Key Engineering Materials Vol. 587

Abstract: Physico-chemical characteristics impact directly or indirectly the bioactive properties of biomaterials, it is then essential to correlate it with their effect in vivo. A panel of biomaterials available on the market, based on Hydroxyapatite (HA) and Tricalcium phosphate (β-TCP) is studied in terms of surface area, hydrophilicity, porosity, zeta potential, crystalline phases and density. This study highlights the dispersity of commercial calcium phosphates (CaP) properties, and demonstrates how the quality criteria required for such bone substitute based on biomimicry concept, whose pores distribution is certainly the more relevant, are often incompletely or not respected according to literature.

Abstract: The Hydroxyapatite (HA), the major component of the inorganic portion of bones, may be obtained from different sources for use as biomaterial in the reconstruction of critical bone defects. Among these resources, the eggshell appears as a promising alternative since it is a waste material which may be reused as a source of calcium carbonate after adequate treatment, giving rise to mineral hydroxyapatite. After morphological and physicochemical adjustments allowing its standardization and utilization, hydroxyapatite (HA) may turn into a potentially useful biomaterial for different experimental purposes. This paper aims to present a viable method for obtaining a hydroxyapatite from Ostrich eggshell by wet precipitation process. This phosphating technique with emphasis on the issue of sustainable reuse of disposable materials allows the production of a synthetic crystalline material with characteristics similar to those of bone and tooth. The structural characterization was performed by X-Ray diffraction and scanning electron microscopy with field emission gun and energy dispersive X-ray in the Military Institute of Engineering.

Abstract: Removal of bacteria is important not only at implantation, but after long-term implant/prosthesis use. This requires strategies that employ different approaches for combating bacteria. Halides have the potential of an additional mechanism, and together with silver may provide a more powerful antibacterial strategy. Silver iodide was synthesized as colloids with a positive and negative charge and incorporated into an amorphous calcium phosphate (ACP) to provide a possible greater antibacterial action. Colloids were characterized by FTIR spectroscopy and the charge measured by zeta potential. Phase analysis by X-ray diffraction patterns confirmed the formation of b-AgI nanoparticles. Minimum inhibitory concentrations (MIC) for preventing the growth of Staphylococcus aureus and Pseudomonas aeruginosa were lower for ACP containing negatively charged silver halides. Amorphous calcium phosphates with silver iodide exhibited good inhibition capacity. Solubility was determined by the increase in pH and the release of silver after 48 hours. The minimum bactericidal concentration (MBC) was also determined. This work has shown the effect of AgI charge in amorphous calcium phosphate for providing antibacterial action.

Abstract: The process is a simple chemical method and aims to produce nano-structured calcium phosphate powders from natural sources, for biomedical applications. For this purpose, Atlantic Deer Cowrie (ADC) shells (Cypraea cervus Linnaeus, 1771) were collected from a local gift store in Istanbul. The empty shells were cleaned and crushed then were ball milled and sieved under 100µm. The raw powders were suspended on a hotplate stirrer for a simple chemical agitation. The temperature was kept at 80°C for 15 min. and then appropriate amount of H₃PO₄ was added by titration into the prepared solution to form calcium phosphate precursors. The solution was stirred on a hotplate for 8 hours then dried at 100°C for 24 hours. Afterwards the resulting dried sediments were collected and heat treated between 400-800°C for 4 hours, dependent on the required specific calcium phosphate phase. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were carried out for identifying various hydroxyapatite (HA), tricalcium phosphate (TCP) and other calcium phosphate phases. Various particle sizes ranging from nano to micron, are obtained depending on the chemistry used and the processing technique applied during the production. A range of calcium phosphate phases can be obtained from ADC shells, by using a simple and economic conversion method. Proper cleaning methods developed and appropriate preparation techniques will enable us to use these nano calcium phosphate powders in orthopedic and dental applications.

Abstract: In this study the formation of calcium phosphate phase via double diffusion method into a hydrogel matrix was investigated and its phase transformation in simulated body fluid was studied. White precipitate was formed within the hydrogel, due to the diffusion of calcium and phosphate ions through the hydrogel matrix in similar pH to human body. Phase composition, microstructure and structural groups in the composite samples were also characterized by X-Ray Diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infra-red (FTIR) analyses. Microstructure of precipitates formed within middle hydrogel, showed that detected materials are composed of carbonated hydroxyapatite and dicalcium phosphate dihydrate (DCPD, brushite). The particle size was about 10 nm .Analysis results showed that after incubation in simulated body fluid, dicalcium phosphate dehydrate phase transformed into crystalline hydroxy apatite.

Abstract: In this present work we could show that a microporous β-TCP ceramic with interconnected porosity and 5 μm median pore diameter is a useful delivery vehicle for drugs and growth factors. However, it is necessary to combine the ceramics with degradable biopolymers, like hydrogels for retarded release. So the drug release could be increased by the factor 7 from 3 up to 21 days with concentrations having an antimicrobial activity. Concerning the growth factor, the release period was prolonged significantly.

Abstract: The difficulty of beta tricalcium phosphate (β-TCP) crystallization in aqueous media opens the question whether β-TCP can be produced using an alternative pathway. Amorphous calcium phosphate (ACP) is metastable in an aqueous environment and prefers a more stable apatite phase. Others have transformed a crystallized calcium deficient hydroxyapatite (Ca-def HAp) into β-TCP, but automatic transformation from ACP to Ca-def HAp followed by transformation to β-TCP has not been addressed. This work shows the formation of Ca-def HAp after different aging times of ACP and the subsequent transition to β-TCP. An amorphous phase with a Ca/P ratio of 1.5 was synthesized, rinsed, filtered and excess fluid removed for maturation. The resulting apatite was monitored with X-ray diffraction at different temperatures. Heating at 700 °C then investigated the transition to β-TCP. It was found that Ca-def HAp formed at short aging times produced a combination of alpha and beta phases, but a longer aging time led to pure β-TCP.

Abstract: The aim of this study is to induce bone from immature muscular tissue in vitro using recombinant human BMP (rhBMP)-2 and expanded polytetrafluoroethylene (ePTFE) as a scaffold. Commercially available rhBMP-2 was used in this experiment. IMTs were harvested from the forelimbs of 20th Sprague-Dawley embryonic rats and placed into a homogenizer with 10ng/μl of rhBMP-2 and then homogenized. The homogenized IMT was placed on ePTFE and cultured for 2 weeks. The analyses of histological observation, electron probe micro analyzer (EPMA), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were carried out following culture. The bone-like tissue, which was made up of osteoblast-like cells and osteoids, was partially observed by H-E staining. Moreover, strong mineral deposition was observed in the extracellular matrix by von Kossa staining. Ca, P and O were detected in the extracellular matrix by EPMA and were confirmed to be at almost the same position based on the findings of synchronized images. XRD patterns and FTIR spectra of specimen were found to have typical hydroxyapatite crystal peaks and spectra, respectively. These results suggest that rhBMP-2 induced IMT differentiation into bone-like tissue in vitro.

Abstract: The aim of this work was to study the phase transformation during the setting reaction of beta tricalcium phosphate (β-TCP) and phosphoric acid with chitosan solution added. To follow the kinetics of the phase transformation, two methods were used: x-ray diffraction (XRD) was used to study the phase evolution during the hardening process in real time, and was also used in samples where the reaction was supposedly stopped in different times using acetone, as indicated in literature. The setting reaction occurs so fast that the phase transformation could not be observed, but it was possible to invalidate the second mentioned method for this system, as it induces the final product dicalcium phosphate dihydrate DCPD (brushite) to be converted into his anhydrous form dicalcium phosphate DCP (monetite). The addition of chitosan in order to improve biocompatibility was successfully done, it could be observed that chitosan inhibits brushite crystallization in the first moment of the reaction, but the final product was not affected by it.

Abstract: Micro-nano structured TiO₂ films were prepared by hydrothermally seed layer-induced synthesis. The results showed that the films were composed of TiO₂ platelets in size of 2μm~10μm. The maximum distance between platelets was ~4 μm. There were TiO₂ nanodots (seed layer) in size of ~100nm between TiO₂ platelets. This structured film was proven to be anatase and more anatase was detected along with hydrothermal synthesis. Water contact angle varied from 103° to 149° along with hydrothermal synthesis and all films showed super-hydrophilicity after UV illumination. These micro-nano structured films obtained in this study could potentially applied in many biomedical applications, e.g., osseointegration film and cell sheet technology, owing to its excellent biocompatibility and UV switchable super-hydrophilicity.