Evaluation of osteoinduction and proliferation on nano-Sr-HAP: a novel orthopedic biomaterial for bone tissue regeneration.

Hydroxyapatite (HAP), a CaP compound similar to the mineral phase present in bone, has excellent biocompatibility but little osseous inductivity. In this study, we evaluated the novel nano-Sr-HAP, in which the calcium of hydroxyapatite was substituted with strontium, which acts as a bone-forming agent. Its biocompatibility and osteoinduction were assayed using marrow mesenchymal stem cells (MSCs) and osteoblasts (OBs) in vitro. We were able to demonstrate that nano-Sr-HAP supported increased OB cell adhesion, proliferation and viability up to 4 days in culture when compared with nano-HAP. MSCs cultured with nano-Sr-HAP showed higher alkaline phosphatase (ALP) activity. More extracellular mineralized nodules were found with nano-Sr-HAP compared to nano-HAP, especially in images of ALP staining. We suggest that nano-Sr-HAP powders possess osteoconductive and osteoinductive properties and have the potential to be used in the repair of bone defects caused by osteoporotic fractures.

Sol-gel preparation of ZrO2-Li2Si2O5 ceramics and their sintering properties.

Despite zirconia (ZrO2) ceramics and lithium disilicate (Li2Si2O5) glass-ceramics have been widely applied on the market for dental restorations, composites that can combine the advantages of both are still demanded. Here we introduced a ZrO2-Li2Si2O5 ceramic with minimized glass phases that fabricated through a sol-gel method and subsequent pressureless sintering. ZrO2-Li2Si2O5 powders were obtained after the gel precursors were heat treated under 800 °C. The gel-derived powders were molded and pressureless sintered under 900-1000 °C to investigate their sintering properties. From the microstructures of the sintered samples, we knew that the densification process was dominated by the growth of Li2Si2O5 grains instead of the growth of ZrO2 grains. Increasing in Li2Si2O5 content can promote ceramic densification. Interestingly, reactions between ZrO2 and Li2Si2O5 were observed with sintering temperature higher than 916 °C, which can increase the porosity of the ceramics. Therefore, both the content of Li2Si2O5 and sintering temperature should be well adjusted to achieve samples with desired properties. Finally, ceramics with flexural strength of 226 MPa and porosity of 0.4% were achieved from powders with moderate Li2Si2O5 content after sintering at 1000 °C.

Co-exchanged montmorillonite: a potential antibacterial agent with good antibacterial activity and cytocompatibility.

As a biocompatible material with rich resources and economic benefits, montmorillonite (MMT) has been widely used in the antibacterial field as a drug carrier and toxin adsorbent. In addition, the distinctive structure of MMT provides a possibility to tune its property in a wide range through ion-exchange. In this study, Co-montmorillonite (CoMMT) was prepared by the ion-exchanging method in a Co(NO3)2 solution and its antibacterial activity and cytocompatibility were investigated. The results showed that Co was introduced into MMT successfully and led to an increase in the interlayer spacing of MMT. Also, CoMMT showed a morphology of irregular aggregates consisting of stacked and intertwined lamellae with a uniform cobalt distribution. Besides, CoMMT had better dispersity and higher specific surface area than unmodified MMT. The antibacterial test results showed that CoMMT had good antibacterial activity against S. aureus and E. coli when the CoMMT concentration was higher than 0.2 mg mL-1 and 0.4 mg mL-1, respectively. The possible antibacterial mechanism of CoMMT was speculated and verified by a combination of SEM and EDS results. In addition, CoMMT showed no obvious cytotoxicity to MC3TC-E1 at the observed antibacterial concentration. These findings demonstrated that CoMMT with good biocompatibility and antibacterial activity could be used as a novel antibacterial agent for tissue engineering.

Interactive effects of cerium and copper to tune the microstructure of silicocarnotite bioceramics towards enhanced bioactivity and good biosafety.

Endowing biomaterials with functional elements enhances their biological properties effectively. However, improving bioactivity and biosafety simultaneously is still highly desirable. Herein, cerium (Ce) and copper (Cu) are incorporated into silicocarnotite (CPS) to modulate the constitution and microstructure for degradability, bioactivity and biosafety regulation. Our results demonstrated that introducing Ce suppressed scaffold degradation, while, co-incorporation of both Ce and Cu accelerated degradability. Osteogenic effect of CPS in vitro was promoted by Ce and optimized by Cu, and Ce-induced angiogenic inhibition could be mitigated by cell coculture method and reversed by Ce-Cu co-incorporation. Ce enhanced osteogenic and angiogenic properties of CPS in a dose-dependent manner in vivo, and Cu-Ce coexistence exhibited optimal bioactivity and satisfactory biosafety. This work demonstrated that coculture in vitro was more appropriately reflecting the behavior of implanted biomaterials in vivo. Interactive effects of multi-metal elements were promising to enhance bioactivity and biosafety concurrently. The present work provided a promising biomaterial for bone repair and regeneration, and offered a comprehensive strategy to design new biomaterials which aimed at adjustable degradation behavior, and enhanced bioactivity and biosafety.

Study on antibacterial and fluoride-releasing properties of a novel composite resin with fluorine-doped nano-zirconia fillers.

OBJECTIVE: A novel composite resin (CR) with fluorine-doped nano-zirconia (F-ZrO2) fillers was developed as an antibacterial restorative material. This article described the synthesis and investigated the fluoride release, antibacterial property and cytotoxicity of the novel CR. METHODS: F-ZrO2 powders with different fluorine contents (0% F-ZrO2, 5% F-ZrO2, 10% F-ZrO2 or 20% F-ZrO2) were synthesized by chemical precipitation method and characterized by XRD, SEM and TEM-EDS. The content and release of fluoride were also determined. 20% F-ZrO2 powers were selected to develop the novel CRs (FZ-25, FZ-50, and FZ-75). The fluoride release from the novel CRs during 28 days was recorded. The antibacterial property of the novel CRs was investigated with direct contact test (DCT) and metabolic activity test (CCK8). The cytotoxicity of the CRs was also evaluated here. RESULTS: F-ZrO2 powders with different fluorine contents were obtained. The fluoride release increased with increasing of the fluoride content. Through the antibacterial performance evaluation, 20% F-ZrO2 powders, which exhibiting the best antibacterial property, were selected as the fillers for preparing the novel CR. The novel CR with F-ZrO2 fillers exhibited an effective antibacterial effect. Compared with the control group, the antibacterial rates of FZ-25, FZ-50 and FZ-75 were 51.65%, 54.14% and 66.80% (p<0.05), respectively. No obvious cytotoxicity of the novel CR was detected in this study. CLINICAL SIGNIFICANCE: The novel CR with continuous fluoride release and proper antibacterial property is expected to be used as an antibacterial material to reduce secondary caries.

Fabrication of enamel-like structure on polymer-infiltrated zirconia ceramics.

OBJECTIVES: The aim of this study is to improve the biological and mechanical properties of zirconia-based PICN (polymer-infiltrated-ceramic-network) materials by fabrication an enamel-like structure on its surface. METHODS: Fluorapatite (FA) arrays were fabricated on zirconia discs by hydrothermal treatment. After polymer infiltration, an enamel-like structure was obtained on zirconia-based PICN materials. Effects of hydrothermal treatment conditions on the FA arrays were investigated by XRD, FTIR and SEM. Human gingival fibroblast cells (HGFs) and Escherichia coli (E. coli) were used to evaluate the cytocompatibility and antibacterial properties. Nanoindentation method was employed to determine elastic modulus and hardness. RESULTS: A facile and pervasive method was developed in this study to fabricate an enamel-like structure constituted of controlled FA arrays and interstitial resin on zirconia-based PICN materials. The obtained FA arrays can significantly promote the adhesion and proliferation of human gingival fibroblasts (HGFs), and further effectively inhibit the growth of Escherichia coli. Owing to the hierarchical structure, the enamel-like structure has achieved a hardness of 1.79 GPa and a lower Young's modulus of 37.4 GPa. SIGNIFICANCES: The enamel-like structure, with excellent biological and mechanical properties, is promising for various applications in dentistry.

Ferric oxide: A favorable additive to balance mechanical strength and biological activity of silicocarnotite bioceramic.

Ideal materials for bone regeneration should have not only a good bioactivity, but also a good mechanical strength to provide an initial support for new bone formation. How to get a balance between high mechanical property and good bioactivity is a challenging issue for bone regeneration materials. In the present work, a biocompatible additive Fe2O3 was selected to optimize the comprehensive properties of a novel calcium phosphate silicate (CPS) ceramic using a mechanical mixing method. The effects of Fe2O3 content on microstructure, bending strength, apatite formation ability and cytocompatibility of Fe-CPS bioceramics were investigated and the related mechanism was also discussed. The obtained Fe-CPS bioceramics showed enhanced mechanical and favorable bioactivity performances. Especially, the Fe-CPS bioceramic with 1.5 wt% Fe2O3 sintered at 1250 °C presented the highest bending strength of 91.9 MPa. While, Fe-CPS bioceramics still exhibited a good ability on apatite formation in simulated body fluid (SBF), and cytocompatibility test revealed that Fe-CPS bioceramics were favorable for cell adhesion and proliferation. All the results indicated that Fe-CPS bioceramics are promising candidate materials for bone regeneration at load bearing applications.

Improved cellular bioactivity by heparin immobilization on polycarbonate film via an aminolysis modification for potential tendon repair.

Tendon repair was an important part during tendon to bone healing. In the present study, heparin molecules were immobilized on the aminolyzed PCL surface to improve the cellular bioactivity for potential tendon repair. The effects of heparin immobilization on protein adsorption behavior and cellular bioactivity of NIH3T3 and ATDC5 cells were investigated. The results were shown as follows.

Ultrasound-assisted synthesis of nanocrystallized silicocarnotite biomaterial with improved sinterability and osteogenic activity.

It has been proved that silicon-substituted calcium phosphate ceramics possess superior bone regeneration and resorbability to HA, while the synthesis of single-phase nanocrystallized high Si-containing calcium phosphate is still a challenge. In the present work, a novel and facile aqueous precipitation method assisted with ultrasonic irradiation was adopted firstly to synthesise a single-phase nanocrystallized calcium silicophosphate (Ca5(PO4)2SiO4, CPS) biomaterial. Crystallization and morphology of Si-apatite precursors synthesized with or without ultrasonic assistance were primarily investigated and the related mechanism was discussed. Moreover, the sinterability, in vitro bioactivity and osteogenic activity of the synthesized CPS were studied in detail. Results showed that an ultrasonic cavitation effect could be beneficial to form a highly dispersive CPS precursor with a single Si-apatite phase, which greatly reduced the calcination temperature of CPS from 1350 °C to 1000 °C. Nanocrystallized CPS powders were obtained successfully under ultrasound-assisted conditions, which showed superior sinterability, in vitro bioactivity and osteogenic activity than those of micron-sized CPS and HA powders. It might be a promising candidate material for bone tissue regeneration applications.

Thermal stability and in vitro bioactivity of Ti-Al-V-O nanostructures fabricated on Ti6Al4V alloy.

This work investigates the thermal stability and in vitro bioactivity of Ti-Al-V-O nanostructures grown on Ti6Al4V alloy through an anodization method. After anodization of the two-phase Ti6Al4V alloy, there were two different kinds of Ti-Al-V-O nanostructure (nanotube arrays grown in the alpha-phase region and irregular nanopores grown in the beta-phase region) that formed on the surface of the alloy. It was found that the Ti-Al-V-O nanotubes can withstand a high temperature of 675 degrees C in air without collapse, whereas the irregular Ti-Al-V-O nanopores presented a lower thermal stability. In vitro simulated body fluid (SBF) testing of heat-treated nanostructures indicated that a quick apatite formation on these nanostructures occurred after only several hours of sample immersion in the SBF.

Anodic fabrication and bioactivity of Nb-doped TiO2 nanotubes.

We report anodic formation of Ti-Nb-O nanotubes on top of a Ti35Nb alloy, and in vitro bioactivity and stem cell response of the anodic nanotubes. It was found that the amorphous Ti-Nb-O nanotubes presented a significantly enhanced in vitro bioactivity (in simulated body fluids) compared to those of undoped TiO2 nanotubes and porous Ti-Nb-O without nanotubular structure. Similar to undoped TiO2 nanotubes, the Ti-Nb-O nanotubes also promote mesenchymal stem cell adhesion and fast formation of extracellular matrix (ECM) materials. The above findings make it possible to further explore the biological properties, such as cell proliferation and drug delivery, of a variety of Ti-alloy-based oxide nanotubes.

High strength polymer/silicon nitride composites for dental restorations.

OBJECTIVES: To fabricate polymer-infiltrated silicon nitride composite (PISNC) and evaluate the potential of PISNC in dental application. METHODS: Porous silicon nitride (Si3N4) ceramics were fabricated through gelcasting and pressureless sintering. Polymer infiltrating was carried out then and composites were obtained after curing of polymer. Flexural strength and microstructures of porous ceramic scaffolds and polymer-infiltrated composites were obtained by three-point bending and SEM, respectively. Phase distributions of polymer-infiltrated ceramics were observed by EDS. Human gingival fibroblast cells (HGFs) were used to evaluate the cytocompatibility and IL-6 release. The cell morphology were observed by SEM. The amount of released IL-6 was investigated using ELISA test system. RESULTS: Porosity and mechanical strength of porous ceramics ranged from 45.1 to 49.3% and 171.8-262.3MPa, respectively. The bicontinuous structure of polymer-infiltrated composites possessed them with excellent mechanical properties. Porosity and mechanical strength of polymer-infiltrated Si3N4 composites ranged from 1.94 to 2.28% and 273-385.3MPa, respectively. Additionally, the PISNC enhanced the initial adhesion and spreading activity of HGFs compared with PMMA. The PISNC showed similar IL-6 release performance with PMMA samples. SIGNIFICANCES: The PISNC is a promising candidate for dental restorations and high-load medical applications.

Reconstruction of calvarial defect of rabbits using porous calcium silicate bioactive ceramics.

In this study, the in vivo bone-regenerative capacity and resorption of the porous beta-calcium silicate (beta-CaSiO(3), beta-CS) bioactive ceramics were investigated in a rabbit calvarial defect model, and the results were compared with porous beta-tricalcium phosphate (beta-Ca(3)(PO(4))(2), beta-TCP) bioceramics. The porous beta-CS and beta-TCP ceramics were implanted in rabbit calvarial defects and the specimens were harvested after 4, 8 and 16 weeks, and evaluated by Micro-CT and histomorphometric analysis. The Micro-CT and histomorphometric analysis showed that the resorption of beta-CS was much higher than that of beta-TCP. The TRAP-positive multinucleated cells were observed on the surface of beta-CS, suggesting a cell-mediated process involved in the degradation of beta-CS in vivo. The amount of newly formed bone was also measured and more bone formation was observed with beta-CS as compared with beta-TCP (p<0.05). Histological observation demonstrated that newly formed bone tissue grew into the porous beta-CS, and a bone-like apatite layer was identified between the bone tissue and beta-CS materials. The present studies showed that the porous beta-CS ceramics could stimulate bone regeneration and may be used as bioactive and biodegradable materials for hard tissue repair and tissue engineering applications.

Bioactive calcium phosphate silicate ceramic surface-modified PLGA for tendon-to-bone healing.

Due to the dissimilar features between the tendon and bone, tendon to bone healing is the most challenging problems in sports medicine. In the present work, a novel bioactive calcium phosphate silicate ceramic (CPS) was coated on the surface of PLGA films using electron beam evaporation (EBE) technique to prepare a tailorable composite film with layered chemical composition similar to tendon-bone interface. The physicochemical behaviors of the CPS-PLGA composite films were characterized and the cytocompatibility were also investigated. It was found that the CPS-modified samples exhibited a significantly improved hydrophilicity and a more negative zeta potential. Cell culture results showed that the CPS-modified samples were beneficial to the attachment and proliferation of rBMSCs and NIH3T3 cells. CPS-modified samples also showed an improved osteogenic activity. The results suggested that CPS-modified PLGA films have great potentials for tendon-bone healing.

Synergetic topography and chemistry cues guiding osteogenic differentiation in bone marrow stromal cells through ERK1/2 and p38 MAPK signaling pathway.

Both the topographic surface and chemical composition modification can enhance rapid osteogenic differentiation and bone formation. Till now, the synergetic effects of topography and chemistry cues guiding biological responses have been rarely reported. Herein, the ordered micro-patterned topography and classically essential trace element of strontium (Sr) ion doping were selected to imitate topography and chemistry cues, respectively. The ordered micro-patterned topography on Sr ion-doped bioceramics was successfully duplicated using the nylon sieve as the template. Biological response results revealed that the micro-patterned topography design or Sr doping could promote cell attachment, ALP activity, and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). Most importantly, the samples both with micro-patterned topography and Sr doping showed the highest promotion effects, and could synergistically activate the ERK1/2 and p38 MAPK signaling pathways. The results suggested that the grafts with both specific topography and chemistry cues have synergetic effects on osteogenic activity of BMSCs and provide an effective approach to design functional bone grafts and cell culture substrates.

Bioinspired structure of bioceramics for bone regeneration in load-bearing sites.

The major problem with the use of porous bioceramics as bone regeneration grafts is their weak mechanical strength, which has not been overcome to date. Here we described a novel way to solve this problem. Beta-tricalcium phosphate (beta-TCP) bioceramics with a bioinspired structure were designed and prepared with a porous cancellous core (porosity: 70-90%) inside and a dense compact shell (porosity: 5-10%) outside that mimics the characteristics of natural bone. They showed excellent mechanical properties, with a compressive strength of 10-80MPa and an elastic modulus of 180MPa-1.0GPa, which could be tailored by the dense/porous cross-sectional area ratio obeying the rule of exponential growth. The in vitro degradation of the bioinspired bioceramics was faster than that of dense bioceramics but slower than that of porous counterparts. The changes in mechanical properties of the bioinspired ceramics during in vitro degradation were also investigated. A concept of the bioinspired macrostructure design of natural bone was proposed which provided a simple but effective way to increase the mechanical properties of porous bioceramics for load-bearing bone regeneration applications. It should be readily applicable to other porous materials.

Enhanced Bioactivity and Bacteriostasis of Surface Fluorinated Polyetheretherketone.

Although polyetheretherketone (PEEK) has been considered as a potential orthopedic and dental application material due to its similar elastic modulus as bones, inferior osseointegration and bacteriostasis of PEEK hampers its clinical application. In this work, fluorinated PEEK was constructed via plasma immersion ion implantation (PIII) followed by hydrofluoric acid treatment to ameliorate the osseointegration and antibacterial properties of PEEK. The surface microstructure, composition, and hydrophilicity of all samples were investigated. Rat bone mesenchymal stem cells (rBMSCs) were cultured on their surfaces to estimate bioactivity. The fluorinated PEEK can enhance the cell adhesion, cell spreading, proliferation, and alkaline phosphatase (ALP) activity compared to pristine PEEK. Furthermore, the fluorinated PEEK surface exhibits good bacteriostatic effect against Porphyromonas gingivalis, which is one of the major periodontal pathogens. In summary, we provide an effective route to introduce fluorine and the results reveal that the fluorinated PEEK can enhance the osseointegration and bacteriostasis, which provides a potential candidate for dental implants.

Enhanced osteogenic activity of poly ether ether ketone using calcium plasma immersion ion implantation.

As a promising implantable material, poly ether ether ketone (PEEK) possesses similar elastic modulus to that of cortical bones yet suffers from bio-inertness and poor osteogenic properties, which limits its application as orthopedic implants. In this work, calcium is introduced onto PEEK surface using calcium plasma immersion ion implantation (Ca-PIII). The results obtained from scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) confirm the modified layer with varying contents of calcium are formed on PEEK surfaces. Water contact angle measurements reveal the increasing hydrophobicity of both Ca-PIII treated surfaces. In vitro cell adhesion, viability assay, alkaline phosphatase activity and collagen secretion analyses disclose improved the adhesion, proliferation, and osteo-differentiation of rat bone mesenchymal stem cells (bMSCs) on Ca-PIII treated surfaces. The obtained results indicate that PEEK surface with enhanced osteogenic activity can be produced by calcium incorporation.

Enhanced osteogenic and selective antibacterial activities on micro-/nano-structured carbon fiber reinforced polyetheretherketone.

Carbon fiber reinforced polyetheretherketone (CFRPEEK) possesses a similar elastic modulus to that of human cortical bone and is considered as a promising candidate to replace metallic surgical implants. However, the bioinertness and deficiency of antibacterial activities impedes the application of CFRPEEK as orthopedic and especially oral implants. In this work, dual zinc and oxygen plasma immersion ion implantation (Zn/O-PIII) is applied to modify CFRPEEK, achieving both zinc incorporation and introduction of unique micro-/nano-structures on the surface. Scanning electron microscopy (SEM) observation reveals the formation of micro-pits with the size of around 800 nm on the CFRPEEK surface. X-ray photoelectron spectroscopy (XPS) test results confirm the existence of ZnO on the near surface. In vitro cell adhesion, viability assay, and real-time PCR analyses disclose enhanced adhesion, proliferation, and osteo-differentiation of mouse osteoblasts (MC3T3-E1) and rat bone mesenchymal stem cells (bMSCs) on the structured surface. Furthermore, the multilevel structures on CFRPEEK exhibit great antibacterial activity to biofilm-positive Staphylococcus aureus (ATCC 25923), MRSA (ATCC 43300) and Staphylococcus epidermidis (ATCC 35984) while show no obvious inhibition to Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853) and biofilm-negative Staphylococcus epidermidis (ATCC 12228). The obtained results indicate that the CFRPEEK surface with specific biological properties can be enhanced by zinc incorporation and multilevel structure introduction, through which the application of CFRPEEK to orthopedic and dental implants can be further broadened.

Influence of sulfur content on bone formation and antibacterial ability of sulfonated PEEK.

Polyetheretherketone (PEEK) is desirable in orthopedic and dental applications because its mechanical properties are similar to those of natural bones but the bioinertness and inferior osteoconduction of PEEK have hampered many clinical applications. In this work, PEEK is sulfonated by concentrated sulfuric acid to fabricate a three-dimensional (3D) network. A hydrothermal treatment is subsequently conducted to remove the residues and the temperature is adjusted to obtain different sulfur concentrations. In vitro cell proliferation and real-time PCR analyses disclose enhanced proliferation and osteogenic differentiation of rat bone mesenchymal stem cells (rBMSCs) on the samples with small sulfur concentrations. The in vitro antibacterial evaluation reveals that all the sulfonated samples possess excellent resistance against Staphylococcus aureus and Escherichia coli. The in vivo rat femur implantation model is adopted and X-ray, micro-CT, and histological analyses indicate that not only the premeditated injected bacteria cells are sterilized, but also new bone forms around the samples with small sulfur concentrations. The in vitro and in vivo results reveal that the samples subjected to the hydrothermal treatment to remove excess sulfur have better osseointegration and antibacterial ability and PEEK modified by sulfonation and hydrothermal treatment is promising in orthopedic and dental applications.