Topography of Polymer Chains Grafted on a Polymer Surface Underwater

Self-assembled nanoparticles containing photosensitizer and polycationic brush for synergistic photothermal and photodynamic therapy against periodontitis

Background

Periodontitis is a chronic inflammatory disease in oral cavity owing to bacterial infection. Photothermal therapy (PTT) and photodynamic therapy (PDT) have many advantages for antibacterial treatment. As an excellent photosensitizer, indocyanine green (ICG) shows prominent photothermal and photodynamic performances. However, it is difficult to pass through the negatively charged bacterial cell membrane, thus limiting its antibacterial application for periodontitis treatment.

Results

In this work, self-assembled nanoparticles containing ICG and polycationic brush were prepared for synergistic PTT and PDT against periodontitis. First, a star-shaped polycationic brush poly(2-(dimethylamino)ethyl methacrylate) (sPDMA) was synthesized via atom transfer radical polymerization (ATRP) of DMA monomer from bromo-substituted β-cyclodextrin initiator (CD-Br). Next, ICG was assembled with sPDMA to prepare ICG-loaded sPDMA (sPDMA@ICG) nanoparticles (NPs) and the physicochemical properties of these NPs were characterized systematically. In vitro antibacterial effects of sPDMA@ICG NPs were investigated in porphyromonas gingivalis (Pg), one of the recognized periodontitis pathogens. A ligature-induced periodontitis model was established in Sprague–Dawley rats for in vivo evaluation of anti-periodontitis effects of sPDMA@ICG NPs. Benefiting from the unique brush-shaped architecture of sPDMA polycation, sPDMA@ICG NPs significantly promoted the adsorption and penetration of ICG into the bacterial cells and showed excellent PTT and PDT performances. Both in vitro and in vivo, sPDMA@ICG NPs exerted antibacterial and anti-periodontitis actions via synergistic PTT and PDT.

Conclusions

A self-assembled nanosystem containing ICG and polycationic brush has shown promising clinical application for synergistic PTT and PDT against periodontitis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01114-w.

Silica particles with immobilized protein molecules and polymer brushes

In this research thermo-responsive polymer brushes and protein molecules are immobilized on the surfaces of silica particles by covalent bonds. Pyridyl disulfide functionalized silica particles are prepared by surface chemical reactions, and thiol-terminated poly(oligo(ethylene glycol) monomethyl ether methacrylate) (POEGMA) and bovine serum albumin (BSA) molecules are grafted to the silica particles by thiol-disulfide exchange reactions. X-ray photoelectron spectroscopy, thermogravimetric analysis, dynamic light scattering, confocal laser scanning microscopy, far-UV circular dichroism and transmission electron microscopy are employed to characterize the polymer/protein mixed layers on silica particles. The POEGMA brushes not only protect the protein molecules but also improve the dispersibility of the hybrid particles in aqueous solution. The activity of the immobilized BSA protein can be controlled by the thermo-responsive POEGMA brushes. At a temperature below the lower critical solution temperature (LCST) of POEGMA, BSA activity is not affected by polymer brushes; however, BSA activity decreases significantly at a temperature above the LCST of POEGMA.

STATEMENT OF SIGNIFICANCE

In this research, both protein molecules and polymer brushes were anchored to the silica particles by highly efficient thiol-disulfide exchange reaction, and their grafting density can easily be determined by UV-vis. Owing to the temperature-sensitive nature of the grafted polymer brushes, the protein molecules can be protected by the collapsed polymer brushes above the LCST, and their catalytic activity can be controlled. Moreover, the protein molecules on silica particles can be easily separated from the solution and can be reused.

Biodegradation of ballast tank coating investigated by impedance spectroscopy and microscopy

This research paper addresses the biodegradation process for ballast tank coatings in marine environments. As part of this new approach, a commercially available ballast tank coating was exposed to bacteria obtained from a culture collection and to a natural bacterial community isolated from a real ballast tank. The natural community was chosen to explore the interaction of natural biofilms with the coating, an aspect, which is not covered in standard procedures. It is shown that biological activity significantly affects the coating properties. Micro-cracks and holes have been identified using AFM. Acidic bacteria generated holes with 0.2-0.9 μm in depth and 4-9 μm in width. Whereas the natural community additionally caused cracks of 2-8 μm in depth and 1 μm in length. The overall effect of this degradation was examined using the EIS technique. However, the bacterial affected coatings (exposed to acid producing bacteria and a natural community) show a decrease in corrosion resistance. Impedance IZI values decreased over time from 1.18 × 10(9) to 1.87 × 10(7) Ω for acidic bacteria and from 1.71 × 10(9) to 2.24 × 10(7) Ω for the natural community, indicating a clear loss in coating resistance over time. It is also revealed that the coating corrosion resistance declines after 40 days of exposure for the natural community, leading to the formation of blisters. Bacterial settling could be linked to some specific biofilm patterns affecting different types of coating attack. It can be concluded that it is necessary to include natural communities in coating degradation studies to identify possible degradation mechanisms and the severity of the attack over time.

Preparation and characterization of pure and mixed monolayers of poly(ethylene glycol) brushes chemically adsorbed to silica surfaces

We prepared pure and mixed monolayers of methoxy-terminated poly(ethylene glycol)s (m-PEG's) chemically attached to silica surfaces by using m-PEG silane coupling agents of three different molecular weights. These films were subsequently characterized in water by atomic force microscopy (AFM). Images of pure m-PEG monolayers showed the formation of polymer brushes on silica. Force curves between two modified surfaces suggested that an increase in the number of oxyethylene (OE) groups from 6 (PEG6 surface) to 43 (PEG43 surface) to 113 (PEG113 surface) decreased the flexibility of the m-PEG chains in the m-PEG brushes. Frictional force measurements also showed that the friction increased in the order PEG6 < PEG43 <PEG113. Because PEG113 had a molecular weight that was greater than the critical molecular weight for entanglement in a PEG melt and displayed the least stretching of its chain, a chain in the PEG113 brush was thought to participate in entanglements or interchain hydrogen bonding. Mixed monolayers of PEG6 and PEG113 were prepared using various fractions of PEG6 and PEG113. Images of mixed PEG6 and PEG113 monolayers showed that the size of the PEG113 islands in the film decreased as the fraction of PEG113 decreased. The force curves between two modified surfaces suggested that the flexibility of the mixed monolayers decreased as the fraction of PEG113 increased. Frictional force measurements also showed that the friction decreased as the fraction of PEG6 in the PEG6-PEG113 mixed film increased. Entanglements were therefore thought to decrease as the fraction of PEG113 in the mixed monolayer decreased.

Double-responsive polymer brushes on the surface of colloid particles

Well-defined poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes were synthesized on the surface of polystyrene latex particles by atom transfer radical polymerization (ATRP). It was found that the surface-initiated polymerization of DMAEMA catalyzed by CuCl/CuCl(2)/bpy was under good control in the solvent of acetone/water at ambient temperature (35 degrees C). High-density PDMAEMA brushes with low polydispersity (PDI 1.21) were obtained. TEM results demonstrate that the PDMAEMA-grafted particles have core-shell structure. Dynamic light scattering studies indicate that the particles with PDMAEMA brushes are both pH and temperature responsive.

Chemical modification of the internal surfaces of cylindrical pores of submicrometer size in poly(ethylene terephthalate)

Chemical modification of the internal surfaces of cylindrical pores with submicrometer pore diameter in a poly(ethylene terephthalate) (PET) film was examined. The modification involved the alkylation of the carboxylic acid on the surfaces with the alkylation reagent containing a fluorescent probe, and it was monitored by observing the change in fluorescent emission intensity. When the N,N-dimethylformamide solution of 4-(bromomethyl)-6,7-dimethoxycoumarin (BrCU), which bore a coumarin fluorophore, was introduced into the pores, the emission and excitation intensities of the membranes increased proportionally with increases of the pore surface areas. Fluorescent spots about 300 nm in diameter, which were located at the positions of the pores, can be observed in the fluorescence microscope image of the membranes, indicating that highly concentrated fluorescent probes are chemically incorporated on the internal surfaces of the cylindrical pores with 210 nm diameter in the membranes. In the reactions of the PET surfaces with BrCU, the fluorescent intensities increased with increases of the contact angles. This result indicates that the hydrophilicity of the internal pore surfaces can be qualitatively modified by controlling the change in the fluorescent intensities.

MMA/DVB emulsion surface graft polymerization initiated by UV light

Methyl methacrylate/1,2-divinylbenzene (MMA/DVB) in an opaque emulsion were successfully grafted onto the surface of polymeric substrate under the irradiation of UV light with benzophenone (BP) as a photoinitiator that was previously coated on the substrate surface. Monomer conversion, grafting efficiency, and grafting yields were determined by the gravimetric method. ATR-IR, AFM, and TEM were used to characterize the surface composition, to observe the topography of the grafted substrates, and to view inter-film colloid particles formed by cross-linking. The results reveal that, with the opaque MMA/DVB emulsion system and CPP film as substrate, the monomer conversion is in the range of 15-55%, the grafting efficiency is about 80%, the grafting yield reaches 5%, and the thickness of the graft layer can be controlled in the range 0.09-1.5 microm. Images of AFM show that the graft layer is piled up by nanoparticles (about 30-50 nm in diameter), which are linked together and tied to the substrate surface with covalent bonds. A possible model of surface graft polymerization including surface initiating, nucleation, and shish kebab growing is put forward to interpreting the above results.