrates a cross-sectional SEM image of the Sn
nanowire.
[0025] FIG. 6D illustrates a SEM image of the Sn nanowire after
chemical etching of the PES cladding.
[0026] FIG. 6E illustrates a pure Sn microwire with a diameter of
about 10 .mu.m after etching of the PES cladding.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0027] FIGS. 1A and 1B illustrate a flowchart illustrating one
illustrative method of thermally drawing a fiber 50 (seen in FIGS.
1B and 1C) containing continuous nanowires 52 (FIG. 1C). Referring
to FIG. 1A, the method starts with operation 100 where a core 2 is
formed with a cladding 4 surrounding the core 2. The core 2 is
typically a metal, metal alloy, or metal matrix. The core 2 may be
crystalline or amorphous material. The cladding 4 jackets or
surrounds the core 4 and is typically made from an amorphous
material such as a polymer, glass, or quartz, whose viscosity
reduces gradually as temperature goes above the material's glass
transition point. According to the invention, at least one or both
of the core 2 and cladding 4 having nanoelements 6 that are
incorporated therein. The nanoelements 6 may include nanoparticles,
nanowires, nanoplates, nanoflakes, nanowhiskers or other
geometries. The nanoelements 6 generally are nanometer sized
particles wherein their largest dimension is 100 nm or less. For
example, the nanoelements 6 may have a size (e.g., diameter) within
the range of 1-100 nm. While the nanoelements 6 may have any number
of geometries currently the most commonly produced nanoelements 6
are nanoparticles that have spherical shapes. Of course, other
shapes are contemplated to fall within the scope if the inventions
described herein.
[0028] The core 2 and cladding 4 are prepared separately and then
mechanically or thermally treated to yield a single nanocomposite
preform. As seen in operation 110 of FIG. 1A, a preform 8 is
fabricated, for example, by rolling the core 2 and cladding 4 in a
sheet 10. The sheet 10 may be formed from the same material used in
the cladding 4. The preform 8 is much larger and typically has a
diameter on the order of about 1 cm although the invention is not
limited by the size of the preform 8. For example, in FIG. 1A, the
sheet 10 may be formed from a glass-based cladding material that
forms a continuous phase with the one or more cores 2 embedded
inside (in this embodiment the cladding 4 is also glass-based).
Typically, vacuum consolidation may be performed in conjunction
with high temperatures to bond the cladding 4 to the core 2. While
FIG. 1A illustrates the preform 8 being formed with a single core 2
it should be understood that the preform 8 may be formed with a
plurality of cores 2 (e.g., stacked or bundled cores 2).
[0029] The nanoelements 6 may be incorporated into the core 2 or
cladding 4 using any number of solid and liquid state processing
methods used for the preparation of bulk nanocomposites. These
methods includes, for example, casting, extrusion, melting,
sonication (e.g., with ultrasound), high-shear mixing,
solution-based processes, severe plastic deformation,
electroplating, electro-codeposition, sintering, and the like. FIG.
3 illustrates the formation of a nanocomposite core 2 using
accumulative roll bonding (ARB) which is one method. In FIG. 3, in
this particular embodiment, the nanoelements 6 are dispersed within
a solution 16 using an ultrasonic transducer 18 or the like. For
example, the solution may include a solvent such as acetone and the
nanoelements 6 are silicon nanoparticles. The dispersion 20
containing the nanoelements 6 is then deposited on a metal foil 22
using a syringe 24 or other applicator. For example, the metal foil
22 may include Sn foil. Next, as seen in FIG. 3, another layer of
metal foil 22 is placed on the deposited dispersion 20 and the
entire structure is then introduced through a pair of rotating
rollers 26 with a small gap to compress the structure. In the
illustrated embodiment, this produces a Sn--Si nanocomposite core
2. A stock Sn--Si nanocomposite can also be produced by
electrocodeposition. Cold extrusion, casting, or other methods are
used to transform the stock Sn--Si nanocomposite into the desired
shape of the core 2. While FIG. 3 illustrates the formation of a
nanocomposite core 2 that includes a metal plus nanoelements 6, in
other embodiments, the nanoelements 6 are incorporated into the
cladding 4 material.
[0030] For the manufacturing of fibers 50 embedded with crystalline
metal nanowires (e.g., gold, platinum, or silver), suitable
nanoelements 6 (e.g., ceramics, oxides, carbides or borides) can be
mixed and dispersed into the metal core 2 in the macroscopic
preform 8 to increase the viscosity of the molten metal; it also
reduces the interfacial energy between the liquid metal of the core
2 and material of the cladding 4 to suppress the fluid instability
during thermal drawing, thus allowing further size reduction of the
metal core 2 to nanoscale sizes. The nanoelements 6 may also
include semiconductor materials, high temperature metals, carbon,
and ceramics. For metals, the presence of the nanoelements 6
suppresses the instability that would otherwise force the creation
of the metal in the nanowires 52 to break and form droplets;
thereby breaking the continuous nature of the elongate nanowire 52.
The presence of the nanoelements 6 enables long length fibers 50 to
be created that have long lengths (greater than 1 meter). As
explained herein, the prior art has not been able to generate
crystalline metal nanowires 52 having useful lengths (e.g., greater
than 1 meter).
[0031] Referring back to FIG. 1A, in operation 120, the preform 8
is then thermally drawn through a furnace 12. The furnace 12 is
part of a fiber drawing furnace which is well known and
commercially available. The fiber drawing furnace operates using a
furnace 12 that applies heat to the preform 8. The preform 8 is
typically loaded above the fiber drawing furnace and upon insertion
the preform 8 necks down on its own and the preform 8 end is
cutaway and fixed to a fiber drawing mechanism (e.g., spool, wheel
or the like). The fiber drawing furnaces enables one to control the
temperature of the furnace 12 which is set at a designated value
above the softening temperature of the glass part of the preform 8.
The speed of the downward linear motion may be controlled by speed
of the fiber drawing mechanism. The diameter (or other dimension)
of the pulled fiber may be monitored during fiber formation. A load
cell may be used as part of the fiber drawing furnace to measure
and monitor the drawing force which is an indicator of fiber
quality and processing condition because it is directly related to
the viscosity of the softened material at the neck-down area 14.
Tension monitoring can be incorporated into the system (along with
measured diameter) and used as a feedback signal to adjust or
modulate the drawing/feeding speed and temperature of the furnace
12.
[0032] Next, as seen in operation 130, the reduced diameter fibers
that have been drawn through the furnace 12 are then cut and placed
in a bundle 26 or stack and then jacketed by the same material 10
that was used to create the preform 8 as illustrated in operation
140. This creates another preform 8' that is then subject to
thermal drawing as seen in operation 150 in FIG. 1B. The newly
formed preform 8' is run through the fiber drawing furnace as
explained above. In this regard, the method provides for iterative
size reduction as each pass through the furnace 12 reduces the
diameter of the core 2 to form the wires. In one embodiment as
illustrated in FIGS. 1A and 1B, two passes through the furnace 12
may be enough to generate a fiber 50 that has continuous
crystalline metal nanowires therein. FIG. 2B illustrates the
process ends after two passes through the furnace 12 whereby the
final fiber 50 has the crystalline metal nanowires therein (step
160). The crystalline metal nanowires have nanometer sized
dimensions, namely, a diameter less than 100 nm. In some
embodiments, the nanowires may have non-circular cross-sectional
shapes. In such instances, the longest cross-sectional dimension of
the nanowire would be less than 100 nm. As seen in FIG. 1B (dashed
line), optionally, additional preforms 8 may be created after the
second preform 8' has been run through the furnace 12. The
additional preforms 8' are created as previously explained whereby
the drawn fibers are cut and bundled or stacked and a new preform
is formed using the same cladding material 10. This new or
additional preform 8' is then run through the furnace 12 again
until the desired final feature size is achieved.
[0033] FIG. 2 illustrates a flowchart illustrating another
illustrative method of thermally drawing a fiber 50 with
cross-sectional views of the core 2, cladding 4, and preform 8
being illustrated. In this embodiment, a first preform 8 is formed
that includes a core 2 and cladding 4. The nanoelements 6 are
dispersed in the core 2, the cladding 4, or both the core 2 and the
cladding 4. The initial preform 8 is subject to thermal drawing and
cutting as seen in operation 200 which generates smaller-sized
fibers 30. These fibers 30 are then bundled or stacked and wrapped
in a cladding 4 to create another preform 8' and then subject to
another thermal drawing and cutting operation as seen in step 210.
Another set of fibers 30' is created with progressively smaller
cores 2 and then bundled and stacked and wrapped in a cladding 4 to
generate another preform 8''. The process of thermally drawing and
cutting may be repeated any additional number of times as
illustrated in step 220 to generate the final fiber 50 containing
the nanowires 52 (FIG. 1C) contained therein.
[0034] FIG. 2 illustrates the final fiber 50 that contains a
proximal end 32 and a distal end 34. As seen in FIG. 2, the distal
end 34 of the fiber 50 has a cross sectional dimension that is much
smaller (<<) than the cross sectional dimension of the
proximal end 32 of the fiber 50. This construction has the
advantage in that the proximal end 32 of the fiber 50 and the wires
52 contained therein can be easily interfaced with back-end
electronic interfaces due to its larger size. Numerous applications
can be enabled by the fibers 50. These include, for example,
applications for thermoelectric generators, battery electrodes, low
current fuses, nano-electrode arrays, reinforcement for composite
materials, sensors for material or sample study at the micro or
nanoscale, metamaterials or plasmonic materials for
telecommunication applications.
[0035] One particular example of a use for the fiber 50 is for
cell-based assays. In particular, the nanowires 52 that are
contained in the fiber 50 can terminate at electrodes 54 (FIG. 4)
that are formed at the distal end 34 of the fiber 50. The
electrodes 54 that are formed at the distal end 34 of the fiber 34
may be active electrodes in which current is applied to the cell or
other sample or, alternatively, the electrodes 54 may be passive
electrodes that are used more for detection purposes.
[0036] FIG. 4 illustrates one such example a fiber 50 that includes
an electrode-embedded fiber with graded dimensions and material
composition between the proximal end 32 and the distal end 34. That
is to say the fiber 50 includes a distal 34 end having a very small
diameter and a proximal end 32 that has a diameter that is much
larger than that of the distal end 34. The distal end 34 of the
fiber includes an array 36 of electrodes 54 that are exposed and
made of biocompatible materials used for interfacing with
biological cells 300. The dimension of every embedded wire 52 is
gradually increased from nanoscale to macroscale (together with the
surrounding insulation tubes) starting from the distal end 34 that
contains the exposed electrodes 54 and moving proximally in the
direction of the proximal end 32. In addition, the constituent
metal of the embedded wires 52 can also be changed from something
with biocompatibility at the distal end 34 to low resistivity for
high fidelity off-chip signal routing. The wider proximal end 32 of
the fiber 50 is connected to an interface device 56 that connects
to 58 control circuitry such as a PCB for signal transmission,
signal receiving, processing, and storage.
[0037] The electrode-embedded fiber 50 illustrated in FIG. 4 may be
used for cellular electrophysiological measurements with
sub-cellular spatial resolution and intracellular phenotyping
capability. The electrode 54 dimension, inter-electrode
arrangement, and material can be designed for different biological
cell types and counts. Typically, the electrode 54 dimension is
significantly smaller than a typical cell size (.about.10-100
.mu.m) so as to spatially confine the emanated electric field for
highly localized measurements as illustrated in FIG. 3 inset. On
the other hand, the electrodes 54 do not need to be unduly small
(i.e. <20 nm) as the goal is to identify and track changes of
intra-cellular components such as nucleus, mitochondria,
chloroplasts, endoplasmic reticulum, Golgi, and even lysosome.
[0038] In the embodiment of FIG. 4, various pairs of electrodes 54
are used to extract the two dimensional spatial impedance
distribution along the surface of the cell. An AC voltage V.sub.AC1
is applied across the E1-E2 pair such that the current emanated
from one electrode penetrates the intracellular space above and in
between the pair. A higher frequency directs the trans-cellular
current to flow nearer to the top cell membrane (dashed traces)
while a lower frequency does the opposite (solid traces). This is
intuitive given that the higher frequency AC current can permeate
the cell membrane and some capacitive subcellular components more
effectively, and vice versa. As a result, the electrode-embedded
fiber 50 has the ability to perform intracellular phenotyping in
the depth (z) dimension by taking differential measurements over
several different AC frequencies. Since the current always starts
and ends with an electrode, the intracellular impedance right above
an electrode can alternatively be extracted by using two nearby
electrodes: by applying an AC voltage V.sub.AC2 across E3 and E5 to
measure impedance above E4 as shown in the FIG. 4 inset.
[0039] For the electrodes 54 in the distal end 34, metals with
known biocompatibility such as gold and platinum may be used; for
the proximally extending remainder of the nano/macro electrodes 54,
metals with low resistivity such as copper or silver may be used as
illustrated starting at the transition 60. For the cladding 4,
materials that are biocompatible, mechanically robust, and
electrically insulating such as glass (for drawing high melting
point metals) and polymer (for drawing low melting point metals)
can be used. In addition, embedding air or vacuum insulation within
the cladding 4 may optionally be used to further minimize
inter-electrode crosstalk.
[0040] The electrode-embedded fiber 50 solves an important
biotic/abiotic interfacing problem. Not only is the
electrode-embedded fiber 50 adaptable to different cell types and
counts requiring different phenotyping resolutions and surface
areas, the electrode-embedded fiber 50 includes a proximal
interface that is amenable to fit the same or similar PCB without
re-design. In other words, the electrode-embedded fiber 50 is
scalable, cheap and disposable while the PCB and chipset are
reusable. The electrode-embedded fiber 50 also takes care of the
dimension and material mismatch between the cell phenotyping
surface and sampling/processing circuitries. In the larger context,
the electrode-embedded fiber 50 approach generally tackles the
nano-to-macro interfacing challenges for 2D interconnection
electrode arrays. Air or vacuum insulation could be embedded inside
the fiber 50 toward ideal electrical interconnection with minimal
parasitic coupling. Note that only the cores of the produced fibers
are needed, the cladding materials can be selectively etched away
using organic solvents for polymer or HF solution for glass or
quartz.
[0041] FIG. 5 illustrates an electrode-embedded fiber 50 cell-based
assay platform. As seen in FIG. 5, cell culture plates 62 are
provided with multiple wells 64. At the bottom of each well 64,
several openings (not shown) are created for the electrode-embedded
fibers 50 to plug in and then seal any resultant gap at the rim.
The proximal end 32 of the electrode-embedded fibers 50 are
connected to precision LCR meter (impedance measuring device) to
perform impedance spectroscopy during platform validation and
actual operation. Each well 64 may have a number of
electrode-embedded fibers 50 that terminate or interface with the
well surface. A cell or multiple cells 300 that sit atop the distal
electrode array of the electrode-embedded fibers 50 may have
hundreds or even thousands of separate electrodes that are covered
by the cell.
[0042] Prior to any cell phenotyping experimentation, the assembled
plates are exposed under UV and injected with buffer solution into
the electrode-embedded fiber-plugged cell culture wells to check
for leaks and sterility. In addition, one can obtain impedance
spectra of the buffer solution without cells using several pairs of
electrodes 54. The cell-based assay is able to examine cellular
morphology, proliferation rate, attachment-adhesion-spreading, and
intra-cellular content changes, which are useful early indicators
of pharmaceutical or adverse cellular effects. The assay platform
of FIG. 5 allows one to detect and quantify these cellular events
in a real-time, label-free, and non-invasive manner.
[0043] The assay platform allows oncologists to perform
assay-directed chemotherapy instead of empirically based therapy,
i.e. drug selection based on clinical trial evidence. Although in
principle many complex factors may also determine the outcomes of
chemotherapy in vivo, the use of the assay platform of FIG. 5 could
ultimately replace the multi-well assays and result in more
rational and personalized treatment decisions in this highly fatal
carcinoma disease. Compared to conventional assays, e.g. cell
viability assays (MTT and ATP assays), the electrode-embedded fiber
assays can provide more informative cellular data as additional
safeguards to predict in vivo response.
[0044] FIG. 6A illustrates a schematic of the macro preform that
was experimentally tested with a Sn--Si nanocomposite core and PES
cladding. About 2 volume % of Si nanoparticles (NPs) with a
diameter of 80 nm were incorporated into the Sn matrix through
electroplating. The macro Sn--Si nanocomposite preform was then
cladded with PES for thermal drawing. The consolidated preform was
fed into a cylindrical furnace at constant feeding speed (50
.mu.m/sec) at 275.degree. C. with a constant drawing speed of
around 6 m/min. Next, the drawn fibers were cut, stacked and
reconsolidated from the first draw following the procedure shown in
FIGS. 1A and 1B. The iterative size reduction enabled by thermal
drawing gives rise to the micro-to-nano metal wires. After drawing,
some polymer claddings were dissolved in Dichloromethane (DCM) to
expose the metal wires for scanning electron microscopy (SEM)
characterization. FIG. 6B illustrates a photographic image of the
drawn electrode-embedded fiber made from the Sn--Si nanocomposite.
FIG. 6C illustrates a cross-sectional SEM image of the Sn nanowire.
As one moves closer to the distal end, the narrower the wire
becomes. FIG. 6D illustrates a SEM image of the Sn nanowire after
chemical etching of the PES cladding. FIG. 6E illustrates a pure Sn
microwire with a diameter of about 10 .mu.m after etching of the
PES cladding. In the thermal drawing method, the nanoelements
incorporated either are pushed to the metal/polymer interface
during drawing, and serve as the interfacial energy modifier, or
stay inside the metal matrix and increase the viscosity of the
molten metal.
[0045] While embodiments of the present invention have been shown
and described, various modifications may be made without departing
from the scope of the present invention. The invention, therefore,
should not be limited except to the following claims and their
equivalents.
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