Active silver nanoparticles for wound healing

The activity of silver nanoparticles against microalgae of the Prototheca genus

AIM

To investigate the in vitro activity of silver NPs (AgNPs) against pathogenic microalgae of the Prototheca genus.

MATERIALS & METHODS

The antialgal potential of AgNPs against Prototheca species of both clinical and environmental origin was assessed from minimum inhibitory (algistatic) and algicidal concentrations. The in vitro cytotoxicity of AgNPs against bovine mammary epithelial cell line was evaluated by means of the standard MTT assay.

RESULTS

AgNPs showed a strong killing activity toward Prototheca algae, as the minimal algicidal concentration (MAC) values matched perfectly the corresponding minimum inhibitory concentration (MIC) values for all species (MAC = MIC, 1-4 mg/l), except P. stagnora (MIC > 8 mg/l). The concentrations inhibitory to pathogenic Prototheca spp. (MIC, 1-4 mg/l) were below the concentrations at which any toxicity in epithelial cells could be observed (CC₂₀ > 6 mg/l).

CONCLUSION

The study emphasizes the potential of AgNPs as a new therapeutic tool for the management of Prototheca infections.

Overview of Silk Fibroin Use in Wound Dressings

Recently, biomimetic wound dressings were introduced as potential replacements for treating skin injuries. Although there are some clinically available skin replacements, the range of wound types and locations necessitates a broader range of options for the clinic. Natural polymeric-based dressings are of central interest in this area due to their outstanding biocompatibility, biodegradability, low toxicity, and non-allergenic nature. Among them, silk fibroin (SF) has exceptional characteristics as a wound dressing. SF-based dressings can also be used as carriers for delivering drugs, growth factors, and bioactive agents to the wound area, while providing appropriate support for complete healing. In this review, we describe recent advances in the development of SF-based wound dressings for skin regeneration.

Modeling Skin Injury from Hot Rice Porridge Spills

The present work analyzes skin burns from spills of hot rice and milk products. The traditional Norwegian rice porridge serves as an example. By testing spills on objects emulating an arm, it was concluded that spills were seldom thinner than 3 mm, and stayed in place due to the viscosity of the porridge for more than one minute. The Pennes bioheat equation was solved numerically for such spills, including heat conduction to the skin and convective heat losses from the porridge surface. Temperatures were analyzed in the porridge and skin layers, and the resulting skin injury was calculated based on the basal layer temperature. Parameters influencing burn severity, such as porridge layer thickness, porridge temperature, removal of the porridge and thermal effects of post scald tempered (15 °C) water cooling were analyzed. The spilled porridge resulted in a prolonged heat supply to the skin, and the skin injury developed significantly with time. The porridge temperature turned out to be the most important injury parameter. A 70 °C porridge temperature could develop superficial partial-thickness burns. Porridge temperatures at processing temperatures nearly instantly developed severe burns. It was demonstrated that prompt removal of the hot porridge significantly reduced the injury development. The general advice is to avoid serving porridge and similar products at temperatures above 65 °C and, if spilled on the skin, to remove it quickly. After such scald incidents, it is advised to cool the injured area by tempered water for a prolonged period to stimulate healing.

Nanocoatings for Chronic Wound Repair-Modulation of Microbial Colonization and Biofilm Formation

Wound healing involves a complex interaction between immunity and other natural host processes, and to succeed it requires a well-defined cascade of events. Chronic wound infections can be mono- or polymicrobial but their major characteristic is their ability to develop a biofilm. A biofilm reduces the effectiveness of treatment and increases resistance. A biofilm is an ecosystem on its own, enabling the bacteria and the host to establish different social interactions, such as competition or cooperation. With an increasing incidence of chronic wounds and, implicitly, of chronic biofilm infections, there is a need for alternative therapeutic agents. Nanotechnology shows promising openings, either by the intrinsic antimicrobial properties of nanoparticles or their function as drug carriers. Nanoparticles and nanostructured coatings can be active at low concentrations toward a large variety of infectious agents; thus, they are unlikely to elicit emergence of resistance. Nanoparticles might contribute to the modulation of microbial colonization and biofilm formation in wounds. This comprehensive review comprises the pathogenesis of chronic wounds, the role of chronic wound colonization and infection in the healing process, the conventional and alternative topical therapeutic approaches designed to combat infection and stimulate healing, as well as revolutionizing therapies such as nanotechnology-based wound healing approaches.

Electroactive biomaterials: Vehicles for controlled delivery of therapeutic agents for drug delivery and tissue regeneration

Electrical stimulation for delivery of biochemical agents such as genes, proteins and RNA molecules amongst others, holds great potential for controlled therapeutic delivery and in promoting tissue regeneration. Electroactive biomaterials have the capability of delivering these agents in a localized, controlled, responsive and efficient manner. These systems have also been combined for the delivery of both physical and biochemical cues and can be programmed to achieve enhanced effects on healing by establishing control over the microenvironment. This review focuses on current state-of-the-art research in electroactive-based materials towards the delivery of drugs and other therapeutic signalling agents for wound care treatment. Future directions and current challenges for developing effective electroactive approach based therapies for wound care are discussed.

Instructive microenvironments in skin wound healing: Biomaterials as signal releasing platforms

Skin wound healing aims to repair and restore tissue through a multistage process that involves different cells and signalling molecules that regulate the cellular response and the dynamic remodelling of the extracellular matrix. Nowadays, several therapies that combine biomolecule signals (growth factors and cytokines) and cells are being proposed. However, a lack of reliable evidence of their efficacy, together with associated issues such as high costs, a lack of standardization, no scalable processes, and storage and regulatory issues, are hampering their application. In situ tissue regeneration appears to be a feasible strategy that uses the body's own capacity for regeneration by mobilizing host endogenous stem cells or tissue-specific progenitor cells to the wound site to promote repair and regeneration. The aim is to engineer instructive systems to regulate the spatio-temporal delivery of proper signalling based on the biological mechanisms of the different events that occur in the host microenvironment. This review describes the current state of the different signal cues used in wound healing and skin regeneration, and their combination with biomaterial supports to create instructive microenvironments for wound healing.

Nanopharmaceuticals for wound healing - Lost in translation?

Today, many of the newly developed pharmaceuticals and medical devices take advantage of nanotechnology and with a rising incidence of chronic diseases such as diabetes and cardiovascular disease, the number of patients afflicted globally with non-healing wounds is growing. This has created a requirement for improved therapies and wound care. However, converting the strategies applied in early research into new products is still challenging. Many of them fail to comply with the market requirements. This review discusses the legal and scientific challenges in the design of nanomedicines for wound healing. Are they lost in translation or is there a new generation of therapeutics in the pipeline?

Applications of Metals for Bone Regeneration

The regeneration of bone tissue is the main purpose of most therapies in dental medicine. For bone regeneration, calcium phosphate (CaP)-based substitute materials based on natural (allo- and xenografts) and synthetic origins (alloplastic materials) are applied for guiding the regeneration processes. The optimal bone substitute has to act as a substrate for bone ingrowth into a defect, as well as resorb in the time frame needed for complete regeneration up to the condition of restitution ad integrum. In this context, the modes of action of CaP-based substitute materials have been frequently investigated, where it has been shown that such materials strongly influence regenerative processes such as osteoblast growth or differentiation and also osteoclastic resorption due to different physicochemical properties of the materials. However, the material characteristics needed for the required ratio between new bone tissue formation and material degradation has not been found, until now. The addition of different substances such as collagen or growth factors and also of different cell types has already been tested but did not allow for sufficient or prompt application. Moreover, metals or metal ions are used differently as a basis or as supplement for different materials in the field of bone regeneration. Moreover, it has already been shown that different metal ions are integral components of bone tissue, playing functional roles in the physiological cellular environment as well as in the course of bone healing. The present review focuses on frequently used metals as integral parts of materials designed for bone regeneration, with the aim to provide an overview of currently existing knowledge about the effects of metals in the field of bone regeneration.

Tannic acid-modified silver nanoparticles for wound healing: the importance of size

Introduction

Silver nanoparticles (AgNPs) have been shown to promote wound healing and to exhibit antimicrobial properties against a broad range of bacteria. In our previous study, we prepared tannic acid (TA)-modified AgNPs showing a good toxicological profile and immunomodulatory properties useful for potential dermal applications.

Methods

In this study, in vitro scratch assay, antimicrobial tests, modified lymph node assay as well as a mouse splint wound model were used to access the wound healing potential of TA-modified and unmodified AgNPs.

Results

TA-modified but not unmodified AgNPs exhibited effective antibacterial activity against Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli and stimulated migration of keratinocytes in vitro. The tests using the mouse splint wound model showed that TA-modified 33 and 46 nm AgNPs promoted better wound closure, epithelialization, angiogenesis and formation of the granulation tissue. Additionally, AgNPs elicited expression of VEGF-α, PDGF-β and TGF-β1 cytokines involved in wound healing more efficiently in comparison to control and TA-treated wounds. However, both the lymph node assay and the wound model showed that TA-modified AgNPs sized 13 nm can elicit strong inflammatory response not only during wound healing but also when applied to the damaged skin.

Conclusion

TA-modified AgNPs sized >26 nm promote wound healing better than TA-modified or unmodified AgNPs. These findings suggest that TA-modified AgNPs sized >26 nm may have a promising application in wound management.

The use of nanoparticles in wound treatment: a systematic review

OBJECTIVE

To analyze the effects of nanoparticle-based dressings on the wound healing process in in vitro animals and human cells based on scientific evidence.

METHOD

A systematic review of the literature in LILACS, PubMed and Science Direct databases. The articles were selected and evaluated for the level of evidence by the application of STROBE.

RESULTS

The sample consisted of 12 articles. The application of the products occurred in surgical wounds, burns, infected wounds and gingival ulcers in laboratory animals, as well as in vitro tests, demonstrating that among other advantages, the nanoparticle-based dressings increased the healing speed, had good antibacterial capacity and were non cytotoxic agents.

CONCLUSION

Based on the analyzed articles, it can be affirmed that dressings containing nanocomposites are quite promising and are shown as a great therapeutic option in wound healing.

Nanomedicine and advanced technologies for burns: Preventing infection and facilitating wound healing

According to the latest report from the World Health Organization, an estimated 265,000 deaths still occur every year as a direct result of burn injuries. A widespread range of these deaths induced by burn wound happens in low- and middle-income countries, where survivors face a lifetime of morbidity. Most of the deaths occur due to infections when a high percentage of the external regions of the body area is affected. Microbial nutrient availability, skin barrier disruption, and vascular supply destruction in burn injuries as well as systemic immunosuppression are important parameters that cause burns to be susceptible to infections. Topical antimicrobials and dressings are generally employed to inhibit burn infections followed by a burn wound therapy, because systemic antibiotics have problems in reaching the infected site, coupled with increasing microbial drug resistance. Nanotechnology has provided a range of molecular designed nanostructures (NS) that can be used in both therapeutic and diagnostic applications in burns. These NSs can be divided into organic and non-organic (such as polymeric nanoparticles (NPs) and silver NPs, respectively), and many have been designed to display multifunctional activity. The present review covers the physiology of skin, burn classification, burn wound pathogenesis, animal models of burn wound infection, and various topical therapeutic approaches designed to combat infection and stimulate healing. These include biological based approaches (e.g. immune-based antimicrobial molecules, therapeutic microorganisms, antimicrobial agents, etc.), antimicrobial photo- and ultrasound-therapy, as well as nanotechnology-based wound healing approaches as a revolutionizing area. Thus, we focus on organic and non-organic NSs designed to deliver growth factors to burned skin, and scaffolds, dressings, etc. for exogenous stem cells to aid skin regeneration. Eventually, recent breakthroughs and technologies with substantial potentials in tissue regeneration and skin wound therapy (that are as the basis of burn wound therapies) are briefly taken into consideration including 3D-printing, cell-imprinted substrates, nano-architectured surfaces, and novel gene-editing tools such as CRISPR-Cas.

Mechanisms Underlying Neurotoxicity of Silver Nanoparticles

The potent antimicrobial properties of nanoparticulate silver (AgNPs) have led to broad interest in using them in a wide range of commercial and medical applications. Although numerous in vivo and in vitro studies have provided evidence of toxic effects, rapid commercialization of AgNP-based nanomaterials has advanced without characterization of their potential environmental and health hazards. There is evidence that AgNPs can be translocated from the blood to the brain, regardless the route of exposure, and accumulate in the brain over time. As the brain is responsible for basic physiological functions and controls all human activities, it is important to assess the hazardous influence of AgNPs released from widely used nanoproducts and possible side effects of AgNP-based therapies. A number of studies have suggested that the size, shape and surface coating, as well as rates of silver ion release and interactions with proteins are the key factors determining the neurotoxicity of AgNPs. AgNPs target endothelial cells forming the blood-brain barrier, neurons and glial cells and leads finally to oxidative stress-related cell death. In this chapter, we review in detail current data on the impact of AgNPs on the central nervous system and discuss the possible mechanisms of their neurotoxic effects.

Modeling Skin Injury from Hot Spills on Clothing

The present work analyzes scald burns from hot beverages, such as coffee and tea, spilled on the lap, i.e., an incident that may occur in daily life. The Pennes bioheat equation is solved numerically for small spills wetting the clothing, i.e., the fabric prevents the spilled liquid from draining away. Temperatures are analyzed in the wetted fabric and the skin layers and the resulting skin injury is calculated based on the basal layer temperature. Parameters influencing burn severity, such as clothing thickness, liquid temperature, removal of fabric and thermal effects of post scald water cooling are analyzed. The fabric cools the water some but represents a threat since the entrapped water results in a prolonged heat supply. The liquid temperature turned out to be the most important injury parameter, where liquid temperature of about 80–85 °C seems to be a limit for developing superficial partial-thickness burns in the present minimum case, i.e., where the liquid just wets the fabric. Spilling water in excess of just wetting the fabric, more severe burns will develop at lower liquid temperatures due to the prolonged heat supply. Higher liquid temperatures will nearly instantly develop more severe burns. It is demonstrated that removal of the clothing within the first seconds after the spill may significantly reduce the scalding severity. The general advice is therefore to avoid excessive heating of beverages and, if the beverage is spilled, to quickly remove the wetted clothing. Prolonged tempered water cooling is advised to improve the healing processes.

Cellular imaging and bactericidal mechanism of green-synthesized silver nanoparticles against human pathogenic bacteria

In recent years, silver nanoparticles (AgNPs) have attracted significant attention in medicinal, biomedical, and pharmaceutical research owing to their valuable physicochemical and antibacterial properties. Leaf sap extract (LSE) from Aloe arborescens can be used as an active ingredient for different biological applications, including wound healing. In this study, we have investigated the use of LSE from A. arborescens as a reducing, stabilizing and capping agent to produce AgNPs during the so called "green synthesis" (G-AgNPs). The objective of this study was to prepare, characterize and evaluate the potential of G-AgNPs against human pathogenic bacteria for the intended use as treatment of infected wounds. When the mixture of silver nitrate solution and LSE was exposed to direct sunlight it yielded a rapid color change from colorless to reddish-brown, indicating the formation of G-AgNPs. Physicochemical characterization such as Single particle inductively coupled plasma mass spectrometry, High resolution transmission electron microscopy and surface chemistry studies (Fourier transform infrared spectroscopy and X-Ray diffraction) revealed a small size in the range of 38±2nm, smooth surface and existence of LSE on the G-AgNPs. G-AgNPs possessed good antibacterial activity against both Pseudomonas aeruginosa and Staphylococcus aureus. The flow cytometry study revealed the increased percentage of dead cells treated by G-AgNPs through cell membrane damage, and it was further confirmed by confocal laser scanning microscopy. Thus, the present study reveals that the novel G-AgNPs demonstrated effective antibacterial properties against both Gram-negative and Gram-positive bacterial strains and shows great potential for its use in the treatment of pathogen infected wounds.

Silver nanoparticle loaded collagen/chitosan scaffolds promote wound healing via regulating fibroblast migration and macrophage activation

Treatment of full-thickness skin defects poses significant clinical challenges including risk of infection and severe scaring. Silver nanoparticle (NAg), an effective antimicrobial agent, has provided a promising therapeutic method for burn wounds. However, the detailed mechanism remains unknown. Hence, we constructed a metallic nanosilver particles-collagen/chitosan hybrid scaffold (NAg-CCS) and investigated its potential effects on wound healing. In vitro scratch assay, immunofluorescence staining and antibacterial activity of the scaffold were all studied. In vivo NAg-CCS was applied in full-thickness skin defects in Sprague-Dawley (SD) rats and the therapeutic effects of treatment were evaluated. The results showed that NAg at a concentration of 10 ppm accelerated the migration of fibroblasts with an increase in expression of α-smooth muscle actin (α-SMA). Furthermore, in vivo studies showed increased levels of pro-inflammatory and scar-related factors as well as α-SMA, while markers for macrophage activation were up-regulated. On day 60 post transplantation of ultra-thin skin graft, the regenerated skin by NAg-CCS had a similar structure to normal skin. In summary, we demonstrated that NAg-CCS was bactericidal, anti-inflammatory and promoted wound healing potentially by regulating fibroblast migration and macrophage activation, making it an ideal dermal substitute for wound regeneration.

Effect of oil gauze silver dressings on diabetic foot ulcers in the elderly

OBJECTIVE

To compare the clinical efficacy and safety of oil gauze silver dressing and silver ions dressing on diabetic ulcers in elderly outpatients.

METHODS

Twenty-two patients with Type-2 diabetic foot ulcers were included in the study conducted at Yantai Yuhuangding Hospital between April 2013 and April 2014. At the time of enrolment they were divided into the silver ions and oil gauze silver groups based on the order of admission. Dressings were changed twice weekly until the ulcer had healed. Clinical efficacy measures were healing outcomes and speed of healing. Adverse events were recorded.

RESULTS

The silver ions and oil gauze silver groups were comparable at baseline (P>0.05). Before treatment, the fasting blood glucose (FBG) and two hour postprandial blood glucose (2h PBG) levels were 6.88±0.50 mmol /L and 15.55±2.47 mmol/L in the oil gauze silver group, and 6.93±0.41 mmol/L and 15.23±2.58 mmol/L in the silver ions group, respectively. After treatment, the FBG and 2h PBG levels were 6.82±0.32 mmol/L and 8.67±0.86 mmol/L in the oil gauze silver group, and 6.85±0.27 mmol/L and 8.83 ± 0.61 mmol/L in the silver ions group, respectively. The healing time of foot ulcers was 23.8±2.7 days in the silver ions group and 15.8±2.5 days in the oil gauze silver group (P<0.05).

CONCLUSION

Oil gauze silver dressings for diabetic foot ulcers were associated with favorable clinical outcomes compared with silver ion dressings, especially with respect to ulcer healing speed.

Modular approach for bimodal antibacterial surfaces combining photo-switchable activity and sustained biocidal release

Photo-responsive antibacterial surfaces combining both on-demand photo-switchable activity and sustained biocidal release were prepared using sequential chemical grafting of nano-objects with different geometries and functions. The multi-layered coating developed incorporates a monolayer of near-infrared active silica-coated gold nanostars (GNS) decorated by silver nanoparticles (AgNP). This modular approach also enables us to unravel static and photo-activated contributions to the overall antibacterial performance of the surfaces, demonstrating a remarkable synergy between these two mechanisms. Complementary microbiological and imaging evaluations on both planktonic and surface-attached bacteria provided new insights on these distinct but cooperative effects.

In vitro antimicrobial and in vivo wound healing effect of actinobacterially synthesised nanoparticles of silver, gold and their alloy

Antibacterial, antifungal and wound healing potential of actinobacterially synthesised Ag, Au and Ag/Au nanoparticles.

Effects of a silver nanomaterial on cellular organelles and time course of oxidative stress in a fish cell line (PLHC-1)

Among the nanomaterials currently in commercial products, those based on silver are the most used, and so there is a high probability that silver nanoparticles (AgNPs) will be released into aquatic environments where they could adversely affect aquatic organisms, including fish. Taking this into account, the aim of the present work was to characterize in depth the mechanisms underlying the toxic action of AgNPs using fish cell lines, determining specifically the contribution of alterations in cellular structures and oxidative stress time course to the cytotoxicity of AgNPs. Since liver plays a key role in detoxification, the hepatoma cell line PLHC-1 was used. Exposure to AgNPs (NM-300K, obtained from the Joint Research Centre Repository) caused alterations at the lysosomal and mitochondrial levels at lower concentrations than those that disrupted plasma membrane (evaluated by means of neutral red, alamarBlue, and 5-carboxyfluorescein diacetate, acetoxymethyl ester assays respectively). AgNO₃, used as a control Ag⁺ ion source, produced similar cytotoxic effects but at lower concentrations than AgNPs. Both silver forms caused oxidative disruption but the initial response was delayed in AgNPs until 6h of exposure. Transmission electron microscopy analysis also evidenced the disruption of mitochondrial structures in cells exposed to cytotoxic concentrations of both forms of silver. At non-cytotoxic concentrations, AgNPs were detected inside the nucleoli and mitochondria, thereby pointing to long-term effects. The present work evidences the mutual interaction between the induction of oxidative stress and the alterations of cellular structures, particularly mitochondria, as cytotoxicity mechanisms not exclusively associated to NPs.

Ameliorating Effects of Green Synthesized Silver Nanoparticles on Glycated End Product Induced Reactive Oxygen Species Production and Cellular Toxicity in Osteogenic Saos-2 Cells

Advanced glycation end-products (AGEs) that result from nonenzymatic glycation are one of the major factors involved in diabetes and its secondary complications and diseases. This necessitates our urge to discover new compounds that may be used as potential AGEs inhibitors without affecting the normal structure and function of biomolecules. In the present study, we investigated the inhibitory effects of AgNP (silver nanoparticles) on AGEs formation as well as their inhibitory effects on glycation mediated cell toxicity via reactive oxygen species (ROS) production and DNA damage. The excitation-emission fluorescence spectroscopy was employed to investigate the interaction of AgNP during glycation. The values of conditional stability constant (log K_a = 4.44) derived from the Stern-Volmer equation indicate that AgNP have strong binding capacity for glycated protein. UV-vis, fluorescence, and Fourier transform infrared spectral data reveal complexation of AgNP with glycated bovine serum albumin, which significantly inhibits AGEs formation in a concentration-dependent manner. Cytotoxic evaluations suggest that simultaneous administration of AgNP and glycated product reduces cell death (42.82% ± 3.54) as compared to the glycated product alone. Similarly, ROS production in AgNP treated cells is significantly less compared to only glycated product treated cells. Although DNA damage studies show DNA damage in both GP and GP-AgNP treated cells, fluorescence activated cell sorting analysis demonstrates that glycated products induce cell death by necrosis, while AgNP cause cell death via apoptotic pathways. AgNP have a positive effect on restoring native protein structure deduced from spectral studies, and hence, inferences can be drawn that AgNP have ameliorating effects on glycated induced cytotoxicity observed in osteogenic Saos-2 cells.

Biomaterials and Nanotherapeutics for Enhancing Skin Wound Healing

Wound healing is an intricate process that requires complex coordination between many cell types and an appropriate extracellular microenvironment. Chronic wounds often suffer from high protease activity, persistent infection, excess inflammation, and hypoxia. While there has been intense investigation to find new methods to improve cutaneous wound care, the management of chronic wounds, burns, and skin wound infection remain challenging clinical problems. Ideally, advanced wound dressings can provide enhanced healing and bridge the gaps in the healing processes that prevent chronic wounds from healing. These technologies have great potential for improving outcomes in patients with poorly healing wounds but face significant barriers in addressing the heterogeneity and clinical complexity of chronic or severe wounds. Active wound dressings aim to enhance the natural healing process and work to counter many aspects that plague poorly healing wounds, including excessive inflammation, ischemia, scarring, and wound infection. This review paper discusses recent advances in the development of biomaterials and nanoparticle therapeutics to enhance wound healing. In particular, this review focuses on the novel cutaneous wound treatments that have undergone significant preclinical development or are currently used in clinical practice.

Characterization of silver particles in the stratum corneum of healthy subjects and atopic dermatitis patients dermally exposed to a silver-containing garment

Silver is increasingly being used in garments to exploit its antibacterial properties. Information on the presence of silver nanoparticles (AgNPs) in garments and their in vivo penetration across healthy and impaired skin from use is limited. We investigated the presence of AgNPs in a silver containing garment and in the stratum corneum (SC) of healthy subjects (CTRLs) and individuals with atopic dermatitis (AD). Seven CTRLs and seven AD patients wore a silver sleeve (13% Ag w/w) 8 h/day for five days on a forearm and a placebo sleeve on the other forearm. After five days, the layers of the SC were collected by adhesive tapes. The silver particles in the garment and SC were characterized by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) and atomic force microscopy (AFM). AFM and SEM revealed the presence of sub-micrometre particles having a broad range of sizes (30-500 nm) on the surface of the garment that were identified as silver. On the SC tapes collected from different depths, aggregates with a wide range of sizes (150 nm-2 μm) and morphologies were found. Most aggregates contained primarily silver, although some also contained chlorine and sulfur. There was no clear difference in the number or size of the aggregates observed in SC between healthy and AD subjects. After use, AgNPs and their aggregates were present in the SC at different depths of both healthy subjects and AD patients. Their micrometre size suggests that aggregation likely occurred in the SC.

Fabrication of electrospun polycaprolactone coated withchitosan-silver nanoparticles membranes for wound dressing applications

In this study, electrospun polycaprolactone membrane coated with chitosan-silver nanoparticles (CsAg), electrospun polycaprolactone/chitosan/Ag nanoparticles, was fabricated by immersing the plasma-treated electrospun polycaprolactone membrane in the CsAg gel. The plasma modification of electrospun polycaprolactone membrane prior to CsAg coating was tested by methylene blue stain and scanning electron microscope. The presence of silver and chitosan on the plasma-treated electrospun polycaprolactone membrane was confirmed by energy-dispersive X-ray spectroscopy and FT-IR spectrum. Scanning electron microscope observation was employed to observe the morphology of the membranes. The release of Ag ions from electrospun polycaprolactone/chitosan/Ag nanoparticles membrane was tested using atomic absorption spectrometry. Electrospun polycaprolactone/chitosan/Ag nanoparticles membrane inherited advantages from both CsAg gel and electrospun polycaprolactone membrane such as: increasing biocompatibility, mechanical strength, and antibacterial activity against both Gram-negative and Gram-positive bacteria. Thus, this investigation introduces a highly potential membrane that can increase the efficacy of the wound dressing process.

Evaluation of the wound healing efficacy of chemical and phytogenic silver nanoparticles

Wound healing requires a series of cellular events and a cascade of co-ordinated and systemic biochemical events. Silver nanoparticles possess many beneficial properties for wound management including antibacterial, anti-inflammatory and pro-healing properties. In this study, the authors investigated the wound healing properties of Cinnamomum verum extract mediated nanosilver (CENS) particles in comparison with 1% povidone iodine, citrate mediate NS and CE treatments. The topical application of CENS showed good antibacterial activity and accelerated wound healing with complete epithelialisation and normal re-growth of hair in all three models of study: namely, excision, incision and dead space models in rats compared with all other treatments. CENS was also found to promote collagen synthesis, stabilise wound besides countering oxidative stress and stimulating cellular proliferation CENS could be a novel therapeutic agent for wound management.

Effects of silver nanoparticles on human dermal fibroblasts and epidermal keratinocytes

Biomedical application of silver nanoparticles (AgNPs) has been rapidly increasing. Owing to their strong antimicrobial activity, AgNPs are used in dermatology in the treatment of wounds and burns. However, recent evidence for their cytotoxicity gives rise to safety concerns. This study was undertaken as a part of an ongoing programme in our laboratory to develop a topical agent for wound healing. Here, we investigated the potential toxicity of AgNPs using normal human dermal fibroblasts (NHDF) and normal human epidermal keratinocytes (NHEK) with the aim of comparing the effects of AgNPs and ionic silver (Ag-I). Besides the effect of AgNPs and Ag-I on cell viability, the inflammatory response and DNA damage in AgNPs and Ag-I–treated cells were examined. The results showed that Ag-I were significantly more toxic than AgNPs both on NHDF and NHEK. Non-cytotoxic concentrations of AgNPs and Ag-I did not induce DNA strand breaks and did not affect inflammatory markers, except for a transient increase in interleukin 6 levels in Ag-I–treated NHDF. The results showed that AgNPs are more suitable for the intended application as a topical agent for wound healing up to the concentration 25 µg/mL.

Bilayer Cryogel Wound Dressing and Skin Regeneration Grafts for the Treatment of Acute Skin Wounds

In this study, the potential of cryogel bilayer wound dressing and skin regenerating graft for the treatment of surgically created full thickness wounds was evaluated. The top layer was composed of polyvinylpyrrolidone-iodine (PVP-I) cryogel and served as the antiseptic layer, while the bottom regenerative layer was made using gelatin cryogel. Both components of the bilayer showed typical features of a cryogel interconnected macropore network, rapid swelling, high water uptake capacity of about 90%. Both PVP and gelatin cryogel showed high tensile strength of 45 and 10 kPa, respectively. Gelatin cryogel sheets were essentially elastic and could be stretched without any visible deformation. The antiseptic PVP-I layer cryogel sheet showed sustained iodine release and suppressed microbial growth when tested with skin pathogens (zone of inhibition ∼2 cm for sheet of 0.9 cm diameter). The gelatin cryogel sheet degraded in vitro in weeks. The gelatin cryogel sheet supported cell infiltration, attachment, and proliferation of fibroblasts and keratinocytes. Microparticles loaded with bioactive molecules (mannose-6-phosphate and human fibrinogen) were also incorporated in the gelatin cryogel sheets for their role in enhancing skin regeneration and scar free wound healing. In vivo evaluation of healing capacity of the bilayer cryogel was checked in rabbits by creating full thickness wound defect (diameter 2 cm). Macroscopic and microscopic observation at regular time intervals for 4 weeks demonstrated better and faster skin regeneration in the wound treated with cryogel bilayer as compared to untreated defect and the repair was comparable to commercial skin regeneration scaffold Neuskin-F. Complete skin regeneration was observed after 4 weeks of implantation with no sign of inflammatory response. Defects implanted with cryogel having mannose-6-phosphate showed no scar formation, while the wound treated with bilayer incorporated with human fibrinogen microparticles showed early signs of skin regeneration; epidermis formation occurred at 2 weeks after implantation.

Burn wound healing properties of asiaticoside and madecassoside

The healing of burn wounds has been widely characterized to be highly intricate, involving processes such as neo-vascularization, granulation, re-epithelialization, inflammation and wound contraction. Various therapies are available for the management of burn wounds; however, a truly effective therapeutic strategy has yet to be identified due to safety issues. The aim of the present study was to assess and confirm the burn wound healing properties of the compounds asiaticoside (AE) and madecassoside (MA), which are found in the herb Centella asiatica. The cytotoxic nature of the AE and MA were inspected and were confirmed to be non-toxic up to 500 ppm. The compounds AE and MA increased monocyte chemoattractant protein-1 production, but caused no significant effect on vascular endothelial growth factor production. In addition, an in vivo animal burn model was employed to represent the features of burn wound healing. Hence, the present results warrant the further investigation of C. asiatica extracts for use in burn healing.

Mesenchymal Stem Cells Increase Neo-Angiogenesis and Albumin Production in a Liver Tissue-Engineered Engraftment

The construction of a three-dimensional (3D) liver tissue is limited by many factors; one of them is the lack of vascularization inside the tissue-engineered construct. An engineered liver pocket-scaffold able to increase neo-angiogenesis in vivo could be a solution to overcome these limitations. In this work, a hyaluronan (HA)-based scaffold enriched with human mesenchymal stem cells (hMSCs) and rat hepatocytes was pre-conditioned in a bioreactor system, then implanted into the liver of rats. Angiogenesis and hepatocyte metabolic functions were monitored. The formation of a de novo vascular network within the HA-based scaffold, as well as an improvement in albumin production by the implanted hepatocytes, were detected. The presence of hMSCs in the HA-scaffold increased the concentration of growth factors promoting angiogenesis inside the graft. This event ensured a high blood vessel density, coupled with a support to metabolic functions of hepatocytes. All together, these results highlight the important role played by stem cells in liver tissue-engineered engraftment.

Tissue distribution and acute toxicity of silver after single intravenous administration in mice: nano-specific and size-dependent effects

BACKGROUND

Silver nanoparticles (AgNPs) are an important class of nanomaterials used as antimicrobial agents for a wide range of medical and industrial applications. However toxicity of AgNPs and impact of their physicochemical characteristics in in vivo models still need to be comprehensively characterized. The aim of this study was to investigate the effect of size and coating on tissue distribution and toxicity of AgNPs after intravenous administration in mice, and compare the results with those obtained after silver acetate administration.

METHODS

Male CD-1(ICR) mice were intravenously injected with AgNPs of different sizes (10 nm, 40 nm, 100 nm), citrate-or polyvinylpyrrolidone-coated, at a single dose of 10 mg/kg bw. An equivalent dose of silver ions was administered as silver acetate. Mice were euthanized 24 h after the treatment, and silver quantification by ICP-MS and histopathology were performed on spleen, liver, lungs, kidneys, brain, and blood.

RESULTS

For all particle sizes, regardless of their coating, the highest silver concentrations were found in the spleen and liver, followed by lung, kidney, and brain. Silver concentrations were significantly higher in the spleen, lung, kidney, brain, and blood of mice treated with 10 nm AgNPs than those treated with larger particles. Relevant toxic effects (midzonal hepatocellular necrosis, gall bladder hemorrhage) were found in mice treated with 10 nm AgNPs, while in mice treated with 40 nm and 100 nm AgNPs lesions were milder or negligible, respectively. In mice treated with silver acetate, silver concentrations were significantly lower in the spleen and lung, and higher in the kidney than in mice treated with 10 nm AgNPs, and a different target organ of toxicity was identified (kidney).

CONCLUSIONS

Administration of the smallest (10 nm) nanoparticles resulted in enhanced silver tissue distribution and overt hepatobiliary toxicity compared to larger ones (40 and 100 nm), while coating had no relevant impact. Distinct patterns of tissue distribution and toxicity were observed after silver acetate administration. It is concluded that if AgNPs become systemically available, they behave differently from ionic silver, exerting distinct and size-dependent effects, strictly related to the nanoparticulate form.

Collagen nanofiber containing silver nanoparticles for improved wound-healing applications

Electrospun nanofibers showing great promise for fabricating nanostructured materials might help to improve the quality of wound care. The present study aimed to investigate the wound-healing potential of collagen nanofiber mats containing silver nanoparticles. Silver nanoparticles (AgNPs) synthesized by the chemical reduction method were incorporated in collagen nanofibers during the electrospinning process. Characterization of electrospun nanofiber mats revealed a mean fiber diameters in the range of 300-700 nm with a sustained release of silver ions shown to follow pseudo-order kinetics. MIC of AgNPs against Staphylococcus aureus and Pseudomonas aeruginosa were evaluated using micro-dilution assay and further antimicrobial activity of fabricated nanofibers was performed. Finally, in vivo studies were performed to demonstrate the wound-healing efficacy of composite nanofibers. In vitro results confirmed the potential antimicrobial efficacy provided by AgNPs and AgNPs composite nanofibers, essential to provide an aseptic environment at the wound site. In vivo study revealed that the rate of wound healing of the composite nanofiber mats was found to be accelerated compared with plain collagen nanofibers. Histology analysis revealed an accelerated re-epithelization, collagen production, and better wound contraction with AgNPs composite collagen nanofibers.

Shape and surface chemistry effects on the cytotoxicity and cellular uptake of metallic nanorods and nanospheres

Metallic nanoparticles (such as gold and silver) have been intensely studied for wound healing applications due to their ability to be easily functionalized, possess antibacterial properties, and their strong potential for targeted drug release. In this study, rod-shaped silver nanorods (AgNRs) and gold nanorods (AuNRs) were fabricated by electron beam physical vapor deposition (EBPVD), and their cytotoxicity toward human skin fibroblasts were assessed and compared to sphere-shaped silver nanospheres (AgNSs) and gold nanospheres (AuNSs). Results showed that the 39.94 nm AgNSs showed the greatest toxicity with fibroblast cells followed by the 61.06 nm AuNSs, ∼556 nm × 47 nm (11.8:1 aspect ratio) AgNRs, and the ∼534 nm × 65 nm (8.2:1 aspect ratio) AuNRs demonstrated the least amount of toxicity. The calculated IC50 (50% inhibitory concentration) value for the AgNRs exposed to fibroblasts was greater after 4 days of exposure (387.3 μg mL(-1)) compared to the AgNSs and AuNSs (4.3 and 23.4 μg mL(-1), respectively), indicating that these spherical metallic nanoparticles displayed a greater toxicity to fibroblast cells. The IC50 value could not be measured for the AuNRs due to an incomplete dose response curve. The reduced cell toxicity with the presently developed rod-shaped nanoparticles suggests that they may be promising materials for use in numerous biomedical applications.

Nanoparticles as potential new generation broad spectrum antimicrobial agents

The rapid emergence of antimicrobial resistant strains to conventional antimicrobial agents has complicated and prolonged infection treatment and increased mortality risk globally. Furthermore, some of the conventional antimicrobial agents are unable to cross certain cell membranes thus, restricting treatment of intracellular pathogens. Therefore, the disease-causing-organisms tend to persist in these cells. However, the emergence of nanoparticle (NP) technology has come with the promising broad spectrum NP-antimicrobial agents due to their vast physiochemical and functionalization properties. In fact, NP-antimicrobial agents are able to unlock the restrictions experienced by conventional antimicrobial agents. This review discusses the status quo of NP-antimicrobial agents as potent broad spectrum antimicrobial agents, sterilization and wound healing agents, and sustained inhibitors of intracellular pathogens. Indeed, the perspective of developing potent NP-antimicrobial agents that carry multiple-functionality will revolutionize clinical medicine and play a significant role in alleviating disease burden.

Nanomaterials for wound healing: scope and advancement

Innovative methods for treating impaired and hard-to-heal wounds are needed. Novel strategies are needed for faster healing by reducing infection, moisturizing the wound, stimulating the healing mechanisms, speeding up the wound closure and reducing scar formation. In the past few years, nanotechnology has been constantly revolutionizing the treatment and management of wound care, by offering novel solutions which include but are not limited to: state-of-the-art materials, so called 'smart' biomaterials and theranostic nanoparticles. Nanotechnology-based therapy has recently announced itself as a possible next-generation therapy that is able to advance wound healing to cure chronic wounds. In this communication, the recent progress in advanced therapy for cutaneous wound healing during last 5 years using a nanotechnology-based approach is summarized.

Metal-Based Antibacterial Substrates for Biomedical Applications

The interest in nanotechnology and the growing concern for the antibiotic resistance demonstrated by many microorganisms have recently stimulated many efforts in designing innovative biomaterials and substrates with antibacterial properties. Among the implemented strategies to control the incidence of infections associated with the use of biomedical device and implants, interesting routes are represented by the incorporation of bactericidal agents onto the surface of biomaterials for the prevention of bacterial adhesion and biofilm growth. Natural products and particularly bioactive metals such as silver, copper and zinc represent an interesting alternative for the development of advanced biomaterials with antimicrobial properties. This review presents an overview of recent progress in the modification of biomaterials as well as the most attractive techniques for the deposition of antimicrobial coatings on different substrates for biomedical application. Moreover, some research activities and results achieved by the authors in the development of antibacterial materials are also presented and discussed.