U.S. patent application number 16/001386 was filed with the patent office on 2018-12-13 for coaxial nozzle configuration and methods thereof.
The applicant listed for this patent is University of Florida Research Foundation, Inc.. Invention is credited to Yong Huang, Yifei Jin.
Application Number | 20180353384 16/001386 |
Document ID | / |
Family ID | 64562447 |
Filed Date | 2018-12-13 |
United States Patent
Application |
20180353384 |
Kind Code |
A1 |
Huang; Yong ; et
al. |
December 13, 2018 |
COAXIAL NOZZLE CONFIGURATION AND METHODS THEREOF
Abstract
Embodiments of the present disclosure provide for coaxial
nozzles, capsule fabrication systems comprising coaxial nozzles,
and methods of capsule fabrication using capsule fabrication
systems. In certain embodiments, coaxial nozzle configurations,
capsule fabrication systems, and methods as described herein can be
used for multi-layered capsule fabrication.
Inventors: |
Huang; Yong; (Gainesville,
FL) ; Jin; Yifei; (Gainesville, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Florida Research Foundation, Inc. |
Gainesville |
FL |
US |
|
|
Family ID: |
64562447 |
Appl. No.: |
16/001386 |
Filed: |
June 6, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62517329 |
Jun 9, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61K 9/4808 20130101;
A61J 3/074 20130101; B05B 1/3086 20130101; A61J 3/07 20130101; B65D
81/3216 20130101 |
International
Class: |
A61J 3/07 20060101
A61J003/07; A61K 9/48 20060101 A61K009/48; B05B 1/30 20060101
B05B001/30 |
Goverment Interests
STATEMENT OF GOVERNMENTAL SUPPORT
[0002] This invention was made with government support under grant
number 1314834 awarded by the National Science Foundation. The
government has certain rights in the invention.
Claims
1. A coaxial nozzle, comprising: a core channel, an annular
channel, and a sheath channel.
2. The coaxial nozzle of claim 1, further comprising one or more
outlet nozzles.
3. The coaxial nozzle of claim 1, wherein the core channel, the
annular channel, and the sheath channel each further comprise an
inlet configured to receive fluid.
4. A capsule fabrication system comprising: a coaxial nozzle,
wherein the coaxial nozzle comprises a core channel, an annular
channel, and a sheath channel, and wherein the coaxial nozzle is
configured to output one or more capsules; a collection bath
configured to receive one or more capsules from the coaxial
nozzle.
5. The capsule fabrication system of claim 4, further comprising a
vibrator attached to or in physical communication with the coaxial
nozzle.
6. The capsule fabrication system of claim 4, further comprising a
fluid delivery system configured to deliver fluid to one or more of
the core channel, the annular channel, and the sheath channel.
7. The capsule fabrication system of claim 4, wherein the one or
more capsules are one or more multi-layered capsules.
8. A method for capsule fabrication, comprising: presenting a
capsule fabrication system, wherein the capsule fabrication system
comprises: a coaxial nozzle, wherein the coaxial nozzle comprises a
core channel, an annular channel, and a sheath channel, and wherein
the coaxial nozzle is configured to output one or more capsules;
wherein the core channel, the annular channel, and the sheath
channel each further comprise an inlet configured to receive fluid;
and a collection bath configured to receive one or more capsules
from the coaxial nozzle; initiating capsule fabrication, comprising
delivering fluid to one or more of the core channel, the annular
channel, and the sheath channel of the capsule fabrication system;
forming a compound flow from the fluid delivered to the one or more
channels, wherein the compound flow comprises one or more of a core
flow, an annular flow, and a sheath flow; introducing a vibration
to the compound flow, developing the one or more capsules;
introducing the one or more capsules to a collection bath
comprising a crosslinking agent; and crosslinking the one or more
capsules to form one or more stabilized capsules.
9. The method of claim 8, wherein the capsule fabrication system
further comprises a fluid delivery system.
10. The method of claim 8, wherein the one or more capsules or one
or more stabilized capsules are multi-layered capsules.
11. The method of claim 8, wherein the one or more capsules or one
or more stabilized capsules are multi-layered capsules.
12. The method of claim 8, wherein the one or more capsules or one
or more stabilized capsules are multi-layered capsules having a
core-shell-shell structure.
13. The method of claim 8, wherein the crosslinking agent is
Ca.sup.2+.
14. The method of claim 8, wherein the fluid comprises
alginate.
15. The method of claim 8, wherein the fluid comprises
CaCl.sub.2.
16. The method of claim 8, wherein the fluid delivered to the core
channel is different from the fluid delivered to the annular
channel, the sheath channel, or both.
17. The capsule fabrication system of claim 4, wherein the one or
more capsules are one or more multi-layered capsules having a
core-shell-shell structure.
Description
CLAIM OF PRIORITY TO RELATED APPLICATION
[0001] This application claims priority to co-pending U.S.
provisional application entitled "COAXIAL NOZZLE CONFIGURATION AND
METHODS THEREOF" having Ser. No. 62/517,329, filed on Jun. 9, 2017,
the contents of which is entirely incorporated herein by
reference.
BACKGROUND
[0003] Encapsulation is a process involving the complete
envelopment of preselected core material with a well-defined porous
or impermeable membrane. Encapsulation has been of great importance
in recent years and has been widely used in many fields including
pharmaceutical, chemical, and food industries, as well as in
various applications related to agriculture, biotechnology, and
medicine, to name a few. The main purpose of encapsulation is to
immobilize, protect, and control the release of entrapped materials
such as flavor, living cells, and pharmaceutical compounds.
[0004] Multi-layered encapsulation has been of great interest for
various pharmaceutical, chemical and food industries and confers
advantages over single-layered encapsulation. Fabrication of
well-defined capsules with more than one shell layer still poses a
significant fabrication challenge, however. As a result, current
techniques are not as effective as desired, and there is a need to
overcome deficiencies in current fabrication techniques.
SUMMARY
[0005] Embodiments of the present disclosure provide for a coaxial
nozzle, which can comprise a core channel, an annular channel, and
a sheath channel. The nozzle can further comprise one or more
outlet nozzles. The core channel, the annular channel, and the
sheath channel of the nozzle each can further comprise an inlet
configured to receive fluid.
[0006] Embodiments of the present disclosure provide for a capsule
fabrication system comprising a coaxial nozzle. The coaxial nozzle
can comprise a core channel, an annular channel, and a sheath
channel, and can be configured to output one or more capsules into
a collection bath. Capsule fabrication systems as described herein
can further comprise a vibrator attached to or in physical
communication with the coaxial nozzle.
[0007] Capsule fabrication systems as described herein can further
comprise a fluid delivery system configured to deliver fluids to
one or more of the core channel, the annular channel, and the
sheath channel.
[0008] One or more capsules outputted by the capsule fabrication
system can be one or more multi-layered capsules.
[0009] Described herein are methods for capsule fabrication.
Methods for capsule fabrication as described herein can comprise:
presenting a capsule fabrication system, comprising a coaxial
nozzle, with a core channel, an annular channel, and a sheath
channel, and configured to output one or more capsules; wherein the
core channel, the annular channel, and the sheath channel each
further comprise an inlet configured to receive fluid; and a
collection bath configured to receive one or more capsules from the
coaxial nozzle; initiating capsule fabrication, comprising
delivering fluid to one or more of the core channel, the annular
channel, and the sheath channel of the capsule fabrication system;
forming a compound flow from the fluid delivered to the one or more
channels, wherein the compound flow comprises one or more of a core
flow, an annular flow, and a sheath flow; introducing a vibration
to the compound flow, developing the one or more capsules;
introducing the one or more capsules to a collection bath
comprising a crosslinking agent; and crosslinking the one or more
capsules to form one or more stabilized capsules.
[0010] Capsule fabrication systems of methods described herein can
further comprise a fluid delivery system. One or more capsules or
one or more stabilized capsules created by methods as described
herein can be multi-layered capsules. Multi-layered capsules
created by methods as described herein can have a core-shell-shell
structure. Crosslinking agents of methods and systems as described
herein can be Ca.sup.2+. Fluids as described herein can comprise
alginate. Fluids as described herein can comprise CaCl.sub.2.
Fluids delivered to the annular channel, the sheath channel, or
both in methods described herein can be the same or can be
different for each respective channel. Multi-layered capsules
formed by systems and methods herein can have a core-shell-shell
structure.
[0011] Other devices, methods, features, and advantages will be, or
become, apparent to one with skill in the art upon examination of
the following drawings and detailed descriptions. It is intended
that all such additional compositions, methods, features, and
advantages be included within this description, be within the scope
of the present disclosure, and be protected by the accompanying
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Many aspects of this disclosure can be better understood
with reference to the following drawings. The components in the
drawings are not necessarily to scale, emphasis instead being
placed upon clearly illustrating the principles of the present
disclosure.
[0013] FIG. 1A shows a photograph and schematic of an embodiment of
a multi-layered capsule fabrication system, more specifically a
double-layered capsule fabrication system. The inset of the
photograph shows an image of an embodiment of a three-layered
coaxial nozzle (scale bar: 10 mm).
[0014] FIG. 1B is a series of photographs depicting methods as
described herein. The photographic series shows an embodiment of a
double-layered capsule being fabricated by the embodiment of the
system of FIG. 1A.
[0015] FIGS. 2A-2C illustrate a schematic of alginate crosslinking
process with the presence of calcium cations. FIG. 2A is an
embodiment of a schematic of alginate solution being crosslinked in
air; FIG. 2B is an embodiment of a schematic of entire alginate
capsule being crosslinked in a calcium chloride (CaCl.sub.2) bath;
and FIG. 2C depicts an embodiment of a fabricated alginate capsule
(note only one layer is shown for illustration in FIG. 2C).
[0016] FIGS. 3A-3F depict a structure of an embodiment of a
three-layered coaxial nozzle and simulation results thereof. FIG.
3A is a schematic of an embodiment of a nozzle assembly. FIG. 3B
shows the structure dimensions of the annular channel of the nozzle
assembly of FIGS. 3A and 3C shows the structure dimensions of the
sheath channel of the nozzle assembly of FIG. 3A. FIG. 3D
demonstrates points selected to evaluate the velocity uniformity in
the channels, and typical simulation results of the velocity
distribution of the annular flow and the sheath flow at the outlet
of the nozzle are shown in FIGS. 3E and 3F respectively.
[0017] FIGS. 4A-4H illustrate an embodiment of a three-layered
coaxial nozzle as described herein. FIG. 4A is a schematic of the
three-layered coaxial nozzle structure. The velocity field of
alginate solution flowing in the annular channel and the sheath
channel are shown in FIGS. 4B and 4C, respectively. FIG. 4D depicts
the assembly of the assembled three-layered coaxial nozzle (scale
bar 4.0 mm), and FIG. 4E shows the view of its nozzle outlets
(scale bars 4.0 mm for FIG. 4E and 0.5 mm for the inset of FIG.
4E). The inner set, middle set, and outer set of the three-layered
coaxial nozzle are shown in FIGS. 4F, 4G, and 4H, respectively. The
scale bars in FIGS. 4F and 4G are 1.0 mm and the scale bar in FIG.
4H is 2.0 mm.
[0018] FIG. 5A is a schematic of an embodiment of a double-layered
capsule.
[0019] FIG. 5B are photographs showing embodiments of
representative alginate capsules. Scale bars are 1.0 mm.
[0020] FIGS. 6A-6F comprise graphs showing the effects of flow
rates on the dimensions of double-layered capsules produced by
embodiments of nozzles and systems as described herein. FIG. 6A
shows capsule and core diameters as a function of core flow rate;
FIG. 6B shows inner and outer shell layer thicknesses as a function
of core flow rate; FIG. 6C depicts capsule and core diameters as a
function of annular flow rate; FIG. 6D shows inner and outer shell
layer thicknesses as a function of annular flow rate; FIG. 6E shows
capsule and core diameters as a function of sheath flow rate; and
FIG. 6F shows inner and outer shell layer thicknesses as a function
of sheath flow rate. The graphs of FIG. 6 additionally show one
standard deviation error bars and data points represent three
samples.
[0021] FIG. 7 is a table showing physical and rheological
properties of alginate solutions with different concentrations
(1.0% and 2.0% (w/v)).
[0022] FIG. 8 is a table showing ranges of structural dimensions of
the annular and sheath channels, as defined in FIGS. 3B and 3C
respectively, according to the present disclosure.
[0023] FIG. 9 is an engineering schematic of a coaxial nozzle as
described herein.
[0024] FIG. 10 defines annotated portions of FIG. 9.
[0025] FIG. 11 is a top view of an embodiment of a middle set of a
coaxial nozzle as described herein.
[0026] FIG. 12 is a side view of the middle set of FIG. 11.
[0027] FIG. 13 is a top view of an embodiment of an inner set of a
coaxial nozzle as described herein.
[0028] FIG. 14 is a side view of the inner set of FIG. 13.
[0029] FIG. 15 is a top view of an embodiment of an outer set of a
coaxial nozzle as described herein.
[0030] FIG. 16 is a side view of the outer set of FIG. 15.
[0031] FIG. 17 is a top view of an embodiment of collar A for a
coaxial nozzle as described herein.
[0032] FIG. 18 is a side view of the collar of FIG. 17.
[0033] FIG. 19 is a top view of an embodiment of collar B for a
coaxial nozzle as described herein.
[0034] FIG. 20 is a side view of the collar of FIG. 19.
[0035] FIG. 21 is an embodiment of a gasket for a coaxial nozzle
according to the present disclosure.
[0036] FIG. 22 is an embodiment of a second gasket for a coaxial
nozzle according to the present disclosure.
DETAILED DESCRIPTION
[0037] Before the present disclosure is described in greater
detail, it is to be understood that this disclosure is not limited
to particular embodiments described, as such may, of course, vary.
It is also to be understood that the terminology used herein is for
the purpose of describing particular embodiments only, and is not
intended to be limiting, since the scope of the present disclosure
will be limited only by the appended claims.
[0038] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
(unless the context clearly dictates otherwise), between the upper
and lower limit of that range, and any other stated or intervening
value in that stated range, is encompassed within the disclosure.
The upper and lower limits of these smaller ranges may
independently be included in the smaller ranges and are also
encompassed within the disclosure, subject to any specifically
excluded limit in the stated range. Where the stated range includes
one or both of the limits, ranges excluding either or both of those
included limits are also included in the disclosure.
[0039] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this disclosure belongs.
Although any methods and materials similar or equivalent to those
described herein can also be used in the practice or testing of the
present disclosure, the preferred methods and materials are now
described.
[0040] All publications and patents cited in this specification are
herein incorporated by reference as if each individual publication
or patent were specifically and individually indicated to be
incorporated by reference and are incorporated herein by reference
to disclose and describe the methods and/or materials in connection
with which the publications are cited. The citation of any
publication is for its disclosure prior to the filing date and
should not be construed as an admission that the present disclosure
is not entitled to antedate such publication by virtue of prior
disclosure. Further, the dates of publication provided could be
different from the actual publication dates that may need to be
independently confirmed.
[0041] As will be apparent to those of skill in the art upon
reading this disclosure, each of the individual embodiments
described and illustrated herein has discrete components and
features which may be readily separated from or combined with the
features of any of the other several embodiments without departing
from the scope or spirit of the present disclosure. Any recited
method can be carried out in the order of events recited or in any
other order that is logically possible.
[0042] Embodiments of the present disclosure will employ, unless
otherwise indicated, techniques of encapsulation, materials
science, mechanical engineering, chemistry, food science,
biotechnology, and the like. Such techniques are explained fully in
the literature.
[0043] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how to perform the methods and use the compositions
and compounds disclosed and claimed herein. Efforts have been made
to ensure accuracy with respect to numbers (e.g., amounts,
temperature, etc.), but some errors and deviations should be
accounted for. Unless indicated otherwise, parts are by weight,
temperature is in .degree. C., and pressure is at or near
atmospheric. Standard temperature and pressure are defined as
20.degree. C. and 1 atmosphere.
[0044] Before the embodiments of the present disclosure are
described in detail, it is to be understood that, unless otherwise
indicated, the present disclosure is not limited to particular
materials, reagents, reaction materials, manufacturing processes,
or the like, as such can vary. It is also to be understood that the
terminology used herein is for purposes of describing particular
embodiments only, and is not intended to be limiting. It is also
possible in the present disclosure that steps can be executed in
different sequence where this is logically possible.
[0045] It must be noted that, as used in the specification and the
appended claims, the singular forms "a," "an," and "the" include
plural referents unless the context clearly dictates otherwise.
Thus, for example, reference to "a support" includes a plurality of
supports. In this specification and in the claims that follow,
reference will be made to a number of terms that shall be defined
to have the following meanings unless a contrary intention is
apparent.
DISCUSSION
[0046] Embodiments of the present disclosure provide coaxial
nozzles, capsule fabrication systems comprising coaxial nozzles,
and methods thereof. Multi-layered encapsulation has been of great
interest for various pharmaceutical, chemical and food industries.
Fabrication of well-defined capsules with more than one shell layer
still poses a significant fabrication challenge. Herein,
multi-layered capsule fabrication systems comprising a coaxial
nozzle to fabricate double-layered (core-shell-shell) capsules
during vibration-assisted dripping are described, along with
embodiments of coaxial nozzles and methods thereof.
[0047] During fabrication, different liquid materials can be
dispensed through their corresponding channels of the coaxial
nozzle to form a compound liquid flow, which comprises a core flow,
an annular flow, and a sheath flow. A high frequency vibration is
introduced to facilitate the breakup of the compound flow and the
formation of double-layered capsules. Through applicable
crosslinking mechanism(s) in a collection bath, capsules with a
core-shell-shell structure can be fabricated.
[0048] For the fabrication of multi-layered capsules, various
technologies have been studied, including compound or coaxial
nozzle-based dripping/jetting, microdrop collision, and
stirring/mixing-based bulk emulsification. During compound or
coaxial nozzle-based fabrication, coaxial nozzles are used to
produce the core droplet surrounded by a shell. When the flow rates
of core and shell solutions increase, the droplet formation
mechanism may change from dripping to jetting. A liquid core jet
can be surrounded by an annular jet, which may be further
surrounded by a carrier stream. For some applications, additional
stimuli may be applied to facilitate the droplet formation process
such as an electric field or vibration.
[0049] During microdrop collision, two inkjet nozzles are utilized
to make droplets from different solutions such as aqueous and
polymer solutions. After the collision of two inkjetted droplets, a
polymer film is generated at the interface between two solutions
due to the solvent exchange mechanism, and a compound droplet is
fabricated with the polymer solution as the shell layer. During
stirring/mixing-based bulk emulsification, two emulsification steps
are typically adopted: a core material is stirred into a shell
polymer solution, and the formed emulsion is further stirred into
an emulsifier-based solution to form double-layered emulsions. The
process can be improved by combining the co-nozzle extrusion with
emulsification. By using a microcapillary device, the coaxial flow
is formed at the exit of a tapered tube, and the outermost fluid is
pumped through the outer coaxial region from the opposite
direction; as the compound flow passes through the exit orifice, it
ruptures into core-shell capsules. While this approach simplifies
the two emulsification step-based conventional fabrication process,
the outermost fluid is used to emulsify the coaxial flow into
core-shell capsules instead of being a layer of the capsules. In
addition, it is difficult to fabricate a double-layered coaxial
glass microcapillary device as well as to control the formation of
a three-layered compound flow in an emulsification flow. Thus, it
is not practical to extend this approach to fabricate capsules with
a well-defined core-shell-shell structure.
[0050] A purpose of encapsulation is to immobilize, protect, and
control the release of entrapped materials such as flavor, living
cells, and pharmaceutical compounds. The capsules fabricated by the
fabrication system(s) described herein with well-defined porous or
impermeable membranes can be used in many fields including
pharmaceutical, chemical, and food industries, as well as in
various applications related to agriculture, biotechnology, and
medicine, to name a few.
[0051] Although single-layered (core-shell) capsules were
successfully fabricated by some approaches, such as compound or
coaxial nozzle-based dripping/jetting, microdrop collision, and
stirring/mixing-based bulk emulsification, to date the fabrication
of multi-layered capsules has not been explored. The feasibility of
multi-layered capsule fabrication using a coaxial dispensing
mechanism and how the geometry of the resulting multi-layered
capsules can be controlled by adjusting corresponding flow rates
are described herein.
[0052] Fabrication of well-defined capsules with more than one
shell layer still poses a significant fabrication challenge.
Herein, embodiments of multi-layered capsule fabrication systems
are developed and described by using a coaxial nozzle to fabricate
double-layered (core-shell-shell) capsules during
vibration-assisted dripping in certain aspects. During fabrication,
different liquid materials can be dispensed through their
corresponding channels of the coaxial nozzle to form a compound
liquid flow, which can comprise a core flow, an annular flow, and a
sheath flow. A high frequency vibration can be introduced to
facilitate the breakup of the compound flow and the formation of
double-layered capsules. Through applicable crosslinking
mechanism(s) in a collection bath, capsules with a core-shell-shell
structure can be fabricated.
[0053] Described herein are coaxial nozzles. Coaxial nozzles as
described herein can be utilized for or configured for capsule
fabrication. Coaxial nozzles as described herein can be configured
for the fabrication of single- or multi-layer capsules. In
embodiments, coaxial nozzles as described herein can be configured
for the fabrication of double-layered capsules. In embodiments,
coaxial nozzles as described herein can be configured for the
fabrication of double-layered capsules having a core-shell-shell
structure.
[0054] Coaxial nozzles as described herein can comprise a core flow
channel, a sheath flow channel, and an annular flow channel.
Channels of coaxial nozzles can reside within discreet physical
structures or can be defined as the space between two or more
physical structures. Channels as described herein can comprise one
or more inlets configured to receive fluid. Coaxial nozzles as
described herein can further comprise one or more outlet nozzles
configured to output material (fluid, capsule, etc) from the
coaxial nozzle. Such nozzles can be arranged as arrays for improved
productivity.
[0055] In certain aspects, an annular channel can have dimensions
D, L.sub.1, L.sub.2, and H, which are described in greater detail
below and demonstrated in the figures. D can be about 7.5 mm to
about 8.5 mm, L.sub.1 can be about 2.0 mm to about 4.0 mm, L.sub.2
can be about 12.5 to about 13.0 mm, and L.sub.3 can be about 2.0 mm
to about 2.5 mm. Considering the size of required multi-layered
capsules, such dimensions can be adjusted from the millimeter to
micrometer scale.
[0056] In certain aspects, the sheath channel can have dimensions
L, D.sub.1, D.sub.2, and H, which are described in greater detail
below and demonstrated in the figures. L can be about 1.5 mm to
about 2.0 mm, D.sub.1 can be about 14.0 mm to about 16.0 mm,
D.sub.2 can be about 11.0 mm to about 13.0 mm, and H can be about
8.0 mm to about 8.6 mm. Considering the size of required
multi-layered capsules, such dimensions can be adjusted from the
millimeter to micrometer scale.
[0057] In an embodiment, a coaxial nozzle can comprise three
components: an inner set, a middle set, and an outer set. These
components can be constructed of metal or metal alloys (such as
stainless steel, titanium, aluminum, and the like), or polymers
(such as polycarbonate (PC), Nylon, acrylonitrile butadiene styrene
(ABS), and the like) and/or glass if special corrosive liquid
materials are utilized.
[0058] An inner set can be configured to provide a core channel,
and can be configured to fit with the middle set to form an annular
channel.
[0059] A middle set can be in the center of a coaxial nozzle and
can provide support to hold the inner set and be configured to form
the annular channel as well as fit with the outer set to form the
sheath channel.
[0060] An outer set can enable the formation of a sheath channel of
the coaxial nozzle in addition to providing a fixture or fixture
for support of the entire nozzle assembly.
[0061] The inner, middle, and outer sets can have orifices. The
inner, middle, and outer sets can have orifices configured to
output fluid components or materials. In certain embodiments, the
through-hole in the inner set can have an inner diameter of about
0.5 mm, length of about 3.0 mm for its outer section, and outer
diameter of about 1.5 mm. The outlet of the middle set can have an
inner diameter of about 2.5 mm and outer diameter of about 3.5 mm.
The outlet of the outer set can have an inner diameter of about 4.5
mm. The core channel can be designed as a straight through hole in
the inner set with a diameter of about 0.5 mm based on the typical
core size of capsules and the machining capability.
[0062] Coaxial nozzles as described herein can further comprise
other components such as collars, screws, and gaskets for proper
operation. Screws can be configured to adjust the size or spacing
of various components in order to tune operation of the nozzles.
Gaskets can be copper gaskets in certain embodiments, top views of
which are shown in FIGS. 21 and 22. Collar covers (embodiments of
which such as those top views shown in FIGS. 17 and 19 and side
view shown in FIGS. 18 and 20) can be configured to seal the space
between different sets.
[0063] A cross-sectional side view of an embodiment of a coaxial
nozzle as described herein is shown in FIG. 9. As depicted in the
side view of FIG. 9, a coaxial nozzle can be a series of nested
annular structures comprising: an outer set 7 (also referred to as
a die in FIG. 10) configured to a receive a middle set 6 (also
referred to as a medium in FIG. 10) through a frustoconical
opening, the middle set 6 in turn configured to receive an inner
set 2 (also referred to as a mandrel in FIG. 10) through a
frustoconical opening.
[0064] The middle set 6 (top view shown in FIG. 11, additional
cross-sectional view shown in FIG. 12) can have an upper lip 201
that is wider than an outlet 203, and which can rest on an upper
surface of the outer set 7, or on a gasket 10 (FIG. 21 or FIG. 22)
which can sit in between the upper surface of the outer set 7 and
lower surface of the lip 201 of the middle set 6. The middle set 6
can have an inlet 209 for receiving a solution and/or solution
supply device 4. The middle set 6 can also have a channel 211 for
receiving a screw, or other adjustment device, which can aid in the
positioning of the middle set 6 and inner set 2 in relation to each
other. The middle set 6 can have a frustoconical opening 16 which
can receive the inner set 2, the inner surface of the frustoconical
opening 205 also forming a bottom surface of and partially defining
the annular channel. The middle set 6 can also have an outer
frustoconical surface 207 which forms the top surface of and
partially defines the sheath channel.
[0065] The inner set 2 (top view shown in FIG. 13, additional
cross-sectional view shown in FIG. 14) can have an upper lip 301
that is wider than an outlet 307, and which can rest on an upper
surface of the middle set 6, or on a gasket 9 (FIG. 21 or FIG. 22)
which can sit in between the upper surface of the middle set 6 and
upper surface of the middle set 6. The inner set 2 can have an
inlet 303 for receiving a solution or solution supply device 4. The
inner set 2 can also have a channel 305 which functions as the core
channel of the coaxial nozzle through which solution passes from
the solution supply device 4 (i.e. the inlet) to the outlet 307 of
the inner set 2. The inner set 2 can have a frustoconical outer
surface 309 which can form a top surface of and partially define
the annular channel.
[0066] The outer set 7 (top view shown in FIG. 15, additional
cross-sectional view shown in FIG. 16) can have an upper surface
401 that receives the lip 201 of the middle set 6 or a gasket 10
(FIG. 21 or FIG. 22) which can sit in between the upper surface 401
of the outer set 7 and lower surface of the lip 201 of the middle
set 6. The outer set 7 can have an inlet 403 for receiving a
solution or a solution supply device 4. The outer set 7 can also
have a channel 407 for receiving a screw, or other adjustment
device, which can aid in the positioning of the middle set 6 and
outer set 7 in relation to each other. The outer set 7 can have a
frustoconical opening 405 which can receive the middle set 6, the
surface of the frustoconical opening 405 also forming a bottom
surface of and partially defining the sheath channel.
[0067] Although examples of dimensions of embodiments of
components, shown in FIGS. 11-22, which form an embodiment of a
coaxial nozzle, as shown in FIG. 9, are depicted in FIGS. 9 and
11-22, these dimensions are not intended to be limiting. One of
skill in the art would understand how to scale up or scale down the
coaxial nozzle or components thereof accordingly.
[0068] Described herein are capsule fabrication systems. Capsule
fabrication systems as described herein can comprise one or more
coaxial nozzles, such as a coaxial nozzle as described above.
Capsule fabrication systems as described herein can comprise a
coaxial nozzle and can be configured for the fabrication of single-
or multi-layer capsules. In embodiments, capsule fabrication
systems as described herein can comprise a coaxial nozzle and can
be configured for the fabrication of double-layered capsules. In
embodiments, capsule fabrication systems as described herein can
comprise a coaxial nozzle and can be configured for the fabrication
of double-layered capsules having a core-shell-shell structure.
[0069] Capsule fabrication systems as described herein can comprise
a coaxial nozzle as described above, a vibrator, a collection bath,
and a solution delivery system. For specific multi-layered capsule
fabrication, capsule fabrication systems as described herein can
comprise auxiliary systems such as temperature control and UV
irradiation systems.
[0070] A vibrator can further comprise a controller which can
contain a waveform generator allowing a user to alter the frequency
or amplitude of the vibrations delivered to the system. Vibrator
controllers as described herein can be a part of the vibrator, or
can be a controller and/or a computing device existing as a
separate stand-alone device in electrical communication with the
vibrator. A vibrator can be attached to or in physical
communication with an outer set. In embodiments, the vibrator can
operate at a frequency of 100 Hz and an amplitude of 10 V.
[0071] A collection bath can be comprised of a fluid, such as
calcium chloride (CaCl.sub.2). Collection baths as described herein
can reside within containers configured to hold fluid. The
collection bath can contain a crosslinking agent (such as
Ca.sup.2+, enzymes, and the like per the type of liquid build
materials) to stabilize formed capsules.
[0072] Solution delivery systems as described herein can comprise
one or more syringes or syringe-based pumps to deliver fluid to one
or more channels. As described herein, each channel can have its
own syringe or syringe-based pump. Solution delivery systems can be
manual delivery or can be automated, in which case they can further
comprise a controller or computing device to vary flow parameters
of fluid delivery to the channel(s).
[0073] Described herein are methods for capsule fabrication.
Methods of capsule fabrication as described herein can comprise a
coaxial nozzle as described herein. Methods of capsule fabrication
as described herein can comprise a capsule fabrication system
comprising a coaxial nozzle. Methods as described herein can
fabricate multi-layered capsules. Methods as described herein can
fabricate single-layered capsules. Methods as described herein can
fabricate double-layered capsules. In embodiments, methods as
described herein can comprise a capsule fabrication system
comprising a coaxial nozzle and can fabricate double-layered
capsules. In embodiments, methods as described herein can comprise
a capsule fabrication system comprising a coaxial nozzle and can
fabricate multi-layered capsules.
[0074] Methods as described herein can comprise capsule initiation,
capsule development, and capsule breakup. During capsule
initiation, different liquid materials (such as liquid or fluid
solutions containing alginate and CaCl.sub.2 solutions) can be
dispensed through their corresponding channels of the coaxial
nozzle. Certain liquid materials are described in the examples
below.
[0075] Different liquid materials can be liquid or fluid solutions,
which can undergo a phase change process after forming capsules in
order to retain their shape. In addition to liquid or fluid
solutions containing alginate and/or liquid or fluid solutions
containing CaCl.sub.2, liquid materials, usually as solvent-based
solutions, suspensions and/or composites, include poly(D,
L-lactide-co-glycolide) (PLG), poly(1,6-bis-p-carboxyphenoxyhexane)
(PCPH), alginate-collagen composites, and the like.
[0076] During capsule development, the liquid materials come
together at the outlet of the coaxial nozzle to form a compound
liquid flow, which can comprise a core flow, an annular flow, and a
sheath flow. A high frequency vibration can then be introduced to
facilitate the breakup of the compound flow and the formation of
double-layered capsules herein. After crosslinking in a collection
bath comprising a crosslinking agent, capsules with a
core-shell-shell structure can be fabricated.
[0077] In methods as described herein, capsules can be formed at
the outlet of the coaxial nozzle by dispensing various solution
flows through corresponding channels, and the capsule formation
process can vary based on parameters such as the velocity or flow
rate of each solution and their material rheological and physical
properties. The solution delivery and vibration system can comprise
three syringe pumps to deliver solutions to corresponding channels
and an ultrasonic vibrator to vibrate the coaxial nozzle at a given
frequency and amplitude to facilitate the breakup of fluid flows
and form multi-layered capsules more effectively. The collection
bath herein can also contain a crosslinking agent (Ca.sup.2+) to
stabilize formed capsules.
[0078] While embodiments of the present disclosure are described in
connection with the Examples and the corresponding text and
figures, there is no intent to limit the invention to the
embodiments in these descriptions. On the contrary, the intent is
to cover all alternatives, modifications, and equivalents included
within the spirit and scope of embodiments of the present
disclosure.
Example 1
[0079] Multi-layered encapsulation has been of great interest for
various pharmaceutical, chemical and food industries. Fabrication
of well-defined capsules with more than one shell layer still poses
a significant fabrication challenge. Described herein is
investigation into the feasibility of using a coaxial nozzle to
fabricate double-layered (core-shell-shell) capsules during
vibration-assisted dripping. A three-layered coaxial nozzle is
described herein. The nozzle has been designed, manufactured, and
tested for double-layered capsule fabrication when using sodium
alginate solutions as the model liquid material for inner and outer
shell layers and calcium chloride solution as the core fluid. To
facilitate the droplet formation process, a vibrator has been
integrated into the fabrication system to provide necessary
perturbation for effective breakup of the fluid flow. It is
demonstrated that double-layered alginate capsules can be
successfully fabricated using a three-layered coaxial nozzle
fabrication system shown and described herein. During fabrication,
increasing the core flow rate can lead to an increase in capsule
and core diameters while the inner and outer shell layer
thicknesses decrease. Increasing annular flow rate can result in an
increase in capsule diameter and inner shell layer thickness while
the outer shell layer thickness decreases. An increase in the
sheath flow rate can lead to an increase in capsule diameter and
outer shell layer thickness but may have no significant effect on
the core diameter and inner shell layer thickness.
1. INTRODUCTION
[0080] Encapsulation, a process involving the complete envelopment
of preselected core material with a well-defined porous or
impermeable membrane, has been of great importance in recent years
and widely used in many fields including pharmaceutical, chemical,
and food industries, as well as in various applications related to
agriculture, biotechnology, and medicine, to name a few. An
important purpose of encapsulation is to immobilize, protect, and
control the release of entrapped materials such as flavor, living
cells, and pharmaceutical compounds.
[0081] For the fabrication of multi-layered capsules, various
technologies have been studied, including compound or coaxial
nozzle-based dripping/jetting, microdrop collision, and
stirring/mixing-based bulk emulsification. During compound or
coaxial nozzle-based fabrication, coaxial nozzles can be used to
produce the core droplet surrounded by a shell. When the flow rates
of core and shell solutions increase, the droplet formation
mechanism may change from dripping to jetting. A liquid core jet
can be surrounded by an annular jet, which may be further
surrounded by a carrier stream. For some applications, additional
stimuli may be applied to facilitate the droplet formation process
such as an electric field (for example, as described in
Lopez-Herrera, J. M., Barrero, A., Lopez, A., Loscertales, I. G.,
and Marquez, M., 2003, "Coaxial Jets Generated from Electrified
Taylor Cones," Journal of Aerosol Science, 34(5), pp. 535-552;
Loscertales, I. G., Barrero, A., Guerrero, I., Cortijo, R.,
Marquez, M., and Ganan-Calvo, A. M., 2002, "Micro/Nano
Encapsulation via Electrified Coaxial Liquid Jets," Science,
295(5560), pp. 1695-1698; Yao, R., Zhang, R., Luan, J., and Lin,
F., 2012, "Alginate and Alginate/Gelatin Microspheres for Human
Adipose-Derived Stem Cell Encapsulation and Differentiation,"
Biofabrication, 4(2), pp. 025007; and Yao, R., Zhang, R., Lin, F.,
and Luan, J., 2012, "Injectable Cell/Hydrogel Microspheres Induce
the Formation of Fat Lobule-Like Microtissues and Vascularized
Adipose Tissue Regeneration," Biofabrication, 4(4), pp. 045003, the
entirety of all of which are incorporated by reference herein) or
vibration (for example as described in Berkland, C., Pollauf, E.,
Varde, N., Pack, D. W., and Kim, K. K., 2007, "Monodisperse
Liquid-Filled Biodegradable Capsules," Pharmaceutical Research,
24(5), pp. 1007-1013; Yao, R., Zhang, R., Lin, F., and Luan, J.,
2012, "Injectable Cell/Hydrogel Microspheres Induce the Formation
of Fat Lobule-Like Microtissues and Vascularized Adipose Tissue
Regeneration," Biofabrication, 4(4), pp. 045003; and Heinzen, C.,
Marison, I., Berger, A., and von Stockar, U., 2002, "Use of
Vibration Technology for Jet Break-Up for Encapsulation of Cells,
Microbes and Liquids in Monodisperse Capsules," Landbauforschung
Volkenrode, SH241, pp. 19-25, the entirety of all of which are
incorporated by reference fully herein). During microdrop
collision, two inkjet nozzles can be utilized to make droplets from
different solutions such as aqueous and polymer solutions. After
the collision of two inkjetted droplets, a polymer film can be
generated at the interface between two solutions due to the solvent
exchange mechanism, and a compound droplet can be fabricated with
the polymer solution as the shell layer. During
stirring/mixing-based bulk emulsification, two emulsification steps
can be adopted: a core material can be stirred into a shell polymer
solution, and the formed emulsion can be further stirred into an
emulsifier-based solution to form double-layered emulsions. The
process can be improved by combining the co-nozzle extrusion with
emulsification. By using a microcapillary device, the coaxial flow
can be formed at the exit of a tapered tube, and the outermost
fluid can be pumped through the outer coaxial region from the
opposite direction; as the compound flow passes through the exit
orifice, it ruptures into core-shell capsules. While this approach
simplifies the two emulsification step-based conventional
fabrication process, the outermost fluid can be used to emulsify
the coaxial flow into core-shell capsules instead of being a layer
of the capsules. In addition, it is difficult to fabricate a
double-layered coaxial glass microcapillary device as well as to
control the formation of a three-layered compound flow in an
emulsification flow. Thus, it may not be practical to extend this
approach to fabricate capsules with a well-defined core-shell-shell
structure.
[0082] Described herein is an embodiment of a coaxial nozzle to
fabricate multi-layered capsules, for example double-layered
(core-shell-shell) capsules during vibration-assisted dripping. Of
the fabrication technologies described above, compound or coaxial
nozzle-based dripping/jetting can be favored due to its simple
implementation. As expected, the multi-layered capsule fabrication
process can produce monodisperse capsules with one core material
enclosed by more than one surrounding shell material. Although
single-layered (core-shell) capsules were successfully fabricated
by the aforementioned fabrication approaches, to date the
fabrication of multi-layered capsules has not been explored.
[0083] The disclosure herein describes the first investigation of
the feasibility of multi-layered capsule fabrication using
embodiments of the coaxial dispensing mechanism and how the
geometry of the resulting multi-layered capsules can be controlled
by adjusting corresponding flow rates. Sodium alginate (NaAlg) has
been selected in this disclosure as the model hydrogel material to
fabricate double-layered capsules, and calcium chloride can be used
as the crosslinking agent to facilitate the formation of alginate
capsules. To facilitate the droplet formation process, ultrasonic
vibration can be applied to the coaxial nozzle during dripping. The
embodiment of a coaxial nozzle-based multi-layered capsule
fabrication system has been validated during the fabrication of
multi-layered capsules, such as double-layered alginate capsules,
providing a versatile approach for effective capsule fabrication.
While alginate and calcium chloride solutions are utilized as
examples throughout the present disclosure, the devices and
approaches as described here can also be applicable to other
capsule fabrication techniques, such as capsule fabrication from
suspensions for example.
2. COAXIAL NOZZLE-BASED FABRICATION APPROACH
[0084] A schematic of an embodiment of a multi-layered capsule
fabrication system is illustrated in FIG. 1A. During fabrication,
different liquid materials can be dispensed through their
corresponding channels of the coaxial nozzle to form a compound
liquid flow, which comprises a core flow, an annular flow, and a
sheath flow. A high frequency vibration can be introduced to
facilitate the breakup of the compound flow and the formation of
double-layered alginate capsules herein. After crosslinking in a
collection bath, capsules with a core-shell-shell structure can be
fabricated. As shown in FIG. 1A, the multi-layered capsule
fabrication system can comprise three components: a multi-layered
coaxial nozzle, a solution delivery and vibration system, and a
collection bath. An important aspect of the multi-layered capsule
fabrication system is the three-layered coaxial nozzle (inset of
FIG. 1A), which can enable capsule fabrication and can influence
the geometry of fabricated capsules. The nozzle can comprise a core
flow channel to form the core layer, an annular flow channel to
form the inner shell layer, and a sheath flow channel to form the
outer shell layer of double-layered capsules. Capsules can be
formed at the outlet of the coaxial nozzle by dispensing various
solution flows through corresponding channels, and the capsule
formation process can vary based on parameters such as the velocity
or flow rate of each solution and their material rheological and
physical properties. The solution delivery and vibration system can
comprise three syringe pumps to deliver solutions to corresponding
channels and an ultrasonic vibrator to vibrate the coaxial nozzle
at a given frequency and amplitude to facilitate the breakup of
fluid flows and form multi-layered capsules more effectively. The
collection bath herein can also contain a crosslinking agent
(Ca.sup.2+) to stabilize formed capsules.
[0085] An embodiment of a multi-layered capsule fabrication system
and schematic is illustrated in FIG. 1A. FIG. 1B illustrates an
embodiment of the fabrication process of a double-layered capsule
with images showing three representative sequential stages during
fabrication: capsule initiation, development, and breakup. Such a
system can be used to fabricate double-layered capsules by
delivering corresponding solutions through the core flow, annular
flow, and sheath flow channels, individually in a sequence or
simultaneously. While using the core and annular flow channels only
(or using the sheath flow channel only to provide a carrier stream
for jet pinch-off control), it can also be utilized to fabricate
single-layered (core-shell) capsules. Due to simple implementation,
the multi-layered capsule fabrication system can be applicable to
the fabrication of various single- and double-layered capsules from
diverse liquid materials in conjunction with suitable crosslinking
mechanisms.
3. MATERIAL SELECTION AND NOZZLE DESIGN
3.1 Material Selection
[0086] Throughout the present disclosure, sodium alginate, a
natural polysaccharide, was selected as a model material to
fabricate the shell layers of double-layered capsules due to its
versatile functionality, mild crosslinking conditions, low cost,
biocompatibility, low toxicity, and environmentally friendly
nature, as well as its wide applications for encapsulation. As
designed, alginate solutions can be dispensed through the annular
and sheath flow channels to form two shell layers each with a
different dye for layer distinction. Aqueous calcium chloride
(CaCl.sub.2) was selected as the core flow as well as collection
bath material, acting as the crosslinking agent for alginate.
Sodium alginate comprises a family of unbranched binary copolymers
of 1,4 linked .beta.-D-mannuronic acid (M units) and
.alpha.-L-guluronic acid (G units). When it interacts with divalent
ions such as Ca.sup.2+ or trivalent ions such as Al.sup.3+, it can
undergo an ionic gelation process, which can occur as such cations
form interchain ionic bonds between G blocks, giving rise to a
stable three-dimensional network of calcium alginate.
3.1.1 Gelation Process Modeling
[0087] The CaCl.sub.2 concentration of the core flow can affect the
gelation rate of the annular alginate flow when traveling in air.
If the CaCl.sub.2 concentration is too high, the sodium alginate
solution can gel immediately once dispensed out of the nozzle,
resulting in a gelled filament before forming a droplet. If the
CaCl.sub.2 concentration is too low, the gelation rate of the inner
surface of the inner shell layer can be slow, which can result in
undesirable diffusion between the sodium alginate and CaCl.sub.2
solutions. As a result, the inner surface of the inner shell layer
may not be well-defined. Thus, it is important to select a suitable
CaCl.sub.2 concentration to fabricate well-defined multi-layered
alginate capsules.
[0088] Since the CaCl.sub.2 concentration of the core flow can be
of interest, FIG. 2A illustrates the interaction between the
CaCl.sub.2 core flow and the alginate annular flow. When the
alginate solution is dispensed into the ambient environment, it can
start interacting with the CaCl.sub.2 core flow.
[0089] The reaction front during alginate gelation is defined as
the region where the most chemical crosslinking takes place and
spatially separates the newly gelled region from the fluid ungelled
alginate region as shown in FIG. 2A. Based on the traveling-wave
hypothesis and diffusive flux of calcium cations through a gelled
structure (as described in Xiong, R., Zhang, Z., Chai, W., Huang,
Y., and Chrisey, D. B., 2015, "Freeform Drop-on-Demand Laser
Printing of 3D Alginate and Cellular Constructs," Biofabrication,
7(4), pp. 045011-1-13, which is fully incorporated by reference
herein), the reaction front position G(t), the distance from the
inner boundary of a single-layered capsule to the edge of the
reaction front, can be obtained as a function of time t as follows
(as described in Braschler, T., Valero, A., Colella, L., Pataky,
K., Brugger, J., and Renaud, P., 2011, "Link between Alginate
Reaction front Propagation and General Reaction Diffusion Theory,"
Analytical Chemistry, 83(6), pp. 2234-2242, which is fully
incorporated by reference herein):
1 + .theta. = ( 1 + L d D c dG ( t ) dt ) exp ( 1 D c G ( t ) dG (
t ) dt ) ( 1 ) .theta. = c 0 N c a 0 ( 2 ) ##EQU00001##
[0090] where .theta. is defined as a shorthand notation of the
calcium cation bulk concentration c.sub.0 with respect to the
concentration of available binding sites N.sub.ca.sub.0, N.sub.c is
the stoichiometric calcium cation-binding capacity per alginate
residue and can be estimated based on the half-eggbox model as
N.sub.c=3/4.sigma..times.(as described in Morris, E. R., Rees, D.
A., Thom, D., and Boyd. J., 1978, "Chiroptical and Stoichiometric
Evidence of a Specific, Primary Dimerisation Process in Alginate
Gelation," Carbohydrate Research, 66(1), pp. 145-154, which is
fully incorporated by reference herein), where a is the guluronic
acid content of alginate and equals 70% in this disclosure, a.sub.0
is the initial bulk concentration of alginate solution in terms of
uronic acid residues and equals 0.025 mol/L in this disclosure,
L.sub.d is the equivalent filter length for the reaction-diffusion
model system (by assuming that all the diffusion happens along the
radial direction, L.sub.d equals 0 in this disclosure), and D.sub.c
is the diffusion coefficient of free calcium cations, which can be
interpolated based on the diffusion coefficient measurement of
calcium cations (as described in Wang, J. H., 1953,
"Tracer-Diffusion in Liquids. IV. Self-Diffusion of Calcium Ion and
Chloride Ion in Aqueous Calcium Chloride Solutions," Journal of the
American Chemical Society, 75(7), pp. 1769-1770, which is fully
incorporated herein by reference) with different bulk
concentrations. By assuming a steady-state concentration gradient
of calcium cations, the steady-state analytical formula of G(t) can
be obtained as follows (as described in Braschler, T., Valero, A.,
Colella, L., Pataky, K., Brugger, J., and Renaud, P., 2011, "Link
between Alginate Reaction front Propagation and General Reaction
Diffusion Theory," Analytical Chemistry, 83(6), pp. 2234-2242,
which is fully incorporated by reference herein):
G(t)= {square root over (2D.sub.c.theta.t+L.sub.d.sup.2)}-L.sub.d
(3)
[0091] The gelation time can be approximated as the breakup period
as described herein, which can be affected by the material
properties and flow rate of the core and shell flows. By
considering that the longest breakup period can be on the order of
1 s (.about.3 s) and the typical annular shell thickness of capsule
can be on the order of 0.1 mm (.about.0.5 mm), the reaction front
position G(t) of CaCl.sub.2 core flow solution with different
concentrations can be calculated. If G(t) is taken as one-tenth of
the annular shell thickness, that is assumed to be 0.5 mm, the
alginate gelation of the inner surface of the inner shell layer may
not significantly affect the jet/flow breakup and capsule formation
process. When the CaCl.sub.2 concentration decreases to 0.5% (w/v),
G(t) is around 0.03 mm (where c.sub.0=0.275.times.10.sup.-2 mol/L
and D.sub.c.about.0.71.times.10.sup.-9 m.sup.2/s), which is lower
than 0.05 mm. As such, the CaCl.sub.2 concentration of the core
flow is selected as 0.5% (w/v) herein.
[0092] After an alginate capsule submerges in the CaCl.sub.2
collection bath, its crosslinking mechanism is depicted in FIG. 2B.
To maintain its spherical morphology, the outer surface of alginate
capsules can be solidified in a timely manner. Thus, a 2.0% (w/v)
CaCl.sub.2 solution was used as the crosslinking and collection
bath. Finally, alginate capsules can be completely crosslinked in
the bath as shown in FIG. 2C.
3.1.2 Material Preparation
[0093] Sodium alginate (Sigma-Aldrich, St. Louis, Mo.) was used to
fabricate the layers of multi-layered capsules: 1.0% (w/v) alginate
solution for the annular flow and 2.0% (w/v) alginate solution for
the sheath flow. During preparation, alginate powder was dissolved
in deionized (DI) water with continuous stirring until completely
dissolved. To distinguish different alginate layers of fabricated
double-layered capsules, fluorescent blue 7-Amino-4-methylcoumarin
(Chem-Impex, Wood Dale, Ill.) was added to the 1.0% (w/v) alginate
solution at a concentration of 0.5% (w/v), and fluorescent green
polyethylene microspheres (UVPMS-BG-1.00, 45-53 .mu.m, Cospheric
LLC, Santa Barbara, Calif.) were added to the 2.0% (w/v) alginate
solution at a concentration of 0.5% (w/v).
[0094] Calcium chloride (CaCl.sub.2; Sigma-Aldrich, St. Louis, Mo.)
was used to crosslink the alginate solutions during capsule
fabrication. CaCl.sub.2 solution was prepared by dissolving
CaCl.sub.2 powder in DI water with continuous stirring until
completely dissolved. Specifically, 0.5% (w/v) CaCl.sub.2 solution
was prepared as the core flow to crosslink the inner surface of
alginate capsules while 2.0% (w/v) CaCl.sub.2 solution was prepared
as the crosslinking bath to crosslink fabricated alginate capsules
as aforementioned.
3.1.3 Rheological Properties Measurement and Results
[0095] Rheological properties of alginate solutions with different
concentrations (1.0% and 2.0% (w/v)) were measured using a
rheometer (ARES LS1, TA, New Castle, Del.) with a cone-plate
measuring geometry (a diameter of 50 mm, a cone-to-plate gap
distance of 46 .mu.m, and a cone angle of 2.64.degree.). To
quantitatively determine the viscosity, steady rate sweeps were
conducted by varying the shear rate from 0.01 to 100 s.sup.-1. By
fitting the shear stress-rate data into the Carreau-Yasuda model,
the zero-shear-rate viscosity can be obtained as shown in FIG. 7
(Table 1). The surface tension was measured using a tensiometer
(DSA10-MK2, Kruss GmbH, Hamburg, Germany) based on the pendant drop
method, and the results are listed in FIG. 7 (Table 1).
3.2 Three-Layered Coaxial Nozzle Design and Fabrication
3.2.1 Three-Layered Coaxial Nozzle Design
[0096] Embodiments of three-layered coaxial nozzles according to
the present disclosure can comprise three stainless steel
components: an inner set, a middle set, and an outer set as shown
in FIG. 3A. In addition to the three sets, FIG. 3A also illustrates
three channels for fluid dispensing: core, annular, and sheath
channels. The inner set can have two functions: to provide the core
channel for the core flow, and to fit with the middle set to form
the annular channel as shown in FIG. 3B. The middle set can be in
the center of the coaxial nozzle and can provide support to hold
the inner set to form the annular channel as well as fit with the
outer set to form the sheath channel. The outer set can enable the
formation of the sheath channel of the coaxial nozzle as shown in
FIG. 3) in addition to being the fixture of the whole nozzle
assembly. The coaxial nozzle can also be attached to the vibrator
via the outer set. Due to the interest in capsule fabrication and
the capacity in micromachining of the stainless steel nozzle sets,
the orifice size of each set can have dimensions as follows. The
through-hole in the inner set can have an inner diameter of 0.5 mm,
length of 3.0 mm for its outlet section, and outer diameter of 1.5
mm; the outlet of the middle set can have an inner diameter of 2.5
mm and outer diameter of 3.5 mm; and the outlet of the outer set
can have an inner diameter of 4.5 mm as shown in FIG. 3A.
[0097] The core channel can be designed as a straight through hole
in the inner set with a diameter of 0.5 mm based on the typical
core size of capsules and the machining capability. FIGS. 3B and C
illustrate the embodiments of structures of both annular and sheath
channels. As seen from these two figures, alginate solutions can be
injected into the channels from their corresponding inlets, which
are perpendicular to the axis of the nozzle. Thus, it is relevant
to design the nozzle assembly for uniform flow fields in the
channels and at the outlet of the nozzle in order to have
well-defined capsules. Specifically, for the annular channel (FIG.
3B), the shaping length L.sub.3, the compression angle (determined
by the inner diameter D and axial length L.sub.2), and the distance
from the inlet to the inclined channel L.sub.1 are to be
determined; for the sheath channel (FIG. 3C), the shaping length L,
the compression angle (determined by the inner diameter D.sub.2 and
distance from the inlet to the shaping section H), and the outer
diameter D.sub.1 are also to be determined. Considering the
machining capability, the ranges of these structure dimensions can
be selected as shown in FIG. 8 (Table 2).
[0098] The aforementioned structural dimensions can be determined
by achieving the uniformity of the flow velocity distribution at
the nozzle outlet. As described herein, the numerical simulation
and analysis of velocity distribution can be performed using FLUENT
15.0 (ANSYS, Canonsburg, Pa., USA) to determine the optimal design
for the three-layered coaxial nozzle. During simulation, the meshes
can be automatically generated, the volume flow rate in the annular
channel can be set to 800 .mu.L/min and that in the sheath channel
can be set to 1600 .mu.L/min, and the inside walls can be set as
non-slip. Based on the experimental design, the 1.0% and 2.0% (w/v)
NaAlg solutions are used as the annular and sheath flows,
respectively, for simulations.
[0099] The numerical simulation of the effects of these structure
dimensions on the flow velocity uniformity is performed using an
orthogonal experiment (L.sub.9 (3.sup.4)) based on the factor and
level numbers as shown in FIG. 8 (Table 2). Overall, nine different
combinations of these structure dimensions can be selected
accordingly as the orthogonal experimental design (FIG. 23). To
evaluate the uniformity of the velocity field at the outlet of the
nozzle, twelve points along the circumferential direction at the
cross-sectional area of the outlet can be selected with an interval
angle of 30.degree. as shown in FIG. 3D. The velocities at these 12
points are collected and the standard deviation of the velocity
S D = 1 N i = 1 N ( x i - x _ ) 2 ##EQU00002##
is calculated as the criteria to assess the uniformity of the
velocity at the outlet, where, SD is the standard deviation of the
velocity, N is the number of the evaluated points (N=12 herein),
x.sub.i is the velocity of i.sup.th point, and x is the average
velocity. For illustration, some typical velocity distributions of
the annular and sheath flows at the outlet of the nozzle are shown
in FIGS. 3E and 3F. Based on the orthogonal experiment results as
shown in FIG. 23, a combination of the structural dimensions can
be: annular channel (D=7.50 mm, L.sub.1=3.00 mm, L.sub.2=12.75 mm,
and L.sub.3=2.25 mm) and sheath channel (L=1.50 mm, D.sub.1=15.00
mm, D.sub.2=12.00 mm, and H=8.28 mm) to minimize the SD values of
the simulation results.
3.2.2 Three-Layered Coaxial Nozzle Manufacturing
[0100] Based on the optimization of the three-layered coaxial
nozzle design, a stainless steel nozzle was manufactured. The
schematic of an embodiment of a three-layered coaxial nozzle
structure is illustrated in FIG. 4A, and the corresponding velocity
field distribution in the annular and sheath channels as simulated
are shown in FIGS. 4B and 4C. When flowing in the channels, the
solutions can have a uniform velocity distribution, and the
velocity can increase evenly in the compression section until the
solutions are dispensed out of the nozzle.
[0101] Embodiments of the fabricated inner (FIG. 4F), middle (FIG.
4G), and outer (FIG. 4H) sets are also shown in FIG. 4, and they
can be assembled together and fixed by eight bolts as shown in FIG.
4D. To avoid the leakage along any interfaces, copper gaskets can
be used between each two connected parts. To ensure the coaxial
alignment of these three channels, four bolts can be used to adjust
the position of the inner set in the middle set, and another four
bolts can be used to adjust the position of the inner-middle set
subassembly in the outer set as shown in FIG. 4D. After assembly,
fine adjustments for optimal coaxial alignment of the channels can
be performed under a microscope as shown in FIG. 4E.
3.3 Experimental Setup and Design
[0102] The core (CaCl.sub.2), annular (NaAlg in blue) and sheath
(NaAlg in green) solutions were provided at different flow rates
accordingly using three independent syringe pumps (Harvard
Apparatus, Holliston, Mass.). The three-layered coaxial nozzle as a
whole can be attached to an ultrasonic vibrator (Etrema Product,
Ames, Iowa), which can be driven by an amplified waveform from a
waveform generator (33522A, Agilent Technologies, Englewood,
Colo.). Specifically, the waveform can be a sinusoidal wave with a
frequency of 100 Hz and an amplitude of 10 V.
[0103] To investigate the effects of flow rate on the capsule
geometry, different flow rates can be used to fabricate
double-layered capsules. The investigated core flow rates were:
100, 200, and 300 .mu.L/min, the annular flow rates were: 600, 800,
and 1000 .mu.L/min, and the sheath flow rates were: 1200, 1600, and
2000 .mu.L/min. After the dissection of gelled capsules, they were
imaged using a fluorescence microscope (EVOS FL, ThermoFisher
Scientific, Waltham, Mass.) with the green fluorescent and blue
fluorescent channels to distinguish two alginate shell layers. The
boundary between the outer and inner layers was determined by
finding the most significant color difference. All quantitative
values of capsule dimensions were reported as mean.+-.standard
deviation with three samples per group. Statistical analysis was
performed using the analysis of variance (ANOVA), and p-values of
less than 0.05 were considered statistically significant.
4. FABRICATION RESULTS
4.1 Representative Double-Layered Capsules
[0104] By adjusting the flow rates of core, annular, and sheath
flows, well-defined double-layered capsules can be fabricated at a
frequency of about 20 capsules/minute based certain setups. FIG. 5A
shows a schematic of embodiments of double-layered capsules
comprising a core layer surrounded by inner and outer shell layers.
After fabrication, capsules can be submerged in the CaCl.sub.2 bath
for 20 minutes for complete gelation, and representative gelled
capsules are shown in FIG. 5B.
[0105] Furthermore, FIG. 5B inset shows a dissected capsule after
complete gelation, and the florescent image of its hemisphere is
captured by fluorescence microscopy. As seen from the inset, the
inner and outer shell layers are clearly distinguishable with a
relatively uniform thickness for each layer, proving the
effectiveness of the multi-layered capsule fabrication system for
the fabrication of double-layered capsules with well-defined
geometry.
4.2 Effects of Core, Annular, and Sheath Flow Rates on Capsule
Geometry
[0106] The effects of core, annular, and sheath flow rates on the
dimensions of fabricated capsules are illustrated herein in terms
of overall capsule and core diameters as well as the thickness of
each shell layer. In particular, the effects of core flow rate on
the geometry of double-layered capsules can be examined by fixing
the annular and sheath flow rates at 800 .mu.L/min and 1600
.mu.L/min, respectively, while varying the core flow rate in the
range of 100-300 .mu.L/min. The geometries of fabricated
double-layered capsules are measured, and their dimensions are
shown in FIGS. 6A and 6B. As seen from FIG. 6A, both capsule and
core diameters can increase with increasing core flow rate. Since
the annular and sheath flow rates remain the same, the resulting
volumes being dispensed do not vary. As such, the increased core
diameter can cause a slight reduction of both inner and outer shell
layer thicknesses as shown in FIG. 6B.
[0107] The effects of annular flow rate on the geometry of
double-layered capsules can be examined by fixing the core and
sheath flow rates at 200 .mu.L/min and 1600 .mu.L/min,
respectively, while varying the annular flow rate in the range of
600-1000 .mu.L/min. The geometries of fabricated double-layered
capsules can be measured, and their dimensions are shown in FIGS.
6C and 6D. As seen in FIG. 6C, with increasing annular flow rate,
the capsule diameter can also increase. Since the core and sheath
flow rates remain the same, the resulting volumes being dispensed
can change. Thus, the core diameter may not change (FIG. 6C).
However, as seen in FIG. 6D, the increasing annular flow rate can
increase the inner shell layer thickness, resulting in an increase
in overall capsule diameter (FIG. 6C) and a reduction of outer
shell layer thickness.
[0108] The effects of sheath flow rate on the geometry of
double-layered capsules can be examined by fixing core and annular
flow rates at 200 .mu.L/min and 800 .mu.L/min, respectively, while
increasing the sheath flow rate from 1200 .mu.L/min to 1600
.mu.L/min to 2000 .mu.L/min. The geometries of fabricated
double-layered capsules are measured, and their dimensions are
shown in FIGS. 6E and 6F. As seen in FIG. 6E, the increase of
sheath flow rate can cause the increase of fabricated capsule
diameter. Since the core and annular flow rates remain the same,
the resulting volumes being dispensed can also be the same. As
such, both the core diameter (FIG. 6E) and the inner shell layer
thickness (FIG. 6F) can change while the outer shell layer
thickness can increase (FIG. 6F).
[0109] As described herein, the selection of the flow rate ranges
can be based on experimental observations, and fabrication
processes can be numerically modeled and validated as a function of
operating conditions for controlled fabrication of capsules with
specific dimensions. In addition, capsule size of embodiments
fabricated herein is around 1500 .mu.m (millimeter scale) in
diameter. For some applications such as controlled drug delivery,
micro-scale capsules are desirable, and other multi-layered coaxial
nozzle set with smaller channel dimensions can be designed and
manufactured.
5. CONCLUSIONS
[0110] Embodiments of a three-layered coaxial nozzle fabrication
system is described herein. Nozzles and capsule fabrication systems
as described herein can be configured to fabricate double-layered
capsules. To facilitate the droplet formation process, a vibrator
can be integrated into the fabrication system to provide necessary
perturbation for effective breakup of the fluid flow into droplets.
Using numerical simulations, orthogonal experiments can be
conducted to optimize the structure of the coaxial nozzle for
capsule fabrication, and such nozzles and systems can be
fabricated. Using sodium alginate solutions as the model liquid
material for inner and outer shell layers and calcium chloride
solution as the core fluid, multi-layered, such as double-layered
capsules can be fabricated. Some conclusions from the disclosure as
described herein can be drawn as follows: [0111] 1. Double-layered
alginate capsules can be successfully fabricated using embodiments
of three-layered coaxial nozzles and capsule fabrication systems
comprising such; and [0112] 2. Operating conditions (core, annular,
and sheath flow rates) can affect the dimensions of fabricated
double-layered capsules. Increasing core flow rate can lead to
increasing capsule and core diameters while the inner and outer
shell layer thicknesses can decrease. Increasing annular flow rate
can result in increased capsule diameter and inner shell layer
thickness while the outer shell layer thickness can decrease.
Increasing sheath flow rate can lead to increased capsule diameter
and outer shell layer thickness but may have little effect on the
core diameter and inner shell layer thickness.
[0113] Additional design and simulation results of orthogonal
experiments for embodiments of systems and methods are shown in
FIG. 23, where X.sub.i illustrates the variable X at the i.sup.th
setting, (variable X=A, B, C and D as defined in FIG. 8 (Table 2)
and i=1, 2, and 3 which depicts three different values of the
corresponding X), SD is the standard deviation of the velocity
which is used to assess the velocity uniformity of the annular and
sheath flows at the nozzle outlet location, T.sub.iX illustrates
the sum of the i.sup.th setting of variable X in different designs
and T.sub.iX=.SIGMA.SD.sub.iX, t.sub.iX is the average value of
T.sub.iX, and R.sub.X is the range of the X.sup.th column and
R.sub.X=Max(t.sub.1X, t.sub.2X, t.sub.3X)-Min(t.sub.1X, t.sub.2X,
t.sub.3X). Herein, R.sub.X is used to assess the sensitivity of
velocity uniformity to different structure dimensions. From the
range analysis as shown in FIG. 23, the effects of different
structure dimensions on the uniformity of the velocity field is
evaluated. Specifically, for the annular channel since
R.sub.A>R.sub.B>R.sub.C>R.sub.D, the inner diameter of the
channel influences the velocity uniformity more significantly than
the other dimensions; for the sheath channel since
R.sub.C>R.sub.A>R.sub.B>R.sub.D, the compression angle
influences the velocity uniformity more significantly than the
other dimensions. When determining the nozzle dimensions, these key
dimensions must be guaranteed first before optimizing the other
dimensions in order to have an optimized three-layered coaxial
nozzle.
[0114] It should be noted that ratios, concentrations, amounts, and
other numerical data may be expressed herein in a range format. It
is to be understood that such a range format is used for
convenience and brevity, and thus, should be interpreted in a
flexible manner to include not only the numerical values explicitly
recited as the limits of the range, but also to include all the
individual numerical values or sub-ranges encompassed within that
range as if each numerical value and sub-range is explicitly
recited. To illustrate, a concentration range of "about 0.1% to
about 5.0%" should be interpreted to include not only the
explicitly recited concentration of about 0.1 wt % to about 5.0 wt
%, but also include individual concentrations (e.g., 1.0%, 2.0%,
3.0%, and 4.0%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%,
and 4.4%) within the indicated range. In an embodiment, the term
"about" can include traditional rounding according to significant
figures of the numerical value. In addition, the phrase "about `x`
to `y`" includes "about `x` to about `y`".
[0115] It should be emphasized that the above-described embodiments
of the present disclosure are merely possible examples of
implementations, and are merely set forth for a clear understanding
of the principles of this disclosure. Many variations and
modifications may be made to the above-described embodiment(s) of
the disclosure without departing substantially from the spirit and
principles of the disclosure. All such modifications and variations
are intended to be included herein within the scope of this
disclosure and protected by the following claims.
* * * * *