Coloured cornea replacements with anti-infective properties: expanding the safe use of silver nanoparticles in regenerative medicine

Cell therapy in the cornea: The emerging role of microenvironment

The cornea is an ideal testing field for cell therapies. Its highly ordered structure, where specific cell populations are sequestered in different layers, together with its accessibility, has allowed the development of the first stem cell-based therapy approved by the European Medicine Agency. Today, different techniques have been proposed for autologous and allogeneic limbal and non-limbal cell transplantation. Cell replacement has also been attempted in cases of endothelial cell decompensation as it occurs in Fuchs dystrophy: injection of cultivated allogeneic endothelial cells is now in advanced phases of clinical development. Recently, stromal substitutes have been developed with excellent integration capability and transparency. Finally, cell-derived products, such as exosomes obtained from different sources, have been investigated for the treatment of severe corneal diseases with encouraging results. Optimization of the success rate of cell therapies obviously requires high-quality cultured cells/products, but the role of the surrounding microenvironment is equally important to allow engraftment of transplanted cells, to preserve their functions and, ultimately, lead to restoration of tissue integrity and transparency of the cornea.

Antibacterial activity, quality and stability study of creams with new potential silver(I) complexes and in vivo case report

The aim of this study was to evaluate the antibacterial activity, quality and stability of creams (at 1 % concentration) prepared with synthesized silver(I) complexes: [Ag(Nam)₂]NO₃·H₂O ( AgNam), [Ag₂(HGly)₂]_n(NO₃)_2n (AgGly) (Nam - nicotin-amide, Gly - glycine) and silver(I) sulfadiazine (AgSD), which is commercially available. Antibacterial activity was evaluated by agar well diffusion method and in in vivo case. The pure silver(I) complexes as well as all three tested creams loaded with AgGly, AgSD and AgNam showed antibacterial potential. Moreover, the creams loaded with AgGly and AgNam showed higher antibacterial effects against S. aureus and B. subtilis than the cream loaded with AgSD. In terms of appearance, all cream samples were opaque and odourless, and no phase separation was observed. Creams were soluble in water (o/w emulsions) and they had a pseudoplastic behaviour. The pH of the creams was in the range of 4.87-5.75. No visible changes were observed in the case of commercially used AgSD cream during one month testing period at conditions -16 ± 1 °C; 6 ± 1 °C and 56 % relative humidity; 20 ± 1 °C and 58 % relative humidity and 40 ± 1 °C and 75 % relative humidity. However, creams containing AgGly and AgNam changed their colour depending on the tested conditions.

Silver nanoparticles modified hFGF2-linking camelina oil bodies accelerate infected wound healing

Bacterial infection wounds are common in life. At present, although various wound materials have shown antibacterial activity, there is a lack of overall strategy to promote wound healing. Therefore, it is necessary to develop multifunctional wound materials. In this study, silver nanoparticles (Ag NPs) modified camelina oil bodies (OB) which surface covalently bonded human fibroblast growth factor 2 (Ag NPs-hFGF2-OB) were designed for the treatment of bacterial infection wounds. The prepared Ag NPs-hFGF2-OB not only act as an antibacterial agent to realize sterilization, but also act as a tissue repair agent that effectively promotes wound healing. Ag⁺ was reduced in situ to Ag NPs by ascorbic acid, and the activity of hFGF2 protein was not affected after hFGF2-OB was modified by Ag NPs, which displaying broad apectrum antibacterial ability for both S. aureus and E. coli, with an antibacterial rate of more than 70 % (the concentration of Ag NPs was 20 μg/mL, the hFGF2 protein concentration was 20 µg/mL). Ag NPs-hFGF2-OB can effectively promote the migration of NIH/3T3 cells, showing good biocompatibility. The mouse bacterial infection wound model experiments proved that the wound healing rate of Ag NPs-hFGF2-OB group (the concentration of Ag NPs was 20 μg/mL, the hFGF2 protein concentration was 20 µg/mL) was much higher than other treatment groups, especially on the 7th day after treatment, the wound healing rate reached 71.71 ± 2.38 %, while the healing rate of other treatment groups were only 34.54 ± 1.10 %, 37.08 ± 2.85 % and 47.99 ± 2.01 %. Therefore, Ag NPs-hFGF2-OB, which can inhibit bacterial growth, promotes collagen deposition, granulation tissue regeneration and angiogenesis without any significant toxicity, shows good potential for application in the repair of bacterial infection wounds.

Silver Halide-Based Nanomaterials in Biomedical Applications and Biosensing Diagnostics

In recent years, silver halide (AgX, X = Cl, Br, I)-based photocatalytic materials have received increasing research attention owing to their excellent visible-light-driven photocatalytic performance for applications in organic pollutant degradation, HER, OER, and biomedical engineering. Ag as a noble metal has a surface plasma effect and can form Schottky junctions with AgX, which significantly promotes electron transport and increases photocatalytic efficiency. Therefore, Ag/AgX can reduce the recombination rate of electrons and holes more than pure AgX, leading to using AgX as a photocatalytic material in biomedical applications. The use of AgX-based materials in photocatalytic fields can be classified into three categories: AgX (Ag/AgX), AgX composites, and supported AgX materials. In this review, we introduce recent developments made in biomedical applications and biosensing diagnostics of AgX (Ag/AgX) photocatalytic materials. In addition, this review also discusses the photocatalytic mechanism and applications of AgX (Ag/AgX) and supported AgX materials.

Recent achievements in nano-based technologies for ocular disease diagnosis and treatment, review and update

Ocular drug delivery is one of the most challenging endeavors among the various available drug delivery systems. Despite having suitable drugs for the treatment of ophthalmic disease, we have not yet succeeded in achieving a proper drug delivery approach with the least adverse effects. Nanotechnology offers great opportunities to overwhelm the restrictions of common ocular delivery systems, including low therapeutic effects and adverse effects because of invasive surgery or systemic exposure. The present review is dedicated to highlighting and updating the recent achievements of nano-based technologies for ocular disease diagnosis and treatment. While further effort remains, the progress illustrated here might pave the way to new and very useful ocular nanomedicines.

Metallic Engineered Nanomaterials and Ocular Toxicity: A Current Perspective

The ocular surface, comprised of the transparent cornea, conjunctiva, and protective tear film, forms a protective barrier defending deeper structures of the eye from particulate matter and mechanical trauma. This barrier is routinely exposed to a multitude of naturally occurring and engineered nanomaterials (ENM). Metallic ENMs are particularly ubiquitous in commercial products with a high risk of ocular exposure, such as cosmetics and sunscreens. Additionally, there are several therapeutic uses for metallic ENMs owing to their attractive magnetic, antimicrobial, and functionalization properties. The increasing commercial and therapeutic applications of metallic ENMs come with a high risk of ocular exposure with poorly understood consequences to the health of the eye. While the toxicity of metallic ENMs exposure has been rigorously studied in other tissues and organs, further studies are necessary to understand the potential for adverse effects and inform product usage for individuals whose ocular health may be compromised by injury, disease, or surgical intervention. This review provides an update of current literature on the ocular toxicity of metallic ENMs in vitro and in vivo, as well as the risks and benefits of therapeutic applications of metallic ENMs in ophthalmology.

Nanoengineered Sprayable Therapy for Treating Myocardial Infarction

We report the development, as well as the in vitro and in vivo testing, of a sprayable nanotherapeutic that uses surface engineered custom-designed multiarmed peptide grafted nanogold for on-the-spot coating of an infarcted myocardial surface. When applied to mouse hearts, 1 week after infarction, the spray-on treatment resulted in an increase in cardiac function (2.4-fold), muscle contractility, and myocardial electrical conductivity. The applied nanogold remained at the treatment site 28 days postapplication with no off-target organ infiltration. Further, the infarct size in the mice that received treatment was found to be <10% of the total left ventricle area, while the number of blood vessels, prohealing macrophages, and cardiomyocytes increased to levels comparable to that of a healthy animal. Our cumulative data suggest that the therapeutic action of our spray-on nanotherapeutic is highly effective, and in practice, its application is simpler than other regenerative approaches for treating an infarcted heart.

Exploring silver nanoparticles for cancer therapy and diagnosis

Nanomaterials have emerged as promising candidates for cancer therapy and diagnosis as they can solve long-term issues such as drug solubility, systemic distribution, tumor acquired resistance, and improve the performance of diagnostic methods. Among inorganic nanomaterials, AgNPs have been extensively studied in the context of cancer treatment and the reported results have raised exciting expectations. In this review, we provide an overview of the recent research on AgNPs antitumoral properties, their application in different cancer treatment modalities, their potential in biosensors development, and also highlight the main challenges and possible strategies to enable its translation to clinical use.

Exploiting the antiviral potential of intermetallic nanoparticles

Viral pandemic outbreaks cause a significant burden on global health as well as healthcare expenditure. The use of antiviral agents not only reduces the spread of viral pathogens but also diminishes the likelihood of them causing infection. The antiviral properties of novel copper-silver and copper-zinc intermetallic nanoparticles against Escherichia coli bacteriophage MS2 (RNA virus) and Escherichia coli bacteriophage T4 (DNA virus) are presented. The intermetallic nanoparticles were spherical in shape and were between 90 and 120 nm. Antiviral activity was assessed at concentrations ranging from 0.05 to 2.0 wt/v% for 3 and 24 h using DNA and RNA virus model organisms. Both types of nanoparticles demonstrated strong potency towards RNA viruses (> 89% viral reduction), whilst copper-silver nanoparticles were slightly more toxic towards DNA viruses when compared to copper-zinc nanoparticles. Both nanoparticles were then incorporated into polymeric fibres (carrier) to investigate their antiviral effectiveness when composited into polymeric matrices. Fibres containing copper-silver nanoparticles exhibited favourable antiviral properties, with a viral reduction of 75% after 3 h of exposure. The excellent antiviral properties of the intermetallic nanoparticles reported in this study against both types of viruses together with their unique material properties can make them significant alternatives to conventional antiviral therapies and decontamination agents.

Transcorneal delivery of topically applied silver nanoparticles does not delay epithelial wound healing

Silver nanoparticles (AgNPs) are a common antimicrobial additive for a variety of applications, including wound care. However, AgNPs often undergo dissolution resulting in release of silver ions, with subsequent toxicity to mammalian cells. The cornea is a primary exposure site to topically administered AgNPs in and around the eye but their impact on corneal wound healing is understudied. Thus, the purpose of this study was to determine in vitro toxicity of AgNPs on corneal epithelial cells and fibroblasts as well as their effects on corneal epithelial wound healing utilizing an in vivo rabbit model. Non-coated 20 nm sized AgNP (AgNP-20) as well as 1% and 10% silver silica NPs (AgSiO₂NPs) were tested at concentrations ranging from 0.05-250 μg/mL. Immortalized human corneal epithelial (hTCEpi) cells and primary rabbit corneal fibroblasts (RCFs) were incubated for 24 h with AgNPs and cell viability was tested. Additionally, a round wound healing assay was performed to determine hTCEpi cell migration. Quantitative real-time PCR and western blot analysis was performed to determine α-smooth muscle actin (α-SMA, a myofibroblast marker) mRNA and protein expression, respectively, in RCFs treated with 50 μg/mL of AgNPs. Corneal epithelial wound healing was evaluated with 1%-AgSiO₂NPs (10 and 250 μg/mL) using an in vivo rabbit model. Rabbits were subsequently euthanized, and histologic sections of the enucleated globes were used to determine corneal penetration of 1%-AgSiO₂NPs with autometallography and hyperspectral darkfield microscopy. Cell viability of both the hTCEpi cells and fibroblasts was significantly decreased by the three AgNPs in a dose dependent manner. Migration of hTCEpi cells was significantly inhibited by the three AgNPs. Alpha-SMA mRNA expression was significantly inhibited with three AgNPs, but only the 1%-AgSiO₂NPs inhibited protein expression of α-SMA. In vivo epithelial wound closure did not significantly differ between groups treated with 10 or 250 μg/mL of 1%-AgSiO₂NPs or vehicle control. The 1%-AgSiO₂NPs penetrated throughout all corneal layers and into the anterior chamber in all treated eyes with no histopathological changes observed. In conclusion, the 1%-AgSiO₂NPs are safe and have potential therapeutic applications through its efficacy of the corneal penetration and reduced scar formation during corneal wound healing.

Hydrogels as Emerging Materials for Cornea Wound Healing

Hydrogel biomaterials have many favorable characteristics including tuneable mechanical behavior, cytocompatibility, optical properties suitable for regeneration and restoration of the damaged cornea tissue. The cornea is a tissue susceptible to various injuries and traumas with a complicated healing cascade, in which conserving its transparency and integrity is critical. Accordingly, the hydrogels' known properties along with the stimulation of nerve and cell regeneration make them ideal scaffold for corneal tissue engineering. Hydrogels have been used extensively in clinical applications for the repair and replacement of diseased organs. The development and optimizing of novel hydrogels to repair/replace corneal injuries have been the main focus of researches within the last decade. This research aims to critically review in vitro, preclinical, as well as clinical trial studies related to corneal wound healing using hydrogels in the past 10 years, as this is considered as an emerging technology for corneal treatment. Several unique modifications of hydrogels with smart behaviors have undergone early phase clinical trials and showed promising outcomes. Financially, this considers a multibillion dollars industry and with huge interest from medical devices as well as pharmaceutical industries with several products may emerge within the next five years.

Recent Progress in Lipid Nanoparticles for Cancer Theranostics: Opportunity and Challenges

Cancer is one of the major leading causes of mortality in the world. The implication of nanotherapeutics in cancer has garnered splendid attention owing to their capability to efficiently address various difficulties associated with conventional drug delivery systems such as non-specific biodistribution, poor efficacy, and the possibility of occurrence of multi-drug resistance. Amongst a plethora of nanocarriers for drugs, this review emphasized lipidic nanocarrier systems for delivering anticancer therapeutics because of their biocompatibility, safety, high drug loading and capability to simultaneously carrying imaging agent and ligands as well. Furthermore, to date, the lack of interaction between diagnosis and treatment has hampered the efforts of the nanotherapeutic approach alone to deal with cancer effectively. Therefore, a novel paradigm with concomitant imaging (with contrasting agents), targeting (with biomarkers), and anticancer agent being delivered in one lipidic nanocarrier system (as cancer theranostics) seems to be very promising in overcoming various hurdles in effective cancer treatment. The major obstacles that are supposed to be addressed by employing lipidic theranostic nanomedicine include nanomedicine reach to tumor cells, drug internalization in cancer cells for therapeutic intervention, off-site drug distribution, and uptake via the host immune system. A comprehensive account of recent research updates in the field of lipidic nanocarrier loaded with therapeutic and diagnostic agents is covered in the present article. Nevertheless, there are notable hurdles in the clinical translation of the lipidic theranostic nanomedicines, which are also highlighted in the present review along with plausible countermeasures.

Antimicrobial nanomedicine for ocular bacterial and fungal infection

Ocular infection induced by bacteria and fungi is a major cause of visual impairment and blindness. Topical administration of antibiotics remains the first-line treatment, as effective eradication of pathogens is the core of the anti-infection strategy. Whereas, eye drops lack efficiency and have relatively low bioavailability. Intraocular injection may cause concurrent ocular damage and secondary infection. In addition, antibiotic-based management can be limited by the low sensitivity to multidrug-resistant bacteria. Nanomedicine is proposed as a prospective, effective, and noninvasive platform to mediate ocular delivery and combat pathogen or even resistant strains. Nanomedicine can not only carry antimicrobial agents to fight against pathogens but also directly active microbicidal capability, killing pathogens. More importantly, by modification, nanomedicine can achieve enhanced residence time and release time on the cornea, and easy penetration through corneal tissues into anterior and posterior segments of the eye, thus improving the therapeutic effect for ocular infection. In this review, several categories of antimicrobial nanomedicine are systematically discussed, where the efficiency and possibility of further embellishment and improvement to adapt to clinical use are also investigated. All in all, novel antimicrobial nanomedicine provides potent and prospective ways to manage severe and refractory ocular infections.

Dermatillomania: Strategies for Developing Protective Biomaterials/Cloth

Dermatillomania or skin picking disorder (SPD) is a chronic, recurrent, and treatment resistant neuropsychiatric disorder with an underestimated prevalence that has a concerning negative impact on an individual’s health and quality of life. The current treatment strategies focus on behavioral and pharmacological therapies that are not very effective. Thus, the primary objective of this review is to provide an introduction to SPD and discuss its current treatment strategies as well as to propose biomaterial-based physical barrier strategies as a supporting or alternative treatment. To this end, searches were conducted within the PubMed database and Google Scholar, and the results obtained were organized and presented as per the following categories: prevalence, etiology, consequences, diagnostic criteria, and treatment strategies. Furthermore, special attention was provided to alternative treatment strategies and biomaterial-based physical treatment strategies. A total of six products with the potential to be applied as physical barrier strategies in supporting SPD treatment were shortlisted and discussed. The results indicated that SPD is a complex, underestimated, and underemphasized neuropsychiatric disorder that needs heightened attention, especially with regard to its treatment and care. Moreover, the high synergistic potential of biomaterials and nanosystems in this area remains to be explored. Certain strategies that are already being utilized for wound healing can also be further exploited, particularly as far as the prevention of infections is concerned.

All That Glitters Is Not Silver-A New Look at Microbiological and Medical Applications of Silver Nanoparticles

Silver and its nanoparticles (AgNPs) have different faces, providing different applications. In recent years, the number of positive nanosilver applications has increased substantially. It has been proven that AgNPs inhibit the growth and survival of bacteria, including human and animal pathogens, as well as fungi, protozoa and arthropods. Silver nanoparticles are known from their antiviral and anti-cancer properties; however, they are also very popular in medical and pharmaceutical nanoengineering as carriers for precise delivery of therapeutic compounds, in the diagnostics of different diseases and in optics and chemistry, where they act as sensors, conductors and substrates for various syntheses. The activity of AgNPs has not been fully discovered; therefore, we need interdisciplinary research to fulfil this knowledge. New forms of products with silver will certainly find application in the future treatment of many complicated and difficult to treat diseases. There is still a lack of appropriate and precise legal condition regarding the circulation of nanomaterials and the rules governing their safety use. The relatively low toxicity, relative biocompatibility and selectivity of nanoparticle interaction combined with the unusual biological properties allow their use in animal production as well as in bioengineering and medicine. Despite a quite big knowledge on this topic, there is still a need to organize the data on AgNPs in relation to specific microorganisms such as bacteria, viruses or fungi. We decided to put this knowledge together and try to show positive and negative effects on prokaryotic and eukaryotic cells.

Recent progress and strategies to develop antimicrobial contact lenses and lens cases for different types of microbial keratitis

Although contact lenses are widely used for vision correction, they are also the primary cause of a number of ocular diseases such as microbial keratitis (MK), etc. and inflammatory events such as infiltrative keratitis (IK), contact lens acute red eye (CLARE), contact lens-induced peripheral ulcer (CLPU), etc. These diseases and infiltrative events often result from microbial contamination of lens care solutions and lens cases that can be exacerbated by unsanitary lens care and extended lens wear. The treatment of microbial biofilms (MBs) on lens cases and contact lenses are complicated and challenging due to their resistance to conventional antimicrobial lens care solutions. More importantly, MK caused by MBs can lead to acute visual damage or even vision impairment. Therefore, the development of lens cases, lens care solutions, and contact lenses with effective antimicrobial performance against MK will contribute to the safe use of contact lenses. This review article summarizes and discusses different chemical approaches for the development of antimicrobial contact lenses and lens cases employing passive surface modifications, antimicrobial peptides, free-radical fabricating agents, quorum sensing quenchers, antibiotics, antifungal drugs and various metals and coatings with antimicrobial nanomaterials. The benefits and shortcomings of these approaches are assessed, and alternative solutions for future developments are discussed.

Nanoengineering the surface of corneal implants: towards functional anti-microbial and biofilm materials

We report the development and use of a light-mediated in situ grafting technology for the surface modification of biosynthetic corneal implants with peptide-capped nanoparticles (15–65 nm). The resulting materials have antimicrobial properties in bacterial suspension and also reduced the extent of biofilm formation. Our in situ grafting technology offers a rapid route for the introduction of antimicrobial properties to premoulded corneal implants, and potentially other soft implant targets.

A rapid and precise route to graft a nano-bactericidal barrier is reported.

Naturally derived DNA nanogels as pH- and glutathione-triggered anticancer drug carriers

Conventional chemotherapeutic drugs are nonselective and harmful toward normal tissues, causing severe side effects. Therefore, the development of chemotherapeutics that can target cancer cells and improve therapeutic efficacy is of high priority. Biomolecules isolated from nature serve as green solutions for biomedical use, solving biocompatibility and cytotoxicity issues in human bodies. Herein, we use kiwifruit-derived DNA to encapsulate doxorubicin (DOX) using crosslinkers, eventually forming DNA-DOX nanogels (NGs). Drug releasing assays, cell viability and anticancer effects were analyzed to evaluate the DNA NGs' applications. The amount of DOX released by the DOX-loaded DNA (DNA-DOX) NGs at acidic pH was higher than that of neutral pH, and high glutathione (GSH) concentration also triggered more DOX to release in cancer cells, demonstrating pH- and GSH-triggered drug release characteristics of the DNA NGs. The IC₅₀ of DNA-DOX NGs in cancer cells was lower than that of free DOX. Moreover, DOX uptake of cancer cells and apoptotic death were enhanced by the DNA-DOX NGs compared to free DOX. The results suggest that the DNA NGs cross-linked via nitrogen bases of the nucleotides in DNA and presenting pH- and GSH-dependent drug releasing behavior can be alternative biocompatible drug delivery systems for anticancer strategies and other biomedical applications.

Multifunctional Nano and Collagen-Based Therapeutic Materials for Skin Repair

A novel strategy is needed for treating nonhealing wounds, which is able to simultaneously eradicate pathogenic bacteria and promote tissue regeneration. This would improve patient outcome and reduce the number of lower limb amputations. In this work, we present a multifunctional therapeutic approach able to control bacterial infections, provide a protective barrier to a full-thickness wound, and improve wound healing in a clinically relevant animal model. Our approach uses a nanoengineered antimicrobial nanoparticle for creating a sprayable layer onto the wound bed that prevents bacterial proliferation and also eradicates preformed biofilms. As a protective barrier for the wound, we developed a thermoresponsive collagen-based matrix that has prohealing properties and is able to fill wounds independent of their geometries. Our results indicate that using a combination of the matrix with full-thickness microscopic skin tissue columns synergistically contributed to faster and superior skin regeneration in a nonhealing wound model in diabetic mice.

Biogenic silver nanoparticles synthesized from Rhododendron ponticum and their antibacterial, antibiofilm and cytotoxic activities

Nanotechnology is being used effectively in many areas contemporarily. Silver nanoparticles (AgNPs) are one of the most crucial and remarkable nanomaterials involved in medical applications. These nanoparticles (NPs) have an important place in nanomedicine, nanotechnology, and in particularly, nanoscience. AgNPs are one of the most widely used materials in antibacterial and antiseptic practices. The synthesis of biogenic AgNPs has been applied as an alternative to physical and chemical synthesis. For this purpose, water extracts of Rhododendron ponticum were used for biosynthesis of AgNPs. Also, AgNPs were characterized by UV-vis spectrophotometer, scanning transmission electron microscope (STEM) and X-ray diffractometer (XRD). The antimicrobial activity of AgNPs synthesized with Rhododendron ponticum was analyzed by the Minimum Inhibition Concentration (MIC) test. Also, the biofilm inhibition test was made, and AgNPs showed a strong effect for biofilm inhibition. In addition, the prepared nanoparticles were tried for cytotoxicity activity with the help of MTT assay in MCF-7 and 4T1 cancer cell lines.

Antimicrobial Nitric Oxide Releasing Contact Lens Gels for the Treatment of Microbial Keratitis

Microbial keratitis is a serious sight threatening infection affecting approximately two million individuals worldwide annually. While antibiotic eye drops remain the gold standard treatment for these infections, the significant problems associated with eye drop drug delivery and the alarming rise in antimicrobial resistance has meant that there is an urgent need to develop alternative treatments. In this work, a nitric oxide releasing contact lens gel displaying broad spectrum antimicrobial activity against two of the most common causative pathogens of microbial keratitis is described. The contact lens gel is composed of poly-ε-lysine (pεK) functionalized with nitric oxide (NO) releasing diazeniumdiolate moieties which enables the controlled and sustained release of bactericidal concentrations of NO at physiological pH over a period of 15 h. Diazeniumdiolate functionalization was confirmed by Fourier transform infrared (FTIR), and the concentration of NO released from the gels was determined by chemiluminescence. The bactericidal efficacy of the gels against Pseudomonas aeruginosa and Staphylococcus aureus was ascertained, and between 1 and 4 log reductions in bacterial populations were observed over 24 h. Additional cell cytotoxicity studies with human corneal epithelial cells (hCE-T) also demonstrated that the contact lens gels were not cytotoxic, suggesting that the developed technology could be a viable alternative treatment for microbial  keratitis.

Corneal Repair and Regeneration: Current Concepts and Future Directions

The cornea is a unique tissue and the most powerful focusing element of the eye, known as a window to the eye. Infectious or non-infectious diseases might cause severe visual impairments that need medical intervention to restore patients' vision. The most prominent characteristics of the cornea are its mechanical strength and transparency, which are indeed the most important criteria considerations when reconstructing the injured cornea. Corneal strength comes from about 200 collagen lamellae which criss-cross the cornea in different directions and comprise nearly 90% of the thickness of the cornea. Regarding corneal transparency, the specific characteristics of the cornea include its immune and angiogenic privilege besides its limbus zone. On the other hand, angiogenic privilege involves several active cascades in which anti-angiogenic factors are produced to compensate for the enhanced production of proangiogenic factors after wound healing. Limbus of the cornea forms a border between the corneal and conjunctival epithelium, and its limbal stem cells (LSCs) are essential in maintenance and repair of the adult cornea through its support of corneal epithelial tissue repair and regeneration. As a result, the main factors which threaten the corneal clarity are inflammatory reactions, neovascularization, and limbal deficiency. In fact, the influx of inflammatory cells causes scar formation and destruction of the limbus zone. Current studies about wound healing treatment focus on corneal characteristics such as the immune response, angiogenesis, and cell signaling. In this review, studied topics related to wound healing and new approaches in cornea regeneration, which are mostly related to the criteria mentioned above, will be discussed.

Nanoparticle Concentration vs Surface Area in the Interaction of Thiol-Containing Molecules: Toward a Rational Nanoarchitectural Design of Hybrid Materials

The effect of accounting for the total surface in the association of thiol-containing molecules to nanosilver was assessed using isothermal titration calorimetry, along with a new open access algorithm that calculates the total surface area for samples of different polydispersity. Further, we used advanced molecular dynamic calculations to explore the underlying mechanisms for the interaction of the studied molecules in the presence of a nanosilver surface in the form of flat surfaces or as three-dimensional pseudospherical nanostructures. Our data indicate that not only is the total surface area available for binding but also the supramolecular arrangements of the molecules in the near proximity of the nanosilver surface strongly affects the affinity of thiol-containing molecules to nanosilver surfaces.

Gentamicin-loaded silk/nanosilver composite scaffolds for MRSA-induced chronic osteomyelitis

Methicillin-resistant Staphylococcus aureus (MRSA) often induces chronic osteomyelitis and then bone defects. Here, gentamicin-loaded silk/nanosilver composite scaffolds were developed to treat MRSA-induced chronic osteomyelitis. AgNO3 was reduced with silk as a reducing agent in formic acid, forming silver nanoparticles in situ that were distributed uniformly in the composite scaffolds. Superior antibacterial properties against MRSA were achieved for the composite scaffolds, without the compromise of osteogenesis capacity. Then gentamicin was loaded on the scaffolds for better treatment of osteomyelitis. In vivo results showed effective inhibition of the growth of MRSA bacteria, confirming the promising future in the treatment of chronic osteomyelitis.

Hybrid lipid-nanoparticle complexes for biomedical applications

Biomolecule-nanoparticle hybrids have proven to be one of most promising frontiers in biomedical research. In recent years, there has been an increased focus on the development of hybrid lipid-nanoparticle complexes (HLNCs) which inherit unique properties of both the inorganic nanoparticles and the lipid assemblies (i.e. liposomes, lipoproteins, solid lipid nanoparticles, and nanoemulsions) that comprise them. In combination of their component parts, HLNCs also gain new functionalities which are utilized for numerous biomedical applications (i.e. stimuli-triggered drug release, photothermal therapy, and bioimaging). The localization of nanoparticles within the lipid assemblies largely dictates the attributes and functionalities of the hybrid complexes and are classified as such: (i) liposomes with surface-bound nanoparticles, (ii) liposomes with bilayer-embedded nanoparticles, (iii) liposomes with core-encapsulated nanoparticles, (iv) lipid assemblies with hydrophobic core-encapsulated nanoparticles, and (v) lipid bilayer-coated nanoparticles. Herein, we review the properties of each hybrid and the rational design of HLNCs for biomedical applications as reported by recent investigations. Future directions in advancing and expanding the scope of HLNCs are also proposed.

Nanomaterials as potential and versatile platform for next generation tissue engineering applications

Tissue engineering (TE) is an emerging field where alternate/artificial tissues or organ substitutes are implanted to mimic the functionality of damaged or injured tissues. Earlier efforts were made to develop natural, synthetic, or semisynthetic materials for skin equivalents to treat burns or skin wounds. Nowadays, many more tissues like bone, cardiac, cartilage, heart, liver, cornea, blood vessels, and so forth are being engineered using 3-D biomaterial constructs or scaffolds that could deliver active molecules such as peptides or growth factors. Nanomaterials (NMs) due to their unique mechanical, electrical, and optical properties possess significant opportunities in TE applications. Traditional TE scaffolds were based on hydrolytically degradable macroporous materials, whereas current approaches emphasize on controlling cell behaviors and tissue formation by nano-scale topography that closely mimics the natural extracellular matrix. This review article gives a comprehensive outlook of different organ specific NMs which are being used for diversified TE applications. Varieties of NMs are known to serve as biological alternatives to repair or replace a portion or whole of the nonfunctional or damaged tissue. NMs may promote greater amounts of specific interactions stimulated at the cellular level, ultimately leading to more efficient new tissue formation. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2433-2449, 2019.

Bactericidal and Cytotoxic Properties of Silver Nanoparticles

Silver nanoparticles (AgNPs) can be synthesized from a variety of techniques including physical, chemical and biological routes. They have been widely used as nanomaterials for manufacturing cosmetic and healthcare products, antimicrobial textiles, wound dressings, antitumor drug carriers, etc. due to their excellent antimicrobial properties. Accordingly, AgNPs have gained access into our daily life, and the inevitable human exposure to these nanoparticles has raised concerns about their potential hazards to the environment, health, and safety in recent years. From in vitro cell cultivation tests, AgNPs have been reported to be toxic to several human cell lines including human bronchial epithelial cells, human umbilical vein endothelial cells, red blood cells, human peripheral blood mononuclear cells, immortal human keratinocytes, liver cells, etc. AgNPs induce a dose-, size- and time-dependent cytotoxicity, particularly for those with sizes ≤10 nm. Furthermore, AgNPs can cross the brain blood barrier of mice through the circulation system on the basis of in vivo animal tests. AgNPs tend to accumulate in mice organs such as liver, spleen, kidney and brain following intravenous, intraperitoneal, and intratracheal routes of administration. In this respect, AgNPs are considered a double-edged sword that can eliminate microorganisms but induce cytotoxicity in mammalian cells. This article provides a state-of-the-art review on the synthesis of AgNPs, and their applications in antimicrobial textile fabrics, food packaging films, and wound dressings. Particular attention is paid to the bactericidal activity and cytotoxic effect in mammalian cells.

Constructing a Novel Three-Dimensional Biomimetic Corneal Endothelium Graft by Culturing Corneal Endothelium Cells on Compressed Collagen Gels

Background:

Endothelium allotransplantation is the primary treatment for corneal decompensation. The worldwide shortage of donor corneal tissue has led to increasing pressure to seek an alternative for surgical restoration of corneal endothelium. Compressed collagen (CC) gels have excellent biocompatibility, simple preparation course and easy to be manipulated. This study aimed to form a new biomimetic endothelium graft by CC.

Methods:

We expanded bovine corneal endothelial cells (B-CECs) on laminin-coated CC to form a biomimetic endothelium graft. Scanning electron microscope was used for ultrastructural analysis and tight junction protein ZO-1 expression was tested by immunohistochemistry.

Results:

The biomimetic endothelium graft, we conducted had normal cell morphology, ultrastructure and higher cell density (3612.2 ± 43.4 cells/mm²). ZO-1 localization at B-CECs membrane indicated the bioengineered graft possess the basic endothelium function.

Conclusions:

A biomimetic endothelium graft with B-CECs expanded on CC sheet was constructed, which possessed cells' morphology similar to that of in vivo endothelial cells and specific basic function of endothelium layer. This method provided the possibility of using one donor's cornea to form multiple uniformed endothelium grafts so as to overcome the shortage of cadaveric cornea tissue.

Effect of nanosilver surfaces on peptide reactivity towards reactive oxygen species

The interaction of a terminal tryptophan residue within collagen mimetic peptides when tethered to nanometric silver surfaces was studied using a combination of steady state spectroscopy, ultrafast spectroscopy, and molecular dynamics experiments. Our findings indicate that the effective interaction between the tryptophan and the metal surface occurs in short-time scales (ps) and it is responsible for improving the colloidal stability of the nanoparticles exposed to free radicals. The extent and efficiency of the interaction depends on factors beyond the peptide length that include conformation and distance from the terminal tryptophan to the metal surface.

A database on the stability of silver and gold nanostructures for applications in biology and biomolecular sciences

Colloidal stability of nanoparticles in biological media is an important consideration when trying to ensure reliable data interpretation of in vitro and in vivo systems. We have developed a detailed colloidal stability library of newly synthesized gold, silver and gold-core silver-shell plasmonic nanoparticles, stabilized with aspartame, glucosamine and sucralose, in various biologically relevant buffers and bacterial and mammalian cell culture media. The stabilizer selection reflects the preference for molecules that are non-toxic, inexpensive, readily available, water soluble and easy-to-replace if that is the end-user preference. An on-line resource provides detailed stability information on each of the 81 systems examined. To illustrate how to utilize this stability library, we conducted bacterial toxicity and biocompatibility experiments through the use of one specific set of nanomaterials in the presence and absence of plasmonic irradiation.

Strategies to design antimicrobial contact lenses and contact lens cases

Contact lens wear is a primary risk factor for developing ocular complications, such as contact lens acute red eye (CLARE), contact lens-induced peripheral ulcer (CLPU) and microbial keratitis (MK). Infections occur due to microbial contamination of contact lenses, lens cases and lens care solution, which are exacerbated by extended lens wear and unsanitary lens care practices. The development of microbial biofilms inside lens cases is an additional complication, as the developed biofilms are resistant to conventional lens cleaning solutions. Ocular infections, particularly in the case of MK, can lead to visual impairment or even blindness, so there is a pressing need for the development of antimicrobial contact lenses and cases. Additionally, with the increasing use of bandage contact lenses and contact lenses as drug depots and with the development of smart contact lenses, contact lens hygiene becomes a therapeutically important issue. In this review, we attempt to compile and summarize various chemical strategies for developing antimicrobial contact lenses and lens cases by using silver, free-radical producing agents, antimicrobial peptides or by employing passive surface modification approaches. We also evaluated the advantages and disadvantages of each system and tried to provide input to future directions. Finally, we summarize the developing technologies of therapeutic contact lenses to shed light on the future of contact lens applications.

NANoPoLC algorithm for correcting nanoparticle concentration by sample polydispersity

Variability in the polydispersity of colloidal nanoparticles results in significant differences in the total number of nanoparticles available for the determination of their concentration, which ultimately affects their bioavailability and biodistribution. In the current work, we developed a novel algorithm, named Nanoparticle Polydispersity Corrector (NANoPoLC), which was shown to render a more realistic calculation of the actual nanoparticle concentration in solution.

Carboxylate Functional Groups Mediate Interaction with Silver Nanoparticles in Biofilm Matrix

Biofilms causing medical conditions or interfering with technical applications can prove undesirably resistant to silver nanoparticle (AgNP)-based antimicrobial treatment, whereas beneficial biofilms may be adversely affected by the released silver nanoparticles. Isolated biofilm matrices can induce reduction of silver ions and stabilization of the formed nanosilver, thus altering the exposure conditions. We thus study the reduction of silver nitrate solution in model experiments under chemically defined conditions as well as in stream biofilms. Formed silver nanoparticles are characterized by state-of-the art methods. We find that isolated biopolymer fractions of biofilm organic matrix are capable of reducing ionic Ag, whereas other isolated fractions are not, meaning that biopolymer fractions contain both reducing agent and nucleation seed sites. In all of the investigated systems, we find that silver nanoparticle-biopolymer interface is dominated by carboxylate functional groups. This suggests that the mechanism of nanoparticle formation is of general nature. Moreover, we find that glucose concentration within the biofilm organic matrix correlates strongly with the nanoparticle formation rate. We propose a simple mechanistic explanation based on earlier literature and the experimental findings. The observed generality of the extracellular polymeric substance/AgNP system could be used to improve the understanding of impact of Ag⁺ on aqueous ecosystems, and consequently, to develop biofilm-specific medicines and bio-inspired water decontaminants.

Plant extracts as green reductants for the synthesis of silver nanoparticles: lessons from chemical synthesis

From conventional synthesis to green transformations: a brief literature overview and insight for the synthesis of Ag nanoparticles.

Poly-L-arginine Coated Silver Nanoprisms and Their Anti-Bacterial Properties

The aim of this study was to test the effect of two different morphologies of silver nanoparticles, spheres, and prisms, on their antibacterial properties when coated with poly-L-arginine (poly-Arg) to enhance the interactions with cells. Silver nanoparticle solutions were characterized by UV-visible spectroscopy, transmission electron microscopy, dynamic light scattering, zeta potential, as well as antimicrobial tests. These ultimately showed that a prismatic morphology exhibited stronger antimicrobial effects against Escherichia coli, Pseudomonas aeruginosa and Salmonella enterica. The minimum bactericidal concentration was found to be 0.65 μg/mL in the case of a prismatic AgNP-poly-Arg-PVP (silver nanoparticle-poly-L-arginine-polyvinylpyrrolidone) nanocomposite. The anticancer cell activity of the silver nanoparticles was also studied, where the maximum effect against a HeLa cell line was 80% mortality with a prismatic AgNP-poly-Arg-PVP nanocomposite at a concentration of 11 μg/mL. The antimicrobial activity of these silver nanocomposites demonstrates the potential of such coated silver nanoparticles in the area of nano-medicine.

3D-Hydrogel Based Polymeric Nanoreactors for Silver Nano-Antimicrobial Composites Generation

This study underscores the development of Ag hydrogel nanocomposites, as smart substrates for antibacterial uses, via innovative in situ reactive and reduction pathways. To this end, two different synthetic strategies were used. Firstly thiol-acrylate (PSA) based hydrogels were attained via thiol-ene and radical polymerization of polyethylene glycol (PEG) and polycaprolactone (PCL). As a second approach, polyurethane (PU) based hydrogels were achieved by condensation polymerization from diisocyanates and PCL and PEG diols. In fact, these syntheses rendered active three-dimensional (3D) hydrogel matrices which were used as nanoreactors for in situ reduction of AgNO₃ to silver nanoparticles. A redox chemistry of stannous catalyst in PU hydrogel yielded spherical AgNPs formation, even at 4 °C in the absence of external reductant; and an appropriate thiol-functionalized polymeric network promoted spherical AgNPs well dispersed through PSA hydrogel network, after heating up the swollen hydrogel at 103 °C in the presence of citrate-reductant. Optical and swelling behaviors of both series of hydrogel nanocomposites were investigated as key factors involved in their antimicrobial efficacy over time. Lastly, in vitro antibacterial activity of Ag loaded hydrogels exposed to Pseudomona aeruginosa and Escherichia coli strains indicated a noticeable sustained inhibitory effect, especially for Ag-PU hydrogel nanocomposites with bacterial inhibition growth capabilities up to 120 h cultivation.

Electroconductive nanoengineered biomimetic hybrid fibers for cardiac tissue engineering

We report for the first time the preparation of a fibrous material composed of surface grafted spherical nanosilver and collagen using one-step electrospinning. The resulting composite showed comparable morphology to the control without nanosilver, but had improved electrical conductivity. Under electrical stimulation, fibrous materials containing nanosilver increased connexin-43 expression and proliferation of neonatal cardiomyocytes. Furthermore, composites containing nanosilver prevented biofilm formation but did not activate macrophages.

Bulk Surfaces Coated with Triangular Silver Nanoplates: Antibacterial Action Based on Silver Release and Photo-Thermal Effect

A layer of silver nanoplates, specifically synthesized with the desired localized surface plasmon resonance (LSPR) features, was grafted on amino-functionalized bulk glass surfaces to impart a double antibacterial action: (i) the well-known, long-term antibacterial effect based on the release of Ag⁺; (ii) an "on demand" action which can be switched on by the use of photo-thermal properties of silver nano-objects. Irradiation of these samples with a laser having a wavelength falling into the so called "therapeutic window" of the near infrared region allows the reinforcement, in the timescale of minutes, of the classical antibacterial effect of silver nanoparticles. We demonstrate how using the two actions allows for almost complete elimination of the population of two bacterial strains of representative Gram-positive and Gram-negative bacteria.

Association models for binding of molecules to nanostructures

The interaction between nanoparticles and molecules determines the activity of nanostructures.

Multi-functional thermo-crosslinkable collagen-metal nanoparticle composites for tissue regeneration: nanosilver vs. nanogold

Collagen–silver/gold biomimetic matrices were developed for cardiac tissue engineering.

Sprayable peptide-modified silver nanoparticles as a barrier against bacterial colonization

Sprayable formulations of AgNPs were prepared by exchanging citrate capping agents with LL37-SH peptides. The AgNP@LL37 material was then combined with type I collagen to form a stable film once sprayed. The AgNP@LL37 spray prevented Pseudomonas aeruginosa (P. aeruginosa) proliferation and eradicated a P. aeruginosa biofilm, while being non-toxic for human skin fibroblasts embedded within 3D artificial skin constructs. Finally, no silver infiltration was observed after spraying on a full-thickness skin wound in a mouse model.

Bioengineered silver nanoparticles using Curvularia pallescens and its fungicidal activity against Cladosporium fulvum

Microorganisms based biosynthesis of nanomaterials has triggered significant attention, due to their great potential as vast source of the production of biocompatible nanoparticles (NPs). Such biosynthesized functional nanomaterials can be used for various biomedical applications. The present study investigates the green synthesis of silver nanoparticles (Ag NPs) using the fungus Curvularia pallescens (C. pallescens) which is isolated from cereals. The C. pallescens cell filtrate was used for the reduction of AgNO₃ to Ag NPs. To the best of our knowledge C. pallescens is utilized first time for the preparation of Ag NPs. Several alkaloids and proteins present in the phytopathogenic fungus C. pallescens were mainly responsible for the formation of highly crystalline Ag NPs. The as-synthesized Ag NPs were characterized by using UV–Visible spectroscopy, X-ray diffraction and transmission electron microscopy (TEM). The TEM micrographs have revealed that spherical shaped Ag NPs with polydisperse in size were obtained. These results have clearly suggested that the biomolecules secreted by C. pallescens are mainly responsible for the formation and stabilization of nanoparticles. Furthermore, the antifungal activity of the as-prepared Ag NPs was tested against Cladosporium fulvum, which is the major cause of a serious plant disease, known as tomato leaf mold. The synthesized Ag NPs displayed excellent fungicidal activity against the tested fungal pathogen. The extreme zone of reduction occurred at 50 μL, whereas, an increase in the reduction activity is observed with increasing the concentration of Ag NPs. These encouraging results can be further exploited by employing the as synthesized Ag NPs against various pathogenic fungi in order to ascertain their spectrum of fungicidal activity.

The Quest for Anti-inflammatory and Anti-infective Biomaterials in Clinical Translation

Biomaterials are now being used or evaluated clinically as implants to supplement the severe shortage of available human donor organs. To date, however, such implants have mainly been developed as scaffolds to promote the regeneration of failing organs due to old age or congenital malformations. In the real world, however, infection or immunological issues often compromise patients. For example, bacterial and viral infections can result in uncontrolled immunopathological damage and lead to organ failure. Hence, there is a need for biomaterials and implants that not only promote regeneration but also address issues that are specific to compromised patients, such as infection and inflammation. Different strategies are needed to address the regeneration of organs that have been damaged by infection or inflammation for successful clinical translation. Therefore, the real quest is for multifunctional biomaterials with combined properties that can combat infections, modulate inflammation, and promote regeneration at the same time. These strategies will necessitate the inclusion of methodologies for management of the cellular and signaling components elicited within the local microenvironment. In the development of such biomaterials, strategies range from the inclusion of materials that have intrinsic anti-inflammatory properties, such as the synthetic lipid polymer, 2-methacryloyloxyethyl phosphorylcholine (MPC), to silver nanoparticles that have antibacterial properties, to inclusion of nano- and micro-particles in biomaterials composites that deliver active drugs. In this present review, we present examples of both kinds of materials in each group along with their pros and cons. Thus, as a promising next generation strategy to aid or replace tissue/organ transplantation, an integrated smart programmable platform is needed for regenerative medicine applications to create and/or restore normal function at the cell and tissue levels. Therefore, now it is of utmost importance to develop integrative biomaterials based on multifunctional biopolymers and nanosystem for their practical and successful clinical translation.

Fungal Isolate Optimized for Biogenesis of Silver Nanoparticles with Enhanced Colloidal Stability

Understanding the synthesis and properties of nanomaterials is critical for reliable applications. Biological systems, such as fungi, have been described as a "green" alternative to synthesis, yet knowledge gaps exist in terms of production variability, comparison with commercial products, and identifying a clear biological advantage over other synthesis methods. In this study, we evaluated 12 fungal isolates of Fusarium oxysporum for Ag nanoparticle production and characterized the resultant biologically produced (biogenic) nanoparticles. We show evidence that isolate selection, temperature, and pH can influence the quantity, size, and shape of nanoparticles. All F. oxysporum isolates produced Ag nanoparticles, but in varied quantities. Increasing incubation temperature increased the quantity, yet nanoparticle diameter was inversely related to temperature. Variations in pH predominately influenced nanoparticle morphology. A direct comparison with commercial, chemically produced Ag nanoparticles yielded physical similarities; however, important differences in surface chemistry are observed. Biogenic nanoparticles show a greater degree of colloidal stability in high-ionic-strength solutions, pointing to a biological advantage associated with the fungal produced layer (corona) surrounding the nanoparticles. It is clear that understanding the organic layer and interfacial interactions will be beneficial in developing innovative applications, particularly in the field of biosensing.

Toxicological Considerations, Toxicity Assessment, and Risk Management of Inhaled Nanoparticles

Novel engineered nanoparticles (NPs), nanomaterial (NM) products and composites, are continually emerging worldwide. Many potential benefits are expected from their commercial applications; however, these benefits should always be balanced against risks. Potential toxic effects of NM exposure have been highlighted, but, as there is a lack of understanding about potential interactions of nanomaterials (NMs) with biological systems, these side effects are often ignored. NPs are able to translocate to the bloodstream, cross body membrane barriers effectively, and affect organs and tissues at cellular and molecular levels. NPs may pass the blood–brain barrier (BBB) and gain access to the brain. The interactions of NPs with biological milieu and resulted toxic effects are significantly associated with their small size distribution, large surface area to mass ratio (SA/MR), and surface characteristics. NMs are able to cross tissue and cell membranes, enter into cellular compartments, and cause cellular injury as well as toxicity. The extremely large SA/MR of NPs is also available to undergo reactions. An increased surface area of the identical chemical will increase surface reactivity, adsorption properties, and potential toxicity. This review explores biological pathways of NPs, their toxic potential, and underlying mechanisms responsible for such toxic effects. The necessity of toxicological risk assessment to human health should be emphasised as an integral part of NM design and manufacture.