New hydrogen donors for amine-free photoinitiating systems in dental materials.

OBJECTIVES: The two-component Camphorquinone (CQ)/aromatic amine system is well-established and clearly corresponds to the reference system used in all photopolymerizable dental adhesives and composites. However, this CQ/amine system still suffers from the presence of aromatic amines that can be referenced as toxic. Therefore, the aim of this work is to develop amine-free photoinitiating systems (PISs) for the polymerization of a representative dental methacrylate resins upon blue light irradiation. The proposed strategy is based on the in-silico design (by molecular modelling) of new hydrogen donors (amine-free) bearing a copolymerizable moiety (methacrylate functionality) to ensure their low migration/leaching properties from the synthesized polymer. The new proposed PISs are compared to the well-established CQ/amine system for the polymerization of different methacrylate blends upon exposure to a commercial blue dental LED centered at 477 nm. METHODS: Molecular orbitals calculations are used to design new hydrogen donors exhibiting low C-H bond dissociation energies. Based on this in-silico design, the syntheses of new co-initiators are reported here for the first time. Real-time FTIR experiments are used to monitor the photopolymerization profiles. Color indexes measurements were also carried out to investigate the bleaching properties of the new proposed systems. RESULTS: Three new co-initiators are proposed as alternatives to aromatic amines in dental materials in combination with camphorquinone. The performances of the new proposed amine-free PISs for the photopolymerization of thick (1.4 mm) samples of methacrylate upon exposure to a blue dental LED under air are excellent. Similar or better polymerization performances are obtained with the new proposed amine-free systems compared to those reached with the CQ/amine reference. Excellent bleaching properties are also found. The involved chemical mechanisms are investigated through molecular orbitals calculations.

Social Self-Sorting of Colloidal Families in Co-Assembling Microgel Systems.

Colloids are valuable model systems to understand the structure and dynamics of matter, explore new self-assembly concepts, and realize advanced materials. Herein, we demonstrate social self-sorting of co-assembled families of colloids by orthogonal host/guest recognition using cyclodextrins. We show that mixtures of four partners self-sort into their respective families without mutual interference. Additionally, the self-assemblies and their interactions are switchable using orthogonal triggers. This study goes beyond previous features of molecular self-sorting, and opens the design space for future self-sorting colloidal systems via rationally designed molecular recognition.

3D DNA Origami Cuboids as Monodisperse Patchy Nanoparticles for Switchable Hierarchical Self-Assembly.

The rational design of anisotropic interaction patterns is a key step for programming colloid and nanoparticle self-assembly and emergent functions. Herein, we demonstrate a concept for harnessing the capabilities of 3D DNA origami for extensive supracolloidal self-assembly and showcase its use for making truly monodisperse, patchy, divalent nanocuboids that can self-assemble into supracolloidal fibrils via programmable DNA hybridization. A change in the number of connector duplexes at the patches reveals that multivalency and cooperativity play crucial roles to enhance superstructure formation. We further show thermal and chemical switching of the superstructures as the first steps toward reconfigurable self-assemblies. This concept lays the groundwork for merging monodisperse 3D DNA origami, featuring programmable patchiness and interactions, with nanoparticle self-assembly.

Hierarchical Self-Assembly of 3D-Printed Lock-and-Key Colloids through Shape Recognition.

Progress in colloid self-assembly crucially depends on finding preparation methods for anisotropic particles with recognition motifs to facilitate the formation of superstructures. Here, we demonstrate for the first time that direct 3D laser writing can be used to fabricate uniform populations of anisotropic cone-shaped particles that are suitable for self-assembly through shape recognition. The driving force for the self-assembly of the colloidal particles into linear supracolloidal polymers are depletion forces. The resulting supracolloidal fibrils undergo hierarchical ordering and form nematic liquid-crystalline domains. Such a behavior could so far not be observed in the absence of an electric field. The study opens possibilities for using direct laser writing to prepare designed colloids on demand, and to study their self-assembly.

Preparation of Highly Monodisperse Monopatch Particles with Orthogonal Click-Type Functionalization and Biorecognition.

Patchy particles are next generation colloidal building blocks for self-assembly and find further use as (bio) sensors. Progress in this direction crucially depends on developing straightforward preparation pathways able to provide patchy particles with highest uniformity and integrating precise, orthogonal, and spatially localized functionalizations to mediate interaction patterns. This continues to be one of the great challenges in colloid science. Herein, a method is shown utilizing functionalized random and block copolymers as microcontact printing inks to prepare patchy particles with outstanding control over patch size and quality. The polymeric nature and tight covalent attachment of the ink prevents flow of the ink over the particle during printing. This minimizes patch broadening and yields very small and extremely uniform patches, which is especially challenging for particle sizes below 10 µm. Click-type (amine/active ester, alkyne/azide, biotin/avidin) reactions can be performed selectively on the patch or on the particle body, rendering the particles interesting for application in imaging, biomolecular detection, and as advanced precision colloid-based building blocks.

Bioactive gyroid scaffolds formed by sacrificial templating of nanocellulose and nanochitin hydrogels as instructive platforms for biomimetic tissue engineering.

A sacrificial templating process using lithographically printed minimal surface structures allows complex de novo geo-metries of delicate hydrogel materials. The hydrogel scaffolds based on cellulose and chitin nanofibrils show differences in terms of attachment of human mesenchymal stem cells, and allow their differentiation into osteogenic outcomes. The approach here serves as a first example toward designer hydrogel scaffolds viable for biomimetic tissue engineering.