Ahmet Pasinli

A new approach in biomimetic synthesis of calcium phosphate coatings using lactic acid–Na lactate buffered body fluid solution

The main objective of this study was to investigate calcium phosphate (CaP) coatings on Ti6Al4V substrates by using the biomimetic technique. To this purpose, a new solution was developed to coat CaP on Ti6Al4V alloy substrates. The newly formulated body fluid (Lac-SBF) contained appropriate amounts of sodium lactate (NaL) and lactic acid (HL), as well as all the other ionic constituents of the human blood plasma. The inorganic ion concentrations of the Lac-SBF solutions were identical with those of human blood plasma. The new Lac-SBF solution of this study eliminated the need for using Tris/HCl or Hepes/NaOH buffers. Prior to coating, Ti6Al4V substrates were chemically treated in NaOH and/or NaOH+H(2)O(2) solutions as an alternative route and then heated at 600 degrees C for 1h in air. In the previous applications, the Cl(-) ion concentration was found to be higher than blood plasma 103mM, which exists in human blood plasma as a result of Tris/HCl which are used to prevent precipitation and to keep the pH level at certain values. In this study, instead of using Tris/HCl, HL/NaL which are generated by human body and do not show any toxic behavior, are used and Cl(-) concentration was kept at 103mM value for the first time. The prepared Lac-SBF was shown to have similar concentration to human blood plasma in terms of all inorganic ions for the first time. Solution properties were evaluated by using turbidimeter, pH meter and rheometer. The coatings were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and a scratch tester. The obtained results are presented and discussed.

Preparation of Hydroxyapatite Coating by Using Citric Acid Sodium Citrate Buffer System in the Biomimetic Procedure

Abstract The present study has been aimed to investigate the preparation and analysis of calcium phosphate (CaP) based hydroxyapatite (HA, Ca10(PO4)6(OH)2) coatings formed on Ti6Al4V alloys in a new buffer environment. The coating process has been performed by means of biomimetic method. In the study, a synthetic body fluid (SBF), which is fully compatible with human blood plasma, has been prepared for the first time in the literature by using the citric acid – sodium citrate buffer system. Using this buffer system will not cause any toxic reactions in the human body. CaP coating of the Ti6Al4V surface has been performed in this new SBF. The surface roughness and thickness specifications of the coatings have been determined, their microstructures have been analyzed by using a scanning electron microscope (SEM), the elemental analysis (EDX) of the coating surfaces and the XRD analysis have been done. The results are presented and discussed.

Nonlinear stress analysis in adhesively bonded single-lap joint

In this investigation, an analytical elastic–plastic solution was proposed for a single-lap joint. A ductile adhesive joint material was used as the bond material. FM-73 was utilized in the study. The influence of the bending moment was neglected in the solution. The solution was modified for shear stresses. The analytical solution was compared with the FEM solution. An ANSYS 10.0 solution was employed in the numerical solution. Both solutions were compared with each other. These two solutions produced close agreements.

Fracturing and adhesion behavior of hydroxyapatite formed by a citric acid and sodium citrate buffer system

Abstract This study aims to examine the fracture and surface adhesion behavior of hydroxyapatite (HA) coatings created in acitric acid – sodium citrate buffer system. Coatings were implemented on the surface of Ti6Al4V. The modulus of elasticity, hardness and adhesion strength values of the presented coatings were determined, the fracture toughness values were calculated and scanning electron microscope (SEM) images were taken as well. Finally, the mechanical properties found by the tests implemented to hydroxyapatite coatings applied on Ti6Al4V, which yielded successful outcomes were compared to the mechanical properties of bone. The fracture toughness achieved in this study was found to be more compatible with the mechanical properties of the original bone itself when compared to the literature findings. Besides, the adhesion strength was found to be remarkably high.

In vivo investigation of calcium phosphate coatings on Ti6-Al-4V alloy substrates using lactic acid - sodium lactate buffered synthetic body fluid

OBJECTIVE The aim of this study was to evaluate the mode of failure and biomechanical characteristics of Ti-6Al-4V anchors biomimetically coated with calcium phosphate (CaP) for soft tissue fixation to bone in an animal model. METHODS The current study included 14 adult New Zealand white rabbits equally divided into two groups. Calcium phosphate-coated Ti-6Al-4V anchors were used in the test group and non-coated Ti-6Al-4V anchors in the control group. A new approach was applied to synthesize the CaP coatings via the biomimetic growth in the Lac-SBF containing Ca(2+) and PO4(3-) ions, Na-lactate and lactic acid (HL). Titanium anchors were implanted into the right tibia, followed by biomechanical tensile strength tests. Histological studies were carried out after removal of anchors (bone-implant surface). RESULTS The CaP-coated Ti-6Al-4V anchors had significantly higher tensile strength (p=0.003) and displacement values (p=0.004) than the non-coated anchors. Control group scores were higher than those of the test group (14 and 9, respectively) in tensile strength tests. CONCLUSION The new CaP coating can be used in orthopedic surgery as catalyzer to improve bone ingrowth. We believe that our research will form a model for further research on biomimetic coatings on Ti-6Al-4V substrates.

Determination of fracture toughness of calcium phosphate coatings deposited onto Ti6Al4V substrate by using indentation technique

In this study, fracture toughness values of calcium phosphate (CaP) coatings deposited onto Ti6Al4V substrate were determined by using Vickers indentation method. In this new patent holding method, the activation processes were performed with NaOH and NaOH+H2O2 on the Ti6Al4V material surface. Thicknesses of CaP coatings were measured from cross-sections of the samples by using optical microscopy. Vickers indentation tests were performed by using microhardness tester. Young’s modulus values of the coatings were determined by using ultra microhardness tester. As a result, fracture toughness (K1C) values of the CaP coatings produced by using two different activation processes, were calculated by using experimental study results. These were found to be 0.43 MPa m1/2 and 0.39 MPa m1/2, respectively. It was determined that the CaP coating on Ti6Al4V activated by NaOH+H2O2 had higher fracture toughness than the CaP coating on Ti6Al4V activated by NaOH.

Lateral Buckling Analysis of Composite Cantilevers with Square Hole using the Finite Element Method

Abstract The influences of hole dimension and position on the lateral buckling behaviour of woven fabric laminated composite cantilever beams having a square hole were investigated. Firstly, the theoretical, experimental and numerical characteristics of critical buckling loads of the beams without holes were investigated and compared with each other. It was shown that there is a good agreement among the theoretical, experimental and numerical results. The ANSYS finite element program was used for the numerical analyses. Furthermore, the numerical analyses of some models with various hole dimensions, different layer thicknesses, square shapes and fiber directions were performed by changing the distance between the hole. It is concluded for a square hole that the increase of the hole dimensions causes decrease of critical lateral buckling loads.

A Model for the Calculation of Mechanical Properties of Hydroxyapatite Coatings on Ti6Al4V Substrate Using Finite Element Methods

The scope of this study is to find out yield curve on the coating-substrate system of hydroxyapatite (HA) by finite element modeling. With this regard, Hydroxyapatite (HA) coatings were successfully formed on Ti6Al4V substrates by using biomimetic technique. Experimental indentation tests were conducted on Dynamic Ultra-micro Hardness test machine. In finite element modeling (FEM), mechanical properties of coatings were determined by using ABAQUS software package. This numerical study was carried out using an axisymmetric FEM model. To calculate the mechanical properties of coating, the resulting load–unload test data of the samples obtained from the experimental indentation tests were analyzed and curvefitted in Kick’s and Meyer’s law for the loading and the unloading part of the loadunload curve respectively. Then, a set of analytical functions that take the pile-up and sink-in effects into account during instrumented sharp indentation were solved using numerical methods These analytical functions were defined within an identified representative plastic strain, er, for the Vickers indenter geometry as a strain level that allows for the description of the indentation loading response independent of strain hardening exponent, n.

To compare the different scaffolds according to porosity's properties

The main purpose of this study is to investigate the increase in osteoblast cells cultured on three different porosity scaffolds in vivo environment. Hence, Collagen + Poly-l-lactic acid (PLLA), Collagen +HA (30 C°), Collagen + HA (37 C°) were studied. During the operation, 20 ml bone marrow was taken for any of patient in sterile conditions. Mesenchymal stem cells were differentiated to osteoblast cells. After the ALP and morphological evaluations were assessed, osteoblast cells were planted on 3 different scaffolds and SEM observations were evaluated. At twenty-fifth day, konfleunt osteoblast cells were observed. Osteoblast cells were watched on Collagen + HA (30 C°) scaffold appropriately. According to our knowledge, in various bone defects, cell cultures on suitable scaffolds are contribute to clinical studies.