U.S. patent application number 11/993120 was filed with the patent office on 2010-10-21 for nano-encapsulated triggered-release viscosity breakers.
Invention is credited to Vinit S. Murthy, Lewis R. Norman, Rohit K. Rana, Michael S. Wong.
Application Number | 20100267594 11/993120 |
Document ID | / |
Family ID | 37595987 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100267594 |
Kind Code |
A1 |
Rana; Rohit K. ; et
al. |
October 21, 2010 |
Nano-encapsulated triggered-release viscosity breakers
Abstract
A method for the encapsulation and triggered-release of
water-soluble or water-dispersible materials. The method comprises
a) providing an amount of electrolyte having a charge, b) providing
an amount of counterion having a valence of at least 2, c)
combining the polyelectrolyte and the counterion in a solution such
that the polyelectrolyte self-assembles to form aggregates, d)
adding a compound to be encapsulated, and e) adding nanoparticles
to the solution such that nanoparticles arrange themselves around
the aggregates. Release of the encapsulated species is triggered by
disassembly or deformation of the microcapsules though disruption
of the charge interactions. This method is specifically useful for
the controlled viscosity reduction of the fracturing fluids
commonly utilized in the oil field.
Inventors: |
Rana; Rohit K.; (Hyderabad,
IN) ; Murthy; Vinit S.; (Guilderland, NY) ;
Wong; Michael S.; (Houston, TX) ; Norman; Lewis
R.; (Duncan, OK) |
Correspondence
Address: |
CONLEY ROSE, P.C.;David A. Rose
P. O. BOX 3267
HOUSTON
TX
77253-3267
US
|
Family ID: |
37595987 |
Appl. No.: |
11/993120 |
Filed: |
June 26, 2006 |
PCT Filed: |
June 26, 2006 |
PCT NO: |
PCT/US06/25026 |
371 Date: |
June 7, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60694039 |
Jun 24, 2005 |
|
|
|
Current U.S.
Class: |
507/251 ;
264/4.32 |
Current CPC
Class: |
C12N 9/96 20130101; C12N
11/04 20130101; A61K 2800/413 20130101; A61Q 19/00 20130101; A61K
2800/412 20130101; B01J 13/02 20130101; C09K 2208/10 20130101; A61K
8/11 20130101; C09K 8/706 20130101; B82Y 5/00 20130101 |
Class at
Publication: |
507/251 ;
264/4.32 |
International
Class: |
C09K 8/92 20060101
C09K008/92; B01J 13/22 20060101 B01J013/22 |
Claims
1. A method for making a nanoencapsulate, comprising: a) providing
an amount of a polyelectrolyte having a charge; b) providing an
amount of a counterion having a valence of at least 2; c) combining
the polyelectrolyte and the counterion in a solution such that the
polyelectrolyte self-assembles to form aggregates; d) adding to the
aggregates a compound to be encapsulated; and e) adding
nanoparticles to the solution such that nanoparticles arrange
themselves around the aggregates.
2. The method according to claim 1 wherein step d) includes aging a
mixture containing the aggregates and the compound to be
encapsulated.
3. The method according to claim 1 wherein step c) is carried out
such that the polyelectrolyte self-assembles to form spherical
aggregates.
4. The method according to claim 1 wherein the compound to be
encapsulated comprises an enzyme.
5. The method according to claim 1 wherein the compound to be
encapsulated comprises an organic dye.
6. The method according to claim 1 wherein the compound to be
encapsulated comprises a sol.
7. The method according to claim 1 wherein the compound to be
encapsulated comprises a ferro-fluid.
8. The method according to claim 1 wherein the compound to be
encapsulated comprises a magnetic contrast agent.
9. The method according to claim 1 wherein the compound to be
encapsulated comprises a cosmetic.
10. The method of claim 1 wherein step d) is carried out so as to
produce sub-micron or micron-sized organic-inorganic spheres in
which the shell consists of nanoparticles and polyelectrolyte
molecules that hold the nanoparticles together.
11. The method according to claim 1 wherein the polyelectrolyte is
functionalized with at least one moiety selected from the group
consisting of organic molecules, organic fluorophores, and
biomolecules.
12. The method according to claim 1 wherein the nanoparticles are
functionalized.
13. The method according to claim 1 wherein the nanoparticles
comprise metals, metal oxides, metal-nonoxides, organic particles,
linear polymer, biomolecules, fullerenols or single/multi-walled
carbon nanotubes.
14. The method according to claim 1 wherein the nanoparticles
comprise silica nanoparticles.
15. The method according to claim 1 wherein at least one of steps
c) and d) is carried out at ambient temperature.
16. The method according to claim 1 wherein steps c) and d) are
carried out simultaneously.
17. The method according to claim 1 wherein steps d) and e) are
carried out simultaneously.
18. The method according to claim 1 wherein steps c)-e) are carried
out sequentially.
19. The nanoencapsulate produced according to the method of claim
1.
20. A method for making treating a hydrocarbon-producing formation,
comprising: a) providing an amount of a polyelectrolyte having a
charge; b) providing an amount of a counterion having a valence of
at least 2; c) combining the polyelectrolyte and the counterion in
a solution such that the polyelectrolyte self-assembles to form
aggregates; d) adding to the aggregates a compound to be
encapsulated; and e) adding nanoparticles to the solution such that
nanoparticles arrange themselves around the aggregates to form
nanoencapsulates; f) including the nanoencapsulates in a
well-servicing fluid; and g) using the well-servicing fluid to
treat a hydrocarbon-producing formation.
21. The method of claim 20, further including the step h) of
releasing the compound from the nanocapsules.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to methods and compositions
for controlled viscosity reduction of fracturing fluids used in
subterranean formations. The method involves both encapsulation and
release of viscosity breakers by using microcapsules assembled from
charged nanoparticles and polyelectrolytes. During the microcapsule
assembly process, breakers such as enzymes, persulphate,
aminocarboxylates, etc., are encapsulated into the shell. The
encapsulated species are released during the disassembly or
deformation of the microcapsules induced by the addition of salt
(NaCl, brine, sea water, etc.). The methods and compositions are
designed in such a way that the reduction of viscosity is initiated
by contacting fracturing fluids with brine solution.
[0002] This method can more generally be utilized for encapsulating
water-soluble or water-dispersible materials in microcapsules
assembled from nanoparticles and, as such, is useful for the
encapsulation and release of a variety of materials. Such materials
include, for example, fluorescent dyes, macromolecules, and
enzymes. As stated above, this method is particularly useful for
the encapsulation of breaker materials used to break fracturing
fluids that are employed in the stimulation of subterranean
formations.
BACKGROUND OF THE INVENTION
[0003] Description of the Related Art
[0004] Hydraulic fracturing of subterranean formations is done to
increase permeability and flow from the formation to a well-bore.
The process involves injecting a fracturing fluid into the
well-bore at extremely high pressure to create fractures in the
rock formation surrounding the bore. The fractures radiate
outwardly from the well-bore and extend the surface area from which
oil or gas drains into the well. Usually a gel, an emulsion or a
foam, having a proppant such as sand or other particulate material
suspended therein is introduced into the fracture. The proppant is
deposited in the fracture and functions to hold the fracture open
after the fluid pressure is released.
[0005] The fracturing fluid typically contains a water soluble
polymer, such as guar gum or a derivative thereof, which provides
appropriate flow characteristics to the fluid and suspends the
proppant particles therein. When the pressure on the fracturing
fluid is released, the fracture closes around the propping agent,
water is forced therefrom and the water-soluble polymer forms a
compact cake. This can prevent oil or gas flow if not removed. To
enhance permeability, viscosity breakers may be included in the
fracturing fluid and reduce the viscosity of the fracturing fluid
by degrading the polymers.
[0006] Currently, breakers are typically either enzymatic breakers
or oxidative breakers. Effective use of breakers requires that the
onset of either enzymatic hydrolysis or oxidative breakdown of the
polymer be controlled. This is needed to prevent any premature
degradation of the polymer which may decrease the fluid's ability
to fracture the subterranean formations.
[0007] There have been several proposed methods for the breaking of
fracturing fluids aimed at eliminating the above problems. The use
of capsules to mask, protect, stabilize, delay or control the
release of various materials is well known and, in particular, the
use of such capsules or microcapsules to encapsulate breaker
materials has been described in, e.g., U.S. Pat. Nos. 4,741,401 to
Walker et al; 4,919,209 to King; 5,110,486 to Manalastar et al;
5,102,558; 5,102,559; 5,204,183 and 5,370,184 all to McDougall et
al; 5,164,099 and 5,437,331 to Gupta et al; and 5,373,901 to Norman
et al.
[0008] Typically, the encapsulated breaker material is formed by
surrounding the breaker material with an enclosure member that is
sufficiently permeable to at least one fluid, generally water,
found in a subterranean formation being treated or to a fluid
injected with the capsule into the formation and which is capable
of releasing the breaker. Generally the breaker is coated or
encapsulated by spraying small particles of the material with a
suitable coating formulation in a fluidized bed or by suspension
polymerization wherein the breaker particles are suspended in a
liquid-liquid system containing a monomer which is capable of
polymerizing to form a polymeric coating surrounding the breaker
particle.
[0009] For example, U.S. Pat. No. 4,506,734 provides a
viscosity-reducing chemical contained within hollow or porous,
crushable and fragile beads. When a fracturing fluid containing
such beads passes or leaks off into the formation or the fluid is
removed by back flowing, any resulting fractures in the
subterranean formation close and crush the beads. The crushing of
the beads then releases the viscosity-reducing chemical into the
fluid. This process is dependent upon the pressure of the formation
to obtain release of the breaker and is thus subject to varying
results dependent upon the formation and its closure rate.
[0010] U.S. Pat. No. 4,741,401 discloses a method for breaking a
fracturing fluid comprised of injecting into the subterranean
formation a capsule comprising an enclosure member containing the
breaker. The breaker is released from the capsule by pressure
generated within the enclosure member due solely to the fluid
penetrating into the capsule whereby the increased pressure causes
the capsule to rupture, releasing the breaker. This method for
release of the breaker would result in the release of the total
amount of breaker contained in the capsule at one particular point
in time. The patent examples disclose the use of the encapsulated
breaker at temperatures ranging from room temperature, 65.degree.
C. to 85.degree. C.
[0011] Although the foregoing methods appear to provide releasable
encapsulated materials, it remains desirable to provide an
alternative method and system that is more economical and gives
equivalent or superior performance. In addition, there remains a
need for a method that provides better control over the release of
viscosity breakers, and, subsequently, sharper control of
fracturing fluid viscosity.
SUMMARY OF THE INVENTION
[0012] The present invention provides a simple method for
encapsulating and releasing various species using
nanoparticle-assembled capsules (NACs) having spherical and
non-spherical shapes. In preferred embodiments, the present methods
for the encapsulation comprise providing a polyelectrolyte having a
positive or negative charge, providing an oppositely charged
counterion having a valence of at least 2, combining the
polyelectrolyte and the counterion in a solution such that the
polyelectrolyte self-assembles to form aggregates, adding the
compound to be encapsulated, allowing the compound to enter the
aggregates, and adding nanoparticles to the solution such that
nanoparticles arrange themselves around the aggregates and
encapsulate the compound.
[0013] There are numerous water-soluble or water-dispersible
compounds that may be encapsulated, including enzymes, organic
dyes, sols such as a ferro fluids, magnetic contrast agents, and
cosmetics. The method may be carried out at ambient
temperature.
[0014] In some embodiments, the final step produces sub-micron or
micron-sized organic-inorganic spheres in which the shell consists
of nanoparticles and polyelectrolyte molecules that hold the
nanoparticles together. The method may further include
functionalizing the polyelectrolyte with at least one moiety
selected from the group consisting of: organic molecules, organic
fluorophores, and biomolecules. Alternatively, or in addition, the
nanoparticles may be functionalized.
[0015] A variety of organic and inorganic nanoparticles such as
metals, metal oxides, metal-non-oxides, organic particles, linear
polymers, biomolecules, fullerenols, and single/multi-walled carbon
nanotubes can be used.
[0016] The herein presented method to encapsulate and release
breakers and various other species using hybrid microcapsules
offers several advantages. The method is extremely simple to carry
out, allows huge flexibility in materials composition, and can be
made environmentally and economically favorable. The ease of
encapsulating a wide variety of compounds makes it viable for a
broad spectrum of applications. The one-step method of
encapsulation during the assembly of NACs occurs in one pot, and
thus there is no need for a large synthesis set-up. NACs can be
used to encapsulate both enzymatic and oxidative viscosity
breakers. The one-step method of releasing the encapsulate by
salt-induced disruption of NACs is simple and does not require any
harsh conditions, as opposed to the extreme pH and/or temperature
treatments generally employed in other methods. These mild
synthesis conditions, which cover a wide pH range, allow the
encapsulation of sensitive organic compounds that would otherwise
be degraded. And, finally, the present composition and processes
can easily be adapted to the procedures for using
breaker-containing fracturing fluids currently employed in the
stimulation of subterranean formations.
[0017] Thus, the present invention comprises a combination of
features and advantages that enable it to overcome various problems
of prior methods. The various characteristics described above, as
well as other features, will be readily apparent to those skilled
in the art upon reading the following detailed description of the
preferred embodiments of the invention, and by referring to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] For a more detailed description of the preferred embodiment
of the present invention, reference will now be made to the
accompanying drawings, wherein:
[0019] FIG. 1 is a schematic representation of the encapsulation
process.
[0020] FIG. 2 is a graph showing the viscosity of guar gel with
time at room temperature.
[0021] FIG. 3 is a graph showing the viscosity of guar gel with
time at 50.degree. C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] The present approach involves nanoparticle assembled
microcapsules (NACs) designed to carry and deliver breakers. The
process herein presented, of polymer self-association in water
followed by nanoparticle deposition and creation of
(sub)micron-sized colloidal microcapsule structures, can be used to
encapsulate water-soluble compounds. Specifically, cationic
polyamines form supramolecular spherical aggregates in the presence
of multivalent anions through ionic crosslinking, and
negatively-charged 12-nm silica nanoparticles electrostatically
deposit around the aggregates to form a closed shell. In order to
encapsulate water soluble compounds such as enzyme or dye molecules
inside these microcapsules, the chosen compounds are added to the
polymer aggregates prior to the addition of silica nanoparticles.
By electrostatic interaction, the encapsulating compounds penetrate
into the aggregates. Upon addition of silica nanoparticles, the
enclosing shell formation takes place, encapsulating the desired
compounds within. Compounds that can be encapsulated include but
are not limited to enzymatic breakers such as .beta.-Mannanase.
[0023] Since the shells of the present microcapsules are made up of
nanoparticles and polymer chains held together by electrostatic
interaction, the structure can be disassembled or deformed by
changing the ionic strength of the aqueous suspension. The addition
of a proper amount of NaCl or brine solution, for example, effects
the release of the encapsulated materials from the microcapsules.
The deformation of the microcapsules was verified using confocal
and optical microscopy. The salt-induced release of the
encapsulated materials from the microcapsules provides a convenient
way to control the release profile, which may lead to wider
applications such as oil-field applications, drug delivery,
etc.
[0024] Polyamines have been used as the structure-directing agent
in the presence of multivalent anions (e.g., sodium sulfate,
trisodium citrate). The general steps for carrying out one
embodiment of the method for the encapsulation of breakers are
discussed in detail below and are shown in FIG. 1.
[0025] Briefly, a desired concentration of polyamines is dissolved
in water. A solution of a desired salt of a multivalent anion is
added to the polyamine solution, at which point the counterions
mediate the self-assembly of polyamines to form spherical
salt-bridged polyamine aggregates. The compound (enzyme or other
species) of interest (to be encapsulated) is then added to the
polymer-counterion aggregates. The suspension is aged for a certain
period, during which time the enzyme or other species penetrates
the aggregates. Next, a sol of a preselected type of nanoparticle
is added to the same suspension, whereupon these nanoparticles
arrange themselves around the polymer aggregates, thus
encapsulating the enzyme or other desired molecules. The resulting
product is sub-micron/micron-sized organic-inorganic spheres, in
which the thick shell consists of nanoparticles and the polyamine
molecules.
[0026] The suspension of enzyme-containing NACs can be used as-is
or separated from the mother-liquor by centrifugation for their
further use. For example, it may be desirable to separate the NACs
for use in viscosity reduction in a fracturing fluid. By way of
example only, enzyme-containing NACs may be added to a guar gel
either at room temperature or elevated temperatures. When desired,
a sufficient amount of salt (NaCl or brine) can be added to the
mixture of guar gel and enzyme-containing NACs so as to cause the
release of enzyme from the NACs.
[0027] To encapsulate the breaker persulfate, its corresponding
salt can be used as the anionic species to crosslink the polymer,
forming spherical aggregates.
[0028] For the embodiment presented in FIG. 1, the encapsulated
compound is preferably negatively charged in order to ensure
effective encapsulation into the polyamine aggregates due to
electrostatic interaction with the positive charges on the polymer.
The charge on the encapsulated compound can be controlled by
changing the pH of the solution.
EXAMPLES
[0029] According to preferred embodiments, one method for preparing
nanoparticle assembled microcapsules (NACs) involves poly-L-lysine
(PLL) as the polyamine, citrate (cit) as the multivalent anion and
silica nanoparticles. .beta.-Mannanase (Megazyme) is used as the
enzymatic breaker. For the enzyme encapsulation in NACs, 25 .mu.L
of the enzyme solution (9 U/ml .beta.-Mannanase) was mixed with 21
.mu.L of PLL and aged for 25 minutes. The resulting solution was
added to a previously aged (25 min) PLL/cit suspension. The
suspension was then aged for another 5 minutes. To this, a
colloidal sol of silica nanoparticles was added and formed a thick
shell surrounding the aggregates.
[0030] Optical brightfield and confocal images of silica
microcapsules encapsulating .beta.-Mannanase enzyme show circular
microcapsules. The composition comprises: 21 .mu.L PLL-FITC (2
mg/ml, 68.6 kD)+125 .mu.L Na.sub.3Cit (5.36 mM)+50 .mu.L
.beta.-Mannanase enzyme (9 units/ml)+125 .mu.L SiO.sub.2 NP (20 wt
%).
[0031] The encapsulation of the enzyme within the resultant NACs
was verified by checking its activity in a 0.5 wt % guar solution.
The guar solution was prepared by sprinkling 0.25 g of Guar to
49.75 g of DI water. After mixing, the solution was further stirred
for 5 minutes and then aged for another 10 minutes without
stirring. The enzyme-containing NAC suspension was then added to
the guar solution while stirring. Viscosity was measured after
specific times using a fans Viscometer (Model 35A). Bob deflection
values were obtained at 100, 200, 300 and 600 rpm, which correspond
to 170, 340, 511 and 1021 1/sec shear rates, respectively.
Viscosity was calculated from the deflection values using
instrument conversion factors.
[0032] The stability of enzyme-containing NACs and
triggered-release of the enzyme from NACs at room temperature are
shown in FIG. 2. The graph shows the change in viscosity of 0.5 wt
% guar gel (with or without containing .beta.-Mannanase enzyme
(0.45 Units) encapsulated in NACs) with time. After 7 hours, 4 ml
of 5M NaCl was added to the gel. [Composition: 21 .mu.L PLL-FITC (2
mg/ml, 68.6 kD)+125 .mu.L Na.sub.3Cit (5.36 mM)+50 .mu.L
.beta.-Mannanase enzyme (9 units/ml)+125 .mu.L SiO.sub.2 NP (20 wt
%)].
[0033] As FIG. 2, FIG. 3 presents the stability of
enzyme-containing NACs and triggered-release of the enzyme from
NACs at a temperature of 50.degree. C. The graph shows the change
in viscosity of 0.5 wt % guar gel containing the bare or
encapsulated enzyme (0.45 Units) in NACs with time at 50.degree. C.
After 3 hours, 4 ml of 5M NaCl was added to the gel. [Compositions:
(circles) two batches of (21 .mu.L PLL-FITC (2 mg/ml, 68.6 kD)+125
.mu.L Na.sub.3Cit (5.36 mM)+25 or 50 .mu.L .beta.-Mannanase enzyme
(9 units/ml)+125 .mu.L SiO.sub.2 NP (20 wt %)); (triangles) two
batches of (42 .mu.L PLL-FITC (2 mg/ml, 68.6 kD)+125 .mu.L
Na.sub.3Cit (5.36 mM)+25 .mu.L .beta.-Mannanase enzyme (9
units/ml)+125 .mu.L SiO.sub.2 NP (20 wt %)].
[0034] The present process can be used to encapsulate and release
enzymatic breakers, and oxidizing and chelating agents, thus having
potential usage in oil field applications. The method to assemble
and disassemble these microcapsules also provides opportunities for
applications in areas as diverse as drug delivery, chemical
storage, contaminated waste removal, gene therapy, catalysis,
cosmetics, magnetic contrast agents (for use in magnetic resonance
imaging), and magneto-opto-electronics. It should be emphasized
that for many of the above applications the method provides
flexibility to meet the required reaction conditions such as pH of
the medium, temperature, etc., for specific applications. The
present methods are extremely amenable to variations, as discussed
below.
Encapsulation of Breakers in NACs
[0035] As described herein, NACs can be assembled from negatively
charged polymers and positively charged nanoparticles. Charged
polymers having additional functional groups that will provide
sites for the breakers to anchor and thereby encapsulate into the
NACs can also be employed. The method can involve cationic
counterions such as metal ions (e.g., Ca.sup.2+) that can have
applications in controlling the rate of cement binding in oil-field
operations.
[0036] Ethylenediamine tetraacetate, EDTA, can serve as the anionic
counteranion, and can also act as a viscosity breaker in the
fracturing fluid. Moreover, the polymers may be functionalized with
organic molecules, organic fluorophores, or biomolecules before the
formation of the encapsulating nanoparticle shell, or the
nanoparticles themselves may be functionalized to have active
species on the outer surface of the spheres. Salt granules (salts
of persulfate, perchlorate, Ca.sup.2+ etc.) can be utilized for
encapsulation, and the encapsulation can be performed by assembling
charged polymers and then silica nanoparticles on the surface of
these granules.
Modification of the NACs
[0037] After formation, the surface of the NACs can be treated with
organic molecules for targeting the delivery site, or with
nanoparticles for compositional and structural variations.
Alternate Methods for Disassembly or Deformation of the NACs
[0038] The NACs can be disassembled or deformed by various methods,
including, but not limited to, changing the ionic strength upon
addition of solutions other than NaCl such as brine or sea water,
changing the pH of the aqueous suspension, and osmotic
pressure.
Modifications of the Method to Encapsulate and Deliver Using
NACs
[0039] The method as herein described can be performed at different
pH conditions and/or synthesis temperatures, using different
solvents, and the synthesis of the microcapsules containing
breakers could be carried out in a flow-type reactor, such as
microfluidic device and aerosol reactor.
Use of NACs Assembled From NPs Other Than Silica
[0040] Charged NPs include: metal nanoparticles, such as gold,
platinum, palladium, copper, silver, rhodium, rhenium, nickel, and
iridium having surface positive/negative charge, alloys of metal
nanoparticles, such as platinum/iridium having surface
positive/negative charge, metal non-oxide nanoparticles, such as
II-VI, III-V and IV quantum dots having surface positive/negative
charge, metal oxide nanoparticles, such as titanium oxide,
zirconium oxide, aluminum oxide, iron oxide, tungsten oxide, cerium
oxide, antimony oxide and silicon oxide having surface
positive/negative charge, and nanoparticles functionalized with
cationic/anionic polymers that can be assembled by adding suitable
counterions. Nanoparticles may also be functionalized with
molecules to provide a hydrophilic or hydrophobic surface. The use
of hydrophobic nanoparticles, such as polystyrene and polypyrrole
may be envisioned. Furthermore, nanoparticles may have diameters of
1-100 nm and may have shapes other than spheres, such as rods,
triangles, and hexagons. Additionally, combinations of
nanoparticles may be employed.
Use of NACs Assembled From Cationic Polymer, Anionic Counterions
and Negatively Charged NPs
[0041] Cationic polymers and anionic counterions that can be used
in the present invention include but are not limited to:
polypeptides and polyamines with different chain lengths with
straight or branched structure, anionic counterions with different
functional groups, such as carboxylates, phosphates and sulfates
(e.g. phosphate and sulfate analogs of citrate and EDTA), and
counterions such as peptides, polypeptides, copolypeptides and
polymers having negative charge (e.g. aspartic acid and glutamic
acid).
Use of NACs Assembled From Anionic Polymer, Cationic Counterions
and Positively Charged Nanoparticles
[0042] Likewise, suitable anionic polymers and cationic counterions
include: polypeptides and polyacids with different chain lengths
with straight or branched structure, cationic counterions such as
metal ions (Ca.sup.2+, Mg.sup.2+, transition metal ions, etc.), and
counterions such as peptides, polypeptides, copolypeptides and
polymers having positive charge (e.g. lysine and histidine).
Alternate Polymers
[0043] Other polymers can be utilized, including cationic/anionic
polymers functionalized with organic molecules, biomolecules and
fluorophores, the blocks of the copolypeptides derived from the 20
natural amino acids (lysine, arginine, histidine, aspartic acid,
glutamic acid, glycine, alanine, valine, leucine, isoleucine,
methionine, proline, phenylalanine, tryptophan, serine, threonine,
asparagine, glutamine, tyrosine, and cysteine), and combinations of
polypeptides.
Applications in Other Areas
[0044] The herein disclosed method may find application in other
areas, such as the encapsulation of enzymes for biochemical
reactions, the encapsulation of organic dyes, the encapsulation of
a sol within the interior of the hollow spheres, such as a
ferro-fluid, as well as applications in drug delivery, chemical
storage, contaminated waste removal, gene therapy, catalysis,
cosmetics, magnetic contrast agents (for use in magnetic resonance
imaging), and magneto-opto-electronics.
[0045] While preferred embodiments of this invention have been
shown and described, modifications thereof can be made by one
skilled in the art without departing from the scope of this
invention. The embodiments described herein are exemplary only and
are not limiting. Accordingly, the scope of protection is not
limited to the embodiments described herein, but is only limited by
the claims which follow, the scope of which shall include all
equivalents of the subject matter of the claims. In the claims that
follow, any sequential recitation of steps is not intended as a
requirement that the steps be performed sequentially, or that one
step be completed before another step is begun, unless explicitly
so stated. The disclosures of all patents, patent applications and
publications cited herein are hereby incorporated herein by
reference to the extent that they describe materials, methods or
other details supplementary to those set forth herein.
* * * * *