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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.

Advances in materials science and engineering through bio-inspiration, at both the micro-and nanoscales, have flourished over recent years. By understanding principles used in nature to produce adhesives and other substances of interest, the field of bio-inspired engineering has emerged as an important area of innovation. In this review, we will focus on bio-adhesives based on three main mechanisms of generating attachment: dry, wet, and chemical adhesion. Dry adhesion, involving micro-to nanoscale filamentous structures, is used by many insects and reptiles to rapidly climb surfaces. Tree frogs and some insects make use of wet adhesion by leveraging capillary forces through the design of attaching structures that increases liquid drainage, and hence increases frictional contact. Finally, chemical adhesion is used by many plants and mollusks, which secrete adhesives composed of proteins, polysaccharides and carbohydrates to generate the strong forces necessary for adhesion. This paper reviews recent discoveries in animal and plant bio-adhesives, and details the mechanisms used in several representative biological systems. We extend the review to include the fundamental principles functioning in each form of adhesion at the micro-and nanoscales. This fast emerging research area has significant implications in the future design of bio-inspired adhesives, and offers further potential for a variety of applications.