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Layer-by-layer deposition of materials to manufacture parts-better known as three-dimensional (3D) printing or additive manufacturing-has been flourishing as a fabrication process in the past several years and now can create complex geometries for use as models, assembly fixtures, and production molds. Increasing interest has focused on the use of this technology for direct manufacturing of production parts; however, it remains generally limited to single-material fabrication, which can limit the end-use functionality of the fabricated structures. The next generation of 3D printing will entail not only the integration of dissimilar materials but the embedding of active components in order to deliver functionality that was not possible previously. Examples could include arbitrarily shaped electronics with integrated microfluidic thermal management and intelligent prostheses custom-fit to the anatomy of a specific patient. We review the state of the art in multiprocess (or hybrid) 3D printing, in which complementary processes, both novel and traditional, are combined to advance the future of manufacturing.

In this paper, we examine prospects for the manufacture of patient-specific biomedical implants replacing hard tissues (bone), particularly knee and hip stems and large bone (femoral) intramedullary rods, using additive manufacturing (AM) by electron beam melting (EBM). Of particular interest is the fabrication of complex functional (biocompatible) mesh arrays. Mesh elements or unit cells can be divided into different regions in order to use different cell designs in different areas of the component to produce various or continually varying (functionally graded) mesh densities. Numerous design elements have been used to fabricate prototypes by AM using EBM of Ti-6Al-4V powders, where the densities have been compared with the elastic (Young) moduli determined by resonant frequency and damping analysis. Density optimization at the bone-implant interface can allow for bone ingrowth and cementless implant components. Computerized tomography (CT) scans of metal (aluminium alloy) foam have also allowed for the building of Ti-6Al-4V foams by embedding the digital-layered scans in computer-aided design or software models for EBM. Variations in mesh complexity and especially strut (or truss) dimensions alter the cooling and solidification rate, which alters the a-phase (hexagonal close-packed) microstructure by creating mixtures of a/a (martensite) observed by optical and electron metallography. Microindentation hardness measurements are characteristic of these microstructures and microstructure mixtures (a/a ) and sizes.

Purpose:To demonstrate the feasibility of a four-dimensional phase contrast (PC) technique that permits spatial and temporal coverage of an entire three-dimensional volume, to quantitatively validate its accuracy against an established time resolved two-dimensional PC technique to explore advantages of the approach with regard to the fourdimensional nature of the data. Materials and Methods:Time-resolved, three-dimensional anatomical images were generated simultaneously with registered three-directional velocity vector fields. Improvements compared to prior methods include retrospectively gated and respiratory compensated image acquisition, interleaved flow encoding with freely selectable velocity encoding (venc) along each spatial direction, and flexible trade-off between temporal resolution and total acquisition time. Results:The implementation was validated against established two-dimensional PC techniques using a well-defined phantom, and successfully applied in volunteer and patient examinations. Human studies were performed after contrast administration in order to compensate for loss of inflow enhancement in the four-dimensional approach. Conclusion:Advantages of the four-dimensional approach include the complete spatial and temporal coverage of the cardiovascular region of interest and the ability to obtain high spatial resolution in all three dimensions with higher signal-to-noise ratio compared to two-dimensional methods at the same resolution. In addition, the four-dimensional nature of the data offers a variety of image processing options, such as magnitude and velocity multi-planar reformation, three-directional vector field plots, and velocity profiles mapped onto selected planes of interest.