The surface electric potential of biomaterials has been extensively proven to play a critical role in stem cells’ fate. However, there are ambiguous reports on the relation of stem cells’ osteogenic capacity to surface potential characteristics (potential polarity and intensity). To address this, we adopted a surface with a wide potential range and both positive/negative polarity in a comprehensive view to get insight into surface potential-regulating cellular osteogenic differentiation. Tb x Dy1–x Fe2 alloy/poly(vinylidene fluoride-trifluoroethylene) magnetoelectric films were prepared, and the film could provide controllable surface potential characteristics with positive or negative polarity and potential (ϕME) intensity variation from 0 to ±120 mV as well as keep the surface chemical composition and microstructure unchanged. Cell culture results showed that osteogenic differentiation of mesenchymal stem cells on both positive and negative potential films was obviously upregulated when the /ϕME/ intensities were set from 0–55 mV. Differently, the highest upregulated osteogenic differentiation on the positive potential films corresponded to the /ϕME/ intensity from 35–55 mV and was better than that on the negative potential films whereas the highest on the negative potential films corresponded to the /ϕME/ intensity from 0–35 mV and was better than that on the positive potential films. This fact could illustrate why previous reports appeared ambiguously; i.e., the comparative result in osteogenic differentiation between the positive and negative potential films strongly depends on the selection of surface potential intensity. On the basis of assaying of the exposed functional sites (RGD and PHSRN) of the adsorbed fibronectin (FN) and the expression of cellular integrin α5 and β1 subunits, the difference in the behavior between the positive and negative potential films was attributed to the distinct conformation of adsorbed fibronectin (FN) and the opposite changing trend with /ϕME/ for the two films, which triggers the osteogenesis-related FAK/ERK signaling pathway to a different extent. This study could provide new cognition for the in-depth understanding of the regulation mechanism underlying surface potential characteristics in cell behaviors.
Electrical stimulation has been proved to be critical to regulate cell behavior. But, cell behavior is also susceptible to multiple parameters of the adverse interferences such as surface current, electrochemical reaction products, and non‐uniform compositions, which often occur during direct electric stimulation. To effectively prevent the adverse interferences, a novel piezoelectric poly(vinylidene fluoride‐trfluoroethylene)(P(VDF‐TrFE)) layer was designed to coat onto the indium tin oxide (ITO) planar microelectrode. We found the electrical stimulation was able to regulate the osteogenic differentiation of mesenchymal stem cells (MSCs) through calcium‐mediated PKC signaling pathway. Meanwhile, the surface charge of the designed P(VDF‐TrFE) coating layer could be easily controlled by the pre‐polarization process, which was demonstrated to trigger integrin‐mediated FAK signaling pathway, finally up‐regulating the osteogenic differentiation of MSCs. Strikingly, the crosstalk in the downstream of the two signaling cascades further strengthened the ERK pathway activation for osteogenic differentiation of MSCs. This P(VDF‐TrFE) layer coated electrical stimulation microelectrodes therefore provide a distinct strategy to manipulate multiple‐elements of biomaterial surface to regulate stem cell fate commitment.
Cell responses to oxide biomaterials depend on the protein adsorption behavior of the biomaterial surface. Thus, the inherent properties of oxide biomaterial surfaces play a key role in this process. However, commonly used biomaterials, such as calcium phosphate and titanium dioxide, have surfaces with strong mineralization, which may interfere with the ability to clarify the key aspects of the oxide biomaterial regarding protein adsorption and cellular processes. Here, nonmineralized crystalline and vitreous silica were selected as model oxide biomaterials to explore the inherent properties of these materials on the absorption behavior of the functional protein fibronectin (Fn) and on the osteogenic differentiation of mesenchymal stem cells (MSCs). We demonstrated that due to the smaller O 1s binding energy, the weaker polarization of oxygen atoms in vitreous silica produced a greater amount of acidic hydroxyls after hydration compared to crystalline silica. These distinct features significantly upregulated the exposure of arginylglycylaspartic acid (RGD) and synergy sites (PHSRN) of Fn and eventually enhanced the osteogenic differentiation of MSCs on vitreous silica surfaces through activation of the integrin-linked kinase (ILK) signaling pathway. Our results highlight the key role of inherent oxide biomaterial crystallinity in protein adsorption and cell behavior.
Convolutional Neural Networks (CNN) are a popular neural network structure for image based applications. This thesis discusses an alternative network, the morphological shared-weight neural network (MSNN) for object detection. In this thesis, three combined network structures are developed for multi-scale object detection. The dataset used for the experiments presented here were created by the author for this thesis study. The convolutional neural network is used as the baseline for judging the performance of the MSNN. Experiments suggest that when training data is limited, the MSNN has a more robust and precise performance as compared with the CNN.
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