Journal of biomechanical engineering
-
This technical brief serves as an update to our previous work characterizing the region-dependence of viscoelastic mechanical properties of the P17 and adult rat brain in the coronal plane (Elkin et al., 2011, "A Detailed Viscoelastic Characterization of the P17 and Adult Rat Brain," J. Neurotrauma, 28, pp. 2235-2244.). Here, modifications to the microindentation device provided for the reliable measurement of load during the ramp portion of load relaxation microindentation tests. ⋯ The shear modulus ranged from ∼0.2 kPa to ∼2.6 kPa depending on region, age, and time scale. Best-fit Prony series parameters from least squares fitting to the indentation data from each region are reported, which describe the shear relaxation behavior for each anatomic region within each age group at both short (<10 ms) and long (∼20 s) time scales. These data will be useful for improving the biofidelity of finite element models of rat brain deformation at short time scales, such as models of traumatic brain injury.
-
An evaluation of wound mechanics is crucial in reflecting the wound healing status. The present study examined the biomechanical properties of healing rat skin wounds in vivo and ex vivo. Thirty male Sprague-Dawley rats, each with a 6 mm full-thickness circular punch biopsied wound at both posterior hind limbs were used. ⋯ On day 21, the ultimate tensile strength of the skin wound tissue approached 50% of the normal skin; while the stiffness of tissue recovered at a faster rate, reaching 97% of its prewounded state. Our results suggested that it took less time for healing wound tissues to recover their stiffness than their maximal strength in rat skin. The stiffness of wound tissues measured by air-jet could be an indicator for monitoring wound healing and contraction.
-
Despite considerable effort over the last four decades, research has failed to translate into consistently effective treatment options for spinal cord injury (SCI). This is partly attributed to differences between the injury response of humans and rodent models. Some of this difference could be because the cerebrospinal fluid (CSF) layer of the human spine is relatively large, while that of the rodents is extremely thin. ⋯ The high injury severity animals had less tissue sparing than the moderate injury severity animals; this difference was statistically significant only within 1.6 mm of the epicenter. These results indicate that future research seeking to elucidate the mechanical origins of primary tissue damage in SCI should consider the effects of CSF. This pig model provides advantages for basic and preclinical SCI research due to its similarities to human scale, including the existence of a human-like CSF fluid layer.
-
Most computational models of abdominal aortic aneurysms address either the hemodynamics within the lesion or the mechanics of the wall. More recently, however, some models have appropriately begun to account for the evolving mechanics of the wall in response to the changing hemodynamic loads. Collectively, this large body of work has provided tremendous insight into this life-threatening condition and has provided important guidance for current research. ⋯ That is, there is a pressing need to include effects of the hemodynamics on both the development of the nearly ubiquitous intraluminal thrombus and the evolving mechanics of the wall, which depends in part on biochemical effects of the adjacent thrombus. Indeed, there is increasing evidence that intraluminal thrombus in abdominal aortic aneurysms is biologically active and should not be treated as homogeneous inert material. In this review paper, we bring together diverse findings from the literature to encourage next generation models that account for the biochemomechanics of growth and remodeling in patient-specific, thrombus-laden abdominal aortic aneurysms.
-
Single ventricle heart defects are among the most serious congenital heart diseases, and are uniformly fatal if left untreated. Typically, a three-staged surgical course, consisting of the Norwood, Glenn, and Fontan surgeries is performed, after which the superior vena cava (SVC) and inferior vena cava (IVC) are directly connected to the pulmonary arteries (PA). In an attempt to improve hemodynamic performance and hepatic flow distribution (HFD) of Fontan patients, a novel Y-shaped graft has recently been proposed to replace the traditional tube-shaped extracardiac grafts. ⋯ The unequal branch design is demonstrated to be unnecessary under most conditions, as it is possible to achieve the same or better performance with equal-sized branches. Two patient-specific examples show that optimization-derived Y-grafts effectively improve the HFD, compared to initial nonoptimized designs using equal branch diameters. An instance of constrained optimization shows that energy efficiency slightly increases with increasing branch size for the Y-graft, but that a smaller branch size is preferred when a proximal anastomosis is needed to achieve optimal HFD.