Attachment and proliferation of dental pulp stem cells on dentine treated with different regenerative endodontic protocols

Aim To investigate the attachment and proliferation of dental pulp stem cells (DPSC) on dentine treated with various endodontic regeneration protocols. Methodology Standardized dentine samples were irrigated with sodium hypochlorite (1.5% NaOCl) and ethylenediaminetetraacetic acid (17% EDTA) and randomized into four treatment groups and two control groups. The treatment groups were treated with a clinically used concentration of triple antibiotic paste (TAP), double antibiotic paste (DAP), calcium hydroxide (Ca(OH)2) or diluted TAP in a methylcellulose system (DTAP) for 1 week. Each sample in the treatment groups was then irrigated with EDTA. The two control groups were treated with EDTA or received no treatment. Dental pulp stem cells were seeded on each dentine specimen (10 000 cells). Lactate dehydrogenase activity assays were then performed to evaluate the attached DPSC after 1 day of incubation. Water-soluble tetrazolium assays were used to determine DPSC proliferation after three additional days of incubation. Friedman's test followed by least significant difference were used for statistical analyses (α = 0.05). Results Triple antibiotic paste and DTAP regeneration protocols, as well as EDTA-treated dentine, caused significant increases in DPSC attachment to dentine. Triple antibiotic paste, DAP and Ca(OH)2 regeneration protocols caused significant reductions in DPSC proliferation on dentine. However, the DTAP regeneration protocol did not have any significant negative effects on DPSC proliferation. Conclusions The clinically used endodontic regeneration protocols that include the use of TAP, DAP or Ca(OH)2 medicament negatively affected DPSC proliferation on dentine. However, the use of DTAP medicament during regenerative endodontic treatment may not adversely affect the proliferation of DPSC

Direct observation of ultrafast lattice distortions during exciton-polaron formation in lead-halide perovskite nanocrystals

The microscopic origin of slow carrier cooling in lead-halide perovskites remains debated, and has direct implications for applications. Slow carrier cooling has been attributed to either polaron formation or a hot-phonon bottleneck effect at high excited carrier densities (> 1018 cm-3). These effects cannot be unambiguously disentangled from optical experiments alone. However, they can be distinguished by direct observations of ultrafast lattice dynamics, as these effects are expected to create qualitatively distinct fingerprints. To this end, we employ femtosecond electron diffraction and directly measure the sub-picosecond lattice dynamics of weakly confined CsPbBr3 nanocrystals following above-gap photo-excitation. The data reveal a light-induced structural distortion appearing on a time scale varying between 380 fs to 1200 fs depending on the excitation fluence. We attribute these dynamics to the effect of exciton-polarons on the lattice, and the slower dynamics at high fluences to slower hot carrier cooling, which slows down the establishment of the exciton-polaron population. Further analysis and simulations show that the distortion is consistent with motions of the [PbBr3]- octahedral ionic cage, and closest agreement with the data is obtained for Pb-Br bond lengthening. Our work demonstrates how direct studies of lattice dynamics on the sub-picosecond timescale can discriminate between competing scenarios, thereby shedding light on the origin of slow carrier cooling in lead-halide perovskites

Nuclear dynamics of singlet exciton fission: a direct observation in pentacene single crystals

Singlet exciton fission (SEF) is a key process in the development of efficient opto-electronic devices. An aspect that is rarely probed directly, and yet has a tremendous impact on SEF properties, is the nuclear structure and dynamics involved in this process. Here we directly observe the nuclear dynamics accompanying the SEF process in single crystal pentacene using femtosecond electron diffraction. The data reveal coherent atomic motions at 1 THz, incoherent motions, and an anisotropic lattice distortion representing the polaronic character of the triplet excitons. Combining molecular dynamics simulations, time-dependent density functional theory and experimental structure factor analysis, the coherent motions are identified as collective sliding motions of the pentacene molecules along their long axis. Such motions modify the excitonic coupling between adjacent molecules. Our findings reveal that long-range motions play a decisive part in the disintegration of the electronically correlated triplet pairs, and shed light on why SEF occurs on ultrafast timescales

High-Frequency Spin Waves in YBa2Cu3O6.15

Pulsed neutron spectroscopy is used to make absolute measurements of the dynamic magnetic susceptibility of insulating YBa2Cu3O6.15. Acoustic and optical modes, derived from in- and out-of-phase oscillation of spins in adjacent CuO2 planes, dominate the spectra and are observed up to 250 meV. The optical modes appear first at 74 meV. Linear-spin-wave theory gives an excellent description of the data and yields intra- and inter-layer exchange constants of J_parallel =125 meV and J_perp = 11 meV respectively and a spin-wave intensity renormalization Z_chi = 0.4.Comment: postscript, 11 pages, 4 figures, Fig.2 fixe

Exchange-Striction Driven Ultrafast Nonthermal Lattice Dynamics in NiO

We use femtosecond electron diffraction to study ultrafast lattice dynamics in the highly correlated antiferromagnetic (AFM) semiconductor NiO. Using the scattering vector (Q) dependence of Bragg diffraction, we introduce Q-resolved effective temperatures describing the transient lattice. We identify a nonthermal lattice state with preferential displacement of O compared to Ni ions, which occurs within ∼0.3  ps and persists for 25 ps. We associate this with transient changes to the AFM exchange striction-induced lattice distortion, supported by the observation of a transient Q asymmetry of Friedel pairs. Our observation highlights the role of spin-lattice coupling in routes towards ultrafast control of spin order

Direct measurement of key exciton properties: Energy, dynamics, and spatial distribution of the wave function

Excitons, Coulomb-bound electron-hole pairs, are the fundamental excitations governing optoelectronic properties of semiconductors. While optical signatures of excitons have been studied extensively, experimental access to the excitonic wave function itself has been elusive. Using multidimensional photoemission spectroscopy, we present a momentum-, energy- and time-resolved perspective on excitons in the layered semiconductor WSe2. By tuning the excitation wavelength, we determine the energy-momentum signature of bright exciton formation and its difference from conventional single-particle excited states. The multidimensional data allows to retrieve fundamental exciton properties like the binding energy and the exciton-lattice coupling and to reconstruct the real-space excitonic wave function via Fourier transform. All quantities are in excellent agreement with microscopic calculations. Our approach provides a full characterization of the exciton wave function and is applicable to bright and dark excitons in semiconducting materials, heterostructures, and devices