Materials Science Forum Vols. 654-656

Abstract: The HAp-(t-ZrO2) ceramic composites with mimetic osteon microstructures were fabricated to investigate the technical feasibility of fabricating natural bone mimetics by a combination of multi-extrusion and rolling processes. The HAp and graphite powders were mixed with ethylene vinyl acetate and stearic acid using a shear mixer, and the mixture was extruded by the multi-extrusion process to create filaments. A HAp sheet was prepared by a rolling process. The HAp filaments and carbon filaments were arranged one by one on the HAp sheet, and the system was rolled to form a mimetic osteon microstructure. Burning out and sintering processes were performed for removal of the organic binder and graphite and for densification. The pore diameter and core of the mimetic osteon microstructure were approximately 50μm and 150μm, respectively. The porosity and bending strength were approximately 60% and 177MPa, respectively in the sample sintered at 1450°C.

Abstract: The quantity and quality of regenerated bone strongly depends on the direction and amplitude of in vivo principal stress; therefore, in vivo stress distribution near bone implants should be optimized on the basis of the morphology of the interface between an implant and bone tissue. In this study, grooves were created on the implant surface in order to improve the surface morphology of the implant for optimizing in vivo stress distribution near the implant. The preferential alignment of the biological apatite (BAp) c-axis, which is a parameter of bone quality and controls the mechanical function of bones, is closely related to stress distribution; therefore, the direction of principal stress should be matched with the direction of the groove on the implant surface. Hip implants were prepared with grooves aligned at different angles from the surface; the grooves were located on the stem portion. These implants were inserted in a beagle femur to investigate the dependency of the quantity and quality of newly formed bone in the grooves on the groove angle. The degree of preferential alignment of the BAp c-axis of the regenerated bone in the grooves strongly depends on the angle of the groove to the principal stress vector that was estimated previously to an animal experiment. The regenerated bone forms anisotropic BAp orientation in response to the principal stress in the grooves; therefore, the direction of the grooves has to be designed on the basis of the stress distribution near the implant.

Abstract: Calcium phosphate bone substitutes are widely used for providing support for the in-growth of hard tissue in various medical applications (e.g., dental, orthopedic). Recently, research involving bone substitutes with interconnected open pore structures has focused on improving the mechanical properties of the substitutes and modifying their surfaces with proteins (e.g., collagen, bone morphogenetic protein) to induce early bone formation. In particular, it is highly desirable to develop a functional gradient-structured bone substitute that has the potential to control the bioresoption rate. A porous BCP scaffold was fabricated by the sponge replica method using a PU sponge. The sponge was dip coated three times followed by oven drying, burning out, and microwave sintering. Several approaches were used to fabricate a functional gradient scaffold. TCP was synthesized using the sol-gel process, and it infiltrated into the pore channel that formed after the burning out of the PU sponge. X-ray diffraction analysis characterized the phase identification of the BCP scaffold. Microstructures of the composites were observed using scanning electron microscopy.

Abstract: Measurements of bone mineral density (BMD) cannot accurately predict the risk of bone fracture in some clinical cases; however, BMD is a useful index for assessing the bone condition. Recently, various parameters related to bone strength have been investigated. Among them, we have focused on the preferential orientation of biological apatite (BAp) crystallites analyzed by microbeam-X-ray diffraction, a powerful tool for analyzing BAp crystallites in bones. BAp, a dominant component of bone, is an anisotropic ionic crystal with a hexagonal lattice. In this study, we investigated the mechanism underlying BAp orientation during endochondral or membranous ossification by administering macrophage colony-stimulating factor (M-CSF) to osteopetrotic (op/op) mice lacking M-CSF. op/op mice were treated with intraperitoneal injections of 5 μg recombinant human M-CSF (rhM-CSF); the first injection was administered on the 14th day after birth. In the treated op/op mice, the bone marrow cavities expanded significantly, and this expansion was accompanied by an increase in the number of osteoclasts. Moreover, the degree of BAp orientation along the longitudinal axis was higher in the treated group than in the untreated group. These results suggest that M-CSF is one of the important parameters controlling the preferential alignment of the BAp c-axis.

Abstract: This work aimed to establish a suitable procedure for establishing wear particle hardness and to investigate if the hardness of articular cartilage wear particles increases with increasing grades of osteoarthritis. To achieve the goals a selection of fresh sheep knee joints were obtained and consequently worn in a specially designed wear simulator. Wear particles were then removed from the joint using a syringe and prepared for hardness testing. In order to test the hardness of the wear particle samples nanoindentation was used. Once completed statistical analyses and correlation analyses were performed in order to find any relationships present. This was the first time that the hardness of the wear particles was tested and studied. As a result of the tests performed a general relationship between wear particle hardness and osteoarthritis grade was able to be determined. It was also determined that further work needed to be conducted on the experimental procedure to increase the accuracy of the results obtained.

Abstract: Hydroxyapatite (HAp), Ca10(PO4)6(OH)2, is known to precipitate on bioactive materials by soaking in simulated body fluid (SBF). The formation of HAp on TiO2 and CaTiO3 surfaces under continuous ultraviolet (UV) irradiation was investigated in this study. Pure Ti substrates were chemically treated with H2O2/ HNO3 solution at 353 K for 20 min to form a TiO2 gel layer. The samples were then hydrothermally treated with an aqueous NH3 or an aqueous Ca(OH)2 solution in an autoclave at 453 K for 12 h. An adhesive and sufficiently crystallized anatase-type TiO2 film or perovskite-type CaTiO3 film could be synthesized on the Ti surface, respectively. The samples were immersed in SBF in darkness or under UV irradiation. The UV irradiation promoted the formation of HAp, which may be due to the generation of functional Ti-OH or Ti-O groups on both surfaces. On the other hand, the UV light also produces electron-hole pairs in the product films. In TiO2, much photogenerated holes migrated to the surface and repelled the Ca2+ ions in the solution. As a consequence, the UV irradiation suppressed the formation of HAp thin film on the surface of TiO2.

Abstract: Terpinen-4-ol is the main constituent of Melaleuca alternifolia essential oil known for its biocidal and anti-inflammatory properties. The possibility of fabricating polymer thin films from terpinen-4-ol using radio frequency (RF) plasma polymerisation for the prevention of the growth of Pseudomonas aeruginosa was investigated, and the properties of the resultant films compared against their biologically active precursor. Films fabricated at 10 W prevented bacterial attachment and EPS secretion, whilst polyterpenol films deposited at 25 W demonstrated no biocidal activity against the pathogen.

Abstract: A combined drug loaded system containing two most common anti-cancer drugs 5-fluorouracil (5-FU) and leucovorin (LV) was designed and prepared by ion crosslinking technology. The resulted nanoparticles are spherical in shape, and the particle size becomes larger when drug combination are loaded. Efficient drug encapsulation efficiency (EE) and drug loading (LC) are obtained due to the strong interaction between drugs and polymer. The combined drugs are distributed in the particles in amorpholous state which are demonstrated by the XRD results.

Abstract: The research work reported in this paper design a novel biodegradable multichamber microstructure for implantable drug controlled release by introducing the approach of topology optimization. It is therefore highly desirable to overcome these restrictions that pre-defined topology of the device result in difficulty to obtain a linear or pulsed drug release profile. The designed biodegradable multichamber microstructure is fabricated using UV-LIGA microfabrication and Micro-molding technique. The simulation results show that the multichamber microstructure exhibits a preferable linear drug release profile.

Abstract: Composites containing saturated fluid are widely distributed in nature, such as saturated rocks, colloidal materials and biological cells. In the study to determine effective mechanical properties of fluid-saturated composites, a micromechanical model and a multi-scale homogenization-based model are developed. In the micromechanical model the internal fluid pressure is generated by applying eigenstrains in the domain of the fluid phase and the explicit expressions of effective bulk modulus and shear modulus are obtained. Meanwhile a multi-scale homogenization theory is employed to develop the homogenization-based model on determination of effective properties at the small scale in a unit cell level. Applying the two proposed approaches, the effects of the internal pressure of hydrostatic fluid on effective properties are further investigated.