Remotely Temporal Scheduled Macrophage Phenotypic Transition Enables Optimized Immunomodulatory Bone Regeneration.

Precise timing of macrophage polarization plays a pivotal role in immunomodulation of tissue regeneration, yet most studies mainly focus on M2 macrophages for their anti-inflammatory and regenerative effects while the essential proinflammatory role of the M1 phenotype on the early inflammation stage is largely underestimated. Herein, a superparamagnetic hydrogel capable of timely controlling macrophage polarization is constructed by grafting superparamagnetic nanoparticles on collagen nanofibers. The magnetic responsive hydrogel network enables efficient polarization of encapsulated macrophage to the M2 phenotype through the podosome/Rho/ROCK mechanical pathway in response to static magnetic field (MF) as needed. Taking advantage of remote accessibility of magnetic field together with the superparamagnetic hydrogels, a temporal engineered M1 to M2 transition course preserving the essential role of M1 at the early stage of tissue healing, as well as enhancing the prohealing effect of M2 at the middle/late stages is established via delayed MF switch. Such precise timing of macrophage polarization matching the regenerative process of injured tissue eventually leads to optimized immunomodulatory bone healing in vivo. Overall, this study offers a remotely time-scheduled approach for macrophage polarization, which enables precise manipulation of inflammation progression during tissue healing.

Anisotropic magneto-mechanical stimulation on collagen coatings to accelerate osteogenesis.

Mechanical stimulation has been considered to be critical to cellular response and tissue regeneration. However, harnessing the direction of mechanical stimulation during osteogenesis still remains a challenge. In this study, we designed a series of novel magnetized collagen coatings (MCCs) (randomly or parallel-oriented collagen fibers) to exert the anisotropic mechanical stimulation using oriented magnetic actuation during osteogenesis. Strikingly, we found the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) were significantly up-regulated when the direction of magnetic actuation was parallel to the randomly-oriented collagen coating surface, in contrast to the down-regulated capacity under the perpendicular magnetic actuation. Moreover, further exerting a parallel mechanical stimulation along the parallel-oriented collagen coating, which cells have been oriented by the oriented collagens, were not only able to up-regulate the osteogenic differentiation of BMSCs but also promote the new bone formation during osteogenesis in vivo. We also demonstrated the anisotropic magneto-mechanical stimulation for the osteogenic differences might be attributed to the stretching or bending tensile status of collagen fibers controlled by the direction of magnetic actuation, driving the α5ß1-dependent integrin signaling cascade. This study therefore got insight of understanding the directional mechanical stimulation on osteogenesis, and also paved a way for sustaining regulation of the biomaterials-host interface.

Graphene/Si-Promoted Osteogenic Differentiation of BMSCs through Light Illumination.

Graphene (Gr) presents promising applications in regulating the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Light illumination is regarded as a spatiotemporally controllable, easily applicable, and noninvasive mean to modulate material responses. Herein, Gr-transferred silicon (Gr/Si) with a Schottky junction is utilized to evaluate the visible-light-promoted osteogenic differentiation of BMSCs. Under light illumination, light-induced charges, owing to the formation of the Schottky junction at the interface of Gr and Si, accumulated on the surface and then changed the surface potential of Gr/Si. The Schottky junction and surface potential at the interface of Gr and Si was measured by photovoltaic test and scanning Kelvin probe microscopy. Alkaline phosphatase (ALP) activity and quantitative real-time polymerase chain reaction (PCR) measurement showed that such variations of surface improved the osteogenic differentiation of BMSCs, and the activation of the voltage-gated calcium channels through surface potential and accumulation of cytosolic Ca2+ could be the reason. Moreover, X-ray photoelectron spectroscopy characterization showed that surface charge could also affect BMSCs differentiation through the promotion or inhibition of the adsorption of osteogenic growth factors. Such light-promoted osteogenic differentiation of BMSCs on Gr/Si may have huge potential for biomedical materials or devices for bone regeneration application.

Comprehensive Evaluation of Surface Potential Characteristics on Mesenchymal Stem Cells' Osteogenic Differentiation.

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 xDy1- xFe2 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 ß1 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.

Insights into the Osteogenic Differentiation of Mesenchymal Stem Cells on Crystalline and Vitreous Silica.

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 O1s 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.

Periodic-Mechanical-Stimulus Enhanced Osteogenic Differentiation of Mesenchymal Stem Cells on Fe3O4/Mineralized Collagen Coatings.

Mechanical stimulus has been demonstrated to be critical to stem cell fate commitment and tissue repair. However, it still remains a challenge to remote control of the mechanical stimulus acting on cells. Here, we designed a magnetic Fe3O4/mineralized collagen coating on titanium substrate to regulate the osteogenic differentiation of mesenchymal stem cells (MSCs). The mode and intensity of the mechanical stimulus acting on cells could be controlled by adjusting the remote applied magnetic field. We demonstrated that the adhesion, proliferation, and differentiation of MSCs were strongly dependent on the mode and intensity of the mechanical stimuli. Strikingly, the periodic mechanical stimulus (12 h every other day, PMS) showed the significantly up-regulated expression of osteogenesis-related markers, ALP, compared to that of the static mechanical stimulus mode. The reason is proposed as (1) initially, PMS mode enables the coatings to have appropriate surface mechanical properties for promoting focal adhesion, integrin expression, and cytoskeleton development of MSCs, letting MSCs have good capability of accepting as well as transferring mechanical stimuli; (2) during MSCs growth, PMS mode may effectively manipulate MSCs cytoskeleton development and movement, and mechanotranduction mechanism could be well activated; thus, MSCs osteogenic differentiation is enhanced. This work therefore provides a novel strategy to engineer bioactive coatings with remote control over the intensity and mode of the mechanical stimulus acting on cells, and would have an impact on the design of smart biomaterial surfaces for orthopedic applications.

Magnetically actuated mechanical stimuli on Fe3O4/mineralized collagen coatings to enhance osteogenic differentiation of the MC3T3-E1 cells.

Mechanical stimuli at the bone-implant interface are considered to activate the mechanotransduction pathway of the cell to improve the initial osseointegration establishment and to guarantee clinical success of the implant. However, control of the mechanical stimuli at the bone-implant interface still remains a challenge. In this study, we have designed a strategy of a magnetically responsive coating on which the mechanical stimuli is controlled because of coating deformation under static magnetic field (SMF). The iron oxide nanoparticle/mineralized collagen (IOP-MC) coatings were electrochemically codeposited on titanium substrates in different quantities of IOPs and distributions; the resulting coatings were verified to possess swelling behavior with flexibility same as that of hydrogel. The relative quantity of IOP to collagen and the IOP distribution in the coatings were demonstrated to play a critical role in mediating cell behavior. The cells present on the outer layer of the distributed IOP-MC (O-IOP-MC) coating with a mass ratio of 0.67 revealed the most distinct osteogenic differentiation activity being promoted, which could be attributed to the maximized mechanical stimuli with exposure to SMF. Furthermore, the enhanced osteogenic differentiation of the stimulated MC3T3-E1 cells originated from magnetically actuated mechanotransduction signaling pathway, embodying the upregulated expression of osteogenic-related and mechanotransduction-related genes. This work therefore provides a promising strategy for implementing mechanical stimuli to activate mechanotransduction on the bone-implant interface and thus to promote osseointegration. STATEMENT OF SIGNIFICANCE: The magnetically actuated coating is designed to produce mechanical stimuli to cells for promoting osteogenic differentiation based on the coating deformation. Iron oxide nanoparticles (IOPs) were incorporated into the mineralized collagen coatings (MC) forming the composite coatings (IOP-MC) with spatially distributed IOPs, and the IOP-MC coatings with outer distributed IOPs (O-IOPs-MC) shows the maximized mechanical stimuli to cells with enhanced osteogenic differentiation under static magnetic field. The upregulated expression of the associated genes reveals that the enabled mechanotransduction signaling pathway is responsible for the promoted cellular osteogenic differentiation. This work therefore provides a promising strategy for implementing mechanical stimuli to activate mechanotransduction on the bone-implant interface to promote osseointegration.

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 V ≈ 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.

Magnetically Assisted Electrodeposition of Aligned Collagen Coatings.

Well-aligned collagen nanofibers are crucial in engineering bioinspired regenerative strategies, such as bone, muscle and cornea. However, keeping the natural bioactive of collagen and controlling its orientation in a coating still remain a challenge. Here we present a novel magnetically assisted electrochemical technique to deposit type-I collagen nanofibers with high alignment onto titanium. The magnetic assistance involved mainly the incorporation of iron oxide nanoparticles (IOPs) and the application of an external magnetic field during the electrochemical deposition. The combination of IOPs with the collagen nanofibrils in electrolyte endowed the nanofibrils with magnetism, which forced the collagen nanofibrils to be straightened and assembled into aligned nanofibers under magnetic field during electrodeposition. The influence of the applied magnetic field on orientational order of the collagen nanofibers in the coatings extended to drying stage. The aligned collagen coatings demonstrated to favorably guide the bone marrow mesenchymal stem cells (BMSCs) grow in the form of elongated morphology, which promoted the cellular osteogenic differentiation dramatically. The present magnetically assisted electrodeposition could emerge as an attractive approach to fabrication of aligned nanofibers on substrates for subsequent uses such as bone tissue engineering.

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.

Chromium removal using resin supported nanoscale zero-valent iron.

Resin supported nanoscale zero-valent iron (R-nZVI) was synthesized by the borohydride reduction method. Batch experiments were conducted to evaluate the factors affecting Cr(VI) removal. It was found that nZVI loads, resin dose, pH value and initial concentration of Cr(VI) were all important factors. Scanning electron microscopy showed that the nZVI particles in R-nZVI became sphere after reacting with Cr(VI). This phenomenon was attributed to the co-precipitation of Cr(III) and Fe(III) on the surface of resin. X-ray diffraction pattern confirmed that Fe(0) diminished after the reaction. At optimum conditions, the Cr(VI) removal efficiency was 84.4% when the initial concentration of Cr(VI) was 20.0 mg/L. Regeneration of R-nZVI and resin was possible. R-nZVI can also remove Cr(III) efficiently. However, the removal mechanisms of Cr(VI) (anion) and Cr(III) (cation) are different. The former is chemical reduction, while the latter is ion exchange at pH below 6.3 and precipitation at pH above 6.3. This study demonstrates that R-nZVI has the potential to become an effective agent for treating wastewater containing Cr(VI) and Cr(III).