The rheological properties of the periodontal ligament are key parameters to understand thehomeostatic stability of the tooth supporting apparatus. The objective of this study is to lay newinsights on the rheological properties and structural information of different regions in murineperiodontal ligament by using atomic force (AFM) and multi-photon microscopy (MPM). A significantvariation in elasticity of different regions was measured. The elasticity of periodontalligament showed a significant tendency to become softer towards the furcation, the nearest areato the center of resistance of the tooth. This can open a new prospective for connecting therheological adaptation of periodontal ligament to the tooth geometry that defines the center ofresistance. Another important finding revealed by the second harmonic generation (SHG) signalexhibited by collagen fibers and measured by MPM is that the orientation of fibers in the furcationregion can both provide space for tooth vertical movement with high compressive loads andprevent horizontal tooth movement. Additionally, it was found that the dispersion of the angles atdifferent levels of cutting indicates homogeneity in the directionality of fibers across differentregions. These results provide an accurate description of the rheological properties and structuralinformation of periodontal ligament, which can serve as a base for comparison with other localand systemic diseases that may influence the periodontal ligament.

Optical Second Harmonic Generation (SHG) is obtained from adsorbed gold nanoparticles with an average diameter of 16 nm at the air / aqueous solution interface in reflection. A detailed analysis of the depth profile of the SHG intensity detected shows that two contributions appear in the overall signal, one arising from the air / aqueous solution interface that is sensitive to the gold nanoparticles surface excess and one arising from the bulk aqueous phase. The latter is an incoherent signal also known as Hyper Rayleigh scattering. The results are in agreement with an analysis involving Gaussian beam propagation optics and Langmuir isotherm. It also reveals discrepancies for the largest concentrations used and proposes a new route for the design of soft metasurfaces.

The degeneration of spiral ganglion neurons (SGNs), which convey auditory signals from hair cells to the brain, can be a primary cause of sensorineural hearing loss (SNHL) or can occur secondary to hair cell loss. Emerging therapies for SNHL include the replacement of damaged SGNs using stem cell-derived otic neuronal progenitors (ONPs). However, the availability of renewable, accessible, and patient-matched sources of human stem cells is a prerequisite for successful replacement of the auditory nerve. In this study, we derived ONP and SGN-like cells by a reliable and reproducible stepwise guidance differentiation procedure of self-renewing human dental pulp stem cells (hDPSCs). This in vitro differentiation protocol relies on the modulation of BMP and TGFβ pathways using a free-floating 3D neurosphere method, followed by differentiation on a Geltrex-coated surface using two culture paradigms to modulate the major factors and pathways involved in early otic neurogenesis. Gene and protein expression analyses revealed efficient induction of a comprehensive panel of known ONP and SGN-like cell markers during the time course of hDPSCs differentiation. Atomic force microscopy revealed that hDPSC-derived SGN-like cells exhibit similar nanomechanical properties as their in vivo SGN counterparts. Furthermore, spiral ganglion neurons from newborn rats come in close contact with hDPSC-derived ONPs 5 days after co-culturing. Our data demonstrate the capability of hDPSCs to generate SGN-like neurons with specific lineage marker expression, bipolar morphology, and the nanomechanical characteristics of SGNs, suggesting that the neurons could be used for next-generation cochlear implants and/or inner ear cell-based strategies for SNHL.