Degradation behavior of novel Fe/ß-TCP composites produced by powder injection molding for cortical bone replacement

When it comes to bone replacement in load-bearing areas, there are currently no adequate biodegradable implants available. Several non-degradable metallic materials fulfill the requirements of biocompatibility and mechanical strength. However, besides magnesium, only iron is a degradable metallic material. The aim of this long-term degradation study was to investigate the effects of iron beta-tricalcium phosphate interpenetrating phase composite on degradation rate and strength in comparison to pure iron. Cylindrical samples with 0–50 vol% beta-tricalcium phosphate (ß-TCP) were prepared by powder injection molding. In addition to dense samples, porous iron samples with a porosity of 60.3 % were produced with polyoxymethylene as a placeholder. Dense and porous samples were immersed in 0.9 % sodium chloride solution (NaCl) or in phosphate buffered saline solution (PBS) for 56 days. Following immersion, the degradation rate, compressive yield strength, and ion release were determined. A maximum degradation rate of 196 µm/year was observed after 56 days for iron with 40 vol% ß-TCP. This was found to be 28 % higher than for pure iron. After immersion, the compressive yield strength of pure iron decreased by 44 % (NaCl) and 48 % (PBS). In comparison, iron with 40 % ß-TCP samples lost <1 % (NaCl) and 9 % (PBS) of strength following immersion. It was demonstrated that the solubility of calcium phosphate enhanced the corrosion processes and led to an increase in degradation, thus showing that the addition of ß-TCP to pure iron can be a promising route for a novel degradable bone substitute material, particularly for load-bearing areas due to the increased strength.     

Role of macropore size in the mechanical properties and in vitro degradation of porous calcium phosphate cements

The goal of the present study was to investigate the effect of macropore size on the compressive strength and in vitro degradation of porous calcium phosphate cements (CPCs). For this purpose, a series of porous CPCs with three different macropore sizes (200-300 μm, 300-450 μm and 450-600 μm) and comparable porosity were prepared by salting-out method, and the study of in vitro degradation behavior was carried out under a constant fluid flow environment. The results showed that the increase in macropore size of CPCs with invariant porosity resulted in a decrease in the compressive strength but an increase in the degradation rate of CPCs significantly, suggesting the possibility that the degradation rate and compressive strength of biomaterials can be regulated by varying the macropore size while maintaining the porosity unchanged.     

Phase transformations during processing and in vitro degradation of porous calcium polyphosphates

A 2-Step sinter/anneal treatment has been reported previously for forming porous CPP as biodegradable bone substitutes [9]. During the 2-Step annealing treatment, the heat treatment used strongly affected the rate of CPP degradation in vitro. In the present study, x-ray diffraction and ³¹P solid state nuclear magnetic resonance were used to determine the phases that formed using different heat treating processes. The effect of in vitro degradation (in PBS at 37 °C, pH 7.1 or 4.5) was also studied. During CPP preparation, β-CPP and γ-CPP were identified in powders formed from a calcium monobasic monohydrate precursor after an initial calcining treatment (10 h at 500 °C). Melting of this CPP powder (at 1100 °C), quenching and grinding formed amorphous CPP powders. Annealing powders at 585 °C (Step-1) resulted in rapid sintering to form amorphous porous CPP. Continued annealing to 650 °C resulted in crystallization to form a multi-phase structure of β-CPP primarily plus lesser amounts of α-CPP, calcium ultra-phosphates and retained amorphous CPP. Annealing above 720 °C and up to 950 °C transformed this to β-CPP phase. In vitro degradation of the 585 °C (Step-1 only) and 650 °C Step-2 annealed multi-phase samples occurred significantly faster than the β-CPP samples formed by Step-2 annealing at or above 720 °C. This faster degradation was attributable to preferential degradation of thermodynamically less stable phases that formed in samples annealed at 650 °C (i.e. α-phase, ultra-phosphate and amorphous CPP). Degradation in lower pH solutions significantly increased degradation rates of the 585 and 650 °C annealed samples but had no significant effect on the β-CPP samples.     

Effect of nanosilica addition on the physicomechanical properties,pore morphology,and phase transformation of freeze cast hydroxyapatite scaffolds

Freeze casting technique is a simple and effective method for the fabrication of porous ceramic structures. The objective of this work is to study the production and characterization of hydroxyapatite/nanosilica (HA/nSiO₂) scaffolds fabricated through this method. In the experimental procedure, the solidified samples were prepared by slurries containing different concentration of HA and nSiO₂ followed by sintering procedure at 1200 and 1350 °C. The phase composition, microstructure, and compressive strength of the scaffolds were characterized by X-ray diffraction, scanning electron microscopy, and mechanical strength test. It was found that the porosity of the scaffolds was in the range of 30–86.5 % and the value of compressive strengths lied between 0.16 and 71.96 MPa which were influenced by nSiO₂ content, cooling rate, and sintering temperature. With respect to porosity, pore size, and compressive strength, the scaffolds with 5 % nSiO₂, the cooling rate of 1 °C/min and the sintering temperature of 1350 °C showed preferable results for bone tissue engineering applications.     

Mechanical modulation and bioactive surface modification of porous Ti–10Mo alloy for bone implants

The objective of this work was to fabricate a suitable porous Ti–10Mo alloy as the human bone replacement implants. The porous Ti–10Mo alloy was fabricated by mechanical alloying and then consolidated by powder metallurgy technique. NH₄HCO₃ powder was used as space-holder. It was indicated that the mean pore size, porosity, compressive strength, and elastic modulus of porous Ti–10Mo alloy could be tailored by the amount of NH₄HCO₃, and then could be matched with those of human bones. Furthermore, porous Ti–10Mo alloy was treated by alkali heat treatment and soaked in the 1.5 times simulated body fluid (1.5SBF). It was observed that the surface and the inside pore wall of porous Ti–10Mo alloy with 25 wt.% NH₄HCO₃ covered with the apatite layer after soaked in 1.5SBF for 28 days. These phenomena indicated that the surface modified porous Ti–10Mo alloy exhibited a high potential for bone-bonding, which was expected to be used as bone tissue implant.     

Powder metallurgy of the porous Ti-13Nb-13Zr alloy of different powder grain size

The objective of the present project was to determine the effects of powder granulation (fraction of grain size) for the Ti-13Nb-13Zr alloy, produced by powder metallurgy, on its porosity, grain cohesion, compressive strength, and Young`s modulus. Two powder fractions, 45–105 µm, and 106–250 µm were applied. The 50 mass pct of NH<sub>4</sub>HCO<sub>3</sub> was added as a space holder. The specimens were in compaction stage uniaxially pressed at pressure 625 MPa for 120 s. The brown bodies were sintered at a temperature 1150°C for 3.5 h. The well-joined grains were observed for both powder granulations. The increase in powder granulation resulted in an increase of porosity from 51% to 59%, and it was only 30% with no space holder used. The compressive strength increased with decreased porosity from 57 to 236 MPa. Young`s modulus was measured as 4.8 GPa for finer powder and 0.9 GPa for coarser powder. It is evident from the results obtained that the applied process parameters, the space holder and its fraction, and the use powder granulation between 45 and 105 µm bring out the porous material fulfilling mechanical and biological requirements specific of load-bearing titanium implants.     

Preparation,mechanical properties and in vitro biodegradation of porous magnesium scaffolds

Magnesium has been recently recognized as a biodegradation metal for bone substitute application. In the present work, porous magnesium foams were prepared by powder metallurgical process. The structural characteristics, mechanical properties and the in vitro biodegradation of the porous Mg specimens were investigated. These open-cellular specimens (porosities: 36–55%; pores: 200–400 μm) have the appropriate mechanical properties and the changeable in vitro degradation rates. These results suggest that the porous magnesium metals have the potential to serve as degradable implants for bone substitute applications.     

How Degradation of Calcium Phosphate Bone Substitute Materials is influenced by Phase Composition and Porosity

The chemical composition of calcium phosphate (CaP) materials for the regenerative therapy of large bone defects is similar to that of bone. Additionally, calcium phosphates show an excellent biocompatibility. Besides the support of defect healing calcium phosphate implants should be completely degraded within an adequate time period to be replaced by newly formed bone. Although degradation of CaP‐implants occurs mainly by dissolution of the material, it is important to characterize the osteoclastic resorption as well, which is involved in native bone remodeling. The degradation of bone substitutes made of calcium phosphate ceramics is influenced by various parameters, such as defect size and localization, the general health situation, and age of the patient, but also material properties are important. Especially, the calcium phosphate composition is crucial for the degradation behavior of a calcium phosphate material. Additionally, at the cellular level the micro‐ and macroporosity, including interconnecting pores, influences both, the dissolution and the osteoclastic resorption. In our study, three different calcium phosphate materials (hydroxyapatite, tricalcium phosphate, and a biphasic calcium phosphate) and two different geometries (dense 2D samples and porous 3D scaffolds) are compared regarding their dissolution and resorption behavior. The results show, that the dissolution of CaP‐ceramics, as examined by the incubation in a degradation solution, depends mainly on the calcium phosphate phase but also on the porosity of the implant. Regarding the resorption, cell proliferation and differentiation of a monocytic cell line as well as the formation of resorption lacunas are analyzed. Cell proliferation is comparable on all phase compositions. Cell differentiation and resorption, however, are influenced by the calcium phosphate phase composition and by the implant porosity as well. By understanding these two mechanisms of degradation, bone substitute materials and, as a result, the bone regeneration of large bone defects using CaP‐ceramics can be improved.     

Elaboration conditions influence physicochemical properties and in vivo bioactivity of macroporous biphasic calcium phosphate ceramics

Two different preparations of biphasic calcium phosphate (BCP) were characterized in vitro: BCP₁ from a mechanical mixture of hydroxyapatite (HA) and -tricalcium phosphate (-TCP) powders, and BCP₂ from calcination of a calcium-deficient apatite (CDA). The structural, physicochemical and mechanical parameters of these two preparations were investigated, and two different macroporous BCP₁ (MBCP₁) and BCP₂ MBCP₂) implants were manufactured and implanted in rabbit bone for in vivo bioactivity studies. Scanning electron microscopy observations showed that MBCP₁ implants had a significantly higher degradation rate (P<0.0001) than MBCP₂ implants. This was probably caused by the presence of calcium oxide impurities in BCP₁ and the more intimate mixture and stable ultrastructure of BCP₂. No significant difference about the newly formed bone rate in these two BCP preparations was observed. Very slight variations in sintering conditions appeared to influence the biodegradation behavior of the two MBCP implants despite their identical HA/-TCP ratios and similar porosity. Precise and complete in vitro characterization enabled us to understand and predict in vivo degradation behavior. © 1999 Kluwer Academic Publishers     

Enhanced repair of a critical-sized segmental bone defect in rabbit femur by surface microstructured porous titanium

Repair of load-bearing bone defects remains a challenge in the field of orthopaedic surgery. In the current study, a surface microstructured porous titanium (STPT) successively treated with H₂O₂/TaCl₅ solution and simulated body fluid was used to repair the critical-sized segmental bone defects in rabbit femur, and non-treated porous titanium (NTPT) and porous biphasic calcium phosphate ceramics (PBCP) were used as control, respectively. A 15 mm long implant was positioned in the femoral defect and stabilized by a plate and screws fixation. After implantation into the body for 1, 3 and 6 months, X-ray observation confirmed that porous titanium groups (NTPT and STPT) provided better mechanical support than PBCP group at the early stage. However, there was no obvious difference in the formed bony callus between PBCP and STPT groups in the later stage, and they both showed better shape of bony callus than NTPT group. Micro-CT and histomorphometric analysis for the samples of 6-month implantation demonstrated that more new bone formed in the inner pores of PBCP and STPT groups than that in NTPT group. Moreover, the biomechanical tests revealed that STPT group could bear larger compressive load than NTPT and PBCP groups, almost reaching the level of the normal rabbit femur. STPT exhibited the enhanced repairing effect on the critical-sized segmental bone defect in rabbit femur, meaning that it could be an ideal material for the repair of large bone defect in load-bearing site.     

Polymeric crystallization and condensation of calcium polyphosphate glass

Calcium polyphosphate (Ca(PO₃)₂)_n (CPP) is under investigation as a resorbable bone biomaterial. Sintering CPP glass particles in humid air produces a porous, interconnected, degradable, crystalline construct that is suitable for connective tissue engineering applications. Porous CPP constructs sintered at 585 °C dissolved in water more rapidly than those sintered at 950 °C. FTIR, ³¹P NMR, powder XRD, and density data for CPP glass and fully crystalline fibers were compared with data for the as-sintered and partially dissolved constructs sintered at 585 or 950 °C. The results suggest that condensation continues during sintering, and CPP glass crystallizes in a process analogous to the crystallization of linear organic polymers. During sintering, water vapor caused hydrolytic degradation of the surface polyphosphate chains, forming a surface layer with different dissolution properties than the particle interior. Thus, sintering CPP glass results in a heterogeneous crystalline product that impacts the dissolution rate of CPP as a degradable biomaterial.     

多孔Nano-dHA/PLA/BCP复合支架的制备及性能研究

为改善常规的多孔聚乳酸/双相钙磷陶瓷(PLA/BCP)支架表面亲水性不佳及降解时呈酸性等不足,采用马弗炉烧结制备的BCP多孔支架浸入纳米缺钙羟基磷灰石/聚乳酸(nano-dHA/PLA)混悬液后,真空干燥得到多孔纳米缺钙羟基磷灰石/聚乳酸/双相钙磷陶瓷(nano-dHA/PLA/BCP)复合支架,利用万能测试机测试支架抗压强度,阿基米德法测定支架孔隙率,扫描电子显微镜(SEM)观察支架表面形貌,并对其保水率和体外降解过程中pH值的变化情况等进行了研究. 结果表明：多孔nano dHA/PLA/BCP复合支架表面粗糙,保水率和强度均有较大提高,在磷酸盐缓冲液（PBS）浸泡过程中pH值下降较慢,在模拟体液（SBF）中浸泡1个月后发现有较多的类骨磷灰石形成.     

Processing and properties of porous titanium with high porosity coated by bioactive titania nanotubes

A porous titanium scaffold with a porosity of 70% and a pore size of about 200–300 μm was fabricated using the space-holder sintering process. Furthermore, the bioactive TiO₂ nanotubes with a tube size of approximately 100 nm were prepared successfully on the surface of the porous titanium by anodization and heat-treatment. The bioactivity of the scaffold was evaluated by immersing the samples into the simulated body fluid for 7 days. Results show that the porous titanium scaffold coated with anatase nanotubes has the superior ability of hydroxyapatite formation. Meanwhile, the scaffold has a high compressive strength of 36.8 MPa, which can be used as a cancellous bone substitute.     

Vanadium doped SnO<Subscript>2</Subscript> nanoparticles for photocatalytic degradation of methylene blue

Nanometric V-doped particles with vanadium concentration varying from 0 to 10% were prepared using the polyol method. The influence of the doping on the textural, structural and optical properties was studied by various methods of characterization. X-ray diffraction (XRD) patterns disclose that nanocrystallites of cassiterite, i.e. rutile-like tetragonal structure SnO₂ and the absence of a new vanadium phase in the XRD pattern in the different concentration of doping were formed after annealing, the ordinary crystallite size decreased from 20.6 to 12.3 when the doping concentration increased from 0 to 10%, respectively. Moreover, the N₂ sorption porosimetry and transmission electron microscopic show that all samples synthesized were constituted of an aggregated network of almost spherical nanoparticles, which sizes changed with the altitude in the doping concentration to 10%. In accordance with UV–visible absorption measurements, this diminution of nanoparticles sizes was followed by a decrease in the band gap value from 3.25 eV, for undoped SnO₂, to 2.75 eV, for SnO₂ doped at 10%. On the other part, the photocatalytic activity of undoped and V-doped SnO₂ nanoparticles was studied using methylene blue (MB) as model organic pollutants. The SnO₂ nanoparticles doped at 10% of vanadium disclosed that the discoloration of MB reached 97.4% after irradiation of 120 min, with an apparent constant rate of the degradation reaching 0.035 min^?1 for MB degradation that was about 2.5 times more than that of pure SnO₂ (0.014 min^?1).     

Synthesis,defect characterization and photocatalytic degradation efficiency of Tb doped CuO nanoparticles

Monoclinic undoped and Tb doped CuO are prepared by solution combustion method and annealed at different temperatures. The effect of annealing and doping on their structural and optical properties of CuO are examined using XRD, FTIR and DRS. The surface and lattice defects in CuO and Tb doped CuO is analyzed qualitatively and quantitatively using positron lifetime and Doppler broadening spectroscopy. The average positron lifetime and electron momentum (energy) S parameter increases owing to the number of vacancies in the CuO lattice upon doping and decreases with increasing temperature. The migration of vacancies from grain to grain boundary region is observed at 600 °C annealed samples. At 800 °C, the overall behavior of lifetime value denotes that the vacancy type defect is recovered, cluster vacancy and microvoids exists with reducing size. The photocatalytic performance of undoped and Tb doped CuO on degradation of methylene blue (MB) and methyl orange (MO) is investigated under visible light for two different lamp power and dye concentration. The influence of annealing temperature and dopant ion on the efficiency is also elaborated. Enhanced photocatalytic efficiency in Tb doped CuO is observed upon annealing. X-ray photoelectron spectroscopy (XPS) result indicates that the valence states of Cu, O and Tb ions exist at the surface of the particles. Brunauer–Emmett–Teller N₂ adsorption–desorption analyses were employed to characterize specific surface area and porosity of Tb doped CuO. The doped CuO with pore size of about ～34 nm have a surface area of 16–28 m²/g. The surface area effect plays an important role in the enhanced catalytic performance on Tb doped catalysts.     

Dark conductivity and transient photoconductivity of nanocrystalline undoped and N-doped TiO2 sol-gel thin films

The dark conductivity and transient photoconductivity of undoped and N-doped porous, sol-gel thin TiO₂ films were studied in vacuum and in air. The dark conductivity of the undoped samples is higher in air and this effect is attributed to adsorbed water. For the N-doped samples, the heavier doping causes a high increase in the dark conductivity, while the presence of Nitrogen somehow prevents the water adsorption in air. The photoconductivity reaches very high values and is sensitive on the environment. The presence of Nitrogen decreases dramatically the photoconductivity and increases significantly the saturating as well as the decay times.     

X-ray photoelectron spectroscopy study and humidity sensing properties of Zn doped SnO2 thin films

Undoped and Zn-doped SnO₂ thin films are deposited onto glass substrates by sol–gel spin coating method. All the films are characterized by X-ray photon spectroscopy (XPS) and Fourier transform infra-red spectroscopy (FTIR). XPS shows that Sn presence as valence of Sn⁴⁺ in the prepared SnO₂ thin films instead of Sn²⁺. In addition, it also exhibits the amount of Zn in SnO₂ thin films, which increases with increasing Zn doping percentage. The Zn (2P_3/2) peak is symmetric and centred at around 1,021.73 eV which shifts to the lower binding energy of 1,020.83 eV for 15 at.% Zn doped SnO₂ thin film. FTIR study is used to describe the local environment of undoped and Zn-doped SnO₂ thin films which also confirms the synthesis of undoped and Zn-doped SnO₂ thin films. It is found that the resistance of SnO₂ thin films increases as Zn doping concentration increases at room humidity. The resistance of all the samples increases as relative humidity (RH) increases. The sensitivity of SnO₂ thin films increases as RH increases while it decreases as Zn doping percentage increases. Response time of SnO₂ thin film decreases as Zn doping percentage increases and recovery time slightly increases with doping percentage.     

Preparation of a biphasic scaffold for osteochondral tissue engineering

Tissue engineering has been developed as a prospective approach for the repair of articular cartilage defects. Engineered osteochondral implants can facilitate the fixation and integration with host tissue, and therefore promote the regeneration of osteochondral defects. A biphasic scaffold with a stratified two-layer structure for osteochondral tissue engineering was developed from biodegradable synthetic and naturally derived polymers. The upper layer of the scaffold for cartilage engineering was collagen sponge; the lower layer for bone engineering was a composite sponge of poly(DL-lactic-co-glycolic acid) (PLGA) and naturally derived collagen. The PLGA–collagen composite sponge layer had a composite structure with collagen microsponge formed in the pores of a skeleton PLGA sponge. The collagen sponge in the two respective layers was connected. Observation of the collagen/PLGA–collagen biphasic scaffold by scanning electron microscopy (SEM) demonstrated the connected stratified structure. The biphasic scaffold was used for culture of canine bone-marrow-derived mesenchymal stem cells. The cell/scaffold construct was implanted in an osteochondral defect in the knee of a one-year old beagle. Osteochondral tissue was regenerated four months after implantation. Cartilage- and bone-like tissues were formed in the respective layers. The collagen/PLGA–collagen biphasic scaffold will be useful for osteochondral tissue engineering.     

Fabrication and characterization of porous calcium polyphosphate scaffolds

Porous calcium polyphosphate (CPP) scaffolds with different polymerization degree and crystalline phases were prepared, and then analyzed by scanning electron microscopy (SEM), Thermmogravimetry (TG) and X-ray diffraction (XRD). Number average polymerization degree was calculated by analyzing the calcining process of raw material Ca(H₂PO₄)₂, as a polycondensation reaction. Amorphous CPP were prepared by the quenching from the melt of Ca(H₂PO₄)₂ after calcining, and CPP with different polymerization degree was prepared by controlling the calcining time. Meanwhile, CPP with the same polymerization degree was prepared to amorphous or different crystalline phases CPP which was made from crystallization of amorphous CPP. In vitro degradation studies using 0.1 M of tris-buffered solution were performed to assess the effect of polymerization degree or crystalline phases on mechanical properties and weight loss of the samples. With the increase of polymerization degree, the weight loss during the degradation decreased, contrarily the strength of CPP increased. The degradation velocity of amorphous CPP, α-CPP, β-CPP and γ-CPP with the same polymerization degree decreased in turn at the same period. The full weight loss period of CPP can be controlled between 17 days and more than 1 year. The results of this study suggest that CPP ceramics have potential applications for bone tissue engineering.     

Structure and superconducting properties of pure and variously doped bulk MgB2 obtained by uniaxial and isostatic hot pressing

The preparation of dense MgB₂ bodies, undoped and doped with different atomic species (Na, Ag, Y), was performed via reactive sintering by uniaxial and isostatic hot pressing, starting from the pure elements, and compared with undoped samples obtained by commercial MgB₂ powder. The superconducting characteristics of the obtained materials, namely critical temperature (T_c) and current (J_c), were obtained through ac susceptibility measurements and compared to their structural features, like phase purity and secondary phases formation and distribution in the MgB₂ matrix. Both the adopted hot pressing techniques gave rise to undoped MgB₂ pieces exhibiting phase purity in the range 85–95% and relative density above 80%; although in most cases the doped samples underwent higher extents of phase decomposition and lesser densification, they all exhibited higher critical temperature and current compared to the corresponding undoped material, indicating a net influence of the doping on the superconducting behaviour of MgB₂, particularly Ag and Y. An opportune quality factor was adopted, to obtain a more reliable comparison between the different MgB₂ samples and evaluation of the samples goodness, in relation to their superconducting characteristics. It was put in evidence that low amounts of doping can improve the superconducting behaviour of MgB₂ and that this influence can be addressed in terms of pinning centres, as there was no experimental evidence of an actual atomic substitutions in the MgB₂ crystal.