Muharrem Timuçin

An investigation of the chemical synthesis and high-temperature sintering behaviour of calcium hydroxyapatite (HA) and tricalcium phosphate (TCP) bioceramics

The experimental conditions for the synthesis of sub-micrometre,spherical particles of calcium hydroxyapatite[Ca10(PO4)6(OH)2] (HA) andtricalcium phosphate [Ca3(PO4)2] (TCP) areinvestigated through chemical coprecipitation from the aqueous solutions ofcalcium nitrate and di-ammonium hydrogen phosphate salts. The precipitationprocess employed was also found to be suitable for the production ofsub-micrometre HA/TCP composite powders in situ. The synthesized pureHA and TCP powders were found to be stable even at 1300°C in air forprolonged heating times. Bioceramic sample characterization was achieved bypowder X-ray diffraction (XRD), scanning electron microscopy (SEM), energydispersive X-ray spectroscopy (EDX), and density and surface area measurements.Crystallographic analyses of HA powders were performed by the Rietveld method onthe powder XRD data.

Fabrication and characterization of porous tricalcium phosphate ceramics

Preforms of beta tricalcium phosphate (β-TCP) ceramics were produced by using a modified slip casting technique. The slip was prepared by suspending custom-made TCP powder and PMMA beads in an aqueous medium stabilized with an acrylic deflocculant. Porous TCP ceramics were obtained by sintering the polymer-free preforms for 2 h at 1000 °C. The XRD pattern for the TCP ceramic indicated that the product was essentially pure β-TCP. SEM examination of pore size and pore size distribution revealed that the ceramic was appropriate for repair of cortical defects.

Slip-casting properties of Si3N4 with Y2O3 and Al2O3 as sintering additives

The effects of particle charging and powder–liquid suspension stability on the slip-casting properties of Si3N4 powder were examined. Y2O3 and Al2O3, used as sintering additives, were seen to affect the dispersion stability of the base material (Si3N4). The zeta potentials of the three powders and the rheological behaviour of the 55 wt% solids-loaded slips, involving known concentrations of a polymeric deflocculant (Dolapix PC33), showed that the multicomponent system can be dispersed stably within the pH range 9–11. Green compacts, obtained by casting these slips into plaster moulds, were found to give densities in the range 50–61% of the theoretical value.

Compositional Modifications in Humidity Sensing MgAl2O4 Ceramics

Abstract. The MgAl2O4 powders were synthesized using the mixed oxide technique. The powders were doped with Na + ion to modify the sintering behavior and the response characteristics of the spinel ceramics. The variations in electrical impedance were determined at room temperature under relative humidity (RH) values ranging from 21 to 98%. The effect of Na2O addition and sintering temperature on the microstructure and humidity sensitivity of MgAl2O4 were investigated.

Osteogenic differentiation of MC3T3-E1 cells on different titanium surfaces

mRNA expressions related to osteogenic differentiation of MC3T3-E1 cells on electro-polished smooth (S), sandblasted small-grit (SSG) and sandblasted large-grit (SLG) surfaces of titanium alloys were investigated in vitro. Gene expression profiles of cells were evaluated using the RT2 Profiler PCR microarray on day 7. Mineralizing tissue-associated proteins, differentiation factors and extracellular matrix enzymes mRNA expressions were measured using Q-PCR. SLG surface upregulated 23 genes over twofolds and downregulated 3 genes when compared to the S surface. In comparison to the SSG surface, at least a twofold increase in 25 genes was observed in the SLG surface. BSP, OCN, OPN, COL I and ALP mRNA expressions increased in the SLG group when compared to the S and the SSG groups. BMP-2, BMP-6 and TGF-β mRNA expressions increased in both the SSG and the SLG surfaces. MMP-2 and MMP-9 mRNA expressions increased as the surface roughness increased. This study demonstrated that surface roughness of titanium implants has a significant effect on cellular behavior and SLG surface apparently increased gene expressions related to osteogenesis when compared to the S and the SSG surfaces.

Mesenchymal Stem Cells and Nano-Bioceramics for Bone Regeneration.

Orthopedic disorders and trauma usually result in bone loss. Bone grafts are widely used to replace this tissue. Bone grafts excluding autografts unfortunately have disadvantages like evoking immune response, contamination and rejection. Autografts are of limited sources and optimum biomaterials that can replace bone have been searched for several decades. Bioceramics, which have the similar inorganic structure of natural bone, are widely used to regenerate bone or coat metallic implants. As people continuously look for a higher life quality, there are developments in technology almost everyday to meet their expectations. Nanotechnology is one of such technologies and it attracts everyones attention in biomaterial science. Nano scale biomaterials have many advantages like larger surface area and higher biocompatibility and these properties make them more preferable than micro scale. Also, stem cells are used for bone regeneration besides nano-bioceramics due to their differentiation characteristics. This review covers current research on nano-bioceramics and mesenchymal stem cells and their role in bone regeneration.

The efficacy of bioceramics for the closure of burr-holes in craniotomy: Case studies on 14 patients

Purpose Bioceramics are currently in use to cover bone defects in orthopedics and craniofacial surgery. But their compatibility and efficacy in cranium were not investigated in detail. The aims of this study were to produce, characterize, and assess the biocompatibility and osteointegration of Si-HA, Si-Sr-HA, HA-Wollastonite, and HA-Wollastonite-Frit bioceramics. Methods Bioceramics were implanted into the burr holes of 14 craniotomy patients who were followed up from three to 24 months. Radiologic and scintigraphic examinations were performed. Results Osteoblastic activity quantified by scintigraphy increased from 6.865 to 22.991±1.682 from four to eight months in the HA-Woll group. Adding fritt into HA-Woll decreased osteoblastic activity at 10 months. Si-Sr-HA displayed significantly higher osteoblastic activity when compared to the craniotomy site at 12 months. The scintigraphic ratio of the bioceramic implanted regions to the craniotomy sites varied between 1.10 and 1.57. Osteoblast formation and establishment of the trabecular pattern of bone was observed in the surroundings of bioceramics in two patients. Conclusion These bioceramics can be safely used to cover the burr holes of craniotomy patients, as well as to close the cranial bone defects.

Periodontal ligament cell behavior on different titanium surfaces

Abstract Aim. The purpose of this study was to investigate proliferation, morphology, mineralization and mRNA expressions of mineralized tissue associated proteins of PDL cells on smooth (S), sandblasted small-grit (SSG), sandblasted large-grit (SLG) and sodium titanate (NaTi) coated titanium alloys, in vitro. Methods and materials: PDL cells were cultured with DMEM media containing 10% FBS on the S, SSG, SLG and NaTi titanium surfaces. PDL cell proliferation, mineralization and immunohistochemistry experiments for Bone Sialoprotein (BSP) were performed. The morphology of the PDL cells was examined using confocal and scanning electron microscopy (SEM). Gene expression profiles of cells were evaluated using a quantitative-polymerase chain reaction (Q-PCR) for type I collagen (COL I), Osteocalcin (OCN), osteopontin (OPN) and Runt-related transcription factor-2 (Runx2) on days 7 and 14. Results. Proliferation results on days 6 and 10 were similar in groups, while those of day 13 revealed a decrease in the NaTi group when compared to the S group. NaTi surface induced BSP mRNA expression which was correlated with mineralization tests and BSP immunostaining results. Increased Runx2 mRNA expression was also noted in the NaTi surface when compared to other surfaces. Conclusions. This study considers the NaTi surface as a potential alternative to SSG and SLG surfaces. This surface might provide a promising environment for PDL ligament-anchored implants.

Apatites for Orthopedic Applications

The complex nature of the bone complicates its reconstruction and arises the use of biomaterials for this purpose. The materials should have similar properties with the bone and can be used in different application. Particularly, beta-tricalcium phosphate (β-TCP) and hydroxyapatite (HAp) are biocompatible, bioactive, and osteoconductive materials having similar properties with the bone. In this review, the applications of tricalcium phosphate and hydroxyapatite in orthopedics are given in terms of graft, carrier, and coating materials.

Nanocrystalline Apatite-Based Biomaterials and Stem Cells in Orthopaedics

Nanocrystalline apatite-based biomaterials and stem cells are emerging research fields in orthopaedic surgery and traumatology that have the potential of improving quality of life of the elderly and enhance health-related socio-economic challenges. Nanocrystalline apatite-based biomaterials and especially calcium phosphate nano-biomaterials exploit new physical, chemical and biological properties that have the possibility to increase surface area and improve tissue integration. Stem cells of adult origin decrease inflammation, increase vascularity and are able to replace degenerated tissue cells during the process of regeneration. The bone is the only human tissue that regenerates. Musculoskeletal disorders including osteoporotic fractures and osteoarthritis decrease quality of life in the elderly and cause severe burden on economics. Nanocrystalline calcium phosphate bioceramics have the ability to prevent or treat osteoporotic fractures when combined with stem cells. These biomaterials may also be used for drug delivery purposes to treat bone infections when combined with stem cell as they can assist in treating osteoarthritis. Current research challenges are trying to overcome the toxicity and carcinogenesis with these cells and nanomaterials. Long-term stability of these cells and materials is another challenge for these materials. This chapter deals with nanocrystalline calcium phosphate bioceramics and mesenchymal stem cells.