Keywords microneedle - transdermal - resveratrol - absorption - polyvinylpyrrolidone K90
Introduction
Resveratrol (Res) is a natural polyphenol extracted from Polygonum cuspidatum , grape, peanut, mulberry, and other plants.[1 ]
[2 ]
[3 ]
[4 ] Res exhibits extensive biological activities, including anticancer, anti-inflammatory,
antioxidant, antiviral, and antineuralgic and heart protection.[5 ]
[6 ]
[7 ]
[8 ]
[9 ]
[10 ] Despite the proven therapeutic efficacy of Res in treating numerous diseases, several
factors impede its optimal effectiveness. These include chemical instability, poor
absorption through the biofilm, and low oral bioavailability due to first-pass metabolism
and rapid elimination.[11 ]
[12 ]
[13 ]
[14 ] Moreover, Res is classified as a Biopharmaceutics Classification System II drug,
exhibiting low aqueous solubility (< 0.05 mg/mL) and high permeability.[15 ] Consequently, the appropriate route of administration of Res is a crucial consideration.
Transdermal drug delivery represents an ideal drug administration method, offering
the potential to maintain a constant blood concentration, reduce adverse reactions,
enhance patient compliance, and increase bioavailability due to its absence of hepatic
first-pass metabolism.[16 ]
[17 ] However, the skin's barrier function represents a significant challenge to drug
penetration,[18 ]
[19 ] particularly regarding the stratum corneum (SC).[20 ] To overcome this challenge, researchers have explored a range of strategies to promote
transdermal drug absorption and penetration. These approaches include microneedles
(MNs),[21 ] iontophoresis,[22 ]
[23 ] sonophoresis,[24 ] magnetophoretic,[25 ] electroporation,[26 ]
[27 ] and photomechanical waves.[28 ] Nevertheless, conventional methods such as electric methods-iontophoresis and electroporation,
and magnetophoretic can create nanosized pores to improve the permeability.[29 ] For insoluble drugs, ionic liquids, sonophoresis, and other technologies cannot
substantially break through the SC barrier,[30 ]
[31 ] which greatly affects the permeation efficiency of drugs. In addition, these methods
employ sophisticated equipment and complex preparation processes, which may result
in discomfort comparable to that experienced during standard needle injection. MNs
are an array of micron-sized needles. They represent the most viable method for circumventing
the SC barrier to deliver therapeutic drugs to the skin.[32 ]
[33 ] Additionally, the length of the MN is only 0.2 to 1.5 mm, which allows for painless
penetration of the skin's SC while maintaining minimal invasiveness.[34 ]
[35 ]
[36 ]
[37 ]
The drug transport method classifies MN patches into five types: solid MNs,[38 ] hollow MNs,[39 ] coated MNs,[40 ] dissolving MNs,[41 ] and hydrogel-forming MNs.[42 ] The first three types of MNs are manufactured from silicon or metals, and if the
needle breaks during administration, it can cause significant damage to the skin.[43 ] The safety of emerging materials such as poly (methyl vinyl ether) co-maleic acid
(PMVE/MA) and methacrylate hyaluronic acid for the preparation of hydrogel MNs has
yet to be confirmed.[44 ] However, the composition of dissolving MNs includes water-soluble matrix materials
such as polylactic acid, polyvinyl pyrrolidone (PVP), hyaluronic acid, polyvinyl alcohol,
and chitosan. The drug is dispersed or dissolved in the needle.[45 ]
[46 ]
[47 ]
[48 ]
[49 ] After insertion into the skin, the needle dissolves when it absorbs water from the
interstitial fluid and releases the drug payload. As a result, the drug is delivered
directly to the skin for therapeutic effect without leaving a sharp needle.[50 ]
[51 ]
[52 ] Additionally, when they come into contact with moisture in the dermis, the tip dissolves
rapidly, thereby facilitating the recovery of damaged skin and minimizing the risk
of infection.[53 ] Currently, dissolving MNs have been developed to deliver a range of drugs, including
genes, peptides, vaccines, and proteins.[54 ]
[55 ]
[56 ]
[57 ]
In this study, a two-step casting procedure was employed to prepare dissolving MNs
for loading Res in the needle tips, for the first time. PVP K90 was selected as the
matrix material. The mechanical properties, morphology, and skin permeability of the
MNs were characterized. Furthermore, the puncture performance, skin recovery, and
drug release profiles following MN treatment were evaluated.
Materials and Methods
Materials
Res (purity > 99%) was purchased from Shanghai Aladdin Biochemical Technology Co.,
Ltd. (Shanghai, China). PVP K90 (Mw = 395.2 Da) was purchased from Boai New Open Source
Medical Technology Group Co., Ltd. (Jiaozuo, China). Glycerin was obtained from Xilong
Science Co., Ltd. (Shantou, China). Sodium carboxymethyl cellulose was purchased from
Anhui Shanhe Medicinal Accessories Co., Ltd. (Anhui, China). Methanol was purchased
from Thermal Fisher Technology Co., Ltd. (Massachusetts, United States). Anhydrous
ethyl alcohol was purchased from National Pharmaceutical Group Chemical Reagent Co.,
Ltd. (Shanghai, China). Chloral hydrate and Laurocapram were purchased from Shanghai
MacLean Biochemical Technology Co., Ltd. (Shanghai, China). Phosphate-buffered saline
(PBS) was purchased from Wuhan Punosai Biotechnology Co., Ltd. (Wuhan, China). Methylene
blue was purchased from Sigma-Aldrich Shanghai Trading Co., Ltd. (Shanghai, China).
All other reagents were of analytical grade and purified water was used throughout
this study.
Male Sprague Dawley (SD) rats (200 ± 20 g) were provided by the Experimental Animal
Center of Jiangxi University of Chinese Medicine (Nanchang, China).
Fabrication of Res-Loaded Microneedles
Dissolving MNs were prepared by the two-step casting method.[58 ] PVP K90 was selected as the best matrix material for the preparation of MN tips
through our pretesting. Briefly, the mixture of tip material and drug was poured into
the MN mold (Taizhou, China). After centrifugation at 5,000 r/min for 10 minutes,
and removing the excess needle tip solution, the MN mold was kept in a desiccator,
dying at room temperature for 30 minutes. Subsequently, the backing material was poured
into the MN mold and centrifuged at 3,000 r/min for 5 minutes. The mold is placed
in a desiccator and dried at 30°C for 24 hours. Finally, the dissolving MNs were demolded
and placed in a desiccator before the experiment.
The tip materials were prepared as follows. The tip solution was prepared by dissolving
PVP K90 in a certain amount of methanol-aqueous solution for ultrasonic dissolution,
then Res powder was added to acquire a mixture of a polymer blend.
The backing materials were prepared as follows. PVP K90 (12 g) and glycerol (0.45 g)
were placed in ultra-pure water (30 mL), stirred until completely dissolved, removed
bubbles by ultrasound, and set aside before the experiment.
Optimization of Res-Loaded Microneedles
Box–Behnken design, a response surface methodology,[59 ] was employed, with centrifugation time (A), solvent concentration (B), and prescription
ratio (Res: matrix) (C) as the investigated index. Two levels of each independent
variable were employed. The parameter values of the independent variable (A, B, and
C) were based on the results of previous single-factor experiments (data were not
shown), and Res drug loading (Y) was selected as the dependent variable. The parameters
and values are detailed in [Table 1 ]. Design-Expert software (Stat-Ease, Wilmington, United States) was used to optimize
the correlation between the independent and dependent variables by generating mathematical
equations, contour, and response surface designs. Accordingly, the experiment was
divided into 17 batches. The criteria for selecting of optimum formulation were mainly
based on the maximum drug loading.
Table 1
Selected independent and dependent variable levels
Level
Independent variables
Lower limit (−1)
Higher limit (+1)
A
5
15
B
20
30
C
0.3
0.5
Dependent variable
Constraints
Y
Maximize
Abbreviations: A, centrifugation time (min); B, solvent concentration (%); C, prescription
ratio (Res: matrix); Y, drug loading of Res-MNs (µg).
Characterizations of Microneedles
The geometry of Res-MNs was evaluated by scanning electron microscope to characterize
the size of the MNs, the tip morphology, and the distribution of the MNs on the array.
Mechanical Strength of Microneedles
The aluminum foil was laid flat, the tip of the Res-loaded MN was placed downward,
and the MN was pressed by applying a force of about 10 N with the thumb for about
30 seconds.[60 ] The MN punctured the aluminum foil. The porosity of the MN and the morphology of
the MN after puncture were assessed.
Methylene blue MNs were prepared by a two-step centrifugation method of methylene
blue solution (1 mg/mL, 2 mL) and PVP K90 (300 mg). Eight-week-old male SD rats were
anesthetized with 5% chloral hydrate solution, and the abdominal hair was removed
with depilatory cream and wiped clean. Subsequently, the methylene blue MNs were pressed
on the rat's abdominal skin and maintained for 10 seconds. After 2 minutes, the MNs
were removed. The punctured skin was observed under an optical microscope.
Solubility of Microneedles after Insertion
The dissolution of MN after skin puncture was observed. Male SD rats were anesthetized
with 5% chloral hydrate and their abdominal hair was removed with a depilatory cream.
The MNs were pressed on the abdominal skin of the rats with a force of about 10 N/cm2 . The MNs were removed from the skin at predetermined intervals of 1, 5, 10, and 20 minutes,
respectively. The dissolved morphology of MNs was observed under an optical microscope.
Safety Evaluation of Res-Microneedles
To prevent the entry of pathogenic microorganisms and toxic substances, and to reduce
the risk of infection, microchannels created by MNs need to be quickly closed after
administration. The MNs were inserted into the depilated skin and fixed with medical
tape. Five minutes later, the MNs were removed from the skin. The micropores in the
skin were photographed with a digital camera at 0, 1, 2, 3, 6, and 12 hours, respectively,
until the micropore in the skin became invisible.
Saturation Solubility Test
The solubilization of PVP K90 for Res was evaluated. Briefly, PVP K90 (25, 50, and
100 mg) was dissolved in aqueous solution (1 mL), respectively, ultrasonic dissolution
for 15 minutes, cooled and added to Res (5 mg) to achieve a mixture containing: (1)
Res: PVP K90 (1:5, w/w), (2) Res: PVP K90 (1:10, w/w), and (3) Res: PVP K90 (1:20,
w/w). The Eppendorf tubes containing solvents and drugs were agitated on a thermostatically
controlled orbital shaker at 37 ± 2°C at a speed of 200 r/min for 24 hours. The sample
was centrifugated to settle down. The supernatant solution was filtered through a
0.22-µm filter and analyzed by high-performance liquid chromatography (HPLC) method.
The blank group only added the same amount of (Res aqueous solution).
Skin Permeability of Res-Loaded Microneedles
The skin permeability of Res-loaded MN was assessed using a multifunction transdermal
diffuser (TP-6, Tianjin, China) and a horizontal diffusion cell (TP-6, Tianjin, China).
The diffusion cell contains a donor chamber and an acceptor chamber, with male SD
rat's skin (2 cm × 2 cm) being located between the chambers. The underside layer was
in contact with the acceptor chamber fluid. The acceptor chamber was filled with the
dissolution medium (PBS, pH = 7.4) and stirred at 600 rpm, maintaining the temperature
at 37°C.
Res (30 mg) and purified water (10 mL) were mixed to form Res suspension (Res-SUS,
3 mg/mL). Res (30 mg) and sodium carboxymethyl cellulose (0.5 g) were dissolved in
purified water (10 mL), and then laurazone (0.1 mL) was added to form Res gel solution
(Res-GEL, 3 mg/mL).
The skin was treated with Res-MNs, Res-SUS, and Res-GEL, respectively, and then sandwiched
between the chambers. Res-MNs were applied to the surface of the skin and pressed
continuously for 1 minute with a force of about 10 N. Res-SUS (0.1 mL) and Res-GEL
(0.1 mL) were applied on the skin of rats. At intervals of 1, 2, 3, 4, 6, 8, 12, and
24 hours, respectively, a sample (an aliquot of 0.2 mL) was collected from the sampling
port of the acceptor chamber, and an equal volume of dissolved medium was added to
maintain the sink condition. The content of Res in the samples was analyzed by the
HPLC method.
High-Performance Liquid Chromatography Analysis
The content of Res in the MNs was determined. Briefly, the tips of the MN patch were
removed from the bottom with a scalpel and dissolved in 2 mL methanol solution. The
solution was swirled for 5 minutes, followed by centrifuging at 4,000 rpm for 10 minutes.
The supernatant was collected and diluted properly, and Res content in the solution
was determined by an LC-20A HPLC (Shimadzu, Kyoto, Japan) with a diamond C18 column
(4.6 mm × 250 mm, 5 µm, California, United States). The flow rate was 1 mL/min and
the column temperature was 30°C. The mobile phase consisted of an equal volume of
methanol and water. The detection wavelength was 308 nm and the injection volume was
20 µL. In the range of 0.1 to 50 µg/mL, there was a good linear relationship between
the peak area (A) and the concentration of Res (X ). The regression equation was A = 136,382X + 1,271.2 (R
2 = 0.9998). The extraction recovery rate, accuracy, and precision all meet the requirements
of biological sample analysis.
Data Analysis
All data were presented as mean ± standard deviation. All experiments were repeated
at least three times. SPSS Statistics 22.0 (SPSS Inc., Chicago, Illinois, United States)
with one-way analysis of variance was used for statistical analysis. A p -value of less than 0.05 is considered statistically significant.
Results and Discussion
Formulation Optimization of Microneedles
With the drug loading of MNs as an index, test results of (A) centrifugation time,
(B) solvent concentration, and (C) formulation are shown in [Table 2 ]. Analysis was conducted using Design Expert 8.0.6 software, and the regression equation
of the drug loading of MNs was obtained as follows: Y = 85.84 + 0.7085A + 0.6292B + 0.1900C − 0.0675AB − 0.6621AC − 0.1161BC − 1.78A2 − 1.70B2 − 1.13C2 .
Table 2
Independent values and response for formulations in Box–Behnken design
Formulations
Independent variables
Response
Y (µg)
A (min)
B (%)
C
1
15
20
0.375
82.56
2
10
25
0.375
86.93
3
5
20
0.375
81.22
4
5
25
0.500
82.64
5
10
25
0.375
85.01
6
15
30
0.375
83.11
7
10
25
0.375
85.77
8
10
25
0.375
86.12
9
10
30
0.300
83.73
10
10
20
0.300
81.45
11
10
20
0.500
82.67
12
15
25
0.500
83.14
13
10
25
0.375
84.78
14
5
30
0.375
82.04
15
5
25
0.300
81.25
16
15
25
0.300
84.67
17
10
30
0.500
84.17
Abbreviations: A, centrifugation time (min); B, solvent concentration (%); C, prescription
ratio (Res: matrix); Y, drug loading of Res-MNs (µg).
The model was established, and then a multiple quadratic regression response surface
model of MN drug loading was obtained. The test results of the influencing factors
(A, B, and C) were analyzed by multiple linear regression and binomial fitting analysis
to verify the significance of the regression model and influencing factors. As can
be seen from [Table 3 ], F = 7.01 and p = 0.0088 in the established regression model. It shows that the difference in the
regression model is very significant. The p -value of the lack of fitting term is 0.55, which is above 0.05, and as a result,
the difference in the model is not significant, indicating that the equation is reliable.
Our data indicated that the test design is reliable, accords with the actual situation,
and is realistic enough to be used in the analysis. Therefore, it is feasible to use
this model to analyze and predict the drug loading of MNs.
Table 3
Analysis of variance of regression model
Source
Sum of squares
Freedom
Mean square
F -value
p -Value
Significant
Model
43.73
9
4.86
7.0100
0.0088
[b ]
A-Centrifugation time (min)
3.90
1
3.90
5.6300
0.0495
[a ]
B-Solvent concentration (%)
3.07
1
3.07
4.4400
0.0732
C-Prescription ratio (Res: matrix)
0.2888
1
0.2888
0.4168
0.5391
AB
0.0182
1
0.0182
0.0263
0.8757
AC
1.81
1
1.81
2.6100
0.1502
BC
0.0556
1
0.0556
0.0802
0.7852
A2
13.41
1
13.41
19.360
0.0032
[b ]
B2
12.24
1
12.24
17.660
0.0040
[b ]
C2
4.58
1
4.58
6.6100
0.0370
[a ]
Residual
4.85
7
0.6929
Lack of fit
1.84
3
0.6119
0.8120
0.5500
Pure error
3.01
4
0.7536
Total difference
48.58
16
Note: The data are presented as the mean ± standard deviation.
a
p < 0.05.
b
p < 0.01.
From the p -value in [Table 3 ], it can be seen that the centrifugation time (A) in the primary item has a significant
effect on the drug loading of MNs. In the quadratic term, the effect of secondary
terms A2 and B2 have extremely significant effects on the drug loading of MNs, and C2 has significant effects on the drug loading of MNs. In the interaction terms, AB,
AC, and BC had no significant effect on the drug loading of MNs. According to the
F value in [Table 3 ], it can be concluded that the effects of three factors on MN drug loading are centrifugation
time (A) > solvent concentration (B) > prescription ratio (C).
[Fig. 1 ] was the response surface and contour map of interaction effects of preparation conditions
(A, B, and C) created by the response surface regression model. The regression fitting
equation of MN drug loading was solved, and the best preparation conditions were obtained:
A = 10.95, B = 25.90, C = 0.40. Under this condition, the drug loading of MNs was
85.96 µg. According to the feasibility of the experiment and practical operation,
the conditions for preparing dissolving MNs were as follows: centrifugation time was
10 minutes, solvent concentration was 25%, and prescription ratio was 0.375. Under
these conditions, the drug loading of MNs was 85.72 µg. The relative error of the
predicted value of the model was only 0.24 µg, indicating that the drug loading conditions
of MNs were optimized by the response surface method, and the parameters of the preparation
scheme were accurate and reliable and had a certain application value.
Fig. 1 3D response surface plots (A , B , and C ) and 2D contour maps (D , E , and F ) for the impact of independent variables on drug loading. (A ) Centrifugation time versus solvent concentration. (B ) Centrifugation time versus prescription ratio. (C ) Prescription ratio versus solvent concentration. (D ) 2D contour maps of centrifugation time versus solvent concentration. (E ) 2D contour maps of centrifugation time versus prescription ratio. (F ) 2D contour maps of prescription ratio versus solvent concentration. 2D, two-dimensional;
3D, three-dimensional.
Although our optimized MN drug loading only varies between 80 and 87 µg ([Table 2 ]), a small increase in drug loading is also meaningful. For insoluble drugs, it can
increase the exposure of drugs to increase the bioavailability. For MN drug delivery,
the dose given is only equivalent to that of the traditional dosage form 1/5 to 1/200,[61 ]
[62 ] which can effectively reduce the number of MN patches. According to existing research,
the effective dose of Res in regulating Human Bone marrow mesenchymal stem cells is
0.1 to 1 µmol/L to regulate self-renewal and multipotency through the SIRT1-SOX2 axis.[63 ] In this paper, the drug loading of each MN was about 86 µg, which is sufficient
to exert the curative effect of Res.
Characterizations
PVP K90 was a nonionic amorphous polymer, which was widely used in transdermal drug
delivery systems because of its solubility in water. In addition, PVP K90 did not
cause skin irritation or sensitization.[64 ]
[65 ] Therefore, PVP-K90 was used to modulate the mechanical strength and brittleness
of MNs. As shown in [Fig. 2 ], Res-MNs had a complete needle shape, which was quadrangular pyramid-shaped, and
the MN plaque was square, the needles were arranged in a 10 × 10 array in a patch
of 8 mm × 8 mm. Compared with pyramids and circles, this shape had better penetration
and higher skin delivery efficiency. The height of MN was 762.5 ± 1.56 µm, and the
distance between MN was 295 ± 1.25 µm. The length of the MN mold was 800 µm and the
MN spacing was 300 µm. Compared with the mold, the size of the prepared MN shrinks
slightly, which may be due to the rapid volatilization of the solvent during the drying
process. When preparing Res-MNs, we choose 25% methanol solution as a solvent, which
not only can effectively inhibit the diffusion of drugs in the tip to the backing
layer but also reduces the large number of bubbles caused by solvent volatilization
in the preparation of MN patches.[66 ] As a result, the influence on the mechanical strength and drug loading of MNs can
be effectively reduced.
Fig. 2 Representative SEM images of dissolving MNs. MNs, microneedles; SEM, scanning electron
microscope.
Mechanical Strength
As shown in [Fig. 3A ], [B ], Res-MN effectively pierced the aluminum foil and formed 100 holes, and the puncture
efficiency (PE) was 100%. As shown in [Fig. 3C ], MN pinholes are dotted on rat skin, consistent with the MN array, with a PE of
100%, indicating that the MNs have sufficient mechanical strength to puncture the
skin and overcome the SC.
Fig. 3 Insertion capacity of the MNs. (A ) Conventional frontal aluminum foil shooting image. (B ) Conventional back aluminum foil shooting image. (C ) Staining image of skin puncture with methylene blue MNs. MNs, microneedles.
Microneedle Dissolution in vivo
The abdominal skin of SD rats was used to evaluate the dissolution of MNs in vivo . The morphological changes of MNs after insertion into 1, 5, 10, and 20 minutes were
observed by optical microscopy, respectively. As shown in [Fig. 4 ], the tip of the MN dissolved in the skin after 1 minute, and the MN gradually dissolved
over time. After 20 minutes, MNs completely dissolved in the skin. The above results
show that MNs could dissolve in the skin and release drugs into the skin after contact
with active epidermis or dermis tissue fluid within a few minutes. The rapid dissolution
of MNs helps to be reliable and easy to use in practice, making patients more compliant.
Fig. 4 Morphological changes of MNs dissolution after insertion into the abdominal skin
of SD rats at 1, 5, 10, and 20 minutes. MNs, microneedles; SD, Sprague Dawley.
Application Safety of Res-Microneedles
The recovery of skin after MN treatment was observed by a digital camera. As shown
in [Fig. 5 ], the micropores formed by MNs almost disappeared 3 hours after implantation, and
only slight wounds were left in the skin. The puncture marks gradually disappeared
over time, and the spots on the skin wounds vanished completely within 12 hours later.
No obvious irritant reaction was observed during the observation period. To sum up,
MNs could penetrate the SC and transport Res directly to the skin lesions, resulting
in minor and reversible damage, which greatly increases the convenience and acceptability
of frequent administration.
Fig. 5 The skin recovery within 12 hours after administration of Res-MNs. Res-MNs, resveratrol-loaded
dissolving microneedles.
Saturation Solubility of Res
The solubility of drugs and matrix materials in solvents was very important to determine
whether the drug distribution in the MNs was uniform and whether the drug loading
was sufficient. PVP K90 was selected as the matrix material of MNs, not only for its
good biocompatibility but also for its good water solubility.[67 ] As shown in [Fig. 6 ], the saturated solubility of Res in different proportions of PVP K90 solution was
1,783.9 ± 10.45 μg/mL (Res: PVP K90, 1:5), 2,008.2 ± 12.5 μg/mL (Res: PVP K90, 1:10),
and 380.4 ± 7.44 μg/mL (Res: PVP K90, 1:20), respectively. However, the average solubility
of Res in ultra-pure water was only 51.9 ± 5.4 μg/mL. The Res solubility of Res: PVP
K90 (1:5, w/w) and Res: PVP K90 (1:10, w/w) was 34 and 38 times higher than that of
Res aqueous solution, respectively, and the difference was extremely significant (p < 0.001). The Res solubility of Res: PVP K90 (1:20, w/w) was about 7 times higher
than that of Res aqueous solution, but there was also a significant (p < 0.05). It's worth exploring whether the Res solubility of Res: PVP K90 (1:20, w/w)
was lower than Res: PVP K90 (1:5, w/w) and Res: PVP K90 (1:10, w/w). The result of
higher the concentration of PVP K90 in the solution, the greater its viscosity, thus
affecting the infiltration of water in the solution into Res and reducing its solubilization.
For the other two groups, the low concentration of PVP K90 has lower viscosity, the
main effect on Res is to increase the dispersion in the solution. Therefore, not only
did the specific surface area of Res improve, but also the hydrophilicity.[68 ]
Fig. 6 The solubilization effect of PVP K90 on Res detected by HPLC. Data were represented
as mean ± standard deviation (n = 3; *p < 0.05; ***p < 0.001 versus Res aqueous solution). HPLC, high-performance liquid chromatography;
Res, resveratrol.
In vitro Skin Penetration of Res-Microneedles
Many previous studies have confirmed that dissolving MNs could be used as an effective
tool to improve the permeability and delivery efficiency of drugs.[69 ] In this experiment, the abdominal skin of SD rats was used as a drug-permeable membrane.
The permeation profiles of Res from different approaches are shown in [Fig. 7 ]. The Res-MN was the highest among all groups at all time points. Pretreatment with
solid MNs created micropores in the skin, facilitating the diffusion of the Res from
the skin SC into the skin dermis. The results showed that the Res-MN released about
35% of the drug within 12 hours, and then slowly released the drug over time. Finally,
about 75% of the drug was released within 24 hours. The Res-SUS and the Res-GEL had
a lower speed of drug delivery, and about 13 and 25% of the drugs were delivered within
12 hours, respectively. Res-MN had excellent drug delivery efficiency, with 5 and
3 times that of the Res-SUS and the Res-GEL within 24 hours. The results confirmed
the promoted effect of MN on the penetration of Res into the skin due to the micropores
created by the MN patch.[70 ] Furthermore, Res content delivered to the receiver compartment was less than that
in the needle, presumably because of the residual drug in the skin.[71 ]
Fig. 7
In vitro penetration curves of Res-MNs, Res-SUS, and Res-GEL. Data were presented as mean ± standard
deviation (n = 3). Res-MNs, resveratrol-loaded dissolving microneedles; Res-SUS, resveratrol suspension;
Res-GEL, resveratrol gel solution.
Conclusion
In the present work, we developed a dissolvable polymeric MN patch loaded with Res
to enhance the absorption of Res in transdermal administration. The Res-MNs were optimized
through the application of the Box–Behnken experimental design method. The MNs, prepared
from the matrix of PVP-K90, exhibited a smooth body, a sharp tip, and no obvious pores
or gaps on the surface. It demonstrated good mechanical strength, enabling penetration
of the skin. Moreover, the obtained MN dissolved rapidly upon absorption of interstitial
fluid following insertion. In addition, the pinhole created by the MN can be expected
to heal within 12 hours, indicating excellent skin recovery. Most notably, the PVP
K90 demonstrated a pronounced solubilization effect on Res, markedly enhancing the
drug-loading capacity of Res within MNs. In vitro , transdermal release studies demonstrated that Res-MNs exhibited excellent drug delivery
efficiency, with a drug delivery amount of about 5 and 3 times that of the Res-SUS
and the Res-GEL, respectively, within 24 hours. To sum up, Res-MNs manufactured from
PVP-K90 not only enhance the solubility of Res but also exhibit notable advantages
in transdermal delivery. Nevertheless, further animal studies are required to assess
the pharmacokinetic and pharmacodynamic profiles of the Res-MNs for their potential
clinical application.
