Formulation and Characterization of a Guava Leaf Hydrogel for Accelerated Healing of Diabetic Wounds

 

Diabetes mellitus is a globally prevalent chronic metabolic disorder that is characterized by persistent hyperglycemia resulting from defects in insulin secretion, insulin action, or both [1]. Studies suggest that over half a billion people are currently affected with diabetes worldwide, which means that over 10.5% of the world’s adult population are diabetic [2]. Among its most debilitating complications, chronic cutaneous wounds or Foot ulceration is the most common complication faced by patients with diabetes mellitus [3]. These wounds exhibit impaired healing and fail to progress through the normal sequential phases of wound repair which exhibit haemostasis, inflammation, proliferation, and remodeling stages, and this disruption leads to chronic wounds [4]. The chronic wounds can be due to multiple factors in diabetes mellitus, including peripheral neuropathy, microvascular dysfunction, immune impairment, and increased oxidative stress associated with excessive reactive oxygen species (ROS) production[5][6].

The most observed causes that interact and ultimately result in ulceration has been identified as neuropathy, deformity, and trauma[7]. The current management of diabetic wounds includes debridement, infection control with systemic or topical antibiotics, growth factor therapies, and advanced wound dressings [8]. However, these approaches of treatment often impose major economic burdens and are limited by high treatment costs, systemic adverse effects, emergence of antibiotic-resistant pathogens, and inadequate wound closure rates [9]. The exploration of phytopharmaceutical alternatives offers an attractive avenue for addressing these limitations, given the established safety profile and multifunctional bioactivity of medicinal plants [10][11].

Psidium guajava, commonly known as guava, has long been employed in traditional medicine systems across tropical and subtropical regions for the treatment of wounds, skin infections, and inflammatory conditions [12]. The leaves of this plant are particularly rich in flavonoids (notably quercetin and kaempferol), tannins, phenolic acids, and terpenoids, which collectively confer potent antimicrobial, antioxidant, and anti-inflammatory properties [13][14]. Quercetin, the major bioactive flavonoid (C₁₅H₁₀O₇; MW 302.24 g/mol), has been shown to promote fibroblast proliferation, stimulate collagen synthesis, and induce angiogenesis, all of which are critical for tissue regeneration [15].

Hydrogels represent an advanced class of wound dressings with the capacity to maintain a physiologically moist microenvironment at the wound interface, facilitate gaseous exchange, permit controlled release of bioactive compounds, and be removed from the wound site without causing re-injury [16][17]. Carbopol 940-based hydrogels offer high viscosity at low polymer concentrations and excellent biocompatibility, while the addition of chitosan, a cationic biopolymer derived from crustacean chitin imparts inherent antimicrobial activity, promotes haemostasis, and enhances cellular adhesion and migration [18][19][20].

Previous studies support the use of hydrogel-based systems for wound care and drug delivery. Additionally, guava leaf extract has demonstrated significant antioxidant and wound-healing potential, contributing to faster wound closure and improved tissue repair [21][22]. Furthermore, hydrogels loaded with guava leaf extract have exhibited favorable swelling properties, antimicrobial activity, and enhanced tissue regeneration. Collectively, these findings provide strong scientific support for the formulation approach used in the present study [23][24][25].

The present study was undertaken to formulate and characterize a guava leaf extract-loaded Carbopol 940–chitosan hydrogel and evaluate its physicochemical properties The integration of plant-derived bioactives with a controlled-release hydrogel platform represents a rational strategy for addressing the multifactorial pathophysiology of diabetic wounds.

MATERIALS AND METHODS

1. Plant Material and Extraction

Fresh guava (Psidium guajava L.) leaves were collected from a botanically authenticated source, washed with distilled water to remove surface contaminants, and shade-dried for 7–10 days to preserve labile phenolic and flavonoid compounds. The dried leaves were coarsely powdered using a mechanical grinder.

Extraction was performed using a Soxhlet apparatus. Fifty grams of leaf powder was extracted with 70% ethanol as solvent for 6–8 h (approximately 15–20 cycles). The extract was filtered through Whatman No. 1 filter paper, and the solvent was removed by evaporation under reduced pressure using a rotary evaporator at 40–50°C. The concentrated greenish-brown extract was stored in amber-coloured airtight containers at 4°C until further use. Maceration in a hydroalcoholic solvent for 48 h with intermittent agitation was used as an alternative extraction method to cross-validate yield.

2. Hydrogel Preparation

Carbopol 940 (1 g) was dispersed in distilled water (100 mL) with gentle stirring until a uniform dispersion was obtained. Separately, chitosan (2 g) was dissolved in 1% (v/v) acetic acid (100 mL) to form a 2% (w/v) chitosan solution. Guava leaf extract (2 g) was incorporated into the Carbopol dispersion under continuous stirring, followed by the slow addition of the chitosan solution. The pH of the resulting mixture was adjusted to 6.5 ± 0.1 by dropwise addition of triethanolamine, which also induced gel formation through neutralization of Carbopol's carboxyl groups. Glycerin was added as a humectant (2% w/w). The final hydrogel was homogenized and stored in sealed glass containers at room temperature.

3. Formulation Composition

Table 2. Summary of physicochemical evaluation parameters and observed results

2. Physical Appearance and Organoleptic Properties

The prepared hydrogel presented as a greenish-brown, translucent, smooth, and homogeneous gel with a characteristic mild herbal odour consistent with the incorporated guava leaf extract. No phase separation, syneresis, or grittiness was observed. This appearance is consistent with the successful incorporation of the polyphenol-rich extract into the polymeric matrix and confirms uniform dispersion.

3. pH and Skin Compatibility

The pH of the optimised formulation was 6.5 ± 0.1, which lies within the physiologically acceptable range for topical preparations (4.5–7.5) and approximates the pH of intact skin (5.5–7.0). Formulations outside this range risk disrupting the cutaneous acid mantle, causing irritation and compromising the epidermal barrier—particularly problematic in the already-compromised skin of diabetic patients. The near-neutral pH also helps maintain the antimicrobial and antioxidant activity of quercetin.

4. Viscosity and Spreadability

The hydrogel exhibited a viscosity of 4500–5000 cP and a spreadability of 7.5 ± 0.2 cm. This viscosity profile ensures that the gel remains at the wound site without premature dripping while allowing easy application with minimal shear. Good spreadability ensures uniform coverage of the wound surface, facilitating homogeneous drug delivery. The slight increase in viscosity relative to the plain base may be attributed to intermolecular hydrogen bonding between the hydroxyl groups of quercetin and flavonoids and the carboxyl groups of Carbopol 940.

5. Swelling Index

A swelling index of 120–130% indicates excellent water absorption capacity. Hydrogels with high swelling capacity effectively absorb wound exudate, prevent maceration of periwound tissue, and maintain the moist wound environment that is indispensable for cell migration, fibroblast activity, and angiogenesis [26]. This property also facilitates the controlled diffusion of quercetin and associated bioactives toward the wound bed, enhancing local therapeutic effect.

6. Drug Content and In Vitro Release

Drug content of 95–98% confirmed efficient and uniform incorporation of guava leaf extract bioactives into the hydrogel matrix, with minimal processing losses. In vitro release studies demonstrated a biphasic profile: an initial burst release (~30% over the first 2 h), attributed to surface-bound quercetin, followed by sustained release reaching ~75% at 24 h. This pattern is pharmacodynamically desirable for chronic wound management, where continuous delivery of antioxidant and antimicrobial agents is required over extended periods. The release data best fitted the Higuchi diffusion model (R² = 0.982), suggesting that drug diffusion through the hydrogel matrix is the predominant release mechanism.

7. Antimicrobial Activity

The hydrogel demonstrated meaningful zones of inhibition against S. aureus (14.2 ± 0.8 mm) and E. coli (12.6 ± 0.6 mm), confirming the preservation of antimicrobial activity following formulation. The plain hydrogel base showed no inhibition. Diabetic wounds are highly susceptible to polymicrobial infections, with S. aureus and E. coli being among the most frequently isolated pathogens. The antimicrobial activity of guava leaf extract is primarily attributed to quercetin and tannic acid, which disrupt bacterial cell membrane integrity and inhibit bacterial enzymes [27].

8. Stability

The hydrogel remained physically stable (no colour change, phase separation, syneresis, or cracking) and chemically stable (pH 6.5 ± 0.2; drug content loss <2%) after 30 days at both 25°C and 40°C storage conditions. This confirms physicochemical compatibility between the guava leaf extract and the polymeric excipients and suggests an acceptable shelf-life suitable for clinical use [28].

9. Comparison with Standard Acceptance Criteria

Table 3. Comparison of formulation parameters with standard acceptance criteria for topical hydrogels

All physicochemical parameters of the optimised guava leaf hydrogel were within the standard acceptance criteria for topical hydrogel preparations, confirming its suitability for wound dressing applications.

CONCLUSION

The present study successfully formulated and characterized a Carbopol 940–chitosan-based hydrogel incorporating guava (Psidium guajava) leaf extract for the management of diabetic wounds. The optimized formulation exhibited desirable physicochemical properties, including appropriate pH, good viscosity, excellent spreadability, high swelling capacity, and uniform drug content, all of which are essential for effective topical application and patient compliance. The hydrogel demonstrated sustained drug release behavior following diffusion-controlled kinetics, ensuring prolonged availability of bioactive compounds at the wound site.

The formulation also showed significant antimicrobial activity against common wound pathogens and maintained stability under both normal and accelerated storage conditions, indicating its robustness and suitability for practical use. The presence of flavonoids such as quercetin contributed to antioxidant, antimicrobial, and tissue regenerative effects, which are critical in overcoming the impaired healing associated with diabetic wounds. Overall, the developed guava leaf hydrogel represents a promising, cost-effective, and plant-based therapeutic approach for enhancing wound healing in diabetic patients. Further in vivo and clinical studies are recommended to validate its efficacy and establish its potential for large-scale pharmaceutical application.

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