This study investigates the role of the biologically relevant polyamines putrescine (PUT), spermidine (SPD), and spermine (SPM) in modulating the structural and mechanical properties of 1% κ-carrageenan hydrogels. Using linear and non-linear rheology, confocal laser scanning microscopy, and turbidity measurements, we show that multivalent polyamines alter the κ-carrageenan network beyond simple charge neutralization. Two distinct mechanical regimes were identified. At isoconcentration (1.2 mM), the storage modulus (G’) increased with cation valency: trivalent SPD and tetravalent SPM increased G’ by more than two orders of magnitude, whereas divalent PUT produced an approximately ten-fold increase. SPD and SPM formed dense, highly aggregated brittle networks, while PUT generated weaker but more ductile filamentous structures. At plateau concentrations, the G’ of PUT- and SPD-crosslinked hydrogels converged to approximately 5 – 6 kPa, indicating an apparent mechanically stable state on the experimental timescale with maximal load-bearing density. These networks became uniformly brittle and exhibited pronounced strain-stiffening and shear-thickening behavior. The results identify polyamines, particularly SPD, as effective modifiers for tuning κ-carrageenan hydrogel architecture and mechanics, with potential applications in food and biomedical systems.

Despite decades of research, the nonlinear mechanics of agar remains poorly understood. In this work, we analyze the mechanical response of soft, hard, and very hard agar hydrogels under nonlinear shear deformation. Low-shear viscoelastic behavior across concentrations was characterized using storage and loss moduli, yield strain, flow point, loss factor, and ductility index. The transition to nonlinear response was examined using Fourier analysis of shear stress signals. To describe the high-shear regime, we employed large-amplitude oscillatory shear (LAOS) rheology. The mechanical response was further analyzed using Lissajous-Bowditch plots (stress versus strain and stress versus shear rate), linking agar network structure to intracycle deformation behavior and energy dissipation. By analyzing strain stiffening, shear thickening, yielding, and intracycle structural dynamics, we quantified dissipation rates across concentrations and constructed fingerprint maps of shear stiffening and thickening at different frequencies. Microstructural insights from rheology were compared with macroscopic characterization using phase-contrast microscopy. The nonlinear rheological analysis revealed that structural reorganization shifts systematically toward lower shear strain values with increasing agar concentration.

Effective biofilm removal from periodontal and peri-implant pockets remains a challenge due to constrained geometry and limited access. This study investigates a novel phenomenon of distant-field cleaning utilizing Er:YAG laser treatment, where removal of bacteria occurs in areas without previously observed cavitation under high-speed imaging. To understand this effect, we developed a transparent zero-gap model simulating a tooth or implant and surrounding soft tissue. We systematically examined the impact of laser fiber insertion depth, cavitation bubble dynamics, the stiffness and roughness of the material, and laser parameters on the cleaning efficiency.Our findings reveal that the removal of bacteria indeed correlates strongly with cavitation occurrence. Deeper optical fiber insertion into the pocket model only enhanced cleaning efficiency by moving the fluid dynamics and enabling deeper water penetration. Surprisingly, high-speed imaging showed no cavitation in distant regions, raising questions about the mechanisms enabling such cleaning. Further investigation uncovered that surface roughness played a critical role in facilitating this distant-field effect. The smooth, transparent surfaces used in imaging experiments suppressed fluid dynamics, while textured surfaces created by 3D-printed molds and bacterial monolayer allowed deeper water penetration and pressure wave propagation. These surface irregularities enabled localized cavitation events and enhanced bacterial disruption, even in regions beyond the laser fiber’s immediate influence.This study emphasizes the significance of surface roughness in test models, highlighting the need for models to closely mimic the conditions of real clinical scenarios for accurate optimization of Er:YAG laser-induced photoacoustic removal of bacteria.

A single cavitation microbubble can transiently disrupt the cellular membrane, providing a chemical-free, targeted drug delivery mechanism. Here, we investigate the spatiotemporal dynamics of membrane permeabilization in an Escherichia coli ( E. coli ) monolayer exposed to a single cavitation event. Using high-resolution fluorescence microscopy and propidium iodide (PI) uptake as a marker of membrane disruption, we tracked the response of 5565 individual cells around the center of the cavitation event over timescales from microseconds to minutes and spatial scales from 1 to 165 µm. PI uptake rates exhibited a strong spatial dependence, with cells closer to the cavitation center showing rapid and extensive permeabilization. A modified Goldman equation describing PI concentrations inside and outside the cells was used and related to the spatiotemporal measurements of fluorescence intensity. The model accurately captured the first-order PI uptake kinetics, which resulted in saturated fluorescence intensity profiles. Additionally, the model predicted an exponential decay of permeability post-cavitation, implicitly suggesting that pore-resealing dynamics were taking place. Membrane permeability decreased with distance as 1/r, with a characteristic decay time of approximately 3.4 min. Our model thus predicts cell damage induced by a single cavitation event in both space and time. In the present case, where the cavitation bubble reached maximum radius of 29.7 µm, we found that at a distance of 11 µm from the cavitation center, ~ 50% of cell membranes are damaged and permeable to PI, but a pore-resealing mechanism reduces this damage to ~ 1% after 10 min. Our results are consistent with existing sonoporation studies and offer novel insights for optimizing cavitation-assisted drug delivery and biofilm disruption strategies.

Physical disruption of bacterial integrity with piezoelectric materials offers a promising alternative to conventional bactericidal chemical treatments. In this study, we investigated the mechanisms of the antibacterial effect of mechanically stimulated poly-(vinylidene fluoride-co-trifluoroethylene) (P-(VDF-TrFE)) piezoelectric material on Escherichia coli cells with modified cell wall layers. Cells with modified peptidoglycan layer, outer membrane, or extracellular polymer matrix were tested for piezoelectric susceptibility either in direct contact with the piezoelectric material or in suspension after mechanical stimulation of the piezoelectric material, during the exponential and stationary growth phase. The results show that the P-(VDF-TrFE) material can electrostatically inhibit the growth of E. coli. The antibacterial efficacy can be further enhanced by the piezoelectric effect under mild mechanical stimulation at 1 Hz. Since most chemical antibacterial agents are effective against exponentially growing bacterial cells, it is a significant finding that piezoelectric stimulation is also very effective against stationary cells. The reduction of surface charges by cell wall modifications increased the resistance of bacteria to the electrostatic effects of P-(VDF-TrFE), but the antibacterial effect could be enhanced by piezoelectricity. Piezoelectric antimicrobial enhancement was most pronounced on cells with disrupted peptidoglycan layer and extracellular matrix removed. Based on the results of this study, one can envision an application of P-(VDF-TrFE)-coated materials on "high-touch" surfaces, such as light switches, doorknobs or countertops, that could be piezoelectrically stimulated by touch, providing an efficient and seamless solution for antibacterial surfaces.

SignificanceHere, we present a photoacoustic method to remove biofilms from periodontal and peri-implant-constrained geometries.AimWe aim to remove biofilms from narrow periodontal and peri-implant model systems with the application of Er:YAG ultrashort laser pulses.ApproachConstruction of zero-gap model system from PDMS and titanium, growth of biofilms on titanium surfaces, and removal of biofilms with Er:YAG USP, 20 mJ, 15 Hz, and 10 s were performed.ResultsThe results suggest that geometry, the vertical position of the laser fiber tip, and the evolution of the primary cavitation bubble significantly affect cleaning effectiveness. Cleaning was higher in the wedge part of the model system. In the zero-gap part of the model system, biofilm cleaning effectiveness was highest at the position of the laser fiber tip and decreased above and below the fiber tip. The dimension of the space in which the cavitation bubble develops determines the size and dynamics of the expanded cavitation bubble and consequently the biofilm cleaning effectiveness.ConclusionsThe obtained results suggest a very good biofilm removal effectiveness in difficult-to-reach narrow geometries mimicking clinical attachment loss in the periodontal/peri-implant pocket.

Tolerance to antimicrobial agents in mature and structured biofilms presents a significant challenge in clinical and industrial applications. The contribution of biofilm physical structure to antimicrobial tolerance remains particularly poorly understood, primarily due to the lack of biofilm structure quantification and manipulation studies. To fill the gap in our knowledge, we have investigated how mechanical and biochemical disruptions of biofilm integrity affect Bacillus subtilis tolerance to antimicrobial agents. Our findings reveal that biofilm structural integrity is a major determinant of tolerance to membrane disrupting antibiotic daptomycin. Biofilm viscoelastic properties as well as antimicrobial tolerance to daptomycin were directly related to the presence of exopolysaccharide EpsA-O. In the absence of EpsA-O bacteria produced weak biofilms with markedly reduced elastic and viscous moduli that correlated with a 3-log reduction in bacterial survival rate when challenged with daptomycin. These findings underscore the protective role of biofilm structure against antibiotics and suggest that targeting biofilm structural integrity could substantially enhance antimicrobial treatment strategies for biofilm-related infections.

Biofilm removal from the apical region of the periodontal or peri-implant pocket, which is very difficult to achieve with mechanical instruments, is a major unresolved issue in dentistry. Here, we propose the use of photoacoustically induced streaming and secondary cavitation to achieve superior cleaning efficacy in the apical region of the periodontal and peri-implant pocket. We have used a prefabricated narrow wedge system that mimics the consistency of periodontal and peri-implant pockets of both healthy and severely inflamed tissue. We studied the effect of single-pulse modality Er:YAG on Pseudomonas aeruginosa biofilm removal. We used different laser energies, fiber-tip positions, and laser treatment durations. The cleaning process was monitored in real-time with a high-speed camera after each individual laser pulse application. The obtained results suggest that biofilm cleaning efficacy in a difficult-to-reach place in healthy model tissue is directly related to the onset of secondary cavitation bubble formation, which correlates with a significant improvement of biofilm removal from the apical region of the periodontal or peri-implant pocket. In comparison to the healthy tissue model, the laser energy in inflamed tissue model had to be increased to obtain comparable biofilm cleaning efficacy. The advantage of photoacoustic cavitation compared to other methods is that laser-induced cavitation can trigger secondary cavitation at large distances from the point of laser application, which in principle allows biofilm removal at distant locations not reachable with a laser fiber tip or other mechanical instruments.

Here, we view biofilm as a nested cybernetic system that cannot be studied in isolation from the dynamics in the rest of the ecosystem. We provide a systems view of B. subtilis development from the inoculation to hibernation. We propose that B. subtilis biofilm development in an aqueous environment is a temporal response to changes in the ecosystem provoked and caused by bacteria. We show that the initial bacterial growth changes physio-chemical parameters of the ecosystem, which in turn trigger the initiation of the biofilm formation and guide its development, structure, and ultimately its decay and dispersion. Formation of the biofilm is just one of the possible outputs of the bacterial cybernetic system. It is not invariably the best response that fits all environmental needs. Viewing biofilm as a cybernetic set of interrelated objects, capable of receiving, storing, processing, and exchanging information with the rest of the ecosystem, should become an integral part of biofilm studies.

Extracellular polysaccharides are crucial components for biofilm development. Although Bacillus subtilis is one of the most characterized Gram-positive biofilm model system, the structure-function of its exopolysaccharide, EpsA-O, remains to be elucidated. By combining chemical analysis, NMR spectroscopy, rheology, and molecular modeling, high-resolution data of EpsA-O structure from atom to supramolecular scale was obtained. The repeating unit is composed of the trisaccharide backbone [→3)-β-D-QuipNAc4NAc-(1→3)-β-D-GalpNAc-(1→3)-α-D-GlcpNAc-(1]n, and the side chain β-D-Galp(3,4-S-Pyr)-(1→6)-β-D-Galp(3,4-S-Pyr)-(1→6)-α-D-Galp-(1→ linked to C4 of GalNAc. Close agreement between the primary structure and rheological behavior allowed us to model EpsA-O macromolecular and supramolecular solution structure, which can span the intercellular space forming a gel that leads to a complex 3D biofilm network as corroborated by a mutant strain with impaired ability to produce EpsA-O. This is a comprehensive structure-function investigation of the essential biofilm adhesive exopolysaccharide that will serve as a useful guide for future studies in biofilm architecture formation.

Cavitation is a potentially useful phenomenon accompanied by extreme conditions, which is one of the reasons for its increased use in a variety of applications, such as surface cleaning, enhanced chemistry, and water treatment. Yet, we are still not able to answer many fundamental questions related to efficacy and effectiveness of cavitation treatment, such as: "Can single bubbles destroy contaminants?" and "What precisely is the mechanism behind bubble's cleaning power?". For these reasons, the present paper addresses cavitation as a tool for eradication and removal of wall-bound bacteria at a fundamental level of a single microbubble and a bacterial cell. We present a method to study bubble-bacteria interaction on a nano- to microscale resolution in both space and time. The method allows for accurate and fast positioning of a single microbubble above the individual wall-bound bacterial cell with optical tweezers and triggering of a violent microscale cavitation event, which either results in mechanical removal or destruction of the bacterial cell. Results on E. coli bacteria show that only cells in the immediate vicinity of the microbubble are affected, and that a very high likelihood of cell detachment and cell death exists for cells located directly under the center of a bubble. Further details behind near-wall microbubble dynamics are revealed by numerical simulations, which demonstrate that a water jet resulting from a near-wall bubble implosion is the primary mechanism of wall-bound cell damage. The results suggest that peak hydrodynamic forces as high as 0.8 μN and 1.2 μN are required to achieve consistent E. coli bacterial cell detachment or death with high frequency mechanical perturbations on a nano- to microsecond time scale. Understanding of the cavitation phenomenon at a fundamental level of a single bubble will enable further optimization of novel water treatment and surface cleaning technologies to provide more efficient and chemical-free processes.

Surfactin uniquely influences lipid bilayer structure by initially inducing membrane invaginations before solubilization. In this study, we exposed DOPC giant vesicles to various surfactin concentrations at different temperatures and observed surfactin-induced membrane invaginations by using differential interference contrast and confocal laser fluorescence microscopy. These invaginations were stable at room temperature but not at higher temperatures. Surfactin molecules induce membrane nanodomains with negative spontaneous curvature and membrane invaginations despite their intrinsic conical shape and intrinsic positive curvature. Considering the experimentally observed capacity of surfactin to fluidize lipid acyl chains and induce partial dehydration of lipid headgroups, we propose that the resulting surfactin-lipid complexes exhibit a net negative spontaneous curvature. We further conducted 3D numerical Monte Carlo (MC) simulations to investigate the behaviour of vesicles containing negative curvature nanodomains within their membrane at varying temperatures. MC simulations demonstrated strong agreement with experimental results, revealing that invaginations are preferentially formed at low temperatures, while being less pronounced at elevated temperatures. Our findings go beyond the expectations of the Israelachvili molecular shape and packing concepts analysis. These concepts do not take into account the influence of specific interactions between neighboring molecules on the inherent shapes of molecules and their arrangement within curved membrane nanodomains. Our work contributes to a more comprehensive understanding of the complex factors governing vesicle morphology and membrane organization and provides insight into the role of detergent-lipid interactions in modulating vesicle morphology.

We have studied the effect of the nature of the alkaline agent (NH4OH, NaOH, (NH4)2CO3, and Na2CO3) on the specific surface area, size, and shape of zinc oxide particles prepared via zinc nitrate precipitation from aqueous and polymer media, followed by thermal decomposition of the precipitates. The precipitation process with the use of NH4OH and NaOH in polyacrylamides has been shown to be favorable for the formation of large hexagon particles, which were larger (up to 1500 nm in size) in the case of NH4OH. The largest specific surface area (up to 98 m2/g) and the smallest particle size ( 20 nm) were offered by the sample prepared via thermal decomposition of the products of reaction between zinc nitrate and ammonium carbonate.

The disinfection and removal of biofilm from titanium dental implants remains a great challenge in oral medicine. Here we present results of novel photoacoustic irrigation laser modalities for biofilm removal in model geometries mimicking the peri-implant pocket. The efficacy of single pulse (Er:YAG-SSP) and dual pulse (Er:YAG-AutoSWEEPS) photoacoustic irrigation modalities were determined for Enterococcus faecalis biofilm decontamination from titanium surfaces in narrow cylindrical and square gap geometries. The density of bacteria as well as the number of live bacteria were determined prior and after different photoacoustic treatments. Both SSP and AutoSWEEPS photoacoustic irrigation techniques removed at least 92% of biofilm bacteria during the 10 s photoacoustic treatment. The effectiveness of cleaning was better in the narrow square gap geometry compared to the cylindrical geometry. The dual pulse Er:YAG-AutoSWEEPS photoacoustic irrigation showed better results compared to SSP modality. No chemical adjuvants were needed to boost the effectiveness of the photoacoustic irrigation in the saline solution. The results imply that photoacoustic irrigation is an efficient cleaning method for debridement and decontamination in narrow geometries and should be considered as a new therapeutic option for the treatment of peri-implant diseases.

ABSTRACT The effects of surface mechanical constraints that may promote or prevent bacterial expansion on semi-solid surfaces are largely unknown. In this work, we have manufactured agar surfaces with different viscoelasticity, topography, and roughness. To capture the essential biophysics of the bacterial expansion we have developed a continuum model that faithfully reproduces the main patterns of the short-range and long-range expansion with two critical parameters: local interfacial forces and colony viscosity. Cohesive energy of the bacterial colony that determines the extent of exploration was dependent on agar surface viscoelasticity. On soft surfaces, bacteria produce low viscoelastic colonies that allow guided population of bacteria to traverse distances that are six orders of magnitude larger than the size of the individual bacterium. Bacteria growing on stiff surfaces produce colonies with significantly increased viscoelasticity that prevent bacterial exploration of new territory and allow formation of a very steep cliff at the edge of the colony. Upon flooding of the rough surfaces, we have induced aquaplaning and spreading of bacteria. A layer of water between the bacterium and surface results in a loss of traction allowing bacteria to spread across the otherwise inhibitory rough surface. The results shed new light on the bacterial ability to rapidly colonize new territories. IMPORTANCE How bacterial cells colonize new territory is a problem of fundamental microbiological and biophysical interest and is key to the emergence of several phenomena of biological, ecological, and medical relevance. Here, we demonstrate how bacteria stuck in a colony of finite size can resume exploration of new territory by aquaplaning and how they fine tune biofilm viscoelasticity to surface material properties that allows them differential mobility. We show how changing local interfacial forces and colony viscosity results in a plethora of bacterial morphologies on surfaces with different physical and mechanical properties.

AgI-SiO2 hybrid powders (HPs) based on SBA-15, MCM-41, and MCM-48 have been prepared by template co-condensation of silica and silver iodide under hydrothermal conditions. The effect of the [Ag]/[Si] ratio and the type of silica matrix on the textural, structural, morphological, and rheological properties of the HPs has been studied. The formation of the target phase of iodargyrite (β-AgI) is dependent both on the ratio of the main components [Ag]/[Si] and on the pore arrangement in the silica matrix, as detected by XRD. The small-angle XRD and low-temperature nitrogen adsorption data have shown the textural and structural properties of AgI-SiO2 hybrid powders to be similar to the porous structure of the initial silica matrices—SBA-15, MCM-41, or MCM-48. A uniform distribution of silver iodide in all silica matrices, SBA-15, MCM-41 and MCM-48, has been demonstrated by energy dispersive microanalysis (EDAX). For AgI-SiO2 powders with various types of pore arrangement, a high fluidity degree has been demonstrated using the data on the natural angle of repose. It has been shown that MCM-48 based β-AgI-SiO2 powders are characterized by the smallest crystallite sizes ( 6 nm), and average size of particles (50 nm) and average size of particle aggregates (13 μm), the highest specific surface area (up to 860 m2/g) and the best fluidity.

The self-binding of bacterial cells, or autoaggregation, is, together with surface colonization, one of the first steps in the formation of a mature biofilm. In this work, the autoaggregation of B. subtilis in dilute bacterial suspensions was studied. The dynamics of cell lysis, eDNA release, and bacterial autoaggregate assembly were determined and related to the spatial autocorrelation of bacterial cells in dilute planktonic bacterial suspensions. The non-random distribution of cells was associated with an eDNA network, which stabilized the initial bacterial cell-cell aggregates. Upon the addition of DNase I, the aggregates were dispersed. The release of eDNA during cell lysis allows for the entrapment of bacterial drifters at a radius several times the size of the dying bacteria. The size of bacterial aggregates increased from 2 to about 100 μm in diameter in dilute bacterial suspensions. The results suggest that B. subtilis cells form previously unnoticed continuum of autoaggregate structures during planktonic growth.

In periodontology and implantology, laser-induced cavitation has not yet been used to treat biofilm-related problems. In this study we have checked how soft tissue affects the evolution of cavitation in a wedge model representing periodontal and peri-implant pocket geometry. One side of the wedge model was composed of PDMS mimicking soft periodontal or peri-implant biological tissue, the other side was composed of glass mimicking hard tooth root or implant surface, which allowed observations of the cavitation dynamics with an ultrafast camera. Different laser pulse modalities, PDMS stiffness, and irrigants were tested for their effect on the evolution of cavitation in the narrow wedge geometry. The PDMS stiffness varied in a range that corresponds to severely inflamed, moderately inflamed, or healthy gingival tissue as determined by a panel of dentists. The results imply that deformation of the soft boundary has a major effect on the Er:YAG laser-induced cavitation. The softer the boundary, the less effective the cavitation. We show that in a stiffer gingival tissues model, photoacoustic energy can be guided and focused at the tip of the wedge model, where it enables generation of secondary cavitation and more effective microstreaming. The secondary cavitation was absent in severely inflamed gingival model tissue, but could be induced with a dual-pulse AutoSWEEPS laser modality. This should in principle increase cleaning efficiency in the narrow geometries such as those found in the periodontal and peri-implant pockets and may lead to more predictable treatment outcomes.

In this work, we combine selective laser melting (SLM) and spark plasma sintering (SPS) to fabricate new materials with high virucidal potential. Various bioactive disc-shaped ceramics, metal alloys, and composites were fabricated and tested against bacteriophage Phi6—a model system for RNA-enveloped viruses. We prepared silver-doped titanium dioxide (TiO2 + 2.5‒10% Ag), copper-doped titanium dioxide (TiO2 + 2.5‒10% Cu), Cu2NiSiCr, and Cu15Ni8Sn composite materials (metal lattices filled with ceramics). The virucidal tests of the ceramic and metal powders were performed in buffered suspensions, while the surfaces of the discs were tested by swabbing. The results show that the virus titer on the TiO2 + 10% Ag ceramic and CuNi2SiCr metal discs decreased by 4 logs after 15 min of exposure to the surfaces compared to the control ceramic and steel discs. We show that SLM 3D printed pre-alloyed CuNi2SiCr filled with bioactive TiO2 + 10% Ag nanopowders and sintered by the SPS process combines the simplicity of printing with the strength and virucidal properties of Ag and Cu materials. The proposed new virucidal materials were also used for the fabrication of prototype elevator buttons.