Hydrogel with silver nanoparticles synthesized by Mimosa tenuiflora for second-degree burns treatment

Advancing burn wound treatment: exploring hydrogel as a transdermal drug delivery system

Burn injuries are prevalent and life-threatening forms that contribute significantly to mortality rates due to associated wound infections. The management of burn wounds presents substantial challenges. Hydrogel exhibits tremendous potential as an ideal alternative to traditional wound dressings such as gauze. This is primarily attributed to its three-dimensional (3D) crosslinked polymer network, which possesses a high water content, fostering a moist environment that supports effective burn wound healing. Additionally, hydrogel facilitates the penetration of loaded therapeutic agents throughout the wound surface, combating burn wound pathogens through the hydration effect and thereby enhancing the healing process. However, the presence of eschar formation on burn wounds obstructs the passive diffusion of therapeutics, impairing the efficacy of hydrogel as a wound dressing, particularly in cases of severe burns involving deeper tissue damage. This review focuses on exploring the potential of hydrogel as a carrier for transdermal drug delivery in burn wound treatment. Furthermore, strategies aimed at enhancing the transdermal delivery of therapeutic agents from hydrogel to optimize burn wound healing are also discussed.

Crosslinked hydrogel loaded with chitosan-supported iron oxide and silver nanoparticles as burn wound dressing

Burns can result in infection, disability, psychosocial and economic issues. Advanced wound dressings like hydrogel absorb exudate and maintain moisture. Considering the antimicrobial properties of silver nanoparticles and iron oxide nanoparticles, the efficiency of cross-linked hydrogel loaded with chitosan-supported iron oxide and silver nanoparticles for burn wounds repair was investigated in animal model. Cellulose hydrogel dressing made from carboxymethylcellulose and hydroxyethylcellulose crosslinked with different concentrations of citric acid (10, 15, 20, and 30%) was produced. The physicochemical characteristics of the synthetized hydrogels including Fourier-Transform Infrared spectroscopy, Thermal behavior, Swelling properties, and Scanning Electron Microscope (SEM) were evaluated. The silver nanoparticles and iron nanoparticles were produced and the characteristics, cytotoxicity, antimicrobial activities and their synergistic effect were investigated. After adding nanoparticles to hydrogels, the effects of the prepared wound dressings were investigated in a 14-day animal model of burn wound. The results showed that the mixture comprising 12.5 ppm AgNps, and IONPs at a concentration ≤100 ppm was non-cytotoxic. Moreover, the formulations with 20% CA had a swelling ratio of almost 250, 340, and 500 g/g at pHs of 5, 6.2, and 7.4 after one hour, which are lower than those of formulations with 5 and 10% CA. The total mass loss (59.31%) and the exothermic degradation happened in the range of 273-335 °C and its Tm was observed at 318.52 °C for hydrogels with 20% CA. Thus, the dressing comprising 20% CA which was loaded with 12.5 ppm silver nanoparticles (AgNPs) and 100 ppm iron oxide nanoparticles (IONPs) indicated better physicochemical, microbial and non-cytotoxic characteristics, and accelerated the process of wound healing after 14 days. It was concluded that the crosslinked hydrogel loaded with 12.5 ppm AgNPs and 100 ppm IONPs possesses great wound healing activity and could be regarded as an effective topical burn wound healing treatment.

Gracilaria salicornia as potential substratum for green synthesis of Cerium Oxide Nanoparticles coupled hydrogel: An effective antimicrobial thin film

Sodium alginate based (SA) hydrogel supplemented Cerium Oxide nanoparticles (CeO2NPs) was produced to fabricate an antimicrobial thin film using an aqueous extract of G. salicornia (Gs). The Gs-CeO2NPs were characterized via SEM, FT-IR, EDX, XRD and DLS, the particle size was 200 nm, agreed with XRD. Gs-SA powder was extracted and incorporated with CeO2NPs. The Gs-SA and its composite thin film (Gs-CeO2NPs-SATF) were characterized including viscosity, FT-IR, TGA, and SEM. The adhesion of Gs-SA coating around Gs-CeO2NPs confirmed via FTIR. The antimicrobial properties of Gs-CeO2NPs and CeO2NPs-SATF were proved in MICs for E. coli and Candida albicans at 62.5 and 250.0 μg/mL. The biofilm inhibition efficiency of CeO2NPs-SATF was 74.67 ± 0.98% and 65.45 ± 0.40% for E. coli and Candida albicans. The CeO2NPs-SATF was polydisperse in nature and film structure gets fluctuated with NPs concentration. Increased NPs into SATF enhances pore size of gel and corroborated with viscous behaviour. The cytotoxicity of Gs-CeO2NP-SA in Artemia salina at higher concentration 100 μg/mL provides less lethal effect into the adult. The antioxidant activity of Gs-CeO2NP-SA in DPPH assay was noticed at 0.6 mg ml-1 with radical scavenging activity at 65.85 ± 0.81%. Thus the Gs-CeO2NP-SATF would be suitable in antimicrobial applications.

Effects including photobiomodulation of galactomannan gel from Cassia grandis seeds in the healing process of second-degree burns

The epithelium recovery of skin-burned wounds has been currently achieved by several therapies, for example, hydrogel-based dressings and photobiomodulation therapy (PBMT). Thus, this work aimed to evaluate the healing activity of Cassia grandis seeds' galactomannan gel, associated or not with PBMT, in second-degree burns. Sixty male Wistar rats were assigned to four groups: Control (CG), Gel (GG), Laser/PBMT (LG), and Laser+Gel (GLG). Burns were made with an aluminum bar (90 °C), and submitted to clinical observations diary and area measurements at specific days. Microscopic analysis was based on histological criteria. The results showed that GG, LG, and GLG had a higher contraction rate (p < 0.05) than CG on the 14th experimental day, not differing from each other (∼95 %). At 21 days, all groups showed complete contraction (p > 0.05). Considering the histological results, LG and GLG showed excellent pro-wound healing properties after 14 days; at 21 days, all groups showed wound recovery compared to previous days. In view of the macroscopic and microscopic observations, the isolated treatments (Gel or Laser) effectively accelerated healing; however, the association (Laser+Gel) promoted re-epithelialization and stromal remodeling with better evolution of epithelium recovery due to the positive synergistic effect, thus emerging as a promising therapeutic alternative in the repair of burns.

Unraveling the New Perspectives on Antimicrobial Hydrogels: State-of-the-Art and Translational Applications

The growing impact of infections and the rapid emergence of antibiotic resistance represent a public health concern worldwide. The exponential development in the field of biomaterials and its multiple applications can offer a solution to the problems that derive from these situations. In this sense, antimicrobial hydrogels represent a promising opportunity with multiple translational expectations in the medical management of infectious diseases due to their unique physicochemical and biological properties as well as for drug delivery in specific areas. Hydrogels are three-dimensional cross-linked networks of hydrophilic polymers that can absorb and retain large amounts of water or biological fluids. Moreover, antimicrobial hydrogels (AMH) present good biocompatibility, low toxicity, availability, viscoelasticity, biodegradability, and antimicrobial properties. In the present review, we collect and discuss the most promising strategies in the development of AMH, which are divided into hydrogels with inherent antimicrobial activity and antimicrobial agent-loaded hydrogels based on their composition. Then, we present an overview of the main translational applications: wound healing, tissue engineering and regeneration, drug delivery systems, contact lenses, 3D printing, biosensing, and water purification.

A Review of Metal Nanoparticles Embedded in Hydrogel Scaffolds for Wound Healing In Vivo

An evolving field, nanotechnology has made its mark in the fields of nanoscience, nanoparticles, nanomaterials, and nanomedicine. Specifically, metal nanoparticles have garnered attention for their diverse use and applicability to dressings for wound healing due to their antimicrobial properties. Given their convenient integration into wound dressings, there has been increasing focus dedicated to investigating the physical, mechanical, and biological characteristics of these nanoparticles as well as their incorporation into biocomposite materials, such as hydrogel scaffolds for use in lieu of antibiotics as well as to accelerate and ameliorate healing. Though rigorously tested and applied in both medical and non-medical applications, further investigations have not been carried out to bring metal nanoparticle-hydrogel composites into clinical practice. In this review, we provide an up-to-date, comprehensive review of advancements in the field, with emphasis on implications on wound healing in in vivo experiments.

Multidrug-Resistant Pathogens in Burn Wound, Prevention, Diagnosis, and Therapeutic Approaches (Conventional Antimicrobials and Nanoparticles)

Multidrug-resistant pathogens are one of the common causes of death in burn patients and have a high risk of nosocomial infections, especially pneumonia, urinary tract infections, and cellulitis. The role of prolonged hospitalization and empirical antibiotics administration in developing multidrug-resistant pathogens is undeniable. In the early days of admitting burn patients, Gram-positive bacteria were the dominant isolates with a more sensitive antibiotic pattern. However, the emergence of Gram-negative bacteria that are more resistant later occurs. Trustworthy guideline administration in burn wards is one of the strategies to prevent multidrug-resistant pathogens. Also, a multidisciplinary therapeutic approach is an effective way to avoid antibiotic resistance that involves infectious disease specialists, pharmacists, and burn surgeons. However, the emerging resistance to conventional antimicrobial approaches (such as systemic antibiotic exposure, traditional wound dressing, and topical antibiotic ointments) among burn patients has challenged the treatment of multidrug-resistant infections, and using nanoparticles is a suitable alternative. In this review article, we will discuss different aspects of multidrug-resistant pathogens in burn wounds, emphasizing the full role of these pathogens in burn wounds and discussing the application of nanotechnology in dealing with them. Also, some advances in various types of nanomaterials, including metallic nanoparticles, liposomes, hydrogels, carbon quantum dots, and solid lipid nanoparticles in burn wound healing, will be explained.

Ulvan/Silver nanoparticle hydrogel films for burn wound dressing

Ulvan is a polysaccharide from green algae that shows good hydrogel film dressing characteristics. Silver nanoparticles (AgNP) can be incorporated into the hydrogel film to improve antibacterial properties and provide a potential burn treatment. In this study, we developed a novel hydrogel film wound dressing composed of ulvan and silver nanoparticles. Two concentrations (0.5 mM and 1 mM) of silver nitrate were used to produce ulvan-silver nanoparticles hydrogel film (UHF-AgNP0.5 and UHF-AgNP1), respectively. The physicochemical characteristics of the hydrogel films were evaluated, including particle size, zeta potential, Fourier transform infrared (FTIR), X-ray diffractometry (XRD), scanning electron microscope and energy-dispersive X-ray (SEM-EDX). Furthermore, the in vitro antimicrobial activity, and second-degree burn wound healing test were evaluated. The UHF-AgNP0.5 showed the highest antimicrobial activity compared to UHF-AgNP1 and UHF film. Meanwhile, an in vivo study using Wistar rats induced second-degree burns showed that UHF-AgNP0.5 significantly accelerated the healing process by regulating the inflammatory process, increasing re-epithelialization, and improving the vascularization process. Ulvan-silver nanoparticle hydrogel films have the ability to accelerate the healing of second-degree burns and are potential candidates for wound dressings.

Green Synthesis of Silver Nanoparticles Using Acacia ehrenbergiana Plant Cortex Extract for Efficient Removal of Rhodamine B Cationic Dye from Wastewater and the Evaluation of Antimicrobial Activity

Silver nanoparticles (Ag-NPs) exhibit vast potential in numerous applications, such as wastewater treatment and catalysis. In this study, we report the green synthesis of Ag-NPs using Acacia ehrenbergiana plant cortex extract to reduce cationic Rhodamine B (RhB) dye and for antibacterial and antifungal applications. The green synthesis of Ag-NPs involves three main phases: activation, growth, and termination. The shape and morphologies of the prepared Ag-NPs were studied through different analytical techniques. The results confirmed the successful preparation of Ag-NPs with a particle size distribution ranging from 1 to 40 nm. The Ag-NPs were used as a heterogeneous catalyst to reduce RhB dye from aqueous solutions in the presence of sodium borohydride (NaBH₄). The results showed that 96% of catalytic reduction can be accomplished within 32 min using 20 μL of 0.05% Ag-NPs aqueous suspension in 100 μL of 1 mM RhB solution, 2 mL of deionized water, and 1 mL of 10 mM NaBH₄ solution. The results followed a zero-order chemical kinetic (R² = 0.98) with reaction rate constant k as 0.059 mol L^-1 s^-1. Furthermore, the Ag-NPs were used as antibacterial and antifungal agents against 16 Gram-positive and Gram-negative bacteria as well as 1 fungus. The green synthesis of Ag-NPs is environmentally friendly and inexpensive, as well as yields highly stabilized nanoparticles by phytochemicals. The substantial results of catalytic reductions and antimicrobial activity reflect the novelty of the prepared Ag-NPs. These nanoparticles entrench the dye and effectively remove the microorganisms from polluted water.

Effects of silver nanoparticles on maternal mammary glands and offspring development under lactation exposure

The widespread applications of silver nanoparticles (AgNPs) throughout our daily lives have raised concerns regarding their environmental health and safety (EHS). Despite an increasing number of studies focused on the EHS impacts of AgNPs, there remain significant knowledge gaps with respect to their potential health impacts on susceptible populations, such as lactating mothers and infants. Herein, we aimed to investigate the deleterious effects of AgNPs with different sizes (20 and 40 nm) and surface coatings (PVP and BPEI) on maternal mice and their offspring following lactation exposure at doses of 20, 100 and 400 μg/kg body weight. We discovered that AgNPs could accumulate in the maternal mammary glands and disrupt the epithelial barrier in a dose-dependent manner. Notably, BPEI-coated AgNPs caused more damage to the mammary glands than PVP-coated particles. Importantly, we observed that, while AgNPs were distributed throughout the blood and main tissues, they were particularly enriched in the brains of breastfed offspring after maternal exposure during lactation, exhibiting exposure dosage- and particle coating-dependent patterns. Compared to PVP-coated nanoparticles, BPEI-coated AgNPs were more readily transferred to the offspring, possibly due to their enhanced deposition in maternal mammary glands. Moreover, we observed reduced body weight, blood cell toxicity, and tissue injuries in breastfed offspring whose dams received AgNPs. As a whole, these results reveal that maternal exposure to AgNPs results in the translocation of AgNPs into offspring via breastfeeding, inducing developmental impairments in these breastfed offspring. This study provides important new insights into the EHS impacts of AgNP consumption during lactation.

Plasma-Activated Hydrogels for Microbial Disinfection

A continuous risk from microbial infections poses a major environmental and public health challenge. As an emerging strategy for inhibiting bacterial infections, plasma-activated water (PAW) has proved to be highly effective, environmental-friendly, and non-drug resistant to a broad range of microorganisms. However, the relatively short lifetime of reactive oxygen and nitrogen species (RONS) and the high spreadability of liquid PAW inevitably limit its real-life applications. In this study, plasma-activated hydrogel (PAH) is developed to act as reactive species carrier that allow good storage and controlled slow-release of RONS to achieve long-term antibacterial effects. Three hydrogel materials, including hydroxyethyl cellulose (HEC), carbomer 940 (Carbomer), and acryloyldimethylammonium taurate/VP copolymer (AVC) are selected, and their antibacterial performances under different plasma activation conditions are investigated. It is shown that the composition of the gels plays the key role in determining their biochemical functions after the plasma activation. The antimicrobial performance of AVC is much better than that of PAW and the other two hydrogels, along with the excellent stability to maintain the antimicrobial activity for more than 14 days. The revealed mechanism of the antibacterial ability of the PAH identifies the unique combination of short-lived species (¹ O₂ , ∙OH, ONOO^- and O₂ ^- ) stored in hydrogels. Overall, this study demonstrates the efficacy and reveals the mechanisms of the PAH as an effective and long-term disinfectant capable of delivering and preserving antibacterial chemistries for biomedical applications.

Fabrication and desired properties of conductive hydrogel dressings for wound healing

Conductive hydrogels are platforms recognized as constituting promising materials for tissue engineering applications. This is because such conductive hydrogels are characterized by the inherent conductivity properties while retaining favorable biocompatibility and mechanical properties. These conductive hydrogels can be particularly useful in enhancing wound healing since their favorable conductivity can promote the transport of essential ions for wound healing via the imposition of a so-called transepithelial potential. Other valuable properties of these conductive hydrogels, such as wound monitoring, stimuli-response etc., are also discussed in this study. Crucially, the properties of conductive hydrogels, such as 3D printability and monitoring properties, suggest the possibility of its use as an alternative wound dressing to traditional dressings such as bandages. This review, therefore, seeks to comprehensively explore the functionality of conductive hydrogels in wound healing, types of conductive hydrogels and their preparation strategies and crucial properties of hydrogels. This review will also assess the limitations of conductive hydrogels and future perspectives, with an emphasis on the development trend for conductive hydrogel uses in wound dressing fabrication for subsequent clinical applications.

Pluronic® F127 Hydrogel Containing Silver Nanoparticles in Skin Burn Regeneration: An Experimental Approach from Fundamental to Translational Research

Presently, skin burns are considered one of the main public health problems and lack therapeutic options. In recent years, silver nanoparticles (AgNPs) have been widely studied, playing an increasingly important role in wound healing due to their antibacterial activity. This work is focused on the production and characterization of AgNPs loaded in a Pluronic® F127 hydrogel, as well as assessing its antimicrobial and wound-healing potential. Pluronic® F127 has been extensively explored for therapeutic applications mainly due to its appealing properties. The developed AgNPs had an average size of 48.04 ± 14.87 nm (when prepared by method C) and a negative surface charge. Macroscopically, the AgNPs solution presented a translucent yellow coloration with a characteristic absorption peak at 407 nm. Microscopically, the AgNPs presented a multiform morphology with small sizes (~50 nm). Skin permeation studies revealed that no AgNPs permeated the skin after 24 h. AgNPs further demonstrated antimicrobial activity against different bacterial species predominant in burns. A chemical burn model was developed to perform preliminary in vivo assays and the results showed that the performance of the developed AgNPs loaded in hydrogel, with smaller silver dose, was comparable with a commercial silver cream using higher doses. In conclusion, hydrogel-loaded AgNPs is potentially an important resource in the treatment of skin burns due to their proven efficacy by topical administration.

Three-Dimensional Evaluation of the Cytotoxicity and Antibacterial Properties of Alpha Lipoic Acid-Capped Silver Nanoparticle Constructs for Oral Applications

There is a need to develop bifunctional scaffolds that provide antibacterial protection while encouraging host cell attachment/proliferation. This study evaluates HyStem^®-C, and photo-cross-linked GelMA hydrogels for encapsulation and stabilisation of silver nanoparticles (AgNPs). We studied the behaviour of AgNPs and matrix interactions within both hydrogel systems. The cell viability of encapsulated human gingival fibroblasts (HGFs) was determined by Prestoblue^® assay and live/dead staining. The release of AgNPs was monitored by inductively coupled plasma-mass spectroscopy. The antibacterial properties of the GelMA-AgNP constructs were determined using disc diffusion. Even distribution of AgNPs in GelMA induced a significant decrease in cell viability (p < 0.0001), whereas AgNP aggregates did not induce cytotoxicity in HyStem^®-C. AgNPs doses ≥ 0.5 µg/mL in GelMA were significantly toxic to the HGFs (p < 0.0001). The release of AgNPs from GelMA after 48 h was 20% w/w for 0.1 µg/mL and 51% for 100 µg/mL of AgNPs. At ≥5 µg/mL, a significant intra-construct bactericidal effect was observed. The disc diffusion assay shows that GelMA-incorporated AgNPs were found to be effective against both Escherichia coli and Staphylococcus aureus at 50 and 100 µg/mL, respectively. Visible photo-cross-linked GelMA stably incorporated AgNPs to provide an antimicrobial regenerative construct for oral applications.

Solubility Enhancement, Formulation Development, and Antibacterial Activity of Xanthan-Gum-Stabilized Colloidal Gold Nanogel of Hesperidin against Proteus vulgaris

The objective of the study was to develop a transdermal nanoformulation of hesperidin (HSP) against Proteus vulgaris (P. vulgaris). Based on the low water solubility of HSP, we prepared HSP-enabled AuNPs stabilized with xanthan gum (XA), referred to as HSP@XA@AuNPs. The HSP@XA@AuNP formulation was evaluated for particle size (43.16 nm), PDI (0.565), zeta potential (−31.9 mV), and entrapment efficiency (56.7%). The HSP@XA@AuNPs gel was developed by incorporating selected formulation grades into a 1% Carbopol gel base and characterized by physical evaluation and rheological studies. The color of the HSP@XA@AuNP gel was light pink, and the texture was very smooth and non-greasy. The gel was shown to be odorless. A field emission scanning electron microscope (FESEM) was used to investigate the shape of HSP@XA@AuNPs further. The drug release was 73.08% for the HSP@XA@AuNPs and 86.26% for the HSP@XA@AuNPs gel in 500 min. The prepared gel showed antimicrobial activity against P. vulgaris with an MIC of 1.78 μg/mL. In conclusion, the HSP@XA@AuNPs gel could be an advanced modality for treating P. vulgaris.

New Amorphous Hydrogels with Proliferative Properties as Potential Tools in Wound Healing

The study and discovery of bioactive compounds and new formulations as potential tools for promoting the repair of dermoepidermal tissue in wound healing is of continuing interest. We have developed a new formulation of amorphous hydrogel based on sodium alginate (NaAlg); type I collagen, isolated by the authors from silver carp tails (COL); glycerol (Gli); Aloe vera gel powder (AV); and silver nanoparticles obtained by green synthesis with aqueous Cinnamomum verum extract (AgNPs@CIN) and vitamin C, respectively. The gel texture of the amorphous hydrogels was achieved by the addition of Aloe vera, demonstrated by a rheological analysis. The evaluations of the cytotoxicity and cell proliferation capacity of the experimental amorphous hydrogels were performed against human foreskin fibroblast Hs27 cells (CRL-1634-ATCC). The developed gel formulations did not show a cytotoxic effect. The hydrogel variant containing AgNPs@CIN in a concentration of 8 µg Ag/gel formulation and hydrogel variant with vitamin C had proliferative activity. In addition, the antibacterial activity of the hydrogels was evaluated against S. aureus ATCC 6538, Ps. aeruginosa ATCC 27853, and E. coli ATCC 25922. The results demonstrated that the gel variant based on AgNPs@CIN in a concentration of 95 µg Ag/gel formulation and the hydrogel based on vitamin C show antibacterial activity. Therefore, the developed hydrogels with AgNPs@CIN and vitamin C could be promising alternatives in wound healing.

Recent developments in the use of gold and silver nanoparticles in biomedicine

Gold and silver nanoparticles (NPs) are widely used in the biomedical research both in the therapeutic and the sensing/diagnostics fronts. Both metals share some common optical properties with surface plasmon resonance being the most widely exploited property in therapeutics and diagnostics. Au NPs exhibit excellent light‐to‐heat conversion efficiencies and hence have found applications primarily in precision oncology, while Ag NPs have excellent antibacterial properties which can be harnessed in biomaterials' design. Both metals constitute excellent biosensing platforms owing to their plasmonic properties and are now routinely used in various optical platforms. The utilization of Au and Ag NPs in the COVID‐19 pandemic was rapidly expanded mostly in biosensing and point‐of‐care platforms and to some extent in therapeutics. In this review article, the main physicochemical properties of Au and Ag NPs are discussed with selective examples from the recent literature.

This article is categorized under:

Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease

Diagnostic Tools > In Vitro Nanoparticle‐Based Sensing

Nanotechnology Approaches to Biology > Nanoscale Systems in Biology

Smart Methylcellulose Hydrogels for pH-Triggered Delivery of Silver Nanoparticles

Infection is a severe complication in chronic wounds, often leading to morbidity or mortality. Current treatments rely on dressings, which frequently contain silver as a broad-spectrum antibacterial agent, although improper dosing can result in severe side effects. This work proposes a novel methylcellulose (MC)-based hydrogel designed for the topical release of silver nanoparticles (AgNPs) via an intelligent mechanism activated by the pH variations in infected wounds. A preliminary optimization of the physicochemical and rheological properties of MC hydrogels allowed defining the optimal processing conditions in terms of crosslinker (citric acid) concentration, crosslinking time, and temperature. MC/AgNPs nanocomposite hydrogels were obtained via an in situ synthesis process, exploiting MC both as a capping and reducing agent. AgNPs with a 12.2 ± 2.8 nm diameter were obtained. MC hydrogels showed a dependence of the swelling and degradation behavior on both pH and temperature and a noteworthy pH-triggered release of AgNPs (release ~10 times higher at pH 12 than pH 4). ¹H-NMR analysis revealed the role of alkaline hydrolysis of the ester bonds (i.e., crosslinks) in governing the pH-responsive behavior. Overall, MC/AgNPs hydrogels represent an innovative platform for the pH-triggered release of AgNPs in an alkaline milieu.

Eco-Friendly Synthesized PVA/Chitosan/Oxalic Acid Nanocomposite Hydrogels Embedding Silver Nanoparticles as Antibacterial Materials

PVA/chitosan (PVA/CS) composite hydrogels incorporating silver nanoparticles (AgNPs) were prepared by double-cross-linked procedures: freeze−thawing and electrostatic interactions. Oxalic acid (OA) was used both for solubilization and ionic cross-linking of CS. AgNPs covered by CS (CS-AgNPs) with an average diameter of 9 nm and 18% silver were obtained in the presence of CS, acting as reducing agent and particle stabilizer. The increase of the number of freeze−thaw cycles, as well as of the PVA:CS and OA:CS ratios, resulted in an increase of the gel fraction and elastic modulus. Practically, the elastic modulus of the hydrogels increased from 3.5 kPa in the absence of OA to 11.6 kPa at a 1:1 OA:CS weight ratio, proving that OA was involved in physical cross-linking. The physicochemical properties were not altered by the addition of CS-AgNPs in low concentration; however, concentrations higher than 3% resulted in low gel fraction and elastic modulus. The amount of silver released from the composite hydrogels is very low (<0.4%), showing that AgNPs were well trapped within the polymeric matrix. The composite hydrogels displayed antimicrobial activity against S. aureus, K. pneumoniae or P. gingivalis. The low cytotoxicity and the antibacterial efficacy of hydrogels recommend them for wound and periodontitis treatment.