Hani Haider

On low-frequency electric power generation with PZT ceramics

Piezoelectric materials have long been used as sensors and actuators, however their use as electrical generators is less established. A piezoelectric power generator has great potential for some remote applications such as in vivo sensors, embedded MEMS devices, and distributed networking. Such materials are capable of converting mechanical energy into electrical energy, but developing piezoelectric generators is challenging because of their poor source characteristics (high voltage, low current, high impedance) and relatively low power output. In the past these challenges have limited the development and application of piezoelectric generators, but the recent advent of extremely low power electrical and mechanical devices (e.g., MEMS) make such generators attractive. This paper presents a theoretical analysis of piezoelectric power generation that is verified with simulation and experimental results. Several important considerations in designing such generators are explored, including parameter identification, load matching, form factors, efficiency, longevity, energy conversion and energy storage. Finally, an application of this analysis is presented where electrical energy is generated inside a prototype Total Knee Replacement (TKR) implant.

The use of piezoelectric ceramics for electric power generation within orthopedic implants

This paper presents the results of tests that demonstrate the feasibility of using piezoelectric (PZT) ceramics to generate in vivo electrical energy for orthopedic implants. Sensors encapsulated within implants could provide in vivo diagnostic capabilities such as the monitoring of implant duty (i.e., walking) cycle, detecting abnormally asymmetric or high forces, sensing misalignment and early loosening, and early detection of wear. Early diagnosis of abnormalities or impending failure is critical to minimize patient harm. However, the routine use of sensors and microprocessors embedded within orthopedic implants for diagnostic and monitoring purposes has been limited by the lack of a long-term self-contained power source capable of lasting the expected 20-year implant lifetimes. By embedding PZT materials within orthopedic implants, a small amount of the mechanical energy generated during normal physical activity can be converted into useful electrical energy. This in vivo energy source can power embedded microprocessors and sensors for a broad range of biomedical uses. The current work investigates the application of this technology to total knee replacement (TKR) implants, but it is applicable to many other implanted biomedical devices.

Lotus Effect in Engineered Zirconia

Patterned micro- and nanostructured surfaces have received increasing attention because of their ability to tune the hydrophobicity and hydrophilicity of their surfaces. However, the mechanical properties of these studied surfaces are not sufficiently robust for load-bearing applications. Here we report transparent nanocrystalline ZrO 2 films possessing combined properties of hardness and complete wetting behavior, which are expected to benefit tribology, wear reduction, and biomedical applications where ultrahydrophilic surfaces are required. This ultrahydrophilic behavior may be explained by the Wenzel model.

Does Vitamin E–Stabilized Ultrahigh-Molecular-Weight Polyethylene Address Concerns of Cross-Linked Polyethylene in Total Knee Arthroplasty?

Concerns about reduced strength, fatigue resistance, and oxidative stability of highly cross-linked and remelted ultrahigh-molecular-weight polyethylene (UHMWPE) have limited its clinical acceptance for total knee arthroplasty. We hypothesized that a highly cross-linked UHMWPE stabilized with vitamin E would have less oxidation and loss of mechanical properties. We compared the oxidation, in vitro strength, fatigue-crack propagation resistance, and wear of highly cross-linked UHMWPE doped with vitamin E to γ-inert-sterilized direct compression-molded UHMWPE (control). After accelerated aging, the control material showed elevated oxidation, loss of small-punch mechanical properties, and loss of fatigue-crack propagation resistance. In contrast, the vitamin E-stabilized material had minimal changes and exhibited 73% to 86% reduction in wear for both cruciate-retaining and posterior-stabilized total knee arthroplasty designs. Highly cross-linked vitamin E-stabilized UHMWPE performed well in vitro.

Thermal stability of nanostructurally stabilized zirconium oxide

Nanostructurally stabilized zirconium oxide (NSZ) hard transparent films were produced without chemical stabilizers by the ion beam assisted deposition technique (IBAD). A transmission electron microscopy study of the samples produced below 150 °C revealed that these films are composed of zirconium oxide (ZrO2) nanocrystallites of diameters 7.5 ± 2.3 nm. X-ray and selected-area electron diffraction studies suggested that the as-deposited films are consistent with cubic phase ZrO2. Rutherford backscattering spectroscopy (RBS) indicated the formation of stoichiometric ZrO2. The phase identity of these optically transparent NSZ films was in agreement with cubic ZrO2, as indicated by the matching elastic modulus values from the calculated results for pure cubic zirconium oxide and results of nanoindentation measurements. Upon annealing in air for 1 h, these NSZ films were found to retain most of their room temperature deposited cubic phase x-ray diffraction signature up to 850 °C. Size effect and vacancy stabilization mechanisms and the IBAD technique are discussed to explain the present results.

Anterior plate supplementation increases ankle arthrodesis construct rigidity.

Background: The success of ankle arthrodesis for the treatment of post-traumatic ankle arthritis depends on achieving and maintaining rigid fixation of the prepared tibiotalar interface. The purpose of this study was to examine the biomechanical effect of anterior plate supplementation of a popular three-screw fusion construct. Methods: Six fresh-frozen cadaver ankles were prepared and instrumented with three partially threaded screws compressing the tibiotalar interface. Testing was done with and without supplementary anterior plate fixation under three different decoupled loading conditions: plantarflexion/dorsiflexion, inversion/eversion, and rotation. Motion at the tibiotalar interface was recorded. Results: Anterior plating increased construct stiffness by a factor of 3.5, 1.9, and 1.4 for the sagittal, coronal, and torsion modes, respectively. Less motion occurred at the tibiotalar interface in all to the three different loading conditions (p = 0.031) with plate supplementation. Conclusions: Compared to screws alone, anterior plate supplementation increases construct rigidity and decreases micromotion at the ankle fusion interface.

Ion beam-induced amorphous-to-tetragonal phase transformation and grain growth of nanocrystalline zirconia.

Nanocrystalline zirconia has recently attracted extensive research interest due to its unique mechanical, thermal and electrical properties as compared with bulk zirconia counterparts, and it is of particular importance for controlling the phase stability of different polymorphs (amorphous, cubic, tetragonal and monoclinic phases) in different size regimes. In this work, we performed ion beam bombardments on bilayers (amorphous and cubic) of nano-zirconia using 1 MeV Kr2+ irradiation. Transmission electron microscopy (TEM) analysis reveals that amorphous zirconia transforms to a tetragonal structure under irradiation at room temperature, suggesting that the tetragonal phase is more energetically favorable under these conditions. The final grain size of the tetragonal zirconia can be controlled by irradiation conditions. A slower kinetics in the grain growth from cubic nanocrystalline zirconia was found as compared with that for the tetragonal grains recrystallized from the amorphous layer. The radiation-induced nanograins of tetragonal ZrO2 are stable at ambient conditions and maintain their physical integrity over a long period of time after irradiation. These results demonstrated that ion beam methods provide the means to control the phase stability and structure of zirconia polymorphs.

Pulse Lavage is Inadequate at Removal of Biofilm from the Surface of Total Knee Arthroplasty Materials

In acute periprosthetic infection, irrigation and debridement with component retention has a high failure rate in some studies. We hypothesize that pulse lavage irrigation is ineffective at removing biofilm from total knee arthroplasty (TKA) components. Staphylococcus aureus biofilm mass and location was directly visualized on arthroplasty materials with a photon collection camera and laser scanning confocal microscopy. There was a substantial reduction in biofilm signal intensity, but the reduction was less than a ten-fold decrease. This suggests that irrigation needs to be further improved for the removal of biofilm mass below the necessary bioburden level to prevent recurrence of acute infection in total knee arthroplasty.

Effects of Patient and Surgical Alignment Variables on Kinematics in TKR Simulation Under Force-Control

Simulation of total knee replacement (TKR) is typically achieved by integrating sliding/rolling motions and loads between the implants articulating surfaces during an activity cycle such as walking. Clinically, however, important variations in implant alignment and duty occur due to variability in patient anatomy/arthritic deformity, compounded by choices or errors in surgical installation. This study investigated the effects of the activity cycle severity, frontal plane alignment, relative femoral/tibial component rotational position, and the tightness of the posterior cruciate ligament (PCL). Seven different (four fixedbearing and three mobile-bearing) cruciate-retaining TKRs with different inherent constraints were tested on a force-control knee simulator. As well as the ISO standard wave forms for walking, an Enhanced Duty Cycle was used. The resulting anterior-posterior displacements and axial rotations were increased with the Enhanced Duty Cycle. Changing the line of action of the compressive force in the frontal plane (varus-valgus over/under-correction) did not appreciably change the kinematics. Rotating the tibial component shifted the rotational curves in the same direction as the misalignment. The PCL tightness produced the most noticeable effect on kinematics; a tight PCL reduced both displacements and rotations, and a loose PCL did the opposite.

Local structures surrounding Zr in nanostructurally stabilized cubic zirconia: Structural origin of phase stability

Local environment surrounding Zr atoms in the thin films of nanocrystalline zirconia (ZrO2) has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. These films prepared by the ion beam assisted deposition exhibit long-range structural order of cubic phase and high hardness at room temperature without chemical stabilizers. The local structure around Zr probed by EXAFS indicates a cubic Zr sublattice with O atoms located on the nearest tetragonal sites with respect to the Zr central atoms, as well as highly disordered locations. Similar Zr local structure was also found in a ZrO2 nanocrystal sample prepared by a sol-gel method. Variations in local structures due to thermal annealing were observed and analyzed. Most importantly, our x-ray results provide direct experimental evidence for the existence of oxygen vacancies arising from local disorder and distortion of the oxygen sublattice in nanocrystalline ZrO2. These oxygen vacancies are regarded as the essential stabil...