Interaction of Laponite with Membrane Components—Consequences for Bacterial Aggregation and Infection Confinement

Abstract

The antimicrobial effects of Laponite nanoparticles with or without loading of the antimicrobial peptide LL-37 was investigated along with their membrane interactions. The study combines data from ellipsometry, circular dichroism, fluorescence spectroscopy, particle size/ζ potential measurements, and confocal microscopy. As a result of the net negative charge of Laponite, loading of net positively charged LL-37 increases with increasing pH. The peptide was found to bind primarily to the outer surface of the Laponite nanoparticles in a predominantly helical conformation, leading to charge reversal. Despite their net positive charge, peptide-loaded Laponite nanoparticles did not kill Gram-negative Escherichia coli bacteria or disrupt anionic model liposomes. They did however cause bacteria flocculation, originating from the interaction of Laponite and bacterial lipopolysaccharide (LPS). Free LL-37, in contrast, is potently antimicrobial through membrane disruption but does not induce bacterial aggregation in the concentration range investigated. Through LL-37 loading of Laponite nanoparticles, the combined effects of bacterial flocculation and membrane lysis are observed. However, bacteria aggregation seems to be limited to Gram-negative bacteria as Laponite did not cause flocculation of Gram-positive Bacillus subtilis bacteria nor did it bind to lipoteichoic acid from bacterial envelopes. Taken together, the present investigation reports several novel phenomena by demonstrating that nanoparticle charge does not invariably control membrane destabilization and by identifying the ability of anionic Laponite nanoparticles to effectively flocculate Gram-negative bacteria through LPS binding. As demonstrated in cell experiments, such aggregation results in diminished LPS-induced cell activation, thus outlining a promising approach for confinement of infection and inflammation caused by such pathogens.

A Shear-Thinning Biomaterial-Mediated Immune Checkpoint Blockade

“…With unique surface properties, Laponite has shown great potential in delivering various chemical and protein drugs, including dexamethasone, cisplatin, 5-fluorouracil, bone morphogenetic protein-2, kartogenin, vascular endothelial growth factor, and antibacterial peptides. − Laponite can be degraded in the physiological environment (particularly acidic conditions, as shown in Figure S3c), generating bioactive/nontoxic products. ,,, In this study, anti-PD-1 molecules could be adsorbed onto the surface of the disk-like Laponite nanoparticles through electrostatic interactions, which could be released in the acidic tumor microenvironment after the degradation of Laponite. For STBs with different Laponite contents, the release of anti-PD-1 was primarily dependent on the degradation of Laponite and diffusion from the gelatin gel network. − The higher content of Laponite in 6NC50 implies that more anti-PD-1 molecules can adsorb onto Laponite nanoplates than in 6NC25.…”

“…The intercalation of proteins between silicate nanoplates can generate tactoids, which are stabilized by electrostatic interactions. The tactoids could be dissolved by the excessive charge from the proteins. , These studies indicated that the release of anti-PD-1 from STB-ICIs could be controlled by optimizing STB formulas. The degradation of Laponite could be promoted in an acidic tumor environment, and tuning the drug loading ratio could also affect the release profile.…”

Nitrogen-Free Cationic Starch Flocculants: Flocculation Performance, Antibacterial Ability, and UF Membrane Fouling Control

“…However, a different behavior was evident for turbidity removal between the single- and trinary-contaminant solutions (Figure e, h) which indicated that the pH-dependence and restabilization of turbidity was less significant for the trinary-contaminant waters. Because the polymers (proteins and polysaccharides) originating from E. coli may have a strong binding interaction with the kaolin colloid particles, this may lead to bridging flocculation of the particles and a reduced sensitivity to flocculation by charge neutralization and to the effects of pH and flocculant dosage …”

Effects of Different Nanoparticles on Microbes

“…Because the laponite nanoparticles are negatively charged and the interaction would be repulsive, the inhibitory effect was less significant than that of gold nanoparticles ( Figure 1 ). However, despite the negative surface charge of the laponite particles ( Table 1 ), these nanoparticles still interacted with the cells, causing cell damage and ultimately death [ 47 , 75 ]. Our data not only supported the surface charge-associated effects but also showed that negatively charged nanoparticles somehow caused bacterial death ( Figure 1 and Figure 3 ).…”

“…As nanoparticles are widely distributed in soils and sediments, gold nanoparticles, ludox and laponite can serve as model metal nanoparticles, colloidal silica and clay nanoparticles, respectively. To date, although there are several studies to investigate the interaction between nanoparticles and bacteria, the toxicity mechanism of nanoparticles on microorganisms needs further investigation [ 45 , 46 , 47 , 48 ]. In this work, we investigated nanoparticle–microbial cell interaction mechanisms.…”