CONTROLLED RELEASE OF TRIAMCINOLONE ACETONIDE
FROM POLYURETHANE IMPLANTABLE DEVICES:
APPLICATION FOR INHIBITION OF INFLAMMATORYANGIOGENESIS
Adriana F. Pereira1, Flávia C. H. Pinto1, Armando Silva-Cunha Junior2, Rodrigo L.
Oréfice3, Eliane Ayres4, Sandra A. L. Moura5, Gisele R. Da Silva1
1
School of Pharmacy, Federal University of São João Del Rei, Divinópolis (MG), Brazil
School of Pharmacy, Federal University of Minas Gerais, Belo Horizonte (MG), Brazil
3
Department of Metallurgical and Materials Engineering, Federal University of Minas Gerais, Belo
Horizonte (MG), Brazil
4
Department of Materials, Technologies and Processes, Minas Gerais State University, Belo Horizonte
(MG), Brazil
5
Center of Research in Biological Sciences, Federal University of Ouro Preto (MG), Brazil
2
E-mail: giselersilva@ufsj.edu.br
The treatment of inflammatory pathologies usually requires repeated administration of conventional
pharmaceutical dosage forms, reducing patient compliance. The development of drug delivery systems
may overcome the drawbacks of the conventional therapy. In this study, implants based on polyurethane
(PU) for local controlled delivery of triamcinolone acetonide (TA) were developed (TA PU implants). The
TA PU implants were characterized by FTIR, SAXS and WAXS. The in vitro and in vivo release of TA
from the PU implants was evaluated. Finally, the efficacy of TA PU implants in suppressing
inflammatory-angiogenesis in a murine sponge model was demonstrated. FTIR results revealed no
chemical interactions between polymer and drug. SAXS results indicated that the incorporation of the
drug did not disturb the polymer morphology. WAXS showed that the crystalline nature of the TA was
preserved after incorporation into the polyurethane matrix. The PU implants controlled TA release. The
TA released from the PU implants efficiently inhibited the inflammatory-angiogenesis induced by sponge
discs in an experimental animal model. TA PU implants could be used as drug delivery systems for the
treatment of inflammatory-angiogenesis diseases because of their local controlled delivery of TA.
Keywords: Waterborne polyurethane dispersion, Local drug delivery system, Implants,
Inflammatory-angiogenesis diseases.
1.
INTRODUCTION
Segmented polyurethane elastomers have been extensively investigated in
different biomedical applications, since they can be biocompatible, biodegradable, and
can also display high mechanical properties [Jiang, 2007; Zhang, 2007]. In the field of
tissue engineering, polyurethanes have been used as biomaterials for scaffold
fabrication. These scaffolds based on polyurethanes serve as a matrix for the cells to
attach, to proliferate and to form a functional tissue that can be implanted into the
patient.5 Accordingly, polyurethane scaffolds have been used for generation of various
tissue constructs, such as nerve conduits [Hausner, 2007; Tongkui, 2009], vascular
grafts [Williamson, 2006; Zhang 2008], and cartilage [Bonakdar, 2010].
Another interesting biomedical application for biodegradable polyurethanes is
related to the use of this type of material to control the release of drugs. Polymers can be
loaded with the therapeutic agent and then implanted in specific organs. They would
provide transport and controlled release of a therapeutic agent at the target site to treat
or prevent different types of diseases [Da Silva, 2009]. Moreover, polyurethane-based
systems can lead to a prolonged and controlled release of antimicrobial drugs
[Francolini, 2010; Huynh, 2010], for antiseptic activity. Polyurethane intravaginal rings
were produced to favor sustained release of antiretroviral agents to prevent the male-tofemale sexual transmission of HIV [Johnson, 2010]. Additionally, polyurethane
nanocomposite implants were designed to control the corticosteroid release for the
treatment of posterior segment ocular diseases [Da Silva, 2011]. The majority of the
polyurethane-based delivery systems has been prepared by simple incorporation of the
drug into the polymeric matrices and processing them into the desired morphology.
Therefore, the drug remains physically entrapped in the polymer, but it is not anchored
through chemical bonds. However, drugs have been also covalently incorporated into
polyurethane foams, and they were released together with biomaterial degradation
[Sivak, 2009].
In this work, waterborne polyurethane dispersion derived from
poly(caprolactone), as soft segments, and isophorone diisocyanate and hydrazine, as
hard segments were synthesized. Additionally, triamcinolone acetonide, a potent antiinflammatory drug, was dispersed into polyurethane prior to casting the films to yield
triamcinolone acetonide-loaded polyurethane implants (TA PU implants). This drug
delivery system was characterized by attenuated total reflectance-Fourier transform
infrared, wide angle and small angle X-ray scattering in order to determine how the
drug can interact with the polymer and affects its morphology. The analyzed structure of
the biomaterial was also useful in understanding the in vitro and in vivo release of TA
from the polyurethane. Finally, the efficacy of the TA-loaded polyurethane implants
was demonstrated by inhibition of inflammatory angiogenesis in a murine sponge
model. In summary, it was hypothesized that the obtained polyurethane implants may
be useful as sustained/controlled delivery systems of TA for the treatment of chronic
inflammatory pathologies.
2.
MATERIALS AND METHODS
2.1
Synthesis of the aqueous polyurethane dispersion
Aqueous polyurethane dispersion (PU) was prepared by a prepolymer mixing
process, using a 250 mL three-neck glass flask equipped with a heating mantel, a
mechanical stirrer and a thermometer. The macrodiol components of polycaprolactonediol (PCL 1000) (Tone Polyol 2221, M n = 1000 g.mol-1) and polycaprolactone-diol
(PCL 2000) (Tone Polyol 0249, M n = 2000 g.mol-1) (Dow -USA) (Sigma-Aldrich),
isophorone diisocyanate (IPDI) (Bayer – Brazil) (NCO/OH ratio of 2.3) and 2, 2bis(hydroxymethyl) propionic acid (DMPA) (98.3%, Fluka) were added to the reactor in
the presence of dibutyl tin dilaurate (DBDLT) (Miracema Nuodex – Brazil) and the
reaction was carried out at 70-75ºC within a nitrogen atmosphere for 4 h. The amount of
free NCO groups on a percentage basis was determined by the standard di-butyl amine
back titration method. After titration, the prepolymer temperature was allowed to drop
to 40 ºC. The carboxylic acid groups were neutralized by the addition of triethylamine
(TEA) (98%, Vetec - Brazil). The mixture was stirred for another 40 min to ensure that
the reaction had been completed. All samples were dispersed by adding deionized water
to the neutralized prepolymer which was stirred vigorously. After the dispersion, the
amount of hydrazine (HZ) (solution 64%, Arch Química - Brazil) enough to react with
free NCO groups was added to the reactor with a small amount of water, and stirring
was continued for another 30 min. This chemical procedure was successful in producing
a polyurethane dispersion with a solid content of about 25%. The composition of the
polyurethane dispersion is shown in Table 1. Films were produced by casting the
dispersion in a Teflon mould and allowing them to dry at room temperature for one
week. Afterwards the films were placed in an oven at 60 ºC for 24 h [Ayres, 2007].
2.2
Incorporation of the drug and preparation of the TA-loaded polyurethane
implants (TA PU implants)
Triamcinolone acetonide (TA) (Sigma-Aldrich, 99.0%) was incorporated into
the polymer by dispersing it in the aqueous polyurethane dispersion prior to casting the
films to yield materials having 20.5wt% of the drug. The dried films were cut into
squares (5 mm in side) in order to obtain the TA-loaded polyurethane implants (TA PU
implants).
2.3
Characterization
Infrared spectra were collected in a Fourier transform infrared
spectrophotometer (FTIR; Perkin Elmer, model Spectrum 1000). Measurements were
carried out using the attenuated total reflectance (ATR) technique. Each spectrum was a
result of 32 scans with a resolution of 4 cm-1.
The measurements of Synchrotron Small Angle X-ray Scattering (SAXS) were
performed using the beam line of the National Synchrotron Light Laboratory (LNLS,
Campinas, Brazil). The photon beam used in the LNLS SAXS beamline comes from
one of the 12 bending magnets of the electron storage ring. The white photon beam is
extracted from the ring through a high-vacuum path. After passing through a thin
beryllium window, the beam is monochromatized (λ = 1.608 Å) and horizontally
focused by a cylindrically bent and asymmetrically cut silicon single crystal. The focus
is located at the detection plane. The X-ray scattering intensity, I(q), was experimentally
determined as a function of the scattering vector “q” whose modulus is given by
q=(4/)sin(θ), where λ is the X-ray wavelength and θ being half the scattering angle.
Each SAXS pattern corresponds to a data collection time of 900s. From the
experimental scattering intensity produced by all the studied samples, the parasitic
scattering intensity produced by the collimating slits was subtracted. All SAXS patterns
were corrected for the non-constant sensitivity of the PSD, for the time varying intensity
of the direct synchrotron beam and for differences in sample thickness. Because of the
normalization procedure, the SAXS intensity was determined for all samples in the
same arbitrary units so that they can be directly compared.
Wide angle x-ray scattering (WAXS) was performed by using a synchrotron
light beam with a wavelength of 1.608Å and an exposition time of 300 s. The scattering
intensity was recorded by a Pilatus (100K, 33mm X 84mm) detector. The sample to
detector distance used was 80mm.
2.4
In vitro release of TA from the PU implants
The in vitro release of TA was carried out under sink conditions during 8
months. As the aqueous solubility of TA is 21.0 gmL at 28oC [Block, 1973], sink
conditions were achieved with at least 181 mL for the evaluated polymeric implants.
The TA PU implants were placed in different erlenmeyers containing 181 mL of
phosphate buffer solution (PBS pH = 7.4) (n = 5). These erlenmeyers were placed inside
an incubator set at 37oC and 30 rpm. At predetermined intervals, 181 mL of the PBS
was sampled and the same volume of fresh PBS was added to each tube. The amount of
TA released from each PU implant was assayed by HPLC method, and expressed as the
cumulative percentage of TA released in the medium. The average of the obtained
measurements was calculated and used to plot the release profile curve.
2.5
In vivo release of TA from the PU implants
The animals were anesthetized with a mixture of (10 mg kg–1) xylazine and (100
mg kg–1) ketamine hydrochloride (i.p.). Their dorsal hair was shaved and the skin wiped
with 70% ethanol. TA PU implants were aseptically inserted into a subcutaneous pouch
that had been made with curved artery forceps through a 1cm long dorsal mid-line
incision. After the implantation procedure, the animals were maintained in individual
cages and provided with chow pellets and water ad libitum. The light/dark cycle was
12:12 h with lights on at 7:00 am and lights off at 7:00 pm. Post-operatively, the
animals were monitored for any signs of infection at the operative site, or upon
discomfort or distress; any mice presenting such signs were immediately sacrificed.
At 7, 15, 30 and 45 days post-implantation, animals (n = 5 for each time) were
euthanized and the TA PU implants were carefully removed from the subcutaneous
pouch of the mice. The TA PU implants were fragmented using a scissor and the pieces
were dissolved in 50 mL of a mixture of acetonitrile and ultra filtrated water (1:1). The
content of TA remaining in the PU implants was measured by the HPLC method [Da
Silva, 2012].
2.6
Preparation of the sponge discs, implantation and treatment
Non-biocompatible sponge discs of 5 mm in thickness, 8 mm in diameter and
approximately 4.6 mg in weight (Vitaform Ltd, Manchester, UK) were used as the
matrix for fibrovascular tissue growth. The sponge discs were soaked overnight in a
70% (V/V) ethanol solution and sterilized by boiling in distilled water for 15 min before
the implantation surgery.
The same implantation procedure described above was carried out in order to
insert the sponge discs incorporated into TA PU implants (treated group) and sponge
discs without the TA PU implants (untreated group). At 7 days post-implantation, mice
(n = 6 for each group) were anesthetized and sacrificed by cervical dislocation and the
sponge discs were carefully removed, dissected free from the adherent tissue, weighed
and fixed in formalin (10% in isotonic saline), embedded in paraffin, and 5 µm-thick
sections were obtained. The sections were stained with hematoxylin and eosin and
examined under a light microscope. The images were digitized through a JVC TK1270/JGB microcamera.
3.
RESULTS AND DISCUSSION
3.1
Characterization
Figure 1 shows infrared spectra of the pure polyurethane (PU, Figure 1.a),
polyurethane containing triamcinolone acetonide (TA PU implant, Figure 1.b) and pure
triamcinolone acetonide (TA, Figure 1.c). A typical infrared absorption bands observed
in TA can be detected in spectra of Figure 1.b and 1.c at 3392 cm-1, that can be
associated with the stretching vibration of hydrogen bonded hydroxyl, and at ~1726 cm1
, corresponding to stretching vibration of the carbonyl group at aliphatic ester bonds.
Other observed infrared absorption bands that are typical of TA are: ~1122 cm-1 –
asymmetric axial deformation of C- O-C bond in aliphatic esters and ~1055 cm-1 –
stretching vibration of C-F. The FTIR results obtained for pure TA were similar to those
previously acquired [Araújo, 2010]. The characteristic infrared absorption bands
observed in polyurethanes can be detected in spectra of Figure 1.a at 3336 cm-1, that can
be associated with the stretching vibration of hydrogen bonded amines, indicating that
isocyanate groups of the isophorone diisocyanate reacted with the hydroxyl and amino
groups forming urethane and urea linkages. Other observed infrared absorption bands
that are characteristic of polyurethane are: ~1722-1600 cm-1 – stretching vibration of the
free carbonyl group of ester groups in poly(caprolactone), urethane and urea bonds, and
hydrogen bonded carbonyl in urethane, indicating the synthesis of the polyurethane;
~2800-3000 cm-1 – stretching vibration of the –CH2 group. An absorption band around
2270 cm-1 was not observed in spectra, which indicated the absence of unreacted NCO
groups [Pereira, 2010]. If this type of chemical group were present, the occurrence of
side reactions which leads to the formation of allophanate or biuret linkages would be
possible [Thomas, 2008]. The absorption bands of the pure polymer can also be
observed in the spectrum of the polyurethane containing TA (Figure 1.b). The presence
of unchanged absorption bands related to PU and TA in the spectra of the produced
materials indicates that the incorporation process preserved the original chemical
structure of the main components (no pronounced chemical interactions between PU
and TA), being TA only partially dissolved in the polymeric matrix.
Figure 1. FTIR spectra of pure polyurethane (PU) (a), polyurethane containing
triamcinolone acetonide (TA PU implants) (b) and triamcinolone acetonide (TA) (c).
Figure 2 shows Small Angle X-ray Scattering (SAXS) data for pure
polyurethane, pure triamcinolone acetonide and polyurethane-loaded triamcinolone
acetonide system. In curve (a) (Figure 2.a) associated with the pure PU, a small and
broad scattering peak can be seen at q close to 0.7 nm-1 which one is usually related to
the electron difference between hard and soft domains frequently present in
polyurethanes. Phase separation in polyurethanes is often driven by large enthalpies of
mixture associated with chemical differences between hard segments (based on urethane
bonds) and soft segments (based on polyol units). The observed peak at qmax = 0.7 nm-1
can be associated with the distance (d) between hard domains by applying the Bragg’s
equation (d = 2/qmax, i.e. d = 8.9nm). The incorporation of TA into PU (Figure 2.b) did
not change significantly the SAXS pattern of the pure polymer, suggesting that no
major changes in morphology of the polymeric system were observed. Only a small
shift of the broad scattering peak at 0.7nm-1 towards higher values of q and an increase
in the scattering intensity at values of q lower than 0.25nm-1 can be seen as, possibly, a
consequence of the presence of TA crystals. Therefore, the presence of TA did not alter
the natural phase-separated structure of pure PU as an indication that the drug did not
interact strongly with the polymer.
Figure 2. SAXS scattering data of pure polyurethane (PU) (a), polyurethane containing
triamcinolone acetonide (TA PU implants) (b) and triamcinolone acetonide (TA) (c).
When collected at wider angles, x-ray scattering (WAXS = wide angle x-ray
scattering) can give information related to the distance between crystalline planes within
a crystallite. Figure 3 reveals that no define scattering peaks can be noted in curves due
to the pure PU containing poly(caprolactone) (Figure 3.a) as a consequence of the
presence of a highly amorphous structure. Crystallization of poly(caprolactone)
segments having low molar mass (< 2,000 g/mol) in polyurethanes is difficult to occur
since these oligomers can not display conformation modes that would result in
crystallization while being confined between hard domains [Ping, 2005]. The diffraction
patterns of pure TA exhibited intense peaks at 2 = 20.8 and 26.3 and some peaks of
lower intensity, indicating the crystalline nature of TA (Figure 3.c). The PU containing
the drug (Figure 3.b) depicted typical diffraction patterns of the crystalline structure of
TA. Although not shifted, the peaks of TA had a slight reduced intensity in TA-loaded
PU implants when compared to pure TA, which may be attributed to the solubilization
of TA when incorporated into polyurethane.
Figure 3. WAXS curves of pure polyurethane (PU) (a), polyurethane containing
triamcinolone acetonide (TA PU implants) (b) and triamcinolone acetonide (TA) (c).
It was clearly observed that the obtained polyurethane was formed by separated
domains of hard and soft segments. The microphase separation was due to the
incompatibility between the hard and soft segments. Polar groups such as urethane in
hard segments can hydrogen bond to each other to favor the formation of hard domains
[Koberstein, 1992]. The microphase structure of the polyurethane can be changed by the
introduction of functional and/or ionic groups into the polymer chains. For example,
ionic groups can interact electrostatically, contributing to the structural arrangement of
the segmented polyurethane [Francolini, 2010], and consequently altering mechanical
properties and solubility [Suchocka-Galas, 1998]. However, according to the obtained
SAXS results, the incorporation of TA into polyurethane did not lead to significant
changes in the natural phase-separated structure of the polymer, suggesting that the drug
was present within the polyurethane as isolated crystals. Furthermore, the FTIR and
WAXS results showed no significant changes in the functional groups and amorphous
pattern of the polyurethane after introduction of the TA into the polymer, indicating not
only the integrity of the polyurethane, but also the maintenance of the chemical and
morphological characteristics of the drug.
3.2
In vitro release of TA from the PU implants
The in vitro release profile of TA from the PU implants was demonstrated in
Figure 4. The PU implants exhibited a minimal burst release of the drug over the first 7
days, followed by a sustained TA release for a period of approximately 8 months. The
PU implants released approximately 64% of the drug in 8 months under sink conditions.
The minimal initial burst observed within 7 days may be due to the rapid dissolution
and diffusion of the drug crystals deposited in the PU implant surface and/or the no
intense chemical interaction between the drug and polymer. However, in the second
stage, the TA was constantly and slowly released from the polymeric implant, which is
most likely due to the hydrophobic character of poly(caprolactone) polymer present in
the soft segments, and consequently its corresponding low permeability to water. The
hydrophobicity of poly(caprolactone) can cause delay in water penetration and
consequently the diffusion of the drug through the polyurethane matrix into the aqueous
release medium was slow [Smith, 2007]. Furthermore, it is necessary to consider that
the biodegradation of the polyurethane, based on poly(caprolactone) in the soft
segments, in PBS medium is also slow, prolonging the period of TA release from the
PU implants. In terms of bonds present in poly(ester urethane), the most susceptible to
hydrolysis are ester bonds. However, the hydrolysis of ester bonds of urethane groups is
one order of magnitude slower relative to ester bonds of the soft segment. Therefore, the
soft segment bonds hydrolyze at a greater rate than hard segment bonds, and govern the
degradation rate of the poly(ester urethanes) [Tatai, 2007]. In summary, at the initial
stage, the TA release was mainly controlled by diffusion mechanism, and it was
expected that the remained drug in PU implants was released, in the second stage, as a
combination of polymer degradation and diffusion of the drug.
Figure 4. In vitro cumulative TA released from PU implants. Results represent mean ±
standard deviation (n = 4).
3.3
In vivo release of TA from the PU implants
The in vivo release profile of TA from the PU implants, which was estimated as
the amount of TA remaining in the implant, is shown in Figure 5. The PU implants
exhibited an initial burst release of the drug over the first 7 days. This initial burst may
be useful in rapidly achieving a local therapeutic concentration. During the first stage,
the concentration of TA delivered by the PU implants was approximately 28.3 µg/day.
In a second stage, that occurred between the 8th and the 45th days of the test, the PU
implants provided the controlled and sustained TA release within subcutaneous tissue of
mice. During this period, the PU implants released the drug at a daily dose of
approximately 18.2 µg. Finally, these biodegradable implants released almost 81% of
the drug in 45 days.
It was considered that the mechanism of TA delivery from the PU implants was
the simultaneous degradation of the polyurethane and the diffusion of the drug through
the polymeric matrix, as previously described. However, the in vivo degradation of the
polyurethane may involve other mechanisms such as the enzymatic hydrolysis by the
presence of esterases and oxidation of the polymer due to the body environment that
contains active moieties such as free radicals. Even though the enzymes are designed for
highly specific interactions with particular biological substrates, some appear capable of
recognizing and acting upon ‘‘unnatural’’ substrates such as polyurethanes [Santerre,
2005].
Accordingly, 64% of the TA was released from PU implants in vitro during 8
months and 81% of the drug was delivered by PU implants in vivo in 45 days. The
differences between the simulated physiological conditions (in vitro test) and the
physiological environment (in vivo test) explain the lack of correlation between the in
vivo and in vitro profile release of TA from the PU implants.
Figure 5. In vivo TA release from PU subcutaneous implants in mice. Sustained release
of the drug was observed up to day 45 post-implantation. Results represent mean ±
standard deviation (n = 5).
3.4
Inhibition of inflammatory angiogenesis in a murine sponge model
The efficacy of TA PU implants in minimizing the inflammatory response and
angiogenesis in a murine sponge model was evaluated. The murine sponge model of
angiogenesis has been extensively used to induce acute as well as chronic inflammatory
responses allowing the characterization of key components of fibrovascular tissue (cell
influx, blood vessels formation, extracellular matrix deposition). The effects of various
anti-inflammatory/anti-angiogenic compounds have been determined using this
implantation technique [Xavier, 2010].
Histological analysis revealed that non-biocompatible sponge discs induced
infiltration of inflammation-mediating cells, representing by macrophages,
polymorphonuclear leukocytes, monocytes, fibroblasts and eventually giant cells form.
The inflammation-mediating cells in the sponge discs of the untreated group were
stained by hematoxylin and eosin (Figure 6.a). The permanence of the sponge matrices
in vivo caused the acute inflammatory response to advance to the chronic phase, which
is characterized by the fibrotic deposition around the non-biocompatible discs and by
the presence of fibroblasts. Capillaries were evident in new vascularized areas of the
sponge discs. By contrast, the cellular response, characterized by the massive
infiltration, and the angiogenesis were inhibited in the sponge discs containing TA PU
implants (Figure 6.b). Additionally, the TA eluted from the polymeric devices
prevented progression to the chronic inflammatory phase revealed by the lack of fibrotic
deposition around the sponge discs on day-7 post-implantation. Therefore, the
glucocorticoid was controlled released from the PU implants directly into the targeted
site and efficiently restricted the pathological condition by inhibiting the production of
proangiogenic/inflammatory/fibrogenic components.
Figure 6. Representative histological sections (stained with hematoxylin and eosin) of
untreated group (a) (sponges) and treated group (sponges containing TA PU implants)
(B). In (a), a dense inflammatory infiltrate was observed. In (b), the number of cells
decreased in the sponge disc due to the TA release from the PU implants. The
polyurethane incorporated into the sponge absorbed hematoxylin during the coloration
process (circle). (a and b) – x40 magnification.
The efficacy of TA PU implants in modulating key components of spongeinduced inflammatory angiogenesis in mice was attributed to the following reasons: (1)
PU implants provided controlled TA release for a prolonged period, and displayed a
persistent therapeutic effect for 7 days; (2) the concentration of TA released from the
PU implants (approximately 28.3 µg/day, according to the in vivo TA release) was
enough to inhibit the cellular uptake in the non-biocompatible sponge and the formation
of new vessels in this experimental model; (3) the preparation technique of the TA PU
implants did not affect the chemical and morphological integrity of the incorporated
drug into the polymeric matrix and released from it, which was confirmed by FTIR,
SAXS and WAXS results. The chemical integrity of the TA is an essential factor that
assured the anti-inflammatory, immunosuppressive and anti-angiogenic actions of the
glucocorticoids by genomic and/or non-genomic mechanisms [Stahn, 2008; Alangari,
2010].
4. CONCLUSION
In this study, TA was incorporated into polyurethane in order to develop a new
implantable drug delivery system. The preparation technique of TA PU implants
provided a uniform distribution of the drug throughout the system. Data obtained from
FTIR showed no pronounced chemical interactions between PU and TA. SAXS results
indicated that the incorporation of TA into the polymeric matrix did not promote any
modification in the microdomain morphology of the polyurethane. Data obtained from
WAXS demonstrated the integrity of the crystalline nature of the TA after incorporation
into polyurethane matrix. The in vitro and in vivo release studies showed that TA was
controlled released from the polymeric implants. The TA-loaded polyurethane implants
efficiently modulated the key components of sponge-induced inflammatory
angiogenesis in mice. Finally, the TA PU implants could locally control the delivery of
this drug in order to inhibit the inflammatory-angiogenesis pathologies.
AKNOWLEDGEMENT
The authors would like to acknowledge the financial support received from the
following institutions: FAPEMIG (Minas Gerais – Brazil), CAPES/MEC (Brazil),
CNPq/MCT (Brazil) and Federal University of São João Del Rei (Minas Gerais –
Brazil).
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