Tuning Surface Microstructure and Gradient Property of Polymer by Photopolymerizable Polysiloxane-modified Nanogels

An Ultrastretchable Gradient Ionogel Induced by a Self-Floating Strategy for Strain Sensing

The fabrication of gradient ionogels for flexible strain sensors remains challenging because of the complex preparation procedures, and it is still difficult to prepare highly stretchable ionogels (strain > 10000%). In this study, a strategy is proposed to successfully fabricate gradient ionogels and apply them to flexible strain sensors by utilizing the self-floating character of the polysiloxane cross-linker. A gradient ionogel with ultrahigh stretchability (>14000%) is prepared via a one-step in situ photopolymerization process of the precursor with long-chain poly(dimethylsiloxane) bis(2-methyl acrylate) (PDMSMA). PDMSMA, which has a self-floating ability and excellent flexibility, induces a gradient composition distribution in the ionogel, thereby endowing the ionogel with superior stretchability and gradient changes in conductivity and adhesivity from the top to the bottom layer. Because of multiple molecular interactions, the bottom surface of the ionogel possesses good resilience and self-adhesion, whereas the top surface, which has a high PDMSMA content, shows a nonsticky performance. As a result, a singular gradient ionogel having both a sticky bottom surface and a nonsticky top surface is achieved. Furthermore, the flexible strain sensor that is created based on these gradient ionogels exhibits high sensitivity (its gauge factor reaching 5.08), a wide detection range (1-1500%), fast response times, and good linearity. Notably, the detection signal remains repeatable over 1000 uninterrupted strain cycles. The fabricated strain sensor was further utilized to monitor joint movements and physiological signals. This work provides a facile strategy for fabricating gradient ionogels and shows their application potential in the field of flexible electronics.

Dexamethasone and zinc loaded polymeric nanoparticles reinforce and remineralize coronal dentin. A morpho-histological and dynamic-biomechanical study

OBJECTIVE

To investigate the effect of novel polymeric nanoparticles (NPs) doped with dexamethasone (Dex) on viscoelasticity, crystallinity and ultra-nanostructure of the formed hydroxyapatite after NPs dentin infiltration.

METHODS

Undoped-NPs, Dex-doped NPs (Dex-NPs) and zinc-doped-Dex-NPs (Zn-Dex-NPs) were tested at dentin, after 24 h and 21 d. A control group without NPs was included. Coronal dentin surfaces were studied by nano-dynamic mechanical analysis measurements, atomic force microscopy, X-ray diffraction and transmission electron microscopy. Mean and standard deviation were analyzed by ANOVA and Student-Newman-Keuls multiple comparisons (p < 0.05).

RESULTS

At 21 d of storage time, both groups doped with Dex exhibited the highest complex, storage and loss moduli among groups. Zn-Dex-NPs and Dex-NPs promoted the highest and lowest tan delta values, respectively. Dex-NPs contributed to increase the fibril diameters of dentin collagen over time. Dentin surfaces treated with Zn-Dex-NPs attained the lowest nano-roughness values, provoked the highest crystallinity, and produced the longest and shortest crystallite and grain size. These new crystals organized with randomly oriented lattices. Dex-NPs induced the highest microstrain. Crystalline and amorphous matter was present in the mineral precipitates of all groups, but Zn and Dex loaded NPs helped to increase crystallinity.

SIGNIFICANCE

Dentin treated with Zn-Dex-NPs improved crystallographic and atomic order, providing structural stability, high mechanical performance and tissue maturation. Amorphous content was also present, so high hydroxyapatite solubility, bioactivity and remineralizing activity due to the high ion-rich environment took place in the infiltrated dentin.

Thiol-Lactam Initiated Radical Polymerization (TLIRP): Scope and Application for the Surface Functionalization of Nanoparticles

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Controlled polymerization techniques make the possible fabrication of polymers with desired molecular weights, narrow dispersity, and tailor-making of advanced hybrid materials. Thiol- Lactam Initiated Radical Polymerization (TLIRP) was introduced in 2002 and developed during the last two decades. The thiol/lactam combination enables one to generate radicals that can initiate the polymerization of vinyl-based monomers. The study of the mechanism and kinetics of TLIRP revealed the characteristics of living polymerization for TLIRP. Moreover, TLIRP has been used successfully for the synthesis of homopolymers, block copolymers, and statistical copolymers with polydispersity below 2.0. Especially, TLIRP provides a very straightforward method for grafting polymer brushes on the surface of nanoparticles. We review herein the systems developed for TLIRP and their applications for macromolecular engineering, emphasizing the surface functionalization of nanoparticles via the grafting-from approach.

Low-Shrinkage Resin Matrices in Restorative Dentistry-Narrative Review

Dimethacrylate-based resin composites restorations have become widely-used intraoral materials in daily dental practice. The increasing use of composites has greatly enhanced modern preventive and conservative dentistry. They have many superior features, especially esthetic properties, bondability, and elimination of mercury and galvanic currents. However, polymeric materials are highly susceptible to polymerization shrinkage and stresses that lead to microleakage, biofilm formation, secondary caries, and restoration loss. Several techniques have been investigated to minimize the side effects of these shrinkage stresses. The primary approach is through fabrications and modification of the resin matrices. Therefore, this review article focuses on the methods for testing the shrinkage, as well as formulations of resinous matrices available to reduce polymerization shrinkage and its associated stress. Furthermore, this article reviews recent cutting-edge developments on bioactive low-shrinkage-stress nanocomposites to effectively inhibit the growth and activities of cariogenic pathogens and enhance the remineralization process.

Polymeric zinc-doped nanoparticles for high performance in restorative dentistry

OBJECTIVES

The aim was to state the different applications and the effectiveness of polymeric zinc-doped nanoparticles to achieve dentin remineralization.

DATA, SOURCES AND STUDY SELECTION

Literature search was conducted using electronic databases, such as PubMed, MEDLINE, DIMDI, Embase, Scopus and Web of Science. A narrative exploratory review was undertaken.

CONCLUSIONS

Polymeric nanospheres (NPs) were efficiently loaded with zinc. NPs sequestered calcium and phosphate in the presence of silicon, and remained effectively embedded at the hybrid layer. NPs incorporation did not alter bond strength and inhibited MMP-mediated dentin collagen degradation. Zn-loaded NPs remineralized the hybrid layer inducing a generalized low-carbonate substitute apatite precipitation, chemically crystalline with some amorphous components, and an increase in mechanical properties was also promoted. Viscoelastic analysis determined that dentin infiltrated with Zn-NPs released the stress by breaking the resin-dentin interface and creating specific mineral formations in response to the energy dissipation. Bacteria were scarcely encountered at the resin-dentin interface. The combined antibacterial and remineralizing effects, when Zn-NPs were applied, reduced biofilm formation. Zn-NPs application at both cervical and radicular dentin attained the lowest microleakage and also promoted durable sealing ability. The new zinc-based salt minerals generated covered the dentin surface totally occluding cracks, porosities and dentinal tubules.

CLINICAL SIGNIFICANCE

Zinc-doped NPs are proposed for effective dentin remineralization and tubular occlusion. This offers new strategies for regeneration of eroded cervical dentin, effective treatment of dentin hypersensitivity and in endodontically treated teeth previous to the canal filling. Zn-NPs also do reduce biofilm formation due to antibacterial properties.

Polymeric nanoparticles for endodontic therapy

The effectiveness of novel polymeric nanoparticles (NPs) application in reducing dentin permeability and facilitating dentin remineralization after endodontic treatment was evaluated. The effect of undoped NPs, zinc, calcium and doxycycline-doped NPs (Zn-NPs, Ca-NPs and D-NPs, respectively) was tested in radicular dentin. A control group without NPs was included. Radicular dentin was assessed for fluid filtration. Dentin remineralization was analyzed by scanning and transmission electron microscopy, energy-dispersive analysis, AFM, Young's modulus (Ei), Nano DMA, Raman, and X-Ray Diffraction analysis. Ca-NPs and Zn-NPs treated dentin exhibited the lowest microleakage with hermetically sealed dentinal tubules and a zinc-based salt generation onto dentin. Zn-NPs favored crystallinity and promoted the highest Ei and functional remineralization at the apical dentin, generating differences between the values of complex modulus among groups. Ca-NPs produced closure of tubules and porosities at the expense of a relative mineral amorphization, without creating zones of stress concentration. The highest sealing efficacy was obtained in Zn-NPs-treated samples, along with the highest values of Young's modulus and dentin mineralization. These high values of Ei were obtained by closing voids, cracks, pores and tubules, and by strengthening the root dentin. When using undoped NPs or Ca-NPs, deposition of minerals occurred, but radicular dentin was not mechanically reinforced. Therefore, application of Zn-NPs in endodontically treated teeth previous to the canal filling is encouraged.

Controlled nanogel and macrogel structures from self-assembly of a stimuli-responsive amphiphilic block copolymer

RAFT polymerization was utilized to prepare an amphiphilic block copolymer containing both hydrophilic and hydrophobic segments. The self-assembly behavior of the block copolymer into nano-scale particulate structures was studied in both water and polar organic solvents. Uniform micelle assemblies were stabilized by reaction within the hydrophobic core, which contained pendant azide groups, through copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry with a dialkyne crosslinker. The reaction preceded efficiently with negligible residual azide functionality and resulted in core-shell nanogel structures that were analyzed by a variety of techniques including light scattering, electron microscopy and the ability to take up hydrophobic molecules. Both thermo- and pH-responsive character of the nanogels and the linear polymers from which they were made were studied through cloud point testing at different pH levels. It was found that these nanogel dispersions in water exhibited the highest cloud point temperatures indicating a highly stable nanogel structure. The solvent-dispersed nanogels were used as building blocks to form extended polymer networks through the inter- as well as intra-particle reaction between hydroxyl groups within the hydrophilic domain of the nanogel shell by crosslinking with a diisocyanate. It was found that as little as 10 wt% nanogel dispersions in solvent reached the percolation threshold to yield highly porous macroscopic networks; while 50 wt% concentrations achieved densely packed and interdigitated nanogels to afford relatively homogeneous structures.

Submicron-to-nanoscale structure characterization and organization of crystals in dentin bioapatites

The aim of this study was to ascertain the crystal morphology and to assess the ultrastructure and texture changes of sound (SD) and caries-affected dentin (CAD) after being restored with Zn-free and Zn-containing amalgam.

Water dispersible siloxane nanogels: a novel technique to control surface characteristics and drug release kinetics

Amphiphilic, water-dispersible, crosslinked siloxane nanogels were synthesized and applied as optically clear, functional coatings on the surface of lens substrates to demonstrate the feasibility of siloxane-nanogels to generate covalently tethered coatings and modify the surface properties of intraocular lens substrates.

A study of nanogels with different polysiloxane chain lengths for photopolymerization stress reduction and modification of polymer network properties

Polysiloxane-based nanogels with different chain lengths can not only reduce polymerization stress, but also improve the flexibility, thermostability and hydrophobic properties of photopolymerization materials.