Preparation of mesoporous bioglass coated zirconia scaffold for bone tissue engineering

Porous yttria-stabilized zirconia (YSZ) has been regarded as a potential candidate for bone substitute due to its high mechanical strength. However, porous YSZ is biologically inert to bone tissue. It is therefore necessary to introduce bioactive coatings onto the walls of the porous structures to enhance its bioactivity. In this study, porous YSZ scaffolds were prepared using a replication technique and then coated with mesoporous bioglass due to its excellent bioactivity. The microstructures were examined using scanning electron microscopy and the mechanical strength was evaluated via compression test. The biocompatibility and bioactivity were also evaluated using bone marrow stromal cell (BMSC) proliferation test and simulated body fluid test.

Porous zirconia scaffold modified with mesoporous bioglass coating

Porous yttria-stabilized zirconia (YSZ) has been regarded as a potential candidate for bone substitute as its high mechanical strength. However, porous YSZ bodies are biologically inert to bone tissue. It is therefore necessary to introduce bioactive coatings onto the walls of the porous structures to enhance the bioactivity. In this study, the porous zirconia scaffolds were prepared by infiltration of Acrylonitrile Butadiene Styrene (ABS) scaffolds with 3 mol% yttria stabilized zirconia slurry. After sintering, a method of sol-gel dip coating was involved to make coating layer of mesoporous bioglass (MBGs). The porous zirconia without the coating had high porosities of 60.1% to 63.8%, and most macropores were interconnected with pore sizes of 0.5-0.8mm. The porous zirconia had compressive strengths of 9.07-9.90MPa. Moreover, the average coating thickness was about 7μm. There is no significant change of compressive strength for the porous zirconia with mesoporous biogalss coating. The bone marrow stromal cell (BMSC) proliferation test showed both uncoated and coated zirconia scaffolds have good biocompatibility. The scanning electron microscope (SEM) micrographs and the compositional analysis graphs demonstrated that after testing in the simulated body fluid (SBF) for 7 days, the apatite formation occurred on the coating surface. Thus, porous zirconia-based ceramics were modified with bioactive coating of mesoporous bioglass for potential biomedical applications.

Nanostructured mesoporous bioglass coated zirconia scaffolds for bone tissue engineering

For the filling and reconstruction of non-healing bone defects, the application of porous ceramic scaffold as bone substitutes is considered to be a reasonable choice. In bone tissue engineering, an ideal scaffold must satisfy several criterias such as open porosity, having high compressive strength (it depends where in body, and if external fixatures are used) and the practicability for cell migration. Many researchers have focused on enhancing the mechanical properties of hydroxyapatite scaffolds by combining it with other biomaterials, such as bioglass and polymers. Nevertheless, there is still a lack of suitable scaffolds based on porous biomaterials. In this study, zirconia scaffolds from two different templates (polyurethane (PU) and Acrylonitrile Butadiene Styrene (ABS) templates) were successfully fabricated with dissimilar fabrication techniques. The scaffold surfaces were further modified with mesoporous bioglass for the purpose of bone tissue engineering. In the study of PU template scaffold, high porosity (~88%) sol-gel derived yttria-stabilized zirconia (YSZ) scaffold was prepared by a polyurethane (PU) foam replica method using sol-gel derived zirconia for the first time, and double coated with Mesoporous Bioglass (MBGs) coating. For the ABS template scaffold, two types of templates (cube and cylinder) with different strut spacings were used and fabricated by a 3D Rapid Prototyper. Subsequently, zirconia scaffolds with low porosity (63±2.8% to 68±2.5%) were fabricated by embedding the zirconia powder slurry into the ABS templates and burning out the ABS to produce a uniform porous structure. The zirconia scaffolds were double coated with mesoporous bioglass by dip coating for the first time. The porosities of the scaffolds were calculated before and after coating. The microstructures were then examined using scanning electron microscopy and the mechanical properties were evaluated using compressive test. Accordingly, relationships between microstructure, processing and mechanical behaviour of the porous zirconia was discussed. Scaffold biocompatibility and bioactivity was also evaluated using a bone marrow stromal cell (BMSC) proliferation test and a simulated body fluid test.

Fabrication of macro-mesoporous zirconia-alumina materials with a 1D hierarchical structure

A series of one dimensional (1D) zirconia/alumina nanocomposites were prepared by the deposition of zirconium species onto the 3D framework of boehmite nanofibres formed by dispersing boehmite nanofibres into butanol solution. The materials were calcined at 773K and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), N2 adsorption/desorption, infrared emission spectroscopy (IES). The results demonstrated that when the molar percentage X=100*Zr/(Al+Zr) was > 30 %, extremely long ZrO2/Al2O3 composite nanorods with evenly distributed ZrO2 nanocrystals on the surface were formed. The stacking of such nanorods gave rise to a new kind of macroporous material without the use of any organic space filler\template or other specific technologies. The mechanism for the formation of long ZrO2/Al2O3 composite nanorods was proposed in this work.

Investigation of ternary zirconia ceramics

Transformation toughening ceramics (TTCs) are engineering materials which combine ceramic properties such as hardness, corrosion resistance and low thermal conductivity with good toughness and mechanical strength. At elevated temperatures their use is limited due to destabilisation of the transformation toughening microstructure (partially stabilised zirconia or PSZ) or creep and hydrothermal degradation (tetragonal zirconia polycrystals or TZPs). Despite these limitations, the use of TTCs, particularly zirconia based, has become widespread. To date, most commercial TTCs are based on combinations of zirconia and one stabilising oxide. This work investigates a zirconia ceramic containing two stabilisers, namely yttria and titania in roughly equal proportions.

YBCO thin films on Yttria stabilized Zirconia and LaAlO3-growth and properties

Laser deposition was used to deposit YBaCuO thin films on Yttria-stabilized Zirconia substrates, at substrate holder temperatures of 710-765 °C. We observed a transition from singlecrystalline to polycrystalline growth at a temperature of ∼750 °C. All films were highly c-axis oriented and had critical temperatures between 89.5 and 92 K. In the twinned singlecrystalline films, the lowest measured microwave surface resistance was 0.37 mΩ at 4.2 K and 21.5 GHz, and the highest critical current 5×106 A/cm2 at 77 K. The polycrystalline films had up to a factor of 50 higher surface resistance and a factor of 10 lower critical current. A meander line resonator made of a film on a LaAlO3 substrate, showed a microwave surface resistance of 5μΩ at 4.2 K and 2.5 GHz. © 1991.

Yttrium barium copper oxide thin films on yttria-stabilized zirconia: growth and properties

Y Ba Cu oxide thin films were grown epitaxially on single cryst. yttria-stabilized zirconia substrates by laser deposition. [on SciFinder(R)]

Preparation of mesoporous bioglass coated zirconia scaffold for bone tissue engineering

Porous yttria-stabilized zirconia (YSZ) has been regarded as a potential candidate for bone substitute due to its high mechanical strength. However, porous YSZ is biologically inert to bone tissue. It is therefore necessary to introduce bioactive coatings onto the walls of the porous structures to enhance its bioactivity. In this study, porous YSZ scaffolds were prepared using a replication technique and then coated with mesoporous bioglass due to its excellent bioactivity. The microstructures were examined using scanning electron microscopy and the mechanical strength was evaluated via compression test. The biocompatibility and bioactivity were also evaluated using bone marrow stromal cell (BMSC) proliferation test and simulated body fluid test.

Magnitude and variability of loading on the osseointegrated implant of transfemoral amputees during walking

This study directly measured the load acting on the abutment of the osseointegrated implant system of transfemoral amputees during level walking, and studied the variability of the load within and among amputees. Twelve active transfemoral amputees (age: 54±12 years, mass:84.3±16.3 kg, height: 17.8±0.10 m) fitted with an osseointegrated implant for over 1 year participated in the study. The load applied on the abutment was measured during unimpeded, level walking in a straight line using a commercial six-channel transducer mounted between the abutment and the prosthetic knee. The pattern and the magnitude of the three-dimensional forces and moments were revealed. Results showed a low step-to-step variability of each subject, but a high subject-to-subject variability in local extrema of body-weight normalized forces and moments and impulse data. The high subject-to-subject variability suggests that the mechanical design of the implant system should be customized for each individual, or that a fit-all design should take into consideration the highest values of load within a broad range of amputees. It also suggests specific loading regime in rehabilitation training are necessary for a given subject. Thus the loading magnitude and variability demonstrated should be useful in designing an osseointegrated implant system better able to resist mechanical failure and in refining the rehabilitation protocol.

An experimental research investigation into disused flat rail wagons as bridges with applications for low volume rural roads in Australia

An experimental laboratory investigation was carried out to assess the structural adequacy of a disused PHO Class Flat Bottom Rail Wagon (FRW) for a single lane low volume road bridge application as per the design provisions of the Australian Bridge Design Standard AS 5100(2004). The investigation also encompassed a review into the risk associated with the pre-existing damage in wagons incurred during their service life on rail. The main objective of the laboratory testing of the FRW was to physically measure its performance under the same applied traffic loading it would be required to resist as a road bridge deck. In order to achieve this a full width (5.2m) single lane, single span (approximately 10m), simply supported bridge would be required to be constructed and tested in a structural laboratory. However, the available clear spacing between the columns of the loading portal frame encountered within the laboratory was insufficient to accommodate the 5.2m wide bridge deck excluding clearance normally considered necessary in structural testing. Therefore, only half of the full scale bridge deck (single FRW of width 2.6m) was able to be accommodated and tested; with the continuity of the bridge deck in the lateral direction applied as boundary constraints along the full length of the FRW at six selected locations. This represents a novel approach not yet reported in the literature for bridge deck testing to the best of the knowledge of the author. The test was carried out under two loadings provided in AS 5100 (2004) – one stationary W80 wheel load and the second a moving axle load M1600. As the bridge investigated in the study is a single lane single span low volume road bridge, the risk of pre-existing damage and the expected high cycle fatigue failure potential was assessed as being minimal and hence the bridge deck was not tested structurally for fatigue/ fracture. The high axle load requirements have instead been focussed upon the investigation into the serviceability and ultimate limit state requirements. The testing regime adopted however involved extensive recording of strains and deflections at several critical locations of the FRW. Three locations of W80 point load and two locations of the M1600 Axle load were considered for the serviceability testing; the FRW was also tested under the ultimate load dictated by the M1600. The outcomes of the experimental investigation have demonstrated that the FRW is structurally adequate to resist the prescribed traffic loadings outlaid in AS 5100 (2004). As the loading was directly applied on to the FRW, the laboratory testing is assessed as being significantly conservative. The FRW bridge deck in the field would only resist the load transferred by the running platform, where, depending on the design, composite action might exist – thereby the share of the loading which needs to be resisted by the FRW would be smaller than the system tested in the lab. On this basis, a demonstration bridge is under construction at the time of writing this thesis and future research will involve field testing in order to assess its performance.

Performance load testing and structural adequacy evaluation of road bridge decks

Many ageing road bridges, particularly timber bridges, require urgent improvement due to the demand imposed by the recent version of the Australian bridge loading code, AS 5100. As traffic volume plays a key role in the decision of budget allocations for bridge refurbishment/ replacement, many bridges in low volume traffic network remain in poor condition with axle load and/ or speed restrictions, thus disadvantaging many rural communities. This thesis examines an economical and environmentally sensible option of incorporating disused flat rail wagons (FRW) in the construction of bridges in low volume, high axle load road network. The constructability, economy and structural adequacy of the FRW road bridge is reported in the thesis with particular focus of a demonstration bridge commissioned in regional Queensland. The demonstration bridge comprises of a reinforced concrete slab (RCS) pavement resting on two FRWs with custom designed connection brackets at regular intervals along the span of the bridge. The FRW-RC bridge deck assembly is supported on elastomeric rubber pads resting on the abutment. As this type of bridge replacement technology is new and its structural design is not covered in the design standards, the in-service structural performance of the FRW bridge subjected to the high axle loadings prescribed in AS 5100 is examined through performance load testing. Both the static and the moving load tests are carried out using a fully laden commonly available three-axle tandem truck. The bridge deck is extensively strain gauged and displacement at several key locations is measured using linear variable displacement transducers (LVDTs). A high speed camera is used in the performance test and the digital image data are analysed using proprietary software to capture the locations of the wheel positions on the bridge span accurately. The wheel location is thus synchronised with the displacement and strain time series to infer the structural response of the FRW bridge. Field test data are used to calibrate a grillage model, developed for further analysis of the FRW bridge to various sets of high axle loads stipulated in the bridge design standard. Bridge behaviour predicted by the grillage model has exemplified that the live load stresses of the FRW bridge is significantly lower than the yield strength of steel and the deflections are well below the serviceability limit state set out in AS 5100. Based on the results reported in this thesis, it is concluded that the disused FRWs are competent to resist high axle loading prescribed in AS 5100 and are a viable alternative structural solution of bridge deck in the context of the low volume road networks.