Influence of strontium for calcium substitution in bioactive glasses on degradation,ion release and apatite formation

Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO₂–P₂O₅–CaO–Na₂O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions.     

The processing,mechanical properties and bioactivity of strontium based glass polyalkenoate cements

The suitability of zinc-based glass polyalkenoate cements (GPCs) for use in orthopaedics can be improved by the substitution of strontium into the glass phase which should impart improved radiopacity and bone forming properties to the cements without retarding strength. The purpose of this research was to produce novel GPCs based on calcium–strontium–zinc-silicate glasses and to evaluate their mechanical properties and biocompatibility with the ultimate objective of developing a new range of cements for skeletal applications. Three glass compositions, based on incremental substitutions of strontium for calcium, were synthesized; BT100 (0.16CaO, 0.36ZnO, 0.48SiO₂), BT101 (0.04SrO, 0.12CaO, 0.36ZnO, 0.48SiO₂) and BT102 (0.08SrO 0.08CaO, 0.36ZnO, 0.48SiO₂). Each glass was then mixed with varying concentrations and molecular weights of polyacrylic acids in order to determine the working times, setting times, compressive strengths and biaxial flexural strengths of the novel cements. The maximum working time and setting time achieved was 29 and 110 s respectively; which, at present is inadequate for current clinical procedures. However, the optimum compressive and biaxial flexural strengths were up to 75 and 34 MPa respectively indicating that these formulations have potential in load bearing applications. Importantly, the substitution of Ca with Sr in the glasses did not have a deleterious effect on strengths or working times. Finally, the bioactivity of the best performing cements was determined in vitro using simulated body fluid. It was found that all cements facilitate the formation of an amorphous calcium phosphate at their surface which increases in density and coverage with time, indicating that these cement will bond directly to bone in vivo.     

Aluminium-free glass polyalkenoate cements: ion release and in vitro antibacterial efficacy

Glass polyalkenoate cements (GPCs) have exhibited potential as bone cements. This study investigates the effect of substituting TiO₂ for SiO₂ in the glass phase and the subsequent effect on cement rheology, mechanical properties, ion release and antibacterial properties. Glass characterization revealed a reduction in glass transition temperature (T _g ) from 685 to 669 °C with the addition of 6 mol % TiO₂ (AT-2). Magic angle spinning nuclear magnetic resonance (MAS-NMR) revealed a shift from ?81 ppm to ?76pmm when comparing a Control glass to AT-2, indicating de-polymerization of the Si network. The incorporation of TiO₂ also increased the working time (T _w ) from 19 to 61 s and setting time (T _s ) from 70 to 427 s. The maximum compressive strength (σ _c ) increased from 64 to 85 MPa. Ion release studies determined that the addition of Ti to the glass reduced the release of zinc, calcium and strontium ions, with low concentrations of titanium being released. Antibacterial testing in E. coli resulted in greater bactericidal effects when tested in aqueous broth for both titanium containing cements.     

Fluoride release from model glass ionomer cements

Glass ionomer cements (GICs) are an important class of biomedical material used extensively for color matched mercury free, dental restorations. GICs can release clinically beneficial amounts of fluoride and have acceptable handling properties which make them suitable as dental restoratives. The fluoride release of model GICs produced from specially synthesized fluoro-alumino-silicate glasses was studied. Nine glasses of varying fluoride content based on 4.5SiO₂–3Al₂O₃–1.5P₂O₅–(5–Z)CaO–ZCaF₂ were synthesized and cement disks were prepared from them. The glass transition temperature reduced with increasing fluorine content of the glass. Fluoride ion release was measured into distilled water as a function of time for up to 140 days using a fluoride ion selective electrode. The quantity of fluoride released was found to be proportional to the fluorine content of the glass at all intervals time. The cumulative fluoride release was proportional to square root time. Substituting strontium for calcium in the glass had little influence on the fluoride release behavior of the cements.     

From tissue retrieval to electron tomography: nanoscale characterization of the interface between bone and bioactive glass

The success of biomaterials for bone regeneration relies on many factors, among which osseointegration plays a key role. Biogran (BG) is a bioactive glass commonly employed as a bone graft in dental procedures. Despite its use in clinical practice, the capability of BG to promote osseointegration has never been resolved at the nanoscale. In this paper, we present the workflow for characterizing the interface between newly formed bone and BG in a preclinical rat model. Areas of bone–BG contact were first identified by backscattered electron imaging in a scanning electron microscope. A focused ion beam in situ lift-out protocol was employed to prepare ultrathin samples for transmission electron microscopy analysis. The bone–BG gradual interface, i.e. the biointerphase, was visualized at the nanoscale with unprecedented resolution thanks to scanning transmission electron microscopy. Finally, we present a method to view the bone–BG interface in three dimensions using electron tomography.     

Evaluation of a novel radiopacifiying agent on the physical properties of surgical spineplex<Superscript>®</Superscript>

Polymethlylmethacrylate (PMMA) is the most frequently used cement for percutaneous vertebroplasty and kyphoplasty. To aid visualisation during surgery cements are doped with radiopacifying agents such as Barium sulphate (Ba₂SO₄) or Zirconium Dioxide (ZiO₂). Mounting research suggests that these agents may impair the biocompatibility of the cements. However, incorporating an alternative radiopacifier agent with excellent biocompatibility would be a significant step forward. Bioactive radiopaque glasses incorporating elements such as strontium (Sr) and zinc (Zn), known to have beneficial and therapeutic effects on bone, are of great interest in this respect. In this study, the Ba₂SO₄ of the commercially available Spineplex^® was incrementally replaced with a radiopaque therapeutic glass composition. The resulting effects on cement setting time, peak isotherm, ultimate compressive strength, Young’s modulus (up to 30 days cement maturation) and radiopacity were evaluated. The substitution lead to an increase in cement setting time from 13.1 mins for Spineplex^® to 16.6–18.3 mins for the glass substituted cements. The peak exotherm during curing was reduced from 74°C for Spineplex^® to a minimum of 51°C for the fully substituted cement, indicating that reduced thermal necrosis in the in vivo setting is likely with these materials. Ultimate compressive strength and Young’s modulus of each formulation showed no significant deterioration due to the substitution. Finally, the radiopacity of the substituted cements were reduced by up to a maximum of 18% in comparison to the control. However, the experimental formulations still maintained radiopacity equivalent to several millimetres of aluminium. As such the substituted cements had substantial equivalence to the Spineplex^® control. In order to assess the clinical relevance of these findings further investigation is warranted.     

Fabrication of spherical CaO–SrO–ZnO–SiO2 particles by sol–gel processing

This study was concerned with the fabrication of ceramic CaO–SrO–ZnO–SiO₂ spherical particles, which are novel candidates for the glass phase in glass polyalkenoate cements (GPCs). GPCs made from these glasses have potential as bone cements because, unlike conventional GPCs, they do not contain aluminum ions, which inhibit the calcification of hydroxyapatite in the body. The glass phase of GPCs require a controllable glass morphology and particle size distribution. Sol–gel processing can potentially be used to fabricate homogenous ceramic particles with controlled morphology. However, a thorough study on preparation conditions of spherical CaO–SrO–ZnO–SiO₂ particles by sol–gel processing has, to date, not been reported. In this study, gels were prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in an aqueous solution containing polyethylene glycol and nitrates of calcium, strontium and zinc. It was possible to control the morphology and size of the gels by varying the H₂O/TEOS molar ratio and the metal ion content in the starting compositions. An aliquot of 3–5 μm homogenous spherical particles were obtained at a H₂O/TEOS molar ratio of 42.6 when the starting composition molar ratios were Sr(NO₃):Ca(NO₃)₂:Zn(NO₃)₂:Si(OC₂H₅)₄ = x:0.12:(0.40 − x):0.48 (0 ≤ x ≤ 0.8). Starting composition limitations are caused by the low solubility of strontium ions in the minimal amount of water used and the acceleration of hydrolysis as well as polycondensation at higher water content.     

High-temperature resistivity and thermoelectric properties of coupled substituted Ca3Co2O6

Polycrystalline samples of Ca_3−xNa_xCo_2−xMn_xO₆ (x=0.0–0.5) have been prepared by the sol-gel cum combustion method using sucrose in order to investigate the effects of the coupled substitution of Na and Mn on Ca and Co sites on the transport properties of Ca₃Co₂O₆(Co326). The products were characterized by Fourier transform infrared spectroscopy, powder x-ray diffraction (XRD), thermogravimetry (TGA), differential thermal analysis and scanning electron microscopy. XRD patterns reveal the formation of single-phase products up to x=0.5. Coupled substitution increases the solubility of both Na and Mn on Ca and Co sites, respectively, in contrast to the limited solubility of Na and Mn (x=0.2) when separately substituted. TGA confirms the formation of the Ca₃Co₂O₆ phase at temperatures ∼720 °C. The grain size of the parent and substituted products is in the range 150–250 nm. Electrical resistivity and Seebeck coefficient were measured in the temperature range 300–800 K. Resistivity shows semiconducting behavior for all the compositions, particularly in the low-temperature regime. The Seebeck coefficient increases with temperature throughout the measured temperature range for all compositions. The maximum Seebeck coefficient (200 μV K⁻¹) is observed for x=0.5 at 825 K, and this composition may be optimal for high-temperature thermoelectric applications.     

Influence of acid washing on the surface morphology of ionomer glasses and handling properties of glass ionomer cements

Acid washing is known to influence the handling properties of ionomer glasses used in glass ionomer cements due to the production of an ion depleted-zone on the surface of the glass particles. The influence of acid washing on the particle size distribution and surface area of four glasses was examined by scanning electron microscopy (SEM), particle size analysis (PSA) and accelerated surface area porosimetry (ASAP) and the working and setting times of cements, produced from the glasses, correlated to changes in surface morphology. A linear relationship was found between the specific surface area of acid-washed SiO₂–Al₂O₃–XF₂–P₂O₅ glasses (X being either calcium or strontium) and their cement working and setting times. These changes directly correlated with increases in the mesopore volume. However, the influence of acid washing on the surface morphology was also found to be glass composition-dependant with the addition of sodium into the glass network resulting in no significant change in the surface area or mesopore volume despite changes in the working and setting time. Through examination of the influence of acid washing and glass composition on the specific surface area improvements in the control of the working and setting times of glass ionomer cements may be achieved.     

Study of the reactivity and <Emphasis Type="Italic">in vitro</Emphasis> bioactivity of Sr-substituted α-TCP cements

In this study the effect of strontium substitution on the hydrolysis of α -tricalcium phosphate (α -TCP) toward the formation of calcium deficient hydroxyapatite (CDHA) was investigated. For that purpose substituted α -TCP powders with 1, 5 and 10 mol% Sr substitution for Ca were synthesized by reacting at 1500 ^∘C stoichiometric amounts of CaCO₃, SrCO₃, and Ca₂P₂O₇, followed by rapid quenching in air. XRD analysis of the powders revealed the presence of α-TCP (traces of β-TCP) with enlarged unit cell volume at increased Sr contents, indicating the incorporation of Sr in the crystal structure. Strontium was also incorporated in the apatite phase as revealed by XRD analysis of the set cements. The hydrolysis of milled α-SrTCP powders and a pure α-TCP (control) was monitored by isothermal calorimetry and the compressive strength of set cements was tested. The results showed a decrease in the reactivity with increasing Sr content and similar final mechanical strength within the Sr series, though lower than the control. The in vitro bioactivity of the set cements after soaking in simulated body fluid for 4 weeks was also tested. The formation of a bone-like apatite layer on the surface of the set cements indicated a potential in vivo bioactivity.     

Synthesis and characterization of manganese containing mesoporous bioactive glass nanoparticles for biomedical applications

Mesoporous bioactive glass (BG) nanoparticles based in the system: SiO₂–P₂O₅–CaO–MnO were synthesized via a modified Stöber process at various concentrations of Mn (0–7 mol %). The synthesized manganese-doped BG nanoparticles were characterized in terms of morphology, composition, in vitro bioactivity and antibacterial activity. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis confirmed that the particles had spherical morphology (mean particle size: 110?nm) with disordered mesoporous structure. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of Mn, Ca, Si and P in the synthesized Mn-doped BG particles. Moreover, X-ray diffraction (XRD) analysis showed that Mn has been incorporated in the amorphous silica network (bioactive glass). Moreover, it was found that manganese-doped BG particles form apatite crystals upon immersion in simulated body fluid (SBF). Inductively coupled plasma atomic emission spectroscopy (ICP-OES) measurements confirmed that Mn is released in a sustained manner, which provided antibacterial effect against Bacillus subtilis, Pseudomonas aeruginosa and Staphylococcus aureus. The results indicate that the incorporation of Mn in the bioactive glass network is an effective strategy to develop novel multifunctional BG nanoparticles for bone tissue engineering.     

In situ synthesised TiO2 ‐chitosan‐chondroitin 4–sulphate nanocomposites for bone implant applications

The artificial materials for bone implant applications are gaining more importance in the recent years. The series titania‐chitosan‐chondroitin 4–sulphate nanocomposites of three different concentrations (2:1:x, where x ‐ 0.125, 0.25, 0.5) have been synthesised by in situ sol–gel method and characterised by various techniques. The particle size of the nanocomposites ranges from 30–50 nm. The bioactivity, swelling nature, and the antimicrobial nature of the nanocomposites were investigated. The swelling ability and bioactivity of the composites is significantly greater and they possess high zone of inhibition against the microorganisms such as Staphylococcus aureus and Escherichia coli. The cell viability of the nanocomposites were evaluated by using MG‐63 and observed the composites possess high cell viability at low concentration. The excellent bioactivity and biocompatibility makes these nanocomposites a promising biomaterial for bone implant applications.Inspec keywords: titanium compounds, filled polymers, nanocomposites, bone, orthopaedics, biomedical materials, sol‐gel processing, nanofabrication, particle size, swelling, microorganisms, cellular biophysics, nanomedicine, prostheticsOther keywords: in situ synthesised TiO₂ ‐chitosan‐chondroitin 4‐sulphate nanocomposites, bone implant applications, artificial materials, in situ sol‐gel method, particle size, swelling nature, antimicrobial nature, microorganisms, Staphylococcus aureus, Escherichia coli, cell viability, MG‐63, biomaterial, size 30 nm to 50 nm, TiO₂      

Synthesis and dissolution behaviour of CaO/SrO-containing sol–gel-derived 58S glasses

The effect of the substitution of strontium for calcium in the tertiary the SiO₂–CaO–P₂O₅ sol–gel bioactive glass 58S (60SiO₂·36CaO·4P₂O₅, mol%) on its structure and its chemical durability on soaking in simulated body fluids was investigated. 58S was selected as a starting composition, and substitution for calcium was carried out from 0 to 100% with an increment of 25%. A novel phosphate source of diethylphosphatoethyltriethoxysilane, which consists of Si and P connected with ethylene group, was used in this work. XRD and FTIR showed that the gels obtained following drying at 130 °C had a typical sol–gel structure, where a continuous amorphous silica gel network and surface bound mineral salts of Ca(NO₃)₂ and Sr(NO₃)₂. Once the gels were heat stabilised to decompose nitrates and incorporate the cations into the network, samples containing Sr formed a strontium silicate crystalline phase. With increasing levels of Sr in the composition, the overall crystallinity of the glass–ceramic increased, while, at the maximum substitution of 100% SrO, macroscopic phase separation was observed, characterised by needle-like crystals of strontium apatite (Sr₅(PO₄)₃OH) and strontium silicate (Sr₂SiO₄) phases in addition to amorphous regions. Dissolution experiments in Tris-buffered solution showed Sr successfully released into the media even though it existed as a crystalline phase in the glass–ceramic. Further, the glass–ceramics induced nucleation and growth of carbonated hydroxyapatite (HA) on their surface suggesting potential bioactivity of the materials. At higher substitutions (75 and 100% SrO for CaO), HA nucleation was not found to occur this may have been due to low amount of phosphate released from the original glass–ceramic as a result of it being locked up in the strontium apatite phase.     

Comparisons of immersion and electrochemical properties of highly biocompatible Ti–15Zr–4Nb–4Ta alloy and other implantable metals for orthopedic implants

Metal release from implantable metals and the properties of oxide films formed on alloy surfaces were analyzed, focusing on the highly biocompatible Ti–15Zr–4Nb–4Ta alloy. The thickness and electrical resistance (R_p) of the oxide film on such an alloy were compared with those of other implantable metals. The quantity of metal released during a 1-week immersion test was considerably smaller for the Ti–15Zr–4Nb–4Ta than the Ti–6Al–4V alloy. The potential (E₁₀) indicating a current density of 10 μA cm⁻² estimated from the anodic polarization curve was significantly higher for the Ti–15Zr–4Nb–4Ta than the Ti–6Al–4V alloy and other metals. Moreover, the oxide film (4–7 nm thickness) formed on the Ti–15Zr–4Nb–4Ta surface is electrochemically robust. The oxide film mainly consisted of TiO₂ with small amounts of ZrO₂, Nb₂O₅ and Ta₂O₅ that made the film electrochemically stable. The R_p of Ti–15Zr–4Nb–4Ta was higher than that of Ti–6Al–4V, i.e. 0.9 Ω cm² in 0.9% NaCl and 1.3 Ω cm² in Eagle''s medium. This R_p was approximately five-fold higher than that of stainless steel, which has a history of more than 40 years of clinical use in the human body. Ti–15Zr–4Nb–4Ta is a potential implant material for long-term clinical use. Moreover, E₁₀ and R_p were found to be useful parameters for assessing biological safety.     

Synthesis and characterization of core–shell nanoparticles and their influence on the mechanical behavior of acrylic bone cements

Core–shell nanoparticles consisting of polybutyl acrylate (PBA) rubbery core and a polymethyl methacrylate (PMMA) shell, with different core–shell ratios, were synthesized in order to enhance the fracture toughness of the acrylic bone cements prepared with them. It was observed by TEM and SEM that the core–shell nanoparticles exhibited a spherical morphology with ca. 120 nm in diameter and that both modulus and tensile strength decreased by increasing the PBA content; the desired structuring pattern in the synthesized particles was confirmed by DMA. Also, experimental bone cements were prepared with variable amounts (0, 5, 10 and 20 wt.%) of nanoparticles with a core–shell ratio of 30/70 in order to study the influence of these nanostructured particles on the physicochemical, mechanical and fracture properties of bone cements. It was found that the addition of nanostructured particles to bone cements caused a significant reduction in the peak temperature and setting time while the glass transition temperature (T_g) of cements increased with increasing particles content. On the other hand, modulus and strength of bone cements decreased when particles were incorporated but fracture toughness was increased.     

Absorption Bands of Carbon Dioxide From 5.3 to 4.6 Microns

Measurements have been made of the frequencies of the infrared absorption lines of CO₂ in the region from 1850 cm⁻¹ to 2150 cm⁻¹. Observations were made at various pressures and pathlengths up to a maximum of 72 meter-atmospheres. Vibration-rotation constants were obtained characterizing the transitions 11^1c0–000, 11^1d0–000, 03^1c0–000, 03^1d0–000, 200–01^1c0, I2^2c0–01^1c0, 12^2d0–01^1d0 for C¹²O₂. The 11^1c0–000 band due to the C¹³O₂ molecule was also measured.     

Multifaceted activities of plant gum synthesised platinum nanoparticles: catalytic,peroxidase, PCR enhancing and antioxidant activities

A single pot, green method for platinum nanoparticles (Pt NP) production was devised with gum ghatti (Anogeissus latifolia). Analytical tools: ultraviolet–visible (UV‐vis), dynamic light scattering, zeta potential, transmission electron microscope, X‐ray diffraction (XRD), and Fourier transform infrared spectroscopy were employed. Wide continuous UV‐vis absorption and black solution colouration proved Pt NP formation. Face‐centred cubic crystalline structure of NP was evidenced from XRD. NPs formed were nearly spherical with a mean particle size of 3 nm. NP demonstrated a myriad of properties including catalytic, peroxidase, polymerase chain reaction (PCR) enhancing and antioxidant activities. Catalytic action of NP was probed via NaBH₄ reduction of arsenazo‐III dye. NP displayed considerable peroxidase activity via catalysis of 3, 3′, 5, 5′‐tetramethylbenzidine oxidation by H₂ O₂. NP showed exceptional stability towards varying pH (3–11), temperature (25–100°C), salt concentration (0–100 mM) and storage time duration (0–12 months). In comparison with horse radish peroxidase, its applicability as an artificial peroxidase is advantageous. NP caused a two‐fold enhancement in PCR yield at 0.4 nM. Also showed significant 1′, 1′ diphenyl picryl‐hydrazyle scavenging (80.1%) at 15 µg/mL. Author envisages that the biogenic Pt NP can be used in a range of biological and environmental applications.Inspec keywords: nanofabrication, ultraviolet spectra, catalysis, molecular biophysics, enzymes, dyes, platinum, electrokinetic effects, transmission electron microscopy, particle size, X‐ray diffraction, visible spectra, pH, nanomedicine, nanoparticles, biochemistry, light scattering, scanning electron microscopy, Fourier transform infrared spectra, reduction (chemical), oxidationOther keywords: antioxidant activities, catalytic action, salt concentration, artificial peroxidase, two‐fold enhancement, PCR yield, multifaceted activities, plant gum synthesised platinum nanoparticles, gum ghatti, anogeissus latifolia, analytical characterisation tools, dynamic light scattering, zeta potential, X‐ray diffraction, XRD, black solution colouration, Pt NP formation, face‐centred cubic crystalline structure, peroxidase activity, ultraviolet‐visible spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, particle size, catalytic activity, PCR enhancing activity, single pot green method, wide continuous UV‐visible absorption, polymerase chain reaction enhancing activity, arsenazo‐III, azo dye decolourisation, 3, 3′, 5, 5′‐tetramethylbenzidine oxidation, pH, environmental conditions, 1′,1′ diphenyl picryl‐hydrazyle scavenging, time 0.0 month to 12.0 month, temperature 25.0 degC to 100.0 degC, Pt     

Alkyl-π engineering in state control toward versatile optoelectronic soft materials

Organic π-conjugated molecules with extremely rich and tailorable electronic and optical properties are frequently utilized for the fabrication of optoelectronic devices. To achieve high solubility for facile solution processing and desirable softness for flexible device fabrication, the rigid π units were in most cases attached by alkyl chains through chemical modification. Considerable numbers of alkylated-π molecular systems with versatile applications have been reported. However, a profound understanding of the molecular state control through proper alkyl chain substitution is still highly demanded because effective applications of these molecules are closely related to their physical states. To explore the underlying rule, we review a large number of alkylated-π molecules with emphasis on the interplay of van der Waals interactions (vdW) of the alkyl chains and π–π interactions of the π moieties. Based on our comprehensive investigations of the two interactions’ impacts on the physical states of the molecules, a clear guidance for state control by alkyl-π engineering is proposed. Specifically, either with proper alkyl chain substitution or favorable additives, the vdW and π–π interactions can be adjusted, resulting in modulation of the physical states and optoelectronic properties of the molecules. We believe the strategy summarized here will significantly benefit the alkyl-π chemistry toward wide-spread applications in optoelectronic devices.     

Wurtzite-derived ternary I–III–O2 semiconductors

Ternary zincblende-derived I–III–VI₂ chalcogenide and II–IV–V₂ pnictide semiconductors have been widely studied and some have been put to practical use. In contrast to the extensive research on these semiconductors, previous studies into ternary I–III–O₂ oxide semiconductors with a wurtzite-derived β-NaFeO₂ structure are limited. Wurtzite-derived β-LiGaO₂ and β-AgGaO₂ form alloys with ZnO and the band gap of ZnO can be controlled to include the visible and ultraviolet regions. β-CuGaO₂, which has a direct band gap of 1.47 eV, has been proposed for use as a light absorber in thin film solar cells. These ternary oxides may thus allow new applications for oxide semiconductors. However, information about wurtzite-derived ternary I–III–O₂ semiconductors is still limited. In this paper we review previous studies on β-LiGaO₂, β-AgGaO₂ and β-CuGaO₂ to determine guiding principles for the development of wurtzite-derived I–III–O₂ semiconductors.     

Alkali ion substituted calcium phosphate cement formation from mechanically activated reactants

Potassium and sodium containing nanoapatite cements were produced from Ca₂KNa(PO₄)₂ by prolonged high energy ball milling of the compound for up to 24 h. This mechanical treatment resulted in the decrease of the crystal size and a partial amorphisation of the cement reactant as shown by X-ray diffraction analysis and the appearance of strong exothermic peaks in differential scanning calorimetry measurements. The pH of water saturated with Ca₂KNa(PO₄)₂ was 12.5 when the material was mechanically activated but was only 9.5 for the untreated compound suggesting an increase in solubility following milling. The cements set following mixing with a 2.5% Na₂HPO₄ solution in clinically acceptable times between 5–12 min and showed compressive strengths of up to 11 MPa after 24 h setting. The strong alkaline pH value of the cements may provide antimicrobial potential for an application in dentistry as pulp capping agents or cavity liners or for the treatment of infected bone sites.