Colloidal Formulations Research Articles

Antimicrobial, antibiofilm and cytotoxic effects of a colloidal nanocarrier composed by chitosan-coated iron oxide nanoparticles loaded with chlorhexidine

ObjectivesThis study evaluated the antimicrobial and antibiofilm effects of a colloidal nanocarrier for chlorhexidine (CHX) on Candida glabrata and Enterococcus faecalis, as well as tested its cytotoxic effect on murine fibroblasts. MethodsIron oxide nanoparticles (IONPs) were coated with chitosan (CS) and loaded with CHX at 31.2, 78 and 156 μg/mL. Antimicrobial effects were assessed by determining the minimum inhibitory concentration (MIC), using the broth microdilution method, and fractional inhibitory concentration index (FICI). Preformed biofilms (48 h) were treated with different concentrations of the nanocarrier (24 h) and quantified by colony-forming units (CFUs), total biomass and metabolic activity. For cytotoxicity, the viability of L929 cells was evaluated by MTT assay after 24 and 48 h of exposure to the nanocarrier. Data were submitted to ANOVA and Fisher LSD or Tukey post-hoc tests (α = 0.05). ResultsMIC and FICI results showed an indifferent interaction among the components of the nanocarrier for all strains evaluated. CHX alone and nanocarrier containing 156 μg/mL CHX did not differ from each other in reducing the number of CFUs. However, the nanocarrier containing 156 μg/mL CHX promoted the highest reductions in total biofilm biomass and metabolism, surpassing the effect of CHX alone. After 24 and 48 h of exposure, the nanocarrier reduced CHX toxicity to the L929 cell at low concentrations. ConclusionThese findings suggest that the CHX nanocarrier has potential to be used in the control of oral diseases associated with C. glabrata and E. faecalis. Clinical relevanceCHX has improved the antibiofilm effect and reduced the cytotoxicity (at low concentrations) when conjugated to CS-coated IONPs. This new colloidal formulation has potential as an alternative antimicrobial agent to pure CHX for the control of biofilm-related oral diseases, such as oral candidiasis and endodontic infections.

Fast Adhesion of Gold Nanoparticles (AuNPs) to a Surface Using Starch Hydrogels for Characterization of Biomolecules in Biosensor Applications.

Gold nanoparticles (AuNPs) are the most thoroughly studied nanoparticles because of their remarkable optical properties. Color changes in assays that use AuNPs can be easily observed with the naked eye, resulting in sensitive colorimetric methods, useful for detecting a variety of biological molecules. However, while AuNPs represent an excellent nano-platform for developing analytical methods for biosensing, there are still challenges that must be overcome before colloidal AuNPs formulation can be successfully translated into practical applications. One of those challenges is the ability to immobilize AuNPs in a solid support. There are many difficulties with controlling both the cluster size and the adhesion of the coatings formed. In addition, many of the techniques employed are expensive and time-consuming, or require special equipment. Thus, a simple and inexpensive method that only requires common lab equipment for immobilizing AuNPs on a surface using Starch Hydrogels has been developed. Starch hydrogels confer a 400% increase in stability to the nanoparticles when exposed to changes in the environment while also allowing for macromolecules to interact with the AuNPs surface. Several starch derivatives were tested, including, dextrin, beta-cyclodextrin and maltodextrin, being dextrin the one that conferred the highest stability. As a proof-of-concept, a SlipChip microfluidic sensor scheme was developed to measure the concentration of DNA in a sample. The detection limit of our biosensor was found to be 25 ng/mL and 75 ng/mL for instrument and naked eye detection, respectively.

Sedimentation Dynamics of Colloidal Formulations through Direct Visualization: Implications for Fuel Cell Catalyst Inks

Quantitative appraisal of real-world colloidal systems in their native state is key for knowledge-based nanoparticle formulations. Analytical centrifugation (AC) is touted as a quantitative methodology examining settling and creaming of dispersions, but an understanding of the main transmission readout is often nonintuitive and complex. Herein, we introduce a new visualization technique, called transmittograms, that readily depicts the time-resolved settling behavior of solid–liquid dispersions, measured by AC. We validate the utility of transmittogram analysis using silica particles. Further, we demonstrate the strength of the approach to study the nanoscale dynamics in complex fuel cell inks.

Cellulose nanocrystals from blueberry pruning residues isolated by ionic liquids and TEMPO-oxidation combined with mechanical disintegration

In the last years, Chile has increased the production of blueberries; consequently, a large number of lignocellulosic residues derived from the harvesting and pruning are being generated. These residues are commonly burned, therefore increasing CO2 emissions. This study focuses on the extraction of two added-value products from blueberry pruning residues (BPRs), cellulose nanocrystals (CNC-IL) isolated using ionic liquid (IL) 1-ethyl-3-methylimidazolium [emim][Cl], and carboxylated nanocellulose (TOCNC), isolated with (2,2,6,6-tetramethylpiperidine-1-yl) oxyl or TEMPO reagent combined with a mechanical disintegration process. These products were characterized by zeta potential (ζ), FTIR, XRD, TGA, AFM, and conductometric titration. Results show oval-shaped CNC-IL particles with lengths of 46.1 ± 9.3 nm; meanwhile, TOCNC were rod-like shaped particles, with lengths of 120.3 ± 30.6 nm. These BPRs showed a promising potential to produce cellulose nanocrystals (CNCs) with different surface properties, opening a new alternative for the production of cellulose nanomaterials (CNMs) with promising applications in colloidal formulations, coatings, among others.

Role of Micro Emulsion Based In-Situ Gelling System of Fluoroquinolone for Treatment of Posterior Segment Eye Diseases (PSED)

The in situ drug delivery system and colloidal formulation like micro emulsion has potential to use in ocular delivery. Micro emulsion provides better permeation of drug through the membrane and provides improved bioavailability. The in situ drug delivery system decreases pre-corneal drainage, increase the contact time of formulation with eye and prolong the release in ocular tissues. Again, in situ gelling system has advantage of delivering accurate and reproducible quantities each time, against any already gelled formulations. To combine the benefits of these two dosage forms, micro emulsion based in situ gelling system can be developed as a novel vehicle for ophthalmic drug delivery. Endophthalmitis is an infection of intraocular fluids like vitreous humor and ocular tissues. To combat the disease, the formulation which provides sufficient concentration in posterior segment eye diseases (PSED) is required.
 Keywords: Posterior segment eye diseases, micro emulsion, drug delivery system, ocular, formulation.

Bioactive Characterization of Packaging Foils Coated by Chitosan and Polyphenol Colloidal Formulations.

Polypropylene (PP) and polyethylene (PE) foils, previously activated by ultraviolet (UV)/ozone, were functionalized using chitosan-extract nanoparticle dispersions. A solution of macromolecular chitosan was applied onto foils as a first layer, followed by the deposition of various extracts encapsulated into chitosan nanoparticles, which were attached as an upper layer. Functionalized foils were analyzed from a bioactive point of view, i.e., regarding antimicrobial and antioxidant activity. Desorption kinetics were also studied. Moreover, barrier properties were examined, as the most important parameter influencing antimicrobial and antioxidant activity. Finally, all these properties were correlated with different surface parameters, determined previously, in order to understand if there is any direct correlation between surface elemental composition, surface charge, contact angle, or morphology and a specific bioactive property. It was shown that great bioactive properties were introduced due to the additive effect of antimicrobial chitosan and antioxidative plant extracts. Moreover, oxygen permeability decreased significantly, and the migration of polyphenols and chitosan from the foil surface was below the OML (overall migration limit), which is very important for food industry applications. Furthermore, surface properties of foils influence to some extent the desired bioactivity.

Physicochemical Characterization of Packaging Foils Coated by Chitosan and Polyphenols Colloidal Formulations.

In this research, antimicrobial polysaccharide chitosan was used as a surface coating for packaging material. The aim of our research was to establish an additive formulation of chitosan and antioxidative plant extracts as dispersion of nanoparticles. Chitosan nanoparticles with embedded thyme, rosemary and cinnamon extracts were synthesized, and characterized for this purpose. Two representative, commercially used foils, polypropylene (PP) and polyethylene (PE), previously activated by UV/ozone to improve coating adhesion, were functionalized using chitosan-extracts nanoparticle dispersions. The foils were coated by two layers. A solution of macromolecular chitosan was applied onto foils as a first layer, followed by the deposition of various extracts embedded into chitosan nanoparticles that were attached as an upper layer. Since active packaging must assure bioactive efficiency at the interface with food, it is extremely important to understand the surface characteristics and phenomena of functionalized foils. The physico-chemical analyses of functionalized foils were thus comprised of surface elemental composition, surface charge, wettability, as well as surface morphology. It has been shown that coatings were applied successfully with an elemental composition, surface charge and morphology that should enable coating stability, homogeneity and consequently provide an active concept of the packaging surface in contact with food. Moreover, the wettability of foils was improved in order to minimize the anti-fogging behavior.

Co-encapsulating CoFe2O4 and MTX for hyperthermia.

Magnetic manotheranostics can be a fascinating charm to diagnose a tumour with MRI, and treatment through hyperthermia. This study aims to synthesise and characterise magnetically responsive polymer colloids (MRPCs). Healthy tissue damage done by chemotherapy session could be minimised by MRPCs. For the colloidal formulation of MRPCs, the oil in water emulsion technique was employed with the aid of sonication and stirring. The organic phase of emulsion contained methotrexate (MTX) drug, Eudragit E100 and CoFe2O4 (synthesised by co-precipitation) in ethanol, and the aqueous phase contained tween 80 in deionised water. The emulsion was optimised by studying/adjusting two different parameters, i.e. the concentration of constituents and sonication cycles. Multiple formulations were produced at sonication amplitude of 60% at 20 kHz, followed by centrifugation and lyophilisation. Characterisation of MRPCs was done for morphology, size measurement (23-25 nm), surface charge (∼15.12), coercivity (∼1549.6 G), magnetisation (2.6 emu) and retentivity (1.34 emu). Drug release in simulating physiological environment (pH = 7.4), was observed for up to 48 h, and, to determine the best release kinetic mechanism results were compared with kinetic models. Magnetic hyperthermia studies showed that MRPCs achieved an acceptable temperature of 42°C, for hyperthermia treatments in cancer patients.

Remote Controlled Autonomous Microgravity Lab Platforms for Drug Research in Space.

Research conducted in microgravity conditions has the potential to yield new therapeutics, as advances can be achieved in the absence of phenomena such as sedimentation, hydrostatic pressure and thermally-induced convection. The outcomes of such studies can significantly contribute to many scientific and technological fields, including drug discovery. This article reviews the existing traditional microgravity platforms as well as emerging ideas for enabling microgravity research focusing on SpacePharma's innovative autonomous remote-controlled microgravity labs that can be launched to space aboard nanosatellites to perform drug research in orbit. The scientific literature is reviewed and examples of life science fields that have benefited from studies in microgravity conditions are given. These include the use of microgravity environment for chemical applications (protein crystallization, drug polymorphism, self-assembly of biomolecules), pharmaceutical studies (microencapsulation, drug delivery systems, behavior and stability of colloidal formulations, antibiotic drug resistance), and biological research, including accelerated models for aging, investigation of bacterial virulence , tissue engineering using organ-on-chips in space, enhanced stem cells proliferation and differentiation.

The Effects of Two Different Creatine Formulations on Muscle Bioenergetics in Men

A novel colloidal creatine formulation has been suggested to be superior to creatine monohydrate for improving plasma creatine levels after single-dose administration in animal research. However, if colloidal creatine supremely affects creatine levels in the skeletal muscle and blood of healthy humans remains currently unknown. This double blind, cross-over, randomized, creatine monohydrate-controlled pilot trial evaluated serum and skeletal muscle levels of creatine before and during single-dose colloidal creatine (Creaphil®) administration in five healthy men. Five healthy volunteers aged 24.0 ± 1.7 years (weight 79.2 ± 7.4 kg; height 181.0 ± 5.7 cm) were supplemented with single dose of 5 g of colloidal creatine or creatine monohydrate, with skeletal muscle and serum levels of creatine monitored at baseline and during post-administration for 10 h in five intervals. At each assessment at the lab, the participants completed magnetic resonance spectroscopy for right vastus medialis muscle and clinical chemistry studies. Colloidal formulation resulted in a more powerful rise in vastus medialis creatine levels comparing to creatine monohydrate, as evaluated with the area under the concentration-time curve calculation (108.5 ± 15.9 mM · h vs. 103.3 ± 15.1 mM · h; P = 0.01). This was accompanied by a significantly higher serum creatine level after colloidal creatine administration at 30 min post-administration (158.4 ± 21.2 μmol/L vs. 121.0 ± 38.9 μmol/L; P = 0.05). No participant reported any adverse events during the trial. These results suggest that colloidal creatine is a preferred and safe alternative to creatine monohydrate for improved creatine bioavailability after single-dose administration. However, more studies are needed to evaluate its effectiveness and safety after long-term supplementation.

ANALYTICAL APPROACHES IN UNVEILING THE COMPATIBILITY OF COLLAGENASE WITH ADDITIVES IN VIEW OF ITS COLLOIDAL DELIVERY

The core objective of present work was to investigate the chemical interactions of selected additives with therapeutic enzyme Collagenase (COLG) and determination of its compatibility for futuristic colloidal formulation. Initially, solubility of COLG with additives was determined and emulsification efficiency of surfactants was examined. FTIR spectra of COLG with its binary blends were compared. Non-denaturing SDS-PAGE and Circular Dichroism (CD) used to investigate primary and secondary structure of enzyme in binary mixture. Finally, the control and accelerated studies was performed by spectroscopy.

Ocular Tolerability and Efficacy of Ebastine Colloidal Formulation in Allergic Conjunctivitis

Allergic conjunctivitis (AC), defined by ocular itching, hyperemia, lacrimation and edema, impairs the quality of life across the globe. Ebastine is available as an oral antihistamine formula, such as tablets and syrup, for allergic disorders. Topical antihistamines are preferred over oral agents since their direct application at the site of action results in rapid onset and superior efficacy with less systemic side effects. The objective of the present work was to evaluate the antiallergic potential of optimized ebastine (1% w/v) colloidal ocular formulation by performing in vitro study like hen's egg chorioallantoic membrane test (HET-CAM) for tolerability and in vivo efficacy study in ovalbumin (OA)-induced allergic conjunctivitis (AC) with acute ocular irritation study. Eye scratching behavior and edema were evaluated after topical antigen challenge. Edema was scored at periodic interval after the instillation of ovalbumin followed by histopathology. The results showed that ebastine (1% w/v) colloidal ocular formulation was effective in inhibiting symptoms of eye inflammation induced by ovalbumin. Further, the study indicated that said formulation has a quick onset and the duration of effect sufficient to provide relief from symptoms for 24 hr. Ocular irritation by HET-CAM assay showed that the developed formulation does not cause any irritation to the blood vessels. Acute ocular irritation test was performed using rabbits and results showed that developed formulation was non-irritant to the eye. The present study revealed that the ocular ebastine formulation could offer a novel therapeutic opportunity against IgE-mediated allergic conjunctivitis.

Development of ulvan‐based emulsions containing flavour and fragrances for food and cosmetic applications

AbstractIn the present work, ulvan, a sulphated polysaccharide of algal origin, was innovatively investigated as stabilizing and emulsifying agent in colloidal formulations containing functional agents for food and cosmetic applications in virtue of its edibility and amphiphilic character. Ulvan was successfully submitted to chemical modification with biocompatible fatty acid moieties to increase the amphiphilic properties of the polysaccharide without compromising its safety profile. Oil in water (O/W) emulsions were developed using the ultrasonication method as an easy and rapid homogenization process. The stability of the obtained formulations was assessed by visual inspection, size distribution and zeta potential analysis. Stable emulsions were obtained by using either native or chemically modified polysaccharide. The most promising formulations based on the use of native ulvan were successfully implemented as clouding and flavouring agents in soft drink beverages and as stabilizing and perfuming agents in body cream milk products. The obtained results may open new perspectives on the exploitation of abundant waste biomasses as sources of biocompatible high value added materials suitable for being applied in critical applications as a safe alternative to synthetic chemicals. In particular ulvan could represent a valuable platform of functional and bioactive compounds with promising properties as stabilizing and emulsifying agents for food and cosmetic applications.

Colloids or powders: Which nanoparticle formulations do cells like more?

Understanding the difference in physicochemical properties and biological response between colloidal and powder formulations of identical materials is important before the given materials are used in a medical milieu. In this study we compared a set of biological effects of colloidal and powder formulations of composite nanoparticles comprising superparamagnetic iron oxide cores and silicate/carbon shells. Magnetic dipole interaction between adjacent nanoparticles was more pronounced in their powders than in their colloidal formulations. Nanoparticles delivered as powders were thus more responsive to the magnetic field, but exhibited reduced uptake in bone and brain cancer cells, including K7M2 osteosarcoma line and U87 and E297 glioblastoma lines. Specifically, while the alternate magnetic field elicited a more rapid heat generation in cell culture media supplemented with the magnetic powders, the nanoparticles dispersed in the same media were uptaken by the cancer cells more copiously. The cellular uptake proved to be more crucial in defining the effect on cell survival, given that suspended formulations elicited a greater degree of cancer cell death in the magnetic field compared to the powder-containing formulations. Because of this effect, colloidal formulations were able to target cancer cells more effectively than the powders: they reduced the viability of all three tested cancer cell lines to a significantly greater degree that the viability of the normal, MDCK-MDR1 cell line. It is concluded that better uptake profile can make up for the lower heating rate in the AC field and lead to a more effective magnetic hyperthermia therapy. These results also demonstrate that the direct delivery of ferrofluids is more optimal than the administration of their constitutive particles as powders.

Phase diagram and surface adsorption behavior of benzyl dimethyl hexadecyl ammonium bromide in a binary surfactant-water system

Phase diagram provides valuable information to describe the phase and aggregation behavior of surfactants. In this study, surface adsorption behavior of benzyl dimethyl hexadecyl ammonium bromide (BDHAB) surfactant in water and their phase formations have been explored. The formation of lyotropic liquid crystalline (LLC) phases in the binary surfactant–water system was analyzed by polarized light microscopy (PLM). A comprehensive phase diagram was established presenting the existence of LLC phases as a function of surfactant concentration and temperature. The observed PLM images reveal that the BDHAB–H2O system exhibits isotropic (L1), hexagonal liquid crystalline (H1), cubic (V1), and lamellar (L∞) phases in a sequential pattern with the increase of surfactant concentration. The recorded LLC phases for bi-tail BDHAB–H2O system have also been compared with the phase diagram of single tail cetyl trimethyl ammonium bromide (CTAB)–H2O system. The present study evidence that the surfactant morphology (i.e., alkyl chain length and surfactant head-group area) has a significant influence on the formation of micellar aggregates. In addition, surface tension measurements were also performed to observe the surface adsorption behavior of BDHAB surfactant. This study will be beneficial in understanding the micelle formation and solubilization behavior of bi-tailed quaternary ammonium cationic surfactants to optimize its colloidal formulations.

Improved Biological Activity and Stability of enzyme L-Asparaginase in Solid Lipid Nanoparticles Formulation

To protect the biological activity of an enzyme during the development of formulations is one of the biggest challenges. The tetrameric form of L-Asparaginase is used to treat Acute Lymphocytic Leukaemia. It possesses shorter in vivo half–life. Using a modified (water/oil)/water-emulsion method followed by solvent evaporation L-Asn was successfully encapsulated at the core of Solid Lipid Nanoparticles made of lipid glyceryl monostearate. This study elucidated that the preparation of L-Asn loaded SLN develop a colloidal formulation with enhanced activity. The in-vitro release profile of the enzyme revealed first bursts has been increased. The study of the lyophilised formulation also shows that the enzyme holds its biological activity and retains its particle size distribution. Consequently, by using an apt combination of homogenisation speed, temperature and additives the storage and biological activity of L-Asn in SLN formulation can be improved. Keywords: L-Asparaginase, Solid Lipid Nanoparticles, Controlled release, Lymphocytic Leukaemia

Electrophoretic Deposition for Lithium-Ion Battery Electrode Manufacture.

Electrophoretic deposition (EPD) has received increasing attention as an alternative manufacturing approach to slurry casting for the production of battery and supercapacitor electrodes. This process is of relevance for industrial scalability as evidently seen in the current electrophoretic paints industry. Nevertheless, the reported work so far have only concentrated on thin films of electrophoretically deposited electrodes for energy storage. Here, the electrochemical performance of thick films (up to tens of μm) as lithium‐ion battery electrodes produced by EPD is reported. A commercially sourced LiN1/3M1/3C1/3O2 (5 to 25 μm particle size) was used in this exemplary investigation. This work shows the production of binder‐free high density active material (>90 %) electrodes. Coin cells were assembled and the battery performance was measured. Tests included: cyclic voltammetry, C‐rate vs capacity, battery cycling and electrochemical impedance spectroscopy. Other investigations also studied: colloidal electrolyte formulation, electrode manufacture, microstructure characterisation and elemental mapping analysis. In short, EPD electrode manufacture can be applied as a platform technology for any battery and supercapacitor material, and the reported manufacturing processes and methodologies represent direct relevance to produce energy storage electrodes useful to practical applications.

Sclareol-loaded hyaluronan-coated PLGA nanoparticles: Physico-chemical properties and in vitro anticancer features.

Sclareol (labd‑14‑ene‑8,13‑diol), a phytochemical compound belonging to labdane-type diterpenes, has recently attracted noteworthy attention because of its peculiar pharmacological properties. The foremost obstacle to an efficacious application and use of this molecule is its unfavorable bioavailability due to its poor aqueous solubility. In this investigation sclareol was encapsulated within PLGA nanoparticles with the aim of favoring its administration in physiological media, increasing its anticancer activity and obtaining a stable colloidal formulation. These nanoparticles containing sclareol were characterized by a mean diameter of 100-150 nm, a narrow size distribution and a negative surface charge. The active compound was efficiently retained by the polymeric structure and did not induce any physical destabilization. The coating of the PLGA nanoparticles with hyaluronic acid (1.5 MDa) increased the antitumor efficacy of the encapsulated drug against human breast cancer cells expressing the hyaluronan receptors (MCF-7 and MDA-MB468) while a similar pharmacological effect was obtained on human colon carcinoma cells (CaCo-2). CLSM analysis demonstrated the intracellular localization of fluorescent nanosystems after 3 h incubation.

Efficacy of a silver colloidal gel against selected oral bacteria in vitro

Background: It is necessary to develop new strategies to protect against bacteria such as S treptococcus mutans, S treptococcus sanguis, and Streptococcus salivarius, which contribute to tooth decay and plaque formation. Our current study investigated the efficacy of a colloidal silver gel in inhibiting biofilm formation by these principal oral bacteria , in vitro. The aim of this study was to assess the efficacy of a colloidal silver gel formulation for inhibiting bacterial biofilm formation (Ag-gel) by the principal bacteria that cause plaque formation and tooth decay. Methods: The effect of Ag-gel on viability of S. mutans, S. sanguis, and S. salivarius was assessed by quantifying their colony forming units (CFU) in presence or absence of the test gel. The effect of this formulation on biofilm-forming ability of these bacteria was studied through scanning electron microscopy. Results: Using the CFU assays, over 6 logs of inhibition (100%) were found for S. mutans, S. sanguis, and S. salivarius for the Ag-gel-treated bacteria when compared with the control gel. In addition, the Ag-gel also inhibited biofilm formation by these three bacteria mixed together. These results were confirmed by scanning electron microscopy. Conclusions: The Ag-gel was effective in preventing biofilm formation by S. mutans, S. sanguis, and S. salivarius. This Ag-gel should be tested for the ability to block plaque formation in the mouth, through its use as a tooth paste.

Efficacy of a silver colloidal gel against selected oral bacteria in vitro

Background: It is necessary to develop new strategies to protect against bacteria such as S treptococcus mutans, S treptococcus sanguis, and Streptococcus salivarius, which contribute to tooth decay and plaque formation. Our current study investigated the efficacy of a colloidal silver gel in inhibiting biofilm formation by these principal oral bacteria , in vitro. The aim of this study was to assess the efficacy of a colloidal silver gel formulation for inhibiting bacterial biofilm formation (Ag-gel) by the principal bacteria that cause plaque formation and tooth decay. Methods: The effect of Ag-gel on viability of S. mutans, S. sanguis, and S. salivarius was assessed by quantifying their colony forming units (CFU) in presence or absence of the test gel. The effect of this formulation on biofilm-forming ability of these bacteria was studied through scanning electron microscopy. Results: Using the CFU assays, over 6 logs of inhibition (100%) were found for S. mutans, S. sanguis, and S. salivarius for the Ag-gel-treated bacteria when compared with the control gel. In addition, the Ag-gel also inhibited biofilm formation by these three bacteria mixed together. These results were confirmed by scanning electron microscopy. Conclusions: The Ag-gel was effective in preventing biofilm formation by S. mutans, S. sanguis, and S. salivarius. This Ag-gel should be tested for the ability to block plaque formation in the mouth, through its use as a tooth paste.