S.H. Oh

Influences of Heating Condition and Substrate-Surface Roughness on the Characteristics of Sol-Gel-Derived Hydroxyapatite Coatings

A prepared transparent HA solution was coated on Ti6Al4V substrates by a spin-coating technique. The crystallization of the sol-gel-derived HA coated on the metallic substrates could be done at relatively low firing temperatures (as low as 600°C). The characteristics of the HA-coated layer were dependent on the surface roughness of substrates and heating conditions such as firing temperature, holding time, heating rate, and atmosphere. The heat treatment at a slow heating rate (<2°C/min.) and a long heating time (>10 hrs) at 600°C in air produced the uniform surface and improved the crystallinity. The HA layer coated on 20 μm grit-blasted substates was more uniform and had fever cracks after firing, compared with that coated on 100 μm grit-blasted rougher substrates.

Hydroxyapatite Coated Porous Alumina as a New Orbital Implant

Abstract. A synthetic hydroxyapatite coated porous alumina ocular orbital impla nt w s developed by polymeric sponge method in order to overcome shortcoming of current corall ine HA implant and to obtain secure attachment of extraocular muscles and fibrovascular i n-growth. It allows porous alumina skeletal to be a load bearing member and synthetic HA coat ing l yer to provide biocompatibility and long-term stability in an eye. It was found that slower heating rate of < 1°C/min at 280°C400°Cwas effective to achieve a dense porous alumina skeletal, and defects on as-sintered alumina skeletal was considerably decreased by the second coating of alumina slurry and sintering. The thickness of coated HA layer was about 20 μm with relatively good bonding to alumina skeletal. From in-vivo study, fibrovascularization was noted at periphery of the implant 2 we eks after implantation in all of the three groups, and to the center of the impla nt 4 and 12 weeks after implantation. This fibrovascularization was most predominant in 500 μm por e-sized group compared to the rest two groups. It is believed that HA coated porous alumina w ill be a good candidate for an artificial orbital implant with improved biocompatibility and long-term stabil ity.

Synthesis of Biocompatible Calcium Phosphate Powders by Using an Eggshell

Pure and biocompatible hydroxyapatite (HAp) and β-tricalcium phosphate (TCP) powders were successfully synthesized by using a re-cycled eggshell and phosphoric acid. The crystallization behavior of the synthesized powders was dependent on the mixing ratio betw een the eggshell and phosphoric acid, the starting condition of the eggshell and calcination te mperature. The HAp and β-TCP were stably synthesized in the 1:1.1 and 1:1.3~1.5 mixing ratio, res pectively. The syntheses were achieved at about 900°C in an air atmosphere. The crystalline development and mi crostructure of the synthesized powders were examined by X-ray diffractometry and scanning electron microscopy.

In Vivo Evaluation of Macroporous Calcium Metaphosphate Ceramic as a Bone Substitute

Calcium metaphosphate(CMP) ceramic in the form of a macroporous block was evaluated as a bone substitute in vivo. Macroporous calcium metaphosphate ceramic blocks with a mean pore size of 250 μm were implanted into either subcutanous pouches or artificial tibial bone defects in rats, and biodegradibility, biocompatibility and osteoconductivity were analyzed, respcectively. The macroporous CMP ceramic blocks implanted into subcutanous pouches permitted ingrowth of vascularized connective tissue without an inflammatory response or a foreign body reaction for 3 weeks after implantation. In addition, there was no remarkable weight change during 3 weeks implanted in subcutanous pouches. The macroporous CMP ceramic blocks implanted into bony defects revealed a favorable connection and direct fusion of newly formed bone from local osseous margin with their framework without insertion of fibrous connective tisssue and did not evoke an inflammatory reaction. The excellent biocompatibility,osteoconductivity, biomechanical strength, and ease of handling fullfill the requirement as a promising bone substitute.

Preliminary Radiological In Vivo Study of Calcium Metaphosphate Coated Ti-Alloy Implants

In order to evaluate the bone-implant integration behavior of biodegradable c lcium metaphosphate (CMP, [Ca(PO 3)2]n) coated metallic implant, as-machined, blasted, and blasted /CMP-coated Ti6Al4V screw-type implants were prepared and asepti cally implanted into male New Zealand white rabbits. CMP sol was prepared by sol-gel process and coate on each substrate by dip and spin coating. The CMP coated layer was smooth and uniform with fine grai s, compared to that of as-machined and as-blasted specimens. Each specimen was inserted i nto the defects of bilateral intratibial metaphysis bone and then followed up for 1 and 6 weeks. From the radiographs at 1 and 6 weeks after implantation, all the implants were shown to be apparent ly well integrated with surrounding bone tissue without interfacial fracture, bony resorption, or ra di lucent lines. With the combination of histological results, CMP-coated group was noticed that bony bridges were extending from the endosteum onto the implants at 6 weeks after implantation, wi th the showing good osseo-intergration compared to other two groups. Introduction The development of a stable direct bonding between bone and implant surface (osteointegration) is the critical issue for the long-term success of orthopedic and denta l impl nts. The establishment and maintenance of osteointegration depends on wound healing, repairing and remodel ing f hard tissues. The tissue response to an implant involves physical factors such as i mplant design and surface topography, and chemical factors such as composition and structure of the material surface [1]. To improve the implant fixation to a host bone, several strategies have been developed focusing on the surface modification of materials. For example, the physical surf ace modification of implants in roughness by various techniques has been attracted, because it has been de monstrated that the osteoblastic cells tend to attach more easily to rough surface [ 4], consequently increasing the bone apposition [5]. Chemical surface modifications have been also realized by cova lent attachment of an organic monolayer anchored by a siloxane network [2], and immobilization of specific adhesive peptides like arginine-glycine-aspartic acid-serine (RGDS) [3]. In addition, the implants coated with different bioactive materials such as calcium phosphates, bioactive glasses [6], diamond-like carbon, and amorphous C-N film [7] enha nced the bonding to bone. However, it has been currently reported that the coating layer w s sometimes delaminated from the substrates. Therefore, as one of the alternatives to solve this proble m, the biodegradable material coating on implants, which may allow the organism to replace the for eign material by new bone tissue in a balanced time schedule, was conductd [8]. Calcium metaphosphate (CM P, [ a(PO3)2]n) is a Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 881-886 doi:10.4028/www.scientific.net/KEM.254-256.881

SU-F-J-24: Setup Uncertainty and Margin of the ExacTrac 6D Image Guide System for Patients with Brain Tumors

PURPOSE This study evaluated the setup uncertainties for brain sites when using BrainLABs ExacTrac X-ray 6D system for daily pretreatment to determine the optimal planning target volume (PTV) margin. METHODS Between August 2012 and April 2015, 28 patients with brain tumors were treated by daily image-guided radiotherapy using the BrainLAB ExacTrac 6D image guidance system of the Novalis-Tx linear accelerator. DUONTM (Orfit Industries, Wijnegem, Belgium) masks were used to fix the head. The radiotherapy was fractionated into 27-33 treatments. In total, 844 image verifications were performed for 28 patients and used for the analysis. The setup corrections along with the systematic and random errors were analyzed for six degrees of freedom in the translational (lateral, longitudinal, and vertical) and rotational (pitch, roll, and yaw) dimensions. RESULTS Optimal PTV margins were calculated based on van Herk et al.s [margin recipe = 2.5∑ + 0.7σ - 3 mm] and Stroom et al.s [margin recipe = 2∑ + 0.7σ] formulas. The systematic errors (∑) were 0.72, 1.57, and 0.97 mm in the lateral, longitudinal, and vertical translational dimensions, respectively, and 0.72°, 0.87°, and 0.83° in the pitch, roll, and yaw rotational dimensions, respectively. The random errors (σ) were 0.31, 0.46, and 0.54 mm in the lateral, longitudinal, and vertical rotational dimensions, respectively, and 0.28°, 0.24°, and 0.31° in the pitch, roll, and yaw rotational dimensions, respectively. According to van Herk et al.s and Stroom et al.s recipes, the recommended lateral PTV margins were 0.97 and 1.66 mm, respectively; the longitudinal margins were 1.26 and 3.47 mm, respectively; and the vertical margins were 0.21 and 2.31 mm, respectively. CONCLUSION Therefore, daily setup verifications using the BrainLAB ExacTrac 6D image guide system are very useful for evaluating the setup uncertainties and determining the setup margin.∑σ.

SU-E-T-247: Determinations of the Optimal Phase for Respiratory Gated Radiotherapy From Statistical Analysis Using a Visible Guidance System

Purpose: Respiratory gated radiation therapy (RGRT) is used to minimize the radiation dose to normal tissue in lung cancer patients. Determination of the optimal point in the respiratory phase of a patient is important in RGRT but it is not easy. The goal of the present study was to see if a visible guidance system is helpful in determining the optimal phase in respiratory gated therapy. Methods: The breathing signals of 23 lung cancer patients were recorded with a Real-time Position Management (RPM) respiratory gating system (Varian, USA). The patients underwent breathing training with our visible guidance system, after which their breathing signals were recorded during 5 min of free breathing and 5 min of guided breathing. The breathing signals recorded between 3 and 5 min before and after training were compared. We performed statistical analysis of the breathing signals to find the optimal duty cycle in guided breathing for RGRT. Results: The breathing signals aided by the visible guidance system had more regular cycles over time and smaller variations in the positions of the marker block than the free breathing signals. Of the 23 lung cancer patients, 19 showed statistically significant differences by time when the values obtained before and after breathing were compared (p < 0.05); 30% and 40% of the duty cycle, respectively, was determined to be the most effective, and the corresponding phases were 30 60% (duty cycle, 30%; p < 0.05) and 30 70% (duty cycle, 40%; p < 0.05). Conclusion: Respiratory regularity was significantly improved with the use of the RPM with our visible guiding system; therefore, it would help improve the accuracy and efficiency of RGRT.

Successful Osteoinduction by Macroporous Calcium Metaphosphate Ceramic-Osteoblastic Cell Complex Implantation

To evaluate as a scaffold for guided bone regeneration, the macroporous c alcium metaphosphate ceramics, having 250 μm or 450μm average pore size in an interconnected framework of structured blocks, were implanted into skid mice subcutaneous pouches for 3 weeks in a form of macroporous calcium metaphosphate ceramic-osteogenic cell complex. T he macroporous calcium metaphosphate ceramics allowed appropriate cellular attachment and proliferation with osteogenic differentiation. In addition, the macroporous calcium metaphosphate cerami -cell complex induced ectopic bone formation effectively along the inner surface of the int erconnecting frame forming a macroporous structure. These findings suggest that macroporous calcium metaphosphate ceramic can be an ideal scaffolding material for guided bone regeneration in ter ms of an excellent delivery vehicle for osteogenic cells. Macroporous calcium metaphospate ceramic als o po sesses excellent biocompatibility, osteoconductivity, and controlled biodegradibility.

Effects of Additives on Pore Structures in Freeze Dried Calcium Phosphate Granules

Porous CMP granule was prepared by freeze-drying method. Rotary fr eeze method was applied to minimize the anisotropic characteristic of the crysta l growth direction of an ice. CMP granules with interconnected macro-pore structure were obtained by the sintering of the freeze-dried body. Sintering temperature, the ratio of water and powder, and the amount of binder were important variables to obtain a desirable pore structure. The controlling of the variables can produce various pore size and porosity. Introduction There have been a variety of unique ceramics fabrication process usi ng freezing phenomena. For example, Mahler and Bechtold[1] and Mahler[2] have reported a free ze-forming process for ceramic fibers using phase separation in a gelled aquesous poly(sil icic acid). In their process, a columnar gel is surrounded and isolated in ice. The direction of ice for mati n is controlled unidirectionally in the solution; fibers result after the ice is thawed. Porous ceramics of this type are expected to be used for the following applications because of their hig h permeability and large surface area: particulate filters for environmental cleanup and reuse, gas or chemical sensors, bioreactors, and support materials for catalysts or absorbents[3]. Calcium metaphospha te (CMP, [Ca (PO3) 2] n) is a biodegradable material that can be used as a bone substitute. Currentl y, two ypes of bone substitute are commercially available; the solid-granule and porous-block forms f calcium phosphate ceramics such as HA and TCP. The solid-granule type of bone substitutes can be made the wide range of size, from μm to mm, but each granule does not have the pores, which maybe enhance the tissue in-growth or anchoring. The porous block type of bone substitutes has pores with various s izes, but cannot be made the wide range of granule size. In this study, porous CMP granule s wer prepared by freeze-drying method. The CMP granules with interconnected macro-pore structure were obtained by the sintering of the freeze-dried body. The porosity and pore size and s h pe were varied with the additives, such as water and binder. The aim of this study was to inves tigat the relationship between pore structure of granules and processing additives of freeze-drying. Materials and Methods Ca(H2PO4)2H2O was thermally treated and crushed to prepare the CMP powder. Crus hed powders were sieved in the 250 meshes and ballmilled in polyurethane m ill jar with using high purity ZrO2 ball-media for 15 hours. Ball-milled slurry was dried in a rotary vacuum evaporator and ground with an agate mortar. The slurry was prepared by the mixing of water (W), binder (B) and dried powder (P). The concentration of CMP powder in the slurry was 25, 33, and 50wt%, and the content of a binder was 2, 3, and 5wt% of the CMP powder weight. The slurr y was poured into a cylindrical bottle, and only the bottle was partly immersed in -40 °C methanol refrigerant in a freezing bath with rotating at 20rpm, as shown in figure 1. The top of the bottle w as open so that the upper surface of the slurry would be exposed to the atmosphere at room tempe rature. Thus, the ice was Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 493-496 doi:10.4028/www.scientific.net/KEM.240-242.493