Lingqing Dong

Facet-Specific Assembly of Proteins on SrTiO3 Polyhedral Nanocrystals

Precisely controlling the protein-nanomaterial interactions at selective sites is crucial in engineering biomolecule composite architectures with tailored nanostructures and functions for a variety of biomedical applications. This strategy, however, is only beginning to be explored. Here, we demonstrate the facet-specific assembly of proteins, such as albumin, immunoglobulin and protamine, on {100} facets of SrTiO3 polyhedral nanocrystals, while none on {110} facets. Molecular dynamics simulations indicate the immobile surface hydration layer might play a barrier role to effectively prevent proteins adsorption on specific {110} facets. This work thus provides new insights into the fundamentally understanding of protein-nanomaterial interactions, and open a novel, general and facile route to control the selective adsorption of various proteins on various nanocrystals.

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 hydroxyl groups regulate the osteogenic differentiation of mesenchymal stem cells on titanium and tantalum metals

Titanium (Ti) and tantalum (Ta) metals have been widely used as implants for their favorable mechanical features and good biocompatibility. However, the results on their osteogenic capacity have been conflicting due to the synergistic effects of complex and multiple material surface features (such as topography, surface chemistries etc.) on cellular behaviors. Here, we directly compare the osteogenic response of mesenchymal stem cells (MSCs) to Ti and Ta metal surfaces with alterable surface hydroxyl groups. Although no difference was found on both surface topographies, cellular adhesion, proliferation, and the expression of osteogenic-related markers were upregulated with the increasing amount of surface hydroxyl groups (-OH) after ultraviolet (UV) light treatment. Moreover, Ti showed better effects in promoting osteogenic differentiation of MSCs than Ta before UV light treatment, but demonstrated the opposite after UV light treatment. These results might be attributed to the comparative quantity of the distinct type of surface hydroxyl groups (bridging-OH and terminal-OH), which regulated the conformation of the initial protein adsorption and subsequent cellular behaviors. Our results demonstrate the central role of the surface hydroxyl groups in mediating cell-material interactions and implicate this interface as helping in optimizing osteointegration of Ti and Ta based orthopaedic and dental implants.

Mediation of cellular osteogenic differentiation through daily stimulation time based on polypyrrole planar electrodes

In electrical stimulation (ES), daily stimulation time means the interacting duration with cells per day, and is a vital factor for mediating cellular function. In the present study, the effect of stimulation time on osteogenic differentiation of MC3T3-E1 cells was investigated under ES on polypyrrole (Ppy) planar interdigitated electrodes (IDE). The results demonstrated that only a suitable daily stimulation time supported to obviously upregulate the expression of ALP protein and osteogenesis-related genes (ALP, Col-I, Runx2 and OCN), while a short or long daily stimulation time showed no significant outcomes. These might be attributed to the mechanism that an ES induced transient change in intracellular calcium ion concentration, which was responsible for activating calcium ion signaling pathway to enhance cellular osteogenic differentiation. A shorter daily time could lead to insufficient duration for the transient change in intracellular calcium ion concentration, and a longer daily time could give rise to cellular fatigue with no transient change. This work therefore provides new insights into the fundamental understanding of cell responses to ES and will have an impact on further designing materials to mediate cell behaviors.

Effect of hierarchical pore structure on ALP expression of MC3T3-E1 cells on bioglass films

Hierarchical porous bioglass films on the tantalum were designed to enhance osteointegration of metallic implants. The films were prepared by a sol-gel method using P123 as the mesopore template and polystyrene microsphere as the nanopore template. The films with 5.4nm mesopores and 100nm nanopores (MBG-100) elicited an obviously elongated morphology of the cultured MC3T3-E1 cells, as a result, a higher alkaline phosphatase level was expressed. It is suggested that the nanopores play an important role in regulating cellular behavior by initial protein adsorption through nanopore curvatures. The mesopores were proven very effective for loading rhBMP-2, and the rhBMP-2 loaded on MBG-100 films showed a better function of enhancing osteogenic differentiation, which is attributed to that the nanopore structure could expedite rhBMP-2 release and provide a microenvironment for intensifying the interaction of rhBMP-2 with the cells. Hence, the cell osteogenic differentiation can be enhanced by hierarchical porous bioglass films through both the porous structure and rhBMP-2 induction.

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.

Surface potential-governed cellular osteogenic differentiation on ferroelectric polyvinylidene fluoride trifluoroethylene films

Surface potential of biomaterials can dramatically influence cellular osteogenic differentiation. In this work, a wide range of surface potential on ferroelectric polyvinylidene fluoride trifluoroethylene (P(VDF-TrFE)) films was designed to get insight into the interfacial interaction of cell-charged surface. The P(VDF-TrFE) films poled by contact electric poling at various electric fields obtained well stabilized surface potential, with wide range from -3 to 915 mV. The osteogenic differentiation level of cells cultured on the films was strongly dependent on surface potential and reached the optimum at 391 mV in this system. Binding specificity assay indicated that surface potential could effectively govern the binding state of the adsorbed fibronectin (FN) with integrin. Molecular dynamic (MD) simulation further revealed that surface potential brought a significant difference in the relative distance between RGD and synergy PHSRN sites of adsorbed FN, resulting in a distinct integrin-FN binding state. These results suggest that the full binding of integrin α5β1 with both RGD and PHSRN sites of FN possesses a strong ability to activate osteogenic signaling pathway. This work sheds light on the underlying mechanism of osteogenic differentiation behavior on charged material surfaces, and also provides a guidance for designing a reasonable charged surface to enhance osteogenic differentiation. STATEMENT OF SIGNIFICANCE The ferroelectric P(VDF-TrFE) films with steady and a wide range of surface potential were designed to understand underlying mechanism of cell-charged surface interaction. The results showed that the charged surface well favored upregulation of osteogenic differentiation of MC3T3-E1 cells, and more importantly, a highest level occurred on the film with a moderate surface potential. Experiments and molecular dynamics simulation demonstrated that the surface potential could govern fibronectin conformation and then the integrin-fibronectin binding. We propose that a full binding state of integrin α5β1 with fibronectin induces effective activation of integrin-mediated FAK/ERK signaling pathway to upregulate cellular osteogenic differentiation. This work provides a guidance for designing a reasonable charged surface to enhance osteogenic differentiation.

Magnetically actuated mechanical stimuli on Fe 3 O 4 /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.

Cell responses on a H2Ti3O7 nanowire film

Alkali treatment has been widely used for the surface modification of Ti and Ti alloys for clinical applications. However, the mechanism underlying the effects of the alkali-treated Ti surface on the cell response still needs to be explored. In this study, we demonstrated that the cell responses on a H2Ti3O7 nanowire film, normally titanate generated on a Ti surface via alkali treatment and ion exchange, were sensitive to the surface hydroxyl groups of the H2Ti3O7 nanowire films, i.e. the total amount as well as comparative ratio of the distinct type of surface hydroxyl groups (bridging-OH and terminal-OH). The surface hydroxyl groups of H2Ti3O7 nanowires were further controlled via heat treatment to produce anatase TiO2 nanowire films. Although there was no difference in both topographies, cells on a H2Ti3O7 nanowire film showed more elongated shape than those on an anatase nanowire film. Moreover, the expression of ALP of cells on H2Ti3O7 upregulated as compared to that on the anatase nanowire film at day 4, suggesting enhanced osteogenic capacity at an early stage. These results could be attributed to the difference in the distinct ratio of the terminal hydroxyl groups to the bridging hydroxyl groups, which was 0.42 for the H2Ti3O7 nanowire film and 0.75 for the anatase nanowire film. It appeared that the bridging hydroxyl groups on H2Ti3O7 were efficient in attracting Ca2+, which influenced the cell morphology and further upregulated the early differentiation.

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.