With the increasing application of improvised explosive devices, the ratio of traumatic ocular injury significantly increased in the past decades, which has become the fourth most happened injury to military deployment. The ocular injury treatment is costly and has been less effective, which influences the military service and life experience of the soldiers. With years of research on the traumatic ocular injury through experiment or computational simulations, the primary blast wave related overpressure was found to induce macular damage, globe rupture. While the influence of the primary blast wave on the posterior part of the eyeball was poorly understood, such as the optic nerve. In this work, we developed a three-dimensional computation model, which included lamina cribrosa (LC), optic nerve and cerebrospinal fluid (CSF). The strain evaluated in optic nerve was found to exceed neural tissue’s physiological loading range, which might explain the vision loss after the blast.

In this work, a computational model of PLLA (Poly L-lactic acid) stent was constructed to study the degradation behavior of the bioabsorbable stent in terms of the loss of mechanical integrity. A degradation model was improved based on experimental data from the literature, as well as a finite element (FE) model was constructed based on the model of the degradation behavior of PLLA material. The results showed that the degradation of the PLLA would switch the material property of stent from a uniform model to a heterogeneous model due to the decline of Young’s modulus locally at each location of the stent. Loss of mechanical integrity of the stent showed a bilinear behavior due to the decline of the Young’s modulus and the locale failure of the structure, respectively. The breakdown pieces of stent will stay a relative longer time in lesion after the loss of the mechanical integrity of the stent due to the nonlinear response of the degradation degree to the degradation time and strain in the material.

Stent implantation is widely used to treat blocked lumen. Stents were meshed structure made of polymers and metal alloys, including stainless steel, cobalt chrome and nitinol [1]. Clinical studies had demonstrated that stents helped to scaffold the diseased lesion up to one year when tissue adapted to the stented environment [2]. However, the permanently implanted stents inside artery were associated with complications such as stent fracture, tissue inflammation, in-stent restenosis and thrombosis [3]. Currently, biodegradable stents are attracting more attention due to its potential long-term efficacy in treating blocked lumens. The detailed characterizations of biodegradable stents are essential for the desired clinical outcomes.

Stent deployment has been widely used to treat narrowed coronary artery. Its acute outcome in terms of stent under expansion and malapposition depends on the extent and shape of calcifications. However, no clear understanding as to how to quantify or categorize the impact of calcification. We have conducted ex vivo stenting characterized by the optical coherence tomography (OCT). The goal of this work is to capture the ex vivo stent deployment and quantify the effect of calcium morphology on the stenting. A three dimensional model of calcified plaque was reconstructed from ex vivo OCT images. The crimping, balloon expansion and recoil process of the Express stent were characterized. Three cross-sections with different calcium percentages were chosen to evaluated the effect of the calcium in terms of stress/strain, lumen gains and malapposition. Results will be used to the pre-surgical planning.

Percutaneous coronary intervention (PCI) is the most common revascularization procedure, in which, fibrocalcific plaques are found in 17–35% of patients undergoing PCI [1]. Numbers will rise with population aging and prolonged statin treatment. Calcifications often lead to stent under expansion and strut malapposition, with increased risk of thrombosis and in-stent restenosis [2]. Presence of calcium strongly inhibits stent performance, a well-documented metric for outcome [3]. The goal of this work is to develop the finite element models for inspecting the influence of the calcium arc extent on the stenting outcomes, such as the stress and strain distribution within the plaque, and the lumen gain following stenting. Finite element method is an effective tool to reveal the mechanism of the stent expansion and its interaction with target lesion, provide guidance for optimal clinical outcomes.

Vesicoureteral reflux (VUR) is the backward flow of urine from the bladder into the kidneys. There are many reasons for this reflux. In 1959, Paquin recommended a tunnel length 5 times the diameter of the ureter to prevent VUR based on anatomical comparisons of postmortem specimens of patients with and without VUR [1]. This has become the standard for current ureteral reimplantation surgery. In 1969, Lyon proposed that the shape of the ureteral orifice was more important than the intravesical tunnel for ureterovesical junction (UVJ) competence [2]. However, this was only considered as a supplement to Paquin’s theory. Lyon’s theory might come into play when using bulking agents to affect the shape and configuration of the ureteral orifice but is not directly taken into consideration during surgical ureteral reimplants. Since Paquin and Lyon, little research has looked at parameters regulating the prevention of VUR or leaking from Mitrofanoff type conduits. A case-control study of megaureter reimplants with and without ureteral tailoring demonstrated equivalent outcomes [3], raising concerns about the validity of the 5:1 rule. Most recently, Villanueva et al. reported that the tunnel length of ureter, which can be modified depending on different surgery cases, is not strictly required to have a 5:1 ratio of the diameter to the length [4]. Accurate quantification of the parameters that affect the ureter mechanics is helpful to improve surgical technique. The aim of this work was to quantitatively inspect Lyon’s theory, i.e., the relationship of intravesical tunnel length and orifice shape with respect to VUR by measuring the pressure required to collapse the ureter for preventing backflow. An enhanced three-dimensional (3D) numerical model was developed considering the interaction between the ureteral orifice and the bladder wall. Parametric studies were then conducted to determine the sensitivity of UVJ competence to the spatial configuration of the intravesical tunnel as well as the ureteral orifice (UO). Two common ureteral orifice shapes, “golf” and “volcano,” as well as different intravesical ureteral tunnel length/diameter ratios, were examined. The required closure pressure was then compared.

Biomechanics of optic nerve head (ONH) has attracted increasing attention in recent years due to its association with ganglion cell damage and tissue remodeling resulted vision impairments [1, 2]. The ONH is exposed to both intraocular pressure (IOP) and intracranial pressure (ICP), separated by the lamina cribrosa (LC) which is regarded as the primary site of axonal injury in glaucoma[3]. The elevated IOP was widely acknowledged as a major risk factor for glaucoma. However, a large number of glaucoma patients never have an increase in IOP [4]. In studies that have looked at lumbar puncture (LP) data, patients with open-angle glaucoma were found to have lower ICPs than non-glaucomatous controls[5]. It suggests that higher translaminar pressure difference across the LC rather than IOP alone may have an important role in the pathogenesis of ONH damage. There were few computational models had been established to investigate the ICP’s role on ONH, such as Ethier et al. found elevated ICP could induce decreased strain within LC using finite element model[6]. However, less experimental data are available for delineating the role of ICP on the behaviors of LC. In this work, we present one dataset from LP patients and reconstruct its two-dimensional computational model of the ONH based on the patient’s images to delineate the role of ICP on ONH mechanics. The changes of LC depth, BMO width and papillary height were compared between the simulation and clinical dataset. The maximum principal strain of LC was calculated to reinforce its link with mechanosensitive cells in ONH.

Stenosis or narrowing of arteries induces a turbulent flow region downstream. Multiple stenosis may lead to flow interference and further disturb the blood flow. This has important clinical implications [1], such as disturbed blood flow and flow recirculation which were correlated with the development of atherosclerosis by upregulating the endothelial cells genes and proteins that cause atherogenesis [2]. Numerical simulation of concentric stenoses by Lee et al [3] have shown that the recirculation zone following the first concentric stenosis affected the flow field at the downstream of the second one, which was dependent on the spacing ratio and degree of stenosis. However, the majority of stenosis is eccentric [2] and the detailed fluid dynamics of multiple stenoses with eccentric constrictions is lacking. The aim of this study is to investigate the interactions between double stenoses with eccentricity using computational fluid dynamics (CFD) simulation. The role of spacing ratio on the recirculation zone and turbulence intensity (TI) were characterized and also compared to concentric cases.

Glaucoma is an eye disease related with vision field loss. Although previous study has investigated the influence of intraocular pressure (IOP) on the glaucoma damage to the lamina cribrosa (LC), the intracranial pressure’s (ICP) effect on the LC has never been elucidated. The goal of this work is to determine the effect of ICP on the LC.

The controlled cortical impact (CCI) model is commonly used for replicating the trauma events. However, the impact parameters vary considerably among different laboratories, making the comparison of research findings difficult. The goal of this work is to quantify the intracranial pressure responses to the input parameters of the CCI device using a surrogate head, i.e., a gel-filled ping pong ball. Findings from this work could be used to better design CCI tests.

The patch material and dimension are two important factors which might affect the surgical outcomes after the aortic arch coarctation repair surgery. To quantity their acute impacts on the biomechanical environment of the repaired aortic arch, an aortic arch model was constructed and the fluid-structure interaction (FSI) technique was utilized to characterize its hemodynamics and wall mechanics. Three different patch materials were considered including pulmonary artery, ECM CorMatrix and Polytetrafluoroethylene (PTFE). The induced wall shear stress, distribution of flow patterns, and von-Mises stress on arterial wall were compared. Results showed that ECM CorMatrix patch had better performance Two different patch dimension (large v.s small) using CorMatrix patch were compared and the relatively smaller patch demonstrated a better hemodynamics than the larger one. No significant difference in terms of wall stress was observed between the different patch sizes.

Aortic allografts have been widely used in treatments of congenital heart diseases with satisfactory clinical outcomes. They were usually cryopreserved and stored for surgical use. The objective of this work was to investigate the effect of cold storage on mechanical properties of aorta, since the compliance mismatch was one important factor associated with the complication after graft surgery. The segments of porcine descending aorta were divided into two groups: the fresh samples which were tested within 24 hours after harvesting served as control group, and frozen samples which were stored in −20°C for 7 days and then thawed. The uniaxial tension tests along circumferential direction and indentation tests were conducted. The average incremental elastic moduli within each stretch range were obtained from the experimental data obtained during tension tests, and the elastic moduli were also calculated by fitting the force-indentation depth data to Hertz model when the tissue was stretched at 1.0, 1.2, 1.4 and 1.6. In addition, the average incremental elastic moduli of both fresh and frozen aortic tissue along axial direction were also obtained by using uniaxial tension tests. The comparison showed that cold storage definitely increased the average incremental elastic modulus of the aortic tissue along circumferential direction; however, the difference is not significant for the elastic moduli along axial direction.

The closed head impact (CHI) rat models are commonly used for studying the traumatic brain injury. Although various impact parameters (e.g., impact depth, velocity, and position) have been investigated by a number of researchers, little is known about the effects of the impactor shape, diameter, and material on the internal responses of the rat brain. In this work, numerical CHI experiments were conducted to investigate the sensitivities of intracranial responses to the impactor details such as impactor shape, diameter, and material. A 3D finite element rat head model with anatomical details was subjected to impact loadings. Results revealed that the impactor shape can affect the intracranial responses significantly. The effect of impactor diameter on the intracranial responses in different brain regions was uniform. In addition, careful attention should be paid when using an extremely compliant material for the impactor, since the actual impact depth might be compensated by the impactor deformation.

The structural topological optimization method is an effective way to find the optimal topology of stents, which could be tailored for targeted stent performance, such as scaffolding ability, foreshortening, potential restenosis rate, etc. The radial stiffness is one of the major characteristics about stent performance. In this work, the homogenization method was utilized for the optimization of stent designs with the objective of maximizing the scaffolding ability of stent, i.e. its radial stiffness. A few design choices were presented by changing the number and distribution of strut connectors while keeping the void volume as 80%. The obtained optimal topology illustrated that the material distribution was mainly determined by the radial stress applied onto the stent. The optimal topology design in this work paves the way for the following dimension design, which can be targeted to the customized stent design for patient-specific lesions.