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A novel method utilizing colloidal gold particles to create speckle patterns on mouse aortas for digital image correlation (DIC) studies is presented. The colloidal gold particles form random, stable, high contrast, variably sized speckles suitable for DIC analysis and can be used to measure local strains during mechanical failure testing. 

Abstract—Elastin is a key structural protein and its pathological degradation deterministic in aortic aneurysm (AA) outcomes. Unfortunately, using current diagnostic and clinical surveillance techniques the integrity of the elastic fiber network can only be assessed invasively. To address this, we employed fragmented elastin-targeting gold nanoparticles (EL-AuNPs) as a diagnostic tool for the evaluation of unruptured AAs. Electron dense EL-AuNPs were visualized within AAs using microcomputed tomography (micro-CT) and the corresponding Gold-to-Tissue volume ratios quantified. The Gold-to-Tissue volume ratios correlated strongly with the concentration (0, 0.5, or 10 U/mL) of infused porcine pancreatic elastase and therefore the degree of elastin damage. Hyperspectralmapping confirmed the spatial targeting of the EL-AuNPs to the sites of damaged elastin. Nonparametric Spearman’s rank correlation indicated that the micro-CT-based Gold-to-Tissue volume ratios had a strong correlation with loaded (q = 0.867, p-val = 0.015) and unloaded (q = 0.830, p-val = 0.005) vessel diameter, percent dilation (q = 0.976, p-val = 0.015), circumferential stress (q = 0.673, p-val = 0.007), loaded (q = 2 0.673, p-val = 0.017) and unloaded (q = 2 0.697, p-val = 0.031) wall thicknesses, circumferential stretch (q = 2 0.7234, p-val = 0.018), and lumen area compliance (q = 2 0.831, p-val = 0.003). Likewise, in terms of axial force and axial stress vs. stretch, the post-elastase vessels were stiffer. Collectively, these findings suggest that, when combined with CT imaging, EL-AuNPs can be used as a powerful tool in the non-destructive estimation of mechanical and geometric features of AAs. 

Digital image correlation (DIC) is a non-destructive and non-contact optical technique to measure deformation and strain of materials. The method is based on optically tracking the displacements of a speckle pattern created on the material surface. In the case of soft tissues such as mouse aorta, there are several advantages to using DIC since it can provide local, rather than global, deformations and it is suitable for large strain measurements, typical of soft tissues taken to failure [1] [2]. For the optimal use of DIC, several requirements should be met for speckle patterning: 1) randomness, 2) high contrast, 3) appropriate size of speckle in the field of view (3-5 pixels), and 4) firm attachment of speckle to specimen during deformation. In previous DIC studies of soft tissues, the methods employed to create a speckle pattern include the use of an airbrush to spray dye or paint on the specimen, or coating the sample with toner powder. However, biological samples must be partially dehydrated before applying paint which may affect the mechanical properties of the specimen, and toner powder is too hydrophobic to adhere well on specimens when submerged in aqueous solution during mechanical testing. In addition, it is difficult to evenly distribute paint or toner powder on the surface of a hydrated biological specimen [2]. Therefore, a novel method utilizing colloidal gold particles to create a speckle pattern on mouse aorta is proposed in this work.