Open access peer-reviewed chapter
Abstract
In the medical field, the problem of healthcare-associated infections (HAIs) is of increasing concern, the COVID-19 pandemic demonstrates the vulnerabilities of modern society, and how little is known about medical ethics and public infection control strategies. As a result, the covering of the surfaces of medical devices and the walls of medical premises with nanocomposites with antibiofilm and microbicidal properties is being tried on an increasingly large scale. The microbial biofilms developed by the bacterial species included in the ESKAPE group are the main sources of contamination that facilitate the dissemination of pathogens in the hospital environment. Therefore, the chapter aims to present the complex physicochemical interactions between microbial biofilms and different types of inert surfaces, starting with biofilm structure, the zeta potential as a physical property of any particle in suspension (macromolecule or living cells), and antimicrobial mechanisms of different nanocomposites with medical applications.
Keywords
- microbial biofilm
- zeta potential
- physico-chemical interactions
- nanocomposite
- antimicrobials
1. Introduction
In the medical field, two major problems are of increasing concern: microbial strains multidrug resistance (MDR) and healthcare-associated infections (HAIs). In direct relation with these two problems, the COVID-19 pandemic demonstrated the vulnerabilities of modern society, and how little is known about medical ethics and public infection control strategies. The MDR phenomenon is constantly expanding, despite the efforts to implement global policies to limit the impact of human health. Health authorities around the world are paying more attention to antibiotic resistance (AR) because of the risk of genetically modified pathogenic microorganisms that are increasingly resistant to common antibiotics [1].
The most feared pathogens that have prolonged contact with antibiotics and have acquired resistance to them are the agents that cause HAIs. Pathogens belonging to the ESKAPE group (
The microbial biofilms developed by the bacterial species included in the ESKAPE group are the main sources of contamination that facilitate the dissemination of pathogens in the hospital environment. The biofilm biotype has been phylogenetically developed by bacteria as a model of a highly efficient strategy for survival in physically and chemically aggressive environments, defining the microbial lifestyle. In this context, the medical area microclimate provides the optimal survival environment for microorganisms and constant reservoir for pathogenic strains dissemination, especially ESKAPE group microorganisms [5, 6, 7, 8].
Structurally, the biofilm contains colloidal vector particles (microbial cells, mineral precipitates, and host biological residues) dispersed in a hydrogel (exopolysaccharides, mucus, collagen, or released DNA) [9]. This functional organization of the biofilm is specific to colloidal systems and explains the viscoelastic colloidal polymer behavior. The specific mechanical and hydrodynamic parameters of the viscous colloidal system are dependent on the interaction with the extracellular polymeric substances matrix (EPS) [9].
The biofilm can actively shape a response to mechanical and chemical stress, modifying hydrodynamic and mechanical parameters [10]. These parameters are dependent on the molecular structure of the monomers that form EPS, on the ions in the water that form the homeostatic system, and on the adhesins with the role of supporting the biofilm on the surfaces. As a result, the covering of the surfaces of medical devices and the walls of medical premises with antibiofilm and microbicidal nanocomposites is being tried on an increasingly large scale. Understanding how these parameters appear and change helps us to establish an effective antimicrobial strategy.
2. The bacterial biofilm
A bacterial biofilm is composed of various components that work together to form a complex and structured community of bacteria. These components include microbial cells, extracellular polymeric substances (EPS), and nonliving materials that can be found in the biofilm matrix [11]. Microbial cells are the living component of the biofilm. They attach to surfaces and grow within the biofilm structure. These cells can be differentiated from their free-floating counterparts by their reduced growth rates and the up- and down-regulation of specific genes [12]. On medical surfaces, biofilm formation provides the bacterial community embedded in the extracellular polymeric substance (EPS) with additional advantages and protection that planktonic bacterial cells lack. These advantages include increased resistance to horizontal gene transfer and antibiotics. Bacterial cells tend to attach to a conditioning layer after overcoming any electrical barriers and go through two attachment phases: reversible and irreversible. In the reversible phase, bacterial attachment to the surface occurs rapidly and is reversible, while in the irreversible phase, the attachment becomes permanent and extends over a longer period. When the bacterial community reaches a certain density, the phenomenon of quorum sensing triggers phenotypic changes that result in the loss of motility and the production of extracellular polymeric substance [13].
After attachment is reversibly achieved, irreversible adhesion gradually develops on that surface. Irreversible attachment is characterized by stronger interactions occurring between the cell surface and the adjacent surface, at less than 1.5 nm [14]. This situation allows the ligands exposed on the cell surface to engage in a strong interaction that “blocks” the connection between the cell and the substrate. As a result, a change in gene expression is initiated, which directs cellular processes toward biofilm formation. Mechano-sensing also generates an orbital motility that restricts the bacteria’s range of motion and increases the time spent near the adhesion surface [15].
EPSs are produced by microbial cells and form the bulk of the biofilm matrix. It consists of a complex mixture of polysaccharides, proteins, nucleic acids, lipids, and other organic and inorganic molecules. EPS acts as a scaffold, providing physical support and stability to the biofilm structure. It also helps trap water and nutrients, creating a favorable microenvironment for bacterial growth. Additionally, EPS can serve as a protective barrier, shielding the bacteria within the biofilm from various stresses, such as antibiotics and the host immune system [16].
In addition to microbial cells and EPS, nonliving materials may also be present in the biofilm matrix. These include mineral crystals, corrosion particles, clay or silt particles, and blood components, depending on the environment in which the biofilm forms. Nonliving materials can become incorporated into the biofilm matrix and contribute to its overall structure. It is important to note that the composition of a bacterial biofilm can vary depending on factors such as the bacterial species present, the environmental conditions, and the specific surface to which the biofilm attaches. Different bacteria may produce different types and amounts of EPS, resulting in variations in biofilm architecture and properties.
Biofilms form on various surfaces, including medical devices, implants, and tissues. They are known to be resistant to antibacterial treatments, making them difficult to eliminate. An antibacterial surface can play a significant role in preventing biofilm formation and disrupting existing biofilms. Several studies have explored the effectiveness of antibacterial surfaces in inhibiting bacterial adhesion and biofilm formation. These surfaces are designed to incorporate or coat antimicrobial agents that can inhibit the growth and attachment of bacteria [17, 18].
The density of electric charge existing on the surface of the bacterial outer membrane is a critical characteristic in the physiological process that directs interactions with the external environment [19]. Three specific factors are involved in the organization and development of biofilms as a social structure for bacterial survival: (i) The physical properties of surfaces intervene in the initial attachment phase and modify cell physiology to achieve irreversible bacterial adhesion; (ii) Chemical properties modulate cell adhesion and their development into biofilm communities; (iii) Chemical communication between cells attenuates growth and influences biofilm phenotypes, controlling community dimensions. If the interaction of bacterial cells with the substrate is governed by weak forces, the cells do not undergo phenotypic changes that would enable them to synthesize a matrix with a robust structure, and the formed biofilms are unstable with an aberrant structure (Figure 1) [20].
Figure 1.
Specific factors are involved in the biofilm organization and development.
The attachment as a physiological phenomenon is much more complex, as it can be influenced by the contribution of electrolytes from the environment as well as by the layer of molecules absorbed on the bacterium’s surface, which can screen the electrostatic field. An important role in these phenomena is played by the nature of the attachment substrate. Most surfaces prone to bacterial colonization are charged with positive or negative electric charge through electrostatic effects or through ionization of functional groups existing on their surface and will electrostatically interact when bacteria with electric charge adhere. In achieving the adhesion process, an important role is played by the nature and properties of the attachment substrate. These properties regulate bacterial physiology by influencing processes such as adsorption, adhesion, and bacterial diffusion and can confer rigidity, mechanical stability, and elasticity to the formed biofilms. By modifying the physiology and metabolism, bacteria transition from the planktonic state to the sessile state and secrete organic polymers and lipopolysaccharides into the environment, which tightly adhere to the surface characteristics to form biofilms.
Although the mechanisms by which bacteria are influenced by substrate properties are known in principle, there are many unknowns regarding how the surface charge interacts, especially in the reversible stage, with bacterial charge. It has been found in recent years that bacterial adhesion is influenced by the electrostatic nature of solid planes as well as the electrostatic charge of tissues [21, 22].
3. Mechanisms preventing the biofilm formation on the surfaces with antimicrobial properties
Antibacterial nanocomposites, which are composed of a matrix material (often a polymer or ceramic) and nanofillers (such as nanoparticles), have emerged as promising candidates for biofilm disruption. These nanocomposites can be designed to deliver antibacterial agents directly to the biofilm, enhancing their efficacy. Biofilm formation on antibacterial surfaces can be prevented through various mechanisms. These mechanisms include surface modification, inhibiting bacterial adhesion, disrupting biofilm development, and targeting specific bacterial behaviors and communication systems. It is important to note that these mechanisms are often used in combination rather than individually. The effectiveness of each mechanism may vary depending on the specific bacteria and surface being targeted. Additionally, the development of new strategies and materials for preventing biofilm formation is an active area of research, with ongoing efforts to improve our understanding of biofilms and develop more effective prevention methods [23, 24].
3.1 Surface modification
One approach is to modify the surface of materials to make them less attractive for bacterial attachment and biofilm formation. This can be achieved by creating a surface with a different physical or chemical property, such as changing the surface roughness, surface charge, or hydrophobicity. For instance, nano-sized features, rough surfaces, or patterned textures create physical barriers and hinder bacterial adhesion. Some antibacterial surfaces can modify their charge to repel bacteria or disrupt the electrostatic interactions between bacteria and the surface. Certain antibacterial surfaces can generate reactive oxygen species, such as hydrogen peroxide, which can damage bacterial cells and inhibit their growth. These modifications can interfere with the initial attachment of bacteria and prevent the formation of a biofilm [25, 26].
3.2 Inhibiting bacterial adhesion
Another strategy is to inhibit the adhesion of bacteria to the surface. This can be done by coating the surface with antimicrobial agents or using materials that release antimicrobial compounds. The controlled release of these agents can kill or inhibit the growth of bacteria and helps to create an inhospitable environment for bacterial attachment and colonization [27, 28].
3.3 Disrupting biofilm development
Once bacteria have attached to a surface, they begin to produce an extracellular matrix that helps to form the biofilm structure. Disrupting the formation of this matrix can prevent biofilm development. One approach is to use enzymes that degrade the extracellular matrix, making biofilm more vulnerable to antibiotics. Other methods include using physical forces, such as high-powered sprays or jets, to mechanically remove the biofilm from the surface [25].
3.4 Targeting bacterial behaviors and communication
Bacteria within a biofilm communicate with each other through a process called quorum sensing. Quorum sensing is a regulatory mechanism used by bacteria to coordinate their behavior based on population density. It involves the production and detection of signaling molecules called autoinducers. These molecules allow bacteria to sense the presence of other bacteria in their environment and regulate the expression of specific genes accordingly. Quorum sensing plays a crucial role in biofilm formation, as it facilitates the coordinated attachment and growth of bacteria on a surface. When bacteria reach a critical population density, the concentration of autoinducers increases, leading to the activation of genes involved in biofilm formation. Antibacterial surfaces can interfere with quorum sensing by disrupting the production or detection of autoinducers. This disruption prevents bacteria from sensing the presence of other bacteria and inhibits the activation of genes necessary for biofilm formation. By targeting quorum sensing, antibacterial surfaces can effectively prevent the formation of biofilms on their surfaces [29, 30, 31].
4. The antimicrobial mechanisms of nanocomposites
The data suggest that the scientific community has shown significant interest in investigating the antibacterial properties of nanoparticles (such as silver, zinc, copper, iron, and gold), the progress in materials science and nanotechnology leading to the development of nanocomposites with multifunctional properties. The most important properties targeted for nanocomposites are antimicrobial and antibiofilm properties by protecting the loaded drug and controlling the release of antimicrobial substances. The different nanoparticles alone or combined with other substances could enhance the microbicidal activity of nanomaterials [32]. The concentration of nanoparticles in a nanocomposite can have a significant impact on its antibacterial properties. Higher concentrations of nanoparticles generally result in stronger antibacterial effects. For example, the concentration of silver nanoparticles (AgNPs) in a nanocomposite was found to influence its antibacterial activity. It was found that the antibacterial effect of AgNPs was strongly influenced by their size, shape, and concentration. Specifically, smaller diameter nanoparticles were found to have stronger antibacterial properties. Additionally, the study demonstrated that the antibacterial activity increased with increasing concentration of AgNPs in the nanocomposite [33].
Furthermore, it was shown that the concentration and type of functional groups on graphene, graphene oxide (GO), and reduced graphene oxide (rGO) can influence nanocomposite antibacterial activity. Higher concentrations of these nanomaterials in a nanocomposite enhance their antibacterial effectiveness. Additionally, the presence of oxygenated functional groups on GO was found to contribute to its antibacterial properties [34].
It is important to note that the specific mechanism by which nanoparticle concentration influences the antibacterial properties of nanocomposites may vary depending on the type of nanoparticles and the target bacteria. Therefore, it is crucial to consider the specific nanoparticles and bacterial strains under investigation when assessing the effects of nanoparticle concentration on antibacterial activity [35].
4.1 Interaction with bacterial cell membrane
One of the main mechanisms of action for nanocomposites is their ability to interact with the bacterial cell membrane. This interaction can lead to the disruption of the cell membrane, compromising its integrity and causing leakage of cellular contents. Metal-based nanocomposites, such as silver or cupper-based nanocomposites, have been found to disrupt bacterial cell membranes, leading to cell death. The nanoparticles in the nanocomposites can bind to the bacterial cell membrane, causing damage and destabilizing the membrane structure. This disruption of the cell membrane can prevent the bacteria from functioning properly and ultimately lead to their death [36, 37, 38]. The AgNP–bacterial interaction can broadly be explained through three mechanisms: (a) the electrostatic attraction between negatively charged AgNPs and positively charged residues of the integral membrane proteins on the bacterial surface; (b) the alteration of structural integrity or physicochemical changes in the bacterial cell wall with extrusion of intracellular material and cell death; (c) the penetration of the bacterial membranes, and internalization inside the cell [39]. Bucuresteanu et al. characterized a new Ca- and Cu-based composite layers coated on TiO2 microparticles, with large applications on various devices including ceramics, plastic, glass, stone, or concrete surfaces, demonstrating an efficient antimicrobial activity in limiting the growth and development of pathogens after at least 2 h of exposure. The biological activity of the TiO2 composite decorated with 10% Ca2+ and 2% Cu2+, demonstrated by the antimicrobial tests and membrane permeability tests, was explained based on the interactions between the negative electric charge of the microbial cell wall and the positively charged composite layers supported on the TiO2 microparticles [40].
4.2 Release of reactive oxygen species (ROS)
Some nanocomposites, such as metal-based nanocomposites, have the ability to generate reactive oxygen species (ROS) when they come into contact with bacterial cells. ROS are highly reactive molecules that can cause damage to bacterial cells by oxidizing cellular components, such as proteins and DNA. The production of ROS by the nanocomposites can lead to DNA damage, protein denaturation, and disruption of cellular processes, ultimately leading to bacterial cell death. ROS can also induce oxidative stress in bacterial cells, further contributing to their destruction. Metal-based nanocomposites, such as silver-based nanocomposites, have been shown to generate ROS, which can be highly effective in killing bacteria [41]. After the uptake of free silver ions into cells, respiratory enzymes can be deactivated, generating reactive oxygen species but interrupting adenosine triphosphate production [42]. Also, chitosan nanocomposites containing zinc oxide nanoparticles have demonstrated significant antibacterial effects, attributed to the generation of ROS and the release of Zn2+ ions, which interfere with bacterial metabolism and cell wall integrity [43].
4.3 Inhibition of cell division
Nanocomposites can also inhibit bacterial cell division, preventing bacteria from proliferating and spreading. This can be achieved through various mechanisms, such as interfering with the synthesis of key proteins involved in cell division or disrupting the formation of the cell wall. Metal-based nanocomposites, such as gold or silver nanocomposites, have been found to inhibit cell division in bacteria, inhibiting DNA replication. As another example, copper nanoparticles produce destruction in the helical structure and link of DNA within and in between its strands [44].
4.4 Enhanced uptake of nanoparticles
Nanocomposites can enhance the uptake of nanoparticles by bacterial cells, increasing their effectiveness in killing bacteria. Nanoparticles with higher surface area-to-volume ratios and adjustable properties, such as shape and composition, can interact more closely with bacterial cells, leading to increased membrane deformation and damage. This enhanced uptake can increase the likelihood of nanoparticles entering bacterial cells and causing damage to essential biological functions [36].
5. Zeta potential (ZP) in context of DLVO theory
To effectively control biofilm, it is indeed important to control the bacteria that form the biofilm. In the context of bacterial biofilms, the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory has been widely used to understand the initial adhesion and subsequent biofilm formation on surfaces [45, 46]. It is known that the majority of bacterial surfaces possess a net negative charge on the outer cellular membrane. This electric charge generates a local membrane potential and is the origin of the electric double layer surrounding the bacterium. The charge has been determined based on measurements of zeta potential and potentiometric titrations [47, 48]. Normally, bacteria tightly adhere to positively charged surfaces and are electrostatically repelled by negatively charged surfaces. However, the repulsive interactions between bacteria and negatively charged surfaces can be overcome by the contribution of extracellular organelles that mediate irreversible adhesion, such as fimbriae, flagella, curli, and pili.
The colloidal systems are used as a model for studying DLVO theory. This model was developed to study “hard” particles that are non-deformable, but its application to studying bacteria has some limitations. Recent modifications to the DLVO theory, including the use of a mathematical model considering bacteria as “soft” particles, have improved the accuracy of simulated interactions between cells and interfaces.
The DLVO theory considers two forces that impact the colloidal stability of bacterial surfaces: van der Waals forces and electrical double-layer forces. Van der Waals forces are attractive forces that bind particles together, while electrical double layer (EDL) forces are repulsive forces that arise from electrostatic interactions in the ionic atmosphere surrounding the particles. The electrical charge of bacterial surfaces plays a crucial role in the electrical double-layer forces described by the DLVO theory [49].
When a bacterial surface is submerged in a liquid, it acquires an electrical charge due to various mechanisms. For example, in water, acidic or basic groups at the bacterial surface can dissociate, resulting in the formation of negative or positive charges. Additionally, ions from the surrounding solution can adsorb or bind to the bacterial surface, leading to an accumulation of charges [49, 50].
In the DLVO theory, the EDL plays a key role in determining the stability of colloidal dispersions. The electrical double layer is formed near the bacterial surface in the liquid medium. It can be divided into two regions: the Stern layer, which is strongly bound to the bacterial surface, and the diffuse layer, which contains loosely associated counterions that are comparatively mobile (Figure 2). The total electrical double layer screens the electrical charge on the bacterial surface and contributes to the repulsive forces between bacterial surfaces [47].
Figure 2.
Adapted model of a bacterial colloidal system used to describe the properties of the Gouy–Chapman–Stern double electric layer (original figure adapted after Dziubakiewicz et al. [48]).
The electrical double-layer repulsion is an entropy-driven repulsion rather than a purely electrostatic energy-driven interaction. The repulsive forces arise from the counterions in the diffuse layer, which counterbalance the surface charges on the bacterial surface. This repulsion contributes to the stability of aqueous dispersions, preventing the aggregation of bacterial surfaces [51].
The zeta potential (ZP) plays a crucial role in quantifying the DLVO theory. The DLVO theory provides a theoretical framework to understand the forces at play, while zeta potential measurement allows for the quantitative assessment of the electrostatic component of these forces; or in other words, ZP is determined by the charge distribution in the electrical double layer [52, 53].
The zeta potential contributes to quantifying the DLVO theory in the following ways [54, 55]:
Determining stability : The zeta potential directly correlates with the stability of colloidal systems. As zeta potential increases, the repulsion force between particles also increases, resulting in greater stability. Conversely, lower zeta potential values indicate reduced repulsion and potential particle aggregation.Characterizing double-layer forces : The zeta potential provides insights into the behavior of the electrical double layer, which plays a key role in the DLVO theory. It helps understand the charge distribution and ion dynamics within the double layer, which influence the net repulsion or attraction forces between particles.Evaluating particle interactions : By quantifying the zeta potential, it can be analyzed how different factors, such as pH, ionic strength, and surface properties, affect particle interactions. Measuring zeta potential under various conditions allows for a comprehensive understanding of the DLVO theory and its application in different contexts.A higher zeta potential corresponds to a stronger repulsion, which leads to increased stability and prevents particle aggregation. By measuring the zeta potential, it is possible to monitor changes in interparticle forces and predict the stability of colloidal systems under different conditions. Bacteria in aqueous solutions can be considered colloidal dispersion. The bacteria act as the dispersed phase while the water acts as the continuous phase [54, 55, 56].
6. Zeta potential, nanocomposite surfaces, and antimicrobial relations
Zeta potential measurements are commonly used to analyze colloidal suspensions, they can also provide valuable information about the surface charge, reactivity of solid surfaces, and evaluation of antibacterial properties of a nanocomposite. Zeta potential plays a significant role in characterization of the interaction between nanocomposites and biofilms. It is a measure of the electrical potential at the shear plane of a particle’s surface in a solution. Nanocomposites with a high positive or negative zeta potential may exhibit enhanced interactions with biofilms, leading to better disruption. The changes in zeta potential depend on the type of nanocomposite being considered. It is important to note that the specific changes in zeta potential for different types of nanocomposites may vary. Factors such as the material composition, size, and stability of the nanoparticles, as well as the presence of other additives or ligands, can all influence the zeta potential behavior. In the case of nanocomposites, which are composed of a matrix material and nanoparticles dispersed within it, the zeta potential can provide valuable information about the stability of the composite. The surface charge of the nanoparticles within the matrix material will contribute to the overall zeta potential of the nanocomposite. By measuring the zeta potential of the nanocomposite, it is possible to assess the stability of the nanoparticles within the composite and understand how they interact with the matrix material. Different factors, such as the surface chemistry, concentration, and pH of the nanocomposite, can affect its nanocomposite zeta potential [57].
6.1 Surface chemistry
The type of surface coating or functionalization of nanoparticles in a nanocomposite can have a significant impact on the zeta potential, and the zeta potential of a nanocomposite can be influenced by the zeta potential of each component. For example, if the nanoparticles have a high positive zeta potential and are dispersed within a polymer matrix with a negative zeta potential, the overall zeta potential of the nanocomposite may be closer to zero or slightly negative [58]. For instance, when moving from a highly negative citrate-capped nanoparticle dispersion to a neutral polymer like PEG, the magnitude of the zeta potential may decrease. Similarly, changing from a negatively charged surface to a positive one can cause a change in the sign of the zeta potential [59].
6.2 Size and morphology of the nanoparticles
Smaller particle size and higher zeta potential are generally associated with increased antibacterial activity, due to greater surface area, improved interaction with bacterial cells, and enhanced electrostatic repulsion. However, the precise influence of size and morphology may vary depending on the composition and characteristics of the nanocomposites and the target bacteria. In the case of nanocomposites, the zeta potential can be affected by the particle size, leading to changes in their behavior and potential applications. This is because a higher zeta potential indicates a stronger electrostatic repulsion between the nanocomposite particles and bacterial cells, preventing their adhesion and inhibiting bacterial growth [64].
6.3 Concentration
The concentration of composite nanoparticles can also influence the zeta potential. A study on the effect of nanoparticle concentration on zeta potential found that an increase in concentration led to a decrease in zeta potential for both positively and negatively charged particles. However, the relationship between concentration and zeta potential may vary depending on the nanocomposite system [34, 65]. This is because a higher zeta potential indicates a stronger electrostatic repulsion between the nanocomposite particles and bacterial cells, preventing their adhesion and inhibiting bacterial growth. One example of a nanocomposite where the zeta potential is affected by the particle size is where graphene oxide (GO) was combined with silver nanoparticles (Ag NPs) to form GO-Ag NP composites [34]. The antibacterial activity of the composites was found to be influenced by the size of the GO sheets. Larger GO-Ag NPs exhibited a higher antibacterial activity compared to smaller GO-Ag NPs. The difference in antibacterial activity was attributed to the different zeta potentials of the composites, with larger GO-Ag NPs having a higher zeta potential. The study also highlighted the importance of the morphologies of nanocomposites, with irregular edges potentially helping to disturb bacterial cell walls [66].
6.4 pH dependence
Zeta potential measurements should always include information about the solution pH, as zeta potential is strongly pH-dependent. Acidic or basic conditions can alter the zeta potential of a nanocomposite. The effect of pH on the zeta potential of a nanocomposite can be explained by the protonation/deprotonation of surface groups on the nanoparticles. These surface groups can interact with the ions present in the solution, leading to changes in the zeta potential. Therefore, the changes in zeta potential can affect the stability and dispersibility of nanocomposite particles. Furthermore, the pH of the surrounding environment can modulate the antibacterial activity of nanocomposite [67].
6.5 Salt dependence
When salt is added to a nanocomposite suspension, it can influence the surface charge and zeta potential by altering the ion concentration in the surrounding medium. The ions from the salt can form an electric double layer around the constituent particles, leading to screening of the surface charge. As a result, the zeta potential may decrease or even change the sign, depending on the type and concentration of the salt used [68].
6.6 Temperature
The temperature can influence the surface charge of nanocomposite layers by affecting the dissociation of surface groups or altering the hydration layer surrounding the particles. The temperature can affect the zeta potential of nanocomposite particles indirectly by influencing other physical properties, such as viscosity and conductivity, of the surrounding medium. Changes in these properties can lead to alterations in the zeta potential [69, 70].
In terms of thermal properties, the matrix material integrated in nanocomposite can influence the thermal conductivity, thermal expansion coefficient, and heat transfer behavior of the nanocomposite. It can also influence the melting and crystallization behavior of the nanocomposite [71]. Similarly, the electrical conductivity and dielectric properties of the nanocomposite can be influenced by the matrix material [72].
6.7 The effect of light
The effect of light on zeta potential depends on the concentration and turbidity of the sample. For the optical configuration used for electrophoretic mobility (and hence zeta potential) measurements, the laser beam must penetrate the sample for scattered light to be detected. If the concentration of the sample is too high, the laser beam can become attenuated by the particles, reducing the amount of scattered light that is being detected. At very high concentrations, no scattered light may be detected at all [73]. This means that when the sample is exposed to light, it needs to allow the laser beam to pass through the sample without significant attenuation or scattering. Light can potentially interact with the particles in the sample and influence the electrical charges surrounding them, thus impacting the zeta potential. Overall, it seems that light can potentially weaken the effect of zeta potential by attenuating or scattering the laser beam used for zeta potential measurement, especially at high concentrations and turbidity. The matrix material can also affect the optical properties of the nanocomposite, such as transparency, refractive index, and light scattering behavior. Different matrix materials can have different interactions with light, leading to variations in the overall optical properties of the nanocomposite.
7. Conclusions
Developing efficient and cost-effective methods for combating healthcare-associated infections is the main challenge of the twenty first century. Recent research has highlighted the importance of microbial biofilms in the emergence and spread of highly virulent pathogens. One of the best measures to prevent infection is to block the development of biofilms on medical surfaces. In addition to the development of new active disinfection methods (such as the discovery of new disinfectants, the use of automated disinfection and ozonation equipment, and the implementation of UV-C robots), there has been a particular emphasis on discovering and using antimicrobial coatings for medical surfaces exposed to viral and microbial pathogen loads. Large-scale implementation of antimicrobial coatings with anti-adherent properties on the surface of medical devices has been carried out. In most cases, they are made from nanoparticles of various patterns and origins: metal, metal-polymer nanocomposites, bimetallic nanoparticles, and polymeric nanoparticles. Future studies aim to deepen the measurements of zeta potential as a robust method to investigate changes in the electrochemical gradient on the surface of microbial cells upon contact with different pathogens.
References
- 1.
Ferrara F, Zovi A, Nava E, Trama U, Vitiello A. SARS-CoV-2 caused a surge in antibiotic consumption causing a silent pandemic inside the pandemic. A retrospective analysis of Italian data in the first half of 2022. Annales Pharmaceutiques Françaises. 2023; 81 (4):627-635. DOI: 10.1016/j.pharma.2023.02.003 - 2.
Pérez Jorge G, Dos Santos R, Goes IC, Gontijo MTP. Les misérables: A parallel between antimicrobial resistance and COVID-19 in underdeveloped and developing countries. Current Infectious Disease Reports. 2022; 24 (11):175-186. DOI: 10.1007/s11908-022-00788-z - 3.
Naylor NR, Atun R, Zhu N, Kulasabanathan K, Silva S, Chatterjee A, et al. Estimating the burden of antimicrobial resistance: A systematic literature review. Antimicrobial Resistance & Infection Control. 2018; 7 :58. DOI: 10.1186/s13756-018-0336-y - 4.
Partridge SR, Kwong SM, Firth N, Jensen SO. Mobile genetic elements associated with antimicrobial resistance. Clinical Microbiology Reviews. 2018; 31 (4):e00088-e00017. DOI: 10.1128/CMR.00088-17 - 5.
Hirsch T, Hubert H, Fischer S, Lahmer A, Lehnhardt M, Steinau HU, et al. Bacterial burden in the operating room: Impact of airflow systems. American Journal of Infection Control. 2012; 40 (7):e228-e232. DOI: 10.1016/j.ajic.2012.01.007 - 6.
Ledwoch K, Dancer SJ, Otter JA, Kerr K, Roposte D, Rushton L, et al. Beware biofilm! Dry biofilms containing bacterial pathogens on multiple healthcare surfaces; a multi-centre study. Journal of Hospital Infection. 2018; 100 (3):e47-e56. DOI: 10.1016/j.jhin.2018.06.028 - 7.
Tacutu L, Năstase I, Bode F. Operating room ventilation with laminar air flow ceiling and a local laminar air flow system near the operating table for the patient. IOP Conference Series: Materials Science and Engineering. 2019; 609 :032014. DOI: 10.1088/1757-899X/609/3/032014 - 8.
Greene C, Wu J, Rickard AH, Xi C. Evaluation of the ability of Acinetobacter baumannii to form biofilms on six different biomedical relevant surfaces. Letters in Applied Microbiology. 2016; 63 (4):233-239. DOI: 10.1111/lam.12627 - 9.
Jamal M, Ahmad W, Andleeb S, Jalil F, Imran M, Nawaz MA, et al. Bacterial biofilm and associated infections. Journal of the Chinese Medical Association. 2018; 81 (1):7-11. DOI: 10.1016/j.jcma.2017.07.012 - 10.
Peterson BW, He Y, Ren Y, Zerdoum A, Libera MR, Sharma PK, et al. Viscoelasticity of biofilms and their recalcitrance to mechanical and chemical challenges. FEMS Microbiology Reviews. 2015; 39 (2):234-245. DOI: 10.1093/femsre/fuu008 - 11.
Donlan RM. Biofilms: Microbial life on surfaces. Emerging Infectious Diseases. 2002; 8 (9):881-890. DOI: 10.3201/eid0809.020063 - 12.
Khambhati K, Patel J, Saxena V, Parvathy A, Jain N. Gene regulation of biofilm-associated functional amyloids. Pathogens. 2021; 10 (4):490. DOI: 10.3390/pathogens10040490 - 13.
Li Y, Gong Z, Lu Y, Hu G, Cai R, Chen Z. Impact of nosocomial infections surveillance on nosocomial infection rates: A systematic review. International Journal of Surgery. 2017; 42 :164-169. DOI: 10.1016/j.ijsu.2017.04.065. Epub 2017 May 3 - 14.
Hazrin-Chong NH, Das T, Manefield M. Surface physico-chemistry governing microbial cell attachment and biofilm formation on coal. International Journal of Coal Geology. 2021; 236 :103671. DOI: 10.1016/j.coal.2020.103671 - 15.
Wang T, Flint S, Palmer J. Magnesium and calcium ions: Roles in bacterial cell attachment and biofilm structure maturation. Biofouling. 2019; 35 (9):959-974. DOI: 10.1080/08927014.2019.1674811. Epub 2019 November 5 - 16.
Karygianni L, Ren Z, Koo H, Thurnheer T. Biofilm matrixome: Extracellular components in structured microbial communities. Trends in Microbiology. 2020; 28 (8):668-681. DOI: 10.1016/j.tim.2020.03.016 - 17.
Ciolacu L, Zand E, Negrau C, Jaeger H. Bacterial attachment and biofilm formation on antimicrobial sealants and stainless steel surfaces. Food. 2022; 11 :3096. DOI: 10.3390/foods11193096 - 18.
Shrestha L, Fan HM, Tao HR, Huang JD. Recent strategies to combat biofilms using antimicrobial agents and therapeutic approaches. Pathogens. 2022; 11 :292. DOI: 10.3390/pathogens11030292 - 19.
Wilhelm MJ, Sharifian Gh M, Wu T, Li Y, Chang CM, Ma J, et al. Determination of bacterial surface charge density via saturation of adsorbed ions. Biophysical Journal. 2021; 120 (12):2461-2470. DOI: 10.1016/j.bpj.2021.04.018 - 20.
Kimkes TEP, Heinemann M. How bacteria recognise and respond to surface contact. FEMS Microbiology Reviews. 2020; 44 (1):106-122. DOI: 10.1093/femsre/fuz029 - 21.
Hong Y, Brown DG. Alteration of bacterial surface electrostatic potential and pH upon adhesion to a solid surface and impacts to cellular bioenergetics. Biotechnology and Bioengineering. 2010; 105 (5):965-972. DOI: 10.1002/bit.22606 - 22.
Renner LD, Weibel DB. Physicochemical regulation of biofilm formation. MRS Bulletin. 2011; 36 (5):347-355. DOI: 10.1557/mrs.2011.65 - 23.
Lee HS, Kim Y. Development of Candida albicans biofilms is diminished by Paeonia lactiflora via obstruction of cell adhesion and cell lysis. Journal of Microbiology and Biotechnology. 2018; 28 (3):482-490. DOI: 10.4014/jmb.1712.12041 - 24.
Ma R, Hu X, Zhang X, Wang W, Sun J, Su Z, et al. Strategies to prevent, curb and eliminate biofilm formation based on the characteristics of various periods in one biofilm life cycle. Frontiers in Cellular and Infection Microbiology. 2022; 12 :1003033. DOI: 10.3389/fcimb.2022.1003033 - 25.
Li P, Yin R, Cheng J, Lin J. Bacterial biofilm formation on biomaterials and approaches to its treatment and prevention. International Journal of Molecular Sciences. 2023; 24 (14):11680. DOI: 10.3390/ijms241411680 - 26.
Yang X, Hou J, Tian Y, Zhao J, Sun Q , Zhou S. Antibacterial surfaces: Strategies and applications. SCIENCE CHINA Technological Sciences. 2022; 65 (5):1000-1010. DOI: 10.1007/s11431-021-1962-x - 27.
Saxena P, Joshi Y, Rawat K, Bisht R. Biofilms: Architecture, resistance, quorum sensing and control mechanisms. Indian Journal of Microbiology. 2019; 59 (1):3-12. DOI: 10.1007/s12088-018-0757-6 - 28.
Singh S, Datta S, Narayanan KB, Rajnish KN. Bacterial exo-polysaccharides in biofilms: Role in antimicrobial resistance and treatments. Journal of Genetic Engineering and Biotechnology. 2021; 19 (1):140. DOI: 10.1186/s43141-021-00242-y - 29.
Boo A, Amaro RL, Stan GB. Quorum sensing in synthetic biology: A review. Current Opinion in Systems Biology. 2021; 28 :100378. DOI: 10.1016/j.coisb.2021.100378 - 30.
Luo Y, Yang Q , Zhang D, Yan W. Mechanisms and control strategies of antibiotic resistance in pathological biofilms. Journal of Microbiology and Biotechnology. 2021; 31 (1):1-7. DOI: 10.4014/jmb.2010.10021 - 31.
Castillo-Juárez I, Maeda T, Mandujano-Tinoco EA, Tomás M, Pérez-Eretza B, García-Contreras SJ, et al. Role of quorum sensing in bacterial infections. World Journal of Clinical Cases. 2015; 3 (7):575-598. DOI: 10.12998/wjcc.v3.i7.575 - 32.
Thambirajoo M, Maarof M, Lokanathan Y, Katas H, Ghazalli NF, Tabata Y, et al. Potential of nanoparticles integrated with antibacterial properties in preventing biofilm and antibiotic resistance. Antibiotics (Basel). 2021; 10 (11):1338. DOI: 10.3390/antibiotics10111338 - 33.
Díez-Pascual AM. Antibacterial action of nanoparticle loaded nanocomposites based on graphene and its derivatives: A mini-review. International Journal of Molecular Sciences. 2020; 21 (10):3563. DOI: 10.3390/ijms21103563 - 34.
Lange A, Sawosz E, Wierzbicki M, Kutwin M, Daniluk K, Strojny B, et al. Nanocomposites of graphene oxide-silver nanoparticles for enhanced antibacterial activity: Mechanism of action and medical textiles coating. Materials (Basel). 2022; 15 (9):3122. DOI: 10.3390/ma15093122 - 35.
Joe A, Park S-H, Kim D-J, Lee Y-J, Jhee K-H, Sohn Y-K, et al. Antimicrobial activity of ZnO nanoplates and its Ag nanocomposites: Insight into an ROS-mediated antibacterial mechanism under UV light. Journal of Solid State Chemistry. 2018; 267 :124-133. DOI: 10.1016/j.jssc.2018.08.003 - 36.
Saravanan H, Subramani T, Rajaramon S, David H, Sajeevan A, Sujith S, et al. Exploring nanocomposites for controlling infectious microorganisms: Charting the path forward in antimicrobial strategies. Frontiers in Pharmacology. 2023; 14 :1282073. DOI: 10.3389/fphar.2023.1282073 - 37.
Warangkar SC, Deshpande MR, Totewad ND, Singh AA. Antibacterial, antifungal and antiviral nanocomposites: Recent advances and mechanisms of action. In: Elnashar MMM, Karakuş S, editors. Biocomposites - Recent Advances. London, UK: IntechOpen; 2023. DOI: 10.5772/intechopen.108994 - 38.
Mathews S, Kumar R, Solioz M. Copper reduction and contact killing of bacteria by iron surfaces. Applied and Environmental Microbiology. 2015; 81 (18). DOI: 10.1128/AEM.01725-15 - 39.
Agnihotri S, Mukherji S, Mukherji S. Size-controlled silver nanoparticles synthesized over the range 5-100 nm using the same protocol and their antibacterial efficacy. RSC Advances. 2014; 4 :3974-3983 - 40.
Bucuresteanu R, Ionita M, Chihaia V, Ficai A, Trusca RD, Ilie CI, et al. Antimicrobial properties of TiO2 microparticles coated with Ca- and Cu-based composite layers. International Journal of Molecular Sciences. 2022; 23 :6888. DOI: 10.3390/ijms23136888 - 41.
Birhanu R, Afrasa MA, Hone FG. Recent progress of advanced metal-oxide nanocomposites for effective and low-cost antimicrobial activates: A review. Journal of Nanomaterials. 2023; 2023 :8435480. DOI: 10.1155/2023/8435480 - 42.
Yin IX, Zhang J, Zhao IS, Mei ML, Li Q , Chu CH. The antibacterial mechanism of silver nanoparticles and its application in dentistry. International Journal of Nanomedicine. 2020; 15 :2555-2562. DOI: 10.2147/IJN.S246764 - 43.
Abdallah Y, Liu M, Ogunyemi SO, Ahmed T, Fouad H, Abdelazez A, et al. Bioinspired green synthesis of chitosan and zinc oxide nanoparticles with strong antibacterial activity against rice pathogen Xanthomonas oryzae pv. oryzae. Molecules. 2020; 25 (20):4795. DOI: 10.3390/molecules25204795 - 44.
Ghazzy A, Naik RR, Shakya AK. Metal–polymer nanocomposites: A promising approach to antibacterial materials. Polymers. 2023; 15 :2167. DOI: 10.3390/polym15092167 - 45.
Hermansson M. The DLVO theory in microbial adhesion. Colloids and Surfaces B: Biointerfaces. 1999; 14 (1-6):105-119. DOI: 10.1016/S0927-7765(99)00029-6 - 46.
Rajupet S, Rashidi A, Wirth CL. Derjaguin-landau-verwey-overbeek energy landscape of a Janus particle with a nonuniform cap. Physical Review E. 2021; 103 (3-1):032610. DOI: 10.1103/PhysRevE.103.032610 - 47.
Chia TW, Nguyen VT, McMeekin T, Fegan N, Dykes GA. Stochasticity of bacterial attachment and its predictability by the extended derjaguin-landau-verwey-overbeek theory. Applied and Environmental Microbiology. 2011; 77 (11):3757-3764. DOI: 10.1128/AEM.01415-10 - 48.
Dziubakiewicz E, Hrynkiewicz K, Walczyk M, Buszewski B. Study of charge distribution on the surface of biocolloids. Colloids and Surfaces B: Biointerfaces. 2013; 104 :122-127. DOI: 10.1016/j.colsurfb.2012.11.018 - 49.
Poortinga AT, Bos R, Norde W, Busscher NW. Electric double layer interactions in bacterial adhesion to surfaces. Surface Science Reports. 2002; 47 (1):1-32. DOI: 10.1016/S0167-5729(02)00032-8 - 50.
Li Y, Li X, Hao Y, Liu Y, Dong Z, Li K. Biological and physiochemical methods of biofilm adhesion resistance control of medical-context surface. International Journal of Biological Sciences. 2021; 17 (7):1769-1781. DOI: 10.7150/ijbs.59025.https://www.ijbs.com/v17p1769.htm - 51.
Hernández VA. An overview of surface forces and the DLVO theory. ChemTexts. 2023; 9 :10. DOI: 10.1007/s40828-023-00182-9 - 52.
Evans E, Ipsen J. Entropy-driven expansion of electric double layer repulsion between highly flexible membranes. Electrochimica Acta. 1991; 36 (11-12):1735-1741. DOI: 10.1016/0013-4686(91)85036-7 - 53.
Lyklema J, van Leeuwen HP, Minor M. DLVO-theory, a dynamic re-interpretation. Advances in Colloid and Interface Science. 1999; 83 (1-3):33-69. DOI: 10.1016/S0001-8686(99)00011-1 - 54.
Muneer R, Hashmet MR, Pourafshary P. Fine migration control in sandstones: Surface force analysis and application of DLVO theory. ACS Omega. 2020; 5 (49):31624-31639. DOI: 10.1021/acsomega.0c03943 - 55.
Vilinska A, Hanumantha RK. Surface thermodynamics and extended DLVO theory of Acidithiobacillus ferrooxidans cells adhesion on pyrite and chalcopyrite. The Open Colloid Science Journal. 2009; 2 :1-14. DOI: 10.2174/1876530000902010001 - 56.
Cabral JP. Water microbiology. Bacterial pathogens and water. International Journal of Environmental Research and Public Health. 2010; 7 :3657-3703. DOI: 10.3390/ijerph7103657 - 57.
Tan NP, Lee CH, Li P. Green synthesis of smart metal/polymer nanocomposite particles and their tuneable catalytic activities. Polymers. 2016; 8 :105. DOI: 10.3390/polym8040105 - 58.
Pochapski DJ, Carvalho Dos Santos C, Leite GW, Pulcinelli SH, Santilli CV. Zeta potential and colloidal stability predictions for inorganic nanoparticle dispersions: Effects of experimental conditions and electrokinetic models on the interpretation of results. Langmuir. 2021; 37 (45):13379-13389. DOI: 10.1021/acs.langmuir.1c02056. Epub 2021 October 12 - 59.
Lagarde A, Dages N, Nemoto T, Demery V, Bartoloa D, Gibaud T. Colloidal transport in bacteria suspensions: From bacteria collision to anomalous and enhanced diffusion. Soft Matter. 2020; 16 :7503-7512. DOI: 10.1039/d0sm00309c - 60.
Díez-Pascual AM. State of the art in the antibacterial and antiviral applications of carbon-based polymeric nanocomposites. International Journal of Molecular Sciences. 2021; 22 (19):10511. DOI: 10.3390/ijms221910511 - 61.
Yu CH, Betrehem UM, Ali N, Khan A, Ali F, Nawaz S, et al. Design strategies, surface functionalization, and environmental remediation potentialities of polymer-functionalized nanocomposites. Chemosphere. 2022; 306 :135656. DOI: 10.1016/j.chemosphere.2022.135656 - 62.
Dimitrakellis P, Kaprou G, Papavieros G, Mastellos DC, Constantoudis V, Tserepi A, et al. Enhanced antibacterial activity of ZnO-PMMA nanocomposites by selective plasma etching in atmospheric pressure. Micro and Nano Engineering. 2021; 13 :100098. DOI: 10.1016/j.mne.2021.100098 - 63.
Ippili S, Jung JS, Thomas AM, Vuong VH, Lee JM, Sha MS, et al. An overview of polymer composite films for antibacterial display coatings and sensor applications. Polymers (Basel). 2023; 15 (18):3791. DOI: 10.3390/polym15183791 - 64.
Smith DE, Dhinojwala A, Moore F. Effect of substrate and bacterial zeta potential on adhesion of mycobacterium smegmatis. Langmuir. 2019; 35 (21):7035-7042. DOI: 10.1021/acs.langmuir.8b03920 - 65.
Biriukov D, Fibich P, Předota M. Zeta potential determination from molecular simulations. The Journal of Physical Chemistry C. 2020; 124 (5):3159-3170. DOI: 10.1021/acs.jpcc.9b11371 - 66.
Teper P, Sotirova A, Mitova V, Oleszko-Torbus N, Utrata-Wesołek A, Koseva N, et al. Antimicrobial activity of hybrid nanomaterials based on star and linear polymers of N,N'-dimethylaminoethyl methacrylate with in situ produced silver nanoparticles. Materials (Basel). 2020; 13 (13):3037. DOI: 10.3390/ma13133037 - 67.
Chenhui H, Yan Z, Zhe Y, Zilin Z, Hongfu F, Qing Y. Experimental study on functional characteristics of pH-sensitive nanoparticles for pressure reduction and augmented injection in tight oil reservoir. Journal of Molecular Liquids. 2020; 311 :113253. ISSN 0167-7322. DOI: 10.1016/j.molliq.2020.113253 - 68.
Padalia H, Baluja S, Chanda S. Effect of pH on size and antibacterial activity of Salvadora oleoides leaf extract-mediated synthesis of zinc oxide nanoparticles. BioNanoScience. 2017; 7 :40-49. DOI: 10.1007/s12668-016-0387-6 - 69.
Gordienko MG, Palchikova VV, Kalenov SV, Belov AA, Lyasnikova NV, Poberezhniy DY, et al. Antimicrobial activity of silver salt and silver nanoparticles in different forms against microorganisms of different taxonomic groups. Journal of Hazardous Materials. 2019; 378 :120754. DOI: 10.1016/j.jhazmat.2019.120754 - 70.
Bakina O, Glazkova E, Pervikov A, Lozhkomoev A, Rodkevich N, Svarovskaya N, et al. Design and preparation of silver–copper nanoalloys for antibacterial applications. Journal of Cluster Science. 2021; 32 :779-786. DOI: 10.1007/s10876-020-01844-1 - 71.
Abdel SS, Aziz HA, Moustafa EB. Role of hybrid nanoparticles on thermal, electrical conductivity, microstructure, and hardness behavior of nanocomposite matrix. Journal of Materials Research and Technology. 2021; 13 :1275-1284. ISSN 2238-7854. DOI: 10.1016/j.jmrt.2021.05.034 - 72.
Al-Saleh MH. Influence of polymer structure on the electrical resistivity of nanocomposite materials. Synthetic Metals. 2020; 265 :116409. ISSN 0379-6779. DOI: 10.1016/j.synthmet.2020.116409 - 73.
Freitas C, Müller R. Effect of light and temperature on zeta potential and physical stability in solid lipid nanoparticle (SLN™) dispersions. International Journal of Pharmaceutics. 1998; 168 (2):221-229. DOI: 10.1016/S0378-5173(98)00092-1