Contribution of exogenous humic substances to phosphorus availability in soil-plant ecosystem: A review

Phosphorus (P) is one of the largest nutrients limiting crop productivity. Meanwhile, P deficiency is a common phenomenon in agricultural soils around the world. Humic substances, as macromolecular polymer, accelerate and strengthen process which transforms P into bio-available forms via a range of chemical reactions and biological interactions. There is now an urgent need to comprehend the work carried out on the interaction among humic substances, soil and plant to better understand their role in the transformation and promotion of soil bioavailable P for plant growth. Herein, we discuss the factors and mechanisms of humic substances influencing P cycling in soil-plant systems, which focus on their contribution to soil P mobilization and plant P acquisition. This review covers how humic substances influence the mobilization and transformation of P in soils, including release of P from residues, and competitive adsorption of P and humic acid or fulvic acid to metallic minerals, as well as exchange with P adsorbed by humic substances. It then discusses a range of contributions to plant available P acquisition such as the release of organic acids from roots caused by humic substances, and promoting the solubilize and/or hydrolyze phosphate by plant and their associated microbes. Notably, we also discuss the challenges of artificial humic substances influencing P cycling in soil-plant systems, which may alleviate the global deficit of soil P resources. Overall, humic substances have become promising for sustainable agriculture over time and have great potential to meet specific soil-plant systems.</p

Facet-Specific Mineralization Behavior of Nano-CaP on Anatase Polyhedral Microcrystals

Biomimetic mineralization of nanocalcium phosphate (CaP) on metal oxide surfaces has gained great interest because of their relevance to osseointegration performance of implant materials. However, precisely controlling the nucleation behavior of mineralized nano-CaP on metal oxide at selective sites still remains a challenge. Here, we demonstrate a phenomenon on facet-specific mineralization on anatase TiO₂ polyhedral microcrystals organized by two facets of {101} and {001} in complete cell culture medium: nano-CaP covers up {101} facets, while there are a few on {001} facets. The comparative experimental results indicate that the preadsorbed fetal bovine serum (FBS) protein on {001} facets might play a barrier role in preventing sequential nucleation of nano-CaP. This work thus provides insight into the understanding of mineralization on metal oxides, and a way to control the mineralization

Visible-Light-Responsive Surfaces for Efficient, Noninvasive Cell Sheet Harvesting

Effective regulation of cell-surface interactions is critical for regenerative medicine and other cell-based therapies. Herein, visible-light-induced cell sheet harvesting based on silicon wafers with a p/n junction [Si­(p/n)] is introduced. Cell sheets could quickly detach from the Si­(p/n) surface after 10 min of visible-light illumination with maintained cell viability and functions. It is found that preadsorbed proteins on the Si­(p/n) surface like BSA and collagen-I show light-induced desorption behaviors. Molecular dynamics simulation also indicates that long-range force caused by the photovoltaic effect of Si­(p/n) under visible-light illumination plays a key role in triggering the release of the preadsorbed protein. It is suggested that such protein desorption behavior mediated by the photovoltaic effect is responsible for cell release. This work not only shows promising potential for cell sheet harvesting, but also provides new insights into protein–material interactions

Cell-Sheet-Derived ECM Coatings and Their Effects on BMSCs Responses

Extracellular matrix (ECM) provides a dynamic and complex environment to determine the fate of stem cells. In this work, light harvested cell sheets were treated with paraformaldehyde or ethanol, which eventually become ECM. Such ECM was then immobilized on titanium substrates via polydopamine chemistry. Their effects on bone marrow mesenchymal stromal cells (BMSCs) behaviors were investigated. It was found that paraformaldehyde-treated ECM coating (PT-ECM) showed a well-maintained microstructure, whereas that of ethanol-treated (ET-ECM) was completely changed. As a result, different amide structures and distributions of ECM components, such as laminin and collagen I, were exhibited. Alkaline phosphatase activity, osteocalcin secretion, related gene expression, and mineral deposition were evaluated for BMSCs cultured on both ECM coatings. PT-ECM was demonstrated to promote osteogenic differentiation much more efficiently than that of ET-ECM. That is ascribed to the preservation of native ECM milieu of PT-ECM. Such ECM acquirement and immobilization method could establish surfaces being able to direct stem cell responses on various materials. That shows promising potential in bone tissue engineering and other related biomedical applications

Ternary Transition Metal Sulfides Embedded in Graphene Nanosheets as Both the Anode and Cathode for High-Performance Asymmetric Supercapacitors

Owing to their low electronegativity, excellent electrical conductivity, high specific capacitance, and rich electrochemical redox sites, various transition metal sulfides have attracted significant attention as promising pseudocapacitive electrode materials for supercapacitors. However, their relatively poor electrical conductivity and large volume changes seriously hinder their commercial applications. Herein, ternary Co_0.33Fe_0.67S₂ nanoparticles are in situ embedded between graphene nanosheets through a facile one-step hydrothermal approach to form a sandwich-like composite. Because of its unique and robust structure, the graphene nanosheet/Co_0.33Fe_0.67S₂ composite (GCFS-0.33) exhibits a high specific capacitance (310.2 C g^–1 at 2 mV s^–1) and superb rate capability (61.8% at 200 mV s^–1) in 3 M KOH aqueous electrolyte. Using transition metal sulfides simultaneously as both positive and negative electrodes, for the first time, an aqueous asymmetric supercapacitor (ASC) was fabricated with the GCFS-0.33 composite as the negative electrode and sulfidized graphene/CoNiAl-layered double hydroxides as the positive electrode with well-separated potential windows. Our fabricated ASC delivered an excellent energy density of 66.8 Wh kg^–1 at a power density of 300.5 W kg^–1 and still retained 13.1 Wh kg^–1 even at a high power density of 29.4 kW kg^–1, which is highly comparable with that of previously reported transition-metal-sulfide-based ASC devices. Moreover, the as-fabricated ASC cell displays impressive long-term cycling stability with a capacitance retention of 102.2% relative to the initial capacitance after 10 000 cycles. This versatile synthetic strategy can be readily extended to synthesize other transition-metal-sulfide-based composites with excellent electrochemical performances

Enhanced Osteointegration of Hierarchical Structured 3D-Printed Titanium Implants

Three-dimensional (3D) printing technology has been widely used to fabricate of various titanium and its alloy implants. However, engineering the 3D printing nanoscaled feature to realize a hierarchical micronano structured surface topography still remains a challenge. On one hand, enhanced bioactivity is always expected on micronano-hybrid biomimetic topography; on the other hand, a typical functional protein in extracellular matrix (ECM) is nanoscaled; therefore, nanoscaled features might affect its binding to specific receptor and subsequent cell response. Here, we engineered a novel hierarchical structure with microparticles and rutile TiO₂ nanorods topography that fabricated by 3D printing of pure titanium followed by a hydrothermal process. Although there was no difference on the microscaled feature before/after nanonization, cellular behaviors including adhesion, proliferation, and osteogenic differentiation of mesenchymal stem cells (MSCs) were significantly upregulated on the hierarchical micronano structured topography. Moreover, we demonstrated that the distinct conformation of the initially fibronectin proteins adsorbed on nanorods was more beneficial to cellular adhesion. <i>In vivo</i> test in a rabbit femur model also demonstrated the favorable for new bone formation on the novel hierarchical micronano structured implant–bone interface. These results therefore suggest that the hierarchical micronano structured topography might be a promising surface feature for the new generation of bone implants

Light-Induced Cell Alignment and Harvest for Anisotropic Cell Sheet Technology

Well-organized orientation of cells and anisotropic extracellular matrix (ECM) are crucial in engineering biomimetic tissues, such as muscles, arteries, and nervous system, and so on. This strategy, however, is only beginning to be explored. Here, we demonstrated a light-induced cell alignment and harvest for anisotropic cell sheets (ACS) technology using light-responsive TiO₂ nanodots film (TNF) and photo-cross-linkable gelatin methacrylate (GelMA). Cell initial behaviors on TNF might be controlled by micropatterns of light-induced distinct surface hydroxyl features, owing to a sensing mechanism of myosin II-driven retraction of lamellipodia. Further light treatment allowed ACS detachment from TNF surface while simultaneously solidified the GelMA, realizing the automatic transference of ACS. Moreover, two detached ACS were successfully stacked into a 3D bilayer construct with controllable orientation of individual layer and maintained cell alignment for more than 7 days. Interestingly, the anisotropic HFF-1 cell sheets could further induce the HUVECs to form anisotropic capillary-like networks via upregulating VEGFA and ANGPT1 and producing anisotropic ECM. This developed integrated-functional ACS technology therefore provides a novel route to produce complex tissue constructs with well-defined orientations and may have a profound impact on regenerative medicine

Harnessing Cell Dynamic Responses on Magnetoelectric Nanocomposite Films to Promote Osteogenic Differentiation

The binding of cell integrins to proteins adsorbed on the material surface is a highly dynamic process critical for guiding cellular responses. However, temporal dynamic regulation of adsorbed proteins to meet the spatial conformation requirement of integrins for a certain cellular response remains a great challenge. Here, an active CoFe₂O₄/poly­(vinylidene fluoride-trifluoroethylene) nanocomposite film, which was demonstrated to be an obvious surface potential variation (Δ<i>V</i> ≈ 93 mV) in response to the applied magnetic field intensity (0–3000 Oe), was designed to harness the dynamic binding of integrin-adsorbed proteins by in situ controlling of the conformation of adsorbed proteins. Experimental investigation and molecular dynamics simulation confirmed the surface potential-induced conformational change in the adsorbed proteins. Cells cultured on nanocomposite films indicated that cellular responses in different time periods (adhesion, proliferation, and differentiation) required distinct magnetic field intensity, and synthetically programming the preferred magnetic field intensity of each time period could further enhance the osteogenic differentiation through the FAK/ERK signaling pathway. This work therefore provides a distinct concept that dynamically controllable modulation of the material surface property fitting the binding requirement of different cell time periods would be more conducive to achieving the desired osteogenic differentiation

Controlled Release of Naringin in Metal-Organic Framework-Loaded Mineralized Collagen Coating to Simultaneously Enhance Osseointegration and Antibacterial Activity

Two important goals in orthopedic implant research are to promote osseointegration and prevent infection. However, much previous effort has been focused on the design of coatings to either enhance osseointegration while ignoring antibacterial activity or vice versa, to prevent infection while ignoring bone integration. Here, we designed a multifunctional mineralized collagen coating on titanium with the aid of metal-organic framework (MOF) nanocrystals to control the release of naringin, a Chinese herbal medicine that could promote osseointegration and prevent bacterial infection. The attachment, proliferation, osteogenic differentiation, and mineralization of mesenchymal stem cells on the coating were significantly enhanced. Meanwhile, the antibacterial abilities against Staphylococcus aureus were also promoted. Furthermore, release kinetics analysis indicated that the synergistic effect of a primary burst release stage and secondary slow release stage played a critical role in the performance and could be controlled by the relative concentrations of MOF and naringin. This work thus provides a novel strategy to engineer multifunctional orthopedic coatings that can enhance osseointegration and simultaneously inhibit microbial cell growth

Surface Atomic Structure Directs the Fate of Human Mesenchymal Stem Cells

Stem cells in contact with materials are able to sense their surface features, integrate extracellular matrix (ECM) protein cues through a signal transduction pathway, and ultimately direct cell fate decisions. However, discovering the interdisciplinary mechanisms of how stem cells respond to inherent material surface features still remains a challenge due to the complex, multicomponent signaling milieu present in the ECM environment. Here, we demonstrate that the fate of human mesenchymal stem cells (hMSCs) can be regulated by the inherent physical cue of the material surface down to atomic-scale features. hMSCs on a TiO-terminated SrTiO₃ {110} substrate tend to differentiate into specific lineage cells (osteoblast, chondrocyte, adipocyte), whereas on a TiO₂-terminated SrTiO₃ {100} substrate they are prone to maintain pluripotency. The experimental observations and molecular dynamics simulations indicate that the distinct conformations of the initially adsorbed serum albumin and fibronectin proteins activate the integrin–focal adhesion cytoskeleton actin transduction pathway and, subsequently, direct the gene and protein expressions of hMSCs. Moreover, we demonstrate that the initial protein adsorption behaviors are dependent on the distinct hydroxyl groups originating from different surface atomic structures as well as the work functions. This work, therefore, provides new insights into the fundamental understanding of cell–material interactions and will have a profound impact on further designing materials to direct the stem cell fate