PREPARATION, CHARACTERIZATION AND STABILITY STUDIES OF SOLID SELF EMULSIFYING DRUG DELIVERY SYSTEM OF NIFEDIPINE

Objective: The objective of this work was to improve the solubility and dissolution rate of Nifedipine by preparing a solid-self micro emulsifying drug delivery system (Solid-smedds). Methods: Liquid-self-emulsifying drug delivery system formulations were prepared by using linseed oil as oil, tween 80 as a surfactant and PEG 400 as cosurfactant. Components were selected by solubility screening studies and the self-emulsifying region was identified by the pseudo-ternary phase diagram. Thermodynamic stability study was performed for the determination of stable liquid-smedds formulation. These formulations were evaluated for self-emulsification time, drug content analysis, robustness to dilution test, particle size analysis, in vitro diffusion study, and Stability study. Solid self-micro emulsifying formulations were prepared by using aerosil-200 at a different ratio. Lf9S (0.65:1) was selected due to its highest drug entrapment efficiency and a decrease in particle size. It was selected for further studies into DSC, SEM, FTIR, and XRD analysis. Results: DSC and XRD result shows that the drug within the formulation was in the amorphous state. From the SEM study, it was observed that the drug has been uniformly distributed and having a smooth surface. From the in vitro dissolution study, it improved the dissolution rate of nifedipine which was 98.70% of drug release where pure drug release only 6.72%. Conclusion: In conclusion, a solid self-micro emulsifying drug delivery system the and drug release also improved the stability of the formulation.


INTRODUCTION
Around 40% of recent drug candidates become poor water solubility and also the oral deliveries of those medicines are usually related to high intrasubject and inter-subject variability, a lack of dose proportionality, low bioavailability. To overcome these issues, several formulation ways are utilized together with specific utilization of surfactants, lipids, permeation enhancers, micronization, salt formation, cyclodextrins, solid dispersion. Newly, the lipid-based formulation has gained a lot of attention with special importance on self-emulsifying drug delivery systems (SEDDS) which is used to boost the bioavailability of orally administered lipophilic drugs. SEDDS or self-emulsifying oil formulations (Seof) outlined as isotropic mixtures of natural or synthetic oils, solid or liquid surfactants or instead, one or additional hydrophilic solvents and co-solvents/surfactants [1]. On delicate agitation, these systems will form fine o/w emulsions (oil-in-water) or self-micro emulsifying drug delivery system (SMEDDS) or microemulsions followed with dilution into liquid media, like epithelial duct (GI) fluids [2]. SEDDS effectively produce emulsions with a droplet size range of 100-200 nm for SMEDDS whereas SNEDDS produce less than 100 nm [3].
Nifedipine is a dihydropyridine calcium channel antagonist that belongs to BCS class-II mainly applied in the treatment of hypertension and angina-pectoris administered by the oral route. It is the most common kind of calcium channel blocker (CCB) and is used for the treatment of hypertension as well as stable, unstable and prinzmetal angina. It is known to exhibit its antihypertensive effect at a very low plasma concentration of 13.4 mg/ml [5]. Taneja et al. [4] had developed a pulsatile microsphere of nifedipine for the treatment of hypertension. It showed slow release of drug initially for 4 h. and at a particular lag time, it followed pulsatile release (after 6 h). In recent studies, nifedipine in combination with Valsartan and Candesartan lowers blood pressure effects in highrisk individuals. Mancia et al. had examined the effects of nifedipine GITS-candesartan cilexetil combination at various doses. This combination therapy has been proved that the effect of blood pressure was lowered as well as decrease the incidence of vasodilatory side effects [5]. Another achievement for the development of a microemulsion system of nifedipine and valsartan which was administered transdermally invitro(rat skin) to observe the permeation rate. The study was suggested that the microemulsion system improved the solubilization as well as transportation of both drugs across rate skin [6].
On another side, nifedipine is used in the treatment of angina, but at high doses, nifedipine increased the risk of out of hospital cardiac arrest due to fatal cardiac arrhythmia [7]. Another important aspect has been reported that nifedipine can promote breast cancer and should be avoided for women who suffer from breast cancer and hypertension. From the report, it was identified that the effects of nifedipine on MCF-7 cells were via the protein kinase B-endothelial constitutive nitric oxide synthase-nitric oxide axis, and on MDA-MB-231 cells via activation of the extracellular signal-regulated kinase pathway [8].
In this study, an attempt was made to improve the solubility and in vitro dissolution of nifedipine by formulating it as S-SMEDDS. Nifedipine, Dimethyl 2, 6-dimethyl-4-(2-nitrophenyl)-1, 4 dihydropyridine-3,5-dicarboxylate, has poor aqueous solubility resulting in low and often irregular bioavailability. The present work provided in improvement in the dissolution rate for nifedipine when formulated as self-emulsifying drug delivery systems. The selfemulsifying mixture that combines good self-emulsifying properties, acceptable solubilization of nifedipine and optimum surfactant, cosurfactant/co-solvent composition was selected, evaluated for droplet size, stability, dissolution, and a Solid SMEDDS was prepared using aerosil 200 as adsorbent. The solid SMEDDS was further evaluated by in vitro dissolution studies and characterized by Scanning electron microscopy (SEM), Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR).
Drug release is a vital and rate-limiting step, mainly for drugs with low solubility and high permeability i.e., biopharmaceutical classification system BCS class II drugs. SEDDS is the technique that can be used to enhance the solubility and dissolution rate of poorly water-soluble drugs.
But Liquid SEDDS having problems like the irritating effect of a high percentage of surfactant on the gastrointestinal mucosa, lower formulation stability and plausible interaction of excipients with capsule shell. To surmount these ostensible problems associated with liquid SEDDS a new technology is investigated known as solid S-SEDDS [9,10]. Solid SEDDS are the solidified self-emulsifying formulation which is prepared by converting liquid/semisolid SEDDS into selfemulsifying powders/nanoparticles by using various solidification techniques such as, nanoparticle technology, melt extrusion, spray drying, and adsorptions to solid carriers [11].

Materials
Nifedipine was a gift sample from G. C. Chemie Pharmie Ltd; Mumbai, India. Almond oil, Soybean oil, castor oil, and linseed oil were supplied by Merck Pvt. Ltd. Tween 80, tween 20, tween 40, span 20 were supplied from Sisco research laboratories Pvt. Ltd. PEG 400, PEG200, propylene glycol, glycerol, PEG 600 were supplied from Sisco research laboratories Pvt. Ltd. Aerosil 200 was supplied from yarrow Chem product Pvt. Ltd.

Solubility screening study
The highest amount of drug solubility was determined by the shake flask method. 500 mg of nifedipine was added to 5 ml of each vehicle containing oil, surfactant, and cosurfactant. Then the mixture was shaken for 72 h to reach a uniform equilibrium state. It was centrifuged (Remi centrifuge equipment) for 10 min. at 5000 rpm. The supernatant was collected and diluted with phosphate buffer (pH 6.8). and quantified by spectrophotometrically at λmax of 238 nm [12,13]

Construction of pseudoternary phase diagram
After the selection of higher drug solubility containing excipients (oil, surfactant, and cosurfactant), the pseudo ternary phase diagram was prepared at 1:1 and 1:2 ratio of the mixture of surfactants and co-surfactants. It determines the self-emulsifying region by taking the different ratios of oil and mixture of surfactant and co-surfactant [Oil: (S-COS) mix] from 9:1 to 1:9. The water was titrated into the mixture with constant stirring to observe the formation of o/w microemulsion The pseudo ternary phase diagram was constructed using software Chemix School (ternary software) [13].

Preparation of sedds formulation of nifedipine
Different SEDDS formulations were prepared by using oil (Linseed oil), surfactant (tween 80) and co-surfactant (PEG 400). In each formulation, the amount of nifedipine (i. e-100 mg/10 ml) was constant. Each of the excipients was exactly weighed and gently mixed. Then the prepared mixtures were mixed with the help of a magnetic stirrer until a homogenous mixture was prepared. Then the prepared homogenous mixture was stored at 25⁰C for further studies [14].

Thermodynamic stability studies
Thermodynamic stability study was done to observe any signs of phase separation, drug precipitation, creaming or cracking. All the smedds formulations were diluted with distilled water and centrifuged at 3500 rpm for 15 min. and check for any phase separation or clear emulsion. Then it was exposed to heating-cooling cycle (4 °C and 45 °C) and freeze-thaw stress cycle (-21 ° and+25 °C) with storage at each temperature for not less than 48 h. All the testing was done in triplicate and observes the extent of phase separation [15].

Self-emulsification time
After thermodynamic stability testing, the stable formulations were taken for visual assessment self-emulsification efficiency. Self-emulsification efficiency study was performed in the USP XXIV type II dissolution apparatus. 1 ml of each smedds formulation was added dropwise into 500 ml of buffer pH 6.8 and 1.2. and maintained at 37 °C with a rotating speed of 50rpm. Then the time is noted for complete emulsification in two different media [16].

Drug content analysis
The liquid-smedds formulation containing 10 mg equivalent drug was taken into 100 ml volumetric flask and diluted it with phosphate buffer pH 6.8 and analyzed by U. V. Visible Spectrophotometer at the λmax of 238 nm.

Droplet size and zeta potential
The droplet size of smedds formulation was determined using a zeta sizer Nano ZS (Malvern instrument, UK) dynamic light scattering particle size analyzer at a wavelength of 635 nm and a scattering angle of 90 °C at 25 °C. The formulation (0.1 ml) was diluting with 100 times with double distilled water and sonicated for at least 30 min. for the reduction of particle size of emulsion [17,18].

Robustness to dilution
All the formulations were taken for checking the robustness of emulsion in diluting with enzyme-free phosphate buffer ph6.8 (simulated intestinal fluid) and 0.1N HCL (simulated gastric fluid). 1 ml of each formulation was subjected to 50, 100, 500, 1000 fold dilution and kept them for 24h. After that, all the formulations were checked for any change in physical appearance i.e. coalescence of oil droplets, drug precipitation or phase separation [19].

In vitro diffusion studies of smedds
The drug release experiment was performed in USP XXIII rotating paddle method using a dialysis bag method. The dialysis membrane was shocked in dialysis media (buffer pH6.8) for 12hr. at room temperature. After that, the liquid-smedds containing 100 mg of nifedipine were filled into soaked dialysis membrane and closed both sides of the dialysis membrane by using thread. Then it was put into the vessel containing 900 ml of phosphate buffer pH6.8 carefully by which the dialysis membrane can easily rotate. The dissolution was performed at 37±0.5 °C for and rotated at 50 rpm for 120 min. At a specific time interval i.e. 15, 30, 45, 60, 75, 90, 105, 120, the aliquot of 5 ml was withdrawn and filtered through a 0.45 µm membrane filter. The same volume of the withdrawn amount should be replenished to maintain the sink condition of dissolution. The concentration of nifedipine was determined by spectrophotometrically at 238 nm. The dissolution of each formulation was performed in triplicate times. The dissolution profile of stable formulations was prepared and compared with the dissolution profile of the pure drug [20,21].

Stability studies
The liquid-smedds sample (LF9L) was selected for stability study at 25±0.5˚C/60±5 % RH(relative humidity) and 40±0.5˚C /75±5 % RH for 3 mo. It is filled in glass vials with a rubber stopper and then placed in Stability chambers. The physical appearance, drug content analysis, and particle size were evaluated with each 1-month interval [22].

Preparation of solid-smedds
Solid self-emulsifying powder formulation was prepared by using adsorption to the solid carrier method, which is a very simple and reliable technique. The optimized formulation was taken for solidsmedds preparation. Aerosil 200 was used in a different ratio to prepare solid smedds in the ratio of 0.50:1, 0.55:1, 0.65:1(adsorbent: liquid smedds). The adsorbent and liquid smedds were mixed in a porcelain dish until a uniform homogenized free-flowing powder was obtained. Then the powder was passed through sieve no. 120 and dried at ambient temperature for further use. These formulations were evaluated for flow property. The developed optimized formulation was characterized for particle size analysis, percentage of drug content and in vitro dissolution study, scanning electron microscopy study(SEM), X-ray diffraction study(XRD), differential scanning calorimetry (DSC), and f. t. i. r study(Fourier transform infrared spectroscopy). The evaluation study was carried out for optimized formulation and compared with pure drug.

Flow properties of solid-smedds
Flow properties of solid smedds were determined by Carr's method. All the samples (0.50:1, 0.55:1, 0.65:1) were poured through the funnel in which the height of powder and its radius was obtained. The angle of repose was calculated using equation tan θ= H/r. The powder preparation having good flow property was selected as an optimized formulation and taken for particle size analysis and drug content analysis [23].

Drug content analysis of solid smedds
SEDDS formulation (equivalent to 10 mg of the drug) was diluted with 100 ml of pH 6.8 phosphate buffer. It was diluted suitably with Phosphate buffer pH 6.8. It was analyzed using UV/vis. Spectrophotometer at 238 nm [24].

The particle size of solid smedds
The particle size and zeta potential of the selected formulation were determined using Zetasizer Nano ZS(Malvern instrument, UV). The formulation was diluting with 100 times with distilled water then the emulsion was taken for analysis of particle size at 25 ⁰C at 90 ⁰C angle [24].

Solid state characterization of optimized solid selfmicroemulsifying formulation
The optimized solid-smedds was analyzed for ftir, DSC, XRD, and SEM analysis to investigate its solid-state properties. DSC thermogram was analyzed in Mettler Toledo DSC. F. t. i. r analyzes the compatibilities between drug and excipients present in the formulation. Each sample was scanned in a ftir spectrophotometer (Spectrum 2 FTIR spectrophotometer, Perkin Elmer) at a range of 4000-400 cm-1. The XRD analysis of the sample was analyzed in an x-ray diffractometer (Rigaku Ultima IV, Japan) and SEM of selfemulsifying powder was performed in the SEM instrument (Zeiss EVO 18 special edition) [25].

In vitro drug release
The in vitro drug release study of solid smedds was performed in the USP XXIII dissolution apparatus at temperature 37±0.5 °C with a rotation speed of 50 rpm. The s-smedds formulations (equivalent to 100 mg) were put into the vessel containing 900 ml buffer pH 6.8(enzyme free simulated intestinal fluid). The entire dissolution was performed for 2 h. At predetermined periods, samples were withdrawn and diluted with phosphate buffer. Then the diluted sample was filtered using a 0.45 µm membrane filter and analyzed drug concentration on UV-spectrophotometer at λmax 238 nm. The same volume of fresh media was replaced after each interval of withdrawn of the sample to maintain the dissolution media constant.

Stability studies
The stability study of optimized s-smedds was performed at 40 °C±2 °C and 75%±5% RH and 25±0.5˚C/60±5 % RH for three months. The samples were analyzed for physical appearance, particle size, and drug content analysis after each one-month interval.

Statistical data analysis
For the data analysis, a one-way analysis of variance (ANOVA) was used to compare the difference between solid-smedds, liquid smedds, and pure drugs by using mean value±standard deviation (SD).

RESULTS
Self-emulsifying preparation is a monophasic clear emulsion that contains oil, surfactant, and co-surfactant. For the analysis of solubility with nifedipine linseed oil, soybean oil, and almond oil were as oil, tween 60, tween 40, span 20 and tween 80 were as a surfactant and PEG 400, PEG 200, PPG, PEG 600 were taken as cosurfactants. The results of solubility in various vehicles were represented in fig. 1. From the analysis, it has been shown that nifedipine shows high solubility in linseed oil (61.23±0.95 mg/ml), Tween 80 (56.47±0.92 mg/ml), PEG 400 (49.98±0.15 mg/ml). Linseed oil is a natural and long-chain triglyceride oil, which have a good solvent capacity for dissolving drugs. Tween 80 is a hydrophilic nonionic surfactant that has a good solubilizing capacity and PEG 400 as co-surfactant which lowers the interfacial tension. Fig. 1: Solubility studies of drug with various oils, surfactants, and cosurfactants. (mean±SD, n=3)

Pseudo-ternary phase diagram
Proper concentration of vehicles that produce stable emulsion must be essential to prepare self-emulsifying formulations. The pseudo ternary phase diagram defines the ternary phase behavior between components and provides proper concentration to prepare a stable emulsion. After water titration, the amount of water used was noted and developed the ternary phase diagram by using ternary software which has written in the method part. Fig. 2(a) and (b) represents the ternary phase diagram of smedds between castor oil, tween 80 and PEG 400 (blue colored region indicate the region of selfemulsification produced by SCOSmix 1:1 ratio and 1:2 ratio. The ternary diagram indicates that among both the SCOSmix ratio, a 1:1 ratio provides a wide self-emulsification region. So this ratio was taken as the superlative ratio for preparation smedds.

Preparation of smedds of nifedipine
After the selection of oil, surfactant and co-surfactant and emulsification region, nine self-emulsifying formulations were prepared at 1:9 to 9:1 ratio where SCOSmix was 1:1 ratio. In all the mixture nifedipine (equivalent to 100 mg) was mixed and kept them for 24 h. at 25 °C. After 24 h., LF1L, LF2L, LF3L, LF4L, LF5L, LF6L, and LF9L were selected as stable because they showed no sign of phase separation and unstable formulations (LF7L and LF8L) are rejected as they showed phase separation.

Thermodynamic stability study
Seven formulations showed stability i.e. there was no phase separation, the appearance of coalescence of oil droplets or any cracking appearance after keeping them for 24 h. of storage. Four formulations were remained stable after thermodynamic stability studies. But three formulations showed phase separation after freeze-thaw stress testing. So four formulations i.e. LF2L, LF3L, LF4L, and LF9L were taken for the evaluation study. Each test was done in triplicates.

Droplet size and zeta potential analysis
In the self-emulsification performance, the particle size of the emulsion is a crucial factor, because it determines the rate and extent of drug release as well as drug absorption. The particle size of formulations was in the nanometer range. LF9L showed a low particle size (249.1 nm) as compared to others. An increase in the ratio of the oil phase and a decrease in the S-Cosmix ratio resulted that the increase in particle size. Smaller in particle size increases drug release and delivers larger interfacial area across which drug can diffuse into the gastrointestinal fluids and thus increases drug absorption.
Zeta potential of linseed oil formulation found to be-16.9 as a negative value which shows that due to the ionization of free fatty acids and glycols present in the oil and surfactants which improves formulation stability by preventing globule coalescence

Drug content analysis
From the drug content analysis, the result showed that three formulations, LF2L, LF3L, LF4L, and LF9L contained between 69.25% to 79.05%.

Robustness to dilution test
Robustness to dilution study is performed to observe the effect of formulation on different pH. In this study, LF2L was unstable because it showed signs of phase separation when diluted with phosphate buffer (pH 6.8) and 0.1N HCL but LF3L, LF4L, and LF9L formulations remained stable for 24hr of dilution with both pH 6.8 and 0.1N HCl. LF2L was rejected for further study due to the observation of phase separation.

In vitro diffusion study of optimized smedds formulation
From the robustness to the dilution test, LF2L was not selected for the in vitro drug diffusion study. The diffusion study of three formulations i.e. LF3L, LF4L, LF9L was performed for 2hr. using a dialysis bag method. The diffusion of the drug from prepared smedds and the pure drug was indicated in fig. 3. The result from in vitro diffusion studies was indicated that LF9L formulation showed more drug release of 54% at 2 h. While pure drug release nifedipine only 6.72% at 2 h. LF3L and LF4L release 45.35% and 46.63%, which was less in comparison to LF9L formulation. Because these formulations contain more oil and less surfactant concentration which produces interruption with the release of the drug into the dissolution media. Drug release at 120 min was compared between LF9L formulation and pure drug using one way ANOVA. From the data analysis, it was suggested that, nifedipine release from LF9L formulation much faster and higher in comparison to the pure drug ( * P<0.05). When SEDDS were exposed to aqueous media, it produces oil in water (o/w) microemulsion, having small globule size. The small globule size permitted drug release at a rapid rate from microemulsion.

Stability study
Based on all evaluation LF9L was selected for stability study to observe any physical and chemical changes within the formulation. The stability study was performed according to ICH guidelines for 3 mo. Initially, the drug content (79.05%), particle size (249.1 nm) and zeta potential (-16.9mv) of LF9L were measured. After 3 mo, at accelerated condition((40±2˚C /75±5 %) the %drug content was reduced to 63% and at 25±2˚C/60±5 %, the %drug content was 69% which indicated that the instability of the formulation was observed due to decrease in assay content. After 3 mo, Particle size was 262.3 nm and zeta potential was-22.3mv at the accelerated condition. Particle size and zeta potential were measured in zeta sizer and results were represented in fig. 4(a) and (b).

Micromeretic study
The flow property of three smedds powders was determined by calculating its angle of repose, tapped density, bulk density, Hausner's ratio, and Carr's index. Out of three formulations, LF9S has good flow property due to its value of angle of repose (22.3), Carr's index (%) (15.6%) and Hausner's ratio (1.15).

Particle size and zeta potential of LF9S
After solidification, the particle size of LF9S was 208.3 nm and zeta potential was-25.8mv which was represented in fig. 4(a) and (b).

Drug content analysis
After solidification, the drug content analysis of LF9S was 85.26% which may be due to reduced particle size after solidification.

Solid-state characterization of LF9S
FTIR spectra of nifedipine (pure drug) and LF9S was represented in fig. 6(A). It was shown that the characteristic peaks of the pure drug were 3328.70 cm-1 (N-H stretching of amine group), 2952.90 cm-1 (C-H aliphatic stretching), 1677.73 cm-1 (C=O stretching of carboxylic group), 1622. cm -1 (C=C aromatic alkene stretching), 1527.07 cm-1 (NO2 stretching) which were observed in the FTIR spectra of LF9S. So it was indicated that there were no chemical incompatibilities between drug and excipients present I formulation.
The X-ray powder diffractometry ( fig. 6(B)) of the pure drug shows some sharp and intense peak which indicated that the drug is present in the crystalline state. The presence of those intense small and sharp peaks was also observed in the physical mixture of drug and aerosil200 which showed that the drug present in the physical mixture is the semi-crystalline state. But in LF9S formulation, the sharp and intense peaks were disappeared which indicated that the drug present in the formulation is in an amorphous state.
DSC thermogram of nifedipine (pure drug) and LF9S was presented in fig. 6(C). DSC of nifedipine shows a sharp endothermic peak at 175 °C, corresponding to its melting points, indicating the crystalline nature of the drug. DSC of LF9S did not show any endothermic peak corresponding to its melting point. So it was concluded that the formulation was present as amorphous or solubilized form. There was a complete absence of crystal structure which represented that the drug was present in the formulation as an amorphous state.

In vitro drug release
The drug release study of LF9S was performed and compared with the release pattern of pure drug and LF9L (smedds formulation). The in vitro dissolution profile of LF9S, pure drug and LF9 was represented in fig. 7. After 1 h of dissolution, LF9S released drugs more than 75%, in which LF9 and pure drug released only 17.22±0.26% and 2.54±0.04% respectively. At 120 min. LF9S release drug more than 97% which was significantly higher than pure drug and LF9L ( * P<0.05). Drug release from LF9S was faster due to increased surface area by use of adsorbent Aerosil 200, increasing the porosity of the formulation and may be due to transformation from crystalline to amorphous form.

Stability study
The stability of LF9S was performed according to ICH guidelines for 3 mo. Initially, the drug content (85.26%), particle size (208 nm) and zeta potential (-18.7mv) were measured. After 3 mo, at 40±2˚C/75±5 %, the % drug content was reduced to 81.39% and at 25±2˚C/60±5 %, the %drug content was to 84.67%. After 3 mo, the Particle size and zeta potential of LF9S were 249.4 nm and-32.2mv respectively ( fig. 8). So there was no such significant difference observed in the assay study. After solidification, the stability is improved as a comparison to LF9 (liquid smedds).  Surfactant and cosurfactant were mixed at 1:1 ratio and 1:2 ratios in which the mixtures of oil, surfactant, and co-surfactant were prepared at 1:9 to 9:1 ratio. From the pseudo-ternary phase diagram, SCOSmix (1:1) produced a reasonably wide selfemulsification region than a 1:2 ratio. The efficiency of emulsification was good when the composition of the surfactant/co-surfactant was taken at the same concentration. It was constructed based on the observations marked during titration after building the phase diagram of different formulations were selected at different point of the ternary phase.
Different formulations were prepared at different concentrations of oil, surfactant, and cosurfactant. Formulations containing (70-80%) oil and SCOSmix (20%-30%) were rejected due to phase separation. Phase separation was initiated because the ratio of oil and SCOSmix contained in the formulation shown incompatibilities keeping after 24h. The seven formulations were stable out of nine formulations. These formulations (9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 1:9) were exposed to heating cooling process, freeze thaw stress testing, centrifugation testing (table 1). Among those, three formulations showed phase separation after freeze-thaw stress testing because of the intolerance of excipients with a change in temperature. These three stable formulations were taken for particle size analysis, drug content analysis, and robustness to the dilution test. Robustness to dilution test was performed at different pH media pH 1.2 and 6.8 to mimic the in vivo conditions revealed no precipitation or phase separation indicating all the formulations were found to be robust towards different pH conditions [11]. So at both pH conditions LF3L, LF4L, LF9L shown stable i.e. no phase separation and drug precipitation after 24hr. But LF2L shown phase separation at both pH conditions. Because the robustness of formulation LF2L after dilution was decreased at both pH conditions (table 2). As the discussed previously the particle size of LF9L was 249.1 nm and zeta potential-16.9mv which shown the least particle size than other formulation. The particle size of LF9L was decreased because the presence of the low amount of oil. As the concentration of SCOSmix is increasing the particle size is decreased. The smaller droplet size indicates more rapid absorption and improves the bioavailability of drug [26]. Due to its least particle size, the percentage of drug content is high and the percentage of drug release was more (54%) in comparison to other formulation and pure drug (6.72%). It may be due to proper composition between proportions of oil and SCOSmix which produced smaller droplet size with the highest drug content in the system. Due to its highest drug content, small droplet size and highest percentage of drug release LF9L is an optimized formulation for further study. It was exposed to different accelerated stability condition for 3 mo at 40 °C±2 °C and 75%±5% RH and 25±0.5˚C/60±5 % RH. After 3 mo the percentage of drug content, particle size, and zeta potential analysis ( fig. 9) were performed. It was seen that the percentage of drug content was reduced and the particle size (262.3 nm) and zeta potential (-22.3mv) were increased due to the rise of instability in the formulation. The instability may be due to incompatibilities with the soft gelatin capsule shell and/or oxidation of lipids present in sedds [27].
So to improve stability, the solid smedds was prepared by using solid adsorbent aerosil 200 at a different ratio. Aerosill 200 is hydrophilic colloidal silicon dioxide which allows to attract and bind moisture to eliminate liquid bridges between solid particles that hinder powder flow [28]. Aerosil 200 was taken at a different ratio to determine the formulation of having good flow property. LF9S was selected due to its good flow property having angle of repose (22.3), Carr's index (%) (15.6%) and Hausner's ratio (1.15). The selected solid smedds LF9S was taken for drug content analysis, particle size, and zeta potential analysis. The percentage of drug content was more due to complete and uniform adsorption of sedds into aerosil 200. The particle size and zeta potential were 208.3 nm and-25.8mv which was less in comparison to liquid sedds ( fig. 5). From the f. t. i. r study, there were no incompatibilities between drug and excipients due to presence of same characteristics peaks in formulation and pure drug ( fig. 6(A)). From the x-ray diffractometric study, the drug present in the formulation is in the amorphous state. It may be due to the uniform adsorptivity of the drug throughout the adsorbent ( fig. 6(B)). The scanning electron microscopic study of formulation showed that the shape of the particle is uniform and distributed uniformly throughout the solid carrier ( fig. 7). From the differential scanning calorimetry, LF9S was present in the formulation at an amorphous state because it showed a straight line within a melting point (175 °C) ( fig. 6(C)). The in vitro dissolution study was performed for 2h. at pH 6.8 dissolution media. At 120 min. LF9S release drug more than 97% which was significantly higher than pure drug and LF9. Drug release from LF9S was faster due to increased surface area by use of adsorbent ( fig. 8). Aerosil 200, increasing the porosity of the formulation and may be due to transformation from crystalline to amorphous form. After an in vitro dissolution study, LF9S was taken for accelerated stability study for a minimum period of 3 mo at 40 °C±2 °C and 75%±5% RH and 25±0.5 °C/60±5 % RH. The drug content analysis, particle size, and zeta potential analysis was performed. The particle size and zeta potential were 249.4 nm and-32.2mv. Which describe that LF9S lied within micron range. There was no such significant difference observed in assay study, particle size and zeta potential analysis. After solidification, the solubility as well as stability was improved as a comparison to LF9L (liquid smedds) formulation.

CONCLUSION
Solid-self emulsifying drug delivery system of nifedipine was successfully prepared by using linseed oil as oil part, Tween 80 as a surfactant, PEG 400 as co-surfactant and Aerosil 200 as adsorbent. Nine liquid self-emulsifying formulations were prepared at a different ratio. The best self-emulsifying formulation (LF9L) which was optimized by different evaluation process and stability study. At accelerated condition after three months, the percentage of drug content was reduced which indicated that the formulation was in instability condition. So to improve stability of the liquid self-emulsifying formulation, it was converted to s-sedds by adsorption to solid carrier technique using aerosil200. After solidification, drug content was more than 85.26% and the particle size was 208 nm. From the in vitro dissolution study, LF9S release 98.70%, which was highest among LF9L and pure drug. From the FTIR study, it was indicated that there were no incompatibilities between drug and excipients. From the DSC and XRD study, it was shown that the drug was present in the formulation as an amorphous form. From the stability analysis, it was seen that no significant difference was observed during drug content analysis. Thus it was concluded that solid SEDDS formulation is capable to enhance solubility and dissolution of poorly water-soluble drugs like nifedipine by using aerosil 200 which improves therapeutic performance.