Addition of bioactive materials such as calcium phosphates or Bioglass, and incorporation of porosity into polyetheretherketone (PEEK) has been identified as an effective approach to improve bone-implant interfaces and osseointegration of PEEK-based devices. In this paper, a novel production technique based on the extrusion freeforming method is proposed that yields a bioactive PEEK/hydroxyapatite (PEEK/HA) composite with a unique configuration in which the bioactive phase (i.e., HA) distribution is computer-controlled within a PEEK matrix. The 100% interconnectivity of the HA network in the biocomposite confers an advantage over alternative forms of other microstructural configurations. Moreover, the technique can be employed to produce porous PEEK structures with controlled pore size and distribution, facilitating greater cellular infiltration and biological integration of PEEK composites within patient tissue. The results of unconfined, uniaxial compressive tests on these new PEEK/HA biocomposites with 40% HA under both static and cyclic mode were promising, showing the composites possess yield and compressive strength within the range of human cortical bone suitable for load bearing applications. In addition, preliminary evidence supporting initial biological safety of the new technique developed is demonstrated in this paper. Sufficient cell attachment, sustained viability in contact with the sample over a seven-day period, evidence of cell bridging and matrix deposition all confirmed excellent biocompatibility.

Existing design criteria for vibration energy harvesting systems provide guidance on the appropriate selection of the seismic mass and load resistance. To harvest maximum power in resonant devices, the mass needs to be as large as possible and the load resistance needs to be equal to the sum of the internal resistance of the generator and the mechanical damping equivalent resistance. However, it is shown in this paper that these rules produce suboptimum results for applications where there is a constraint on the relative displacement of the seismic mass, which is often the case. When the displacement is constrained, increasing the mass beyond a certain limit reduces the amount of harvested power. The optimum load resistance in this case is shown to be equal to the generator's internal resistance. These criteria are extended to those devices that harvest energy from a low-frequency vibration by utilizing an interface that transforms the input motion to higher frequencies. For such cases, the optimum load resistance and the corresponding transmission ratio are derived.

The structure-borne tones generated by the main gearbox are the primary components of helicopter interior noise. Recently, a kind of periodic strut has been designed to isolate the multispectral vibration from transmitting to the cabin, for their specific stop-band characteristics. Using multicell optimization, the disorders are designed into the strut to obtain better vibration and noise reduction effect. The dynamic model of the periodic strut is firstly established by combining the spectral element method and the transfer matrix method. On this basis, a multi-objective multivariable genetic algorithm is adopted to optimize the geometry by taking the maximum attenuation as the performance objective function. Then, a near-periodic structure is achieved. Compared with the perfect periodic strut, the optimal one has a much wider and deeper stop band, which is critical for a better vibration and noise attenuation effect. In addition, a method is presented to analyze the wave propagation to explore the increase of width and depth of the bandgaps more closely. Experimental investigations are then carried out on a pair of original and optimal struts to validate the improvements. It is shown that 26.22% more attenuation is achieved through this structural optimization.