measured results indicated that the infill shape did not greatly affect the dielectric properties.Although sample E had no infill, the inclusion of the lid and base made up 33% of the total volume. To examine the effects of the external walls, sample F was printed with the same honeycomb infill with thinner bottom base but without the top lid. The thicknesses of the base and the honeycomb infill part of sample F were 0.2 mm and 2.2 mm, respectively. The measured results showed that sample F had a lower permittivity and loss tangent value than sample E, due to its lower PLA volume fraction. CONCLUSIONThis letter has presented the feasibility of creating low loss dielectric substrates with various relative permittivities and loss tangent values using conventional 3D printing. Voids were introduced inside the substrates which were printed in one process. The volume fraction of air in the host material affected the dielectric properties more significantly than the infill shape. The permittivity and loss factor of the substrate were reduced by the increasing air volume fraction. Therefore, the permittivity and loss tangent of the dielectric substrate can be tailored to the desired values by extrapolating from the sample results produced here.These highly customisable dielectric materials will improve the flexibility of antenna design and related EM applications. The automatic fabrication process also allows the dielectric properties to be graded within one structure. ance evaluations.

In this work we have investigated the effects of strontium (Sr) dopant on in vitro protein release kinetics and in vivo osteogenic properties of plasma sprayed hydroxyapatite (HA) coatings, along with their dissolution behavior. Plasma sprayed HA coatings are widely used in load-bearing implants. Apart from osseointegration, the new generation of HA coating is expected to deliver biomolecules and/or drugs that can induce osteoinduction. This paper reports the preparation of crystalline and amorphous HA coatings on commercially pure titanium (Cp-Ti) using inductively coupled radio frequency (RF) plasma spray, and their stability at different solution pH. Coatings prepared at 110 mm working distance from the nozzle showed average Ca ion release of 18 and 90 ppm in neutral and acidic environments, respectively. Decreasing the working distance to 90 mm resulted in the formation of a coating with less crystalline HA and phases with higher solubility products, and consequently higher dissolution over 32 days. A 92% release of a model protein bovine serum albumin (BSA) in phosphate buffer with pH of 7.4 was measured for Sr doped-HA coating, while only a 72% release could be measured for pure HA coating. Distortion of BSA during adsorption on coatings revealed strong interaction between the protein and the coating, with an increase in α-helix content. Osteoid formation was found on Sr-HA implants as early as 7 weeks post implantation compared to HA coated and uncoated Ti implants. After 12 weeks post implantation, osteoid new bone was formed on HA implants; whereas, bone mineralization started on Sr-HA samples. While no osteoid was formed on bare Ti surfaces, bone was completely mineralized on HA and Sr-HA coatings after 16 weeks post implantation. Our results show that both phase stability and chemistry can have significant influence towards in vitro and in vivo response of HA coatings on Ti implants.

β-tricalcium phosphate (β-TCP) is a versatile bioceramic for the use in many orthopedic and dental applications due to its excellent biocompatibility and biodegradability. Recently, the addition of additives to β-TCP has been proven to improve bone repair and regeneration, however, the underlying mechanism of enhanced bone regeneration is still unknown. In this study, strontium oxide (SrO), silica (SiO 2 ), magnesia (MgO), and zinc oxide (ZnO) were added to β-TCP for dense discs fabrication followed by in vitro evaluation using a preosteoblast cell line. Cell viability and gene expression were analyzed at day 3 and day 9 during the cell culture. MgO and SiO 2 were found to significantly enhance and expedite osteoblastic differentiation. A potential mechanism was introduced to explain the additive induced osteoblastic differentiation. In addition, in vivo characterizations showed that porous 3D printed MgO-SiO 2 -TCP scaffolds significantly improved new bone formation after 16 weeks of implantation. This study shows beneficial effects of additives on osteoblastic viability and differentiation in vitro as well as osteogenesis in vivo, which is crucial towards the development of bone tissue engineering scaffolds.

Calcium phosphate (CaP) ceramics show significant promise towards bone graft applications because of the compositional similarity to inorganic materials of bone. With 3D printing, it is possible to create ceramic implants that closely mimic the geometry of human bone and can be custom-designed for unusual injuries or anatomical sites. The objective of the study was to optimize the 3D-printing parameters for the fabrication of scaffolds, with complex geometry, made from synthesized tricalcium phosphate (TCP) powder. This study was also intended to elucidate the mechanical and biological effects of the addition of Fe and Si in TCP implants in a rat distal femur model for 4, 8, and 12 weeks. Doped with Fe and Si TCP scaffolds with 3D interconnected channels were fabricated to provide channels for micronutrients delivery and improved cell-material interactions through bioactive fixation. Addition of Fe into TCP enhanced early-stage new bone formation by increasing type I collagen production. Neovascularization was observed in the Si doped samples after 12 weeks. These findings emphasize that the additive manufacturing of scaffolds with complex geometry from synthesized ceramic powder with modified chemistry is feasible and may serve as a potential candidate to introduce angiogenic and osteogenic properties to CaPs, leading to accelerated bone defect healing.

Iron (Fe) is a vital element and its deficiency causes abnormal bone metabolism. We investigated the effects of Fe and its concentration in β-tricalcium phosphate (β-TCP) on physicomechanical properties and in vitro proliferation and differentiation of osteoblasts. Our results showed that Fe addition at concentrations of 0.5 wt. % (0.5 Fe-TCP) and 1.0 wt. % (1.0 Fe-TCP) inhibits the β-TCP to α-TCP phase transformation at sintering temperature of 1250 °C. Addition of 0.25 wt. % Fe (0.25 Fe-TCP) increased the compressive strength of β-TCP from 167.27±16.2 MPa to 227.10±19.3 MPa. After 3 days of culture, surfaces of 0.5 Fe-TCP and 1.0 Fe-TCP samples were covered by osteoblast cells, compared to that of pure and 0.25 Fe-TCP. Cells grew to confluency on all Fe-doped samples after 7 days of culture and monolayer sheetlike cellular structure was found at 11 days. Optical cell density and alkaline phosphatase activity were significantly higher on Fe-doped samples and the highest values were found in 0.5 Fe-TCP samples. Our results show that Fe concentration had significant effect on physical and mechanical properties of TCP ceramics, and also on the in vitro osteoblast cellular interactions in TCP ceramics.