Ganesh Thiagarajan - US grants

The objective of this project is to develop validated Neural Network models built upon a multi-scale approach and to demonstrate the utility of these models in a musculoskeletal model of the leg. These models will describe the non linear, rate dependent, non-homogenous dynamic response of menisci-tibio-femoral articulations in a computationally efficient modular package. The proposed research will include the development of four different computational models of increasing scale, novel methods to bridge the various scales, and model validation through a dynamic knee loading machine and clinical gait lab measurements. The final product will be publicly available Neural Network models that can be exported to commercial integrated development environments or in-house multi-body models. This work will be a valuable asset to the musculoskeletal research community providing computational tools that may aid research in broad areas such as human movement, prosthetics, tissue engineering, sport injury, and disease.

The research objective of this Faculty Early Career Development (CAREER) Program project is to develop a fracture-constitutive multi-scale model which is able to simulate dynamic fracture in concrete subjected to extreme loadings. The non-linear and fracture behavior of concrete when subjected to dynamic loads such as blast and impact is an increasingly important consideration when designing critical protective structures. To validate the model to be developed, test data collected from a drop tower impact test and blast response data obtained from a shock tube test on reinforced concrete panels will be used. The impact and blast loading tests will be conducted at the US Army Corps of Engineers-Engineering Research and Development Center at Vicksburg, Mississippi. The numerical model will be able to simulate discrete crack initiation without any pre-specifications about the crack path. The numerical model will be implemented in the popular commercial finite element programs ABAQUS and LSDYNA and verified using the project data and other available experimental test data. The behavior of a seven story reinforced concrete structure subjected to blast loading will be simulated and studied. The enhancements to the numerical model will also be utilized in the PI's current study of the mechanical behavior of nano-sized particles such as minerals and collagen fibrils present in dentin and bone.

For broader impact and dissemination of the results, the project will develop educational materials for designers and educators. Examples given in Federal Emergency Management Agency Publication 451 will be augmented to include the blast loading case, as specified in ASCE 7 commentary. The research results will also be made available to code writing bodies such as ACI 318 to incorporate the strain rate effects in design provisions. Besides the graduate students, the undergraduate students will also be involved in the project through NSF and the university programs such as SEARCH. Outreach activities with High School students will be incorporated through the NSF funded project ARROWS.

Osteoporosis is a disease of low bone mass and increased risk of fracture. Exercise can increase bone size and help protect against fractures. This project aims to improve understanding of how bone cells detect bone loading. The bone cell thought to be the load detector is called the "osteocyte". Osteocytes communicate with each other and to other cells on the surface of the bone to change bone size to match the loads on the bone. The goal of the work is to determine how bone deformation and fluid flow are detected and changed into a chemical signal that the cell uses to communicate to other cells. Mechanical loading will be related to the biological response of the cell using advanced cell biological methods. The outcomes of this research will determine the role of solid-fluid interaction mechanics in the activation of bone formation to help explain and mitigate age related bone loss. The project will offer local high school students, especially female students, one day research camps and encourage them to pursue engineering and medical education. Undergraduate students will work on various aspects of the project.

The objective is to gain a better understanding of the role of multiscale mechanics - from macro-scale bone strains to micro-scale strains (local bone matrix and lacunar strain and the corresponding fluid flow shear stress on the cell membrane) in mechanotransduction at the osteocyte cellular level. We plan to study these effects using the activation of the Wnt/beta-catenin signaling pathway in osteocytes as a readout for their response to loading. This pathway is known to be important in mediating load related bone formation. The methods include experimental studies using axial loading experiments on mouse whole forearm, novel microscale axial loading experiments on murine ulna sections using the MicroXCT-200 (Carl Zeiss/Xradia) to determine lacunar strains. Newly developed multiplexed 3D confocal microscopy techniques will be used for 3D modelling of osteocytes and their lacunar fluid space for fluid-structure interaction FE models.