Built-in microscale electrostatic fields induced by anatase-rutile-phase transition in selective areas promote osteogenesis

Laser-assisted manipulation of Volta potential pattern on the TC4 surface for improved hBMSCs osteogenesis

The Ti6Al4V (TC4) alloy, a prevalent biomedical material in orthopedics, still faces limitation of the insufficient osseointegration. To improve the bioactivity of TC4, introducing the electric environment onto the TC4 surface may be an effective way in the view of the necessity of endogenous electric microenvironment in bone regeneration. Herein, a Volta potential pattern was engendered on the TC4 surface via parallel laser patterning, so as to promote the osteogenic differentiation of cells. A 15 W laser successfully transformed the original α + β dual phase towards radially distributed lath-like martensite phase in the laser treated region. The atomic lattice distortion between the heterogeneous microstructures of the laser treated and untreated regions leads to a significant Volta potential fluctuation on the TC4 surface. The Volta potential pattern as well as the laser-engraved microgrooves respectively induced mutually orthogonal cell alignments. The hBMSCs osteogenic differentiation was significantly enhanced on the laser treated TC4 surfaces in comparison to the surface without the laser treatment. Moreover, a drastic Volta potential gradient on the TC4 surface (treated with 15 W power and 400 μm interval) resulted in the most pronounced osteogenic differentiation tendency compared to other groups. Modulating the electric environment on the TC4 surface by manipulating the phase transformation may provide an effective way in evoking favorable cell response of bone regeneration, thereby improving the bioactivity of TC4 implant.

Engineered Bio-Heterojunction with Infection-Primed H2 S Liberation for Boosted Angiogenesis and Infectious Cutaneous Regeneration

Photodynamic therapy (PDT) acts as a powerful weapon against infectious diseases for its enormous antimicrobial activity that quickly elicits storms of reactive oxygen species (ROS). Nevertheless, redundant ROS during treatment inevitably bring detriments in revascularization. To address this dilemma, an innovative P-N bio-heterojunction (bio-HJ) material consisting of p-type copper sulfide (p-CuS), n-type bismuth sulfide (n-Bi2 S3 ), and lactate oxidase (LOx) for effective treatment of recalcitrant infectious wounds by promoting angiogenesis is devised. LOx exhausts lactic acid accumulated in infection environment and converts it to hydrogen peroxide (H2 O2 ), which subsequently yields bactericidal hydroxyl radicals (·OH) via Fenton-like reactions. Ultimately, the P-N bio-HJs exert synergistic photothermal, photodynamic, and chemodynamic effects for rapid bacterial annihilation. Moreover, in vitro and RNA-seq analyses reveal that the crafted bio-HJs dramatically expedite the proliferation of L929 cells and promote angiogenesis by up-regulating angiogenic gene expression in hypoxia-inducible factor-1 (HIF-1) signaling pathway, which may ascribe to the evolution of H2 S in response to the infection microenvironment. Critically, results of in vivo experiments have authenticated that the bio-HJs significantly boost healing rates of full-thickness wounds by slaughtering bacteria, elevating angiogenesis, and promoting cytothesis. As envisioned, this work furnishes a novel tactic for the effective treatment of bacteria-invaded wound using H2 S-liberating P-N bio-HJs.

Metallurgical manipulation of surface Volta potential in bimetals and cell response of human mesenchymal stem cells

Bioelectricity plays an overriding role in directing cell migration, proliferation, differentiation etc. Tailoring the electro-extracellular environment through metallurgical manipulation could modulate the surrounding cell behaviors. In this study, different electric potential patterns, in terms of Volta potential distribution and gradient, were created on the metallic surface as an electric microenvironment, and their effects on adherent human mesenchymal stem cells were investigated. Periodically and randomly distributed Volta potential pattern, respectively, were generated on the surface through spark plasma sintering of two alternatively stacked dissimilar metals films and of a mixture of metallic powders. Actin cytoskeleton staining demonstrated that the Volta potential pattern strongly affected cell attachment and deformation. The cytoskeletons of cells were observed to elongate along the Volta potential gradient and across the border of adjacent regions with higher and lower potentials. Moreover, the steepest potential gradient resulting from the drastic compositional changes on the periodic borders gave rise to the strongest osteogenic tendency among all the samples. This study suggests that tailoring the Volta potential distribution and gradient of metallic biomaterials via metallurgical manipulation is a promising approach to activate surrounding cells, providing an extra degree of freedom for designing desirable bone-repairing metallic implants.

A 3D biomimetic optoelectronic scaffold repairs cranial defects

Bone fractures and defects pose serious health-related issues on patients. For clinical therapeutics, synthetic scaffolds have been actively explored to promote critical-sized bone regeneration, and electrical stimulations are recognized as an effective auxiliary to facilitate the process. Here, we develop a three-dimensional (3D) biomimetic scaffold integrated with thin-film silicon (Si)-based microstructures. This Si-based hybrid scaffold not only provides a 3D hierarchical structure for guiding cell growth but also regulates cell behaviors via photo-induced electrical signals. Remotely controlled by infrared illumination, these Si structures electrically modulate membrane potentials and intracellular calcium dynamics of stem cells and potentiate cell proliferation and differentiation. In a rodent model, the Si-integrated scaffold demonstrates improved osteogenesis under optical stimulations. Such a wirelessly powered optoelectronic scaffold eliminates tethered electrical implants and fully degrades in a biological environment. The Si-based 3D scaffold combines topographical and optoelectronic stimuli for effective biological modulations, offering broad potential for biomedicine.

Design of N-Type Textured Bi2 Te3 with Robust Mechanical Properties for Thermoelectric Micro-Refrigeration Application

Thermoelectric refrigeration is one of the mature techniques used for cooling applications, with the great advantage of miniaturization over traditional compression refrigeration. Due to the anisotropic thermoelectric properties of n-type bismuth telluride (Bi₂ Te₃ ) alloys, these two common methods, including the liquid phase hot deformation (LPHD) and traditional hot forging (HF) methods, are of considerable importance for texture engineering to enhance performance. However, their effects on thermoelectric and mechanical properties are still controversial and not clear yet. Moreover, there has been little documentation of mechanical properties related to micro-refrigeration applications. In this work, the above-mentioned methods are separately employed to control the macroscopic grain orientation for bulk n-type Bi₂ Te₃ samples. The HF method enabled the stabilization of both composition and carrier concentration, therefore yielding a higher quality factor to compare with that of LPHD samples, supported by DFT calculations. In addition to superior thermoelectric performance, the HF sample also exhibited robust mechanical properties due to the presence of nano-scale distortion and dense dislocation, which is the prerequisite for realizing ultra-precision machining. This work helps to pave the way for the utilization of n-type Bi₂ Te₃ for commercial micro-refrigeration applications.

The combination of a 3D-Printed porous Ti-6Al-4V alloy scaffold and stem cell sheet technology for the construction of biomimetic engineered bone at an ectopic site

Cell sheet technology has been widely used in bone tissue engineering and regenerative medicine. However, controlling the shape and volume of large pieces of engineered bone tissue remains impossible without additional suitable scaffolds. Three-dimensional (3D) printed titanium (Ti) alloy scaffolds are mostly used as implant materials for repairing bone defects, but the unsatisfactory bioactivities of traditional Ti-based scaffolds severely limit their clinical applications. Herein, we hypothesize that the combination of bone marrow mesenchymal stem cell (BMSC) sheet technology and 3D porous Ti–6Al–4V (PT) alloy scaffolds could be used to fabricate biomimetic engineered bone. First, various concentrations of BMSCs were directly cocultured with PT scaffolds to obtain complexes of osteoblastic cell sheets and scaffolds. Then, as an experimental control, an osteoblastic BMSC sheet was prepared by continuous culturing under osteogenic conditions for 2 weeks without passaging and used to wrap the scaffolds. The BMSC sheet was composed of several layers of extracellular matrix (ECM) and a mass of BMSCs. The BMSCs exhibited excellent adherent, proliferative and osteogenic potential when cocultured with PT scaffolds, which may be attributed to the ability of the 3D microstructure of scaffolds to facilitate the biological behaviors of cells, as confirmed by the in vitro results. Moreover, the presence of BMSCs and ECM increased the angiogenic potential of PT scaffolds by the secretion of VEGF. Micro-CT and histological analysis confirmed the in vivo formation of biomimetic engineered bone when the complex of cocultured BMSCs and PT scaffolds and the scaffolds wrapped by prepared BMSC sheets were implanted subcutaneously into nude mice. Therefore, the combination of BMSC sheet technology and 3D-printed PT scaffolds could be used to construct customized biomimetic engineered bone, offering a novel and promising strategy for the precise repair of bone defects.

Janus electro-microenvironment membrane with surface-selective osteogenesis/gingival healing ability for guided bone regeneration

Guided bone regeneration is widely applied in clinical practice to treat alveolar bone defects. However, the rate of healing of severe alveolar bone defects is slow, and there is a high incidence of soft tissue wound dehiscence. In this study, we propose a barrier membrane with a Janus electro-microenvironment (JEM) to achieve side-selective bone regeneration and soft tissue healing. The JEM membrane was constructed using a polarized polyvinylidene fluoride ferroelectric membrane with different surface potentials on either side. It promoted osteogenic differentiation and bone regeneration on the negatively polarized side (JEM-) and soft tissue regeneration on the positively polarized side (JEM+). Further investigation revealed that the JEM-mediated promotion of bone formation was related to mitochondrial autophagy, as indicated by depolarization of the mitochondrial membrane potential and the expression of LC3, Pink I, and Parkin. Moreover, the gingival healing promoted by JEM+ was related to oxidative phosphorylation in mitochondria, as indicated by the upregulation of mitochondrial complexes I–V and an increase in ATP generation. The design concept of the JEM provides a new avenue for regulating tissue regeneration between different tissue interfaces.

Functionalization of TiO2 for Better Performance as Orthopedic Implants

This review mainly focuses on the surface functionalization approaches of titanium dioxide (TiO₂) to prevent bacterial infections and facilitate osteointegration simultaneously for titanium (Ti)-based orthopedic implants. Infection is one of the major causes of implant failure. Meanwhile, it is also critical for the bone-forming cells to integrate with the implant surface. TiO₂ is the native oxide layer of Ti which has good biocompatibility as well as enriched physical, chemical, electronic, and photocatalytic properties. The formed nanostructures during fabrication and the enriched properties of TiO₂ have enabled various functionalization methods to combat the micro-organisms and enhance the osteogenesis of Ti implants. This review encompasses the various modifications of TiO₂ in aspects of topology, drug loading, and element incorporation, as well as the most recently developed electron transfer and electrical tuning approaches. Taken together, these approaches can endow Ti implants with better bactericidal and osteogenic abilities via the functionalization of TiO₂.

Tunable Electrical Conductivity and Simultaneously Enhanced Thermoelectric and Mechanical Properties in n-type Bi2 Te3

The recent growing energy crisis draws considerable attention to high-performance thermoelectric materials. n-type bismuth telluride is still irreplaceable at near room temperature for commercial application, and therefore, is worthy of further investigation. In this work, nanostructured Bi₂ Te₃ polycrystalline materials with highly enhanced thermoelectric properties are obtained by alkali metal Na solid solution. Na is chosen as the cation site dopant for n-type polycrystalline Bi₂ Te₃ . Na enters the Bi site, introducing holes in the Bi₂ Te₃ matrix and rendering the electrical conductivity tunable from 300 to 1800 Scm^-1 . The solid solution limit of Na in Bi₂ Te₃ exceeds 0.3 wt%. Owing to the effective solid solution, the Fermi level of Bi₂ Te₃ is properly regulated, leading to an improved Seebeck coefficient. In addition, the scattering of both charge carriers and phonons is modulated, which ensured a high-power factor and low lattice thermal conductivity. Benefitting from the synergistic optimization of both electrical and thermal transport properties, a maximum figure of merit (ZT) of 1.03 is achieved at 303 K when the doping content is 0.25 wt%, which is 70% higher than that of the pristine sample. This work disclosed an effective strategy for enhancing the performance of n-type bismuth telluride-based alloy materials.

Modulation Doping Enables Ultrahigh Power Factor and Thermoelectric ZT in n-Type Bi2 Te2.7 Se0.3

Bismuth telluride-based thermoelectric (TE) materials are historically recognized as the best p-type (ZT = 1.8) TE materials at room temperature. However, the poor performance of n-type (ZT≈1.0) counterparts seriously reduces the efficiency of the device. Such performance imbalance severely impedes its TE applications either in electrical generation or refrigeration. Here, a strategy to boost n-type Bi₂ Te_2.7 Se_0.3 crystals up to ZT = 1.42 near room temperature by a two-stage process is reported, that is, step 1: stabilizing Seebeck coefficient by CuI doping; step 2: boosting power factor (PF) by synergistically optimizing phonon and carrier transport via thermal-driven Cu intercalation in the van der Waals (vdW) gaps. Theoretical ab initio calculations disclose that these intercalated Cu atoms act as modulation doping and contribute conduction electrons of wavefunction spatially separated from the Cu atoms themselves, which simultaneously lead to large carrier concentration and high mobility. As a result, an ultra-high PF ≈63.5 µW cm^-1 K^-2 at 300 K and a highest average ZT = 1.36 at 300-450 K are realized, which outperform all n-type bismuth telluride materials ever reported. The work offers a new approach to improving n-type layered TE materials.

Microscopic Volta potential difference on metallic surface promotes the osteogenic differentiation and proliferation of human mesenchymal stem cells

Endogenous microscopic electric cues play an essential role in bone's remodeling and self-repair. Modulating the extracellular electrical environment, by means of external electric stimulation or changing surface potential of implants, was manifested to facilitate the osteointegration. The microscopic potential difference, originating from heterogeneous microstructures of materials, may mimic the endogenous electric signals to stimulate surrounding cells. In this study, the spark-plasma sintered Ti/Ta hybrid metal was fabricated and utilized to realize a surface microscopic potential difference at the same magnitude as endogenous potentials. Activated by the electric stimulation, the mesenchymal stem cells exhibited the anisotropic and polygonal cellular morphology on the Ti/Ta hybrid metal. The microscopic electric potential difference coordinated the cells proliferation on the subsequent days. Moreover, the results showed that the osteo-lineage differentiation on Ti/Ta hybrid metal were in vitro boosted over the control groups. Tailoring microstructures of material to obtain a reasonable electric microenvironment may be a necessary principle to achieve more favorable cell responses to implants, suggesting an extra degree of freedom in bone-repairing material design.

Biomedical Implants with Charge-Transfer Monitoring and Regulating Abilities

Transmembrane charge (ion/electron) transfer is essential for maintaining cellular homeostasis and is involved in many biological processes, from protein synthesis to embryonic development in organisms. Designing implant devices that can detect or regulate cellular transmembrane charge transfer is expected to sense and modulate the behaviors of host cells and tissues. Thus, charge transfer can be regarded as a bridge connecting living systems and human-made implantable devices. This review describes the mode and mechanism of charge transfer between organisms and nonliving materials, and summarizes the strategies to endow implants with charge-transfer regulating or monitoring abilities. Furthermore, three major charge-transfer controlling systems, including wired, self-activated, and stimuli-responsive biomedical implants, as well as the design principles and pivotal materials are systematically elaborated. The clinical challenges and the prospects for future development of these implant devices are also discussed.

Evolution of anodised titanium for implant applications

Anodised titanium has a long history as a coating structure for implants due to its bioactive and ossified surface, which promotes rapid bone integration. In response to the growing literature on anodised titanium, this article is the first to revisit the evolution of anodised titanium as an implant coating. The review reports the process and mechanisms for the engineering of distinctive anodised titanium structures, the significant factors influencing the mechanisms of its formation, bioactivity, as well as recent pre- and post-surface treatments proposed to improve the performance of anodised titanium. The review then broadens the discussion to include future functional trends of anodised titanium, ranging from the provision of higher surface energy interactions in the design of biocomposite coatings (template stencil interface for mechanical interlock) to techniques for measuring the bone-to-implant contact (BIC), each with their own challenges. Overall, this paper provides up-to-date information on the impacts of the structure and function of anodised titanium as an implant coating in vitro and in/ex vivo tests, as well as the four key future challenges that are important for its clinical translations, namely (i) techniques to enhance the mechanical stability and (ii) testing techniques to measure the mechanical stability of anodised titanium, (iii) real-time/in-situ detection methods for surface reactions, and (iv) cost-effectiveness for anodised titanium and its safety as a bone implant coating.

Novel cell sources for bone regeneration

A plethora of both acute and chronic conditions, including traumatic, degenerative, malignant, or congenital disorders, commonly induce bone disorders often associated with severe persisting pain and limited mobility. Over 1 million surgical procedures involving bone excision, bone grafting, and fracture repair are performed each year in the U.S. alone, resulting in immense levels of public health challenges and corresponding financial burdens. Unfortunately, the innate self-healing capacity of bone is often inadequate for larger defects over a critical size. Moreover, as direct transplantation of committed osteoblasts is hindered by deficient cell availability, limited cell spreading, and poor survivability, an urgent need for novel cell sources for bone regeneration is concurrent. Thanks to the development in stem cell biology and cell reprogramming technology, many multipotent and pluripotent cells that manifest promising osteogenic potential are considered the regenerative remedy for bone defects. Considering these cells' investigation is still in its relative infancy, each of them offers their own particular challenges that must be conquered before the large-scale clinical application.

Enhanced biocompatibility and osteogenic differentiation of mesenchymal stem cells of titanium by Sr-Ga clavate double hydroxides

To improve in vivo osseointegration of pure titanium implant, Sr-Ga clavate double hydroxide (CDH) coating was grown in situ on a titanium (Ti) substrate with simple hydrothermal and calcination treatments at 500 °C. The obtained coating on the Ti substrate (Ti-CDH and Ti-CDH500) was researched by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). Ti-CDH exhibited a sustained release profile of metal ions and maintained a slightly alkaline environment. The CDH coating was beneficial for osteogenic differentiation of mesenchymal stem cells (MSCs), which were reflected by the results of cellular assays, including alkaline phosphatase activity (ALP), cell mineralization capability (ARS), and osteogenesis-related gene expression. Besides, Ti-CDH could effectively improve the autophagic levels in MSCs, which further promoted osteogenic differentiation of MSCs. Hence, the Ti surface with Sr-Ga CDH modification supplied a simple and effective strategy to design biomaterials for bone generation.

Controlling 1T/2H heterophase junctions in the MoS2 microsphere for the highly efficient photocatalytic hydrogen evolution

The 1T/2H heterophase junction MoS2 microspheres were fabricated for a highly efficient photocatalytic hydrogen evolution.

Bioactive polymeric materials and electrical stimulation strategies for musculoskeletal tissue repair and regeneration

Electrical stimulation (ES) is predominantly used as a physical therapy modality to promote tissue healing and functional recovery. Research efforts in both laboratory and clinical settings have shown the beneficial effects of this technique for the repair and regeneration of damaged tissues, which include muscle, bone, skin, nerve, tendons, and ligaments. The collective findings of these studies suggest ES enhances cell proliferation, extracellular matrix (ECM) production, secretion of several cytokines, and vasculature development leading to better tissue regeneration in multiple tissues. However, there is still a gap in the clinical relevance for ES to better repair tissue interfaces, as ES applied clinically is ineffective on deeper tissue. The use of a conducting material can transmit the stimulation applied from skin electrodes to the desired tissue and lead to an increased function on the repair of that tissue. Ionically conductive (IC) polymeric scaffolds in conjunction with ES may provide solutions to utilize this approach effectively. Injectable IC formulations and their scaffolds may provide solutions for applying ES into difficult to reach tissue types to enable tissue repair and regeneration. A better understanding of ES-mediated cell differentiation and associated molecular mechanisms including the immune response will allow standardization of procedures applicable for the next generation of regenerative medicine. ES, along with the use of IC scaffolds is more than sufficient for use as a treatment option for single tissue healing and may fulfill a role in interfacing multiple tissue types during the repair process.

Wireless Electrochemotherapy by Selenium-Doped Piezoelectric Biomaterials to Enhance Cancer Cell Apoptosis

Cancer residues around the surgical site remain a significant cause of treatment failure with cancer recurrence. To prevent cancer recurrence and simultaneously repair surgery-caused defects, it is urgent to develop implantable biomaterials with anticancer ability and good biological activity. In this work, a functionalized implant is successfully fabricated by doping the effective anticancer element selenium (Se) into the potassium-sodium niobate piezoceramic, which realizes the wireless combination of electrotherapy and chemotherapy. Herein, we demonstrate that the Se-doped piezoelectric implant can cause mitochondrial damage by increasing intracellular reactive oxygen species levels and then trigger the caspase-3 pathway to significantly promote apoptosis of osteosarcoma cells in vitro. Meanwhile, its good biocompatibility has been verified. These results are of great importance for future deployment of wireless electro- and chemostimulation to modulate biological process around the defective tissue.

Integrating 3D Printing and Biomimetic Mineralization for Personalized Enhanced Osteogenesis, Angiogenesis, and Osteointegration

Titanium (Ti) alloy implants can repair bone defects at load-bearing sites. However, they mechanically mismatch with the natural bone and lack customized adaption with the irregularly major-sized load-bearing bone defects, resulting in the failure of implant fixation. Mineralized collagen (MC), a building block in bone, can induce angiogenesis and osteogenesis, and 3D printing technology can be employed to prepare scaffolds with an overall shape customized to the bone defect. Hence, we induced the formation of MC, made of hydroxyapatite (HAp) nanocrystals and collagen fibers, in 3D-printed porous Ti₆Al₄V (PT) scaffolds through in situ biomimetic mineralization. The resultant MC/PT scaffolds exhibited a bone-like Young's modulus and were customized to the anatomical contour of actual bone defects of rabbit model. We found that the biocompatibility and osteogenic differentiation are best when the mass ratio between HAp nanocrystals and collagen fibers is 1 in MC. We then implanted the MC/PT scaffolds into the customized radius defect rabbit model and found that the MC/PT scaffolds significantly improved the vascularized bone tissue formation and integration between new bone and the implants. Therefore, a combination of 3D printing and biomimetic mineralization could lead to customized 3D PT scaffolds for enhanced angiogenesis, osteogenesis, and osteointegration. Such scaffolds represent novel patient-specific implants for precisely repairing irregular major-sized load-bearing bone defects.

Effect of Local Alkaline Microenvironment on the Behaviors of Bacteria and Osteogenic Cells

The interactions between material surfaces and bacteria/cells have been widely investigated, based on which biomaterials with antibacterial and osteogenic abilities can be designed to conquer implant failures. The pH of environments is known to affect bacterial growth and bone formation/resorption, and it is possible that the antibacterial and osteogenic abilities of biomaterials can be simultaneously improved by regulating their surface alkalinity. Herein, we fabricated many kinds of films with various alkalinity levels on titanium surface to explore the effect of local alkaline microenvironments around material surfaces on the behaviors of bacteria and osteogenic cells. Both Gram-positive and -negative bacteria were cultured on sample surfaces to investigate their antibacterial effects. Cell adhesion, proliferation, and alkaline phosphatase (ALP) activities were investigated by culturing both bone mesenchymal stem cells (MSCs) and osteoblast cells on sample surfaces. The results show that an appropriate local alkaline environment can effectively inhibit the growth of both Gram-positive and -negative bacteria through inactivating ATP synthesis and inducing oxidative stress. Meanwhile, it can promote the osteogenic differentiation of bone MSCs and enhance the proliferation and ALP activities of osteoblast cells. In conclusion, material surfaces endowed with appropriate alkalinity can possess antibacterial and osteogenic properties, which provide a novel strategy to design multifunctional biomaterials for bone generation.

Enhanced Osseointegration of Hierarchically Structured Ti Implant with Electrically Bioactive SnO2-TiO2 Bilayered Surface

The poor osseointegration of Ti implant significantly compromise its application in load-bearing bone repair and replacement. Electrically bioactive coating inspirited from heterojunction on Ti implant can benefit osseointegration but cannot avoid the stress shielding effect between bone and implant. To resolve this conflict, hierarchically structured Ti implant with electrically bioactive SnO₂-TiO₂ bilayered surface has been developed to enhance osseointegration. Benefiting from the electric cue offered by the built-in electrical field of SnO₂-TiO₂ heterojunction and the topographic cue provided by the hierarchical surface structure to bone regeneration, the osteoblastic function of basic multicellular units around the implant is significantly improved. Because the individual TiO₂ or SnO₂ coating with uniform surface exhibits no electrical bioactivity, the effects of electric and topographic cues to osseointegration have been decoupled via the analysis of in vivo performance for the placed Ti implant with different surfaces. The developed Ti implant shows significantly improved osseointegration with excellent bone-implant contact, improved mineralization of extracellular matrix, and increased push-out force. These results suggest that the synergistic strategy of combing electrical bioactivity with hierarchical surface structure provides a new platform for developing advanced endosseous implants.

Intrinsically ferromagnetic Fe-doped TiO2 coatings on titanium for accelerating osteoblast response in vitro

The microenvironment can regulate osteoblast behavior during integration of implants with host bones. An intrinsically magnetic field induced by an Fe³⁺ doped TiO₂ coating was applied herein to enhance the cytocompatibility of Ti. Porous TiO₂ incorporated with different amounts of Fe (2.27-11.07 wt%) was directly prepared on Ti by micro-arc oxidation. The microstructure, roughness, wettability, ion releasing and magnetic property of TiO₂ coatings were investigated. Cell behavior, including adhesion, proliferation, differentiation, collagen secretion and extracellular matrix mineralization on coating surfaces was evaluated. The results show that incorporation of Fe³⁺ did not significantly alter the phase component, topography, roughness and wettability of coatings, and with increased doses of Fe³⁺, trace amounts of Fe³⁺ were released into the media, whereas the Ca²⁺ accumulation concentration slightly decreased. Fe-Doped TiO₂ displayed a weak ferromagnetic property, and its saturation magnetization value increased initially and then decreased with the increased dose of Fe. Compared with the undoped, proliferation, expression of osteogenesis-related genes, collagen secretion and extracellular matrix mineralization of osteoblasts were enhanced with Fe doped ones, especially for those with 4.25 wt% Fe. By analyzing the structures and properties of different surfaces and their osteoblast responses, it is deduced that the ferromagnetism of Fe doped TiO₂ plays a key role in enhancing osteoblast behavior. Such a result provides a new perspective for the potential application of ferromagnetic coatings in bone repair.

Modulating Surface Potential by Controlling the β Phase Content in Poly(vinylidene fluoridetrifluoroethylene) Membranes Enhances Bone Regeneration

Bioelectricity plays a vital role in living organisms. Although electrical stimulation is introduced in the field of bone regeneration, the concept of a dose-response relationship between surface potential and osteogenesis is not thoroughly studied. To optimize the osteogenic properties of different surface potentials, a flexible piezoelectric membrane, poly(vinylidene fluoridetrifluoroethylene) [P(VDF-TrFE)], is fabricated by annealing treatment to control its β phases. The surface potential and piezoelectric coefficients (d₃₃ ) of the membranes can be regulated by increasing β phase contents. Compared with d₃₃  = 20 pC N^-1 (surface potential = -78 mV) and unpolarized membranes, bone marrow mesenchymal stem cells (BM-MSCs) cultured on the d₃₃  = 10 pC N^-1 (surface potential = -53 mV) membranes have better osteogenic properties. In vivo, d₃₃  = 10 pC N^-1 membranes result in rapid bone regeneration and complete mature bone-structure formation. BM-MSCs on d₃₃  = 10 pC N^-1 membranes have the lowest reactive oxygen species level and the highest mitochondrial membrane electric potential, implying that these membranes provide the best electrical qunantity for BM-MSCs' proliferation and energy metabolism. This study establishes an effective method to control the surface potential of P(VDF-Trfe) membranes and highlights the importance of optimized electrical stimulation in bone regeneration.

Using an Engineered Galvanic Redox System to Generate Positive Surface Potentials that Promote Osteogenic Functions

Successful osseointegration of orthopaedic and orthodontic implants is dependent on a competition between osteogenesis and bacterial contamination on the implant-tissue interface. Previously, by taking advantage of the highly interactive capabilities of silver nanoparticles (AgNPs), we effectively introduced an antimicrobial effect to metal implant materials using an AgNP/poly(dl-lactic- co-glycolic acid) (PLGA) coating. Although electrical forces have been shown to promote osteogenesis, creating practical materials and devices capable of harnessing these forces to induce bone regeneration remains challenging. Here, we applied galvanic reduction-oxidation (redox) principles to engineer a nanoscale galvanic redox system between AgNPs and 316L stainless steel alloy (316L-SA). Characterized by scanning electron microscopy , energy-dispersive X-ray spectroscopy, atomic force microscopy, Kelvin probe force microscopy, and contact angle measurement, the surface properties of the yield AgNP/PLGA-coated 316L-SA (SNPSA) material presented a significantly increased positive surface potential, hydrophilicity, surface fractional polarity, and surface electron accepting/donating index. Importantly, in addition to its bactericidal property, SNPSA's surface demonstrated a novel osteogenic bioactivity by promoting peri-implant bone growth. This is the first report describing the conversion of a normally deleterious galvanic redox reaction into a biologically beneficial function on a biomedical metal material. Overall, this study details an innovative strategy to design multifunctional biomaterials using a controlled galvanic redox reaction, which has broad applications in material development and clinical practice.

Valence State Manipulation of Cerium Oxide Nanoparticles on a Titanium Surface for Modulating Cell Fate and Bone Formation

Understanding cell-biomaterial interactions is critical for the control of cell fate for tissue engineering and regenerative medicine. Here, cerium oxide nanoparticles (CeONPs) are applied at different Ce4+/Ce3+ ratios (i.e., 0.46, 1.23, and 3.23) to titanium substrate surfaces by magnetron sputtering and vacuum annealing. Evaluation of the cytotoxicity of the modified surface to cultured rat bone marrow mesenchymal stem cells (BMSCs) reveals that the cytocompatibility and cell proliferation are proportional to the increases in Ce4+/Ce3+ ratio on titanium surface. The bone formation capability induced by these surface modified titanium alloys is evaluated by implanting various CeONP samples into the intramedullary cavity of rat femur for 8 weeks. New bone formation adjacent to the implant shows a close relationship to the surface Ce4+/Ce3+ ratio; higher Ce4+/Ce3+ ratio achieves better osseointegration. The mechanism of this in vivo outcome is explored by culturing rat BMSCs and RAW264.7 murine macrophages on CeONP samples for different durations. The improvement in osteogenic differentiation capability of BMSCs is directly proportional to the increased Ce4+/Ce3+ ratio on the titanium surface. Increases in the Ce4+/Ce3+ ratio also elevate the polarization of the M2 phenotype of RAW264.7 murine macrophages, particularly with respect to the healing-associated M2 percentage and anti-inflammatory cytokine secretion. The manipulation of valence states of CeONPs appears to provide an effective modulation of the osteogenic capability of stem cells and the M2 polarization of macrophages, resulting in favorable outcomes of new bone formation and osseointegration.

Electrically bioactive coating on Ti with bi-layered SnO2–TiO2 hetero-structure for improving osteointegration

SnO₂–TiO₂ surface with the bi-layered structure on Ti provides internal electric stimulation to promote osteointegration of implant.

Review: the potential impact of surface crystalline states of titanium for biomedical applications

In many biomedical applications, titanium forms an interface with tissues, which is crucial to ensure its long-term stability and safety. In order to exert control over this process, titanium implants have been treated with various methods that induce physicochemical changes at nano and microscales. In the past 20 years, most of the studies have been conducted to see the effect of topographical and physicochemical changes of titanium surface after surface treatments on cells behavior and bacteria adhesion. In this review, we will first briefly present some of these surface treatments either chemical or physical and we explain the biological responses to titanium with a specific focus on adverse immune reactions. More recently, a new trend has emerged in titanium surface science with a focus on the crystalline phase of titanium dioxide and the associated biological responses. In these recent studies, rutile and anatase are the major two polymorphs used for biomedical applications. In the second part of this review, we consider this emerging topic of the control of the crystalline phase of titanium and discuss its potential biological impacts. More in-depth analysis of treatment-related surface crystalline changes can significantly improve the control over titanium/host tissue interface and can result in considerable decreases in implant-related complications, which is currently a big burden on the healthcare system.

Bone-Inspired Spatially Specific Piezoelectricity Induces Bone Regeneration

The extracellular matrix of bone can be pictured as a material made of parallel interspersed domains of fibrous piezoelectric collagenous materials and non-piezoelectric non-collagenous materials. To mimic this feature for enhanced bone regeneration, a material made of two parallel interspersed domains, with higher and lower piezoelectricity, respectively, is constructed to form microscale piezoelectric zones (MPZs). The MPZs are produced using a versatile and effective laser-irradiation technique in which K_0.5Na_0.5NbO₃ (KNN) ceramics are selectively irradiated to achieve microzone phase transitions. The phase structure of the laser-irradiated microzones is changed from a mixture of orthorhombic and tetragonal phases (with higher piezoelectricity) to a tetragonal dominant phase (with lower piezoelectricity). The microzoned piezoelectricity distribution results in spatially specific surface charge distribution, enabling the MPZs to bear bone-like microscale electric cues. Hence, the MPZs induce osteogenic differentiation of stem cells in vitro and bone regeneration in vivo even without being seeded with stem cells. The concept of mimicking the spatially specific piezoelectricity in bone will facilitate future research on the rational design of tissue regenerative materials.

Nanocomposite Membranes Enhance Bone Regeneration Through Restoring Physiological Electric Microenvironment

Physiological electric potential is well-known for its indispensable role in maintaining bone volume and quality. Although implanted biomaterials simulating structural, morphological, mechanical, and chemical properties of natural tissue or organ has been introduced in the field of bone regeneration, the concept of restoring physiological electric microenvironment remains ignored in biomaterials design. In this work, a flexible nanocomposite membrane mimicking the endogenous electric potential is fabricated to explore its bone defect repair efficiency. BaTiO3 nanoparticles (BTO NPs) were first coated with polydopamine. Then the composite membranes are fabricated with homogeneous distribution of Dopa@BTO NPs in poly(vinylidene fluoridetrifluoroethylene) (P(VDF-TrFE)) matrix. The surface potential of the nanocomposite membranes could be tuned up to -76.8 mV by optimizing the composition ratio and corona poling treatment, which conform to the level of endogenous biopotential. Remarkably, the surface potential of polarized nanocomposite membranes exhibited a dramatic stability with more than half of original surface potential remained up to 12 weeks in the condition of bone defect. In vitro, the membranes encouraged bone marrow mesenchymal stem cells (BM-MSCs) activity and osteogenic differentiation. In vivo, the membranes sustainably maintained the electric microenvironment giving rise to rapid bone regeneration and complete mature bone-structure formation. Our findings evidence that physiological electric potential repair should be paid sufficient attention in biomaterials design, and this concept might provide an innovative and well-suited strategy for bone regenerative therapies.