Study on physicochemical properties and in vitro bioactivity of tricalcium silicate–calcium carbonate composite bone cement

In this article, a novel bone cement composed of tricalcium silicate (Ca(3)SiO(5); C(3)S) and calcium carbonate (CaCO(3)) was prepared with the weight percent of CaCO(3) in the range of 0, 10, 20, 30, and 40%. The initial setting time was dramatically reduced from 90 to 45 min as the content of CaCO(3) increased from 0 to 40%, and the workable paste with a liquid/powder (L/P) ratio of 0.8 ml/g could be injected between 2 and 20 min (nozzle diameter 2.0 mm). The composite cement showed higher mechanical strength (24-27 MPa) than that of the pure Ca(3)SiO(5) paste (14-16 MPa). Furthermore, the composite cement could induce apatite formation and degrade in the phosphate buffered saline. The results indicated that the Ca(3)SiO(5)-CaCO(3) paste had better hydraulic properties than pure Ca(3)SiO(5) paste, and also the composite cement was bioactive and degradable. The novel bone cement could be a potential candidate as a bone substitute.     

Evaluation of in vitro bioactivity and biocompatibility of Bioglass®-reinforced polyethylene composite

The bioactivity and biocompatibility of Bioglass®-reinforced high-density polyethylene composite (Bioglass®/HDPE) have been evaluated in simulated body fluid (SBF) and by in vitro cell culture, respectively. The formation of a biologically active hydroxy-carbonate apatite (HCA) layer on the composite surface after immersion in SBF was demonstrated by thin-film X-ray diffraction, infrared spectroscopy and scanning electron microscopy, indicating the in vitro bioactivity of Bioglass®/HDPE composites. The HCA layer was formed on the 40 vol% composite surface within 3 days immersion in SBF at a formation rate comparable to those on bioactive glass-ceramics, showing that in vitro bioactivity could be obtained in a composite. Furthermore, the composite was biocompatible to primary human osteoblast-like cells. In comparison with unfilled HDPE and tissue culture plastic control, a significant increase in cellular metabolic activity was found on the composite. Therefore, Bioglass®/HDPE composites have a promising biological response as a potential implant material.     

Calcium–phosphate–silicate composite bone cement: self-setting properties and in vitro bioactivity

In this study, a novel low temperature setting calcium phosphate–silicate cement was obtained by mixing CaHPO₄ · 2H₂O (DCPD) and Ca₃SiO₅ (C₃S) with 0.75 M sodium phosphate buffers (pH = 7.0) as liquid phase. The self-setting properties of the obtained DCPD/C₃S paste with liquid to powder ratio (L/P) of 0.6 ml/g, such as setting times, injectability, degradability and compressive strength were investigated and compared with that of DCPD/CaO cement system. The results indicated that, with the weight ratio of C₃S varied from 20% to 40%, the workable DCPD/C₃S pastes could set within 20 min, and the hydrated cement showed significantly higher compressive strength (around 34.0 MPa after 24 h) than that of the DCPD/CaO cement system (approximately 10.0 MPa). Furthermore, the in vitro pH value of the cements was investigated by soaking in simulated body fluid (SBF) for 12 h, and the result indicated that the DCPD/C₃S did not induce significant increase or decrease of pH value in SBF. Additionally, the composite cement possesses better ability to support and stimulate cell proliferation than the DCPD/CaO cement. With good hydraulic properties, improved biocompatibility and moderate degradability, the novel DCPD/C₃S bone cement may be a potential candidate as bone substitute.     

In vitro and in vivo biocompatibility of graded hydroxyapatite–zirconia composite bioceramic

To obtain bioceramics with good osteoinductive ability and mechanical strength, graded hydroxyapatite–zirconia (HA–ZrO₂) composite bioceramics were prepared in this work. The biocompatibility of the bioceramics was investigated in vitro based on acute toxicity and cytotoxicity tests and hemolysis assay. Results showed the studied graded HA–ZrO₂ had little toxicity to mouse and L929 mouse fibroblasts. Also, hemolysis assay indicated a good blood compatibility of the bioceramics. Based on the results of in vitro tests, animal experiments were performed on white New Zealand rabbits by implantation into hip muscles and femur. It was found that the graded HA–ZrO₂ composite bioceramics exhibited superior osteoinductive ability, which may be a promising bioceramics implant.     

Initial in vitro biocompatibility of a bone cement composite containing a poly-ε-caprolactone microspheres

The biocompatibility of a reinforced calcium phosphate injectable bone substitute (CPC-IBS) containing 30% poly-ε-caprolactone (PCL) microspheres was evaluated. The IBS consisted of a solution of chitosan and citric acid as the liquid phase and tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) powder as the solid phase with 30% PCL microspheres. The surface of the CPC-IBS was observed by SEM, and analyzed by EDX profiles. The initial setting of the sample was lower in the IBS containing 0% citric acid than in the IBS containing 10 or 20% citric acid. The compressive strength of the PCL-incorporated CPC-IBS was measured using a Universal Testing Machine. The 20% citric acid samples had the highest mechanical strength at day 12, which was dependent on both time and the citric acid concentration. The in vitro bioactivity experiments with simulated body fluid (SBF) confirmed the formation of apatite on the sample surfaces after 2, 7, and 14 days of incubation in SBF. Ca and P ion release profile by ICP method also confirmed apatite nucleation on the CPC-IBS surfaces. The in vitro biocompatibility of the CPC-IBS was evaluated by using MTT, cellular adhesion, and spreading studies. In vitro cytotoxicity tests by MTT assay showed that the 0 and 10% CPC-IBS was cytocompatible for fibroblast L-929 cells. The SEM micrograph confirmed that MG-63 cells maintained their phenotype on all of the CPC-IBS surfaces although cellular attachment was better in 0 and 10% CPC-IBS than 20% samples.     

The effect of loading icariin on biocompatibility and bioactivity of porous β-TCP ceramic

In order to enhance the ability of calcium phosphate-based biomaterials for bone defect repair, icariin (Ica), one natural product with ability of promoting osteoblasts differentiation in vitro and enhancing bone formation in vivo, was loaded into porous β-tricalcium phosphate ceramic (β-TCP) disks. The obtained Ica-loaded porous β-TCP ceramic (Ica/β-TCP) disks were characterized by SEM. The SEM photos indicated that the disks had porous structure and the surface morphology of the porous β-TCP ceramic (β-PTCP) disks had no obvious difference from the Ica/β-TCP disks. The Ica release curve of Ica/β-TCP disks showed a burst release during the first 1 day and the concentration of released Ica during the first 3 days had low cytotoxicity. The loading Ica in Ica/β-TCP disks hardly affected the attachment and morphology of Ros17/28 cells, however, the Ica/β-TCP disks were favorable to supporting the proliferation and differentiation of Ros17/28 cells better compared with the β-PTCP disks. There was plenty of bone-like apatite formed on the surface of Ica/β-TCP disks soaked in SBF solution for three days. After back intramuscular implantation of rats for three months, no obvious osteogenic evidence was detected in β-PTCP disks, but new bone formation was observed in Ica/β-TCP disks. Fibrous tissues and slight inflammatory reaction was also found in the Ica/β-TCP disks and β-TCP disks. Therefore, the loading Ica did not change the biocompatibility of β-TCP ceramic, but enhanced the bioactivity of β-TCP ceramic in vivo. The Ica/β-TCP ceramic had potential to be used for bone defect repair.     

Effect of glass–ceramic microstructure on its in vitro bioactivity

Two routes were used to obtain a glass–ceramic composed of 43.5 wt % SiO₂ – 43.5 wt % CaO – 13 wt % ZrO₂. Heat treatment of a glass monolith produced a glass–ceramic (WZ1) containing wollastonite-2M and tetragonal zirconia as crystalline phases. The WZ1 did not display bioactivity in vitro. Ceramizing the glass via powder technology routes formed a bioactive glass–ceramic (WZ2). The two glass–ceramics, WZ1 and WZ2, were composed of the same crystalline phases, but differed in microstructure. The in vitro studies carried out on WZ2 showed the formation of an apatite-like layer on its surface during exposure to a simulated body fluid. This paper examined the influence of both chemical and morphological factors on the in vitro bioactivitity. The interfacial reaction product was examined by scanning and transmission electron microscopy. Both instruments were fitted with energy-dispersive X-ray analyzers. Measurements of the pH made directly at the interface of the two glass–ceramics were important in understanding their different behavior during exposure to the same physiological environment.     

Microstructure–toughness relationships in calcium aluminate cement–polymer composites using instrumented scratch testing

We investigate the influence of the microstructure on the fracture properties of calcium aluminate cement/polymer composites. We carry out microscopic scratch tests during which a Rockwell C diamond probe pushes across the surface of a polished specimen under a linearly increasing vertical force. We extend the scratch fracture method to heterogeneous materials. The scratch test induces a ductile-to-brittle transition as the penetration depth increases. Scanning electron microscopy imaging shows that the low porosity and the strong cement-binder interphase favor toughening mechanisms such as crack trapping and bridging. Nonlinear fracture mechanics theory yields the fracture toughness in the fracture-driven regime. The fracture toughness of macro-defect-free (MDF) cement is found to decrease as the polymer-to-cement ratio increases. This decrease in the fracture resistance can be explained by the decrease in anhydrous cement content and the increase in the inter-particle distance between cement grains. By evaluating the fracture toughness of the micro-constituents of MDF cement, we show that the high value of the fracture toughness at the composite level stems from tough calcium aluminate phases and a highly packed non-porous granular microstructure.     

Solvent effect on the sol–gel synthesis of lithium aluminate

Lithium aluminate was prepared from different alcohols as solvents. Aluminum sec-butoxide was dissolved with ethyl, isopropyl or n-butyl alcohol and hydrolyzed simultaneously with LiOH. The resulting solids were characterized by XRD, DTA, TGA and SEM. Lithium aluminates were also prepared by fusion and peroxide methods as comparison in thermal behavior. It was found that the precursors are semi-cristalline Al-Li mixed carbonates if ethyl or isopropyl alcohol was used, whereas a highly cristalline Al–Li hydroxyl was obtained with the n-butyl alcohol. In the ethyl and isopropyl calcined preparations (800°C), the carbonates were partially eliminated, while the highest yield of γ-LiAlO₂ phase was obtained in the n-butyl sample.     

Synthesis and properties of bone cement materials in the calcium phosphate–calcium sulfate system

We have studied the influence of the cement liquid composition and the relationship between the components of the calcium sulfate–precipitated calcium phosphate system in a wide concentration range on the setting time, phase composition, microstructure, and mechanical properties of cement materials. The results demonstrate that the greatest promise is held by a magnesium phosphate-based cement liquid which, when mixed with powder, forms a high-strength phase, leading to a considerable increase in the strength of the cements. The addition of 20 wt % calcium sulfate to the starting mixture ensures dispersion hardening of the cements. We have obtained new cement materials offering a strength of up to 60 MPa, which are expected to find medical applications.     

Composition and properties of silver-containing calcium carbonate–calcium phosphate bone cement

The introduction of silver, either in the liquid phase (as silver nitrate solution: Ag(L)) or in the solid phase (as silver phosphate salt: Ag(S)) of calcium carbonate–calcium phosphate (CaCO₃–CaP) bone cement, its influence on the composition of the set cement (C-Ag(L) and C-Ag(S) cements with a Ca/Ag atomic ratio equal to 10.3) and its biological properties were investigated. The fine characterisation of the chemical setting of silver-doped and reference cements was performed using FTIR spectroscopy. We showed that the formation of apatite was enhanced from the first hours of maturation of C-Ag(L) cement in comparison with the reference cement, whereas a longer period of maturation (about 10 h) was required to observe this increase for C-Ag(S) cement, although in both cases, silver was present in the set cements mainly as silver phosphate. The role of silver nitrate on the setting chemical reaction is discussed and a chemical scheme is proposed. Antibacterial activity tests (S. aureus and S. epidermidis) and in vitro cytotoxicity tests (human bone marrow stromal cells (HBMSC)) showed that silver-loaded CaCO₃–CaP cements had antibacterial properties (anti-adhesion and anti-biofilm formation) without a toxic effect on HBMSC cells, making C-Ag(S) cement a promising candidate for the prevention of bone implant-associated infections.     

Effect of fluoride coating on in vitro dynamic degradation of Mg–Zn alloy

A compact and flat fluoride coating with some pores was prepared on a Mg–Zn alloy in order to control its degradation behavior. The electrochemical tests demonstrated that the real impedance (Z_re) of the fluoride-coated Mg–Zn was approximately 10 times as large as that of the untreated alloy. The free corrosion potential (E_corr), compared to that of the uncoated Mg–Zn alloy, increased 646 mV for the coated metal. The free corrosion current (I_corr) of the Mg–Zn specimen with the fluoride film was about one tenth of that of the uncoated one. The in vitro dynamic degradation tests showed that the average weight loss of the fluoride-coated Mg–Zn was lower than that of the untreated alloy in the initial 4 h of the tests, indicating the film could function as a barrier coating on Mg–Zn matrix. However, the coating cracked and peeled severely after 4 h dynamic tests, which implied that the fluoride coating could not endure the sustaining washing of the modified simulated body fluid.     

Microstructure,mechanical properties,and in vitro biocompatibility of spark plasma sintered hydroxyapatite–aluminum oxide–carbon nanotube composite

In the present work, HA reinforced with Al₂O₃ and multiwalled carbon nanotubes (CNTs) is processed using spark plasma sintering (SPS). Vickers micro indentation and nanoindentation of the samples revealed contrary mechanical properties (hardness of 4.0, 6.1, and 4.4 GPa of HA, HA–Al₂O₃ and HA–Al₂O₃–CNT samples at bulk scale, while that of 8.0, 9.0, and 7.0 GPa respectively at nanoscale), owing to the difference in the interaction of the indenter with the material at two different length scales. The addition of Al₂O₃ reinforcement has been shown to enhance the indentation fracture toughness of HA matrix from 1.18 MPa m^1/2 to 2.07 MPa m^1/2. Further CNT reinforcement has increased the fracture toughness to 2.3 times (2.72 MPa m^1/2). In vitro biocompatibility of CNT reinforced HA–Al₂O₃ composite has been evaluated using MTT assay on mouse fibroblast L929 cell line. Cell adhesion and proliferation have been characterized using scanning electron microscopy (SEM), and have been quantified using UV spectrophotometer. The combination of cell viability data as well as microscopic observations of cultured surfaces suggests that SPS sintered HA–Al₂O₃–CNT composites exhibit the ability to promote cell adhesion and proliferation on their surface and prove to be promising new biocompatible materials.     

The influence of multiscale fillers on the rheological and mechanical properties of carbon-nanotube–silica-reinforced epoxy composite

Multiscale fillers were fabricated through synthesis of carbon nanotubes (CNTs) on silica microparticles by the use of chemical vapor deposition. Three types of catalyst precursors with different concentrations and reaction times were investigated to find the optimal conditions for CNT synthesis. The produced multiscale fillers of CNT–silica were incorporated within epoxy resin to fabricate a multiscale composite. Rheological analysis and tensile and impact tests were performed to study the effect of fillers on the structural properties of composites. The rheological results demonstrated a similar viscous behavior between CNT–silica suspensions and epoxy, which implies that there was no critical increase of viscosity. Significant improvements in the elastic modulus and tensile and impact strength were achieved for epoxy matrix filled with the optimal fraction of multiscale fillers. The reinforcing efficiency of multiscale fillers was evaluated by comparing the results of micromechanical models with experimental data.     

Effect of solvents on the preparation of lithium aluminate by sol–gel method

γ-Lithium aluminate was prepared by sol–gel method using lithium methoxide and aluminum-sec-butoxide precursors in i-propanol, n- and tert-butanol. Clear gels could be obtained due to the addition of ethylacetoacetate and the dried solids were calcined at 550 and 900 °C. The resulting solids were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermo-gravimetric analysis/differential thermal analysis (TGA/DTA). γ-Lithium aluminate with the highest purity was obtained with t-butanol solvent and LiAl₅O₈ was the second major phase.     

The influence of target stoichiometry on early cell adhesion of co-sputtered calcium–phosphate surfaces

The nature of the initial interaction between calcium phosphate (Ca–P) thin films and osteoblasts can be influenced by a number of different properties including the phase, crystallinity, stoichiometry and composition of the surface. There is still a strong interest in developing and studying Ca–P surfaces that have the ability to accurately control the osteoblast response. Radio frequency (RF) magnetron sputtering is a technique that allows for accurate control of the properties of deposited Ca–P coatings and has been studied extensively because of this fact. In this work, Ca–P coatings were co-deposited using RF magnetron sputtering in order to study the effect of changing the target stoichiometry on the initial in vitro behavior of MG63 osteoblast-like cells. The samples produced were analysed both as-deposited and after thermal annealing to 500 °C. After annealing XPS analyses of the samples co-deposited using tricalcium phosphate (TCP) materials gave a Ca/P ratio of 1.71 ± 0.01, as compared to those co-deposited from hydroxyapatite (HA) materials, with a Ca/P of 1.82 ± 0.06. In addition to this, the curve fitted XPS data indicated the presence of low levels of carbonate in the coatings. Despite this the XRD results for all of the annealed coatings were shown to be characteristic of pure HA with a preferred 002 orientation. The atomic force microscopy results also highlighted that both types of coatings had surface features of a similar size (200–220 nm). Both surfaces exhibited a degree of surface degradation, even after 1 h of cell culture. However, the TCP derived surfaces showed an enhanced osteoblastic cell response in terms of cell adhesion and cell proliferation in the earlier stages of cell culture than the surfaces deposited from HA. An improvement in the initial cell attachment and a potential for increased cell proliferation rates is viewed as a highly advantageous result in relation to controlling the osteoblast response on these surfaces.     

Study on the mechanical performance and application of the composite cement–asphalt mixture

The rigidity of matrix mixture asphalt (MMA) is increased by the combination with cement mortar, and the performance of asphalt pavement has been better changed in the stabilities of high temperature rut and low temperature cracking and water damage. The research problems in this project mainly focus on the combinations among cement mortar and MMA and mechanical performance of composite cement–asphalt mixture (CCAM), etc. In the project, the CCAM is produced by pouring cement mortar into MMA, and the mechanical performance of CCAM has been researched. The research contents include the production technology and mechanical performance and construction technology of CCAM. Through the test data of CCAM in the mechanical performance, and compared with the performance of AC-16 MMA, the paper has analysed the mechanical performance and application of CCAM in high temperature rut and low temperature cracking and water damage, the components design and production technology and construction technology of CCAM have been put forward. The rigidity of MMA has been improved and the mechanical performance of CCAM has also met the design standards, it is suggested that CCAM can be applied as a new composite pavement materials.     

The preparation and mechanical properties of carbon–carbon/lithium–aluminum–silicate composite joints

Silica carbide modified carbon cloth laminated C–C composites have been successfully joined to lithium–aluminum–silicate (LAS) glass–ceramics using magnesium–aluminum–silicate (MAS) glass–ceramics as interlayer by vacuum hot-press technique. The microstructure, mechanical properties and fracture mechanism of C–C/LAS composite joints were investigated. SiC coating modified the wettability between C–C composites and LAS glass–ceramics. Three continuous and homogenous interfaces (i.e. C–C/SiC, SiC/MAS and MAS/LAS) were formed by element interdiffusions and chemical reactions, which lead to a smooth transition from C–C composites to LAS glass–ceramics. The C–C/LAS joints have superior flexural property with a quasi-ductile behavior. The average flexural strength of C–C/LAS joints can be up to 140.26 MPa and 160.02 MPa at 25 °C and 800 °C, respectively. The average shear strength of C–C/LAS joints achieves 21.01 MPa and the joints are apt to fracture along the SiC/MAS interface. The high retention of mechanical properties at 800 °C makes the joints to be potentially used in a broad temperature range as structural components.     

The effect of adding organic polymers on the handling properties, strengths and bioactivity of a Ca–Sr–Zn–Si glass polyalkenoate cement

This work demonstrates the addition of a number of naturally occurring proteins/polymers to a zinc based glass polyalkenoate cements (GPCs). Chitin (Chi.), collagen (Col.), cysteine (Cys.) and keratin (Ker.) were added with the intention of improving the bioactivity of this cement. Initial testing involved characterization of the glass with X-ray diffraction (XRD) and differential thermal analysis (DTA) before and after sterilization with γ-irradiation. No significant changes occurred as a result of sterilization. Handling properties of the modified cements were not significantly different from those of the control, BT 101 (Working T _w—36 s, and setting time T _s—70 s) except for Chi. (30 s, p ≤ 0.016) and Cys. (105 s, p ≤ 0.0001) respectively. Comparison of the mechanical properties of BT 101 (compression—σ_c and biaxial flexural—σ_f) to the modified cements revealed a significant decrease in σ_c with Chi. and Col., after 1, 7 and 30 days. However, there were little changes occurring in σ_f. Cement structural testing was investigated and found that the addition of these polymers greatly reduced the cements surface area, however, the only significant change to occur in the solubility testing was Ker. (p ≤ 0.009). Simulated body fluid (SBF) testing resulted in increased calcium phosphate (CaP) deposition of Chi. and Col. compared to BT 101. Cell culture studies determined only Col. significantly increased (p ≤ 0.0001) in comparison to the control cement.     

Preparation of graded zirconia–CaP composite and studies of its effects on rat osteoblast cells in vitro

Hydroxyapatite (HAP) has excellent biocompatibility and bone bonding ability, but it is mechanically weak and brittle. To overcome this problem, we prepared a graded composite with calcium phosphide (CaP, decomposed from HAP during sintering) coating on the surface of zirconia (ZrO₂) ceramics. The mechanical properties and microstructure characteristics were studied with various techniques. The biocompatibility of graded ZrO₂–CaP composite was examined with rat osteoblast cells (OB cells) in vitro. Its effects on the production of alkaline phosphatase (ALP), Interleukin-6 (IL-6) and Growth-transforming Factor-β (TGF-β) by the OB cells were measured. The results showed that the mean tensile strength of the graded ZrO₂–CaP composites was 17.8 MPa, the maximum bending strength was 1112.24 MPa, and K_IC was 7.3–11.4 MPa·m^1/2, indicating that the composite was physically strong for use as an implant material. The ALP activity, IL-6 and TGF-β concentrations of the graded composite treated OB cells were much higher than that of the pure ZrO₂ treated group. There was no significant difference in ALP activity, the IL-6 and TGF-β concentrations between the graded ZrO₂–CaP composite group and HAP. The cytotoxicity of the composite material to rat fibroblast cells was insignificant. The graded zirconia–CaP composite greatly facilitated the proliferation and differentiation of rat OB cells in vitro, demonstrating excellent biocompatibility.