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

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

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

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

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