The effect of composition on ion release from Ca–Sr–Na–Zn–Si glass bone grafts

Controlled delivery of active ions from biomaterials has become critical in bone regeneration. Some silica-based materials, in particular bioactive glasses, have received much attention due to the ability of their dissolution products to promote cell proliferation, cell differentiation and activate gene expression. However, many of these materials offer little therapeutic potential for diseased tissue. Incorporating trace elements, such as zinc and strontium, known to have beneficial and therapeutic effects on bone may provide a more viable bone graft option for those suffering from metabolic bone diseases such as osteoporosis. Rational compositional design may also allow for controlled release of these active ions at desirable dose levels in order to enhance therapeutic efficacy. In this study, six differing compositions of calcium–strontium–sodium–zinc–silicate (Ca–Sr–Na–Zn–Si) glass bone grafts were immersed in pH 7.4 and pH 3 solutions to study the effect of glass composition on zinc and strontium release in a normal and extreme physiological environment. The zinc release levels over 30 days for all zinc-containing glasses in the pH 7.4 solution were 3.0–7.65 ppm. In the more acidic pH 3 environment, the zinc levels were higher (89–750 ppm) than those reported to be beneficial and may produce cytotoxic or negative effects on bone tissue. Strontium levels released from all examined glasses in both pH environments similarly fell within apparent beneficial ranges—7.5–3500 ppm. Glass compositions with identical SrO content but lower ZnO:Na₂O ratios, showed higher levels of Sr²⁺ release. Whereas, zinc release from zinc-containing glasses appeared related to ZnO compositional content. Sustainable strontium and zinc release was seen in the pH 7.4 environment up to day 7. These results indicate that the examined Ca–Sr–Na–Zn–Si glass compositions show good potential as therapeutic bone grafts, and that the graft composition can be tailored to allow therapeutic levels of ions to be released.     

Hydrogel/bioactive glass composites for bone regeneration applications: Synthesis and characterisation

Due to the deficiencies of current commercially available biological bone grafts, alternative bone graft substitutes have come to the forefront of tissue engineering in recent times. The main challenge for scientists in manufacturing bone graft substitutes is to obtain a scaffold that has sufficient mechanical strength and bioactive properties to promote formation of new tissue. The ability to synthesise hydrogel based composite scaffolds using photopolymerisation has been demonstrated in this study. The prepared hydrogel based composites were characterised using techniques including Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray spectrometry (EDX), rheological studies and compression testing. In addition, gel fraction, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), porosity and swelling studies of the composites were carried out. It was found that these novel hydrogel bioglass composite formulations did not display the inherent brittleness that is typically associated with bioactive glass based bone graft materials and exhibited enhanced biomechanical properties compared to the polyethylene glycol hydrogel scaffolds along. Together, the combination of enhanced mechanical properties and the deposition of apatite on the surface of these hydrogel based composites make them an ideal candidate as bone graft substitutes in cancellous bone defects or low load bearing applications.     

Preparation of the Silver-Superconductor Composite by Deposition of the Silver Nanoparticles in the Bismuth Cuprate Superconductor

BiSCCO (Bi–Sr–Ca–Cu–O) is high temperature superconductor with a lot of possible applications. Interfaces between superconductors and metal conductors are one of the technological problems. In this work, silver-superconductor composite was prepared by using flow of silver nanoparticles suspension in DMF (N,N-dimethylformamide) through superconductor’s pore system. Silver nanoparticles were prepared by reaction of silver nitrate with DMF. Properties of prepared composite were measured by SEM charting, XRD and critical current measurements. SEM chart showed uniform distribution of silver across sample. XRD and critical current measurements validated superconducting properties of prepared composite. In the future, materials based on this method could be used as an interface between superconductors and metals or as a base for superconducting composite with much better mechanical properties.     

Development and performance analysis of PCL/silica nanocomposites for bone regeneration

In the present article, several developments of biocomposites containing silica nanoparticles intended for bone regeneration are reported. Nanocomposites of poly(ε-caprolactone) (PCL) and silica, in which either the silica nanoparticles or the PCL have been modified in order to improve interfacial adhesion through chemical graft between the phases are hereafter described. The composites are characterized with respect to their chemical–physical and mechanical properties. Their biocompatibility and capacity to induce the osteoblastic phenotype in human bone marrow mesenchymal stem cells have been assessed.     

Low temperature fabrication of high strength porous calcium phosphate and the evaluation of the osteoconductivity

Porous NaO₂–MgO–CaO–P₂O₅ bioglass doped beta-tri-calcium phosphate (β-TCP) bioceramic possessing high mechanical properties and well pore structure with high porosity and high pore connectivity has been prepared through dipping method with the porous polyurethane as the pore forming template. The sintering mechanism and the mechanical properties of the bioglass doped β-TCP scaffold have been investigated by the X-ray diffraction (XRD) analysis, Scanning electron microscope (SEM) and thermal differential analysis (DTA). The scaffold’s in vivo osteoconductivity has been evaluated by implantation of scaffolds into the femurs of New Zealand rabbits. The results show that the porous structure can achieve the densification process at a low temperature about 950°C by a solid solution sintering mechanism and hence dense macropore scaffold with a compressive strength of 4.32 MPa when the porosity is 75% has been obtained. The in vivo test shows that the Na₂O–MgO–CaO–P₂O₅ bioglass doped porous β-TCP bioceramic has a relatively fast bone formation after implantation; after 1 month implantation new deposited bone tissue has been detected on the strut of the porous scaffold and degraded particles also has been found on the surface of the new formed bone. After 6 months implantation the porous scaffold has been thoroughly covered with new formed bone. Results show that the Na₂O–MgO–CaO–P₂O₅ bioglass doped porous β-TCP bioceramic is potential bone tissue engineering scaffold for orthopedic use.     

Effect of compound organification of montmorillonite on the structure and properties of polypropylene/montmorillonite nanocomposites

In this paper, reactive organic montmorillonite (RMMT), prepared with compound alkylammoniums, were used in ternary-monomer solid phase graft copolymerization in order to enhance the melting intercalation of montmorillonite (MMT), stabilize the intercalated structure, and prepare the exfoliated polypropylene/montmorillonite (PP/MMT) nanocomposites (PPMN). The structure and properties of PPMN were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), etc. Results show that the compound organification, solid phase graft copolymerization really favored the melting intercalation. The compound organification and exothermic process of the solid phase copolymerization promoted the melting intercalation. The mechanical properties, melt flow rate and Vicat softening point of PPMN significantly had a preferable reinforced state at 6–8 phr PP/MMT graft copolymers (PPGM). The increase of the mechanical properties and thermal properties was owed to the reinforcement of the exfoliated MMT and the compatibilization of the oligomers built by the polar monomers during the solid phase graft copolymerization. The improvement of the fluidity of PPMN derived from the plasticization of the exfoliated MMT and oligomers. Translated from Chinese Journal of Materials Research, 2006, 20(2): 197–202 [译自: 材料研究学报]     

Effect of processing parameters on the microstructure and mechanical behavior of silica-calcium phosphate nanocomposite

Silica-calcium phosphate nanocomposite (SCPC) is a bioactive ceramic characterized by superior bone regenerative capacity and resorbability when compared to traditional bioactive ceramics. The aim of the present study is to evaluate the effect of processing parameters on the microstructure and mechanical properties of SCPC. Cylinders were prepared by pressing the ceramic powder at 200, 300 or 400 MPa and sintering at 900, 1000 or 1100°C for 3 h, respectively. XRD results indicate that the crystalline structure of the material is made of β-NaCaPO₄ and α-cristobalite solid solutions. The increase in sintering temperature results in an increase in the grain size and the formation of a melting phase that coats the grains. TEM analyses reveal that the melting phase is amorphous and rich in silicon. The mechanical properties of SCPC cylinders are dependent on the content of the melting phase and the microstructure of the material. The ranges of compressive strength and modulus of elasticity of the SCPC are 62–204 MPa and 6–14 GPa, respectively, which are comparable to those of cortical bone. The results suggest that the interaction between crystalline and amorphous phases modulated the mechanical behavior of SCPC. It is possible to engineer the mechanical properties of SCPC by controlling the processing parameters to synthesize various fixation devices for orthopedic and cranio-maxillofacial applications.     

Biodegradable and semi-biodegradable composite hydrogels as bone substitutes: morphology and mechanical characterization

Biodegradable and semi-biodegradable composite hydrogels are proposed as bone substitutes. They consist of an hydrophilic biodegradable polymer (HYAFF 11) as matrix and two ceramic powders (α-TCP and HA) as reinforcement. Both components of these composites have been of great interest in biomedical applications due to their excellent biocompatibility and tissue interactions, however they have never been investigated as bone substitute composites. Morphological and mechanical analysis have shown that the two fillers behave in a very different way. In the HYAFF 11/α-TCP composite, α-TCP is able to hydrolyze in contact with water while in the HYAFF 11 matrix. As a result, the composite sets and hardens, and entangled CDHA crystals are formed in the hydrogel phase and increases in the mechanical properties are obtained. In the HYAFF11/HA composite the ceramic reinforcement acts as inert phase leading to lower mechanical properties. Both mechanical properties and microstructure analysis have demonstrated the possibility to design hydrophilic biodegradable composite structures for bone tissue substitution applications.     

Hyaluronan-based heparin-incorporated hydrogels for generation of axially vascularized bioartificial bone tissues: in vitro and in vivo evaluation in a PLDLLA–TCP–PCL-composite system

Smart matrices are required in bone tissue-engineered grafts that provide an optimal environment for cells and retain osteo-inductive factors for sustained biological activity. We hypothesized that a slow-degrading heparin-incorporated hyaluronan (HA) hydrogel can preserve BMP-2; while an arterio–venous (A–V) loop can support axial vascularization to provide nutrition for a bio-artificial bone graft. HA was evaluated for osteoblast growth and BMP-2 release. Porous PLDLLA–TCP–PCL scaffolds were produced by rapid prototyping technology and applied in vivo along with HA-hydrogel, loaded with either primary osteoblasts or BMP-2. A microsurgically created A–V loop was placed around the scaffold, encased in an isolation chamber in Lewis rats. HA-hydrogel supported growth of osteoblasts over 8 weeks and allowed sustained release of BMP-2 over 35 days. The A–V loop provided an angiogenic stimulus with the formation of vascularized tissue in the scaffolds. Bone-specific genes were detected by real time RT-PCR after 8 weeks. However, no significant amount of bone was observed histologically. The heterotopic isolation chamber in combination with absent biomechanical stimulation might explain the insufficient bone formation despite adequate expression of bone-related genes. Optimization of the interplay of osteogenic cells and osteo-inductive factors might eventually generate sufficient amounts of axially vascularized bone grafts for reconstructive surgery.     

Structure and properties of novel electrospun tussah silk fibroin/poly(lactic acid) composite nanofibers

The tussah silk fibroin (TSF)/poly(lactic acid) (PLA) composite nanofibers with different composition ratios were prepared by electrospinning with 1,1,1,3,3,3-Hexafluoro-2-propanol as the solvent. The morphology and secondary structure of the fibers were characterized by Scanning electronic microscope, Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The thermal and mechanical tests were also performed. The spinnability of TSF solution was improved significantly through adding 10% PLA, and the average diameter of the fibers decreased from 583 nm to 178 nm with an obvious improvement in fiber diameter uniformity. In addition, the mechanical properties of electrospun nanofibers increased evidently after blending 10% PLA, whereas the thermal properties kept stable. FTIR and XRD analysis indicated the addition of 5% PLA could induce a conformation transformation of TSF from random coil and α-helix to β-sheet, however, when PLA content was more than 10%, the β-sheet structure of TSF in composite nanofibers decreased, and the phase separation of two compositions occurred. Therefore, when PLA content exceeded 15%, the average diameters of TSF/PLA composite nanofibers increased and appeared to be polarized, moreover, the mechanical properties of the fibers decreased with the increase of PLA content, and the fibers displayed the mechanical behavior of PLA component more.     

Comparison of an experimental bone cement with a commercial control, Hydroset™

Glass polyalkenoate cements based on strontium calcium zinc silicate glasses (Zn-GPCs) and high molecular weight polyacrylic acids (PAA) (MW; 52,000–210,000) have been shown to exhibit mechanical properties and in vitro bioactivity suitable for arthroplasty applications. Unfortunately, these formulations exhibit working times and setting times which are too short for invasive surgical applications such as bone void filling and fracture fixation. In this study, Zn-GPCs were formulated using a low molecular weight PAA (MW; 12,700) and a modifying agent, trisodium citrate dihydrate (TSC), with the aim of improving the rheological properties of Zn-GPCs. These novel formulations were then compared with commercial self-setting calcium phosphate cement, Hydroset™, in terms of compressive strength, biaxial flexural strength and Young’s modulus, as well as working time, setting time and injectability. The novel Zn-GPC formulations performed well, with prolonged mechanical strength (39 MPa, compression) greater than both vertebral bone (18.4 MPa) and the commercial control (14 MPa). However, working times (2 min) and rheological properties of Zn-GPCs, though improved, require further modifications prior to their use in minimally invasive surgical techniques.     

Sol–gel method to fabricate CaP scaffolds by robocasting for tissue engineering

Highly porous calcium phosphate (CaP) scaffolds for bone-tissue engineering were fabricated by combining a robocasting process with a sol–gel synthesis that mixed Calcium Nitrate Tetrahydrate and Triethyl Phosphite precursors in an aqueous medium. The resulting gels were used to print scaffolds by robocasting without the use of binder to increase the viscosity of the paste. X-ray diffraction analysis confirmed that the process yielded hydroxyapatite and β-tricalcium phosphate biphasic composite powders. Thus, the scaffold composition after crystallization of the amorphous structure could be easily modified by varying the initial Ca/P ratio during synthesis. The compressive strengths of the scaffolds are ~6 MPa, which is in the range of human cancellous bone (2–12 MPa). These highly porous scaffolds (~73 vol% porosity) are composed of macro-pores of ~260 μm in size; such porosity is expected to enable bone ingrowth into the scaffold for bone repair applications. The chemistry, porosity, and surface topography of such scaffolds can also be modified by the process parameters to favor bone formation. The studied sol–gel process can be used to coat these scaffolds by dip-coating, which induces a significant enhancement of mechanical properties. This can adjust scaffold properties such as composition and surface morphology, which consequently may improve their performances.     

Processing and compression testing of Ti6Al4V foams for biomedical applications

Open cell Ti6Al4V foams (60% porosity) were prepared at sintering temperatures between 1,200 and 1,350 °C using ammonium bicarbonate particles (315–500 μm) as space holder. The resulting cellular structure of the foams showed bimodal pore size distribution, comprising macropores (300–500 μm) and micropores (1–30 μm). Compression tests have shown that increasing sintering temperature increased the elastic modulus, yield and compressive strength, and failure strain of foams. The improvements in the mechanical properties of foams prepared using smaller size Ti64 powder with bimodal particle distribution were attributed to the increased number of sintering necks and contact areas between the particles. Finally, the strength of foams sintered at 1,350 °C was found to satisfy the strength requirement for cancellous bone replacement.     

Effect of anorthite and diopside on dielectric properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/glass composite based on high strength of LTCC substrate

The green sheet of an alumina filler/glass matrix, which is a glass–ceramic based on an anorthite and diopside composite, is a low-fired substrate material for microelectronic packaging. In this study, alumina/glass sheets were prepared using a tape-casting process. The mechanical and dielectric properties of the sintered bodies were examined as a function of the sintering temperature. The volume of the crystalline phases was considered with the peak area of the XRD intensity for evaluating the alumina/glass composite. The flexural strength and dielectric properties of the sintered alumina/glass composites were 167.2 ± 13.1 MPa for the four-point bending test, 5.51 for the dielectric constant and 2,078 MHz for the quality factor, respectively. The dielectric constant was dependent on the volume of crystalline phases present. Jinho Kim and Seongjin Hwang equally contributed to the article.     

Mesoporous titania–silica composite from sodium silicate and titanium oxychloride. Part I: grafting method

In this study, we report a versatile method for designing a titania–silica composite using relatively inexpensive precursors. The composite was synthesized by grafting (impregnating) a precursor of a guest component into the preformed host’s solid network. The latter was prepared using sodium silicate as a silica precursor in the presence of cetyltrimethylammonium bromide (CTAB). A freshly prepared solution of titanium oxychloride (TiOCl₂, titania precursor that is relatively stable) was introduced into the host’s network to develop a titania–silica composite with initial ratio of Ti:Si = 1. The final product has the overall ratio of Ti:Si = 7:3 and was obtained after calcination for 5 h at 600–1000 °C. The XRD patterns for the calcined samples indicate the presence of TiO₂, and there was a significant increase in peak intensity as the calcination temperature increased. EDS, XRF, and FT-IR analyses indicated the formation of a highly pure composite rich in Ti, Si, and O. A Si–O–Ti band at 954 cm⁻¹ was observed, confirming the formation of a titania–silica composite. A composite with optimum properties (homogenous dispersion of the composite and less individual oxide phase separation) was obtained at 600 °C. A similar experiment was also conducted in the absence of CTAB. In this case, the final product was microporous, rendering it unsuitable for some applications.     

TiO<Subscript>2</Subscript>/graphene composite from thermal reaction of graphene oxide and its photocatalytic activity in visible light

In this study, the P25 TiO₂ nanoparticles and graphene sheets (GSs) composite were prepared from a facile thermal reaction of graphene oxide. Its microstructures and photocatalytic properties were characterized and measured using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) specific area analysis, X-ray photoelectron spectroscopy (XPS), FT-IR spectra, and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy. Compared with pure P25 nanoparticles, the results reveal that (1) there is a red shift about 20 nm in the absorption edge of the P25/graphene composite; (2) the photocurrent of the composite is about 15 times higher than that of pure P25; (3) the visible light photocatalytic activity of the composite is enhanced greatly on decomposition of methylene blue (MB). The photocatalytic mechanism of the P25/graphene composite is also discussed.     

Mechanical and degradation behavior of polymer-calcium sulfate composites

Calcium sulfate (CS) is one of the oldest bone graft materials still in use. Its main limitations are poor handling characteristics, poor mechanical properties, and a resorption rate that is too fast for some applications. The present study investigated the effect of viscous polymers, such as carboxymethylcellulose (CMC) and hyaluronan (HY), on the handling characteristics, mechanical properties, and degradation behavior of CS. CMC and HY were added to CS at concentrations from 1–10 wt%. Addition of CMC to CS at more than 4 wt% produced a putty-like material and decreased the density of the composite, while also increasing flexural and compressive strength at higher loadings. Incorporation of CMC produced a concentration-dependent increase in water absorption and degradation rate. At an equivalent loading, HY-containing CS composites showed better compressive strength than CS with CMC. Overall, addition of CMC or HY to CS resulted in composite materials with better handling characteristics and improved mechanical properties after set, however the degradation rate of the augmented materials was increased. These properties suggest that the enhanced CS materials may be useful in certain clinical situations, such as filling non-uniform bone defects and situations that require mechanical integrity of the bone graft substitute during implantation.     

Preparation and characterization of dense nanohydroxyapatite/PLLA composites

Synthetic bone graft substitutes based on PLLA have been largely studied during the past decade. PLLA/hydroxyapatite composites appear as promising materials for large bone defect healing. In this study dense PLLA/nano-hydroxyapatite composites were prepared by hot pressing. Dense samples were investigated rather than porous scaffolds, in order to shed light on possible correlations between intrinsic mechanical properties and nano-hydroxyapatite concentration. Hydroxyapatite deagglomerated by wet attrition milling, and further dispersed into chloroform was used (median diameter = 80 nm). Particle size distribution measurements and transmission electron microscopy show evidence that particle size and dispersion are maintained throughout the successive steps of composite processing. Mechanical properties were tested (uni-axial and diametral compression tests) as a function of nano-hydroxyapatite content. Increasing concentrations of nano-hydroxyapatite (0, 25 and 50 wt.%) increase the Young's modulus and the mechanical strength of the composite; at the same time, the failure mechanism of the material changes from plastic to brittle. Young's modulus over 6 GPa and uniaxial compressive strength over 100 MPa have been achieved. These values expressed in terms of intrinsic tensile and shear strengths indicate that 50 wt.% nano-hydroxyapatite containing samples develop properties comparable to those of cortical bone. PLLA/nano-hydroxyapatite composites are thus promising candidates to develop bioresorbable porous bone substitutes showing superior mechanical performance.     

Needle-like nano hydroxyapatite/poly(l-lactide acid) composite scaffold for bone tissue engineering application

In this paper, a new nano-hydroxyapatite / poly (l-lactide acid) (nHAP/PLLA) composite scaffold comprising needle-like nHAP particles was prepared. In the first step, the identification and morphology of chemically synthesized HAP particles were determined by XRD, EDX, FTIR and SEM analyses. The needle-like nHAP particles with an average size of approximately 30–60 nm in width and 100–400 nm in length were found similar to needle-like bone nano apatites in terms of chemical composition and morphology. In the second step, nHAP and micro-sized HAP (mHAP) particles were used to fabricate HAP filled PLLA (HAP/PLLA) composites scaffolds using solid–liquid phase separation method. The porosity of scaffolds was up to 85%, and their average macropore diameter was in the range of 64–175 µm. FTIR and XRD analyses showed the presence of molecular interactions and chemical linkages between HAP particles and PLLA matrix. The compressive strength of nanocomposite scaffolds could high up to 8.46 MPa while those of pure PLLA and microcomposite scaffolds were 1.79 and 4.61 MPa, respectively. The cell affinity and cytocompatibility of the nanocomposite scaffold were found to be higher than those of pure PLLA and microcomposite scaffolds. Based on the results, the newly developed nHAP/PLLA composite scaffold is comparable with cancellous bone in terms of microstructure and mechanical strength, so it may be a suitable alternative for bone tissue engineering applications.     

OTS-modified HA and its toughening effect on PLLA/HA porous composite

In this paper, hydroxyapatite (HA) particles was modified with long-chain organic silane-Octadecyltrichlorosilane (OTS), and the modified particles were further used for preparing Poly(l-lactic acid) PLLA/HA porous composite. The modified particles were characterized by means of XRD, FTIR, and XPS techniques. Both XPS and FTIR results showed that OTS had been combined with HA, and the formation of P–O–Si bond, a covalent bond, on the HA particle surface was confirmed by XPS. OTS-modified HA particles were used to prepare porous composites by thermally induced phase separation method. The results showed that the composite had an interconnected pore structure with 100–300 μm macropores. With OTS dosage increasing during modification, the mechanical properties of PLLA/OTS-modified HA porous composites increased obviously. These results showed that OTS modification can effectively improve the interface compatibility between HA surface and PLLA.