Celaletdin Ergun

Enhanced functions of osteoblasts on nanophase ceramics

Select functions of osteoblasts (bone-forming cells) on nanophase (materials with grain sizes less than 100 nm) alumina, titania, and hydroxyapatite (HA) were investigated using in vitro cellular models. Compared to conventional ceramics, surface occupancy of osteoblast colonies was significantly less on all nanophase ceramics tested in the present study after 4 and 6 days of culture. Osteoblast proliferation was significantly greater on nanophase alumina, titania, and HA than on conventional formulations of the same ceramic after 3 and 5 days. More importantly, compared to conventional ceramics, synthesis of alkaline phosphatase and deposition of calcium-containing mineral was significantly greater by osteoblasts cultured on nanophase than on conventional ceramics after 21 and 28 days. The results of the present study provided the first evidence of enhanced long-term (on the order of days to weeks) functions of osteoblasts cultured on nanophase ceramics; in this manner, nanophase ceramics clearly represent a unique and promising class of orthopaedic/dental implant formulations with improved osseointegrative properties.

An in vitro evaluation of the Ca/P ratio for the cytocompatibility of nano-to-micron particulate calcium phosphates for bone regeneration

Calcium phosphate based bioceramics have been widely used for orthopedic applications due to their chemical similarity to natural bone. The Ca/P stoichiometry of calcium phosphates strongly influences their performance under biological conditions, which have not yet been fully elucidated to date. For this reason, the objective of this in vitro study was to understand the relationship between the Ca/P ratio of nano-to-micron particulate calcium phosphate substrates and their biological properties, such as osteoblast (bone-forming cell) viability, collagen production, alkaline phosphatase activity and nitric oxide (NO) production. A group of calcium phosphates with Ca/P ratios between 0.5 and 2.5 were obtained by intentionally adjusting the Ca/P stoichiometry of the initial reactants necessary for calcium phosphate precipitation. For samples with 0.5 and 0.75 Ca/P ratios, tricalcium phosphate (TCP) and Ca(2)P(2)O(7) phases were observed. In contrast, for samples with 1.0 and 1.33 Ca/P ratios, the only stable phase was TCP. For samples with a 1.5 Ca/P ratio, the TCP phase was dominant; however, small amounts of the hydroxyapatite (HA) phase started to appear. For samples with a 1.6 Ca/P ratio, the HA phase was dominant. Lastly, for samples with 2.0 and 2.5 Ca/P ratios, the CaO phase started to appear in the HA phase which was the dominant phase. Moreover, the average grain size and the average pore size decreased from micron-scale (e.g. 1370nm for a 0.5 Ca/P ratio) to nano-scale (e.g. 262nm for a 2.5 Ca/P ratio) with increasing Ca/P ratios. The porosity (%) of calcium phosphate substrates also decreased with increasing Ca/P ratios. Previous in vitro results demonstrated increased osteoblast adhesion on calcium phosphates with higher Ca/P ratios (up to 2.5). The present study showed that the collagen production by osteoblasts was similar between all the calcium phosphates but slightly lower with a 1.6 Ca/P ratio. Greater alkaline phosphatase activity by osteoblasts was observed in all the cultures with various calcium phosphates (0.5-2.5 Ca/P ratios) than in the control (only cells in culture). Ca/P ratios of <2 and 1 optimized osteoblast viability and promoted alkaline phosphatase activity in osteoblasts, respectively. However, the presence of the CaO phase in Ca/P ratios 2.0 increased osteoblast NO production and decreased osteoblast viability. In summary, this study provided evidence that the Ca/P ratio of calcium phosphate is a very important factor that should be considered when selecting nano-to-micron particulate calcium phosphates for various orthopedic applications.

The effect of combined delivery of recombinant human bone morphogenetic protein-2 and recombinant human vascular endothelial growth factor 165 from biomimetic calcium-phosphate-coated implants on osseointegration.

OBJECTIVES The delivery of growth factors for enhanced osseointegration depends on the effectiveness of the carrier systems at the bone-implant interface. This study evaluated the effect of solo and dual delivery of recombinant human bone morphogenetic protein-2 (rhBMP-2) and recombinant human vascular endothelial growth factor (rhVEGF(165) ) from biomimetically octacalcium phosphate-coated implants on osseointegration. MATERIALS AND METHODS Biomimetic implants, bearing either a single growth factor (BMP or VEGF) or their combination (BMP+VEGF), were established, and compared with acid-etched (AE, control) and biomimetic implants without growth factor (CAP). Implants were placed into frontal skulls of nine domestic pigs. The quality of osseointegration was evaluated using microradiographic and histomorphometric analysis of bone formation inside four defined bone chambers of the experimental implant at 1, 2 and 4 weeks. RESULTS Biomimetic implants, either with or without growth factor, showed enhanced bone volume density (BVD) values after 2 and 4 weeks. This enhancement was significant for the BMP and BMP+VEGF group compared with the control AE group after 2 weeks (P<0.05). All biomimetic calcium-phosphate (Ca-P) coatings exhibited significantly enhanced bone-implant contact (BIC) rates compared with the uncoated control surface after 2 weeks (P<0.05). However, the combined delivery of BMP-2 and VEGF did not significantly enhance BIC at the final observation period. CONCLUSION It was concluded that the combined delivery of BMP-2 and VEGF enhances BVD around implants, but not BIC. Therefore, it may be assumed that changes in the surface characteristics should be considered when designing growth factor-delivering surfaces.

Osteoblast adhesion on novel machinable calcium phosphate/lanthanum phosphate composites for orthopedic applications.

Lanthanum phosphate (LaPO(4), LP) was combined with either hydroxyapatite (HA) or tricalcium phosphate (TCP) to form novel composites for orthopedic applications. In this study, these composites were prepared by wet chemistry synthesis and subsequent powder mixing. These HA/LP and TCP/LP composites were characterized in terms of phase stability and microstructure evolution during sintering using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Their machinability was evaluated using a direct drilling test. For HA/LP composites, LP reacted with HA during sintering and formed a new phase, Ca(8)La(2)(PO(4))(6)O(2), as a reaction by-product. However, TCP/LP composites showed phase stability and the formation of a weak interface between TCP and LP machinability when sintered at 1100 degrees C, which is crucial for achieving desirable properties. Thus, these novel TCP/LP composites fulfilled the requirements for machinability, a key consideration for manufacturing orthopedic implants. Moreover, the biocompatibility of these novel LP composites was studied, for the first time, in this paper. In vitro cell culture tests demonstrated that the LP and its composites supported osteoblast (bone-forming cell) adhesion similar to natural bioceramics (such as HA and TCP). In conclusion, these novel LP composites should be further studied and developed for more effectively treating bone related diseases or injuries.

Synthesis and characterization of Ag-containing calcium phosphates with various Ca/P ratios

Ag-containing calcium phosphate (CaP) powders were synthesized by a precipitation method using aqueous solutions of calcium nitrate, silver nitrate, and ammonium phosphate. The powders were sintered at temperatures ranging from 1173 to 1473 K. The charged atomic ratios of (Ca+Ag)/P and Ag/(Ca+Ag) in solution were varied from 1.33 to 1.67 and from 0 to 0.30, respectively. The Ag content in the as-precipitated CaP powders increased with the charged Ag/(Ca+Ag) atomic ratio in solution and was lower than the charged Ag/(Ca+Ag) value. The as-precipitated CaP powders consisted of hydroxyapatite (HA) as the main phase. Ag nanoparticles were observed on the as-precipitated HA particles under all conditions of Ag addition. After the sintering, HA, β-TCP (tricalcium phosphate), α-TCP, and β-CPP (calcium pyrophosphate) were mainly detected as CaPs on the basis of the Ca/P atomic ratio of the as-precipitated powders. The addition of Ag stabilized the β-TCP phase, and the distribution of Ag in β-TCP was homogeneous. A metallic Ag phase coexisted with HA. The solubility of Ag in HA was estimated to be 0.0019-0.0061 (Ag/(Ca+Ag)) atomic ratio, which was lower than that in β-TCP (higher than 0.0536) and higher than that of β-CPP (below the detection limit of analyses).

In vitro performance of Ag-incorporated hydroxyapatite and its adhesive porous coatings deposited by electrostatic spraying

Bacterial infection of implanted materials is a significant complication that might require additional surgical operations for implant retrieval. As an antibacterial biomaterial, Ag-containing hydroxyapatite (HA) may be a solution to reduce the incidences of implant associated infections. In this study, pure, 0.2mol% and 0.3mol% Ag incorporated HA powders were synthesized via a precipitation method. Colloidal precursor dispersions prepared from these powders were used to deposit porous coatings onto titanium and stainless steel substrates via electrostatic spraying. The porous coating layers obtained with various deposition times and heat treatment conditions were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Scratch tests were conducted to assess the adhesion strength of the coating. Antibacterial activity of Ag-incorporated HA was tested towards Escherichia coli (E. coli) at various incubation times. Osteoblast adhesion on Ag-incorporated HA was evaluated to assess biocompatibility. Improvement in adhesion strength of the coating layer was observed after the heat treatment process due to mutual ionic diffusion at the interface. The Ag-incorporated HA killed all viable E. coli after 24h of incubation, whereas no antibacterial activity was detected with pure HA. In addition, in vitro cell culture tests demonstrated osteoblast adhesion similar to pure HA, which indicated good cytocompatibility. In summary, results of this study provided significant promise for the future study of Ag-incorporated HA for numerous medical applications.

Comparison and validation of finite element analysis with a servo-hydraulic testing unit for a biodegradable fixation system in a rabbit model

The aim of this study was the biomechanical validation of three-dimensional finite element analysis (FEA) with a servo-hydraulic testing unit (STU) for a resorbable fixation system (RFS) in a rabbit model. Bilateral mandibular vertical body osteotomies (BMVBO) were performed in 15 female New Zealand rabbits. The animals were divided into three groups. The STU and FEA tests were done immediately after surgery in group 1 (1 day), at the first postoperative month in group 2, and at the third postoperative month in group 3. Both stress tests were carried out by applying vertical forces at the lower incisal edge, loading from 0 N force and increasing this until breakage occurred at the bone. The maximum forces that the hemimandibles could stand and the amount of deformation were recorded and analysed with the FEA and STU tests. We found the STU and FEA test results to be similar and that they could be used interchangeably for groups 1 and 3. However, the FEA results differed most from the real STU values in group 2 because of callus formation that had not ossified at the osteotomy line.

In Situ Synthesis of B4C / TiB2 Composites from Low Cost Sugar Based Precursor

In the present study, a method based on sulfuric acid dehydration of sugar was developed to synthesis a precursor material, which can yield B4C/ TiB2 composites at much lower temperatures compared to traditional carbothermal methods. The precursor material for pure B4C and B4C / TiB2 composites were heat treated at 1650oC under Ar and Ar+H2 atmosphere. Then the samples were characterized by X-ray diffraction (XRD) and crystallized B4C and B4C / TiB2 composites can be obtained at 1650oC

Synthesis and Characterization of Ag Doped Hydroxylapatite as an Antibacterial Scaffolds Material

Not many studies have been found in the literature on the effect of Ag ions on the structure and phase stability of hydroxylapatite which may be recognized as important information in the scaffold fabrication. The objective of the current study is to develop a better understanding on the structure and behavior of the antibacterial Ag incorporated hydroxylapatite. In order to do this, Ag doped hydroxylapatite was made by a precipitation method, and sintered in air at 1300oC. The materials were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), density measurements and scanning electron microscopy (SEM).

Ion Nitriding of CoCrMo Alloys

Medical grade cast CoCrMo alloy (F75) was ion nitrided under different process parameters including time (2, 9 hr) and temperature (600, 800 0C) at a gas mixture of 80%N2–20%H2. The nitrided surfaces were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). MicroVickers hardness tests were done on the cross sections of the nitrided specimens to investigate the hardness profile. The significant effects of nitriding temperature and time on the microstructure and hardness value of nitrided surface layers were displayed.