1. INTRODUCTION:

The raft-forming system also referred to as oral in-situ gel-forming system has become a useful technology in improving gastric retention and localized controlled delivery of drugs in the stomach. Upon oral delivery, the homogeneous raft-forming suspension will immediately gel as soon as it comes into contact with gastric fluid to create a cohesive viscous, low-density, gel layer known as a raft. Such a raft is suspended in gastric contents¹, which is known to extend the period of gastric residence, enhance local therapeutic action, and predictable drug release. There are a number of gastroretentive technologies such as mucoadhesive systems^2,3, floating systems^4–6^,⁷ ,magnetic systems⁸, ion-exchange resins⁹, and raft-forming systems^10–12. The raft approach is one of the most unique approaches among them; it includes the following characteristics: quick gelation, floating, mechanical properties and entrapment of the drug in a stable float (form)¹⁰. Natural cationic polymers, including sodium alginate^{1,11,12,13,14}, xanthan gum^11,15, guar gum^16,17, gellan gum¹⁸, and anionic polymers, including chitosan^19,20, are typically used to make raft systems. Alternative modified polymers such as HPMC in varying molecular weights such as HPMC K100, K40, K15 and K4^11,12,10 are also applied. Alone or in combination, these polymers form floating structurally stable rafts. The most popular parent polymer is sodium alginate. L. The study by Srinivas et al. revealed that the formulations in the cases of alginates as well as HPMC K4 and xanthan gum yielded stable in-situ gelling rafts with an appropriate viscosity, lower than gastric fluid density, a lag time of buoyancy at 15.34-26.12s, and total floating time over 12h^11,21. Other mentioned blends of sodium alginate with xanthan gum, HPMC K100, Carbopol 934, gellan gum, and HPMC K4 gave floating rafts with pH 6.989, floating time 12-24h, instantaneous gelation (5±2 to 16±2) and short lag time^{11,10,15,13,18}. HPMC K100-containing rafts were particularly strong, with tightly-formed gel frameworks and an extremely fast gelation rate. Equally, the use of xanthan gum, sodium alginate and HPMC K4 created rafts with pH 6.989 and floating time >12hours, 1.051-0.058 raft density and thickness 1.8±0.26 -3.6±0.008mm^11,22. R. Munusamy et al. developed raft Carbopol-guar with a gelling time of 12-34s, floating time of around 12h, raft weight of 2.0522772g, volume of 2.1993281ml and 12h drug release of 74-88%^23,24. Alginate, gellan gum, pectin, guar gum and xanthan gum raft forming chewable tablets also exhibited high raft strength with sodium alginate providing the most robust structures (10.25g)^23,25,26. The current research will screen and determine the best polymer to use in forming rafts. With sodium alginate as the mother polymer, we assessed interpolymer (alginate, guar gum, and HPMC) and intrapolymer (HPMC) behaviors (K100, K40, K15, K4). Metronidazole as the model drug was incorporated into six different formulations (F1-F6) and evaluated in the following aspects: physicochemical properties, gel integrity, buoyancy, and drug release²⁷. This study aims to determine the most practical polymer blend to achieve sustained gastric retention, enhanced local curative effect against Helicobacter pylori, less drug variability and increased adherence by patients through studying the effects of each polymer on the gel structure, floating effect, and release kinetics.

2. MATERIALS AND METHODS:

2.1. Materials Used: Sodium alginate and Tri-sodium citrate were procured from Loba Chemie Pvt. Ltd. Hydroxypropyl methylcellulose (HPMC) grades K100M and K4M were obtained from Yaddow Chem Products, while HPMC K40M and HPMC K15M were sourced from MP Biomedicals, LLC. Guar gum was also purchased from Loba Chemie Pvt. Ltd. Additional chemicals, including hydrochloric acid, were obtained from Merck Life Science Private Limited, and potassium chloride was purchased from Sisco Research Laboratories Pvt. Ltd. Metronidazole was kindly gifted by Holden Medical Laboratories Pvt. Ltd. Double-distilled water prepared in the laboratory was used throughout the study. Whatman Grade 1 filter paper was employed for filtration procedures.

2.2. Formulation Strategy for Raft-Forming in Situ Gels: Table 1 was used to formulate suspensions. Each batch was a combination of sodium alginate, guar gum, and four grades of HPMC and calcium carbonate served as crosslinker in addition to an effervescent agent. In the first solution, tri sodium citrate (0.25percent) was dissolved in 100ml of distilled water and the mixture stirred and then maintained at the required temperature until a smooth homogeneous and viscous solution was obtained. Gradually the calcium carbonate was added and it was constantly stirred and stirred. Finally, 0.5% metronidazole (model drug) was added to the mixture to complete the mixture. The rest of the five formulations were made according to the same procedure^1,11,16,28.

Table 1: Composition of Raft-Forming In-Situ Gel Formulations (F1-F6)

Ingredients	F1	F2	F3	F4	F5	F6
Sodium Alginate	3%	3%	3%	3%	3%	3%
Tri-Sodium Citrate	0.25%	0.25%	0.25%	0.25%	0.25%	0.25%
HPMC K 100	0.6%	_	_	_	_	_
HPMC K 40	_	0.6%	_	_	_	_
HPMC K 15	_	_	0.6%	_	_	_
HPMC K 4	_	_	_	0.6%	_	_
Guar gum	_	_	_	_	0.6%	_
Calcium Carbonate	2%	2%	2%	2%	2%	2%

2.3. Visual Characteristics and Ph Profiling of Formulations: Each formulation was visually inspected against a black-white background. A 5 ml sample was added to 0.1 N HCl (pH 1.2), pH 2 HCl buffer, and pH 4 phosphate buffer. After Raft formation, pH changes were recorded using a calibrated digital pH meter (CL 46+) ^11,16.

2.4. Evaluation of In-Vitro Gelation Behavior: An in-vitro gelling study was performed by adding 5 ml of formulation into 50 ml of gelation media (0.1 N HCl pH 1.2, pH 2 HCl buffer, and pH 4 phosphate buffer) at 37 ± 0.5°C. The sol-to-gel conversion time and complete dissolution time were recorded ^11,29.

2.5. Buoyancy Assessment of Raft-Forming Gels: For the in-vitro buoyancy study, 10 ml of each formulation was placed on a watch glass and transferred into a Type II dissolution apparatus containing 500 ml of dissolution media: 0.1 N HCl (pH 1.2), pH 2 HCl buffer, and pH 4 phosphate buffer. The temperature was maintained at 37 ±0.5°C, with the rotation speed set at 50 rpm. The floating lag time was recorded as the time required for the gelled mass to rise to the surface, while the total floating time was measured as the duration for which the system remained buoyant ¹¹.

2.6. Viscosity Profiling of In-Situ Gels: A rotating programmable cone-and-plate viscometer (Modular Compact Rheometer, MCR 102, Anton Paar) was used to measure formulation viscosity at 25 ± 2°C. A small sample was placed on the plate, and excess material was carefully trimmed to ensure accurate, interference-free measurements^1,11,18.

2.7. Determination of Formulation Density: Each formulation was calculated using the method of the displacement of water. To start with, 50mL of freshly prepared gelation media; 0.1N HCl (pH=1.2), 2 HCl buffer, and 4 phosphate buffer were added in a 100mL beaker with 5ml of the formulation. It was allowed to stand (30min) to allow the formation of the gel. Upon gelation, the surplus acid was decanted carefully and the weight of the gel noted. The gel was then moved to a 50mL measuring cylinder, original volume noted, water was put in until that mark, and the displaced volume was measured. The change in volume of water with the gel and without the gel was calculated to obtain the density^11,16.

2.8. Evaluation of Raft Volume and Expansion: The measurement was done by weighing a 250mL beaker and recording the weight of the beaker. Then the 20mL of the prepared formulation was combined to 150mL of three pH media, pH 1.2(0.1N HCl), pH 2(HCl buffer), and pH 4(phosphate buffer) and allowed to mix without stirring after 30 minutes to allow the formation of the raft. When the raft had formed the height that it had formed within the beaker was noted on the outside of the beaker. The weight of the beaker, the liquid and the raft was then computed together. The raft was then removed with extreme care and weighed separately; and then the rest of the fluid was disposed of. Lastly, water was again added until the level of the mark was reached and the beaker was re-weighed to obtain the accurate level of the raft^1,16.

2.9. Evaluation of Raft Thickness: 10ml of the prepared formulation was introduced into 150ml of gastric media-0.1 N HCl (pH 1.2), pH 2 HCl buffer, and pH 4 phosphate buffer-in a 250ml beaker, maintained at 37°C. After Raft formation, its thickness was measured at three different points around the beaker using a digital vernier caliper to ensure accuracy and uniformity^1,16.

2.10. Evaluation of Raft Resilience and Strength: This test evaluated the Raft’s durability under intensified motion. First, the Raft was formed in a beaker containing 50ml of three pH media-0.1 N HCl (pH 1.2), pH 2 HCl buffer, and pH 4 phosphate buffer-maintained at 37°C. The fully formed Raft was then transferred to a tumble mixer operating at 20rpm to simulate continuous agitation. Its structural integrity was monitored until it fragmented into two or more pieces, each with a minimum diameter of 15mm^1,11,16.

2.11. Evaluation of Swelling Behavior: The swelling behavior of the Raft was evaluated by placing 20ml of the formulation in 0.1N HCl (pH 1.2, 37°C) until Raft formation. The formed Raft was removed, dried for two days, and then immersed in water at 30°C. Its weight was recorded at 60, 120, 180, 240, and 300 minutes. Swelling behavior was calculated from the progressive weight changes over time¹.

2.12. FTIR Analysis of Formulation Components: The FTIR spectra of pure HPMC K100M and the dried, ground F1 formulation were recorded in the 4000-400 cm⁻¹ range to identify any potential drug-excipient interactions. Samples were prepared using the KBr disk method and compressed with a hydrostatic press, ensuring clear and accurate spectral analysis^1,11.

2.13. Assessment of Drug Release Profiles: The in-vitro release of metronidazole from the in- situ gel Raft was evaluated using a USP Type II dissolution apparatus at 37±0.5°C and 50rpm. 900ml of freshly prepared 0.1N HCl (pH 1.2) served as the dissolution medium. 10ml of formulation was carefully added to the vessel to form the Raft. Samples (5ml) were withdrawn at 5, 10, 15, 30, 45, 60, and 120 minutes, replacing an equal volume of buffer to maintain sink conditions. Drug release was analyzed at 277nm using a UV spectrophotometer (SHIMADZU UV1900-1)^11,18.

3. RESULTS AND DISCUSSION:

Gastroesophageal reflux disease (GERD) is a widespread gastrointestinal disease when the stomach contents that have become acidic reflux back into the esophagus leading to heartburn and regurgitation among other symptoms. Among numerous existing treatments, raft-forming preparations have gained a new option and become effective and more friendly to patients. These systems rapidly produce a gel-like, buoyant, rafty top, which floats over the stomach contents forming a powerful physical barrier which prevents reflux. Rafters based on alginate are particularly considered to give quick and protracted relief. The success of this strategy is demonstrated in the products like Gaviscon Double Action, Gaviscon Original, Peptic Liquid, and Aglycon pills¹.

3.1. Visual Characteristics and Ph Profiling of Formulations: All formulations appeared as smooth, cream-coloured suspensions with an elegant, uniform texture. pH plays a crucial role in ensuring patient comfort during oral administration, as inappropriate acidity can irritate the mouth and throat. Notably, all prepared formulations exhibited a well-balanced pH in the range of 3 to 7, ensuring both stability and patient acceptability. The detailed pH values are presented in Table 2^11,16

Fig 1: A suspension containing Alginate F6, B suspension containing Alginate with guar gum F5, C suspension containing Alginate with HPMC K100 F1.

3.2. Evaluation of In-Vitro Gelation Behavior: The in-vitro gelling study was conducted using simulated gastric conditions at pH 1.2, pH 2 (HCl buffer), and pH 4 (phosphate buffer). All formulations demonstrated rapid gelation upon contact with each medium. At pH 2, the former rafts were partially floating, while at pH 4 they remained non-floating, reflecting pH-dependent raft behavior. As summarized in Table 2, formulation F1 exhibited the fastest gelation time (≈4 seconds), whereas F6 and F5 required 15 and 12 seconds, respectively- significantly longer than F1^11,18.

Fig: 2 Raft formed in different pH

3.3. Buoyancy Assessment of Raft-Forming Gels: This study evaluated floating behaviour across pH 1.2, 2, and 4. The time required for the formulation to rise to the surface defines the floating lag time, while its duration of buoyancy represents the total floating time. Impressively, all formulations maintained floating for over 24 hours ¹¹.

3.4. Viscosity Profiling of In-Situ Gels: Viscosity is a critical parameter in suspension formulations, influencing both storage stability by reducing particle sedimentation and ease of administration. Results (Table 3) showed viscosities ranging from 9.88 Pa-s (F1, containing HPMC 100) to 1.43 Pa-s (F6, containing sodium alginate). All formulations exhibited a decrease in viscosity with increasing shear rate, demonstrating shear-thinning (pseudoplastic) behavior. This property is advantageous for pharmaceutical applications, as it minimizes sedimentation while allowing the formulation to be easily poured and administered to patients^1,11,18.

3.5. Determination Of Formulation Density: All formulations (F1-F6) exhibited post- gelation densities ranging from 0.733 to 0.939g/cm³, significantly lower than that of gastric fluid (1.004g/cm³). This favorable density profile confirms their strong floating capability, ensuring stable raft formation and sustained gastric retention-key requirements for effective raft-based therapy^1,16.

3.6. Evaluation of Raft Volume and Expansion: CO₂ generation plays a vital role in expanding the raft structure, as calcium carbonate dissociates in acidic conditions to release gas and enhance buoyancy. Table 3 presents the raft volume values for all formulations. F6 demonstrated the lowest raft volume (≈18.95 mL), likely due to its reduced viscosity, while F1 exhibited the highest raft volume (40.18 mL), reflecting superior CO₂ entrapment and stronger raft formation ^1,16.

3.7. Evaluation of Raft Thickness: The thickness of all formulations ranged from 12.15 to 16.32 mm, reflecting consistent raft formation across batches. Among them, F1 produced the thickest raft, while F6 showed the thinnest, attributed to their lower and higher polymer concentrations, respectively. Overall, only minimal variation in raft thickness was observed across F1-F6 ^1,11,16.

3.8. Evaluation of Raft Resilience and Strength: Raft resilience reflects the Raft’s ability to resist disintegration under simulated gastric movement, influenced by drug dose, component quality, polymer concentration, and Raft strength. As shown in Table 3, all tested formulations exhibited excellent resilience, remaining intact for >4 hours under experimental conditions ^1,11,16.

3.9. Evaluation of Swelling Behavior: The swelling study evaluated each dried raft’s capacity to absorb water when immersed in distilled water at room temperature. As shown in Table 3, all formulations demonstrated remarkably high swelling, ranging from 92.24% to 95.31%, attributed to their interconnected porous structures that promote efficient water uptake¹.

3.10. Assessment of Drug Release Profiles: The key objective of the in-vitro release study was to design an optimized floating raft system using different polymers and HPMC grades to achieve a sustained, therapeutically relevant drug release profile. Preliminary trials employing various polymers-individually and in combination-helped identify suitable release modifiers capable of providing controlled and extended drug release. Based on these findings, sodium alginate, guar gum, HPMC K100M, HPMC K40M, HPMC K15M, and HPMC K4M were selected for the final formulation design. The in-vitro drug release was evaluated under simulated gastric conditions (pH 1.2). Across all gastroretentive formulations, drug release ranged from 33.44% to 88.57% within 2 hours. Formulations F1-F6 exhibited release values of 33.44%, 41.39%, 88.57%, 84.32%, 43%, and 46%, respectively. Among them, F1 displayed the slowest release, whereas F3 exhibited the fastest release within the 2hour evaluation window (Table 2). The use of multiple polymers, especially in combination, significantly improved the modulation of drug release by forming strong, viscous gel barriers. The varied release behavior can be attributed to differences in the molecular weights of the HPMC grades. HPMC K100M, having the highest molecular weight, forms a highly viscous gel layer that creates a dense, tortuous diffusion pathway-substantially slowing drug release compared to HPMC K40M, HPMC K15M, and HPMC K4M. Consequently, the drug-release pattern followed the order: HPMC K4M > HPMC K15M > Sodium alginate > Sodium alginate + Guar gum > HPMC K40M > HPMC K100M, confirming that higher-viscosity matrices provide superior sustained-release control^12,30.

Table 2: Evaluation of Physicochemical and In-Vitro Performance Parameters of Raft-Forming In-Situ Gel Formulations (F1-F6)

Formulation	Gelling Time (sec)	Gelling duration (h)	Floating lag time (h)	Floating Duration (h)	pH Change			Swelling %	CPR 2 hrs. in 1.2 pH %
Formulation	Gelling Time (sec)	Gelling duration (h)	Floating lag time (h)	Floating Duration (h)	1.2	2	4	Swelling %	CPR 2 hrs. in 1.2 pH %
F1	4	>24	9	>24	3	4	6	93.67	33.44
F2	5	>24	12	>24	3	5	6	90.13	41.39
F3	7	>24	11	>24	2	4	5	94.55	88.57
F4	10	>24	15	>24	3	4	6	95.31	84.32
F5	12	>24	17	>24	3	4	7	95.40	43.52
F6	15	>24	18	>24	2	5	6	92.24	46.80

4. CONCLUSION:

This research has managed to develop a gastroretentive in-situ gel with the help of sodium alginate, guar gum and various grades of HPMC. Batches were all of good viscosity, capable of gelation, high floating capacity and able to release drugs. Most notably, the controlled-release performance of batch F1, which contained HPMC K100M, was the most efficient and only 33% of the drug was released after 2hours, compared to F2-F6 which released a substantial amount. F1 was also well buoyed, and it took more than 24hours in the simulated gastric fluid. These findings support the claim that the high-viscosity HPMC K100M in combination with sodium alginate has a significant effect on the properties of strength of rafts, length of flotation, and control of drug release, and thus the viscosity is a determinant factor that define the functionality of floating drug delivery systems (FDDS).

5. ACKNOWLEDGEMENTS:

The authors express their sincere gratitude to the Instrumentation Laboratories, Department of Pharmaceutical Technology, Jadavpur University, for providing invaluable support and access to advanced facilities that significantly strengthened this research.

6. CONFLICT OF INTERESTS:

The authors affirm that this research was conducted with complete transparency and objectivity, and they declare no conflicts of interest related to this work.

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Received on 21.03.2025 Revised on 15.09.2025

Accepted on 26.01.2026 Published on 02.07.2026

Available online from July 15, 2026

Asian J. Res. Pharm. Sci. 2026; 16(3):217-224.

DOI: 10.52711/2231-5659.2026.00033

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Creative Commons License.

Shila Barman, Arindam Sarkar, Adarsha Bachhar, Sanchita Mandal*

2. MATERIALS AND METHODS:

3. RESULTS AND DISCUSSION:

Figure 5: Dissolution study of formulations

Fig 6: FTIR of HPMC100(A) and F1 formulation(B)

7. REFERENCES:

Formulation	Density (g/cm3)	Viscosity (pa-s)	Thickness(mm)	Raft Volume (ml)	Raft resilience (h)
F1	0.939	9.88	16.32	40.18	>4
F2	0.904	8.2	13.38	34.92	>4
F3	0.763	6.1	15.12	29.24	>4
F4	0.838	5.1	14.28	19.15	>4
F5	0.893	8.1	15.34	33.64	>4
F6	0.733	1.43	12.15	18.95	>4