Sustainable phyto-fabrication of silver nanoparticles using Gmelina arborea exhibit antimicrobial and biofilm inhibition activity

Increase in bacterial resistance to commonly used antibiotics is a major public health concern generating interest in novel antibacterial treatments. Aim of this scientific endeavor was to find an alternative efficient antibacterial agent from non-conventional plant source for human health applications. We used an eco-friendly approach for phyto-fabrication of silver nanoparticles (AgNPs) by utilizing logging residue from timber trees Gmelina arborea (GA). GC-MS analysis of leaves, barks, flowers, fruits, and roots was conducted to determine the bioactive compounds. Biosynthesis, morphological and structural characterization of GA-AgNPs were undertaken by UV-Vis spectroscopy, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometer (XRD). GA-AgNPs were evaluated for antibacterial, antibiofilm, antioxidant, wound healing properties and their toxicity studies were carried out. Results identified the presence of terpenoids, sterols, aliphatic alcohols, aldehydes, and flavonoids in leaves, making leaf extract the ideal choice for phyto-fabrication of silver nanoparticles. The synthesis of GA-AgNPs was confirmed by dark brown colored colloidal solution and spectral absorption peak at 420 nm. Spherical, uniformly dispersed, crystalline GA-AgNPs were 34-40 nm in diameter and stable in solutions at room temperature. Functional groups attributed to the presence of flavonoids, terpenoids, and phenols that acted as reducing and capping agents. Antibacterial potency was confirmed against pathogenic bacteria Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus by disc diffusion assay, MIC and MBC assay, biofilm inhibition assay, electron-microscopy, cell staining and colony counting techniques. The results from zone of inhibition, number of ruptured cells and dead-cell-count analysis confirmed that GA-AgNPs were more effective than GA-extract and their bacteria inhibition activity level increased further when loaded on hydrogel as GA-AgNPs-PF127, making it a novel distinguishing feature. Antioxidant activity was confirmed by the free radical scavenging assays (DPPH and ABTS). Wound healing potential was confirmed by cell scratch assay in human dermal fibroblast cell lines. Cell-proliferation study in human chang liver cell lines and optical microscopic observations confirmed non-toxicity of GA-AgNPs at low doses. Our study concluded that biosynthesized GA-AgNPs had enhanced antibacterial, antibiofilm, antioxidant, and wound healing properties.

Synthesis, Characterization, Antibacterial and Wound Healing Efficacy of Silver Nanoparticles From Azadirachta indica

Bacteria are the causative agents of numerous diseases. Ever increasing number of bacterial infections has generated the need to find new antibiotic materials and new ways to combat bacterial infections. Our study investigated Azadirachta indica (AI) as an alternate source of antibiotic compounds. Phytochemical and GC-MS analysis revealed presence of flavonoids, phenolic compounds, terpenoids and terpenes. Aqueous extracts of leaves were used to synthesize silver nanoparticles (AI-AgNPs), as established by colorimetric confirmation with maximum absorbance peak at 400 nm. Optimized reaction parameters produced high yield of stable AI-AgNPs, which were characterized by UV-Vis spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy. Results confirmed particle diameter of 33 nm and spherical shape of AI-AgNPs. Fourier transform infrared spectroscopy inferred the presence of functional groups in bioactive constituents involved in conversion of silver ions into elemental silver by acting as capping and reducing agents during formation of AI-AgNPs. X-ray diffraction revealed their crystalline nature. Toxicity studies on Drosophila validated normal egg laying capacity and eclosion of F1 generation on AI-AgNPs (100 μg/mL). DPPH (65.17%) and ABTS (66.20%) assays affirmed strong radical scavenging effect of AI-AgNPs (500 μg/mL). The antibacterial activity of AI-AgNPs (1,000 μg/mL) was confirmed by disc diffusion assay with zone of inhibition against Bacillus cereus (17.7 mm), Escherichia coli (18.7 mm), Pseudomonas aeruginosa (10.3 mm), and Staphylococcus aureus (17.7 mm). Minimum inhibitory concentration and minimum bactericidal concentration values for AI-AgNPs ranged between 390 and 780 μg/mL. Higher bacterial suppression by AI-AgNPs in comparison with AI-extract was further divulged by prominent damage to the bacterial cell walls, disintegration of cell membranes and outflow of intercellular content as evident in SEM images. AI-AgNPs were loaded on PF127 (biocompatible-biodegradable polymer) to form a viscous, spreadable, hydrogel that demonstrated enhanced antibacterial properties in disc diffusion assay (13-18.7 mm). When topically applied on mice, AI-AgNPs-PF127 hydrogel did not show symptoms of skin irritation. Application of AI-AgNPs-PF127 hydrogel on wound sites in mice, significantly increased the wound contraction rate. Our studies present a simple green route to synthesize AI-AgNPs with enhanced antibacterial and free-radical scavenging efficacy; and AI-AgNPs-PF127 hydrogel as a low-toxic, eco-friendly delivery vehicle with potential in wound healing.

Biosynthesis of Silver Nanoparticles from Melia azedarach: Enhancement of Antibacterial, Wound Healing, Antidiabetic and Antioxidant Activities

PURPOSE

Global demand for novel, biocompatible, eco-friendly resources to fight diseases inspired this study. We investigated plants used in traditional medicine systems and utilized nanotechnology to synthesize, evaluate, and enhance potential applications in nanomedicine.

METHODS

Aqueous leaf extract from Melia azedarach (MA) was utilized for bio-synthesis of silver nanoparticles (MA-AgNPs). Reaction conditions were optimized for high yield and colloidal stability was evaluated using UV-Vis spectroscopy. MA-AgNPs were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Standard methods were used to analyze the antibacterial, wound healing, antidiabetic, antioxidant, and cytotoxic activities.

RESULTS

The formation of MA-AgNPs at room temperature was confirmed by stable brown colloidal solution with maximum absorbance at 420 nm (UV-Vis Spectroscopy). MA-AgNPs were spherical (SEM), uniformly dispersed, 14-20 nm in diameter (TEM), and crystalline in nature (XRD). Presence of elemental silver was confirmed by peak at 3 KeV (EDX). FTIR data revealed the presence of functional groups which indicate phyto-constituents (polyphenols, flavonoids, and terpenoids) may have acted as the reducing and capping agents. MA-AgNPs (1000 µg/mL) showed larger zone of inhibition than MA-extract in the disk diffusion assay for human pathogenic gram positive bacteria, Bacillus cereus (34 mm) and gram negative, Escherichia coli (37 mm), thus confirming their higher antibacterial activity. The cell scratch assay on human dermal fibroblast cells revealed potential wound healing activity. The MA-AgNPs (400 µg/mL) demonstrated high antidiabetic efficacy as measured by α-amylase (85.75%) and α-glucosidase (80.33%) inhibition assays and antioxidant activity as analyzed by DPPH (63.83%) and ABTS (63.61%) radical scavenging assays. Toxic effect of MA-AgNPs against human chang liver cells (CCL-13) as determined by MTS assay, optical microscopic and CMFDA dye methods was insignificant.

CONCLUSION

This sustainable, green synthesis of AgNPs is a competitive alternative to conventional methods and will play a significant role in biomedical applications of Melia azedarach.