Thermal bulk curing of epoxy resins is a non-energy efficient method. On the other hand classical photocuring techniques for epoxy resins are limited to quite thin layers, due to the limited penetration depth of UV-light. We show that Radical Induced Cationic Frontal Polymerization (RICFP) is a promising technique for the energy efficient bulk curing of epoxy resins. The combination of a C-C labile compound (1,1,2,2tetraphenylethanediol) as a thermal radical initiator with diaryliodonium salts results upon local thermalor photoinitiation in a self-sustaining front moving along the formulation and curing cationically curable resins completely. This allows the curing of monomer formulations in places that are not easily accessible or on objects that cannot be thermally cured because of their thermal instability or size. In this paper we report about first basic investigations on RICFP of several epoxy resins with C-C-labile compounds and compare them to common thermal radical initiators. Fig. 1 Structure of the bisphenol A diglycidylether resin (BADGE). † Electronic supplementary information (ESI) available. See

Radical induced cationic frontal polymerization (RICFP) is an extremely powerful and elegant alternative curing technique that allows cationic bulk curing of epoxy resins with very little energy consumption, as well as curing in compartments that are not readily accessible. We recently introduced a bisphenol‐A diglycidylether (BADGE) based system that allows the bubble‐free photocuring of this widely used epoxy resin. In this article, we describe the high storage stability and possibilities to influence the curing speed via the initiator concentrations of different formulations. These properties allow the adjustment of the frontal polymerization to ones need. We also show that the (thermo)mechanical and electrical properties of frontal cured epoxy polymers compares favorably with those of state of the art material. Finally, different strategies to overcome the challenges on producing epoxy resin based mica composites via RICFP are presented. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3751–3759

Novel cationic photoinitiators based on the non-nucleophilic [Al(OC(CF3)3)4]− anion were prepared and their high efficiency was presented in comparison to benchmark systems.

Radical induced cationic frontal polymerization (FP) is a technique that allows the curing of huge epoxy parts (e.g., rotors of generators and construction composites), as well as parts with < 1 mm, within minutes instead of hours to days using only a fraction of the energy. Even harsh environmental conditions, like being submerged in water, cannot stop the FP

Bone regeneration requires porous and mechanically stable scaffolds to support tissue integration and angiogenesis, which is essential for bone tissue regeneration. With the advent of additive manufacturing processes, production of complex porous architectures has become feasible. However, a balance has to be sorted between the porous architecture and mechanical stability, which facilitates bone regeneration for load bearing applications. The current study evaluates the use of high resolution digital light processing (DLP) -based additive manufacturing to produce complex but mechanical stable scaffolds based on β-tricalcium phosphate (β-TCP) for bone regeneration. Four different geometries: a rectilinear Grid, a hexagonal Kagome, a Schwarz primitive, and a hollow Schwarz architecture are designed with 400 μm pores and 75 or 50 vol% porosity. However, after initial screening for design stability and mechanical properties, only the rectilinear Grid structure, and the hexagonal Kagome structure are found to be reproducible and showed higher mechanical properties. Micro computed tomography (μ-CT) analysis shows <2 vol% error in porosity and <6% relative deviation of average pore sizes for the Grid structures. At 50 vol% porosity, this architecture also has the highest compressive strength of 44.7 MPa (Weibull modulus is 5.28), while bulk specimens reach 235 ± 37 MPa. To evaluate suitability of 3D scaffolds produced by DLP methods for bone regeneration, scaffolds were cultured with murine preosteoblastic MC3T3-E1 cells. Short term study showed cell growth over 14 d, with more than two-fold increase of alkaline phosphatase (ALP) activity compared to cells on 2D tissue culture plastic. Collagen deposition was increased by a factor of 1.5–2 when compared to the 2D controls. This confirms retention of biocompatible and osteo-inductive properties of β-TCP following the DLP process. This study has implications for designing of the high resolution porous scaffolds for bone regenerative applications and contributes to understanding of DLP based additive manufacturing process for medical applications.

Novel modifications of the synthetic polymer poly(vinyl alcohol) (PVA) were developed for application in the field of biomedical engineering. PVA was modified with allyl succinic anhydride, norbornene anhydride as well as with c-thiobutyrolactone to produce macromers with reactive ene and thiol groups, respectively. Cytotoxicity studies have shown that the material exhibits almost no cell-toxicity, when used in concentrations of 1 and 0.1 wt % for 24 h. The obtained macromers were photocrosslinked via thiol-ene chemistry. Storage stability of the macromer mixtures with different concentrations of pyrogallol as stabilizer were investigated. Photorheometry was employed to optimize mixtures concerning reactivity based on their thiol-to-ene ratio, photoinitiator concentration, and macromer content. The crosslinked hydrogels were studied concerning their swellability. To form hydrogels with cellular structure twophoton-polymerization (2PP) was employed. Processing windows for 2PP of selected mixtures were determined.

OBJECTIVES: The load-bearing capacity of ultra-thin occlusal veneers made of 3D-printed zirconia were compared to the ones obtained by fabricating these reconstructions by CAD/CAM milling zirconia or heat-pressing lithium-disilicate. METHODS: On 60 extracted human molars, the occlusal enamel was removed and extended into dentin. Occlusal veneers of 0.5 mm thickness were digitally designed. The specimens were divided into 3 groups (n = 20 each) differing in the restorative material and the fabrication technique of the occlusal veneer. (1) 3DP: 3D-printed zirconia (Lithoz); (2): CAM: milled zirconia (Ceramill Zolid FX); (3) HPR: heat-pressed lithium disilicate (IPS e.max Press). After conditioning procedures, the restorations were adhesively bonded onto the conditioned tooth. Thereafter, all specimens were aged in a chewing simulator by exposure to cyclic fatigue and temperature variations. Subsequently the specimens were statically loaded and the load which was necessary to decrease the maximum load by 20% and initiate a crack (F initial ) and the load which was needed to fracture the specimen (F max ) were measured. Differences between the groups were compared applying the Kruskal-Wallis (KW) test and the Wilcoxon-Mann-Whitney-Test (WMW: p < 0.05). RESULTS: The median F initial values for the groups 3DP, CAM and HPR were 1'650 N, 1'250 N and 500 N. The differences between all three groups were statistically significant (KW: p < 0.0001). The median F max values amounted to 2'026 N for the group 3DP, 1'500 N for the group CAM and 1'555 N for the group HPR. Significant differences were found between 3DP and CAM (WMW: p = 0.0238). SIGNIFICANCE: Regarding their load-bearing capacity, 3D-printed or milled zirconia, as well as heat-pressed lithium disilicate, can be recommended as restorative material for ultra-thin occlusal veneers to prosthetically compensate for occlusal tooth wear. Despite statistically significant differences between the restoration materials, all load-bearing capacities exceeded the clinically expected normal bite forces.

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