Synthesis and characterization of environmentally benign, semifluorinated polymers and their applications in drug delivery

Article abstract of DOI:10.1016/j.jfluchem.2016.09.001

We describe the synthesis, physicochemical studies and pharmaceutical assessment of a class of pegylated semifluorinated amphiphilic block-copolymers based on short pendant fluorinated side chains attached to moderately hydrophobic units. These polymers allowed us to investigate how the balance between hydrophobicity and fluorophilicity in the polymer can be tuned to match that of small molecules to be used in drug delivery. Remarkably, we found that using short perfluoroethyl groups in the polymer allows the preferential stabilization of nanoemulsions based on isoflurane, a fluorinated anesthetic made partly hydrophobic by the presence of a chlorine atom. In comparison, nanoemulsions of sevoflurane, a purely fluorophilic anesthetic, were not as stable. The lipophilicity of the polymers was also investigated in regards to solvation of hydrophobic molecules. Surface properties such as critical micelle concentration (CMC) and surface tension demonstrated the uniqueness of these fluorinated amphiphiles. Finally, the use of short perfluoroethyl chains makes these polymers environmentally benign in terms of bioaccumulation and toxicity.

Full text of DOI:10.1016/j.jfluchem.2016.09.001

Journal of Fluorine Chemistry 190 (2016) 75–80
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis and characterization of environmentally benign,
semifluorinated polymers and their applications in drug delivery
Michelle C. Fleetwooda, Aaron M. McCoya, Sandro Mecozzia,b,
*
a
Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53705, United States
b
School of Pharmacy, Division of Pharmaceutical Sciences, University of Wisconsin-Madison, Madison, WI 53705, United States
A R T I C L E I N F O
A B S T R A C T
Article history:
We describe the synthesis, physicochemical studies and pharmaceutical assessment of a class of
pegylated semifluorinated amphiphilic block-copolymers based on short pendant fluorinated side chains
attached to moderately hydrophobic units. These polymers allowed us to investigate how the balance
between hydrophobicity and fluorophilicity in the polymer can be tuned to match that of small molecules
to be used in drug delivery. Remarkably, we found that using short perfluoroethyl groups in the polymer
allows the preferential stabilization of nanoemulsions based on isoflurane, a fluorinated anesthetic made
partly hydrophobic by the presence of a chlorine atom. In comparison, nanoemulsions of sevoflurane, a
purely fluorophilic anesthetic, were not as stable. The lipophilicity of the polymers was also investigated
in regards to solvation of hydrophobic molecules. Surface properties such as critical micelle
concentration (CMC) and surface tension demonstrated the uniqueness of these fluorinated amphiphiles.
Finally, the use of short perfluoroethyl chains makes these polymers environmentally benign in terms of
bioaccumulation and toxicity.
Received 3 August 2016
Received in revised form 31 August 2016
Accepted 2 September 2016
Available online 4 September 2016
Keywords:
Semifluorinated polymers
Drug delivery
Fluorous anesthetics
ã 2016 Elsevier B.V. All rights reserved.
1. Introduction
synthesized commercially by polymerization of fluorinated
oxetane monomers, using a Lewis acid catalyst and nucleophilic
Perfluorinated compounds are heavily utilized [1] in fire-
fighting applications, cosmetics, paints, lubricants and pharma-
ceutical formulations [2]. However, longer chain fluorocarbons
have been replaced for general use in the US with short-chain
perfluoroethers. This was done out of concern for bioaccumulation
and general toxicity [3]. Specifically, perfluorooctanoic acid (PFOA)
and perfluorooctanesulfonic acid (PFOS), which were used as
surfactants during the synthesis of perfluorinated polymers, have
received the most attention after their detection in places ranging
from remote areas in the Arctic to blood samples of the general U.S.
population [4,5]. Perfluorocarbon bioaccumulation and toxicity
tend to increase with longer chain length, with groups composed
of four perfluorinated carbons (perfluorobutyl) or less being
considered safe for humans [2–4].
initiator [5,6]. The most common fluorocarbon used is a
perfluoroethyl, a fluorous group significantly shorter than longer
fluorocarbons that have shown toxicity and bioaccumulation [6].
These issues have been shown to decrease with shortening of
fluorous molecules to six carbons or less [4,7]. The Polyfoxã line
has undergone all required environmental and health related
studies and has been granted full regulatory approval by The
United States EPA, allowing for the manufacture and sale of these
environmentally-benign products [8].
Pharmaceutical applications of perfluorocarbon derivatives are
based on the unique physicochemical properties of fluorous
compounds, including thermal and chemical stability, biological
inertness, high surface tension, and the ability of dissolving large
amounts of oxygen. Previous studies have shown that highly
fluorinated amphiphilic diblock copolymers can successfully be
used for emulsifying fluorous anesthetics in drug delivery
applications [9–11]. With the inclusion of perfluorooctyl bromide
(PFOB), an FDA-approved additive, these polymers were shown to
stably emulsify sevoflurane (Fig. 1) at concentrations up to 20–30%
v/v, a significant increase over the 3.5% v/v concentration of
sevoflurane that can be achieved with a classical hydrophobic
emulsion as Intralipid [11]. In contrast, the same polymers were
Short fluorocarbons are used in a variety of industrial materials.
For instance, the OMNOVA Polyfoxã line lists polymers in which
short perfluoroethers are used for the purpose of achieving optimal
properties in paints and coatings. The Polyfoxã surfactants are
* Corresponding author at: University of Wisconsin-Madison, 777 Highland Ave.,
Madison, 53705, United States.
E-mail address: sandro.mecozzi@wisc.edu (S. Mecozzi).
http://dx.doi.org/10.1016/j.jfluchem.2016.09.001
0022-1139/ã 2016 Elsevier B.V. All rights reserved.

76
M.C. Fleetwood et al. / Journal of Fluorine Chemistry 190 (2016) 75–80
2. Results and discussion
CF3
Cl
F
2.1. Polymer synthesis
F3C
O
F
F3C
O
F
The synthesis of these block co-polymers was adapted from
patents [14,15] and earlier work done in our group [16] (Scheme 1).
In glacial acetic acid, the triol, 1,1,1-tris(hydroxymethyl)ethane (1),
was treated with sulfuric acid and sodium bromide to generate
hydrogen bromide in situ to give the dibrominated product, 3-
bromo-2-bromomethyl-2-methylpropyl acetate (2), as the major
substitution product. Under biphasic conditions, the acetate was
cleaved with sodium hydroxide allowing for in situ cyclization to
give 3-(bromomethyl)-3-methyloxetane (3). This was then
functionalized with 1H,1H-pentafluoropropan-1-ol. This reaction
was found to work best under phase transfer conditions. Both
oxetane monomers (3 and 4) were purified by distillation, but
yields were lower than expected due to the high volatility of these
molecules. Pegylation was achieved by using the terminal alcohol
of methoxy polyethylene glycol (mPEG) as a macroinitiator in the
presence of boron trifluoride diethyl etherate to carry out a ring-
opening polymerization of the fluorous oxetane. Two methoxy
polyethylene glycol lengths of 1000 and 5000 g/mol were used to
make different diblock copolymers and explore their ability at
emulsifying and encapsulating lipophilic and fluorophilic mole-
cules.
Fig. 1. Chemical structures of sevoflurane and isoflurane.
not able to stabilize properly emulsions of isoflurane (Fig. 1), likely
due to the increased lipophilicity of this compound as opposed to
sevoflurane. Due to a chloride substitution for one trifluoromethyl
group, isoflurane has a lower fluorine content than sevoflurane
(51% w/w vs. 67% w/w), making the molecule more lipophilic. To
date, the best formulations to emulsify isoflurane are based on
classical surfactants and provide a concentration of anesthetic
between 8 [12] and 15% v/v [13]. We reasoned that in order to
stably emulsify this anesthetic, a surfactant must include a balance
between fluorophilicity and lipophilicity that would be close or
match that of isoflurane. The new diblock copolymer described
below is composed of a very short hydrophobic backbone to which
a pendant perfluoroethyl is attached, similarly to the composition
of some of the OMNOVA Polyfoxã polymers. Pegylation of this
small oligomer leads to the formation of an amphiphilic polymer,
which is highly water-soluble and can be used to efficiently
emulsify isoflurane when using a specific size of the hydrophobic/
fluorophilic perfluoroether moiety.
Resulting polymers were purified by an automated
CombiFlash1 system. Polymerization yielded products with 3–
10 oxetane monomers added. Four different fractions, composed of
a mixture of perfluoroether telomers added were isolated. The
Scheme 1. Synthesis of Mx(F2Ox)y. Note on nomenclature: M corresponds to mPEG, with the following number being the average molecular weight. (F2Ox) indicates the
opened oxetane monomer with a perfluoroethyl side chain.

M.C. Fleetwood et al. / Journal of Fluorine Chemistry 190 (2016) 75–80
77
mPEG-1000 polymers contain a 3–4 and 4–5 unit fractions, while
1500
1000
500
0
M5(F2Ox)3 iso
M5(F2Ox)4 iso
M5(F2Ox)7 sevo
M5(F2Ox)3 sevo
the mPEG-5000 contains fractions composing of 3–5 and 7–9 units
added. This polydispersity agrees with similar behavior reported in
the literature [17,18].
2.2. Physicochemical characterization
Dynamic light scattering (DLS) was applied to measure the
average size of the amphiphilic aggregates in solution. The particle
size data are summarized in Table 1. As expected, as the length of
hydrophobic chain increases, so does the aggregate size. The
polymer sizes are consistent with known micelle-forming
fluorocarbon polymers according to PEG size [9]. Note that
cryogenic transmission electron microscopy (cryo-TEM) is com-
monly used to validate the aggregate shape. However, these
amphiphiles contain a relatively small hydrophobic core compared
to a large mPEG chain, which is highly solvated and indistinguish-
able from vitrified water [19].
The critical micelle concentrations (CMC) of these polymers
were estimated by measuring the surface tension of polymer
solutions at various concentrations. Increasing the concentration
of the polymer under the CMC leads to a linear decrease in the
surface tension. At the CMC, micelle formation begins and any
additional surfactant will aggregate and not affect the surface
tension any longer. It has been shown that substitution of fluorine
atoms for hydrogen decreases an amphiphile’s surface activity for
aqueous solutions, which promotes micellization at lower con-
centrations [20]. The CMC was unaffected by the length of
hydrophilic segment (PEG), but had a slight increase as more
hydrophobic monomers were added.
0
100
200
300
400
Time (day)
Fig. 2. Change in particle sizes of fluoropolymer-based emulsions with time:
(green) M5(F2Ox)7 with sevoflurane; (purple) M5(F2Ox)3 with sevoflurane; (blue)
M5(F2Ox)3 with isoflurane, (red) M5(F2Ox)4 with isoflurane. All emulsions
contained 20% of respective fluorous anesthetic and 10% perfluorooctyl bromide
(a stabilizing additive) [8,9] and were prepared in saline (0.9% w/w NaCl). Note
standard error bars are removed for clarity. They are available in the Supporting
information. (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
hydrophobic monomers led to a significant difference in stability
between sevoflurane and isoflurane emulsions, the latter being
remarkably more stable. The main mechanism of destabilization of
fluorocarbon-based emulsions is molecular diffusion, better
known as Ostwald ripening [21]. In this mechanism, individual
molecules of fluorous anesthetic diffuse out of smaller particles,
due to the higher curvature of these particles and therefore higher
chemical potential, to join larger growing droplets. The rate of
increase of the droplets’ volume over time is a linear function of the
interfacial tension, the solubility and diffusion of the dispersed
perfluorocarbon in the aqueous phase, and the particle radius [21].
Plotting particle size vs. time gives a fair representation of
emulsion stability. For practical use, IV injectable emulsions must
maintain a mean diameter ꢀ500 nm within an 11-month period
when stored at 5 ꢁC [10].
Fig. 2 shows the ripening behavior with time of emulsions of
sevoflurane and isoflurane made with the polymer containing
either 3, 4, or 7 units of the perfluoroether telomer. While the
sevoflurane emulsion showed a quick increase in particle size and
eventual phase-separation, isoflurane led to a much more stable
formulation containing 20% v/v of anesthetic, with particle size
staying around 400 nm for over a year. Polymers with longer
fractions of polyoxetane were poorly water-soluble and thus
unable to make sevoflurane or isoflurane emulsions.
The variation of particle size between the emulsions of polymer
M5(F2Ox)3 can be explained when considering the chemical
structure of both polymer and fluorous anesthetic. Sevoflurane has
a greater fluorine content than isoflurane and will be solubilized
better by a fully fluorophilic chain. The hydrophobic chain used in
these polymers contains a short perfluoroethyl group, as well as a
polyether backbone, giving the polymer both lipophilic and
fluorophilic properties. Therefore, we ascribe the difference in
stability between the two emulsions to a better match between the
hydrophobicity/fluorophilicity balance of the polymer with that of
isoflurane.
To evaluate the lipophilicity of the aggregate’s core, attempts at
solubilizing a lipophilic molecule were undertaken. We used the
anticancer agent paclitaxel as a model lipophilic small molecule.
We found that the presence of short fluorocarbons in the micelle
core prevents the binding and encapsulation of purely hydropho-
bic molecules. This result suggests that the micellar core is not
adequately lipophilic for drug encapsulation, which makes sense,
as there are pendant fluorous chains throughout which repel
molecules that are not fluorophilic.
2.3. Emulsion stability
The results on the poor loading of lipophilic molecules within
the micellar core suggest that the polyoxetane block is more
fluorophilic than lipophilic. To test this conclusion, the emulsifi-
cation of fluorinated anesthetics was studied, specifically looking
at possible differences between the fluorophilic sevoflurane and
the more lipophilic isoflurane (Fig. 2). Previous studies have shown
that PEG-based copolymers with a fluorocarbon core can form
stable emulsions with sevoflurane. The polymers used in those
studies typically contained a purely fluorophilic fluorocarbon
chain with more than eight carbon atoms [9,10]. In contrast, use of
polymers with perfluoroethyl groups attached as side chains of
Table 1
The particle size data.
Particle Size (nm)a
pCMC (Àlog (M) Æ SD)b
3. Conclusions
Polymer
M1(F2Ox)3–4
M1(F2Ox)4–5
M5(F2Ox)3–5
M5(F2Ox)7–9
4.35 Æ 1.00
5.014 Æ 0.03
4.770 Æ 0.03
4.995 Æ 0.08
N/A
In summary, we have synthesized amphiphilic diblock copoly-
mers where a methoxy-PEG is attached to a short block with a
hydrophobic backbone and perfluoroethyl side chains. The size of
the hydrophobic/fluorophilic moiety affected surface properties
such as critical micelle concentration, hydrophobic drug encapsu-
lation and nanoemulsion stability. It was found that the short
15.74 Æ 0.631
4.51 Æ 0.753
15.61 Æ 0.322
a
Particle sizes of fluoropolymer-based aggregates. Data are given with the
standard deviation (n = 3). Each measurement was repeated three times.
b
Critical micelle concentration determined by surface tension. Each measure-
ment repeated four times. CMC of M5(F2OX)7–9 was not determined due to
insufficient yields of this polymer fraction.
pendant perfluoroethyl side chain induced
a balance of

78
M.C. Fleetwood et al. / Journal of Fluorine Chemistry 190 (2016) 75–80
hydrophobicity and fluorophilicity optimal for emulsification of
isoflurane. In contrast, the more fluorophilic sevoflurane formed
unstable emulsions and the encapsulation of purely hydrophobic
molecules was not possible at therapeutic concentrations, con-
firming the mixed lipophilic/fluorophilic environment provided by
the perfluoro telomer block.
3 M sodium hydroxide (100 mL). Tetrabutylammonium bromide
(1.32 g, 4.09 mmol) was added and reaction stirred vigorously
under argon and heated to reflux. After 24 h, reaction was stopped
and layers were separated. Dichloromethane was gently removed
under reduced pressure. Oil was purified by vacuum distillation,
collecting fraction at 50 ꢁC to give 5.07 g (43.9%).1H NMR (400 MHz,
Highly concentrated, 20% v/v emulsions of isoflurane were
possible with the polymer containing up to three or four units of
perfluoroether telomer. The emulsions were found to be stable
over a period of 12 months.
CDCl3): d 4.38 (d, J = 6.4 Hz, 2H), 4.33 (d, J = 6.4 Hz, 2 H), 3.59 (s, 2 H),
1.37 (s, 3 H). 13C NMR (100 MHz, CDCl3):
22.62.
d 80.74, 41.63 (2C), 40.79,
These results indicate that fluorophilic behavior can be induced
using short, perfluoroethyl groups. Potential metabolism products
of such short fluorocarbons do not bioaccumulate [3,4] and
therefore toxicity considerations will not be a limiting factor for
their application.
4.5. Synthesis of 3-(1H,1H-perfluoropropan-1-oxymethyl)-3-
methyloxetane (4)
3-(Bromomethyl)-3-methyloxetane (5.07 g, 30.76 mmol), pen-
tafluoropropan-1-ol (4.73 g, 31.49 mmol), tetrabutylammonium
bromide (246.3 mg, 0.764 mmol) and water (4.5 mL) were added to
a 100 mL round-bottom flask with stir bar, flask flushed with argon
and heated to 95 ꢁC. Potassium hydroxide (4.36 g, 40% solution in
water) was added over 10 min to the stirring reaction at 95 ꢁC.
Reaction was left overnight under argon. Mixture was then allowed
to cool to room temperature and dichloromethane (12 mL) was
added and layers separated. The aqueous layer was extracted with
dichloromethane (20 mL). Combined organic layers were dried
over anhydrous magnesium sulfate and the solvent gently
removed by rotary evaporation. The remaining oil was purified
by vacuum distillation, collection fractions at 20 ꢁC to yield 1.05 g
4. Experimental
4.1. Materials
Paclitaxel was purchased from LC Laboratories. Isoflurane was
purchased from Piramel Healthcare. Sevoflurane was purchased
from Abbott Labs and normal saline (AirLife sterile 0.9% NaCl for
irrigation USP) from Braun Medical Inc. Fluorous alcohols and
perfluorooctyl bromide were purchased from SynQuest. All other
reagents and solvents were of ACS grade or higher, were purchased
from Sigma-Aldrich, and were used as received, unless otherwise
specified.
(57% yield). 1H NMR (400 MHz, CDCl3):
d 4.49 (d, J = 6 Hz, 2 H), 4.37
(d, J = 6 Hz, 2 H), 3.96 (tq, J = 12, 1.2 Hz, 2 H), 3.69 (s, 2 H) 1.32 (s, 3 H).
13C NMR (100 MHz, CDCl3): 79.83, 78.32, 68.24 (t, J = 26.8 Hz),
40.15, 21.11. Carbons containing F’s were not visible with the used
acquisition scans. 19F NMR (376 MHz, CDCl3): À84.01 (s, 3F),
À123.59 (t, J = 12.4 Hz, 2F).
4.2. Instrumentation and methods
1H, 13C and 19F NMR experiments were conducted on a Varian
UNITY INOVA-400 NMR spectrometer at 25 ꢁC using deuterochloro-
form (CDCl3) as the solvent with TMS as an internal reference.
Surfactants were purified by automated flash chromatography
using a CombiFlash1 Rf 4x system equipped with ELSD for
compound visualization and a REDI-Sep Rf Gold C-18 silica high-
performance aqueous reverse phase cartridge. Products were
eluted with a 10–100% methanol in water (0.1% formic acid)
gradient.
4.6. Synthesis of M1(F2Ox)n (5-1)
Monomethoxy polyethylene glycol (430 mg, average molecular
weight = 880 g/mol) was dissolved in 7 mL anhydrous dichloro-
methane. Boron trifluoride–diethyl ether complex (75 mL) was
added under argon and the mixture was allowed to stir for 30 min.
Solution was then cooled in and ice bath and fluorous oxetane 4
(1.00 g) dissolved in dichloromethane was added drop wise over
the course of 30 min. The reaction was stirred under argon
overnight and brought to room temperature. Reaction was then
quenched with water and diluted with water (5 mL) and brine
(5 mL) to break up emulsion. Layers were separated and the
aqueous layer was extracted with dichloromethane (2 Â 5 mL).
Organic layers were combined and dried over anhydrous magne-
sium sulfate and filtered. The solvent was removed under low
pressure and the residue was purified by reverse-phase flash
chromatography to yield 563 mg (64% yield). 1H NMR (400 MHz,
4.3. Synthesis of 3-bromo-2-bromomethyl-2-methylpropyl acetate (2)
1,1,1-Tris(hydroxymethyl)ethane (TME) (25.58 g, 212.9 mmol)
was weighed into a 500 mL round bottom flask and glacial acetic
acid (100 mL) was added, stirring vigorously for 2 h to partially
dissolve TME. Sodium bromide (65.75 g, 638.97 mmol) was added
and reaction fitted with addition funnel and flushed with argon.
Sulfuric acid (25 mL, 511 mmol) was added drop wise over 1 h, and
the flask fitted with condenser and heated to 110 ꢁC. After 7 days,
heat was turned off and reaction came to room temperature. The
reaction was then diluted with 250 mL water and layers separated.
Organic layer was washed with water (100 mL), 0.5 M sodium
hydroxide (2 Â 200 mL), and brine (200 mL). The reaction was then
dried over anhydrous magnesium sulfate and filtered. Crude oil
was purified by flash column, packing with hexane and eluting
with 5% ethyl acetate/hexane to collect first product only. Oil was
isolated by rotary evaporation to give 58.42 g (95% yield). 1H NMR
CDCl3):
3.37 (m, 11 H), 3.18 (m, 50 H), 0.90 (m, 46 H). 19F NMR (376 MHz,
CDCl3):
À84.07 (m, 3F), À123.84 (m, 2F).
d 3.84 (t, J = 12.8 Hz, 34 H), 3.65 (m, 80 H), 3.43 (m, 20 H),
d
4.7. Synthesis of M5(F2Ox)n (5-2)
Monomethoxy polyethylene glycol (2.24 g, average molecular
weight = 4200 g/mol) was dissolved in 7 mL anhydrous dichloro-
(400 MHz, CDCl3):
d
4.06 (s, 2H), 3.45 (dd, J = 12.8,10.4 Hz, 4H), 2.08
methane. Boron trifluoride–diethyl ether complex (55 mL) was
(s, 3H), 1.17 (s, 3H). 13C NMR (100 MHz, CDCl3):
38.5, 34.7, 31.8, 25.5, 22.9, 21.0, 20.4, 14.3.
d
170.6, 67.3, 39.2,
added under argon and the mixture was allowed to stir for 30 min.
Solution was then cooled in and ice bath and fluorous oxetane 4
(1.05 g) in dichloromethane solution was added drop wise over the
course of 30 min. The reaction was stirred under argon overnight
and brought to room temperature. Reaction was then quenched
with water, diluted with water (5 mL) and brine (5 mL) to break up
emulsion. Layers were separated and the aqueous layer was
4.4. Synthesis of 3-(bromomethyl)-3-methyloxetane (3)
3-Bromo-2-bromomethyl-2-methylpropyl acetate (20.13 g,
69.92 mmol) was dissolved in dichloromethane (100 mL) and

M.C. Fleetwood et al. / Journal of Fluorine Chemistry 190 (2016) 75–80
79
extracted with dichloromethane (2 Â 5 mL). Organic layers were
combined and dried over anhydrous magnesium sulfate and
filtered. The solvent was removed under low pressure. Polymer
was purified by reverse-phase flash chromatography to yield
Solutions were then allowed to equilibrate for 24 h. Surface
tensions were measured on a KSV sigma 701 tensiometer (KSV
Instruments, Helsinki, Finland) equipped with a Julabo F12-MC
circulator for constant temperature control. Custom round rod
made of platinum with a diameter of 1.034 nm with wetted length
of 3.248 mm was used. First, the rod was submerged into absolute
alcohol and flame dried with a Bunsen burner for 4 s, then repeated
after 4 min and hung on instrument and allowed to cool to room
temperature without touching any surface. Before running the
experimental samples, the surface tension of Millipore water was
measured as control to confirm vial and rod were fully cleaned and
surface tension was within 1 of 78.2 mN/m. The surface tension
measurements began with the least concentrated solution and
proceed to successively more concentrated solutions. The surface
tension at each concentration was measured in quadruplet and
average recorded. The critical micelle concentration value was
determined from crossover point of two lines: the baseline of
minimal surface tension and the slope where surface tension
showed linear decline; error determined by weighted least squares
analysis .
1.408 g (55% yield). 1H NMR (400 MHz, CDCl3):
d 3.84 (t, J = 12.8 Hz,
79 H), 3.65 (m, 480 H), 3.43 (m, 41 H), 3.37 (m, 30 H), 3.18 (m,
124 H), 0.90 (m, 108 H). 19F NMR (376 MHz, CDCl3):
3F), À123.84 (m, 2F).
d
À84.07 (m,
4.8. Micelle preparation—solvent evaporation method (SEM)
Polymer is dissolved in methanol or acetonitrile to a desired
concentration. Polymer solution and additive (e.g., paclitaxel in
acetonitrile) are added to a 25 mL round bottom flask and rotated
for 5 min at 60 ꢁC on a rotary evaporator, no vacuum, and then the
solvent was removed in vacuo with rotation for 15 min. The film
was then dispersed with Millipore water heated to 60 ꢁC and
filtered with a 0.45-mm nylon filter.
4.9. Preparation of fluorous anesthetic nanoemulsions
Polymer solution in normal saline solution (10 mM, 11.9 mL)
was prepared freshly. Normal saline was made with 0.9% (w/w) of
sodium chloride.
Acknowledgments
We thank the University of Wisconsin-Madison, the Robert
Draper Technology Innovation Fund, and the Center for Nano-
medicine in the School of Pharmacy at the University of Wisconsin-
Madison for generous funding. The authors would like to thank Dr.
Glen Kwon for instrumentation use and thoughtful discussions.
Sevoflurane or isoflurane (3.4 mL) and perfluorooctyl bromide
(1.7 mL) were added to the polymer solution, for a total volume of
17 mL. The homogenizer and microfluidizer were previously
cleaned with 70% and 100% ethanol, followed by 70% and 100%
methanol, and finally with three rinses of Millipore water to
remove any solvents from previous washes. Once prepared the
mixture is then homogenized with the high-speed homogenizer
(Power Gen 500, Fisher Scientific, Hampton, NH) for 1 min at
21000 rpm at room temperature. The crude emulsion made with
the high speed homogenizer was further homogenized with a
Microfludizer (model 110 S, Microfluidics Corp., Newton, MA) for
1 min under 5000 psi with the cooling bath kept at 15 ꢁC. The final
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the
online
version,
at
http://dx.doi.org/10.1016/j.
jfluchem.2016.09.001.
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in plastic centrifuge tubes (Corning Inc., Corning, NY) at 4 ꢁC.
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