Formulation And Evaluation of Wound Healing Gel and Anti-Oxidant Protective from Onion Peel Extract

Wound healing is a complex and dynamic biological process that involves the restoration of tissue integrity after injury. It consists of several overlapping phases including hemostasis, inflammation, proliferation, and remodeling. Proper wound management is essential to prevent infection, reduce healing time, and restore normal tissue function. Despite the availability of synthetic drugs and topical formulations, many of them may cause adverse effects, delayed healing, or antibiotic resistance. Therefore, the exploration of natural products with therapeutic potential has gained increasing attention in recent years (1).

Medicinal plants and plant-derived compounds have been widely used in traditional medicine for the treatment of wounds and skin disorders. Natural products are considered safer, cost-effective, and biologically active due to the presence of phytochemicals such as flavonoids, tannins, phenolic compounds, and alkaloids. These compounds exhibit multiple pharmacological activities including antioxidant, antimicrobial, anti-inflammatory, and tissue regenerative effects, which contribute to the wound healing process (2).

Onion (Allium cepa L.) is one of the most commonly consumed vegetables worldwide and belongs to the family Amaryllidaceae. It is widely used not only as a food ingredient but also for its medicinal properties. Onion contains various bioactive compounds such as quercetin, kaempferol, sulfur-containing compounds, flavonoids, and phenolic acids that exhibit strong antioxidant and anti-inflammatory activities (3). These bioactive constituents play a significant role in protecting cells from oxidative stress and enhancing tissue repair.

The outer dry layer of onion, commonly known as onion peel, is usually discarded as agricultural waste during food processing. However, studies have reported that onion peel contains a higher concentration of phenolic compounds and flavonoids, particularly quercetin, compared to the edible portion of the onion. These compounds possess strong antioxidant properties which help neutralize free radicals and reduce oxidative damage in tissues (4). Due to these properties, onion peel extract has potential applications in pharmaceutical and cosmetic formulations.

Oxidative stress plays an important role in delaying wound healing by causing cellular damage and prolonging inflammation. Antioxidants can scavenge free radicals, reduce oxidative stress, and promote faster tissue regeneration. Therefore, natural antioxidant sources such as onion peel extract may contribute significantly to the wound healing process (5).

Topical gel formulations are widely used for wound treatment because they provide better drug penetration, easy application, non-greasy nature, and improved patient compliance. Gels also help maintain a moist environment at the wound site, which is beneficial for tissue regeneration and faster healing. Incorporation of herbal extracts into gel formulations can enhance therapeutic activity while minimizing side effects (6).

Considering the rich phytochemical composition and strong antioxidant potential of onion peel, it can be utilized as a promising natural ingredient for wound healing formulations. The present study focuses on the extraction of bioactive compounds from onion peel, formulation of a topical gel, and evaluation of its wound healing and antioxidant activities.

METHOD OF PREPARATION

Preparation of Onion Peel Extract Gel for Wound-Healing and Antioxidant Activity

1. Preparation of Plant Material

Fresh outer dry peels of onion were collected from a local market. The collected peels were carefully inspected to remove any damaged or contaminated material. The peels were washed thoroughly with distilled water to eliminate dust, soil particles, and other impurities. After washing, the peels were spread evenly on clean trays and allowed to dry under shade at room temperature for several days. Shade drying was preferred to prevent degradation of heat-sensitive phyto constituents such as flavonoids and phenolic compounds.

Once completely dried, the peels were ground into a coarse powder using a mechanical grinder. The powdered material was passed through a suitable sieve to obtain uniform particle size. The powdered onion peel was stored in an airtight container, protected from moisture and light, until further use for extraction.

2. Preparation of Onion Peel Extra

Solvent Extraction Method

The extraction of bioactive constituents from onion peel powder was carried out using a hydro-alcoholic solvent system. A measured quantity of onion peel powder was accurately weighed and transferred into a Soxhlet extraction apparatus. A mixture of ethanol and water (70:30) was used as the extraction solvent, as this solvent system effectively extracts both polar and moderately non-polar phyto constituents.

The extraction process was continued for several cycles until the solvent in the siphon tube became colourless, indicating complete extraction of active compounds. After completion of extraction, the collected extract was filtered through muslin cloth followed by Whatman filter paper to remove any solid residues.

The filtrate was concentrated using a rotary evaporator under reduced pressure at controlled temperature to prevent thermal degradation of active constituents. The concentrated extract was further dried to obtain a semisolid mass. The dried extract was weighed to calculate percentage yield and stored in a refrigerator until formulation development.

 3. Preparation of Gel Base

A suitable gelling agent such as Carbopol 934 was selected for the preparation of the gel base due to its excellent thickening and stabilizing properties. The required quantity of Carbopol was slowly dispersed in a measured volume of purified water with continuous stirring to prevent lump formation. The dispersion was allowed to stand for sufficient time to ensure complete hydration and swelling of the polymer.

Preservatives such as methyl paraben and propyl paraben were dissolved separately in a small quantity of warm distilled water or propylene glycol and added to the hydrated polymer solution. Propylene glycol was used as a humectant and solvent to enhance penetration of the active constituents into the skin.

4. Incorporation of Onion Peel Extract into Gel Base

A calculated amount of dried onion peel extract was dissolved in a small quantity of propylene glycol to obtain a uniform solution. This step ensures proper solubilization and even distribution of the extract within the gel base.

The extract solution was added gradually to the hydrated polymer dispersion with continuous mechanical stirring to ensure uniform mixing. Care was taken to avoid incorporation of air bubbles during mixing, as air entrapment may affect the stability and appearance of the final formulation.

After complete mixing, triethanolamine was added dropwise to adjust the pH of the formulation. The addition of triethanolamine neutralizes the Carbopol dispersion, leading to gel formation. The pH was adjusted to a range compatible with skin application.

 5. Final Processing of the Gel

The prepared gel was stirred continuously until a uniform, smooth consistency was achieved. The final formulation was allowed to stand to remove any entrapped air bubbles. The gel was then transferred into clean, dry, collapsible aluminium tubes or airtight containers.

The filled containers were properly labelled and stored at room temperature for further evaluation station

 6. Precautions Taken During Preparation

Several precautions were observed during the preparation process to ensure quality and reproducibility of the formulation:

• All glassware and equipment were cleaned and dried before use.
• Extraction was performed under controlled temperature to prevent degradation of phyto constituents.
• Continuous stirring was maintained during gel preparation to avoid lump formation.
• Air incorporation was minimized during mixing.
• pH adjustment was performed carefully to maintain skin compatibility.
• The final formulation was stored in airtight containers to prevent contamination and moisture absorption.

7. Summary of Preparation Method

The method of preparation involved three major stages: extraction of bioactive constituents from onion peel, preparation of gel base, and incorporation of extract into the gel matrix. The hydro-alcoholic extraction method ensured efficient recovery of antioxidant and wound-healing compounds. The use of Carbopol as a gelling agent provided appropriate viscosity and stability. Proper mixing and pH adjustment resulted in a smooth, homogeneous, and stable gel formulation suitable for topical wound-healing application

METHODS OF EVALUATION OF WOUND HEALING GEL

The prepared wound-healing gel was subjected to various physicochemical, biological, and stability evaluation tests to determine its quality, safety, efficacy, and suitability for topical application. The following evaluation parameters were carried out.

 1. Organoleptic Evaluation

The gel formulation was visually inspected for colour , odour, texture, clarity, and homogeneity. The presence of any lumps, grittiness, or phase separation was carefully observed. A uniform and smooth appearance indicates proper formulation and good compatibility of ingredients

 2. pH Determination

The pH of the gel was determined using a calibrated digital pH meter. About 1 g of gel was dispersed in 10 mL of distilled water and allowed to stand for equilibration. The electrode was immersed in the sample, and the pH was recorded. The test ensures that the formulation is compatible with skin and does not cause irritation.

 3. Viscosity Measurement

Viscosity of the gel was measured using a Brookfield viscometer at room temperature. A suitable spindle was selected, and the sample was placed in the viscometer container. The reading was recorded at different rotational speeds. Viscosity helps in determining the flow behaviour and retention of the gel at the wound site.

4. Spread ability Test

Spread ability was evaluated using the glass slide method. A fixed amount of gel was placed between two clean glass slides. A specific weight was applied on the upper slide to spread the gel uniformly. The time taken for the upper slide to move a fixed distance was recorded. Spread ability is calculated using the formula:

Where:

S = Spread ability

M = Weight tied to upper slide

L = Length moved

T = Time taken

Good spread ability ensures ease of application and uniform drug distribution.

 5. Extrud ability Test

The gel was filled into collapsible aluminium tubes. A specific amount of pressure was applied to extrude the gel. The quantity of gel extruded and ease of extrusion were observed. This test determines the practical usability of the formulation.

 6. Drug Content Uniformity

A known quantity of gel was accurately weighed and dissolved in a suitable solvent. The solution was filtered and analysed using a UV-Visible spectrophotometer at a specific wavelength. The absorbance was recorded, and drug content was calculated. Uniform drug content ensures consistent therapeutic effect.

7. In-Vitro Drug Release Study

The in-vitro release study was performed using a Franz diffusion cell apparatus. A suitable semi-permeable membrane was mounted between donor and receptor compartments. The gel was placed in the donor compartment, and phosphate buffer (pH 6.8) was used as receptor medium. Samples were withdrawn at predetermined intervals and analysed spectrophotometrically. This study determines the release profile of active constituents from the gel.

8. Antioxidant Activity (DPPH Assay)

The antioxidant activity of the gel was evaluated using the DPPH free radical scavenging method. Different concentrations of the gel extract were mixed with DPPH solution and incubated in the dark. The absorbance was measured at 517 nm using a UV-Visible spectrophotometer. The percentage inhibition was calculated to determine antioxidant potential.

9. In-Vitro Wound Healing Study (Scratch Assay)

Fibroblast cells were cultured in appropriate growth medium. A uniform scratch was created on the cell monolayer using a sterile pipette tip. The gel extract was applied to the cells, and wound closure was observed under a microscope at different time intervals. The percentage of cell migration was calculated to evaluate wound-healing potential.

10. In-Vivo Wound Healing Study

Excision Wound Model

Healthy laboratory animals were anesthetized, and a circular excision wound of predetermined size was created on the dorsal surface. Animals were divided into control, standard, and test groups. The gel was applied topically once daily. Wound area was measured periodically, and percentage wound contraction was calculated using the formula:

% , Wound , Contraction = \frac{Initial , Wound , Area - Specific , Day , Area}{Initial , Wound , Area} \times 100

The time required for complete epithelialization was also recorded.

 11. Skin Irritation Test

The gel was applied to a shaved area of skin and observed for signs of redness, swelling, or irritation over 24– 72 hours. The absence of adverse reactions indicates safety for topical use.

12. Stability Studies

The gel formulation was stored under different temperature conditions such as room temperature and accelerated conditions. Physical appearance, pH, viscosity, and drug content were evaluated at regular intervals. Stability testing ensures shelf life and formulation integrity.

13. Statistical Analysis

All experimental data were expressed as mean ± standard deviation. Statistical analysis was performed using appropriate statistical methods such as one-way ANOVA. A p-value less than 0.05 was considered statistically significant.

1.Physical Appearance

The prepared gel was visually examined for color, clarity, texture, and presence of any particulate matter. The observation ensures uniformity and patient acceptability.

2.pH Determination

The pH of the gel was measured using a calibrated digital pH meter at room temperature. A small quantity of gel was dispersed in distilled water and tested

3. Spread ability Test

Spread ability was determined by placing the gel between two glass slides and applying a standard weight. The time taken for the slides to separate was recorded.

4. Viscosity Measurement

Viscosity was measured using a Brookfield viscometer at 25°C.

5. Drug Content Uniformity

A known quantity of gel was dissolved in ethanol and analysed using a UV-Visible spectrophotometer.

7. In-Vitro Wound Healing Activity (Scratch Assay)

The wound closure percentage was measured at different time intervals.

8. Stability Study

The gel was stored under different conditions and evaluated periodically.