Concave octopus-like PtCu nanoframe mediated photo-electro Fenton catalysis for fast organic dyestuff elimination.

In this work, a photo-electro Fenton catalytic nanoplatform based on concave octopus-like PtCu nanoframes was fabricated for organic dyestuff degradation. The electrochemical oxidation reaction was performed to generate hydrogen peroxide (H2O2) on the interface of PtCu nanoframes via a promising electro-Fenton process for on-demand aqueous remediation.

Adsorption Force of Fibronectin: A Balance Regulator to Transmission of Cell Traction Force and Fluid Shear Stress.

Osteoblasts actively generate cell traction force (CTF) to sense chemical and mechanical microenvironments. Fluid shear stress (FSS) is a principle mechanical stimulus for bone modeling/remodeling. FSS and CTF share common interconnected elements for force transmission, among which the role of the protein-material interfacial force (Fad) remains unclear. Here, we found that, on the low Fad surface (5.47 ± 1.31 pN/FN), CTF overwhelmed Fad to partially desorb FN, and FSS exacerbated the desorption, resulting in disassembly of the actin cytoskeleton and focal adhesions (FAs) to reduce CTF and establishment of a new mechanical balance at the FN-material interface. Contrarily, on the high Fad surface (27.68 ± 5.24 pN/FN), pure CTF or the combination of CTF and FSS induced no FN desorption, and FSS promoted assembly of actin cytoskeletons and disassembly of FAs, regaining new mechanical balance at the cell-FN interface. These results indicate that Fad is a mechanical regulator for transmission of CTF and FSS, which has never been reported before.

Adsorption force of fibronectin controls transmission of cell traction force and subsequent stem cell fate.

The transmission of cell traction force (CTF) to underlying biomaterials is essential for adhered cells to measure and respond to their mechanical microenvironment. Given that the protein layer adsorbed on materials lies between the cells and materials, we hypothesize that the interfacial strength of protein-material interfaces (i.e., the adsorption force of proteins, Fad) should have an important role in regulating the transmission of CTF. To test this hypothesis, rat mesenchymal stem cells (rMSCs) were cultured on poly(dimethyl siloxane) (PDMS) substrates with different Fad of fibronectin (FN), and the transmission of CTF was observed by immunofluorescence staining of FN and deformation of PDMS. As revealed, FN on substrates with low Fad is more liable to be desorbed by CTF, which prevents the transmission of CTF to substrates. In contrast, high Fad facilitates the transmission of CTF from rMSCs to the FN layer and PDMS substrates so that rMSCs can perceive the mechanical properties of substrates. We further demonstrated that the divergent transmission of CTF on low and high Fad substrates regulates the lineage specifications of rMSCs. Our study confirms the important role of Fad in CTF transmission and provides a new perspective to gain insights into cell-material interactions and cell fates, which may help to guide the design of better biomaterials.

Stretching-induced nanostructures on shape memory polyurethane films and their regulation to osteoblasts morphology.

Programming such as stretching, compression and bending is indispensible to endow polyurethanes with shape memory effects. Despite extensive investigations on the contributions of programming processes to the shape memory effects of polyurethane, less attention has been paid to the nanostructures of shape memory polyurethanes surface during the programming process. Here we found that stretching could induce the reassembly of hard domains and thereby change the nanostructures on the film surfaces with dependence on the stretching ratios (0%, 50%, 100%, and 200%). In as-cast polyurethane films, hard segments sequentially assembled into nano-scale hard domains, round or fibrillar islands, and fibrillar apophyses. Upon stretching, the islands packed along the stretching axis to form reoriented fibrillar apophyses along the stretching direction. Stretching only changed the chemical patterns on polyurethane films without significantly altering surface roughness, with the primary composition of fibrillar apophyses being hydrophilic hard domains. Further analysis of osteoblasts morphology revealed that the focal adhesion formation and osteoblasts orientation were in accordance with the chemical patterns of the underlying stretched films, which corroborates the vital roles of stretching-induced nanostructures in regulating osteoblasts morphology. These novel findings suggest that programming might hold great potential for patterning polyurethane surfaces so as to direct cellular behavior. In addition, this work lays groundwork for guiding the programming of shape memory polyurethanes to produce appropriate nanostructures for predetermined medical applications.

Adsorption force of fibronectin on various surface chemistries and its vital role in osteoblast adhesion.

The amount, type, and conformation of proteins adsorbed on an implanted biomaterial are believed to influence cell adhesion. Nevertheless, only a few research works have been dedicated to the contribution of protein adsorption force. To verify our hypothesis that the adsorption force of protein on biomaterial is another crucial mediator to cell adhesion, fibronectin (FN) adsorbed on self-assembled monolayers (SAMs) with terminal -OH, -CH3, and -NH2 was quantified for FN adsorption force (F(ad)) by utilizing a sphere/plane adsorption model and parallel plate flow chamber. As revealed, F(ad) on SAMs followed a chemistry-dependence of -NH2 > -CH3 ≫ -OH. It is further demonstrated that F(ad) together with FN conformation could regulate the late osteoblast adhesion and the consequent reorganization of the adsorbed FN and fibrillogenesis of the endogenous FN. Our study suggests that protein adsorption force plays a key role in cell adhesion and should be involved for better biomaterial design.

Surface chemistry modulates osteoblasts sensitivity to low fluid shear stress.

Low fluid shear stress (FSS) is the mechanical environment encountered by osteoblasts in implanted bones or native bones of bed rest patients. High sensitivity of osteoblasts to low FSS is beneficial to osteogenesis. We hypothesize that this sensitivity might be regulated by chemical microenvironment provided by scaffolds. To confirm this hypothesis, self-assembled monolayers (SAMs) were used to provide various surface chemistries including OH, CH3 , and NH2 while parallel-plate fluid flow system produced low FSS (5 dynes/cm(2) ). Alterations in S-phase cell fraction, alkaline phosphatase activity, fibronectin (Fn), and collagen type I (COL I) secretion compared to those without FSS exposure were detected to characterize the sensitivity. Osteoblasts on OH and CH3 SAMs demonstrated obvious sensitivity while on NH2 SAMs negligible sensitivity was observed. Examination of the cell aspect ratio, orientation, and focal adhesions before and after FSS exposure indicates that the full spreading and robust focal adhesions on NH2 SAMs should be responsible for the negligible sensitivity through increasing the cell tolerance to low FSS. Despite the higher sensitivity, the Fn and COL I depositions on both OH and CH3 SAMs after FSS exposure were still less than on NH2 SAMs without FSS exposure. These results suggest that elaborate design of surface chemical compositions is essential for orchestration of surface chemistry with low FSS to realize both high sensitivity and high matrix secretion, facilitating the formation of functional bone tissues in implanted bone.

The responses of osteoblasts to fluid shear stress depend on substrate chemistries.

Natural bone tissue receives chemical and mechanical stimuli in physiological environment. The effects of material chemistry alone and mechanical stimuli alone on osteoblasts have been widely investigated. This study reports the synergistic influences of material chemistry and flow shear stress (FSS) on biological functions of osteoblasts. Self-assembled monolayers (SAMs) on glass slides with functional groups of OH, CH3, and NH2 were employed to provide various material chemistries, while FSS (12 dynes/cm(2)) was produced by a parallel-plate fluid flow system. Material chemistry alone had no obvious effects on the expressions of ATP, nitric oxide (NO), and prostaglandin E2 (PGE2), whereas FSS stimuli alone increased the production of those items. When both material chemistry and FSS were loaded, cell proliferation and the expressions of ATP, NO and PGE2 were highly dependent on the material chemistry. Examination of the focal adhesion (FA) formation and F-actin organization of osteoblasts before FSS exposure indicates that the FA formation and F-actin organization followed similar chemistry-dependence. The inhibition of FAs and/or disruption of F-actins eliminated the material dependence of FSS-induced ATP, PGE2 and NO release. A possible mechanism is proposed: material chemistry controls the F-actin organization and FA formation of osteoblasts, which further modulates FSS-induced cellular responses.

The optimal combination of substrate chemistry with physiological fluid shear stress.

Osteoblasts on implanted biomaterials sense both substrate chemistry and mechanical stimulus. The effects of substrate chemistry alone and mechanical stimulus alone on osteoblasts have been widely studied. This study investigates the optimal combination of substrate chemistry and 12dyn/cm(2) physiological flow shear stress (FSS) by examining their influences on primary rat osteoblasts (ROBs), including the releases of ATP, nitric oxide (NO), and prostaglandin E2 (PGE2). Self-assembled monolayers (SAMs) on glass slides with -OH, -CH3, and -NH2 were employed to provide various substrate chemistries, whereas a parallel-plate fluid flow system produced the physiological FSS. Substrate chemistry alone exerted no observable effects on the releases of ATP, NO, and PGE2. Nevertheless, when ROBs were exposed to both substrate chemistry and FSS, the ATP releases of NH2 were upregulated about 12-fold compared to substrate chemistry alone, while the ATP releases of CH3 and OH was similarly increased 7-fold at the peak. Similar trends were observed for the releases of NO and PGE2. The expressions of ATP, NO, and PGE2 followed the pattern of NH2-FSS>Glass-FSS>CH3-FSS≈OH-FSS. ROBs on NH2 produced the optimal combination of substrate chemistry with the physiological FSS. The F-actin organization and focal adhesion (FA) formation of ROBs on various SAMs without FSS were examined. NH2 produced the best results whereas CH3 and OH produced the worst ones. Inhibition of FAs and/or disruption of F-actin significantly decreased the releases of FSS-induced PGE2, NO, and/or ATP. Consequently, a mechanism was proposed that the best F-actin organization and FA formation of ROBs on NH2 lead to the optimal combination of substrate chemistry with the 12dyn/cm(2) physiological FSS. This mechanism gives guidance for the design of implanted biomaterials and bioreactors for bone tissue engineering.