Optimization and characterization of transdermal film of curcumin containing natural oils as permeation enhancer by response surface methodology

Priyanka Kriplani¹, Kumar Guarve², Uttam Singh Baghael³

Introduction

Osteoarthritis (OA) is a chronic inflammatory disease that affects people of age ≥60.It is reported to affect 14-47% of Indian population. [1-2]. Hormonal, genetic, aging, metabolic and mechanical factors regulate the biology of the articular cartilage by complex molecular mechanisms [3]. Major causes behind OA are obesity, joint location, genetic predisposition etc. Clinical implications associated with OA are: Joint pain and stiffness occurs which is related to use, pain occurs on movement with restricted range and cracking of joints may occur. [4]. The treatments available for OA are acetaminophen, nonsteroidal anti-inflammatory drugs (NSAIDs) cyclooxygenase COX-2 selective inhibitors , opoid analgesics and opoids are taken in case of severe pain.

There are many problems associated with the above mentioned drugs like (a) NSAIDs do not slow down the advancement of ailment as they do not impede any immune-inflammatory reactions but only interfere in the production of prostaglandin by cyclooxygenase. [5-6]. (b) It has been reported in literature that a huge segment of patients neither show any response to the current treatments available nor reprieve the treatments available in the market. (c) Prolonged use of these drugs lead to adverse reactions such as Liver infection, gastrointestinal damage and may lead to heart failure [7-8]. Therefore there is a need of both effective and safe new drug substances to overcome the situation. Since ages the medicines were derived from plants [9]. The demand of herbal drugs is therefore increasing day by day to treat various ailments with less toxic effects and better therapeutic effects. Another key reason to proceed from synthetic to herbal drugs is the liberation of human and veterinary medicines in the environment by various routes is becoming the significant issue of human and environmental health concern. For example diclofenac is a widely used non-steroidal anti-inflammatory drug (NSAID) is known to inhibit the cyclooxygenase activity, responsible for the synthesis of prostanoids which can increase the synthesis of other eicosanoids and chronic exposure to environmental diclofenac may result in side effects such as kidney failure and intestinal pathology which may be detrimental to the health and survival of aquatic vertebrates [10]. Various herbal preparations are available in the market but they are either not stable or are having solubility problems leading to less or zero therapeutic effect. Therefore, Novel drug delivery system has come into the picture. [11]. Inclusion of plant actives in novel drug delivery system overcomes the problems associated with crude plant extracts [12-13]. From time immemorial, curcumin (Zingiberaceae), the principal plant active of renowned Indian spice turmeric (Curcuma longa) has been used as inflammatory agent in ayurvedic medicine system. Curcumin interplays with multiple molecular targets i.e. TNF-α, IL-1β, IL-6, IL-8, NF-κB, and COX-2 [14]. However its low aqueous solubility leads to its low oral bioavailability i.e. only 40-45% of its oral dose reaches systemic circulation owing to its metabolism in intestinal mucosa and by liver which in turn restricts its oral use [15-16]. Innumerable problems are associated with the oral ingestion of drugs such as many patients may experience gastrointestinal irritation and intolerance from single dose and many may develop severe gastrointestinal irritations (ulceration) on prolonged treatment. Pain medications if administered orally may have undesirable effects on cognition and level of consciousness. The topical preparations allow for pain relief without undue risk of undesired sedation and altered cognition [17]. Therefore there is a need to develop transdermal drug delivery system of antiinflammatory herbs to overcome these difficulties and low oral bioavailability of curcumin also motivates us to study topical preparation. Moreover presently the herbal drugs present in the market are not properly optimized in respect to excipients utilized which restricts their utilization as compare to synthetic drugs [18-19]. So the aim of the present study is to prepare optimized transdermal film of curcumin containing natural oils i.e jojoba oil and peppermint oil as permeation enhancers by utilizing factorial design. EC is nontoxic, nonallergic polymer having good film forming properties for the preparation of tough films. Hydrophilic polymer, HPMC was added to EC to increase the release rate. This can be attributed to the leaching of soluble polymer on contact with water leading to formation of pores thus boosting the release of drug [20-21]. In the first step designing of experimental trials using multiple factorial design technique was carried out, while in the second step optimization of best composition of variables for the transdermal patch was performed employing Derringer's desirability functional method. Design-Expert software 11 was used to design trials and to obtain optimized formulation by analyzing response surface plots.

3

Experimental

Materials and methods

Chemicals

Curcumin and hydroxy propyl methyl cellulose (HPMC) was obtained as gift sample from Sanat products limited, Delhi ([email protected]), ethyl cellulose (EC), dibutyl phthalate (DBT), polyethylene glycol 400 (PEG 400), jojoba oil and peppermint oil were purchased from VK chemicals, Ambala Cantt.

Experimental design

Preliminary study indicated that the factors such as proportion of HPMC and EC and percentage of natural oils were majorly influencing the mechanical property of film and dissolution behavior. Therefore, in the present study multiple factorial design was adopted to optimize the above formulation factors and to evaluate the main effect on responses such as % elongation of film and permeation behavior. All the independent and dependent variables were mentioned in Table 1 and Table 2. Statistical analysis for the present study was performed employing 45 day trial version of Design-Expert software (Version DX11.0, Stat-Ease Inc., Minneapolis, MN, USA). Experimental design of different batches of matrix film and the obtained responses are presented in Table 2 [22-23].

Preparation of transdermal patches

The transdermal patches were prepared by solvent casting technique by using bangles. The casting solutions for transdermal patches were prepared as per composition stated in Table 3 and Table 4. Weighed quantities of HPMC and EC were dissolved in measured quantities of ethanol and chloroform (1:1). The drug curcumin 20mg is dissolved in the solvent mixture along with natural oils as permeation enhancer which was mixed thoroughly to form homogeneous mixture. This mixture was then poured onto the mercury surface placed in the petridish in between bangle and then covered using glass funnels and allowed to dry at room temperature for 24 hr by solvent evaporation. The patches were removed and cut into required dimension. The prepared patches are kept in dessicator for 2 days for further drying and wrapped in aluminium foil and then packed in self sealing covers [24].

Table 3. Multiple Factorial experimental design for the preparation of different batches and their obtained responses for Elongation Table 4. Multiple factorial experimental design for the preparation of different batches and their obtained responses for 3

patches containing peppermint oil as permeation enhancer.

Std Run Factor 1 Factor 2 Factor 3 Actual R1 A:HPMC B.EC C:peppermint oil 12 1 200 200 0.4 75.8 13 2 100 200 0.4 55.6 3 3 100 200 0.3 53.5 10 4 100 100 0.3 45 18 5 200 100 0.4 68.6 14 6 300 150 0.4 77.5 9 7 100 100 0.3 45.04 11 8 300 200 0.4 80.5 8 9 200 100 0.3 60.3 7 10 300 100 0.3 80.2 5 11 200 150 0.3 68.1 2 12 200 200 0.3 72.4 4 13 300 150 0.3 75.5 16 14 100 150 0.4 52.3 15 15 200 150 0.4 70.2 19 16 100 100 0.4 48.6 17 17 300 100 0.4 85.5 1 18 300 200 0.3 78.6 6 19 100 150 0.3 50.2

patches containing jojoba oil as permeation enhancer.

Std Run Factor 1 Factor 2 Factor 3 Actual A:HPMC B:EC C:Jojoba oil Elongation 15 1 100 150 0.3 55.4 14 2 200 150 0.3 70.4 17 3 200 100 0.3 62.5 4 4 300 150 0.4 74.6 9 5 100 100 0.4 50.3 3 6 100 200 0.4 56.5 16 7 300 100 0.3 81.4 5 8 200 150 0.4 71.3 1 9 300 200 0.4 82 7 10 300 100 0.4 85.9 12 11 100 200 0.3 55.4 6 12 100 150 0.4 53.2 18 13 100 100 0.3 46 13 14 300 150 0.3 76.2 2 15 200 200 0.4 75.4 11 16 200 200 0.3 74.2 8 17 200 100 0.4 68 10 18 300 200 0.3 76 Actual R2 Predicted R1 Predicted R2 Drug Elongation Drug permeation permeation 78 70.84 78.05 74.4 56.26 76.33 72.9 52.56 75.08 94.2 47.46 91.23 90.4 65.74 94.21 89.6 82.87 87.85 94.5 47.46 91.23 83.4 85.43 79.78 89.4 62.05 92.96 94.3 76.63 94.68 79.4 64.60 84.88 76.3 67.15 76.80 87.2 79.18 86.60 86.2 53.70 84.41 81.2 68.29 86.13 95.6 51.15 92.49 96.4 80.32 95.93 81.62 81.73 78.52 85.3 50.01 83.16 R1 Actual R2 Predicted R1 Predicted R2 Drug Elongation Drug permeation permeation 87.4 53.11 83.68 80.6 66.39 85.67 91.5 64.27 93.44 91.6 81.85 89.36 96.5 53.19 93.15 75.5 57.42 77.60 94.9 77.55 95.43 82.6 68.58 87.37 84.4 83.97 81.58 97.1 79.74 97.13 73.7 55.23 75.90 87.5 55.30 85.38 94.6 51.00 91.45 88.5 79.66 87.66 79.5 70.69 79.59 77.2 68.51 77.89 91.6 66.46 95.14 82.6 81.78 79.88

Preformulation study of the drug: Curcumin

Preformulation study is defined a study of physical and chemical properties of a drug substance alone and in combination with excipients. Organoleptic properties, melting point, solubility studies and calibration of curcumin was done. The objective of the study is to generate information useful in developing stable and bioavailable dosage form.

FTIR study

The FTIR of curcumin, polymers and the patches -1 containing curcumin was done at a resolution of 4cm -1 over 400-4000cm wavelength region. The FTIR spectrophotometer (model: Shimadzu Analytical India Pvt. Ltd (SAIP).) employed Attenuated Total Reflectance –FTIR technique to determine IR transmission spectra and record the characteristic peaks [23].

Folding endurance

The folding endurance was determined manually by taking a strip of patch (4X2cm) and repeatedly folding it at the same place till it breaks. Folding endurance is considered as the number of times the film is folded at the same place without breaking/cracking [24].

Thickness

Thickness of the patches was determined by using digital vernier calliper (Mityutoyo, Japan) at different locations. Average values and standard deviations were determined (25).

Weight variation

2 Weight variation was done by weighing 1.76cm area of film accurately on digital balance (Sartorious, Germany BT224S, d=0.1mg) and the average of three determinations was calculated [26].

Percentage elongation

The elongation percentage was calculated using custom elongation testing apparatus; the percentage elongation was determined by using equation 1.

% elongation= [L2-L1]/L1*100 Where, L1 is the initial length and L2 is the final length of the film [23].

Percentage moisture content [25]

The prepared films were weighed individually and kept in a desiccator containing fused calcium chloride at room temperature for 24 h. After 24 h, the films were are weighed and determined the percentage moisture content from the below mentioned Percentage moisture content= (Initial weight−Final weight)/Finalweight×100.

Moisture uptake, swelling ratio and erosion studies

[27] 1cmX1cm patch specimens were taken for moisture uptake, swelling ratio and erosion studies. For moisture uptake study, the patch specimens were initially weighed (W⁰) and then placed in stability chamber (model: Climate Chamber ICH/ICH L, Memmert GmbH þ Co. KG, Germany) set at 25±2°C temperature and 75% relative humidity. The specimens were removed after constant weight is achieved (Wu).Moisture uptake was calculated by the following equation:

Moisture uptake = Wu-W⁰/W⁰ For swelling ration and erosion studies patches were dried overnight at 60±2°C. Then the patches were weighed (W⁰) and dipped in 5ml of distilled water. After that the patches were placed in stability chamber set at 25±2°C temperature and 75% relative humidity for 48hours. These hydrated patches were weighed(Ws) and then dried again at 60±2°C overnight, and weighed again(Wd).the percentage swelling ratio and percentage erosion were then calculated by following formulas given below; % Swelling ratio = Ws – W⁰ / W⁰X 100 % Erosion = W⁰ – Wd / W⁰X 100

Percent drug content

Patches of 2cmX2cm are cut from different locations. Each patch sample was soaked in phosphate buffer (pH 5.5) in 10ml volumetric flask and then sonicated at 25°C for 30min. The solutions were then centrifuged for 15min at 5200rpm. Finally the solutions were filtered through 0.45mm filters and analyzed spectrophotometrically [28].

In vitro drug release studies

The formulated patches are adhered to the cellophane paper and then attached to the franz diffusion cell such as that the drug releasing surface was towards the receptor 2 compartment with diffusion area of 0.785cm . The receptor compartment is filled with phosphate buffer of pH 7.4 at 37°C.The buffer is stirred magnetically. At predetermined intervals, samples (5ml) are withdrawn and replaced with the same volume of phosphate buffer. The collected samples were diluted with equal volumes of ethanol and the absorbance was recorded at 416.0 nm [29-31].

Results and discussion

Preformulation studies

Organoleptic properties of curcumin were determined by various tests. Curcumin was yellowish orange powder with acrid taste without any odor. Its melting point was found to be 181°C±1°C.

Determination of absorption maxima (λ max)

The wave length of light in the ultra violet range at which the compound shows the maximum absorbance is called as λmax. Calibration Curve of Curcumin at 416.0 nm is taken and curve show in Figure 1.

2 Correlation Co-efficient (r ) = 0.999 Equation for regressed line y =0.2043x-0.0044, Slope of regressed line =0.2043 Where x = Concentration (μg/ml), y = Absorbance (nm)

FTIR study

The FT-IR spectra of pure curcumin showed absorption -1 bands at 3629 cm which indicate the presence of OH -1 group. Peak at 2933cm indicate the presence of C-H -1 stretching. Peak at 1716cm shows ketone C-O stretching -1 and peak at 1312cm is attributed to enol C-O peak. Peak -1 at 1653 cm show the presence of C=C stretching. Peak at -1 1196 cm indicates the presence of O-H bend (phenolic).

-1 CH vibration of aromatic ring occurs at 814cm . Mixing curcumin with polymers in the form of physical mixture and development of optimized formulation did not show interference with the characteristic drug peaks. This finding confirms compatibility of the drug with the

Physicochemical evaluation of transdermal patches

Physicochemical evaluation of the prepared formulations (Figure 3) was carried out in terms of weight variation, thickness, folding endurance, moisture content, moisture uptake, swelling ratio, erosion and drug content. Variables like Moisture content, Moisture uptake, swelling ratio and erosion have a large impact on release behavior of drug from transdermal patches [24].

The moisture uptake, Moisture content, Moisture uptake, swelling ratio and erosion of all the formulations was determined (Table 5 and Table 6). It can be concluded that as the concentration of hydrophilic polymer (HPMC) increases in the patches, the Moisture content, Moisture uptake, swelling ratio and erosion of patches increases as the hydrophilic part of the polymer blend dissolves and erodes easily on contact with aqueous media.

Analysis of suitability of model

The essential components of this statistical design comprise of input variables and their response, experiment design, running experiment, statistical analysis and optimization of formulation. Multiple factorial designs was used to study the combined effect of process variables like HPMC concentration, EC concentration and natural oils concentration at different variables on dependant variables i.e. percent elongation and drug permeation. To analyze the adequacy of models, experimental data was fitted to various polynomial

Source Sequential p-value Adjusted R² Linear < 0.0001 0.9198

2FI 0.1432 0.9352 Quadratic 0.0304 0.9613 models including linear, interactive, cubic and quadratic and statistical tests such as sequential model sum of squares and model summary was prepared (Table 7 and

Folding % Drug Moisture % % Erosion

Predicted R²

0.8906 Suggested

0.8970 0.9170 Aliased

Source Sum of Squares df Mean Square

Mean vs Total 81375.95 1 81375.95

Linear vs Mean 3033.51 3 1011.17

2FI vs Linear 76.62 3 25.54 Quadratic vs 2FI 70.66 2 35.33 Residual 69.87 10 6.99 Total 84626.60 19 4454.03

Source Sequential p-value Lack of Fit p- Linear < 0.0001 0.0502

2FI 0.2036 0.0532 Quadratic 0.0012 0.0939

Source Sum of Squares df Mean Square

Mean vs Total 1.399E+05 1 1.399E+05

Linear vs Mean 856.97 3 285.66

2FI vs Linear 47.41 3 15.80 Quadratic vs 2FI 78.72 2 39.36 Residual 27.54 10 2.75 Total 1.409E+05 19 7415.92

Source Sequential p-value Adjusted R² Linear < 0.0001 0.8614

2FI 0.2607 0.8756 Quadratic 0.1188 0.9053

Source Sum of Squares df Mean Square

Mean vs Total 81972.01 1 81972.01

Linear vs Mean 2190.03 3 730.01

2FI vs Linear 83.21 3 27.74 Quadratic vs 2FI 75.01 2 37.51 Residual 123.91 9 13.77 Total 84444.17 18 4691.34

Source Sequential p-value Lack of Fit p- Linear < 0.0001

2FI 0.3023 Quadratic 0.0078

Source Sum of Squares df Mean Square

Mean vs Total 1.347E+05 1 1.347E+05

Linear vs Mean 786.01 3 262.00

2FI vs Linear 36.85 3 12.28 Quadratic vs 2FI 65.01 2 32.50 Residual 33.46 9 3.72 Total 1.357E+05 18 7536.32

Effect of formulation variables on % elongation of the film

ANOVA was used to evaluate experimental data and p value of regression coefficients was used to measure significance as shown in table 6. Percent Elongation is a

69.85 < 0.0001 Suggested

2.18 0.1432 5.06 0.0304 Aliased

value Adjusted R² Predicted R²

0.8175 0.7693 Suggested

0.8423 0.7813 0.9509 0.8993 Aliased

27.88 < 0.0001 Suggested

1.78 0.2036 14.29 0.0012 Aliased

Predicted R²

0.8078 Suggested

0.7899 0.7867 Aliased

36.22 < 0.0001 Suggested

1.53 0.2607 2.72 0.1188 Aliased

value Adjusted R² Predicted R²

0.8217 0.7694 Suggested

0.8348 0.7877 0.9314 0.8691 Aliased

27.11 < 0.0001 Suggested

1.37 0.3023 8.74 0.0078 Aliased A soft film has low percent elongation and tensile strength whereas hard and brittle films are characterized by low elongation and moderate tensile strength. A film having high tensile strength and high elongation is considered as soft and tough film [32]. So, in order to

Fit statistics

of film required percentage of plasticizer is incorporated [33]. The elongation percentage varies from 45-85.5% (peppermint oil) and 46-85.9% (jojoba oil) as shown in Table 2. Linear model was observed to fit for the percent elongation response with a p value and F value of <0.0001 and 69.85 in case of patches containing peppermint oil and <0.0001 and 36.1 in case of patches formulated with jojoba oil respectively. It was found that linear coefficients (A, B, C) were significant for the chosen model. P value was used to judge interaction strength between variables and significance of individual coefficients [34]. It is clear from the response surface plot that both concentration of natural oils and HPMC percentage (C) are the significant variables affecting the percent elongation in positive manner with a p value of

Source Sum of Squares df Mean Square

Model 3033.51 3 1011.17 A-HPMC 2730.79 1 2730.79 B-EC 83.59 1 83.59 C-peppermint oil 64.10 1 64.10 Residual 217.14 15 14.48 Lack of Fit 217.14 14 15.51 Pure Error 0.0008 1 0.0008 3250.65 18

Cor Total

Std. Dev. 3.80 R² 65.44

Mean Adjusted R²

C.V. % 5.81 Predicted R²

Adeq Precision

Source Sum of Squares df Mean Square

Model 856.97 3 285.66 A-HPMC 38.03 1 38.03 B-EC 837.85 1 837.85 C-peppermint oil 7.43 1 7.43 153.67 15 10.24

Residual

Lack of Fit 153.63 14 10.97 Pure Error 0.0450 1 0.0450 Cor Total 1010.64 18

Fit Statistics

Std. Dev. 3.20 R² 0.8479 Mean 85.81 Adjusted R² 0.8175 3.73 0.7693

C.V. % Predicted R²

Adeq Precision 14.2019 In response surface graphs such as contour and 3D plots (Figure 4), increase in HPMC proportion in the polymer mixture provides higher tensile strength to the film as shown in figure 4a, 4b, 4c and 4d. For a drug delivery <0.0001 (Table 9). Permeation enhancers weaken the cohesion forces between polymer chains or interrupt polymer chains thereby increasing mobility of chains and hence improving flexibility of polymer matrix [35, 36]. The accuracy of the model to determine the percent elongation of film was affirmed by the ANOVA of 2 observed values which yielded linear relationship with R value of 0.8078% (Table 9). The linear equation generated by software is given below:

% Elongation = +13.28*HPMC+ 2.12*EC+1.09* jojoba oil (patches containing jojoba oil as permeation enhancer) % Elongation = +14.59*HPMC-2.55*EC+1.85* peppermint oil (patches containing peppermint oil as permeation enhancer).

69.85 < 0.0001 significant 188.64 < 0.0001 5.77 0.0297 4.43 0.0526 19387.80 0.0056 significant 0.9332 0.9198 0.8906 21.7470 27.88 < 0.0001 significant 3.71 0.0732 81.78 < 0.0001 0.7257 0.4077 243.86 0.0502 not significant system for skin application a hard and tough film is desired [37]. In case of jojoba oil, the %R1 (85.9) was observed highest for experimental run 7 followed by 82 for experimental run 9.Similarly for peppermint oil, the % R1 (85.5) was observed highest for experimental run 17 followed by 80.5 for experimental run 8. It is revealed from Figure 4 that with increase in concentration of EC (hydrophobic polymer), decrease in tensile strength was observed. It can be concluded that the preparation

containing high concentration of HPMC and natural oils has higher tensile strength [22-23].

Effect of formulation variables on % drug permeation of the film

ANOVA was used to evaluate experimental data and pvalue of regression coefficients was used to measure significance as shown in table 6. Generally, the drug permeation is a good tool to illustrate the dissolution characteristics of the film [38]. A film that has low drug permeation has poor dissolution properties. The use of the proper percentage of permeation enhancer and the type and concentration of hydrophilic/hydrophobic polymer enhances the drug release from the film [39, 40]. The data presented in table 2 demonstrated that drug release percent ranged from 72.9 to 96.4% (peppermint oil) and 73.7 to 97.1% (Jojoba oil) respectively. Linear model was observed to fit for response % drug permeation with a p and F value of <0.0001 and 27.88 (Peppermint oil) and <0.0001 and 27.11 (jojoba oil) respectively. For this model linear coefficients A and B were found to be significant. P-value was used to determine the significance of individual coefficients and interaction strength between variables. From response surface plot it is revealed that the concentration of HPMC and natural oils are the major variables influencing the drug permeation percent in positive trend with p-value of <0.0001 (Table 10). The accuracy of the model was 2 confirmed by the R value (0.7694%) for patches containing peppermint oil and 0.8217 for patches containing jojoba oil respectively as determined by the ANOVA of the observed values which yielded linear relationships (Table 5). The linear equation generated by software is given below:

% Drug permeation = +1.99*HPMC-7.7*EC+0.8500* jojoba oil (patches containing jojoba oil as permeation enhancer) % Drug permeation = +1.72*HPMC-8.08*EC+0.6286* peppermint oil (patches containing peppermint oil as permeation enhancer).

Mean Square

Fit Statistics

From the equation it is revealed that both factors A and C have positive influence on the %drug release of the films.

It is also displayed in patches containing jojoba oil as permeation enhancer, factor A having coefficient value of 1.99 has higher impact than factor C having coefficient value of 0.8500.Similar results are observed in case of patches containing peppermint oil as permeation enhancer. Factor A has coefficient value of 1.72 while factor C has coefficient value of 0.6286. The response surface plots also show the same response as mentioned above. (Figure 5). Figure 5a, 5b, 5c and 5d reveals that as the proportion of HPMC increases in polymer mixture percent drug permeation also increases. Therefore, it was concluded that the increase in HPMC and natural oils percentage has direct influence on the film's drug permeation. With the increase in natural oil concentration (0.3- 0.4ml) and HPMC (300-100mg) concentration, drug release was found to increase. The percent drug permeation was observed to be highest (97.1%) for experimental run 7 followed by 96.5% for experimental run 9 in case of patches containing jojoba oil. Similarly, in case of patches containing peppermint oil, the drug permeation was found to be highest for experimental run 17 i.e 96.4% followed by 95.6% for experimental run 16.

Linear correlation plots are illustrated between observed and predicted values for the responses (Figure 6a, 6b, 6c

Source Sum of Squares df

786.01 3

Model

A-HPMC 47.60 1 B-EC 725.41 1 C-Jojoba oil 13.01 1 Residual 135.31 14 Cor Total 921.32 17 Std. Dev. 3.11 Mean 86.52 Adjusted R² C.V. % 3.59 Predicted R² 2 and 6d). The predicted R value in case of patches containing jojoba oil (0.7694) was in complete agreement 2 with adjusted R value (0.8217) as the difference between the two was found to be less than 0.2 and incase of 2 patches containing peppermint oil predicted R was found 2 to be 0.7693 and adjusted R value was found to be 0.8175. [22-23] Permeation enhancers decrease the lag time which occurs due to decrease in diffusional path length of drug which is attributed to changes in stratum corneum. Jojoba oil contains fatty acids like docosenoic, eicosenoic, myristic acid and oleic acid. Myristic acid is reported to have similar composition as skin oil which leads to complete and faster absorption of drug. Oleic acid also enhances the epidermal permeability by perturbation of stratum corneum lipid bilayers and lacunae formation thereby distrupting molecular packaging and level of hydration which contributes to increased permeation [41]. Peppermint (Mentha piperita Linn.) itself acts as anti-inflammatory agent, can exert synergistic effect on inflammation [42]. Release of drug in patches containing peppermint oil depends on presence of terpenes i.e cineol, limonene and pinene and menthol. Terpenes loosen the existing network of hydrogen bonds between ceramides which results in higer permeation of drug across stratum corneum [41,43].

262.00 27.11 < 0.0001 significant 47.60 4.93 0.0435 725.41 75.05 < 0.0001 13.01 1.35 0.2655 9.67 R² 0.8531 0.8217 0.7694

(a) (b)

Optimization

As we all know that release of drug from transdermal film varies with structure and morphology of polymer matrix and physicochemical properties of drug [44]. Hydrophilic nature of HPMC(X1) exerts positive effect on release of curcumin owing to its high water absorbing property.

This in turn increases the porosity and pore diameter of polymer matrix thereby allowing drug molecules to diffuse out easily [45]. Moreover increase in HPMC loading results in faster dissolution of polymer matrix resulting in formation of channels for diffusion of drug from the film [46]. On the other hand natural oils also contribute to good permeation of curcumin. It also enhances curcumin diffusion by decreasing the skin barrier resistance reversibly. It has also been indicated in literature that if the drug is soluble in polymer matrix, its thermodynamic activity increases in base resulting in its enhanced permeation [47-49]. As a final point after analysis of experimental variables an optimum formulation of curcumin film containing peppermint oil Responses Predicted Observed % Elongation 66.44 68.3 % Drug release 85.50 83.9 Residual = predicted value-observed value with acceptable drug release and elongation was derived to contain 200mg HPMC, 150mg EC and 0.35ml of oil (Figure 7). In case of patches containing jojoba oil the optimum formulation was found to contain 300mg of HPMC, 100.21mg of EC, and 0.39ml of oil (Figure 8). The observed, predicted values, the residuals and prediction error percentage for the optimized formulation is demonstrated in Table 11 and Table 12.

Desired mechanical and physicochemical properties were ensured by the predicted values of responses for optimized formulation. The predicted values of responses for the optimized transdermal film were very close to the observed values with no considerable prediction error percentage (below 6%) and residuals. This outcome confirms that the optimization technique used is highly reliable and reproducible for the development of curcumin transdermal film with high quality attributes [22, 23].

Residual Prediction error (%) ±1.9 2.861 ±1.6 1.871

Prediction error = predicted value-observed value/predicted value*100.

Responses Predicted Observed % Elongation 79.7 81 % Drug release 97.1 96.5 Residual = predicted value-observed value Residual Prediction error (%) ±1.3 1.6311 ±0.6 0.6179

Conclusion

The multiple factorial designs was an efficient tool in optimizing the three variables used to prepare curcumin TDDS through studying their effect on the quality attributes and permeation behavior of the prepared curcumin-loaded transdermal films. The optimized formulations showed good physicochemical and mechanical properties as well as enhanced permeation characteristics. Patches containing jojoba oil as permeation enhancer showed better in vitro permeation and elongation than patches containing peppermint oil. The in vitro study reveals that the formulations containing natural oils as permeation enhancers and herbal drug (curcumin) has the potential to be used as effective alternative to the current drugs available in the market to treat arthritis. More research, optimization and invivo studies of herbal formulations must be done to get better products in future.

References

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