INTRODUCTION:

Microsponges are solid phase, porous, polymeric microspheres that have large porous surface for effective drug loading. Microsponges deliver a drug efficiently at minimum dose and also enhance the stability of drug, reduce side effects, and modify drug release profiles

Microsponges comprises of highly cross-linked, polymeric porous microspheres consisting numerous interconnected voids in the particle, loaded with active pharmaceutical agent within a collapsible structure. Microsponges have large porous surface to entrap wide range of active pharmaceutical agents in different doses that can be released at desired site of absorption. The pores of microsponges forms continuous arrangement open towards the exterior surface of microsponges which allows the outward diffusion of the entrapped drug with a controlled rate depending upon the size of the pores.^{2, 3}

Celecoxib is a highly selective COX-2 inhibitor and primarily inhibits this isoform of cyclooxygenase (and thus causes inhibition of prostaglandin production), whereas traditional NSAIDs inhibit both COX-1 and COX-2. Celecoxib is approximately 7.6 times more selective for COX-2 inhibition over COX-1. In theory, this selectivity allows celecoxib and other COX-2 inhibitors to reduce inflammation (and pain) while minimizing gastrointestinal adverse drug reactions (e.g. stomach ulcers) that are common with non-selective NSAIDs.⁴

Materials and methods:

Various materials and equipment’s used to carry out the experimental work are given in the following list:

Table 1: List of Materials for Formulation

Material	Procured from
Celecoxib	Prudence pharma
Eudragit S100	Evonik
Polyvinyl alcohol	SD fines
Triethyl Citrate	SD fines
Ethanol	Merck
Sodium lauryl sulphate	SD fines
Purified Water	-Inhouse

Table 2: List of Reagent

Sr. No.	Reagents	Suppliers of Materials
1	Hydrochloric acid	SD fines
2	Phosphate buffer 6.8	SD fines
3	Phosphate buffer 7.2	SD fines

Formulation of Microsponges:

Drug loading in microsponges can be effected in two ways, one-step process or by two-step process; based on physico-chemical properties of drug to be loaded. If the drug is typically an inert non-polar material, it will create porous structure. Such drug is called porogen. Porogen drug, which neither hinders the polymerization nor become activated by it and stable to free radicals is entrapped with one-step process.

Quasi-emulsion solvent diffusion method:

The microsponges can also be prepared by quasi-emulsion solvent diffusion method using the different polymer amounts. To prepare the inner phase, polymer is dissolved in ethyl alcohol. Then, drug can be then added to solution and dissolved under ultrasonication at 35˚C. The inner phase is poured into the PVA solution in water (outer phase). After 3 hour of stirring the microsponges were formed. The microsponges were filtered and dried at 40°C for 8 hours.⁵

Table 3: Composition of Various Microsponge Formulations:

Batch	Dug: Polymer ratio (w/w)	Drug(mg)	Polymer(mg)	TEC (%, w/v)	Ethanol (ml)	PVA solution (% w/v)
M1	1:1	300	300	1	20	2
M2	2:1	400	200	1	20	2
M3	3:1	600	200	1	20	2
M4	4:1	800	200	1	20	2
M5	5:1	1000	200	1	20	2
M6	1:2	200	400	1	20	2
M7	1:3	200	600	1	20	2

· Morphology and Particle Size Studies:

The morphology and surface characteristics of the microsponges were studied using scanning electron microscope (SEM). All the samples were coated with gold–palladium alloy under vacuum. Coated samples were then examined using LEO 430 SEM analyzer.

· Drug Content and Encapsulation Efficiency:

Microsponges (100mg) were crushed and extracted using 10mL methanol by vortexing and centrifuging at 2000 rpm for 10min.Then insoluble residue was separated and the supernatant was analysed in HPLC at 248nm after appropriate dilution. Then, the encapsulation efficiency, percentage yield, and drug loading were calculated by the following equation.

Encapsulation efficiency (EE):

= × 100

Percentage yield (PY):

=× 100

Drug loading (DL):

= × 100

In Vitro Drug Release: ⁷

Following procedure was employed throughout the study to determine the in vitro dissolution rate for all the formulations.

Dissolution study of microsponges was carried out in USP dissolution test apparatus I (Electro lab TDT O8L) stirred at 100 rpm and temperature of 37 ± 0.5˚. Drug release was monitored for 10 hr and samples were withdrawn periodically and sink conditions were maintained by replacing with equal amount of fresh dissolution medium. The dissolution was carried out at different pH condition using HCl buffer (pH 1.2) for 2 hr, phosphate buffer (pH 6.8) for next 6 hr, and phosphate buffer (pH 7.2) for subsequent hours to simulate the GIT condition. After 10 hr study, the samples were analyzed by HPLC at 248 nm. (Table-4).

As the drug is from BCS class 2, 2% SLS solution was used in the dissolution media.

Stability Study:

The stability of microsponges was carried out as per ICH guidelines in accelerated conditions. The microsponge formulation was kept at 40˚C ± 2˚C and 75% ± 5% RH for three months. After 3 months microsponges were analyzed for physical appearance, in vitro drug release, and FTIR spectroscopy.

RESULTS:

Effect of drug polymer ratio on drug content and % yield:

Table 5: Effect of drug polymer ratio on % Yield and drug content.

Batch	Drug: Polymer ratio (w/w)	% Yield	% Drug content
M1	1:1	58.66±1.87	87.09±0.25
M2	2:1	59.72±4.39	78.61±2.25
M3	3:1	65.50±2.77	95.19±1.42
M4	4:1	77.80±2.11	88.58±1.56
M5	5:1	58.50±3.70	91.85±2.68
M6	1:2	51.20±2.85	76.12±1.52
M7	1:3	36.52±1.25	65.18±0.85

Effect of inner phase solvent amount:

It was observed that when the volume of internal phase (ethanol) was increased from 20 to 25 ml, microsponge % yield were decreased. Good microsponges were produced only when 20 ml of internal phase was used.

Table 6: Effect of inner phase solvent amount

Volume of inner Phase (ml)	% Yield
25	56.22
20	77.85
15	Not found

Effect of stirring speed:

The effect of stirring rate on the size of microsponges was studied. As the stirring speed was increased, microsponges of smaller size were obtained, as shown in Table. When the rate of stirring was increased from 300 to 500 rpm, the mean particle size decreased from 92±4.45 to 60.25±5.67 μm

Table 7: Effect of stirring speed on particle size

Batch	Stirring speed(rpm)	Particle size(µm)
M4	300	92±8.21
M4	400	85±12.52
M4	500	60±4.53
M4	600	27±6.32

Characterisation of Microsponges:

Fourier transform infrared analysis:

Prepared microsponges were analyzed by FT-IR to study any drug interaction, there was no any drug interaction as the results shows the peaks of drug and polymer both. Results are shown in following figure.

Differential scanning calorimetry analysis:

DSC studies of microsponges was carried out to study any change in melting point of drug due to encapsulation, there was no change in melting point as shown in figure

Fig 3: DSC result of microsponge

Morphology and Particle Size Studies:

The particle size of developed microsponges was analyzed by Zeta Sizer, which showed the average size of microsponges was within the range of 61.12 𝜇m to 67.59𝜇m. The particle size of microsponges was affected by volume of solvent and concentration of Eudragit, as increase in volume of ethanol produces less viscous solution, which resulted in smaller particle size.

The microsponges’ formulation M5 was visualized by scanning electron microscope to assess the morphology of microsponges. SEM image revealed porous surface as shown in Figure and no drug particles were observed on the surface of the microsponges.

Fig 4: SEM image of microsponges

Size µm

Fig 5: Particle size distribution

In Vitro Drug Release:

The in vitro release of drug from microsponges is shown in Figure. Results of in vitro drug release revealed that 15 to 20% of celecoxib was released from the microsponges in initial 4 h and 71.52% to 85.26 % of drug was released after 10h. The drug release suggested that Eudragit S100 prevented the premature release of curcumin in the upper GIT, since it is a pH sensitive polymer having threshold pH value above 6, which bypasses the GIT and showed drug release above pH 6. Release rate of Celecoxib from microsponges increased after 4 h, due to the exposure of formulations to pH 6 which is above the solubilizing pH of Eudragit S100 polymer.

Table 8: Cumulative % drug release

Time (hr)	Cumulative % drug release
Time (hr)	M5	M4	Marketed
0	0	0	0
1	3.061±0.25	1.061±0.15	54.00±0.31
2	14.24±0.31	6.248±0.23	81.25±0.85
3	24.18±0.19	13.18±0.56	85.12±1.16
4	43.41±0.28	21.41±0.17	87.13±1.23
5	52.22±1.23	32.22±0.46	90.84±0.45
6	65.61±0.62	38.61±0.86	94.46±0.48
7	68.00±1.12	46.00±1.3	95.75±0.18
8	71.83±0.27	54.83±0.42	95.85±0.24
9	73.63±0.34	63.63±0.31	95.85±0.24
10	85.25±0.29	71.52±0.86	95.85±0.24

Fig 6: Dissolution studies of microsponges

Stability Study:

The stability study for final trial was done for 3 months by packing in air tight container in humidity chamber (40˚C/73% RH)

The results are shown under compatibility results, where all the parameters of formulation including, physical parameters, content uniformity and dissolution profile where within specification limit. So it indicates optimized formulation of celecoxib were stable.

No changes in the FT-IR spectra for each of the formulation was found to check if there were any peak shift and was compared with the FT-IR graph of the formulation taken initially to check stability of the product.

DISCUSSION:

The present study was aimed at developing colon specific drug delivery system using eudragit S100 as a polymer in the formulation of microsponges. It was earlier reported that eudragit S100 can be used as a colon targeting polymer hence exploring his properties in the microsponge formulation. Microsponges are porous in nature and can provide control release of drug that’s why microsponge drug delivery was the choice of formulation. Hence optimized formula of celecoxib microsponge provided to be efficient in releasing the drug at specific site for duration of 10 hrs.

The quasi-emulsion solvent diffusion method used for the preparation of the microsponges was simple, reproducible, and rapid. Various drug polymer ratios were tried to get theoptimized formula such as (1:1, 2:1, 3:1, 4:1, 5:1) Furthermore, it was observed that as drug:polymer ratio increased, particle size decreased and production yield increase to the particular limit. This is probably due to the fact that at higher relative drug content, the amount of polymer available per microsponge to encapsulate the drug becomes less, thus reducing the thickness of the polymer wall and hence, smaller microsponges. Out of all the ratios 4:1 was selected as optimized drug polymer ratio.

The effect of stirring rate on the morphology of microsponges was also investigated. The dispersion of the drug and polymer into the aqueous phase was found to be dependent on the agitation speed. As the speed was increased the size of microsponges was reduced and uniform spherical microsponges were formed. It was also noted that at higher stirring rate the production yield was decreased. Possibly at the higher stirring rates the polymer adhered to paddle due to the turbulence created within the external phase, and hence production yield decreased. Different stirring speeds were tried (300rpm, 400rpm, 500rpm, 600rpm) out of these 500 rpm was selected as optimized stirring speed.

Failure to form microsponges on increasing the volume of internal phase from 15 to 20 ml may be due to incomplete removal of internal phase solvent with the result that the droplets could not solidify as most of the internal phase remained in the droplets. This warrants the use of internal phase solvent in an appropriate amount to ensure the formation of quasi emulsion droplets, and solidification of the drug and polymer thereafter.

The microsponge formulations were subjected to in vitro dissolution studies and the data was analysed using various mathematical models. On the basis of highest regression value the best fit was observed for Higuchi matrix model.

This study presents a new approach for the preparation of modified microsponges. The microsponges exhibited characteristics of an ideal delivery system for colon targeting. The unique compressibility of microsponges offers a new alternative for producing different pharmaceutical formulations.

CONFLICT OF INTEREST:

No.

REFERENCES:

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2. Rajendra Jangde, Microsponges for colon targeted drug delivery system: An overview, Asian J. Pharm. Tech. 2011; Vol. 1: Issue 4, Pg 87-93

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Received on 02.12.2019 Modified on 31.12.2019

Asian J. Res. Pharm. Sci. 2020; 10(2):73-78.

DOI: 10.5958/2231-5659.2020.00014.4

Drug name	Dosage form	USP apparatus	Speed (rpm)	Medium	Volume (ml)	Recommended sampling time
Celecoxib	Microsponge	USP – I (Basket)	100	HCL buffer pH 1.2	900	2hr
				Phosphate buffer pH 6.8	900	6hr
				Phosphate buffer pH 7.2	900	2hr