Key Engineering Materials Vol. 631

Abstract: We have previously developed biodegradable β-tricalcium phosphate (β-TCP) cement based on the chelate-setting mechanism of inositol phosphate (IP6). The β-TCP cement powder for the cement fabrication was prepared via a novel powder preparation process, in which the starting β-TCP powders were prepared by simultaneous ball-milling and surface-modification in the IP6 solution. In the present study, the novel powder preparation process was applied to an α-TCP powder, and effect of milling time and beads size for ball-milling on the material properties of the α-TCP powders was investigated. The α-TCP powder ball-milled in 1000 ppm IP6 solution for 4 h with 2 mm-diameter beads was composed of single phase α-TCP with the smallest particle size of 2.2 µm. Dissolution of 4 h-milled α-TCP powder was approximately twice higher than that of starting α-TCP powder before ball-milling. The α-TCP powder with high dissolution property prepared via the novel powder preparation process is potential candidate for fabrication of the chelate-setting cement.

Abstract: In this study the effects of adding silica and alumina nanoparticles on flow ability and compressive strength of cementitious composites based on Portland cement were investigated. In the first stage, the rheological behavior of different samples containing nanosilica, nanoalumina and polypropylene, polyvinyl alcohol and polyethylene fibers were evaluated. With increasing of nanoparticles in fresh samples, the slump flow diameter reduced. Fibers reduced the flow ability of the samples and viscosity increased. With increasing of the micro silica particles to cement ratio from 2/1 to 2/2, the slump flow diameter increased. By adding silica and alumina nanoparticles up to 3% and 2% respectively, the compressive strength increased and after decreased. Samples containing silica nanoparticles and fibers had the highest compressive strength.

Abstract: Calcium carbonate (CaCO₃) has been known as one of the components of carbonate apatite (CO₃Ap) cement. Calcite is one of the polymorph of CaCO₃ with big particle size and excellent stability. In contrast, vaterite has small particle size and a metastable phase. To discover the effect of particle size on the properties of CO₃Ap cement, this study investigated the different particle size of vaterite; calcite from vaterite, which has almost similar particle size and shape with vaterite; grounded calcite and ungrounded calcite. The powder phase of calcite or vaterite combined with dicalcium phosphate anhydrous (DCPA) was mixed with 0.8 mol/L of Na₂HPO₄ solution in 0.45 liquid to powder ratio. The paste was packed into a split stainless steel mold, covered with glass slide and kept at 37°C and 100% relative humidity for a period of time. XRD and FT-IR analysis revealed that CO₃Ap cement consisted of vaterite and DCPA transformed to pure B-type CO₃Ap in 72 hours while CO₃Ap cement that consisted of calcite with different particle size was not completely transformed to CO₃Ap even until 240 hours. We concluded that CO₃Ap cement consisted of vaterite with small particle size and metastable phase properties is more effective as starting material due to its fast transformation to CO₃Ap.

Abstract: In this study the structural and chemical properties of barnacle shell based bioceramic materials (i.e. hydroxyapatite, whitlockite, monetite and other phases) were produced by using mechano-chemical (hot-plate) conversion method. Cleaned barnacle shells were ball milled down to <75µm in diameter. Differential thermal and gravimetric analyses (DTA/TGA) were performed to determine the exact CaCO₃ content. Sample batches of 2g were prepared from the fine powders produced. For each batch, the required volume of an aqueous H₃PO₄ solution was calculated in order to set the stoichiometric molar ratio of Ca/P equal to 1.5 for ß-tricalcium phosphate (ß-TCP) or to 1.667 for hydroxyapatite (HA). The temperature was set to 80°C for 15 minutes to complete the process. After the titration of the equivalent amount of H₃PO₄ into the prepared solution, agitation was carried out on a hot-plate (i.e. mechano-chemical processing) for 8 hours. The sediments formed were dried and the resulting TCP and HA powders were calcined at 400°C and 800°C respectively. For complete characterization of the bioceramics produced, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) analyses were carried out. The current study proposes a simple, economic and time efficient method for nano-bioceramic production.

Abstract: Objectives: The aim of this study was to compare colour stability of two self-adhesive flowable composites with four methacrylate-based composites (three flowable composites and one universal resin-based composite) after immersion in water at 60°C for 30 days.Methods: The study was conducted using the following five shade A2 flowable composites (n=30): one microhybrid (G-aenial Universal Flo), one universal (X-Flow), one nanohybrid (Premise flowable) and two self-adhesive (Vertise Flow and experimental GF-10) and one microhybrid universal resin-based composite (G-aenial Posterior). A spectrophotometer (CIEL*a*b* system) was used to measure colour stability before and after immersion. Statistical analysis was performed with one-way ANOVA and Fisher test.Results: Samples immersed in water at 60°C for one month showed a significant colour change in all groups (p<.001) that was visually perceptible (∆E>3.3). Experimental self-adhesive flowable (12.25±0.84) and X-Flow (11.56±3.26) composites showed higher levels of ∆E, while Premise flowable showed a lower level of colour change (3.47±1.26). These results approximated clinically acceptable colour change values (∆E≤3.3). Water ageing at 60°C produced a significant change in colour in all the composites. The high temperature may explain the degradation of the resin matrix.

Abstract: Poly (L-lactic acid)/organically modified montmorillonite (PLLA/OMMT) nanocomposites were fabricated by a solution intercalation method. OMMT, modified with quaternary alkylammonium ion, was prepared by alkyltrialkoxysilane. The differential scanning calorimetry measurement revealed that the crystallization temperatures of PLLA/OMMT nanocomposites were at around 110 °C regardless of the existence of OMMT or the weight fraction of them. X-ray diffraction patterns suggested that the (001) diffraction was around 2θ = 2.5°. The TEM image showed variously expanded interlayer galleries of OMMT and partially exfoliated silicate layer unit in the matrix. Board-shaped specimens for mechanical property tests were fabricated by compression-molding at 190 °C (including 30 min annealing at 110 °C). The flexural modulus of the nanocomposites increased with increasing content of OMMT. Vickers hardness of the nanocomposites were almost same independent on weight fraction of OMMT.

Abstract: Hydroxyapatite is a calcium phosphate ceramic that is used as a biomaterial. It has been studied extensively as a candidate biomaterial for prosthetic applications. Hydroxyapatite (HA) does not have the mechanical strength to enable it to succeed in long term load bearing applications. Therefore, Its mechanical properties may be improved with addition of zirconia powders. The aim of this study is to improve the mechanical properties of the hydroxyapatite by producing composite material including zirconia and silica powders. Therefore, hydroxyapatite was mixed with 5 wt% zirconia, 5 wt% silica powders and then this pressed mixture were sintered at different temperatures (1100-1300°C). The sintering behavior, microstructural characteristics and mechanical properties were investigated.

Abstract: We precipitated Apatite Nucleus (AN) by raising pH of SBF. We mixed various concentration of AN in polylactic acid (PLA) and pressed by uniaxial press and cold isostatic press. We investigated the effect of AN concentration on bioactivity. We fabricated composite of PLA and AN configurating the shape by using 3D printer. The composite showed high bioactivity.

Abstract: Hydroxyapatite is a kind of calcium phosphate that has generated great interest as an advanced orthopedic and dental implant candidate. Although HA has excellent biocompatibility, it’s poor mechanical properties limit its use as an implant material. Therefore HA is preferred as a main component in composite materials. The aim of this study is to determine the characterization and bioactivity of HA-ZrO₂ composites with the addition of 5 and 10 wt% commercial inert glass (CIG). The highest density and Vickers microhardness were obtained in HA-ZrO₂-5 wt% CIG composite sintered at 1300 °C. The highest compression strength was measured in HA-ZrO₂-5 wt% CIG composite sintered at 1200 °C. The in vitro bioactivity tests were performed on the composites having the highest physical and mechanical properties. The apatite formation was observed on all samples subjected to bioactivity tests. As a result, the optimum mechanical properties and bioactivity were obtained on HA-ZrO₂- 5 wt% CIG composite sintered at 1200 °C.

Abstract: Natural bone is formed by a complex composite, essentially constituted of biological apatite and fibers of collagen. The combination of materials such as biopolymers and bioceramics may result in an interesting material for application in bone tissue regeneration. This work aims to obtain polymeric fibers containing Poly (Lactic-co-Glycolic Acid) and Poly (Isoprene), supplemented with hydroxyapatite (HA) and α-tricalcium phosphate (TCP). The thermal, mechanical and morphological properties of the fibers were evaluated . Even presenting a larger diameter, fibers with α-TCP presented lower elastic modulus than fibers with HA. Both fibers presented similar thermal behavior, with glass transition temperature in the same range that the one presented by raw PLGA and similar degradation temperatures. Is safe to say that the presence of ceramics in the fibers have a potential for further investigations aiming bone tissue regeneration.