U.S. patent application number 13/653909 was filed with the patent office on 2013-04-25 for dried formulations of nanoparticle-coated capsules.
This patent application is currently assigned to University of South Australia. The applicant listed for this patent is University of South Australia. Invention is credited to Clive Allan PRESTIDGE, Spomenka Simovic.
Application Number | 20130101651 13/653909 |
Document ID | / |
Family ID | 37498019 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130101651 |
Kind Code |
A1 |
PRESTIDGE; Clive Allan ; et
al. |
April 25, 2013 |
DRIED FORMULATIONS OF NANOPARTICLE-COATED CAPSULES
Abstract
A method of producing a dried formulation for an active
substance such as a drug compound is described. The method involves
dispersing a discontinuous phase (e.g. an oil-based or lipidic
medium) comprising the active substance into a continuous phase
(e.g. water) so as to form a two-phase liquid system comprising
droplets of said discontinuous phase, allowing nanoparticles to
congregate at the phase interface at the surface of the droplets
such that at least one layer of nanoparticles coat the droplets and
thereby provide sufficient structural integrity to the droplets to
enable the subsequent removal of the continuous phase, and
thereafter removing the continuous phase from the
nanoparticle-coated droplets to produce a dried formulation.
Inventors: |
PRESTIDGE; Clive Allan;
(Semaphore South, AU) ; Simovic; Spomenka;
(Adelaide, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of South Australia; |
Adelaide |
|
AU |
|
|
Assignee: |
University of South
Australia
Adelaide
AU
|
Family ID: |
37498019 |
Appl. No.: |
13/653909 |
Filed: |
October 17, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12902769 |
Oct 12, 2010 |
8303992 |
|
|
13653909 |
|
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11916570 |
Dec 5, 2007 |
|
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PCT/AU2006/000771 |
Jun 7, 2006 |
|
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12902769 |
|
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Current U.S.
Class: |
424/401 ;
424/490; 427/2.14; 427/213.3; 977/773; 977/892; 977/906 |
Current CPC
Class: |
A23V 2002/00 20130101;
A61K 2800/412 20130101; A61K 2800/413 20130101; A61K 9/14 20130101;
A61K 47/28 20130101; B01J 13/22 20130101; B82Y 5/00 20130101; A61K
9/1271 20130101; A61K 8/11 20130101; A23L 33/115 20160801; A61Q
17/04 20130101; A61K 8/0241 20130101; A61K 8/63 20130101; A61K
9/5115 20130101; A61J 3/005 20130101; A61K 9/127 20130101; A61K
47/24 20130101; A61K 8/04 20130101; A61K 47/02 20130101; A61K 9/10
20130101; A61K 8/25 20130101; A61K 31/7088 20130101; B01J 13/02
20130101; A61K 9/5192 20130101; A61K 8/553 20130101; A61K 2800/651
20130101; A61K 38/00 20130101; A61K 9/501 20130101; A61K 9/1075
20130101; A61Q 19/00 20130101; A61J 3/02 20130101; A61K 9/5089
20130101; A23P 10/35 20160801; A61K 8/06 20130101 |
Class at
Publication: |
424/401 ;
424/490; 427/2.14; 427/213.3; 977/773; 977/892; 977/906 |
International
Class: |
A61K 8/02 20060101
A61K008/02; A61K 9/14 20060101 A61K009/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2005 |
AU |
2005902937 |
Claims
1. A method of producing a dried formulation for an active
substance, said method comprising the steps of: (i) dispersing a
discontinuous phase comprising an active substance into a
continuous phase so as to form a two-phase liquid system comprising
droplets of said discontinuous phase, each of said droplets having,
at its surface, a phase interface; (ii) allowing nanoparticles
provided to said two-phase liquid system to congregate at the phase
interface to coat said surface of the droplets in at least one
layer of said nanoparticles, wherein said at least one layer of
nanoparticles provides sufficient structural integrity to the
droplets to enable the subsequent removal of the continuous phase;
and (iii) removing the continuous phase from the
nanoparticle-coated droplets to produce a dried formulation.
2. A method of producing a dried formulation for an active
substance, said method comprising the steps of: (i) dispersing a
discontinuous phase comprising an active substance into a
continuous phase so as to form a two-phase liquid system comprising
droplets of said discontinuous phase, each of said droplets having,
at its surface, a phase interface; and (ii) removing the continuous
phase to produce a dried formulation, during which nanoparticles
provided to said two-phase liquid system congregate at the phase
interface to coat said surface of the droplets in at least one
layer of said nanoparticles, wherein said at least one layer of
nanoparticles provides sufficient structural integrity to the
droplets to withstand the removal of the continuous phase.
3. The method of claim 1, wherein the discontinuous phase is an
oil-based or lipidic medium and the continuous phase is
aqueous.
4. The method of claim 1, wherein the discontinuous phase is
aqueous and each droplet is surrounded by a single or multiple
lipid bilayer, and the continuous phase is also aqueous.
5. The method of claim 3, wherein either or both of the
discontinuous and continuous phases comprises an emulsifier to
stabilise the emulsion prior to the congregation of the
nanoparticles.
6. The method of claim 5, wherein the emulsifier is lecithin or
oleylamine.
7. The method of claim 1, wherein the active substance is selected
from nutriceutical substances, cosmetic substances and drug
compounds.
8. The method of claim 7, wherein the active substance is selected
from lipophilic drug compounds and the discontinuous phase is an
oil-based or lipidic medium.
9. The method of claim 3, wherein the nanoparticles are provided by
dispersing the nanoparticles in the discontinuous phase prior to
the formation of the two-phase liquid system in step (i).
10. The method of claim 3, wherein the nanoparticles are provided
by dispersing the nanoparticles in both the discontinuous phase and
the continuous phase prior to the formation of the two-phase liquid
system in step (i).
11. The method of claim 3, wherein the nanoparticles are provided
in an amount such that the mass ratio of the discontinuous phase to
nanoparticles is at least 1:0.05.
12. The method of claim 1, wherein the nanoparticles have
hydrophilic surfaces.
13. The method of claim 1, wherein the droplets are coated with an
inner and outer layer of nanoparticles, the nanoparticles of the
inner layer having hydrophobic surfaces and the nanoparticles of
the outer layer having hydrophilic surfaces.
14. The method of claim 12, wherein the nanoparticles having
hydrophilic surfaces are silica nanoparticles.
15. The method of claim 1, wherein said nanoparticles have an
average diameter in the range of 20-80 nm.
16. The method of claim 15, wherein said nanoparticles have an
average diameter of about 50 nm.
17. The method of claim 1, wherein the size of said nanoparticles
is such that the ratio of nanoparticle size to the size of the
nanoparticle-coated droplets is about 1:10.
18. The method of claim 1, wherein step (ii) is conducted in the
presence of an amount of electrolyte in the range of
0.5.times.10.sup.-4 to 1.times.10.sup.-1 M.
19. The method of claim 18, wherein the electrolyte is NaCl.
20. The method of claim 1, wherein step (iii) is performed by spray
drying.
21. The method of claim 1, wherein the nanoparticle-coated droplets
of the dried formulation can be readily re-dispersed to form a
two-phase liquid system which is substantially identical or similar
in composition to that from which the dried formulation was
prepared after storage at room temperature for 24 hours.
22. A method of producing a dried formulation for an active
substance, said method comprising the steps of: (i) dispersing an
oil-based medium comprising an active substance into an aqueous
phase so as to form a two-phase liquid system comprising droplets
of said oil-based medium, each of said droplets having, at its
surface, a phase interface; (ii) allowing nanoparticles provided to
said two-phase liquid system to congregate at the phase interface
to coat said surface of the droplets in at least one layer of said
nanoparticles, wherein said at least one layer of nanoparticles
provides sufficient structural integrity to the droplets to enable
the subsequent removal of the continuous phase, and wherein the
average diameter of the nanoparticles is in the range of 20-80 nm,
and the nanoparticles are provided at a mass ratio of the
discontinuous phase to nanoparticles of at least 1:0.05; and (iii)
removing the continuous phase from the nanoparticle-coated droplets
to produce a dried formulation.
23. The method of claim 22, wherein either or both of the
discontinuous and continuous phases comprises an emulsifier to
stabilise the emulsion prior to the congregation of the
nanoparticles.
24. The method of claim 22, wherein the emulsifier is lecithin or
oleylamine.
25. The method of claim 22, wherein the active substance is
selected from nutriceutical substances, cosmetic substances and
drug compounds.
26. The method of claim 25, wherein the active substance is
selected from lipophilic drug compounds.
27. The method of claim 22, wherein the nanoparticles are provided
by dispersing the nanoparticles in the discontinuous phase prior to
the formation of the two-phase liquid system in step (i).
28. The method of claim 22, wherein the nanoparticles are provided
by dispersing the nanoparticles in both the discontinuous phase and
the continuous phase prior to the formation of the two-phase liquid
system in step (i).
29. The method of claim 22, wherein the nanoparticles have
hydrophilic surfaces.
30. The method of claim 22, wherein the droplets are coated with an
inner and outer layer of nanoparticles, the nanoparticles of the
inner layer having hydrophobic surfaces and the nanoparticles of
the outer layer having hydrophilic surfaces.
31. The method of claim 29, wherein the nanoparticles having
hydrophilic surfaces are silica nanoparticles.
32. The method of claim 22, wherein said nanoparticles have an
average diameter of about 50 nm.
33. The method of claim 22, wherein the size of said nanoparticles
is such that the ratio of nanoparticle size to the size of the
nanoparticle-coated droplets is about 1:10.
34. The method of claim 22, wherein step (ii) is conducted in the
presence of an amount of electrolyte in the range of
0.5.times.10.sup.-4 to 1.times.10.sup.-1 M.
35. The method of claim 34, wherein the electrolyte is NaCl.
36. The method of claim 35, wherein step (ii) is conducted in the
presence of about 1.times.10.sup.-4 NaCl.
37. The method of claim 22, wherein step (iii) is performed by
spray drying.
38. The method of claim 22, wherein the nanoparticle-coated
droplets of the dried formulation can be readily re-dispersed to
form a two-phase liquid system which is substantially identical or
similar in composition to that from which the dried for was
prepared, after storage at room temperature for 24 hours.
39. A dried formulation produced in accordance with claim 1.
40. The formulation of claim 39, wherein the discontinuous phase is
an oil-based or lipidic medium and the continuous phase is
aqueous.
41. The formulation of claim 39, wherein the discontinuous phase is
aqueous and each droplet is surrounded by a single or multiple
lipid bilayer underlying the at least one layer of nanoparticles,
and the continuous phase is also aqueous.
42. The formulation of claim 40, wherein either or both of the
discontinuous and continuous phases comprises an emulsifier.
43. The formulation of claim 42, wherein the emulsifier is lecithin
or oleylamine.
44. The formulation of claim 39 wherein the active substance is
selected from nutriceutical substances, cosmetic substances and
drug compounds.
45. The formulation of claim 44, wherein the active substance is
selected from lipophilic drug compounds and the discontinuous phase
is an oil-based lipidic medium.
46. The formulation of claim 39, wherein the nanoparticles have
hydrophilic surfaces.
47. The formulation of claim 39, wherein the droplets are coated
with an inner and outer layer of nanoparticles, the nanoparticles
of the inner layer having hydrophobic surfaces and the
nanoparticles of the outer layer having hydrophilic surfaces.
48. The formulation of claim 46, wherein the nanoparticles having
hydrophilic surfaces are silica nanoparticles.
49. The formulation of claim 39, wherein said nanoparticles have an
average diameter in the range of 20-80 nm.
50. The formulation of claim 49, wherein said nanoparticles have an
average diameter of about 50 nm.
51. The formulation claim 39, wherein the size of said
nanoparticles is such that the ratio of nanoparticle size to the
size of the nanoparticle-coated droplets is about 1:10.
52. The formulation of claim 39, wherein the nanoparticle-coated
droplets can be readily re-dispersed to form a two-phase liquid
system which is substantially identical or similar in composition
to that from which the formulation was prepared, after storage at
room temperature for 24 hours.
Description
[0001] This application is a continuation of U.S. Ser. No.
12/902,769, filed Oct. 12, 2010, which is a continuation of U.S.
Ser. No. 11/916,570, filed Dec. 5, 2007, now abandoned, which is a
371 filing of PCT/AU2006/000771, filed Jun. 7, 2006 which claims
priority from Australian Patent Application No. 2005902937, filed
Jun. 7, 2005. These prior applications are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to the encapsulation by
nanoparticles of a liquid droplet or a lipid vesicle to form a
stable capsule.
BACKGROUND OF THE INVENTION
[0003] The development of new forms of active substances such as
drug compounds and pesticides, as well as a desire to increase the
efficacy of existing substances, has created a need to develop new
and effective ways of delivering substances to their appropriate
targets. It is likely that many potentially useful active
substances have not been commercialised because of inadequate
formulation. In many cases, the inability to formulate the active
substance into a deliverable form could simply be due to solubility
problems.
[0004] Although useful as vehicles for the delivery of active
substances, most emulsions and liposomes are limited by the fact
they are thermodynamically unstable and, generally, over time, will
coalesce and may eventually separate into two distinct liquid
phases (emulsions) or will degrade and release the fluid-filled
core into the surrounding media (liposomes). This instability is
exacerbated in veterinary and pharmacological applications since
the vehicles are used under circumstances (e.g. increased salt
(electrolyte) or variations in pH) which put a severe strain on the
vehicle structure. The degradation of vehicles containing active
substances is undesirable since considerable time and effort is
spent in formulating the delivery system. In the veterinary,
pharmaceutical and nutriceutical industries in particular, if
vehicle stability is compromised, the bioavailability of the active
substance may be affected.
[0005] Particle stabilised emulsions are known, however, the
stability of the resulting capsules remains poor over a period of
time. This means that it is difficult to transport the capsules
over long distances and it is difficult to store the capsules for a
delayed time of use. As the capsules degrade, the active substance
(e.g. a drug compound or a pesticide) within the capsules can leach
out, or may be released without control. Leaching or uncontrolled
release of active substances can pose a serious problem in the
delivery of certain drugs in the body, since one intent of the
encapsulation process is to shield healthy cells from the drug's
toxicity and prevent the drug from concentrating in vulnerable
tissues (e.g. the kidneys and liver).
[0006] Existing preparations of particle stabilised vehicles
(capsules) are usually dispersed in a liquid in order that the
capsules can be delivered to the body as a liquid suspension. These
liquid formulations usually have a low active substance content to
liquid ratio and, in addition, during storage or transport, there
is a risk of microbial growth in the liquid which can cause serious
infections or spoilage.
[0007] A further problem is coalescence of the capsules to form
capsules with an increased diameter. Larger capsules are less
stable over time, and larger capsules cannot be delivered to some
areas where the diameter of the capsule will not be permitted (e.g.
capillaries in the body). Further to this, active substance release
profiles are correlated with interfacial surface area. It is
important, therefore, that capsule size remain constant in order
that the release profile of the active substance is maintained.
[0008] Accordingly, it is an object of the present invention to
provide a capsule for the delivery and/or dry storage of an active
substance which has a relatively long shelf-life and is therefore
easy to store or transport and may have a reduced risk of microbial
growth during storage.
SUMMARY OF THE INVENTION
[0009] A method of producing a dried formulation for an active
substance, said method comprising the steps of: [0010] (i)
dispersing a discontinuous phase comprising an active substance
into a continuous phase so as to form a two-phase liquid system
comprising droplets of said discontinuous phase, each of said
droplets having, at its surface, a phase interface; [0011] (ii)
allowing nanoparticles provided to said two-phase liquid system to
congregate at the phase interface to coat said surface of the
droplets in at least one layer of said nanoparticles, wherein said
at least one layer of nanoparticles provides sufficient structural
integrity to the droplets to enable the subsequent removal of the
continuous phase; and [0012] (iii) removing the continuous phase
from the nanoparticle-coated droplets to produce a dried
formulation.
[0013] The discontinuous phase may be dispersed in the continuous
phase to form a two-phase liquid system (e.g. an emulsion) by any
of the methods well known to persons skilled in the art (e.g. by
homogenisation).
[0014] Preferably, the discontinuous phase is an oil-based or
lipidic medium (e.g. a phospholipid preparation), and the
continuous phase is aqueous.
[0015] However, alternatively, the discontinuous phase is aqueous
and the continuous phase is an oil-based or lipidic medium.
[0016] Also alternatively, the discontinuous phase is aqueous and
each droplet is surrounded by a single or multiple lipid bilayer
(i.e. thereby forming a liposome), and the continuous phase is also
aqueous.
[0017] Either or both of the discontinuous and continuous phases
may comprise an emulsifier to stabilise the emulsion prior to the
congregation of the nanoparticles. Suitable emulsifiers include
lecithin, oleylamine, sodium deoxycholate,
1,2-distearyl-sn-glycero-3-phosphatidyl ethanolamine-N,
stearylamine and 1,2-dioleoyl-3-trimethylammonium-propane.
Preferably, the emulsifier is oleylamine which confers a positive
charge to the droplets.
[0018] The emulsifier will typically be provided in an amount in
the range of 0.0001 to 10 wt % of the emulsion, more preferably, in
the range of 0.01 to 1 wt % of the emulsion.
[0019] The active substance may be selected from nutriceutical
substances, cosmetic substances (including sunscreens), pesticide
compounds, agrochemicals and foodstuffs. However, preferably, the
active substance is selected from drug compounds. The active
substance may be a biological agent such as a peptide, protein or
nucleic acid (e.g. deoxyribonucleic acid (DNA)). Such biological
agents are particularly suitable for formulation within capsules
comprising liposomes.
[0020] The nanoparticles may have hydrophilic or hydrophobic
surfaces. However, when the discontinuous phase is an oil-based or
lipidic medium, preferably the nanoparticles will have hydrophilic
surfaces. In one preferred embodiment, the droplets will be coated
with a single layer, or multiple layers, of hydrophilic
nanoparticles. However, in another preferred embodiment, the
droplets will be coated with at least two layers of nanoparticles,
the inner layer of nanoparticles having hydrophobic surfaces while
the outer layer of nanoparticles have hydrophilic surfaces.
[0021] The nanoparticles may be positively or negatively
charged.
[0022] Preferably, said nanoparticles have an average diameter of
5-2000 nm, more preferably 20-80 nm, and most preferably about 50
nm. Also, preferably, the size of the nanoparticles will be such
that the ratio of nanoparticle size to the size of the
nanoparticle-coated droplets (i.e. capsules) is in the range of 1:4
to 1:20 and, more preferably, is about 1:10.
[0023] Preferably, the nanoparticles are composed of silica,
however nanoparticles composed of other substances (e.g. titania
and latex) are also suitable.
[0024] Congregation of the nanoparticles (e.g. by self-assembly
and/or adsorption) at the phase interface results in the coating of
the surface of the droplets in at least one layer of nanoparticles
such that sufficient structural integrity is provided to the
droplets so that they may withstand removal of the continuous phase
to produce a dried formulation. By "structural integrity", it is to
be understood that the capsules substantially retain the active
substance (i.e. the capsules do not exhibit substantial leaching of
the active substance) and do not substantially coalesce with one
another to form larger capsules over time. To achieve such
structural integrity may require providing the nanoparticles to the
two-phase liquid system within a particular concentration
range.
[0025] Preferably, the congregation of the nanoparticles at the
phase interface occurs in the presence of an amount of electrolyte
suitable to enhance the congregation of the nanoparticles at the
phase interface. The amount of the electrolyte will typically be at
least 0.5.times.10.sup.-4 M, preferably, at least 1.times.10.sup.-3
M. However, preferably, the concentration of electrolyte will be no
more than 1.times.10.sup.-1 M.
[0026] Preferably, the electrolyte is NaCl.
[0027] The removal of the continuous phase is a drying step which
may be performed using a rotary evaporator. Alternatively, the
removal of the continuous phase may be performed by freeze drying,
spray drying or fluidised bed procedures.
[0028] Following step (ii) but prior to the drying step, additional
nanoparticles may be added to the two-phase liquid system, if
desired.
[0029] The capsules of the dried formulation may be readily
re-dispersed into a liquid to re-form a two-phase liquid system. In
particular, the re-dispersed capsules may form a capsule-based
emulsion (which might be a capsule-based liposome emulsion) which
is substantially identical or similar in composition to that from
which the dried formulation was prepared after storage at room
temperature for 24 hours, and more preferably, after storage at
room temperature for 2 months. "Substantially identical or similar"
in this context is intended to mean that the average diameter size
of the capsules is the same or varies from the original capsules by
no more than a factor of about 4 times (i.e. the average diameter
size of the re-dispersed capsules is no more than 4 times greater
in size or 4 times less in size than the original capsules).
Further, preferably, few (if any) of the re-dispersed capsules have
a diameter size greater than 10 .mu.m; for example, preferably less
than 5% of the re-dispersed capsules, by volume, have a diameter
size of greater than 10 .mu.m). The re-dispersed capsules are
stable and typically show no substantial degradation after 24 hours
storage at room temperature (i.e. after 24 hours, the average
diameter size of the re-dispersed capsules remains at no more than
4 times greater in size or 4 times less in size than the original
capsules, and preferably less than 5% of the re-dispersed capsules,
by volume, have a diameter size of greater than 10 .mu.m).
[0030] In a variation of the present invention, prior to the
removal of the continuous phase, the capsules may be provided with
a polymer layer around the periphery to modify the interfacial
properties of the capsule.
[0031] In a further variation, the discontinuous phase may,
optionally, be cross-linked or otherwise comprise a gelling
material so as to form a matrix. While re-dispersed capsules from
dried formulations produced in accordance with the present
invention are permeable (i.e. the nanoparticle coating will be
porous), and thereby typically show controlled release of the
active substance at rates dependent upon the degree of permeability
(e.g. a capsule with a lower degree of permeability (i.e. a
"semi-permeable" capsule), will show sustained release of the
active substance), the inclusion of a cross-linked or gelled matrix
within the discontinuous phase can be used to provide further
control to the release of the active substance from the capsules,
particularly sustained release.
[0032] In a still further variation of the present invention, the
nanoparticles provided to the two-phase liquid system congregate at
the phase interface while the continuous phase is being removed
(i.e. during the drying step).
[0033] Thus, in a second aspect, the present invention provides a
method of producing a dried formulation for an active substance,
said method comprising the steps of: [0034] (i) dispersing a
discontinuous phase comprising an active substance into a
continuous phase so as to form a two-phase liquid system comprising
droplets of said discontinuous phase, each of said droplets having,
at its surface, a phase interface; and [0035] (ii) removing the
continuous phase to produce a dried formulation, during which
nanoparticles provided to said two-phase liquid system congregate
at the phase interface to coat said surface of the droplets in at
least one layer of said nanoparticles, wherein said at least one
layer of nanoparticles provides sufficient structural integrity to
the droplets to withstand the removal of the continuous phase.
[0036] The method of the second aspect is particularly suitable
wherein the droplets are negatively charged, and the nanoparticles
to be used are negatively charged, hydrophilic nanoparticles.
[0037] In a third aspect, the present invention provides a dried
formulation for an active substance, said formulation comprising
droplets formed by dispersing a discontinuous phase comprising an
active substance into a continuous phase so as to form a two-phase
liquid system, wherein each droplet is coated in at least one layer
of said nanoparticles and the continuous phase has been
removed.
[0038] The formulation comprises droplets formed by dispersing a
discontinuous phase into a continuous phase to form a two-phase
liquid system. As with the methods of the first and second aspects
of the present invention, preferably the discontinuous phase is an
oil-based or lipidic medium and the continuous phase is aqueous.
Either or both of the discontinuous and continuous phases may
comprise an emulsifier (e.g. lecithin) to stabilise the emulsion
prior to coating with at least one layer of nanoparticles.
[0039] The active substance may be selected from those mentioned
above.
[0040] Preferably, said nanoparticles have an average diameter of
5-2000 nm, more preferably 20-80 nm, and most preferably about 50
nm. Also, preferably, the size of the nanoparticles will be such
that the ratio of nanoparticle size to capsule size is in the range
of 1:4 to 1:20 and, more preferably, is about 1:10.
[0041] Preferably, the nanoparticles are composed of silica,
however nanoparticles composed of other substances (e.g. titania
and latex) are also suitable.
[0042] The capsules of the dried formulation may be readily
re-dispersed into a liquid to re-form a two-phase liquid system. In
particular, the re-dispersed capsules may form a capsule-based
emulsion which is substantially identical or similar in composition
to that from which the dried formulation was prepared.
[0043] In variations of the formulation of the present invention,
the capsules may be provided with a polymer layer around the
periphery to modify the interfacial properties of the capsule.
Also, the discontinuous phase may, optionally, be cross-linked or
otherwise comprise a gelling material so as to form a matrix, which
may enable controlled release of an active substance (i.e.
sustained release) from the capsules.
[0044] The present invention provides a method for producing dried
formulations of nanoparticle-coated capsules comprising a drug
compound. An advantage of such formulations is that the dried
capsules (e.g. in the form of a dry powder), have a long shelf life
and do not exhibit substantial leaching of the drug compound over
times that drug formulations are commonly stored (e.g. 1 to 9
months). In addition, the capsules have a low propensity to
coalescence. The dried capsules can be readily re-dispersed into a
liquid to re-form a stable emulsion, thereby providing a useful
drug formulation for the pharmaceutical industry. The capsules can
be readily stored and/or transported dry.
[0045] In addition, the nanoparticle coating on the droplets of the
capsules can protect labile active substances (i.e. chemically
unstable substances) from degradation caused by acidity (i.e. low
pH), oxidation and crystallisation, etc. The nanoparticle coating
is also resistant to water (i.e. the nanoparticle coat does not
substantially expand or degrade in the presence of water).
[0046] The ability to protect the active substances from the
degradative effects of acidity, makes the dried formulation of the
present invention particularly useful in the oral administration of
labile drug compounds (i.e. where it is desirable that the drug
compound be protected from the high acidity of the stomach before
reaching the small intestine where the drug compound may be
adsorbed into the bloodstream).
[0047] In a further aspect, the present invention provides a
formulation for an active substance, said formulation comprising
droplets formed by dispersing a discontinuous phase comprising an
active substance into a continuous phase so as to form a two-phase
liquid system, wherein each droplet is coated in at least one layer
of said nanoparticles.
[0048] The formulation of the further aspect can be dried or,
otherwise, can be used in its liquid form.
[0049] In one preferred embodiment of the formulation of the
further aspect, the capsules are provided with a polymer layer
around the periphery to modify the interfacial properties of the
capsule. In this way, the capsules may be made to be
"lipoadhesive", particularly if the polymer layer has adhesive
properties with lipid-like surfaces. One significant aspect of this
is that the capsules can be then be engineered to adhere to
particular sites in vivo (e.g. mucoadhesive polymer layers
facilitate adhesion to mucous membranes), thereby ensuring long
contact times and effective transport of the active substance. This
can be particularly useful for the delivery of poorly soluble drug
compounds to various parts of the gastrointestinal tract (i.e. to
improve bioavailability). It may also be used to facilitate
delivery of an active substance to the mouth.
[0050] The combination of polymers and nanoparticles at the capsule
surface can lead to further controlled release properties.
[0051] The invention will be generally discussed hereinafter in
relation to drug delivery from emulsions but it is not so
restricted and as mentioned above, nanoparticles may congregate at
the phase interface of other suitable vehicles (e.g. liposomes and
solid particles).
[0052] Throughout this specification and the claims that follow
unless the context requires otherwise, the words "comprise" and
"include" and variations such as "comprising" and "including" will
be understood to imply the inclusion of a stated integer or group
of integers but not the exclusion of any other integer or group of
integers.
[0053] The reference to any prior art in this specification is not,
and should not be taken as, an acknowledgment or any form of
suggestion that such prior art forms part of the common general
knowledge.
[0054] Specific embodiments of the invention will now be described
in some further detail with reference to and as illustrated in the
accompanying figures. These embodiments are illustrative, and not
meant to be restrictive of the scope of the invention. Suggestions
and descriptions of other embodiments may be included within the
scope of the invention but they may not be illustrated in the
accompanying figures or alternatively features of the invention may
be shown in the figures but not described in the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] An illustrative embodiment of the present invention is
discussed hereinafter with reference to the accompanying drawings
wherein:
[0056] FIG. 1 is a cross-sectional schematic of an emulsion known
in the art;
[0057] FIG. 2 is a cross-sectional schematic of a
nanoparticle-stabilised emulsion according to the present
invention;
[0058] FIG. 3 is a graph to show adsorption isotherms of
hydrophilic silica nanoparticles assembling at the oil water
interface;
[0059] FIG. 4 is a graph to show adsorption isotherms of
hydrophobic silica nanoparticles assembling at the oil water
interface;
[0060] FIG. 5 is a flow chart showing the steps involved in
obtaining the dry capsules of the present invention;
[0061] FIG. 6 is a schematic of the processes involved in obtaining
the capsules of the present invention as well as showing the
re-dispersion of the capsules;
[0062] FIG. 7a shows the emulsion droplet size range;
[0063] FIG. 7b is the tabular form of FIG. 7a, showing the emulsion
droplet size range;
[0064] FIG. 8 shows the average diameter of the silica
nanoparticles in nanometres; and
[0065] FIG. 9 shows the long-term physical stability of negatively
charged emulsions in the presence of increasing concentrations of
hydrophilic silica nanoparticles.
DESCRIPTION OF PREFERRED EMBODIMENT
[0066] FIG. 1 is a cross-sectional schematic of a two-phase liquid
system referred to as an emulsion having a discontinuous oil phase
in the form of droplets 10 dispersed in a continuous aqueous phase
12, thereby defining a phase interface 14. After a period of time,
adjacent oil droplets 10 will coalesce (the beginning of phase
separation) to form larger oil droplets. If an emulsion is not
stabilised by an emulsifier localised in the thin film 16, then
coalescence of the emulsion will occur within minutes. Eventually
the oil phase 10 and aqueous phase 12 will have completely
separated into the two component phases (oil and water).
[0067] FIG. 2 shows the system of FIG. 1 where droplets 10 have
been stabilised by nanoparticles 18 at the interface 14. Two
otherwise immiscible liquids (10 and 12) have thereby formed a
stabilised emulsion (nb. FIG. 2 is a schematic and nanoparticles 18
are not drawn to scale with respect to droplets 10).
[0068] In the preferred embodiment, as described above, the
discontinuous phase is an oil-based or lipidic medium and the
continuous phase is aqueous. However, the discontinuous phase may
be an aqueous phase dispersed in an oil-based or lipidic medium.
Further, the discontinuous phase may be aqueous and each droplet
surrounded by a single or multiple lipid bilayer (i.e. thereby
forming a liposome), and the continuous phase is also aqueous.
[0069] In order to improve biocompatibility of the emulsion, the
oil phase can be a fatty-food simulant such as a triglyceride (e.g.
Miglycol 812.TM.). Alternatively, the oil phase can be a silicone
such as polydimethlysiloxane (PDMS), or any other oily medium which
will form an emulsion with an aqueous phase.
[0070] Nanoparticles 18 are dispersed in a liquid by sonication and
provided to the emulsion in order to coat each droplet 10 in at
least one layer of nanoparticles. In a preferred embodiment, the
liquid dispersion comprises 1% by weight (1 wt %) of nanoparticles
in an aqueous medium (i.e. 1 g of nanoparticles per 100 ml).
However, other weight % dispersions can be usefully employed. Upon
addition, the nanoparticles congregate at the phase interface 14
(e.g. by self-assembly). Alternatively, rather then being added to
the preformed emulsion, nanoparticles 18 can be first dispersed in
either phase (i.e. the oil or aqueous phase) or both phases (i.e.
the oil and the water phase) and, as an emulsion is formed,
nanoparticles 18 will congregate at the phase interface 14.
Nanoparticles 18 form at least a partial coating over the surface
of droplets 10 (phase interface 14). The resulting
nanoparticle-coated droplet is referred to as a capsule 20.
[0071] Preferably, the ratio of nanoparticle size to capsule size
is between 1:4 and 1:20. The nanoparticles 18 which stabilise the
emulsion may have an average diameter in the range 5 nm-2000 nm and
may be made from any suitable material (e.g. titania or latex).
Preferably, the nanoparticles are silica nanoparticles having an
average diameter of between 20-80 nm. In the preferred embodiment,
the nanoparticles have an average diameter of approximately 50 nm
and the capsule diameter size ranges between 200-850 nm with an
average capsule size of approximately 500 nm. The approximate ratio
of nanoparticle to capsule size is therefore, preferably about
1:10.
[0072] In a preferred embodiment, the nanoparticles are
Aerosil.RTM. silica nanoparticles (Degussa AG, Dusseldorf,
Germany). The surfaces of nanoparticles 18 may be chemically or
physically modified to hydrophobise the nanoparticles 18.
[0073] Capsule 20 has a liquid core 22 (the discontinuous phase)
which may comprise or contain active substance 24. Preferably, the
liquid core 22 is a hydrophobic or lipidic medium and contains a
lipophilic active substance 24 therein. It is an option, however,
that the liquid core 22 is aqueous and has a hydrophilic active
substance 24 dissolved therein. In FIG. 2, the cross-sectional
depiction shows active substance 24. The active substance may be
any substance which is required to be protected and/or delivered by
capsule 20. The active substance may be selected from nutriceutical
substances, cosmetic substances (including sunscreens), pesticide
compounds, agrochemicals and foodstuffs. In the preferred
embodiment, the active substance 24 is a drug compound. The active
substance 24 may be wholly or partially soluble or dispersible
within liquid core 22. Also, the oil phase may, optionally, be
cross-linked or otherwise comprise a gelling material so as to form
a matrix which can enable controlled release of an active substance
(i.e. sustained release) from the capsules.
[0074] It is an option that the outer surface of the capsules 20 be
coated with a layer that improves the interfacial properties of the
capsules. For example, in drug delivery, capsules 20 may be further
coated with a polymer layer around the periphery of capsule 20 to
increase the bioadhesivity of the capsule to cells within the body.
Such a layer may comprise a polymer selected from methylcellulose,
hydroxypropylcellulose, ethylcellulose, polyethyleneglycols,
chitosan, guar gum, alginates, eudragit and pemulen, etc. Other
coatings around the capsule 20 which improve or modify the
interfacial properties of the capsule may be used. An example of
the preparation of a coated capsule is given in Example 5.
Drying the Capsules
[0075] A delivery system which is dry and can be transported,
stored and/or administered as a powder is an advantage in many
industries, such as the pharmaceutical industry, since dry powder
formulations usually have a higher active substance content
compared with an aqueous formulation. This means that less volume
of the delivery system is required for administration of an
effective amount of active substance. The increase in active
substance content in dry formulations is mainly due to the
elimination of unnecessary liquids.
[0076] FIG. 5 is a flow chart outlining the processes involved in
obtaining the dried formulation. In step 26, the amount (i.e.
volume of nanoparticle 1 wt % dispersion) of nanoparticles and,
optionally, the properties of nanoparticles 18, provided to the
emulsion, are selected or otherwise controlled so that capsules 20
can withstand the removal of the continuous phase during a
subsequent drying step (discussed further below). The nanoparticles
should provide sufficient structural integrity to the coated
droplets (capsules) to enable the subsequent removal of the
continuous phase to produce the dry formulation. A capsule having
"structural integrity" substantially retains the active substance
within its core and does not exhibit substantial leaching of the
active substance and also does not substantially coalesce with
other capsules to form larger capsules over time. To achieve such
structural integrity may require providing the nanoparticles to the
two-phase liquid system within a particular concentration range as
described below.
[0077] The emulsion can be dried by any suitable method, for
example freeze drying, spray drying or fluidised bed techniques. In
step 28, the emulsion is dried by spray-drying and the resulting
dried capsules are collected in a suitable vessel.
[0078] FIG. 6 depicts the dried capsules 20 in vessel 33. Dried
capsules 20 have nanoparticles 18 congregated at their surface 14.
Once dried, it is an option that dried capsules 20 are delivered in
dry form (step 32). Dry formulations have increased active
substance loading, thereby reducing the amount of formulation that
is required. A further advantage is that the risk of microbial
growth, which can cause serious infections or spoilage, is reduced
in dry formulations compared with liquid formulation.
[0079] Not all capsules formed in the wet phase are able to be
dried (i.e. some capsules lack the abovementioned structural
integrity). Table 1 below shows the results of a number of
experiments in which the capsules collapsed during the drying
step.
[0080] Table 1 shows that of the 27 different tested variations
(using hydrophilic silica nanoparticles with an average diameter of
about 50 nm, and an oil-based discontinuous phase stabilised with
lecithin (negatively charged oil droplets) or oleylamine
(positively charged droplets) within an aqueous continuous phase),
19 combinations formed capsules which maintained their structural
integrity during removal of the continuous phase. In the first six
rows of the table, a dry powder of capsules could not be obtained
due to loss of structural integrity and subsequent degradation of
capsules. The experiments shown in rows G show the oil to
nanoparticle mass ratios which formed dry capsules.
[0081] It can be seen that an oil to nanoparticle mass ratio of at
least 1:0.05 was required in order to be able to produce dried
capsules with positively charged droplets, and that an oil to
nanoparticle mass ratio of at least 1:0.2 was required in order to
be able to produce dried capsules with negatively charged
droplets.
TABLE-US-00001 TABLE 1 Emulsion and hydrophilic silica nanoparticle
amounts to produce dry capsules. The oil droplets were stabilised
with lecithin or oleylamine. Volume [NaCl] of Volume in overall
Ratio of emulsion of Mass mixture Overall Oil (wt): (10 wt %
particles Mass of volume mixture particles Row Label oil) (1 wt %)
of oil particles (1 .times. 10.sup.-x M) volume (wt) A Dried 10 ml
10 ml 1 g 0.1 g 10.sup.-4 20 ml 1:0.1 capsules not obtained B Dried
10 ml 10 ml 1 g 0.1 g 10.sup.-2 20 ml 1:0.1 capsules not obtained C
Dried 10 ml 5 ml 1 g 0.05 g 10.sup.-4 20 ml 1:0.05 capsules not
obtained D Dried 10 ml 5 ml 1 g 0.05 g 10.sup.-2 20 ml 1:0.05
capsules not obtained E Dried 10 ml 1 ml 1 g 0.01 g 10.sup.-4 20 ml
1:0.01 capsules not obtained F Dried 10 ml 1 ml 1 g 0.01 g
10.sup.-2 20 ml 1:0.01 capsules not obtained G Dried 1 ml 10 ml 0.1
g 0.1 g 10.sup.-4 20 ml 1:1 capsules obtained H Dried 1 ml 10 ml
0.1 g 0.1 g 10.sup.-2 20 ml 1:1 capsules obtained I Dried 1 ml 10
ml 0.1 g 0.1 g 10.sup.-1 20 ml 1:1 capsules obtained J Dried 1 ml
10 ml 0.1 g 0.1 g 10.sup.-4 11 ml 1:1 capsules obtained K Dried 1
ml 5 ml 0.1 g 0.05 g 10.sup.-4 20 ml 1:0.5 capsules obtained L
Dried 1 ml 5 ml 0.1 g 0.05 g 10.sup.-2 20 ml 1:0.5 capsules
obtained M Dried 1 ml 5 ml 0.1 g 0.05 g 10.sup.-1 20 ml 1:0.5
capsules obtained N Dried 1 ml 5 ml 0.1 g 0.05 g 10.sup.-4 6 ml
1:0.5 capsules obtained O Dried 1 ml 5 ml 0.1 g 0.05 g 10.sup.-2 6
ml 1:0.5 capsules obtained P Dried 1 ml 5 ml 0.1 g 0.05 g 10.sup.-4
10 ml 1:0.5 capsules obtained Q Dried 1 ml 5 ml 0.1 g 0.05 g
10.sup.-2 10 ml 1:0.5 capsules obtained R Dried 1 ml 5 ml 0.1 g
0.05 g 10.sup.-1 10 ml 1:0.5 capsules obtained S Dried 5 ml 5 ml
0.5 g 0.05 g 10.sup.-4 100 ml 1:0.1 capsules obtained T Dried 5 ml
15 ml 0.5 g 0.15 g 10.sup.-4 100 ml 1:0.3 capsules obtained U Dried
5 ml 25 ml 0.5 g 0.25 g 10.sup.-4 100 ml 1:0.5 capsules obtained V
Dried 5 ml 50 ml 0.5 g 0.5 g 10.sup.-4 100 ml 1:1 capsules obtained
W Dried 5 ml 95 ml 0.5 g 0.95 g 10.sup.-4 100 ml 1:2 capsules
obtained X Dried 25 ml 25 ml 2.5 g 0.25 g 10.sup.-4 100 ml 1:0.1
Capsules obtained Y Dried 25 ml 50 ml 2.5 g 0.5 g 10.sup.-4 100 ml
1:0.2 capsules obtained Z Dried 25 ml 95 ml 2.5 g 0.95 g 10.sup.-4
100 ml 1:0.4 capsules obtained .alpha. Dried 50 ml 50 ml 5 g 0.5 g
10.sup.-4 100 ml 1:0.1 capsules obtained .beta. Dried 15 ml 7.5 ml
1.5 g 0.075 g 10.sup.-4 100 ml 1:0.05 capsules obtained .PSI. Dried
15 ml 15 ml 1.5 g 0.15 g 10.sup.-4 100 ml 1:0.1 capsules obtained
.delta. Dried 15 ml 30 ml 1.5 g 0.3 g 10.sup.-4 100 ml 1:0.2
capsules obtained .epsilon. Dried 25 ml 12.5 ml 2.5 g 0.125 g
10.sup.-4 100 ml 1:0.05 capsules obtained .phi. Dried 25 ml 25 ml
2.5 g 0.25 g 10.sup.-4 100 ml 1:0.1 capsules obtained .gamma. Dried
25 ml 47.5 ml 2.5 g 0.475 g 10.sup.-4 100 ml 1:0.2 capsules
obtained .eta. Dried 50 ml 25 ml 5 g 0.25 g 10.sup.-4 100 ml 1:0.05
capsules obtained Dried 50 ml 50 ml 5 g 0.5 g 10.sup.-4 100 ml
1:0.1 capsules obtained
[0082] The capsules of experiments A to R, T to W, Y, Z, .delta.
and .gamma. were prepared from emulsions stabilised with lecithin
(i.e. negatively charged droplets), while the capsules of
experiments S, .alpha. to .psi., .epsilon., .phi., .eta. and .tau.
were prepared from emulsions stabilised with oleylamine (i.e.
positively charged droplets). The capsules of experiments A to R
were dried using rotary evaporation, while the capsules of
experiments S to .tau. were dried using spray-drying.
Properties of Driable Capsules
(1) Wettability of Nanoparticles
[0083] Nanoparticles 18 (e.g. silica nanoparticles) can be modified
to be hydrophobic. In a preferred embodiment, the surfaces of
nanoparticles 18 are modified with organosilanes (e.g.
dimethylchlorosilane). The coalescence behaviour of capsule 20 is
dependent upon the hydrophobicity or hydrophilicity of
nanoparticles 18, as well as the coverage of nanoparticles 18 at
the emulsion droplet interface 14. At full or partial coverage of
hydrophilic nanoparticles 18, capsules 20 still display some degree
of enlargement behaviour (i.e. the diameter of the capsules
increase during coalescence). In contrast, emulsion droplets coated
by more than one layer of hydrophobic nanoparticles 18 (under
conditions of coagulation in the presence of high salt
concentrations (e.g. 1.times.10.sup.-1 M)), form stable flocculated
networks rather than enlarged capsules. Experiments have revealed
that in the wet phase, it is preferable that nanoparticles 18 have
a hydrophobic surface which reduces the occurrence of capsule 20
coalescence.
[0084] However, while hydrophobic nanoparticles form a stable wet
phase capsule with good protection of the active substance, further
experiments have indicated that hydrophilic nanoparticles better
stabilise capsules during a drying phase. That is, the results of
these experiments have indicated that if the nanoparticles have a
hydrophobic surface, then the capsules may be unstable during the
drying step. This may be due to migration of the hydrophobic
nanoparticles into the oil of the emulsion droplet, resulting in
instability of the capsules. It is an option therefore, that
droplets are first coated with a hydrophobic layer of nanoparticles
to create a stable wet phase. The resulting capsules can then be
further coated by a hydrophilic layer of nanoparticles to stabilise
the capsule during a drying phase. The further coat of hydrophilic
nanoparticles can be applied by adding the nanoparticles to the
continuous phase and allowing them to congregate onto the surface
of the capsule while the wet phase is "standing" and/or during the
drying phase.
(2) Effect of Salt Concentration on Nanoparticle Congregation
[0085] Typical isotherms for hydrophilic silica nanoparticles
adsorbing at a model oil water interface 14 are shown in FIG. 3. It
is clear that salt (electrolyte) addition dramatically increases
nanoparticle adsorption, Preferably, the nanoparticles congregate
at the phase interface in the presence of an amount of electrolyte
suitable to enhance the congregation of the nanoparticles at the
phase interface. The amount of the electrolyte will typically be
less than 1.times.10.sup.-1 M (preferably, at least
1.times.10.sup.-3 M and more preferably, at least
0.5.times.10.sup.-4 M). In the preferred embodiment, NaCl is used,
however it will be understood by persons skilled in the art that
any electrolyte may be used.
[0086] While not wishing to be bound by theory, it is considered
that the free energy of nanoparticle adsorption increases
significantly with salt addition due to a reduction in the range of
nanoparticle-droplet and nanoparticle-nanoparticle lateral
electrostatic repulsion. In high salt concentrations (e.g.
1.times.10.sup.-2 and 1.times.10.sup.-1 M NaCl), adsorption amounts
for hydrophilic nanoparticles 18 correspond to approximately 75%
and just over 100% of an equivalent hexagonally close-packed
monolayer of hard spheres respectively. The fractional surface
coverage is an approximation calculated from the ratio of adsorbed
amount of nanoparticles 18 and the theoretical value for a
hexagonally close packed monolayer (i.e. 200 mgm.sup.-2 for 50 nm
diameter nanoparticles).
(3) Effect of Charged Oil Droplets on Nanoparticle Congregation
[0087] It is an option that, prior to the addition of nanoparticles
18, a negatively charged phospholipid monolayer, such as lecithin
or a positively charged oleylamine is used as a stabiliser to
stabilise the oil droplets of the emulsion (emulsifier 14 is shown
in FIG. 1). Both lecithin and oleylamine are fat emulsifiers which
help to prevent droplets 10 from coalescing before nanoparticles 18
congregate. Other stabilisers similar to oleylamine, which are
particularly useful in the present invention, include
1,2-distearyl-sn-glycero-3-phosphatidyl ethanolamine-N,
stearylamine and 1,2-dioleoyl-3-trimethylammonium-propane.
[0088] Experiments have shown that negatively charged phospholipid
stabilised triglyceride droplets do not strongly interact with
hydrophilic silica nanoparticles. This is evidenced by adsorption
studies, freeze fracture SEM and is supported by EDAX surface
elemental analysis. Positively charged oleylamine stabilised
triglyceride droplets on the other hand, strongly interact with
hydrophilic silica nanoparticles as evidence by adsorption studies,
charge reversal and freeze-fracture SEM.
(4) Phase from which Nanoparticles Congregate
[0089] As stated above, the nanoparticles can be first dispersed in
either phase (oil or water) and, as an emulsion is formed, the
nanoparticles will congregate at the phase interface.
[0090] Initial studies have shown that very few negatively charged
nanoparticles from the aqueous phase (less than 5%) congregate at
the droplet surface of negatively charged droplets (e.g. droplets
stabilised with lecithin), although greater levels of nanoparticle
congregation has been observed with droplets of silicone (i.e.
PDMS). Positively charged droplets however, are coated by
nanoparticles dispersed within the aqueous phase.
(5) Oil: Nanoparticle Mass Ratio
[0091] The oil (g) to nanoparticle (g) ratio plays an important
role in preparing capsules which can withstand the drying step
(i.e. driable capsules). That is, an oil to nanoparticle mass ratio
of at least 1:0.02 is considered to be necessary in order to
produce dried capsules. However, preferably, an oil to nanoparticle
mass ratio of at least 1:0.05 and, more preferably, at least 1:0.2,
is used.
Properties of Redispersible Capsules
[0092] The capsules are prepared so as to remain stable and do not
substantially coalesce to form capsules with an increased diameter.
The present invention therefore has the advantage of maintaining
the release profile of the active substance contained within the
capsule as well as maintaining the small size of the capsules. The
small size of the capsules both increases surface area and allows
the capsules to be delivered to target areas which require a small
capsule size (e.g. blood capillaries). Capsules 20 may therefore
have a longer shelf life than prior capsule formulations and can be
stored and/or transported for later use.
[0093] Preferably, the dried capsules 20 can be re-dispersed (shown
by step 30) in a liquid (preferably water) to re-form a stabilised
emulsified product. Not all dried capsules are satisfactorily
re-dispersible and again, the properties selected during capsule
formation are important. Dried capsules in accordance with the
present invention, however, can be made to re-disperse in a liquid
to form an emulsion which is substantially identical or similar in
composition to that from which the dried formulation was prepared.
This means that the average capsule diameter size is the same or
varies from the original capsule by no more than a factor of about
4 times and, preferably, shows few (i.e. less than 5% by volume),
if any, capsules with a diameter size of greater than 10 .mu.m.
[0094] The re-constitutive properties following the re-dispersion
of capsules of Table 1 in phosphate buffer are shown in Table 2
below. The reconstitution mark rates how similar the reconstituted
emulsion compared with the emulsion from which the capsules were
dried.
[0095] The re-constitutive properties following re-dispersion of
capsules of Table 1 in acidic medium after 2 months of storage at
room temperature are shown in Table 3 below.
TABLE-US-00002 TABLE 2 Average capsule size and reconstitution
rating following re-dispersion of capsules (in phosphate buffer (pH
= 7.2)) listed in Table 1. 0.01 g of powder was dissolved in 4 g of
phosphate buffer 10.sup.-4 M after 24 hours from drying (size
measured using Malvern Mastersizer) Average Average Row drop size
re-dis- (from Oil: before persed D Vol % Recon- Table particle
drying drop size (v, 0.9) above stitution 1) ratio (.mu.m) (.mu.m)
(.mu.m) 10 .mu.m mark G 1:0.1 1.04 1.27 -- 2 Very good H 1:0.1 1.82
1.99 -- 5 Good I 1:0.1 8.93 22.04 -- 19 Poor J 1:0.1 13.67 28.89 --
24 Poor K 1:0.05 0.76 1.04 -- 0.5 Excellent L 1:0.05 0.94 1.55 --
0.5 Excellent M 1:0.05 12.99 56.6 -- 87 Very poor N 1:0.05 26.75
47.3 -- 89 Very poor O 1:0.05 5.87 30.05 -- 31 Very poor P 1:0.05
1.52 2.51 -- 0 Excellent Q 1:0.05 0.88 2.15 -- 0 Excellent R 1:0.05
1.36 5.23 -- 2 Very good S 1:0.1 -- -- -- -- Oily paste T 1:0.3 --
25 88 98 Very poor U 1:0.5 -- 0.52 0.65 0 Excellent V 1:1 -- 0.78
1.27 0 Excellent W 1:2 -- 0.55 0.68 0 Excellent X 1:0.1 -- -- -- --
Oily paste Y 1:0.2 -- 40.3 131.12 98 Very poor Z 1:0.4 -- 1.02
16.96 95 Very poor .alpha. 1:0.1 -- -- -- -- Oily paste .beta.
1:0.5 -- 0.82 2.57 0 Excellent .PSI. 1:1 -- 0.53 0.72 0 Excellent
.delta. 1:2 -- 0.72 1.17 0 Excellent .epsilon. 1:0.5 -- 0.46 0.66 0
Excellent .phi. 1:1 -- 0.66 0.98 0 Excellent .gamma. 1:2 -- 0.58
0.78 0 Excellent .eta. 1:0.5 -- 0.46 0.66 0 Excellent 1:1 -- 0.52
0.72 0 Excellent control -- -- 0.67 0.92 0 Excellent (only
silica)
TABLE-US-00003 TABLE 3 Average capsule size and reconstitution
rating following re- dispersion of the capsules in acidic media (pH
= 2, adjusted with hydrochloric acid) after 2 months of storage
(measured using Malvern Mastersizer) Row Average Vol % (from
Oil:particle drop size D (v, 0.9) above Reconstitution Table 1)
ratio (.mu.m) (.mu.m) 10 .mu.m mark S 1:0.1 -- -- -- Oily paste T
1:0.3 54.6 133.6 98 Very poor U 1:0.5 4.7 10.1 Below 5 Good V 1:1
2.39 7.42 Below 2 Very good W 1:2 0.55 0.68 0 Excellent X 1:0.1 --
-- -- Oily paste Y 1:0.2 105.2 167 98 Very poor Z 1:0.4 3 39.3 50
Very poor .alpha. 1:0.1 -- -- -- Oily paste control -- 0.64 0.93 0
Excellent (only silica)
[0096] It is clear that the capsules of experiments U, V and W
showed the best re-dispersibility and reconstitution after 2 months
of storage (nb. after 8 months of storage, the respective average
drop size of U, V and W, were 4.34 .mu.m, 2.59 .mu.m and 1.65
.mu.m, against 3.34 .mu.m of the control). These capsules were
produced in the presence of a relatively low amount of electrolyte
(i.e. 1.times.10.sup.-4 M) and with an oil to nanoparticle mass
ratio of at least 1:0.5. They were prepared from negatively charged
oil droplets (stabilised with lecithin). It is considered that for
such negatively charged oil droplets, an oil to nanoparticle ratio
of at least 1:0.2 is required to achieve droplets that are wholly
coated in nanoparticles.
[0097] On the other hand, for positively charged oil droplets (e.g.
stabilised with oleylamine), it is considered that the droplets
interact more strongly with the nanoparticles and, therefore, the
minimum oil to nanoparticle ratio is less; in particular, an oil to
nanoparticle mass ratio of at least 1:0.05 is believed to be
required to produce dried capsules that can be re-dispersed to form
a capsule-based emulsion which is substantially identical or
similar to that from which the dried formulation was prepared. This
ratio is believed to result in the production of wholly coated
droplets, however, it is preferable to use an oil to nanoparticle
mass ratio of least 1:0.1.
[0098] The optimum ratio of nanoparticles (g/cm.sup.3) to lecithin
(g/cm.sup.3) has been found to be 5:1 when nanoparticles congregate
from the oil phase. The optimum ratio of nanoparticles (g/cm.sup.3)
to oleylamine (g/cm.sup.3) has been found to be
1:10 when the nanoparticles congregate from either the oil or the
water phase.
Example 1
a) Preparation and Characterisation of Emulsion Stabilised by
Lecithin
[0099] Lecithin (0.6 g) stabiliser was dissolved in triglyceride
(Miglyol 812.TM.) (10 g), and then added to water (total sample
weight: 100 g) under mixing using a rotor-stator homogeniser
(11,000 rpm, 10 minutes, pH=6.95.+-.0.2). Alternatively, a high
pressure homogeniser (5 cycles, 5 mBars) can be used for production
of the emulsion. After 24 hours, the emulsion was characterised in
terms of size (laser diffraction Malvern Mastersizer) and zeta
potential (PALS). Droplet size distribution is shown in FIG. 9a and
FIG. 9b. The droplet size ranges from 0.20-0.86 .mu.m.
b) Preparation of Nanoparticles
[0100] An aqueous dispersion of silica (Aerosil.RTM.) nanoparticles
(1 wt %) was prepared by sonication over at least a one hour
period. FIG. 8 shows that the average silica nanoparticle size was
approximately 50 nm.
c) Capsule Formation
[0101] Emulsion formed in step (a) and nanoparticle dispersion (b)
were mixed together. Subsequently, the volume of the mixture can be
varied if desired by the addition of water. The salt concentration
can be in the range of 1.times.10.sup.-4 to
1.times.10.sup.-1.
d) Drying--Removal of Continuous Phase
[0102] In order to prepare dry emulsion powders, an emulsion and
hydrophilic silica dispersion were mixed in 20 ml vials and
spray-dried under following conditions: flow rate 5 ml/min.,
aspirator setting 10, air flow 0.6 m.sup.3/min, inlet temperature
160.degree. C. and outlet temperature 85.degree. C.
e) Redispersion and Characterisation of Capsules
[0103] Emulsions were redispersed in phosphate buffer (pH=7.2) and
acidic media (pH=2) and the drop size distribution measured using a
Malvern Mastersizer and Malvern Zetasizer Nano. Dry emulsion
powders were imaged using SEM. Scanning electron microscopy was
performed using a Philips SEM 515, operating at 15 kV. A thin layer
of the samples was placed on double adhesive tape, slicked on
SEM-stubs. The samples were coated with gold by a Balzers SCD 050,
Balzer Union AG sputter prior to microscopy. The SEM images showed
mono-disperse, smooth, spherical capsules which maintain their
structural integrity even under the high vacuum required during
imaging. There was no evidence of capsule aggregation as is often
observed with SEM images of silica nanoparticles themselves. The
capsules imaged had diameters within the range 100 to 300 nm
indicating that the capsules are discrete oil droplets coated with
at least one layer of nanoparticles.
Example 2
a) Preparation of Emulsions
[0104] Simple Oil/Water lipid emulsions, containing 10% a 20%
triglyceride (Miglyol.RTM. 812) as the oil phase, were prepared by
high-pressure homogenizer at 500-1000 bar and ambient temperature.
Negatively and positively charged emulsion oil droplets have been
achieved by using lecithin and oleylamine respectively, as
emulsifiers initially added to the oil phase. In the case of silica
incorporated emulsions, silica nanoparticles were added to the oil
phase or aqueous phase of emulsions, initially stabilised by
lecithin or oleylamine, and sonicated for 60 minutes before
homogenisation.
b) Size Analysis
[0105] Size measurements were carried out using laser diffraction
by Malvern.RTM. Mastersizer (Malvern Instruments, UK) following
appropriate dilution of samples with MiliQ water.
c) Freeze-Fracture Scanning Electron Microscopy
[0106] A freeze-fracture SEM technique (Philips XL 30 FEG scanning
electron microscope with Oxford CT 1500 cryotransfer system) was
used to image the oil droplets. The precise method for effective
imaging of the droplets depends on the sample properties such as
nanoparticle type and coverage. Generally, the methodology contains
emulsion cryofixation, fracturing, etching, platinum coating and
imaging.
d) Physical Stability Tests
[0107] Long-term physical stability of emulsions was assessed by
size analysis of emulsion droplets at determined for intervals up
to 3 months storage at ambient temperature.
D (v, 0.5), D (v, 0.9) and specific surface area were considered as
indicators of physical stability of emulsions.
e) Visual Inspection
[0108] Organoleptic characteristics (i.e. evidence of creaming and
coalescence) of emulsions have been recorded in parallel with size
analysis. (nb. since oil is less dense than the water each oil drop
is prone to floating upwards. This process is called creaming--the
oil droplets will gradually form a dense layer at the top of the
sample). The degree of creaming and phase separation is assessed by
visual observation of emulsions at given time intervals.
Coalescence can be determined by monitoring the mean droplet
diameter of the emulsions during storage period. Organoleptically,
the appearance of large oil droplets or a layer of free oil on the
emulsion surface is the indicators of a coalesced emulsion.
Example 3
a) Long-Term Physical Stability
[0109] Long term physical stability of emulsions has been improved
in the presence of silica nanoparticles.
[0110] D (v, 0.9) of emulsions initially stabilised by lecithin, in
the absence and presence of silica nanoparticles has been shown in
(FIG. 9). D (v, 0.9) of silica-added emulsions was effectively
unchanged during storage at room temperature for 3 months, whereas
emulsions solely stabilised by lecithin have shown a 3-fold
increase in D (v, 0.9).
Example 4
[0111] In this example, dried capsule formulations were prepared
from liposomes.
a) Liposome Preparation
[0112] 0.3317 g lecithin and 0.1085 g cholesterol were dissolved in
20 ml chloroform and evaporated under vacuum. 20 ml MilliQ water
was added with periodic sonication.
[0113] Liposomal dispersions were mixed with aqueous dispersions of
silica nanoparticles and spray-dried using standard procedure.
Sample 1: Liposome dispersion 5 g and 95 g of 1 wt % silica
nanoparticle dispersion; Sample 2: Liposome dispersion 5 g and 95 g
5 wt % silica nanoparticle dispersion; and Sample 3: Liposome
dispersion 30 g and 70 g 5 wt % silica nanoparticle dispersion. B)
Reconstitution in MilliQ Water after 24 Hours
[0114] The reconstitution of liposome-based capsules is shown in
Table 4 below. The dried liposome capsules showed good
re-dispersion properties, with the size distribution of the
re-dispersed capsules being within the range of 0.5 to 5 .mu.m.
TABLE-US-00004 TABLE 4 z-average drop size Polydispersibility Zeta
potentials Sample (.mu.m) index (PDI) (mV) 1 5.1 0.305 -4.94 .+-.
5.5 2 3.44 1.000 -19.4 .+-. 16.4 3 2.43 0.2 -26.1 .+-. 21.8
Example 5
a) General Preparation Method
Miglyol 10 g
Lecithin 0.6 g or Oleylamine 1 g
Silica 0.2-0.5 g
[0115] Polymer aqueous dispersion (hydroxypropyl methyl cellulose 1
wt % or chitosan 0.5 wt % or carbomer 0.1 wt %) to 100.0
[0116] Lecithin or oleylamine is dissolved in Miglyol and silica is
added and redispersed in Miglyol. After polymer dispersion
addition, the mixture is sonicated for 40 minutes and spray dried
using standard procedures.
[0117] Samples were investigated for re-dispersibility in phosphate
buffer, pH=7.2 using Malvern Zetasizer Nano after 24 hours storage
at RT.
[0118] The re-dispersibility of samples is shown in Tables 5 to 10
(where PDI is the polydispersibility index):
i) Formulation 1:
Migliol 10 g
Oleylamine 1 g
Silica 0.2 g
[0119] Polymer aqueous dispersion (hydroxypropylmethyl cellulose 1
wt %) to 100.0
TABLE-US-00005 TABLE 5 Before Spray Drying z-average dry powder
re-dispersion in buffer drop size Zeta potentials z-average Zeta
potentials (.mu.m) PDI (mV) drop size PDI (mV) 0.364 0.375 +35.4
.+-. 5.24 0.932 0.123 +19.9 .+-. 7.03
ii) Formulation 2:
Migliol 10 g
Oleylamine 1 g
Silica 0.5 g
[0120] Polymer aqueous dispersion (hydroxypropylmethyl cellulose 1
wt %) to 100.0.
TABLE-US-00006 TABLE 6 Before Spray Drying z-average dry powder
re-dispersion in buffer drop size Zeta potentials z-average Zeta
potentials (.mu.m) PDI (mV) drop size PDI (mV) 0.324 0.445 +35.5
.+-. 8.54 1.05 0.123 +18.8 .+-. 10.2
iii) Formulation 3:
Migliol 10 g
Lecithin 0.6 g
Silica 0.5 g
[0121] Polymer aqueous dispersion (hydroxypropylmethyl cellulose 1
wt %) to 100.0.
TABLE-US-00007 TABLE 7 Before Spray Drying z-average dry powder
re-dispersion in buffer drop size Zeta potentials z-average Zeta
potentials (.mu.m) PDI (mV) drop size PDI (mV) 0.451 0.449 -6.02
.+-. 18 2.16 0.385 -10.1 .+-. 9.31
iv) Formulation 4:
Migliol 10 g
Oleylamine 1 g
Silica 0.5 g
[0122] Polymer aqueous dispersion (carbomer 0.1 wt %) to 100.0.
TABLE-US-00008 TABLE 8 Before Spray Drying z-average dry powder
re-dispersion in buffer drop size Zeta potentials z-average Zeta
potentials (.mu.m) PDI (mV) drop size PDI (mV) 0.618 0.519 -58.5
.+-. 10.1 1.9 0.907 -29 .+-. 14.3
v) Formulation 5:
Migliol 10 g
Lecithin 0.6 g
Silica 0.5 g
[0123] Polymer aqueous dispersion (carbomer 0.1 wt %) to 100.0.
TABLE-US-00009 TABLE 9 Before Spray Drying z-average dry powder
re-dispersion in buffer drop size Zeta potentials z-average Zeta
potentials (.mu.m) PDI (mV) drop size PDI (mV) 0.545 0.432 -51.2
.+-. 5.13 2.8 1.000 -25.8 .+-. 15.6
vi) Formulation 6:
Migliol 10 g
Oleylamine 1 g
Silica 0.5 g
[0124] Polymer aqueous dispersion (chitosan 0.5 wt %) to 100.0.
TABLE-US-00010 TABLE 10 Before Spray Drying z-average dry powder
re-dispersion in buffer drop size Zeta potentials z-average Zeta
potentials (.mu.m) PDI (mV) drop size PDI (mV) 0.556 0.497 +73.3
.+-. 12.5 1.53 0.450 +48.5 .+-. 4.8
Example 6
[0125] In this example, formulations of dried capsules were
produced using oleylamine as an emulsion stabiliser and tested for
re-dispersion and reconstitution after 24 hours and 3 months
storage at room temperature.
A) Preparation and Characterisation of Emulsion Stabilised by
Oleylamine
[0126] Oleylamine (1.0 g) stabiliser was dissolved in triglyceride
(Miglyol 812.TM.) (10 g), and then added to water (total sample
weight: 100 g). Emulsion was produced using high pressure
homogenizer (5 cycles, 5 mBars pressure). After 24 hours, the
emulsion was characterised in terms of size (laser diffraction
Malvern Mastersizer) and zeta potential (PALS). The droplet size
ranges from 0.20-1.5 .mu.m.
b) Preparation of Nano Particles
[0127] An aqueous dispersion of silica (Aerosil.RTM.) nanoparticles
(1 wt %) was prepared by sonication over at least a one hour
period. FIG. 8 shows that the average silica nanoparticle size was
approximately 50 nm.
c) Capsule Formation
[0128] Emulsion formed in step (a) and nanoparticle dispersion (b)
were mixed together in the ratios shown in Table 11 below.
Subsequently, the volume of the mixture can be varied if desired by
the addition of water. The salt concentration can be in the range
of 1.times.10.sup.-4 to 1.times.10.sup.-1.
d) Drying--Removal of Continuous Phase
[0129] In order to prepare dry emulsion powders, an emulsion and
hydrophilic silica dispersion were mixed in 20 ml vials and
spray-dried under following conditions: flow rate 5 ml/min.,
aspirator setting 10, air flow 0.6 m.sup.3/min, inlet temperature
160.degree. C. and outlet temperature 85.degree. C.
e) Redispersion and Characterisation of Capsules
[0130] Emulsions were redispersed in phosphate buffer (pH=7.2) and
acidic media (pH=2) and the drop size distribution was measured
using a Malvern Mastersizer and Malvern zetananosizer. Results are
shown in Table 11.
TABLE-US-00011 TABLE 11 Ratio of oil (wt):particles Average drop
size Average drop size Sample (wt) after 24 hours (.mu.m) after 3
months (.mu.m) 1 1:0.1 3.65 2.5 2 1:0.3 11.5 6.17 3 1:0.5 12.66
5.25 4 1:1 6.84 3.31 5 1:2 6.37 6.7
[0131] Modifications and variations such as would be apparent to
persons skilled in the art are deemed to be within the scope of the
present invention. For example, although the invention is generally
discussed with reference to emulsion droplets, the techniques
discussed can generally be applied to liposomes, other vesicle
systems and other similar vehicles. For example, at least one layer
of nanoparticles may congregate at the phase interface of the lipid
layer of a vesicle and the continuous phase in which the vesicle is
dispersed.
* * * * *