COLLECTIVE MOTION AND PHASE DIAGRAM OF SELF-PROPELLED VIBRATED HARD SQUARES

In equilibrium, matter condenses into ordered phases due to the combined effects of inter-particle interactions and entropy. In this dissertation, we explore the self-propulsion of particles as an additional nonequilibrium consideration in the mechanisms for ordering. Our experiments employ square-shaped hard particles; in equilibrium, when particle motions are randomly directed, squares form entropically-stabilized phases in which first their orientations, and then their positions, get locked in relative to each other, depending on the density of coverage. When the square tiles are modified to have small propulsion along some body-fixed axis we find that their tendency to order is profoundly altered. Adding such \u27activity\u27(quantified by the persistence length of motion along the mobility direction) to particles can produce new ‘phases’ and mechanisms for ordering not seen in equilibrium materials. In the first study, we study a system of vibrated self-propelled granular particles with high persistence length on a horizontal plane within a circular boundary. The particles are square and designed to have polar motion along one body diagonal. When they hit the boundary they align along the boundary but also \u27walk\u27 along the boundary. Given a large enough initial density in the plane, particles spontaneously migrate to the boundary, form a ring, and perform a stable 1D rotational gear-like motion with a direction chosen by their net polarization. For a fully polarized single ring, we find that the collective velocity surpasses the free single-particle velocity. This collective velocity increases as the density of particles in the ring increases, which is counterintuitive for a normal traffic problem. The spatial correlations of particle velocity fluctuations decay exponentially with a length scale that increases with density. There is thus increased cooperativity in the system. However, the temporal correlation shows that velocity fluctuations are very short-lived. In a second project, we study the effect of varying the persistence length of individual particle motion in an ensemble of squares held at fixed density. We find that adding activity to the particles qualitatively modifies their phase diagram relative to that of passive squares. At large enough activity (just as in the previous study), particles always migrate to the boundary and form a high-density ordered state. At smaller values of activity, different phases are seen as a function of density. At low density, the particles form an isotropic fluid. As the density increases, particles separate into a high-density ordered region while the remaining particles remain in the fluid state. Above a finite density, the phase coexistence curve terminates and all particles freeze into an ordered state. The start and end density of the coexistence region is found to be a function of activity. %(NM). The coexistence region emerges purely due to the effect of activity in the system. We also discuss dynamics within the dense, ordered state. In the final project in this thesis, we studied by simulation the effect on collective behavior of changing the symmetry of single particle activity. In addition to passive squares (that is, squares with isotropic mobility), we study polar, bipolar, and chiral mobilities. For each of these choices of symmetry we also choose different axes for the activity relative to the particle shape. We thus have six different kinds of particles and compare their corresponding phase behavior. We find that different symmetries of activity have quite different phase states. For a fixed symmetry of activity, changing the direction of symmetry leads to much smaller changes in phase behavior

Bioceramic micro-fillers reinforce antibiofilm and remineralization properties of clear aligner attachment materials

Introduction: Clear aligners, while offering a more hygienic alternative to fixed appliances, are still associated with challenges including plaque accumulation and enamel demineralization. The aim of the present study was to investigate the antibiofilm and remineralization effectiveness of innovative flowable composite attachments containing bioceramic micro-fillers.Methods: Four experimental attachments were formulated and bonded to human enamel specimens: 3M Filtek Supreme flowable composite (Filtek SF) + 10% bioactive glass 45S5 (BAG), Filtek SF + 30% BAG, Filtek SF + 10% Bredigite (BRT), Filtek SF + 30% BRT. Plaque biofilms were grown on the bonded enamel using a standardized protocol and the biofilm-killing effect was assessed by confocal laser scanning microscopy and scanning electron microscopy. Vickers microhardness was measured to evaluate the remineralization effect of the attachments containing bioceramic fillers after acid challenge. Shear bond test was performed to assess the bonding strength.Results: Attachments with bioceramic fillers significantly inhibited plaque biofilm growth in 3 weeks on enamel, contributing over 20% bacterial cell killing in 10% filler groups and over 30% killing in 30% filler groups. All four experimental groups demonstrated significantly higher microhardness values than the control group without fillers on the attachment side. The shear bonding strength was not compromised in the attachments with micro-fillers.Discussion: Proper incorporation of bioceramic micro-fillers in attachments provides an innovative approach for clear aligner therapy with reinforced antibiofilm and remineralization effects without weakening shear bonding strength

Antibacterial coatings on titanium surfaces: A comparison study between in vitro single-species and multispecies biofilm

Dental plaque is a biofilm that Causes dental caries, gingivitis, and periodontitis. Most of the studies in antibacterial coatings have been conducted by in vitro Single-species biofilm formation, but oral biofilm involves more than 700 different bacterial Species that are able to interact. Therefore, new studies are focused on in vitro multispecies biofilm models that mimic in vivo biofilms. The aim Of the present work was to study different antibacterial coatings onto titanium surfaces and evaluate the in vitro antimicrobial properties of the surfaces on two different bacterial species and an oral biofilm. The lactate dehydrogenase assay determined that treated samples did not affect fibroblast viability. In addition, the viability of microorganisms on modified samples was evaluated by a LIVE/DEAD BacLight bacterial viability kit. Although a decrease in viable bacteria onto, treated samples was obtained, the results Showed differences in effectiveness when single-biofilm and oral plaque were tested. It confirms, as we expected, the distinct sensitivities that bacterial strains have. Thus, this multispecies biofilins model holds a great potential to assess antibacterial properties Onto samples for dental purposes.Postprint (author’s final draft

Experimental and Theoretical Investigation of Multispecies Oral Biofilm Resistance to Chlorhexidine Treatment

We investigate recovery of multispecies oral biofilms following chlorhexidine gluconate (CHX) and CHX with surface modifiers (CHX-Plus) treatment. Specifically, we examine the percentage of viable bacteria in the biofilms following their exposure to CHX and CHX-Plus for 1, 3, and 10 minutes, respectively. Before antimicrobial treatment, the biofilms are allowed to grow for three weeks. We find that (a). CHX-Plus kills bacteria in biofilms more effectively than the regular 2% CHX does, (b). cell continues to be killed for up to one week after exposure to the CHX solutions, (c). the biofilms start to recover after two weeks, the percentage of the viable bacteria recovers in the 1 and 3 minutes treatment groups but not in the 10 minutes treatment group after five weeks, and the biofilms fully return to the pretreatment levels after eight weeks. To understand the mechanism, a mathematical model for multiple bacterial phenotypes is developed, adopting the notion that bacterial persisters exist in the biofilms together with regulatory quorum sensing molecules and growth factor proteins. The model reveals the crucial role played by the persisters, quorum sensing molecules, and growth factors in biofilm recovery, accurately predicting the viable bacterial population after CHX treatment.Fundación Obra Social de La CaixaFundación CanadáFundación Ramón Areces (Postdoctoral Scholarship

The promise and challenges of utility-scale compressed air energy storage in aquifers

Widely distributed aquifers have been proposed as effective storage reservoirs for compressed air energy storage (CAES). This aims to overcome the limitations of geological conditions for conventional utility-scale CAES, which has to date used caverns as the storage reservoirs. As a promising technology, compressed air energy storage in aquifers (CAESA) has received increasing attention as a potential method to deal with the intermittent nature of solar or wind energy sources. This article presents a selective review of theoretical and numerical modeling studies as well as field tests, along with efficiency and economic analyses, to assess the feasibility of the emerging technology. Although some field tests suggest that a large bubble could be created in aquifers to sustain the working cycles at target rates, challenges remain before the technology can be recommended for wide deployment. The geological critical safety factors affecting the gas bubble development and sustainability of operation cycles include the geological structure, aquifer depth, and hydrodynamic and mechanical properties, such as porosity, permeability, compressibility, and mineral composition. Moreover, the injection/withdrawal well configurations and oxidation reactions caused by the oxygen in compressed air should also be considered. The failed attempt of renewable energy combined with CAESA in Iowa is described and the lessons learned are summarized. Combining CAESA with thermal storage, using CO2 as cushion gas, horizontal wells or hydraulic fracturing, and man-made boundaries are proposed to improve CAESA efficiency but need further study for future applications

Antibiofilm peptides against oral biofilms

The oral cavity is a major entry point for bacteria and other microorganisms. Oral biofilms are formed by mixed communities of microorganisms embedded in an exopolysaccharide matrix. Biofilms forming on dental hard or soft tissue are the major cause of caries and endodontic and periodontal disease. Human oral biofilms exhibit high resistance to antimicrobial agents. Antibiofilm peptides constitute a diverse class of host-defense molecules that act to combat invasion and infection with biofilms. Different in vitro and in vivo biofilm models with quantitative analysis have been established to provide predictable platforms for the evaluation of the antibiofilm effect of oral antibiofilm peptides. These peptides have engendered considerable interest in the past decades as potential alternatives to traditional disinfecting agents due to their ability to target bacterial biofilms specifically, leading to the prevention of biofilm formation and destruction of pre-existing biofilms by Gram-positive and -negative bacterial pathogens and fungi. At the same time, challenges associated with the application of these antibiofilm peptides in dental practice also exist. The production of effective, nontoxic, and stable antibiofilm peptides is desired in both academic and industrial fields. This review focuses on the antibiofilm properties of current synthetic peptides and their application in different areas of dentistry

Antimicrobial and Antibiofilm Properties of Bioceramic Materials in Endodontics

Microbes are prevalent in the root canals of necrotic teeth, and they are the cause of primary and post-treatment apical periodontitis. Bacteria can dwell within the infected root canal system as surface-adherent biofilm structures, which exhibit high resistance to antimicrobial agents. Bioceramic materials, with their biocompatible nature and excellent physico-chemical properties, have been widely used in dental applications, including endodontics. This review focuses on the application of bioceramic technology in endodontic disinfection and the antibiofilm effects of endodontic bioceramic materials. Different bioceramic materials have shown different levels of antibiofilm effects. New supplements have emerged to potentially enhance the antibiofilm properties of bioceramics aiming to achieve the goal of microbial elimination in the root canal system.Dentistry, Faculty ofOral Biological and Medical Sciences (OBMS), Department ofReviewedFacult