We are primarily interested in biomechanical problems, current work is main focused on injury biomechanics. Our approaches are diverse, combining “classical” mechanics with quantitative medical imaging, high- performance computing, and discovery experiments. We use model systems to address following thematic questions: (a) Is there a definitive correlation between mechanical stimulus and injury? (b) What factors are predictive of injury?
Can does-response curves be developed to establish a link between severity and frequency of mechanical stimulus and associated injury or damage?
(c) What are the mechanisms of injury?
Can biomechanics based approaches be used to detect early stages of injury to support detection, diagnosis, mitigation, and prevention?
Research Topics:
Some of the work described below was part of Principal Investigator's doctoral and postdoctoral work. 1) Mechanics of Head Trauma: Traumatic brain injury (TBI) is a critical public health problem worldwide with an estimated 10 million people affected annually. The rate of TBI incidences continues to grow with the increased adoption of motorized vehicles in developing countries, the faster pace of sports, and asymmetric military conflicts around the world. According to the World Health Organization (WHO), TBI will likely be the major cause of death and disability by the year 2020. Currently, we are developing high-fidelity computational models of brain biomechanics that are valid over the range of injury scenarios and pathological outcomes. This approach integrates information on the events that cause TBI with models of the anatomy and physiology of the living human brain to study the onset and specific forms of traumatic brain injury. Injury scenarios that we are interested in studying are road traffic accidents (especially motorbike accidents), falls to the elderly and children, blast loading (especially blast mining), and sports accidents. Typical pathological outcomes as a result of impact to the head are diffuse axonal injury (DAI), epidural and subdural hematomas (EDH/SDH), contusions and parenchymal hematomas, subarachnoid and intraventricular hemorrhage (SAH/IVH), vascular injury, and diffuse brain swelling. Our goal is to examine the correlation between injury scenario (or loading) and pathological outcome, including degree and likely locations of injury. We have developed a computational modeling approach that can be used to estimate the location and extent of diffuse axonal injury (DAI) in subject-specific human brains. The model captures the essential features of diffuse axonal injury, which is characterized by damage to neural axons, using an axonal strain injury criterion. The subject-specific model incorporates structural information for individual subject obtained using magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI). The subject-specific models are informed by macroscopic experiments (on human volunteers) and maintain a high degree of biofidelity. Using event reconstruction approaches coupled with multiscale mechanics analyses, we try to delineate stress state in the brain during injury causing events and also try to understand mechanisms that lead to neuronal degeneration.
(I) Retinal ganglion cells of noninjured and injured optic nerve. Micrographs of normal retina (A), and retina of injured optic nerve 2 weeks after impact injury (B). (Adopted from Yoles & Schwartz, Experimental Neurology, 153, 1998.) (II) Simplified computational model of the human eye and optic nerve (A). Shearing stresses in the optic nerve and orbital fat. The interaction of the rotational loading with the anatomical structures results in substantial heterogeneity of the stress field (B).
2) Biomechanics of Indirect Traumatic Optic Neuropathy (ITON): Indirect Traumatic Optic Neuropathy (ITON) refers to an injury of the optic nerve often resulting in partial or complete loss of vision. ITON is a rare complication in patients with head injuries, affecting predominantly young patients. The majority of patients do not recover useful vision in the affected eye, and many are left unable to perceive light. The hallmark of ITON is it generally occurs without obvious evidence of external eye injury. In addition, ITON is oftentimes missed on standard radiologic examinations such as computed tomography, magnetic resonance imaging. Its natural history, mechanisms, and pathology remain undetermined and it continues to be a diagnostic and therapeutic dilemma. This underscores the need to accurately understand tissue- and cellular-level injury biomechanics in order to delineate clinical ITON.
Our focus for this research is the application of imaging and mechanics (both experimental and computational) based approaches to better understand the biomechanics, causative mechanisms and pathophysiological responses following ITON. As a preliminary work in this area, we have built a simplified computational model to study the biomechanics of the optic nerve when it is subjected to impact forces. Using this model, we are exploring two fundamental hypotheses regarding the biomechanics of ITON: 1) rapid rotation of the globe of the eye causes avulsion of the optic nerve 2) a sudden deformation of the globe of the eye leads to an acute increase in ocular pressure. Our preliminary results indicate that there exist a complex set of stress state as stress wave propagates through globe-optic nerve parenchyma, as a result of the forces delivered by an impact.
Underwash effect beneath the helmet as a result of blast loading.
3) Protection against Impact: We are interested in designing better personal protective equipments and passive protection strategies to mitigate effects of a blow to the head. Current helmets are typically good at protecting against linear impact, but their role in protection against mitigation of rotational accelerations and blast load is not fully understood. In the past, we have demonstrated that for certain scenarios, the mitigation offered by the military helmets against the blast loading is marginal. For example, we have shown that blast waves can focus in the gap between the head and the helmet (head-helmet subspace), thus, amplifying the effects of blast wave rather than mitigating it.
4) Response of Reinforced Concrete under Blast Loading: In collaboration with Dr. Mohd.Ashraf Iqbal, we are studying the response of reinforced concrete against the blast loading. We are particularly interested in modeling blast wave propagation through air, its interaction with the concrete slab using fluid-structure interaction (FSI) and subsequent wave propagation through reinforced concrete. Experiments are also conducted to capture the physics and validate the computational models.