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The ElectroNanospray™ Process
An Overview of the Technology and Its Biomedical Applications
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Website: www.nanocopoeia.com
Email: [email protected]
©2008 Nanocopoeia, Inc.
Executive Summary
Nanocopoeia Inc. has developed a novel electrospray system for the production of nanoparticles.
The business of Nanocopoeia is the therapeutic use of those nanoparticles in medical applications.
Our patented ElectroNanospray™ (ENS) process is currently being used to produce complex
coatings for medical devices and to nanoformulate drugs for enhanced bioavailability.

Medical Device Coatings: Medical device coatings are used in combination with the device
as a site specific drug delivery mechanism. They can also be used to improve the
integration of devices with patient tissues. Coatings are a critical component of
cardiovascular, ophthalmic, and orthopedic implants. One market-defining advance has
been the application of drug eluting coatings onto cardiovascular stents. These coatings
were originally designed to prevent smooth muscle cell growth that leads to a re-narrowing
of the vessel in a process known as restenosis. However, recent reports indicate that there
are significant problems with the long term efficacy of the current drug eluting stent (DES)
designs and highlight the need for improved functionality for next generation coatings. The
ENS process is ideally suited for creating this next generation of DES coatings. The unique
nature of the ElectroNanospray process allows for deposition of coatings onto highly
complex surfaces in ways that are superior to more traditional coating methods. It is highly
adaptable and can work with a wide range of drugs and biologic agents including proteins,
peptides and DNA. In addition, the process can create unique nanoparticulate coatings that
allow for the engineering of specific drug elution and surface morphologies not possible with
the current coating technologies.

Drug Formulations: Poor water solubility of drug agents is a major problem for the
pharmaceutical industry. A therapeutic compound that has issues with solubility is
generally very difficult to administer and requires large doses that often lead to complicating
side effects. This leads to poor patient compliance and uncertain efficacy for that specific
treatment. It is estimated that 40% of newly discovered drug candidates that are identified
by high through put screening or other engineered design approaches are very poorly
soluble. As a result, many of these candidate compounds are rejected for further
development despite the fact that they may show promising therapeutic activity in cellbased studies. A significant feature of the ENS system is the patented coaxial sprayhead
nozzle. This design enables the combination of two separate streams of compounds at the
tip of the spray nozzle. By spraying drug in one stream and encapsulating agents in the
other, we are able to create core shell nanoparticles in a single step. By controlling the size
of the particles and the appropriate pairing of drug and encapsulating agent, we are able to
achieve dramatic improvements in the ability to deliver insoluble drugs. The dramatic
increase in surface area that is created by the nanoformulation process causes the
compound to become suspendable in solution in a way that mimics solubility.
Nanoformulation enables enhanced bioavailability through this mechanism. The ENS
process is inherently efficient; uniquely positioning Nanocopoeia as a provider of
formulation solutions to pharmaceutical companies by enabling the screening of those drug
candidates in appropriate biologic systems.
The ElectroNanospray process is essentially the same for both the creation of medical device
coatings and the development of drug nanoformulations. The synergy between the optimization of
process parameters for both applications allows us to advance these two distinct business areas in
parallel to achieve a greater return on our efforts.
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Electrospray and its broader applications
The most common method of producing particles is through pneumatic means where pressurized
gas is used to create the aerosols. Electrospray is an alternative method that generates particles
via electrostatic charging. It was first described by John Zeleny in 1914 (Physical Review (1914)
3:69-91). The term “electrospray” has been used to describe two distinct approaches. In one, a
liquid is sprayed using pneumatic or other means to generate particles and then an electric field is
applied to charge the pre-formed particles. In the second approach, described by Zeleny, the
particles are generated from a liquid by the force of the electric field itself. In this process, a large
voltage is applied to a conductive liquid that has the capacity to hold only a finite amount of charge.
When the charge exceeds this capacity, the liquid becomes unstable and breaks apart into a mist
of highly charged particles. These charged particles repel one another and traverse the electric
field of the system until they encounter a grounded or oppositely charged surface. As these
particles fly towards a grounded surface most of the solvent evaporates before the particle reaches
the surface. By carefully controlling this solvent evaporation, many unique particles and coatings
can be created as described below.
Electrospray has a wide range of industrial and scientific applications. It is used in industrial
painting applications because it produces high quality finishes. It is used in analytical chemistry to
generate ionized molecules for analysis and identification in a process called mass spectroscopy.
It has been used for mixing drug powders and for generating air-born particles for targeted drug
delivery into the lungs. In material science, it has been used to create ceramic films and ceramic
nanoparticles. Small spray nozzles are even proposed for use as propulsion systems for micro
satellites.
Electrospray Basics:
Nanocopoeia’s technology uses electrospray in the so called “cone-jet electrospray” mode of
operation (Fig. 1).
Figure 1. A capillary spray head progressing from the start of spray
(droplet, left) to a "pulsating mode" (middle figure) and finally, the stable
"cone-jet" mode (right) that produces a range of nanoscale particle
sizes with narrow distributions.
The cone-jet mode of electrospray is the most stable mode of operation and can produce highly
uniform monodisperse particles, ranging from a few nanometers in diameter up to micron-sized
particles. In its simplest form of operation, a conductive solution is passed through a small
capillary and a high voltage is applied. Figure 2 provides a schematic showing the forces at work to
form the particles.
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Flow of
Solvent Carrier
And Active Agent
Under Pressure
Cone Jet
Filament of Solvent
And Active Agent
+
Capillary
High Voltage
~3-6000 V
Forces Liquid Stream
Into Cone Jet
+ Charge
Positively
Charged Particles
Of Solvent Actively
Repel, Achieve High
Velocity
+
+
+
+
+
Charged
Nanoparticles
Develop as Solvent
Carrier Evaporates
(High Surface Area)
Nanofilament Emerges
From Cone Jet
Filament Breaks Up
Into Charged Particles
(see exploded view)
Particles Neutralized
At Target
Negative Charge on
Target
Negative Charge on Target
Figure 2. Electrospray fundamentals. This schematic depicts
a capillary operating in cone jet mode operating at high voltage.
The nanofilament emerging from the cone jet breaks up into
like-charged particles which form the spray. These particles are
attracted to the negatively charged target.
The size of the nanoparticles generated by the electrospray process is governed by two key
variables, conductivity of the liquid and flow rate. Their relationship can be described by the
following equation:
D = 1.4735+319.24*(Q/K)1/3
where particle size D (in nm) is a function of the cube root of flow (Q) divided by conductivity (K) of
the solution (Fig. 3). Chen et al. (Journal of Aerosol Science (1995) 26(6):963-77) demonstrated
that monodisperse particles can be engineered to range in size from as small as 4 nm (about the
size of a protein molecule), up to micron sized particles (about the size of an E. coli bacterium).
Thus, by carefully adjusting the conductivity of the spray fluid and flow rate, we can tightly control
the size of nanoscale particles that are generated by the process. This ability to control the scale of
the particles has important implications for medical device coatings and drug formulation as
described below.
200.0
D (nm) = 1.4735 + 319.24*(Q/K)1/3
p
R=0.99867
150.0
100.0
50.0
0.0
10-2
10-1
(Q/K)
100
1/3
Figure 3. Relationship of particle size
to flow rate and conductivity.
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Unique aspects of ElectroNanospray™ technology
Nanocopoeia’s technology, which we call the ElectroNanospray™ (ENS) process, is based on the
work of David Pui and Da-Ren Chen at the University of Minnesota. They have published
extensively on the physical principles involved in producing nanoparticles by electrospray. Their
innovations have resulted in 6 issued US Patents and numerous additional continuations and
pending applications which are owned by the University of Minnesota. Nanocopoeia is the
exclusive licensee of this intellectual property portfolio and holds world-wide commercialization
rights for all fields. In addition to the University of Minnesota intellectual property portfolio,
Nanocopoeia has filed both method and material patents for several specific areas of application;
both medical and industrial. International coverage has been sought in Europe, Japan, China, and
Australia. Nanocopoeia is committed to an aggressive campaign to protect the fundamental value
of the intellectual property portfolio of the company.
What differentiates ENS from other processes is a unique co-axial spray nozzle. This patented
nozzle allows us to create complex, composite nanoscale particles from a wide range of
compounds. These compound particles form the basis of many of the specialized coatings and
drug formulations that Nanocopoeia has developed. With the coaxial capillary nozzle, two spray
streams of different composition merge at the cone jet tip. This has two significant implications: it
permits spraying of materials that are difficult to spray by traditional methods (e.g. immiscible
fluids) and it also creates the possibility of encapsulating the core fluid material, resulting in “coreshell” nanoparticles (Fig. 4).
Liquid 1
Liquid 2
Apply high
voltage ~4 kV
 Griseofulvin 60-80 nm
 Eudragit: 160-190 nm
Nanofibril breaks into
charged nanoparticles
Transmission electron
microscope image.
Figure 4. Dual capillary nozzle generates composite particles.
Nanoformulations of highly insoluble drugs can be created in a single
step by encapsulation the drug with surfactants or polymers. This is an
example of griseofulvin nanoparticles created by encapsulation with
Eudragit
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Synergy between medical device and drug formulation applications
The ENS system can produce engineered nanoparticles for a wide range of applications; industrial
as well as health care. Nanocopoeia is specifically focused on commercializing this technology for
medical applications. The business model is to enable innovation in two interrelated fields; medical
device coatings and nanoformulation of pharmaceutical compounds. There is a significant and
efficient ability to leverage technology development between these two applications. In fact, they
follow an identical set of physical and chemical principles through to the formation of particles at
the cone jet. For purposes of illustration, the process can be broken down into two broad steps.
The first step involves all the parameters needed to create a nanoparticle. In their simplest forms,
these nanoparticles are comprised of a drug and a carrier (e.g. a polymer). In the case of medical
device coatings, the most common application is to combine a drug (such as an antiproliferative
agent in the case of drug eluting stents) and a polymer into a spray droplet. In the case of drug
nanoformulations, a drug is combined with an encapsulant that can be a polymer or some other
agent (e.g. a surfactant) that promotes dispersal or suspension into a solution. Thus, in both cases,
multiple spray streams combine at the cone jet to generate a complex composite particle with
nanoscale dimensions and the associated beneficial properties.
Up until this point, the physical parameters of the processing system are essentially identical.
Further, the chemical information gained in one system (e.g. knowledge of how a drug and polymer
interact) is applicable to both medical device coatings and nanoformulation. This allows us to
exploit the knowledge gained in one application to rapidly adapt the process for the other. The two
applications diverge downstream of the particle formation. In both systems, a highly charged
particle is created and in both systems these particles follow the electric field to coat a grounded or
oppositely charged surface. In the case of medical device coatings, the goal is to create a
conformal film that merges at some level to create a tightly adherent surface. In the case of drug
nanoformulations, we must achieve the opposite outcome - the particles need to remain discrete in
order to promote nano-scale suspendability. This creates the ability to disperse the therapeutic
agents throughout the body, rendering them more readily bioavailable. Thus, the particles are
collected in a manner that allows us to maintain their individual character. The two therapeutic
applications of the process are described in more detail, below.
Medical Device Coatings
In 2003, the medical device industry was transformed with the introduction of the drug-eluting
coronary stent (DES). This DES class of products took the existing bare metal stent, which was
designed to prop open coronary arteries after balloon angioplasty or ablation, and added a time
release drug coating designed to prevent scar tissue from forming (restenosis). So-called
“convergence products” combining implantable medical devices and therapeutic agents introduced
a powerful new aspect to device performance.
In 2007, worldwide sales of drug eluting stent treatments were projected to exceed $7 billion.
Instead, in mid-2006 and throughout 2007, the industry crashed due to problems with device
performance and due to a lack of patient compliance with their required adjunct therapies. Future
industry as a whole is still scrambling to understand and address the device failures. The next
generations of product will be designed to address the disease mechanisms associated with
atherosclerosis. These therapies will target vessel re-endothelialization and disease treatment
instead of purely mechanical support and deterrence of scar tissue formation. All segments of the
research population: industry, academia, and government clearly appreciate the need to provide
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advanced product design addressing the therapeutic issues found to be lacking in the current
generation of products.
In the face of this rapid product evolution, there is considerable opportunity for technology that
improves the therapeutic value of the stent coating. Engineered coating applications enable the
intentional design of the coating performance to a therapeutic specification. The ENS process is
ideal for this purpose. Nanoparticles can be applied as uniform coatings to the complex
architecture such as those found in coronary stents. Coating characteristics can be engineered to
result in surfaces ranging from a smooth film to progressively more “open matrix” coatings with
drug:polymer combination nanoparticles of increasing size. These surface characteristics are
directly related to the drug elution profile of the combination device. This degree of control offers
important potential advantages over current coating methods:






Improved coating efficiency for reduced waste of costly materials
Non-line-of-sight coating for improved adherence around struts and angles
Deposition of pharmaceutical agents within the matrix of polymer and onto the coating
surface
Intentional design of continuous and/or pulsatile drug release
Ability to apply multi-laminate coatings targeting a specific time course release of
multiple active agents
Differential coating of the surfaces of the device to facilitate site specific therapy.
Using both biodegradable and biostable polymers Nanocopoeia has developed several unique
coating configurations, ranging from a smooth two dimensional coating, to a high surface area,
nanoparticle-based, “open matrix.” The ENS system produces highly consistent coatings, with
repeatability in terms of both in quality and in weight. In Figure 5, a run lot of stents coated with the
poly(lactide-co-ε-caprolactone) and dexamethasone is shown, where the coating weight had a
coefficient of variation less than 3 percent.
Lot Coating Weight Variation
Stent Coating Weight (g)
PLCL Open Matrix Coating
600
550
500
Mean ± SD
513.6 ± 12.9 g
CV = 2.5%
450
400
1
2
3
4
5
6
7
8
9
10
11
Stent Number
Figure 5. The ENS coating process is highly
reproducible. Lot run of coating weights in µg
on 12 mm, 316L stainless steel stents.
Coefficient of variation in coating weights was
2.5%. Coating comprised of poly(lactide-co-εcaprolactone) and dexamethasone in a 10:1 ratio
by weight.
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One aspect of the ENS process that differentiates it from traditional device coating methodologies
is that coatings can be engineered to tune the release profile of the drug. As mentioned above, the
ENS process produces monodisperse nanoscale particles of drugs and polymers. These particles
can be applied to surfaces in a range of morphologies (Fig. 6). In contrast, the other spray
techniques used to produce medical device coatings produce particles with diameters of 10-20 µm
or larger that result in solvent-polymer droplets that flow as they hit the surface to form a conformal
film. Nanocopoeia has found that varying the structure of the polymer impacts drug release
profiles.
A
B
C
TPE4 Smooth Film
TPE4 Hybrid (300 SF/100 OM)
TPE4 Open Matrix
35
Dexamethasone % Dose
30
A
25
20
B
15
C
10
OpenOpen
matrix
(C)
TPE4
Matrix
Composite
TPE4
Hybrid (B)
SF Inner, OM Outer
Closed
matrixFilm
(A)
TPE4
Smooth
5
0
0
5
10
15
Days
20
25
30
Figure 6. Engineering substrate morphology
to control drug release profiles. Different
coating architectures produce different release
profiles. Dexamethasone eluting
arbIBS
polymer (10% wt. vol) was sprayed under
varying conditions to generate a smooth, closed
matrix (A) a particulate, open matrix (C) and a
hybrid consisting of an open matrix base,
covered with a thin closed matrix topcoat (B). As
shown in the graph, release profiles are
determined by the polymer morphology. The
release profiles can be further altered by
controlling the diameter of the open matrix
particles.
Figure 6, shows three morphologies that were produced by varying conditions in the ENS process;
a smooth coating, similar to those found on cardiovascular stents (A), a hybrid coating consisting of
a particulate base material and smooth top coating (B) and a particulate, open matrix coating (C).
Our ability to design surface morphology at nanoscale dimensions is a significant advance that can
be exploited to generate active nanoscale coatings for tuning drug release profiles.
The ENS coating system is highly flexible in terms of therapeutic selection. Coatings have been
made using a variety of therapeutic agents, such as drugs (dexamethasone, rapamycin, paclitaxel,
gentamicin, etc.) peptides (insulin B chain, angiotensin I), intact proteins (albumin) and plasmid
DNA. Importantly, the proteins and nucleic acids spray without apparent disruption to their
structure and function. This supports the use of ENS in the development of the next generation of
therapeutic coatings, so called “biologics” materials.
Nanocopoeia is targeting commercial opportunities for medical device coatings in the areas of
intravascular products such as stents, catheters, and guidewires through a subsidiary business
called NanoInterventions. NanoInterventions has developed a small animal model for
development and testing of cardiovascular implant therapies. Nanocopoeia will provide fee-forservice coating designs and coated products to NanoInterventions as a contractor. In addition to
its service/pre-clinical testing business, NanoInterventions is developing a proprietary drug eluting
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stent product which it will carry through pre-clinical development and then seek a partnership with
a market leader to market the product.
Other medical device applications such as implantable orthopedic products, tissue implants, and
ophthalmology products will be commercialized via targeted partnerships with leading device
manufacturers in those areas.
Drug nanoformulation
Drug discovery and development is an enormously costly endeavor, with as much as $40 billion
invested annually in discovery alone. Novel chemical entities with potential therapeutic activity are
typically discovered in one of two ways. The first is by using a high throughput screening process
which matches compounds against a library of disease states to determine if a prospective
compound has a likelihood of activity against a particular disease or condition. The second is
through a computer based design algorithm that calculates the most likely chemical structure for a
successful therapeutic outcome. Many drug leads developed using these methods exhibit issues
with solubility and an inability to deliver the therapeutic agent in vivo. It is estimated that 40-50
percent of these new chemical entities are poorly water soluble. Poor water solubility hinders
further development, due to the challenges of evaluating efficacy in biologic models for a poorly
bioavailable compound. These compounds are typically shelved with no further development
activity even if they show promising therapeutic activity in cell culture.
Nanocopoeia has developed a method using our ENS process that consistently results in multiplefold improvements in water solubility, or more precisely, “nanoscale suspendability.” ENS is used
to create either bare drug nanoparticles or coated, core:shell nanoparticles in a single, “bottom up”
processing step rather than a multi-step “top down” process like wet milling or homogenization;
both are techniques used to break down larger, insoluble particles; requiring secondary processing
to create a monodisperse range of particle size. A further advantage of ENS produced drug
formulations is the ability to produce coated nanoparticles in that single processing step.
Nanocopoeia has optimized two techniques which can be employed to collect a dosage form of the
nanoformulated drug compounds. One is to spray the nanoparticles directly into a liquid and the
other is to collect them in dry form on a substrate for re-suspension in liquid at a later time. The
second method produces a convenient, dry, shelf stable format ideal for sterile delivery into
biological models. It also has resulted in significantly improved drug solubility (nanosuspendability).
An example of a nanoformulated drug immobilized on a stable substrate was shown previously in
Figure 4 where an insoluble drug, griseofulvin, was encapsulated with a standard pharmaceutical
coating polymer as the particles were generated by the electric field. Figure 7 shows an example of
how drug particles can be sheathed with polymeric surfactants and then layered onto a substrate
for future delivery.
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Coaxial Spray
Stream


Dissolvable
film
Model drug particle
Excipient (e.g.
polyvinylpyrolidone,
polysorbate 80, etc.)
Figure 7. Schematic illustrating how
ElectroNanospray™-generated particles can
be coated with various surfactant materials
and deposited in dry form onto a dissolvable
substrate for later resuspension. Typical
surfactants used include the polymer
polyvinylpyrolidone and polysorbate 80
(Tween 80®).
This approach has been used to enhance solubility for three poorly water soluble drugs:
griseofulvin, an antifungal; nifedipine, a calcium-channel blocker; and carbamazepine, an
anticonvulsant. All three are well-established drugs in clinical practice, but have very low to nondetectible solubility in water, making them ideal model compounds for development using the ENS
process.
Using the coaxial spray nozzle, a solution of each drug in the relevant solvent system (e.g. alcohol,
acetone, or tetrahydrofuran) was co-sprayed with solvent and various surfactant materials,
including those listed above. The substrate was a thin film of polyvinyl alcohol or stainless steel.
As a first step in the formulation process, the drug compound input for the ENS process is
dissolved into a solvent system compatible with the drug material. This solvent can be a traditional
solvent that would not be acceptable or usable in a biological system because the solvent flashes
off as a result of the production process leaving nanoparticles with no solvent component. When
the electric field causes the material stream to break into nanoparticles, each discrete particle has
an enormous surface area to volume characteristic. Because of this surface area, solvent
evaporation occurs rapidly, enabling the drug and surfactant materials to be deposited in dry form
onto the substrate. Concentration of drug in phosphate-buffered saline was measured in three
ways: in the “neat” suspension made when the dry film was placed into buffer, a filtrate of this
material was passed through a 1 µm pore size (1,000 nm) nylon filter, and a filtrate of this material
was passed through a 0.2 µm (200 nm nylon filter typically used for performing sterile filtration of
culture medium. Evaluation using two different measurement systems (of spray stream and in
liquid) yielded particle sizes of approximately 60 nm. Figure 8 shows the improvement in solubility
(suspendability) over the raw drug powder.
H2O solubility
Concentration, µg/ml
800
<200 nm
<1000 nm
674 692
700
640
unfiltered
600
500
420
415
413
400
340
270
300
200
100
125
8.64
17
0
Figure 8. ENS nanoformulations increase
aqueous solubility of drug compounds.
Water solubility for catalogue-sourced drug
powder versus nanoformulated drug
prepared using ENS process. Drug
concentration measured by routine HPLC
method. Concentration measured in “neat”
solution and after filtration through 1.0 µm
and 0.2 µm nylon filter. Figure at left for
each set lists measured solubility in buffer,
using the same method.
0
Griseofulvin
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Nifedipine
Carbamazepine
May 2008
This approach has proven to be robust, with similar results obtained for other single and
combination surfactant systems. The dissolvable film substrate is convenient, but not essential to
obtain the improvements.
Nanocopoeia is targeting commercial activity in drug discovery and development as a formulation
resource for industry and academic researchers. Nanocopoeia can work with those researchers to
create an efficient and effective way to leverage existing libraries of compounds with known
solubility issues but potentially great commercial potential. A particular advantage of the
ElectroNanospray process is the ability to work with very small quantities of expensive research
grade materials that the compounding pharmacists can make of these materials.
Summary
The ENS process is a highly robust system for creating complex nanoparticles in a single
processing step. The system provides exquisite control over particle size and particle composition.
Optimizing the process for each application enables the engineering of unique medical device
coatings and drug nanoformulations. Furthermore, the unique process development leverage that
occurs between the creation of medical device coatings and the formulation of drugs translated
through the spraying of particles, means that information learned in one field can be applied
directly as improvements to the other. This technology has the potential to accelerate the
translation of basic research findings in clinically relevant therapies.
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