Qin He Zhang

Experimental Study on Construction of Vascularized Bone Graft with Osteoinductive Calcium Phosphate Ceramics In Vivo

This study was to aimed to explore a new method for fabricating a bone substitute, which is constructed of vascularized bone graft with osteoinductive calcium phosphat e cer mics in vivo. A total of 32 small and 16 big ceramic cylinders were prepared, and bone-like apatite l yer was formed on the surface and the pore walls of ceramics in revised simulate d body fluid (RSBF). The smaller ceramics cylinders were implanted in dorsal muscles of dogs to evaluate the osteoinductive capacity. The bigger cylinders were mixed with fresh bone tissue and were implanted near a branch of femoral blood vessel in the dog’s leg muscles to construct vascularized bone gr afts. After implantation for 6 and 12 weeks, the specimens were harvested. The specimens were evalua t d by blood vessel staining, histological observation, tetracycline fluorescence labeling, Tc–MDP SPECT and mechanical tests. The results showed that bone formation was found in all the samples a nd bone grafts had good blood supply. This result indicated that this kind of calcium phosphate cera mi s had a good osteoinductivity and that vascularized bone grafts could be constructed wi th osteoinductive calcium phosphate ceramics in vivo. Introduction Bone defect is a common disease in clinic and to date, there is no s atisfactory method to treat the segmental bone defect. At present, autograft, allograft, xenograft and alloplasm materials could be used for repairing bone defects. Autograft is the best bone substitute, but it causes a secondary wound. Allograft and xenograft may bring immune response and infectious dise ase. Alloplasm material have been developed as a major bone substitute [1]. An ideal bone substitute should possess good biological and mechanical properties. The biological properties of an i deal bone substitute include biocompatibility, osteoconductivity, osteoinductivity, osteogenesis capabilit y. In 1980s, the appearance of tissue engineering brought about opportunities for repairing bone defects. Great achievements have been obtained in this field in the last 20 years [2] . But there are still some challenges ahead for bone tissue engineering [3]. Until now, no tissue e ngine ring bone composed of scaffold and cultured cells in vitro has been permitted to be applied in clinic [4]. Calcium phosphates ceramics are frequently used as bone substitute m a erials because of their similarity to the mineral phase of bone, absence of antigenicity, a nd excellent osteoconductivity. Some studies have proved that calcium phosphate ceramics with special str u ture could induce bone formation in soft tissue [5]. Based on the exploration of the osteoinducti ve mechanism, Zhang [6] proposed a new concept of bone tissue engineering in vivo, i.e., bone grafts could be constructed directly with osteoinductive biomaterials singly or osteoinductive biom aterials mixed with fresh bone tissue in some areas of the body. This study was conducted to explore a new method for fabricating bone substitute, which constructed vascularized bone graft with osteoinductive c alcium phosphate in vivo. Materials and Methods Preparation of the ceramics Calcium phosphate ceramics was prepared by H 2O2 foaming method and sintered at 1250oC for 3 hours with wet-synthetic calcium phosphate powde r. The chemistry of Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 801-804 doi:10.4028/www.scientific.net/KEM.254-256.801

Prediction Models and Generalization Performance Study in Electrical Discharge Machining

In the past decade, artificial neural network(ANN) has been applied in Electrical discharge machining(EDM). However, most of them only discuss parameter prediction or optimization result, few tell how to improve generalization performance. In this study, machining process models have been established based on different training algorithms of ANN, namely Levenberg-Marquardt algorithm (LM), Resilient algorithm (RP), Scaled Conjugate Gradient algorithm (SCG) and Quasi-Newton algorithm(BFGS). All models have been trained by same experimental data, checked by another group data, their generalization performance are compared. Take LM as the example, some main factors that may influence generalization performance are discussed.

Experimental Research on Technology of Ultrasonic Vibration Aided Electrical Discharge Machining (UEDM) in Gas

Ultrasonic vibration aided electrical discharge machining (UEDM) in gas is an electrical discharge machining (EDM) technology, in which gases such as air and oxygen are used as dielectrics and ultrasonic vibration is applied. UEDM in gas can avoid environment pollution, the most serious disadvantage of conventional EDM in kerosene-based oil or other dielectric fluids, and it is environmental-friendly. The technology also possesses virtues of wide applications, high machining efficiency and simple tool electrodes and so on. The principle of UEDM in gas is introduced in this paper. Experiments have been carried out to study the effects of machining parameters on material removal rate (MRR), surface roughness of the workpiece and tool electrode wear ratio (TWR), and the experiments results have also been analyzed.

In Vitro Simulation of Calcium Phosphate Crystallization from Dynamic Revised Simulated Body Fluid

A dynamic device was designed to study the formation of bonelike apatite on the inner surface of biphasic porous calcium phosphate in RSBF in vitro. The ceramics were examined with scanning electron microscopy (SEM), energy dispersive spectroscop y (EDS) and Infrared spectroscopy (IR). Spherical amorphous crystal on the surface pore walls and sheet-shaped crystals on the inner pore walls of the ceramics were found. According to co -cultured with bone marrow stromal cell (BMSCs), the cell response to the samples was investigated with SEM and MTT assay. Introduction Formation of bone-like apatite is one of the important subjects in os teoinductivity of bioceramics. The in vivo process of apatite formation is usually simulated in vitro by precipitation of calcium phosphates from supersaturated calcium and phosphate-containing solutions. D ynamic method, introduced by Duan et al. [1, 2] recently, is closer to physiological condition than static imme rsion assay. However, the pH value of simulated body fluid (SBF) changes with time after immersion, in which calcium phosphates precipitate to form non-stoichiometric hyd yoxyapatite. In addition, the simulation in vitro is different from physiological condition in vivo in that CO2 is produced in the process of metabolism in vivo . To simulate the behavior of calcium phosphate ceramics veritably, a modified CO2 supplying device was designed to adjust the pH value and to enhance bu ffer a ility of solution and porous biphase calcium phosphate ceramics were immersed in a revised body fluid (R-SBF) introduced by Kim et al. . Subsequently, cell biocompatibility was investigated by MTT test. Materials and Methods Biphasic porous calcium-phosphate ceramics (HA/ α-TCP=60/40) were prepared by foaming with H2O2. The cylindrical-shaped samples ( 4×8mm) were cleaned by ultrasonication. 4–4,5–dimethylthiazol-2-y1-2,-diphenyltetrazolium bromide (MTT) was purc hased from Sigma Chemical Co. (USA), and DMEM/F12 (1:1) medium was purchased from Hyclone Co (USA ). Experiments on the formation of bone-like apatite in revised simulate d body fluid (R-SBF) were performed at 37°C and a stable pH (7.4), which was controlled by filling CO2 gas into R-SBF storage tank at a suitable rate. R-SBF flowed at a rate of 2 m l/min by a peristaltic pump (Fig. 1). HA/α-TCP was immersed for 2 to 7 days in R-SBF. After that, sample s were removed, washed with distilled water for several times, then, dried at 50°C and split in halves. The microstructures of the samples were analyzed with scanning electron microscopy (SEM). The Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 7-10 doi:10.4028/www.scientific.net/KEM.254-256.7

An Experimental Study of the Effects of Electrode Shapes on Micro-EDM Performances

In this paper, experiments were conducted to investigate the effects of cylindrical electrode and helical electrode on the micro electrical discharge machining (EDM) performances during micro-hole machining of titanium alloy. The results show that the material removal rate (MRR) and the tool wear rate (TWR) increase with open circuit voltage, regardless of electrode shapes. Compared to the cylindrical electrode, helical electrode can result in higher MRR and lower relative tool wear ratio (RTWR). It can be concluded that the helical electrode is more suitable than cylindrical electrode for machining micro parts.

Penetration Force in Biopsy under Condition of Biomimetic Vibration

Biopsy is a common medical procedure to treat and diagnose prostate cancer and breast cancer. Needle insertion is a critical step in biopsy, but the inserting force has a big effect on precision of needle insertion. A new method is presented to reduce the penetration force, and then improve the precision of needle insertion in this paper. Preloaded piezo actuator was introduced to provide biomimetic vibration for needle during needle insertion into a pork liver, just as a fascicle insertion into the skin by a mosquito. The experimental results showed that the penetration force was reduced 26.7% compared with the force without biomimetic vibration.

Ringing Effect and Reversed Current Analysis of RC-Pulse Generator in Electrical Discharge Machining

RC-pulse generator has a simple structure and it is easy to be made and repaired. Especially RC-pulse generator can provide high frequency and low energy discharges. Therefore RC-pulse generators are used in micro-EDM field. But its high tool wear ratio and low efficiency restrict its applications. Ringing effect is considered to have effect on the defects. This research was done to study the ringing effect in electrical discharge. Taguchi method was used and discharge curves of voltage and current were recorded and analyzed. Ringing effect plays a key role in discharges and reversed current. A waveform model established with ringing effect theory is almost the same as the waveforms recorded in the experiment. Reversed current exists in almost a half time of discharge period which is the representation of ringing effect. Suitable process parameters can reduce reversed current and proper improvements could eliminate reversed current which will reduce the tool wear ratio and increase the efficiency in RC-pulse generator.

Thermal Mechanical Coupled 3D Finite Element Simulation of Large H-Beam in Hot Rolling Process

In order to research the forming process of H-beam, based on the large H-beam production line of HN600x200, the Standard and Explicit solver of ABAQUS are synthetically used to establish finite element model for rolling process and inter-pass thermolysis process. The reciprocation multi-pass rolling process simulation procedure based on the re-meshing technology is used to simulate the whole production process form blanks to finish products, and the continuity of data is ensured. Based on the simulation results, the deformation and rolling force of the roller as well as the metal flowing law and temperature field of workpiece are discussed emphatically. The results clearly show that the displacement of roller contains the elastic deformation and the deflection, and the counterforce of left adds to the counterforce of right is about equal to the resultant force. The simulation results are compared with the measuring results, which proves the correctness of simulation.

The Analysis of Processing Factors for Electro-Arc Machining

Electro-arc machining is similar with traditional electrical discharge machining (EDM) while the pulse duration of electro-arc machining is longer than that of EDM. The longer discharge was named arcing, and the arcing could lead to high material remove rate (MRR) and low tool wear ratio (TWR). Processing factors including discharge medium, tool polarity, tool material, voltage and rotational speed were chosen as input parameters on MRR and TWR. Taguchis method was used to evaluate their effects. All of the five processing factors had effects on MRR and TWR. The effects and the mechanism are also discussed.

A New Theoretical Model of Material Removal for Diamond Wheel Drilling Hard and Brittle Materials

In this paper, a method using diamond wheel to drill holes in hard and brittle materials is introduced. A technological basis for cost-effective drilling requires a fundamental understanding of the prevailing drilling mechanism. According to the investigation of brittle materials in indentation, the machining mechanism of drilling based on the fracture mechanics concept is analyzed, and a new theoretical model of material removal rate is proposed. According to this model, the material removal rate increases in accordance with the increase of static load applied, the rotation speed of the diamond wheel, and the grain size of abrasive. Test results show that diamond wheel drilling is an effective method for machining hard and brittle materials. Introduction As a kind of typical hard and brittle material, engineering ceramics are differentiated from traditional ceramics by the specialized properties they process, high hardness, high thermal resistance, chemical steadiness, and low thermal or electrical conductivity and so on. Because of these special performances, engineering ceramics are expected to be used increasingly in a number of high-performance applications ranging from electronic and optical devices to heatand wear-resistant parts [1-2]. Until today, their application have mostly been limited to the electronic and optical devices. One reason is to be sought in the limitation on the forming process prior to sintering, which restrict generation of complex geometry and make it difficult to ensure adequate accuracy and surface finish. There is also a considerable deficit in terms of the production or machining of more complex geometries in the hardened post-sintering state, with limitations on either the performance or the forming capacity of the majority of processes in current use. Machining of engineering ceramics to final dimension is demanding and expensive. Tight tolerances and dimensions with acceptable surface and sub-surface damages are something only attainable at great cost. So research into the areas of more efficient material removal processes are beginning to gather momentum in the past years especially in the ways and means to reduces the occurrences of faults or cracks in the sub-surface of the machined ceramics [3-5]. The property profile of these materials allows an economic production of structural parts only by finishing with diamond tools or special machining technologies. Grinding shows hereby the highest significance due to its attainable removal rates. A kind of machining method for drilling holes in engineering ceramics by using a rotary diamond wheel is proposed in this paper. It can increase the material removal rate, and improve the surface finish. This paper intends to further the understanding of the basic mechanisms of diamond wheel drilling ceramics and predict the material removal rate in terms of the static load applied, the grain size of abrasive, and rotation speed of the drilling tool. As a typical example of hard and brittle materials, in diamond wheel drilling, ceramic removal is believed to be the result of brittle failure. To understand this process, it is helpful to study the indentation of hard and brittle materials, because the abrasive particles acting on workpiece surface are just like indenters. Investigation of Hard and Brittle Material in Indentation Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 406-410 doi:10.4028/www.scientific.net/KEM.259-260.406