U.S. patent application number 10/343583 was filed with the patent office on 2004-01-22 for encapsulation of liquid template particles.
Invention is credited to Antipov, Alexei, Donath, Edwin, Gleb, Sukhorukov, Seibt, Horst, Voigt, Andreas.
Application Number | 20040013738 10/343583 |
Document ID | / |
Family ID | 26006594 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040013738 |
Kind Code |
A1 |
Voigt, Andreas ; et
al. |
January 22, 2004 |
Encapsulation of liquid template particles
Abstract
The invention relates to a method for applying a shell to liquid
template particles, comprising the following steps: (a) preparation
of an emulsion of liquid template particles in a continuous liquid
or gel phase, whereby at least one amphiphilic polyelectrolyte or
polyelectrolyte complex, or a copolymer of charged hydrophilic
monomers and oil soluble monomers is dissolved in the fluid
template particles and/or the continuous phase and a film is formed
at the phase boundary between the liquid template particle and the
continuous phase and (b) application of a shell to the film formed
at the phase boundary.
Inventors: |
Voigt, Andreas; (Berlin,
DE) ; Gleb, Sukhorukov; (Postdam, DE) ;
Antipov, Alexei; (Golm, DE) ; Donath, Edwin;
(Giesenhorst, DE) ; Seibt, Horst; (Berlin,
DE) |
Correspondence
Address: |
SUTHERLAND ASBILL & BRENNAN LLP
999 PEACHTREE STREET, N.E.
ATLANTA
GA
30309
US
|
Family ID: |
26006594 |
Appl. No.: |
10/343583 |
Filed: |
January 31, 2003 |
PCT Filed: |
August 1, 2001 |
PCT NO: |
PCT/EP01/08899 |
Current U.S.
Class: |
424/490 ;
264/4.1; 504/359 |
Current CPC
Class: |
A61K 9/5026 20130101;
B01J 13/10 20130101; B01J 13/22 20130101; B01J 13/02 20130101; A61K
9/5192 20130101; A61K 9/5089 20130101; A61K 9/5138 20130101; Y10T
428/2984 20150115 |
Class at
Publication: |
424/490 ;
264/4.1; 504/359 |
International
Class: |
A01N 025/28; A61K
009/16; A61K 009/50; B01J 013/02; B01J 013/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 2, 2000 |
DE |
100 37 707.6 |
Oct 11, 2000 |
DE |
100 50 382.9 |
Claims
1. Method for applying a shell to liquid template particles
comprising the steps: (a) providing an emulsion of liquid template
particles in a continuous liquid or gel phase whereby at least one
amphiphilic polyelectrolyte or polyelectrolyte complex or a
copolymer of charged hydrophilic monomers and oil-soluble monomers
is dissolved in the liquid template particles or/and the continuous
phase thus forming a film at the phase boundary between the liquid
template particle and the continuous phase and (b) applying a shell
to the film formed at the phase boundary.
2. Method as claimed in claim 1, characterized in that, an oil
phase is used as the liquid template particle and an aqueous or an
aqueous-gel-like phase is used as the continuous phase.
3. Method as claimed in claim 1 or 2, characterized in that, the
liquid template particles are selected from particles having a
diameter of up to 50 .mu.m, in particular up to 10 .mu.m.
4. Method as claimed in one of the claims 1 to 3, characterized in
that, the liquid template particles comprise a solution, an
emulsion or a suspension.
5. Method as claimed in one of the claims 1 to 4, characterized in
that, the liquid template particles are composed of a
liquid-crystalline substance or contain such a substance.
6. Method as claimed in one of the claims 1 to 5, characterized in
that, the template particles contain an active substance.
7. Method as claimed in claim 6, characterized in that, the active
substance is selected from catalysts, polymers, dyes, sensor
molecules, flavourings, drugs, herbicides, insecticides,
fungicides.
8. Method as claimed in claim 6 or 7, characterized in that, the
active substance is selected from oils, in particular perfume oils,
pharmaceutical oils and active pharmaceutical substances dissolved
or dispersed in oil.
9. Method as claimed in one of the claims 1 to 8, characterized in
that, the amphiphilic polyelectrolyte contains simplex compounds of
polycationic polymers and anions.
10. Method as claimed in one of the claims 1 to 8, characterized in
that, the amphiphilic polyelectrolyte contains simplex compounds of
polyanionic polymers and cations.
11. Method as claimed in one of the claims 1 to 8, characterized in
that, the amphiphilic polyelectrolyte contains polyfunctional
zwitterionic surfactants.
12. Method as claimed in one of the previous claims, characterized
in that, the amphiphilic polyelectrolyte is used in an amount of up
to 2% by weight based on the weight of the template particles.
13. Method as claimed in one of the previous claims, characterized
in that, the application of the shell comprises a layered assembly
or/and a precipitation of multilayers or/and a coacervation from
the continuous liquid phase.
14. Method as claimed in one of the previous claims, characterized
in that, the components used to form the shell comprise at least
one polyelectrolyte.
15. Method as claimed in claim 14, characterized in that, the
components used to form the shell comprise two oppositely charged
polyelectrolytes.
16. Method as claimed in claim 15, characterized in that, the
components used to form the shell comprise a polyvalent
low-molecular cation and a negatively charged polyelectrolyte or a
polyvalent low-molecular anion and a positively charged
polyelectrolyte.
17. Method as claimed in one of the previous claims, characterized
in that, the film-forming components are placed first in a
complexed form in the coating emulsion and the components are
transferred onto the boundary layer between the template particle
and the continuous phase by changing the media conditions.
18. Method as claimed in one of the previous claims, characterized
in that, the components required to form the shell comprise at
least one macromolecule.
19. Method as claimed in claim 18, characterized in that, a
biopolymer, an abiogenic polymer or a mixture thereof optionally in
combination with low-molecular biogenic or/and abiogenic substances
is used.
20. Method as claimed in one of the previous claims, characterized
in that, nanoparticles having electrical, magnetic or optical
properties are used to form the shell.
21. Method as claimed in one of the previous claims further
comprising the disintegration of the liquid template particles.
22. Method as claimed in one of the previous claims further
comprising on at least partial disintegration of the shell.
23. Method as claimed in one of the previous claims, characterized
in that, a shell having a thickness of 1 to 100 nm is formed around
the template particles.
24. Method as claimed in one of the previous claims, characterized
in that, a shell having a thickness of 1 to 50 nm is formed around
the template particles.
25. Method as claimed in one of the previous claims, characterized
in that, a chemical reaction is carried out in or/and on the
shells.
Description
DESCRIPTION
[0001] The invention concerns a method for applying a shell to
liquid template particles.
[0002] DE 198 12 083.4, DE 199 07 552.2, EP 98 113 181.6 and WO
99/47252 disclose a method for producing capsules coated with a
polyelectrolyte shell by applying polyelectrolytes in layers on
template particles. An advantage of this method over earlier
methods for producing microcapsules is that it enables the
production of monodisperse capsules having a defined wall
thickness. Liquid template particles can also be coated. However,
since liquid template particles have a relatively low stability,
the object of the invention was to provide an improved process for
coating liquid template particles which at least partially
eliminates the disadvantages of the prior art.
[0003] This object is achieved by a method for applying a shell to
liquid template particles comprising the steps (a) providing an
emulsion of liquid template particles in a continuous liquid or gel
phase whereby at least one amphiphilic polyelectrolyte or
polyelectrolyte complex or/and at least one copolymer of charged
hydrophilic monomers and oil-soluble monomers is dissolved in the
liquid template particles or/and the continuous phase thus forming
a film at the phase boundary between the liquid template particle
and the continuous phase and (b) applying a shell to the film
formed at the phase boundary.
[0004] It was surprisingly found that the formation of a film at
the phase boundary between the liquid template particle and the
continuous liquid or gel phase results in a stabilization of the
liquid template particle which considerably facilitates the
subsequent application of a shell.
[0005] The encapsulation process according to the invention enables
the encapsulation of any colloidal liquid particles e.g. emulsified
oil droplets in a continuous aqueous or non-aqueous liquid phase.
An oil phase is particularly preferably used as the liquid template
particles and an aqueous phase e.g. a salt-containing aqueous
solution in which the salt concentration is preferably between
0.001 mM and 1 M or more is particularly preferably used as the
continuous liquid phase. Furthermore the process also allows the
use of continuous gel phases and in particular aqueous gel
phases.
[0006] An essential feature of the present invention is that a film
is formed at the boundary between the template particle and
continuous liquid phase. If oil droplets are used as template
particles, a polyelectrolyte or polyelectrolyte complex can be used
for this purpose which is soluble in the oil phase. Alternatively
or in addition the polyelectrolyte or polyelectrolyte complex can
also be dissolved in the continuous liquid phase e.g. an aqueous
phase. Furthermore it is also possible to use surface-active
copolymers which contain monomers of different polarity.
[0007] For example simplex compounds can be used as amphiphilic
polyelectrolytes which contain (a) polycationic polymers and
anions, for example monomeric anions such as salts of organic acids
e.g. carboxylic acids or even polymeric anions such as
polyacrylates or (b) polyanionic polymers and cations e.g. cationic
monomers or polymers. The oleophilic behaviour of these types of
compound can be influenced by the selection of the corresponding
counterion for the polymer. Moreover it is also possible to use
polyfunctional zwitterionic surfactants which are also amphiphilic
compounds. In special cases it is possible to use combinations of
polyfunctional surfactants and polyelectrolyte/counterion pairs.
The concentration of the polyelectrolyte is preferably up to a
maximum of 2% by weight, particularly preferably 0.01 to 1% by
weight based on the total weight of the liquid template particle.
Experience has shown that liquid template particles and in
particular oil droplets which contain a combination of a simplex
compound and a polyfunctional surfactant can be dispersed
particularly well and droplets are obtained having a uniform size
distribution. Furthermore the dispersions formed during the
processing are more stable.
[0008] Examples of amphiphilic polyelectrolytes are simplex
compounds of polycations containing ammonium ions and hydrophobic
organic anions such as the salts of organic acids e.g. carboxylic
acids having 10 or more carbon atoms or polyanions such as
polyacrylate or polymethacrylate. Specific examples are
poly(diallyl-dimethyl)ammonium stearate, palmitate, oleate or
ricinolate, poly[alkyl-methyl-bis(polyoxyethylene)-ammonium]-po-
lyacrylate or
poly[alkyl-dihydroxyethyl-ethyl-ammonium]-polyacrylate where the
molecular weight of the polycation is preferably .gtoreq.150,000 D
and particularly preferably .gtoreq.200,000 D. Examples of suitable
polyfunctional surfactants are amphiphilic polymers with cationic
ammonium groups and anionic sulfinate, sulfonate, sulfate,
phosphonate, phosphate or/and carboxylate groups. Specific examples
of suitable surfactants are
alkyl-bis(polyoxyethylene)-ammonium-sulfobetaine-sulfinat- e,
alkyl-bis(polyoxyethylene)-ammonium-sulfobetaine-sulfonate,
ethylated alkyl- or dialkyl-ammonium betaine or
alkyldimethyl-ammonium-propyl-modif- ied polysiloxanes or
siloxane-sulfobetaine-sulfones.
[0009] The emulsion drops to be coated can have a size of up to 50
.mu.m. However, the size of the drops is preferably up to 10 .mu.m,
particularly preferably 5 nm to 10 .mu.m and most preferably 5 nm
to 5 .mu.m. The size of the drops can be adjusted by suitable
treatment methods e.g. ultrasound, emulsification with a dispersing
agent, extrusion or/and by adding surface-active substances to the
continuous liquid phase.
[0010] The liquid template particles may be a homogeneous liquid.
They can, however, also comprise a solution, an emulsion or a
suspension. Furthermore the liquid template particles can consist
of a liquid-crystalline substance or contain such a substance. In a
preferred embodiment template particles are encapsulated which
contain an active substance e.g. they themselves represent an
active substance. In general active substances can be encapsulated
which are dissolved or dispersed in the liquid template particle.
The active substance can for example be selected from catalysts,
polymers, dyes, sensor molecules, flavourings, pharmaceutical
agents, herbicides, insecticides, fungicides, oils in particular
pharmaceutical or cosmetic oils e.g. perfume oils or solids that
are soluble in oil or can be dispersed in oil, in particular
pharmaceutical active substances.
[0011] Organic liquids such as alcohols or hydrocarbons e.g.
hexanol, octanol, octane or decane can also for example be
encapsulated. Such capsules filled with an organic liquid that is
not miscible with water can also be used for chemical reactions
e.g. polymerization reactions. Hence the monomer can be
concentrated specifically in the inner space of the capsules as a
result of its distribution equilibrium. Optionally it is also
possible to already enclose the monomer solution in the interior
before the start of the synthesis.
[0012] The method according to the invention enables the production
of capsules for enclosing active substances. The inner space can be
loaded with molecules by varying the permeability of the shell as a
function of the external physical and chemical parameters. A state
of high permeability is adjusted for loading purposes. The enclosed
material is subsequently retained by changing the external
parameters or/and closing the pores for example by condensing the
shell or by chemical or/and thermal modification of the pores or
channels.
[0013] The method according to the invention allows charged or/and
uncharged components to be deposited on the template particles. In
a preferred embodiment of the invention the components required to
form the shell contain at least one polyelectrolyte for example two
oppositely charged polyelectrolytes or/and a polyvalent metal
cation and a negatively charged polyelectrolyte.
[0014] Polyelectrolytes are generally understood to mean polymers
having ionically dissociable groups which may be a component or
substituent of the polymer chain. The number of these ionically
dissociable groups in the polyelectrolytes is usually large enough
to ensure the water-solubility of the polymers in a dissociated
form (also referred to as polyions). The term polyelectrolyte as
used herein also refers to ionomers in which the concentration of
the ionic groups is not sufficient to make them water soluble, but
which have sufficient charges for a self-assembly. The shell
preferably contains "true" polyelectrolytes. Polyelectrolytes are
divided into polyacids and polybases depending on the type of the
dissociable groups. Polyanions which can be inorganic as well as
organic polymers are formed from polyacids when they dissociate
with cleavage of protons.
[0015] Polybases contain groups which are able to accept protons
e.g. by reaction with acids to form salts. Polybases can have
groups in the chains or side groups that are dissociable and form
polycations by accepting protons.
[0016] Polyelectrolytes that are suitable according to the
invention are biopolymers such as alginic acid, gum arabic, nucleic
acids, pectins, proteins and other biopolymers that may be
chemically modified such as ionic or ionizable polysaccharides e.g.
carboxymethyl cellulose, chitosan and chitosan sulfate, lignin
sulfonates and synthetic polymers such as polymethacrylic acid,
polyvinylsulfonic acid, polyvinylphosphonic acid and
polyethyleneimine.
[0017] Suitable polyanions comprise naturally occurring polyanions
and synthetic polyanions. Examples of naturally occurring
polyanions are alginate, carboxymethylamylose,
carboxymethylcellulose, carboxymethyldextran, carageenan, cellulose
sulfate, chrondroitin sulfate, chitosan sulfate, dextran sulfate,
gum arabic, guar gum, gellan gum, heparin, hyaluronic acid, pectin,
xanthan and proteins at an appropriate pH. Examples of synthetic
polyanions are polyacrylates (salts of polyacrylic acid), anions of
polyamino acids and copolymers thereof, polymaleinate,
polymethacrylate, polystyrene sulfate, polystyrene sulfonate,
polyvinyl phosphate, polyvinyl phosphonate, polyvinyl sulfate,
polyacrylamidemethylpropane sulfonate, polylactate,
poly(butanediene/maleinate), poly(ethylene/maleinate),
poly(ethacrylate/acrylate) and poly(glycerylmethacrylate).
[0018] Suitable polybases comprise naturally occurring polycations
and synthetic polycations. Examples of suitable naturally occurring
polycations are chitosan, modified dextrans, e.g.
diethylaminoethyl-modif- ied dextrans, hydroxymethylcellulose
trimethylamine, lysozyme, polylysine, protamine sulfate,
hydroxyethylcellulose trimethylamine and proteins at appropriate pH
values. Examples of synthetic polycations are polyallyl-amine,
polyallylamine hydrochloride, polyamines,
polyvinylbenzyl-trimethyl-ammonium chloride, polybrene,
polydiallyldimethylammonium chloride, poly-ethyleneimine,
polyimidazoline, polyvinylamine, polyvinylpyridine,
poly(acryl-amide/methacryloxypropyltrimethylammonium bromide),
poly(diallyldimethyl-ammonium chloride/N-isopropylacrylamide),
poly(dimethylaminoethylacrylate/acrylamide),
polydimethylaminoethylmethac- rylate,
polydimethylaminoepichlorohydrin, polyethyleneiminoepichlorohydrin-
, polymethacryloxyethyltrimethylammonium bromide,
hydroxypropylmethacrylox- yethyldimethylammonium chloride,
poly(methyldiethylaminoethylmethacrylate/- acrylamide),
poly(methyl/guanidine), polymethylvinylpyridinium bromide,
poly(vinylpyrrolidone/dimethyl-aminoethylmethacrylate) and
polyvinylmethylpyridinium bromide.
[0019] Linear or branched polyelectrolytes can be used. The use of
branched polyelectrolytes leads to less compact polyelectrolyte
multifilms having a high degree of wall porosity. The capsule
stability can be increased by cross-linking polyelectrolyte
molecules within or/and between the individual layers e.g. by
cross-linking amino groups with aldehydes.
[0020] It is also possible to use amphiphilic polyelectrolytes,
e.g. amphiphilic block or random copolymers having a partial
polyelectrolyte character. Such amphiphilic copolymers consist of
units of different functionality e.g. acidic or basic units on the
one hand and hydrophobic units on the other hand such as styrenes,
dienes or siloxanes etc. which can be arranged as blocks or
randomly distributed over the polymer. The permeability or other
properties of the capsule walls can be adjusted in a defined manner
by using copolymers which change their structure as a function of
the external conditions. These may for example be weak
polyelectrolytes, polyampholytes or copolymers having a
poly(N-isopropylacrylamide) component e.g.
poly(N-isopropylacrylamide acrylic acid) which due to the
equilibrium of hydrogen bridges, change their water solubility as a
function of the temperature which is associated with swelling.
[0021] The release of enclosed active substances can be regulated
via the disintegration of the capsule walls by using
polyelectrolytes that can be degraded under certain conditions e.g.
photolabile, acid-labile, base-labile, salt-labile or thermolabile
polyelectrolytes. Furthermore conductive polyelectrolytes or
polyelectrolytes having optically active groups can be used as
capsule components for special applications.
[0022] The properties and composition of the polyelectrolyte shell
of the capsules according to the invention can be adjusted in a
defined manner by suitable selection of the polyelectrolytes. The
composition of the shells can be varied over a wide range by
selection of substances for the layer structure. There are
basically no limitations with regard to the polyelectrolytes or
ionomers that are used provided the molecules have a sufficient
charge or/and the ability to bind to the underlying layer by other
types of interaction such as hydrogen bonds and/or hydrophobic
interactions.
[0023] Hence suitable polyelectrolytes are low molecular
polyelectrolytes or polyions and also macromolecular
polyelectrolytes such as polyelectrolytes of biological origin.
[0024] The permeability of the shell wall is of particular
importance for the use of the capsules. As already stated above,
the large number of polyelectrolytes that are available enables the
production of numerous shell compositions having different
properties. In particular the electric charge of the outer shell
can be adapted to the intended use. Moreover the inner shell can be
adapted to the respective encapsulated active substances which can
for example lead to a stabilization of the active substance.
Furthermore the permeability of the shell wall can be influenced by
the selection of the polyelectrolytes in the shell and by the wall
thickness as well as ambient conditions. This enables a selective
design of the permeability properties and a defined change in these
properties.
[0025] The permeability properties of the shell can be further
modified by pores in at least one of the polyelectrolyte layers.
Such pores can be formed by the polyelectrolytes themselves if a
suitable choice is made. In addition to the polyelectrolytes, the
shell can also contain other substances in order to achieve a
desired permeability. Thus the permeability to polar components can
be lowered by incorporating nanoparticles having anionic or/and
cationic groups or surface-active substances such as surfactants
or/and lipids. The incorporation of selective transport systems
such as carriers or channels in the polyelectrolyte shell and in
particular in lipid layers enables an exact adaptation of the
transversal transport properties of the shell to the respective
intended use. The pores or channels of the shell wall can be opened
or closed in a specific manner by chemical modification or/and
change of the ambient conditions. Thus for example a high salt
concentration of the surrounding medium leads to a high
permeability of the shell wall.
[0026] A first embodiment of the method according to the invention
comprises the application of polyelectrolytes in layers on the
liquid template particles that have been pretreated by adding
amphiphilic polyelectrolytes. The application of polyelectrolytes
in layers preferably comprises several and in particular more than
four process steps in which oppositely charged polyelectrolytes are
successively deposited from the continuous liquid phase onto the
template particle.
[0027] A second embodiment of the method according to the invention
comprises a complex precipitation of multilayers or coacervation of
several e.g. two oppositely charged polyelectrolytes. In this
process the coating components in a complexed form are added first
to the coating emulsion e.g. as complexes of two oppositely charged
polyelectrolytes, and the components are transferred
(redistributed) onto the boundary layer between the template
particle and continuous phase by changing the media conditions. In
order to carry out this process the film-forming components are for
example kept in a solution e.g. in an alkaline solution in which
the two are present simultaneously but without reacting with one
another. The template particles to be coated are added to this
solution. Subsequently it is titrated with acid, e.g. HCl, into the
neutral range which results in an encapsulation of the template
particles. After separation of the encapsulated particles from the
complexes in the free solution e.g. by filtration, centrifugation,
sedimentation (creaming) or phase separation, the template
particles can be dissolved if necessary.
[0028] In a further preferred embodiment the surface precipitation
can occur from a solution containing a complex consisting of a
low-molecular ion and an oppositely charged polyelectrolyte.
Examples of suitable low-molecular ions are metal cations,
inorganic anions such as sulfate, carbonate, phosphate, nitrate
etc., charged surfactants, charged lipids and charged oligomers in
combination with an appropriate oppositely charged polyelectrolyte.
A dispersed source for the one polyelectrolyte is generated in this
process while the other polyelectrolyte is present at the same
time. The polyelectrolyte of the complex can be the polycation as
well as the polyanion. The choice depends on the template particles
used and other conditions. In this embodiment for example a
positively charged polyelectrolyte with a multiply negatively
charged low-molecular anion e.g. sulfate is added to a solution of
the negatively charged polyelectrolyte and a suspension of the
template particles which results in a coating of the template
particles. The coated template particles can for example be
separated from the free complexes by centrifugation, filtration and
subsequent washing and--provided they are soluble particles--be
dissolved to produce microcapsules.
[0029] Another preferred embodiment comprises surface precipitation
from a solution containing partially destabilized polyelectrolyte
complexes (polycation/polyanion) by adding salt or/and pH
variation. In this process there is a gradual transfer of
polyelectrolytes from the complexes onto the template surface. This
can be accomplished by introducing and stirring the negatively and
positively charged polyelectrolyte in an aqueous solution having a
high salt content preferably a salt content of .gtoreq.0.5 mol/l,
e.g. 1 M NaCl. The template particles are coated after addition to
the solution. The coated template particles can for example be
isolated by centrifugation, filtration, sedimentation or other
known phase separation methods and, subsequent washing and
optionally dissolved to generate microcapsules.
[0030] In yet another preferred embodiment the shell comprises
low-molecular cations e.g. metal cations and at least one
negatively charged polyelectrolyte. Divalent cations and in
particular trivalent cations are for example used as cations.
Examples of suitable cations are alkaline earth metal cations,
transition metal cations and rare earth element cations such as
Ca.sup.2+, Mg.sup.2+, Y.sup.3+, Tb.sup.3+ and Fe.sup.3+. On the
other hand it is also possible to use monovalent cations such as
Ag.sup.+. Template particles coated with a metal layer can be
produced by reducing the metal cations.
[0031] In yet another preferred embodiment the components that are
necessary to form the shell comprise at least one macromolecule
e.g. an abiogenic macromolecule such as an organic polymer or a
biomolecule such as a nucleic acid e.g. DNA, RNA or a nucleic acid
analogue, a polypeptide, a glycoprotein or a polysaccharide having
a molecular weight of preferably .gtoreq.5 kD, and particularly
preferably of .gtoreq.10 kD. The macromolecules can carry charges
such as nucleic acids or be uncharged such as polysaccharides e.g.
dextran. The macromolecules can optionally be combined with
polyelectrolytes or/and polyvalent metal cations in which case
combinations of macromolecular and low-molecular biological cell
substances, macromolecular and low-molecular abiogenic substances
and macromolecular and biogenic and abiogenic substances can for
example be used.
[0032] In yet a further preferred embodiment the components that
are added to form the shell comprise a mixture of several
polyelectrolytes or/and lipids or/and proteins or/and peptides
or/and nucleic acids or/and other organic and inorganic compounds
of biogenic or abiogenic origin. A suitable composition of the
liquid continuous phase with regard to salt content, pH value,
cosolvents, surfactants and a suitable selection of the coating
conditions e.g. temperature, rheological conditions, presence of
electrical or/and magnetic fields, presence of light etc. results
in a self-assembly of the diverse shell components on the templates
to form complex structures having a wide variety of biomimetic
properties.
[0033] The application according to step (b) of the method
according to the invention occurs under conditions such that a
shell of a defined thickness is formed around the template which is
in the range of 1 to 100 nm, preferably 1 to 50 nm, particularly
preferably 5 to 30 nm and most preferably 10 to 20 nm. When applied
in layers, the wall thickness and the homogeneity of the capsule
shell are determined by the number and composition of the layers
and by the precipitation process, which essentially depends on the
concentration of the template particles, the concentration of the
coating components and the rate of the solubility change in the
liquid phase which causes the precipitation.
[0034] An application by means of precipitation can for example be
carried out by firstly adding a part of the components forming the
shell to the liquid phase and subsequently adding one or more
additional shell components. Such a precipitation step can for
example be used for a combination of metal cations and oppositely
charged polyelectrolytes. Another method of precipitation is that
the components required to form the shell are already completely
present in the liquid phase and a change in the liquid phase occurs
which results in the precipitation. This change in the liquid phase
can for example comprise a change of the pH value and/or a change
in the composition of the liquid phase e.g. by adding a solvent
component or/and removing a solvent component. Thus for example
hydrophilic biopolymers such as DNA or polysaccharides can be
precipitated by adding ethanol to an aqueous liquid phase, whereas
polyelectrolyte combinations can be precipitated by evaporating off
an organic solvent such as acetone from the liquid phase.
[0035] The components used to form the shell can alternatively or
in addition also comprise nanoparticles e.g. organic or inorganic
nanoparticles, in particular nanoparticles having electrical,
magnetic or optical properties e.g. magnetite or CdTe.
[0036] The coating method according to the invention can
additionally comprise at least one additional coating step before
or/and after the precipitation step. Such an additional coating
step can for example comprise the application of one or more lipid
layers or/and the application of layers of polyelectrolytes.
[0037] The permeability of a shell can be modified by depositing
lipid layers or/and amphiphilic polyelectrolytes on the
polyelectrolyte shell. This can result in a very substantial
reduction of the permeability of the shells to small and polar
molecules. Examples of lipids that can be deposited on the shells
are lipids which carry at least one ionic or ionogenic group e.g.
phospholipids such as dipalmitoylphosphatidic acid or zwitterionic
phospholipids such as dipalmitoylphosphatidyl choline or fatty
acids or corresponding long chain alkylsulfonic acids. The use of
zwitterionic lipids enables the deposition of lipid multilayers on
the shell.
[0038] The application of polyelectrolytes in layers can for
example be carried out as described in WO 99/47252. The layered
assembly of the shells can for example be combined with the
precipitation step according to the invention in such a manner that
firstly a small number e.g. 1 to 4 layers of polyelectrolytes are
layered onto the template particles which is followed by a
precipitation step. Alternatively or additionally it is also
possible to deposit layers of polyelectrolytes on the shell after
the precipitation steps. A chemical reaction can also occur in
or/and on the shells.
[0039] The method according to the invention allows the production
of capsules whose size distribution corresponds to that of
emulsions and which in contrast to surfactant-stabilized systems,
exhibit no change in their size distribution in the sense of an
Ostwald maturation. The capsules are very stable towards chemical,
biological, mechanical and thermal stress. If they have a suitable
composition they can be dried and resuspended. They can be stored
as a concentrate in aqueous or aqueous-gel like phases.
[0040] The invention is further elucidated by the following figures
and examples.
[0041] FIG. 1 shows an embodiment of the method according to the
invention comprising a one step formation of a polyelectrolyte/ion
shell on colloidal liquid template particles.
[0042] FIG. 2 shows another embodiment of the method according to
the invention comprising a self-assembly of polymer films on the
surface of colloidal liquid particles.
[0043] FIGS. 1 and 2 show a schematic representation of two
embodiments of the method according to the invention. In FIG. 1 a
suspension of liquid template particles with added amphiphilic
polyelectrolytes (2) is produced which contains metal ions e.g.
ions of a polyvalent metal or ions of a noble metal such as
Ag.sup.+ (4). An ion/polyelectrolyte shell is precipitated on the
template particles by dropwise addition of a solution containing
negatively charged polyelectrolyte molecules (6). The coated
template particles (8) can be further processed in various ways.
Thus empty capsules (10) can be produced by dissolution of the
template particles. Metal-coated capsules (12) are obtained by
reducing the metal ions. By applying layers of oppositely charged
polyelectrolytes (14a, 14b) it is possible to produce capsules with
an anisotropic shell in which case the inner part is an
ion/polyclectrolyte shell and the outer part is a
polyelectrolyte/polyelectrolyte shell assembled in layers. Empty
capsules (18) can be subsequently produced by dissolving the
template particles. The inner ion/polyelectrolyte part of the shell
can be dissolved by removing the metal ions (4) such that the
polymer (6) is encapsulated in the interior of the shell formed
(20) by the oppositely charged polyelectrolytes (14a, 14b).
[0044] Another embodiment of the method according to the invention
is shown in FIG. 2. A suspension of colloidal liquid template
particles with added amphiphilic polyelectrolytes (32) is placed in
a liquid phase which contains a polymer e.g. a nucleic acid, a
protein, a polysaccharide or a synthetic polymer in a dissolved
form. The polymer is precipitated to form template particles (36)
coated with the polymer by changing the solvent composition e.g. by
the dropwise addition of ethanol or another solvent in which the
polymer is insoluble or only poorly soluble. Deposition of layers
of oppositely charged polyelectrolytes (38a, 38b) allows the
production of coated template particles with an anisotropic shell
(40) where the inner section of the shell is formed by the
precipitated polymer and the outer section is formed by layers of
oppositely charged polyelectrolytes. If soluble template particles
are used it is possible to dissolve them to form a polymer (42)
encapsulated in the polyelectrolyte/polyelectrolyte shell.
EXAMPLES
Example 1
[0045] Preparation of Droplet Emulsions Stabilized by Amphiphilic
Polyelectrolytes
[0046] 1.1
[0047] 0.1 g of a mixture of
hexadecyl/octadecyl-bis(polyoxyethylene)-3-su-
lfopropyl-ammonium-betaine and sodium
hexadecyl/octadecyl-bis(polyoxyethyl-
ene)-2-sulfinato-3-sulfopropyl-ammonium-betaine and
poly(diallyldimethyl)ammonium-stearate (weight ratio of simplex
compound to polyfunctional surfactant 2:1) is dissolved in 10 g
oil.
[0048] 1.2
[0049] 0.05 g of a mixture composed of
hexadecyl/octadecyl-bis(polyoxyethy-
lene)-3-sulfopropyl-ammonium-betaine and sodium
hexadecyl/octadecyl-bis(po-
lyoxyethylene)-2-sulfinato-3-sulfopropyl-ammonium-betaine and
poly[alkylmethyl-bis(polyoxyethylene)-ammonium]-polyacrylate
(weight ratio of simplex compound to polyfunctional surfactant 2:1)
is dissolved in 10 g oil.
[0050] 1.3
[0051] 0.05 g poly(diallyldimethyl)ammonium-poly(stearate) or
poly(diallyldimethyl)-ammonium-poly(erucic acid) is dissolved in 10
g oil.
[0052] 1.4
[0053] 0.05 g alkyl-dimethyl-ammonium-propyl-modified polycationic
polysiloxane is dissolved in 10 g oil.
[0054] 1.5
[0055] 0.02 g of a mixture of
hexadecyl/octadecyl-bis(polyoxyethylene)-3-s-
ulfopropyl-ammonium-betaine and
sodium-hexadecyl/octadecyl-bis(polyoxyethy-
lene)-2-sulfinato-3-sulfopropyl-ammonium-betaine is dissolved in 10
g oil.
Example 2
[0056] Layered Assembly of Polyelectrolyte Multilayers on Oil
Droplets
[0057] The modified oil phase according to the instructions 1.1 to
1.5 is emulsified in aqueous solutions of suitable
polyelectrolytes. The process is preferably continued using a
polyanion in the aqueous phase in the case of 1.1, 1.3 and 1.4 and
a polycation in the aqueous phase in the case of 1.2. 1.5 can be
processed further in polycationic as well as in polyanionic
systems. The resulting polyelectrolyte complexes in the oil/water
phase boundary give the emulsion the necessary temporary stability
towards coalescence and also stabilize the phase boundary itself so
that it is possible to continue using known stepwise or one-step
processes for the generation of polyelectrolyte multilayers.
[0058] 1 ml oil (unmodified or modified with an amphiphilic
polyelectrolyte as described in example 1.1 or 1.3) is emulsified
with 5 ml poly(styrenesulfonate sodium salt) (PSS) having a
molecular weight of 70,000 D from Aldrich (1 mg/ml in 0.5 M NaCl)
by means of ultrasound e.g. with an Ultraturrax. This results in
the formation of a first polyelectrolyte double layer at the phase
boundary between the emulsion droplets and the continuous aqueous
phase.
[0059] Subsequently 10 ml poly(allylamine hydrochloride) (PAH)
having a molecular weight of 50 to 65,000 D from Aldrich (1 mg/ml
in 0.5 M NaCl) is admixed while shaking to generate a second layer.
The third layer is formed by adding 15 ml PSS and the fourth layer
is formed by adding 20 ml PAH. A total of up to 10 layers (tenth
layer 50 ml PAH) are formed in this manner.
[0060] Multiple washing in a separating funnel results in stable
emulsions. This can be optionally followed by cross-linking steps
e.g. by glutardialdehyde.
Example 3
[0061] Complex Precipitation or Coacervation from Alkaline PSS/PAH
Solution using Emulsion Droplets as the Template
[0062] An initial solution of the two polyelectrolytes is prepared
in which they are both present simultaneously in solution without
reacting with one another. This is achieved by firstly adding 100
ml 0.1% (w/w) NaOH solution containing 0.1 M NaCl. 300 mg PSS (MW
70,000) and 200 mg PAH (MW 50-65,000) are successively dissolved in
this solution. It is shaken until complete dissolution. This
solution is stable for several hours. 20 ml oil (unmodified or
modified according to formulations 1.1 to 1.5) is added. It is
subsequently emulsified with an Ultraturrax and then rapidly
titrated into the neutral range with 10% (w/w) HCl. The emulsion is
subsequently purified e.g. washed several times in a separation
funnel. This results in an emulsion which is stable for months.
Example 4
[0063] One-Step Precipitation from a Solution Containing a Complex
of a Polyelectrolyte and a Multivalent Ion
[0064] Solution I: 1 ml PSS solution (2 mg/ml) is mixed with 200
.mu.l of a Y(NO.sub.3).sub.3 solution (2.times.10.sup.-2 M). The
resulting charge ratio between sulfate and yttrium is 5:3.
[0065] Solution II: 400 .mu.l oil is mixed with 1 ml water. The
mixture is emulsified for 3 to 4 minutes with ultrasound in an
Ultraturrax.
[0066] Solution I is then rapidly added to solution II and the
resulting emulsion is shaken in a vortex for 2 minutes. The
emulsion is stable for more than 20 hours and can optionally be
used as a starting system for further coatings.
* * * * *