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Scaffolds encourage the new tissue formation through biological substitution of the damaged or lost tissues. Therefore, scaffold characteristics become more important and should be precisely controlled. Production of scaffolds using a three dimensional (3d) printer appears as a promising method in terms of enabling homogeneous pore distribution and uniform pore size arrangement. In this study, polylactic acid (PLA) scaffold structures were obtained through 3d printing, based on the design parameters such as the scaffold geometry, porosity (%), pore shape, pore size, and the pore interconnectivity. An open source computer-aided design (CAD) program (Interface Scaffold) was employed to design the PLA scaffolds. Scaffold structures with ~72% porosity were generated through a 3D Systems Cube 2nd Generation 3d printer. The design parameters have been optimized by the scaffold design software tool, which includes different unit cells, i.e. Schwartz P, Schwartz D, Gyroid, Skeletal (1-4), Neovius and W (iWP) for designing scaffold structures through mathematical formulations. It was found out that the mean pore size of the 3d-printed Gyroid unit cell scaffolds vary between 1.9 mm and ~4.54 mm according to the microstructural observations done by a scanning electron microscope (SEM).

α-alumina, hydroxyapatite (HA) and bioactive glass are all promising bioceramic materials with specific properties. However, there is a limited amount of work involving their composites. Therefore, this work focuses on preparation and characterization of alumina-HA-bioactive glass composites. HA, α-alumina and bioactive glass powders were prepared through wet chemical precipitation, sol-gel and conventional melting-quenching processes, respectively. Composite pellets were formed by pressing the bioceramic powder mixture and then sintering at 1250 °C for 1 h. Chemical phase analyses proved that α-alumina, whitlockite, anorthite and sodium calcium silicate phases were found in the sintered samples. Bioceramic composite pellets exhibited pretty low compression strength (∼28.50–47.3 MPa) due to high apparent porosity (∼28–30%). Microstructure observations showed that calcium phosphate (CaP) based precipitations with different morphologies were developed on the surface of the composites depending on the immersion time in phosphate buffered saline solution. This was attributed to the favorable bioactivity behavior of the material.

Alumina (alpha-Al2O3) and hydroxyapatite (HA, Ca-10(PO4)(6)(OH)(2)) are well-known for being clinically successful bioceramic materials. In this work, in-vitro biological characterization of the sol-gel alumina-bovine hydroxyapatite composite powders was realized. Alumina powders were synthesized through the sol-gel process. First, boehmite (AlOOH) sol was prepared utilizing aluminium isopropoxide (Al(OC3H7)(3), AIP) as the starting precursor. Bovine hydroxyapatite (BHA) powders, which can be defined as naturally derived calcium phosphate powders were added as 10, 20, 30, and 50% wt. of AIP to each AlOOH sol. Homogeneous dispersion of the BHA powders in the AlOOH sol was managed due to employing Na-alginate as a kind of thickener. Gelation of the AlOOH-BHA mixtures was carried out at 110 degrees C for 3h. After drying, AlOOH-BHA mixtures were heat-treated at 1300 degrees C for 2h. Chemical, microstructural, thermal, and physical properties of the precursors/process products were characterized with X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Fluorescence Spectroscopy (XRF), Differential Thermal Analysis (DTA), and Scanning Electron Microscopy - Energy Dispersive Spectroscopy (SEM-EDS) analyses. Indirect MTT assay was done to evaluate the biocompatibility of the Al2O3-BHA based biocomposite extracts using the L929 cell line. It is found that all Al2O3-BHA composite extracts with varying doses of 25% and 50% had no negative effect on the cell viability. In addition, % cell viability decreased with the increasing of the extract concentration. It can be concluded that the prepared Al2O3-BHA composites can be a good candidate for biomedical applications. Scientific Research Project Coordination Unit of Istanbul UniversityIstanbul University [4201] This work was supported by Scientific Research Project Coordination Unit of Istanbul University [grant number 4201].

Hydroxyapatite (HA) can be defined as a major member of bioceramic materials world. Production of HA in different forms, especially powder, is still worth to be investigated depending on the development of additive manufacturing systems which get attention in biomedical market, recently. Therefore, in this research, it is aimed to synthesize HA powders following the wet chemical precipitation technique and perform a detailed characterization including chemical, physical, microstructural and mechanical studies. Reaction temperature (30 °C, 50 °C and 85 °C), acid addition rate (slow and rapid acid addition rates) and heat-treatment temperature (950 °C and 1250 °C) were the considered process parameters. After the reaction between the alkaline (calcium hydroxide, Ca(OH) 2 ) and acid (ortho-phosphoric acid, H 3 PO 4 ) precursors, maturation of the precipitate, decantation of the precipitate and the by-product, drying and eventually heat-treating the precipitate were sequentially done. X-Ray Diffraction (XRD) analyses, Fourier Transform Infrared Spectroscopy (FT-IR) analyses, Differential Thermal-Thermogravimetric Analysis (DTA-TGA), Scanning Electron Microscope/Energy Dispersive Spectroscopy (SEM/EDS) observations, Vickers microhardness and compression strength tests and bulk density, apparent porosity (%) measurements based on the Archimedes’ Principle were carried out to characterize the synthesized HA powders and HA pellets. It is found that a low reaction temperature such as 30 °C and rapid acid addition rate (5.5 ml/min) are proper process parameters to acquire uniform and spherical-like HA powders with ~ 0.2–0.3 µm mean particle size. HA pellets exhibit a high amount of apparent porosity (~ 23–26%) and this situation can be indicated as an important advantage for the transition and penetration of the body fluids towards the pores.

Hydroxyapatite (HA) is the most well-known mineral among the bioactive ceramic materials. HA crystals can be described as the calcium and phosphorus source that provides the sufficient density and strength of the bone as well as the bioactivity. Wet chemical precipitation technique has practical advantages such as simplicity of the experimental stages, low reaction temperatures, and the possibility of controlling the chemical composition and microstructure properties of the final product with harmless by-products. Therefore in this study, HA powders were synthesized by the wet chemical precipitation technique where calcium hydroxide (Ca(OH) 2 ) was used as the calcium source precursor while orthophosphoric acid (H 3 PO 4 ) as the phosphorus source precursor. There are several factors -such as the pH value of the reaction solution, dropping rate of the acid solution into the alkaline solution, temperature of the reaction solution, the stirring rate, etc.- that play role in the wet chemical precipitation process and some of these parameters were investigated in this work. Each of these factors individually may influence the crystal and/or amorphous phases that are obtained at the end of the process. Preparation and reaction of the precursor solutions, aging of the final solution and precipitation, filtrating and washing, drying and eventually heat treating the precipitation are the main steps that were carried out throughout the synthesis process. X-Ray Diffraction (XRD), Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) and Fourier Transform Infrared Spectroscopy (FTIR) characterization studies were applied in order to determine the chemical, microstructural and molecular bonding properties of the powders produced.

In this study, alumina–hydroxyapatite–tricalcium phosphate (α-Al 2 O 3 –HA–TCP) porous composite powders were produced and characterized. At first, boehmite sol (AlOOH) was obtained via sol–gel process by using aluminium isopropoxide (Al(OC 3 H 7 ) 3 ) as the starting material. Bovine hydroxyapatite (BHA) powders derived from deproteinized bovine bones were added as 10, 20, 30 and 50% weight of the starting material to each boehmite sol. Also Na-alginate was added to the boehmite sol as the dispersive agent. Subsequently, gelation for 3 h at 110 °C was applied to each sol mixture. Finally, gelated samples were heat treated for 2 h at 500, 800, 1000 and 1300 °C. DTA–TGA, XRD, FTIR and SEM-EDS analyses were used to characterize the obtained composite powders composed of α-Al 2 O 3 –HA–TCP phases. In order to investigate porosity properties, powders were pressed with hydraulic manual press and formed into pellets. Later these pellets were sintered for 2 h at 1300 °C. Apparent porosity and bulk density tests were applied to the pellets. The evaluation of these tests results indicate that a novel α-Al 2 O 3 –HA–TCP composite material with ∼38–44% apparent porosity has been produced.

Alumina (α-Al2O3) and hydroxyapatite (Ca10(PO4)6(OH)2) are biocompatible ceramic materials. Alumina is described as “bioinert” while hydroxyapatite as “bioactive”. These ceramics can be used in production of orthopedic prostheses, dental implants and bone filling materials either separately or in composite form. Especially porous materials attract attention due to their supportive structure for cell and tissue growth/development.Alumina was derived via sol-gel method. Firstly, boehmite (AlOOH) sol was produced by hydrolyzing the starting material, aluminium iso-propoxide (AIP, Al(OC3H7)3). Then this sol was mixed with hydroxyapatite powders (Bovine Hydroxyapatite, BHA) obtained from bovine bones. Subsequently, the mixture was gelated at 110 °C for 3 hours and the resulting gel mixture was heat treated at 1300 °C for 2 hours. BHA powders were not synthetic and added as 10 and 30 wt.% of AIP to the boehmite sol. Irregular shape of the powders produced after the heat treatment was interpreted as a sign of porosity.SEM-EDS and XRD characterization studies were performed on heat treated powders. XRD results showed that powders were composed of α-alumina and apatite based phases such as tricalcium phosphate and hydroxyapatite. SEM images of the composite powders indicated that neck bonds were not formed between α-alumina and apatite based phases. Comparison of SEM images and EDS results of pure BHA and composite powders revealed that pure BHA powders possess granular particle shape. Furthermore, needle shaped alumina particles were observed in the composite sample with 10 wt.% BHA. Finally, it has been found out that alumina particles were placed layer by layer in the composite powders with 30 wt.% BHA.

Oxidation creates an important problem with the increasing temperature and additionally if one of the components contains an amount of carbon, then there will be a COx emission risk which has a detrimental effect for the atmosphere. One of the methods to prevent the oxidation of silicon carbide (SiC) is to coat it with Al2O3 which has high thermal stability. In this study, the properties of Al2O3 coated SiC composite powders were examined to prevent the oxidation of SiC particles by developing a thermal barrier coating and it is aimed to contribute for reducing the gases which make a greenhouse effect and cause global warming. Firstly, boehmite sol was prepared via the sol gel route and then 5 wt% β-SiC (< 100 nm) nanosized particles were added to the boehmite sol and gelation was completed. Alumina coated SiC powders were heat treated at 100, 550, 1,000, 1,300 and 1,600°C under dry air and argon atmospheres. Characterisation analyses showed that alumina coated SiC particles underwent to slightly internal oxidation with the partial oxidation depending on the oxygen ion mobility during the transformation from boehmite to alumina in the interior atmosphere while alumina coated SiC particles gained oxidation resistance against the outer atmosphere.