The ambient electrocatalytic N2 reduction reaction (NRR) enabled by TiO2 has attracted extensive recent attention. Previous studies suggest the formation of Ti3+ in TiO2 can significantly improve the NRR activity, but it still remains unclear what kinds of Ti3+ are effective. Herein, it is demonstrated that mixed‐valent Cu acts as an effective dopant to modulate the oxygen vacancy (VO) concentration and Ti3+ formation, which markedly improves the electrocatalytic NRR performance. In 0.5 m LiClO4, this electrocatalyst attains a high Faradic efficiency of 21.99% and a large NH3 yield of 21.31 µg h−1 mgcat.−1 at –0.55 V vs reversible hydrogen electrode, which even surpasses most reported Ti‐based NRR electrocatalysts. Using density function theory calculations, it is evidenced that mixed‐valent Cu ions modulate the TiO2 (101) surface with multiple oxygen vacancies, which is beneficial for generating different Ti3+ 3d1 defect states localized below the Fermi energy. N2 activation and adsorption are effectively strengthened when Ti3+ 3d1 defect states present the splitting of eg and t2g orbitals, which can be modulated by its coordination structure. The synergistic roles of the three ion pairs formed by the VO defect, including Cu1+–Ti4+, Ti3+–Ti4+ and Ti3+–Ti3+, are together responsible for the enhanced NRR performance.

Titanium‐based catalysts are needed to achieve electrocatalytic N2 reduction to NH3 with a large NH3 yield and a high Faradaic efficiency (FE). One of the cheapest and most abundant metals on earth, iron, is an effective dopant for greatly improving the nitrogen reduction reaction (NRR) performance of TiO2 nanoparticles in ambient N2‐to‐NH3 conversion. In 0.5 m LiClO4, Fe‐doped TiO2 catalyst attains a high FE of 25.6 % and a large NH3 yield of 25.47 μg h−1 mgcat−1 at −0.40 V versus a reversible hydrogen electrode. This performance compares favorably to those of all previously reported titanium‐ and iron‐based NRR electrocatalysts in aqueous media. The catalytic mechanism is further probed with theoretical calculations.

A low dose of 1μg rhBMP-2 was immobilised by four different functionalising techniques on recently developed poly(l-lactide)-co-(ε-caprolactone) [(poly(LLA-co-CL)] scaffolds. It was either (i) physisorbed on unmodified scaffolds [PHY], (ii) physisorbed onto scaffolds modified with nanodiamond particles [nDP-PHY], (iii) covalently linked onto nDPs that were used to modify the scaffolds [nDP-COV] or (iv) encapsulated in microspheres distributed on the scaffolds [MICS]. Release kinetics of BMP-2 from the different scaffolds was quantified using targeted mass spectrometry for up to 70days. PHY scaffolds had an initial burst of release while MICS showed a gradual and sustained increase in release. In contrast, NDP-PHY and nDP-COV scaffolds showed no significant release, although nDP-PHY scaffolds maintained bioactivity of BMP-2. Human mesenchymal stem cells cultured in vitro showed upregulated BMP-2 and osteocalcin gene expression at both week 1 and week 3 in the MICS and nDP-PHY scaffold groups. These groups also demonstrated the highest BMP-2 extracellular protein levels as assessed by ELISA, and mineralization confirmed by Alizarin red. Cells grown on the PHY scaffolds in vitro expressed collagen type 1 alpha 2 early but the scaffold could not sustain rhBMP-2 release to express mineralization. After 4weeks post-implantation using a rat mandible critical-sized defect model, micro-CT and Masson trichrome results showed accelerated bone regeneration in the PHY, nDP-PHY and MICS groups. The results demonstrate that PHY scaffolds may not be desirable for clinical use, since similar osteogenic potential was not seen under both in vitro and in vivo conditions, in contrast to nDP-PHY and MICS groups, where continuous low doses of BMP-2 induced satisfactory bone regeneration in both conditions. The nDP-PHY scaffolds used here in critical-sized bone defects for the first time appear to have promise compared to growth factors adsorbed onto a polymer alone and the short distance effect prevents adverse systemic side effects.

BackgroundImproved understanding of the interactions between bone cells and endothelial cells involved in osteogenesis should aid the development of new strategies for bone tissue engineering. The aim of the present study was to determine whether direct communication between bone marrow stromal cells (MSC) and human umbilical vein endothelial cells (EC) could influence the osteogenic potential of MSC in osteogenic factor-free medium.MethodsAfter adding EC to MSC in a direct-contact system, cell viability and morphology were investigated with the WST assay and immnostaining. The effects on osteogenic differentiation of adding EC to MSC was systematically tested by the using Superarray assay and results were confirmed with real-time PCR.ResultsFive days after the addition of EC to MSC in a ratio of 1:5 (EC/MSC) significant increases in cell proliferation and cellular bridges between the two cell types were detected, as well as increased mRNA expression of alkaline phosphatase (ALP). This effect was greater than that seen with addition of osteogenic factors such as dexamethasone, ascorbic acid and β-glycerophosphate to the culture medium. The expression of transcription factor Runx2 was enhanced in MSC incubated with osteogenic stimulatory medium, but was not influenced by induction with EC. The expression of Collagen type I was not influenced by EC but the cells grown in the osteogenic factor-free medium exhibited higher expression than those cultured with osteogenic stimulatory medium.ConclusionThese results show that co-culturing of EC and MSC for 5 days influences osteogenic differentiation of MSC, an effect that might be independent of Runx2, and enhances the production of ALP by MSC.

Producing ammonia (NH3) by electrocatalytic N2 fixation is a promising and environmentally friendly strategy, in comparison to the Haber–Bosch process with high consumption of energy and CO2 emissions. Because of the extremely high bond energy, it is indispensable to explore valid catalysts to activate the triple bond. In this paper, Cr-doped CeO2 nanorods are developed to serve as non-noble-metal electrocatalysts for an electrocatalytic N2 reduction reaction. Introducing Cr into the catalyst leads to an increase of the oxygen vacancies. In a 0.1 M Na2SO4 solution, the Cr0.1CeO2 nanorods achieve a high Faradaic efficiency (3.84%) and a large NH3 yield (16.82 μg h–1 mgcat. –1) at −0.7 V versus reversible hydrogen electrode. The Cr0.1CeO2 nanorods also exhibit high stability during the reaction.

IntroductionA major determinant of the potential size of cell/scaffold constructs in tissue engineering is vascularization. The aims of this study were twofold: first to determine the in vitro angiogenic and osteogenic gene-expression profiles of endothelial cells (ECs) and mesenchymal stem cells (MSCs) cocultured in a dynamic 3D environment; and second, to assess differentiation and the potential for osteogenesis after in vivo implantation.MethodsMSCs and ECs were grown in dynamic culture in poly(L-lactide-co-1,5-dioxepan-2-one) (poly(LLA-co-DXO)) copolymer scaffolds for 1 week, to generate three-dimensional endothelial microvascular networks. The constructs were then implanted in vivo, in a murine model for ectopic bone formation. Expression of selected genes for angiogenesis and osteogenesis was studied after a 1-week culture in vitro. Human cell proliferation was assessed as expression of ki67, whereas α-smooth muscle actin was used to determine the perivascular differentiation of MSCs. Osteogenesis was evaluated in vivo through detection of selected markers, by using real-time RT-PCR, alkaline phosphatase (ALP), Alizarin Red, hematoxylin/eosin (HE), and Masson trichrome staining.ResultsThe results show that endothelial microvascular networks could be generated in a poly(LLA-co-DXO) scaffold in vitro and sustained after in vivo implantation. The addition of ECs to MSCs influenced both angiogenic and osteogenic gene-expression profiles. Furthermore, human ki67 was upregulated before and after implantation. MSCs could support functional blood vessels as perivascular cells independent of implanted ECs. In addition, the expression of ALP was upregulated in the presence of endothelial microvascular networks.ConclusionsThis study demonstrates that copolymer poly(LLA-co-DXO) scaffolds can be prevascularized with ECs and MSCs. Although a local osteoinductive environment is required to achieve ectopic bone formation, seeding of MSCs with or without ECs increases the osteogenic potential of tissue-engineered constructs.

Significant evidence has indicated that poly(L-lactide)-co-(ɛ-caprolactone) [(poly(LLA-co-CL)] scaffolds could be one of the suitable candidates for bone tissue engineering. Oxygen-terminated nanodiamond particles (n-DP) were combined with poly(LLA-co-CL) and revealed to be positive for cell growth. In this study, we evaluated the influence of poly(LLA-co-CL) scaffolds modified by n-DP on attachment, proliferation, differentiation of bone marrow stromal cells (BMSCs) in vitro, and on bone formation using a sheep calvarial defect model. BMSCs were seeded on either poly(LLA-co-CL)- or n-DP-coated scaffolds and incubated for 1 h. Scanning electron microscopy (SEM) and fluorescence microscopy were used in addition to protein and DNA measurements to evaluate cellular attachment on the scaffolds. To determine the effect of n-DP on proliferation of BMSCs, cell/scaffold constructs were harvested after 3 days and evaluated by Bicinchoninic Acid (BCA) protein assay and SEM. In addition, the osteogenic differentiation of cells grown for 2 weeks on the various scaffolds and in a dynamic culture condition was evaluated by real-time RT-PCR. Unmodified and modified scaffolds were implanted into the calvaria of six-year-old sheep. The expression of collagen type I (COL I) and bone morphogenetic protein-2 (BMP-2) after 4 weeks as well as the formation of new bone after 12 and 24 weeks were analyzed by immunohistochemistry and histology. Scaffolds modified with n-DP supported increased cell attachment and the mRNA expression of osteopontin (OPN), bone sialoprotein (BSP), and BMP-2 were significantly increased after 2 weeks of culture. The BMSCs had spread well on the various scaffolds investigated after 3 days in the study with no significant difference in cell proliferation. Furthermore, the in vivo data revealed more positive staining of COL I and BMP-2 in relation to the n-DP-coated scaffolds after 4 weeks and presented more bone formation after 12 and 24 weeks. n-DP modification significantly increased cell attachment and differentiation of BMSCs on poly(LLA-co-CL) scaffolds in vitro and enhanced bone formation in vivo.

Titanium-based catalysts are needed to achieve electrocatalytic N 2 reduction to NH 3 with alarge NH 3 yield and ahigh Faradaic efficiency (FE). One of the cheapest and most abundant metals on earth, iron, is an effective dopant for greatly improving the nitrogen reduction reaction (NRR) performance of TiO 2 nanoparticles in ambient N 2 -to-NH 3 conversion. In 0.5 m LiClO 4 ,F e-doped TiO 2 catalyst attains ah igh FE of 25.6 %a nd al arge NH 3 yield of 25.47 mgh À1 mg cat À1 at À0.40 Vv ersus ar eversible hydrogen electrode.This performance compares favorably to those of all previously reported titanium-and iron-based NRR electrocatalysts in aqueous media. The catalytic mechanism is further probed with theoretical calculations.Asanessential activated nitrogen source,NH 3 is extensively used to manufacture dyes,p olymers,f ertilizers,a nd explosives,and it also serves as carbon-neutral energy carrier with high energy density. [1][2][3] To date,the dominant industrial route for NH 3 synthesis is the Haber-Bosch process using N 2 and H 2 as the feeding gases,b ut this process operates at high temperature and high pressure,a nd consumes al arge amount of energy while emitting CO 2 . [4] Electrochemical N 2 reduction offers an attractive alternative in an environmentally benign and sustainable manner,b ut the strong N N bond is fairly inert and thus difficult to break in ac hemical reaction, underlying the need for electrocatalysts with high activity in the nitrogen reduction reaction (NRR). [5][6][7][8] Noble metals perform the NRR efficiently;however, their scarcity and high cost limits their application in large-scale N 2 reduction. [8][9][10][11] NRR research has thus shifted to development of noble-metal-free alternatives. [12][13][14][15][16][17][18][19][20][21][22][23][24] TiO 2 is highly adaptable as asemiconductor catalyst because of its long-term thermodynamic stability,n atural abundance,a nd nontoxicity. [25] Recent studies have demonstrated that TiO 2 with oxygen defects has good electrocatalytic activity for the NRR, [26,27] and heteroatoms (B, [28] C, [29] V, [30] and Zr, [31] )a re effective dopants to enhance the NRR performances of TiO 2 catalysts. However,T i-based catalysts that simultaneously achieve al arge NH 3 yield with ah igh Faradaic efficiency (FE) are not available thus far.As one of the cheapest and most abundant metals on the earth, [32] Fe also exists in biological nitrogenases for natural N 2 fixation. [33] Fe compounds have been widely utilized as catalysts for artificial N 2 fixation in the Haber-Bosch [4] and electrochemical [34][35][36][37][38][39] processes.I ti st hus natural for us to explore use of Fe as ad opant for TiO 2 ,w hich has not been reported before.Herein, we report on our recent experimental results that Fe-doped TiO 2 is superior in performances for electrocatalytic N 2 reduction under ambient conditions.I n 0.5 m LiClO 4 ,t his catalyst achieves ah igh FE of 25.6 %a nd al arge NH 3 yield of 25.47 mgh À1 mg cat À1 at À0.40 Vv ersus ar eversible hydrogen electrode (...