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Gold nanoparticles are materials with unique optical properties that have made them very attractive for numerous biomedical applications. With the increasing discovery of techniques to synthesize novel nanoparticles such as star-shaped gold nanoparticles for biomedical applications, the safety and performance of these new nanomaterials must be systematically assessed before use. In this study, gold nanostars (AuNSTs) with multibranched surface structures were synthesized, and their influence on the cytotoxicity of human skin fibroblasts and rat fat pad endothelial cells (RFPECs) were assessed and compared with that of gold nanospheres (AuNSPs) with unbranched surfaces. Results showed that the AuNSPs with diameters of approximately 61.46 nm showed greater toxicity with fibroblast cells and RFPECs compared with the synthesized AuNSTs with diameters of approximately 33.69 nm. The AuNSPs were lethal at concentrations of 40 μg/mL for both cell lines, whereas the AuNSTs were less toxic at higher concentrations (400 μg/mL). The calculated IC50 (50% inhibitory concentration) values of the AuNSPs exposed to fibroblast cells were greater at 1 and 4 days of culture (26.4 and 27.7 μg/mL, respectively) compared with the RFPECs (13.6 and 13.8 μg/mL, respectively), indicating that the AuNSPs have a greater toxicity to endothelial cells. It was proposed that possible factors that could be promoting the reduced toxicity effects of the AuNSTs to fibroblast cells and RFPECs, compared with the AuNSPs may be size, surface chemistry, and shape of the gold nanoparticles. The reduced cell toxicity observed with the AuNSTs suggests that AuNSTs may be a promising material for use in biomedical applications.

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Commercially pure titanium (c.p. Ti) is one of the best metallic biomaterials for bone tissue replacement. However, one of its main drawbacks, which compromises the service reliability of the implants, is the stress-shielding phenomenon (Young's modulus mismatch with respect to that one of the bone). Several previous works attempted to solve this problem. One alternative to solve that problem has been the development of biocomposites implants and, more recently, the fabrication of titanium porous implants. In this work, porous samples of c.p. Ti grade 4 were obtained using conventional powder metallurgy technique. The influence of the processing parameters (compacting pressure and sintering temperature) on the microstructure features (size, type, morphology, and percentage of porosity), as well as on the mechanical properties (compressive yield strength, and conventional and dynamic Young's modulus) were investigated. The results indicated that there is an increment in density, roundness of pores, and mean free path between them as compacting pressure and/or sintering temperature is increased. The Young's modulus (conventional and dynamic) and yield strength showed the same behavior. Better stiffness results, in the central part of cylindrical samples, were obtained for a uniaxial compression of 38.5 MPa using a sintering temperature of 1273 K and 1373 K (1000°C and 1100°C). An evaluation of porosity and Young's modulus along a cylindrical sample divided in three parts showed that is possible to obtain a titanium sample with graded porosity that could be used to design implants. This approach opens a new alternative to solve the bone resorption problems associated with the stress-shielding phenomenon.

The high Young's modulus of titanium with respect to that one of the bone is the main cause of the stressshielding phenomenon, which promotes bone resorption around implants. Development of implants with a low Young's modulus has gained increased importance during the last decade, and the manufacturing of porous titanium is one of the routes to reduce this problem. In this work, porous samples of commercially pure titanium grade IV obtained by powder metallurgy with ammonium bicarbonate (NH 4 HCO 3 ) as space-holder were studied. Evaluations of porosity and mechanical properties were used to determine the influence of compaction pressure for a fixed NH 4 HCO 3 content. Measurements by ultrasound tests gave Young's modulus results that were low enough to reduce stress shielding, whilst retaining suitable mechanical strength. Biological tests on porous cp Ti showed good adhesion of osteoblasts inside the pores, which is an indicator of potential improvement of osteointegration.

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