Human dental pulp stem cells (hDPSCs) show significant potential for exploitation in novel regeneration strategies, although lack of understanding of their responses to bacterial challenge constrains their application. The present study aimed to investigate whether lipopolysaccharide (LPS), the major pathogenic factor of Gram-negative bacteria, regulates the differentiation of hDPSCs and which intracellular signaling pathways may be involved. LPS treatment significantly promoted the differentiation of hDPSCs demonstrable by increased mineralized nodule formation and mRNA expression of several odontoblastic markers in a dose-dependent manner. While inhibition of TLR4, p38, and ERK signaling markedly antagonized LPS-mediated differentiation of hDPSCs. The inhibition of JNK and NF-κB signaling had no detectable effect on LPS activation of hDPSCs. LPS stimulation resulted in phosphorylation of NF-κB p65, IκB-α, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) in DPSCs in a time-dependent manner, which was markedly suppressed by their specific inhibitors, respectively. Data demonstrated that LPS promoted odontoblastic differentiation of hDPSCs via TLR4, ERK, and P38 MAPK signaling pathways, but not NF-κB signaling.

TiO 2 loaded with crystalline nano silver (c-Ag/TiO 2 ) was successfully synthesized by a one-step low-temperature hydrothermal method in aqueous solution using tetra-n-butyl titanate and AgNO 3 as precursors. The structure and morphology were characterized by Auger electron spectroscopy (AES), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-Vis absorption spectra (UV-Vis) and fluorescence spectra (FS). The photocatalytic activity was tested with photocatalytic degradation of hydrogen sulfide (H 2 S) gas. The results show that the nano silver particles of Ag/TiO 2 prepared by the one-step lowtemperature hydrothermal method are crystalline, while they are amorphous when prepared by the conventional UV reduction deposition method (a-Ag/TiO 2 ). The photocatalytic activity of the c-Ag/TiO 2 prepared by the hydrothermal method was found to have a significant improvement for H 2 S degradation, being more than 2 times over that of the a-Ag/TiO 2 prepared by the conventional method.

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LPS may influence pulp healing through enhancing the adhesion and migration of human dental pulp stem cells when it enters into pulp during pulp exposure or deep caries.