Osteogenic and Chondrogenic Differentiation of rBMSCs on Microsphere-Based Scaffolds Sintered Using Subcritical CO2

Large bone defects remain a major clinical orthopedic challenge. It has been predicted that osteoarthritis will affect over 100 million adults in the United States by the year 2030. Current treatments for repairing bone defects include the use of bone grafts (autologous and allogenic) or implants (polymeric or metallic). These approaches have significant limitations due to insufficient supply, potential disease transmission, rejection, cost and the inability to integrate with the surrounding host tissue. The engineering of bone and cartilage tissue offers new therapeutic strategies to treat bone defects. Several scaffold-based approaches have been used in the past. However, this thesis presents a novel microsphere-based scaffold approach, sintered using subcritical carbon dioxide for osteogenic and chondrogenic tissue regeneration. As a next step in the fabrication of three-dimensional tissue engineered scaffolds, this thesis primarily focused on subcritical carbon dioxide sintering for forming scaffolds, performance of these scaffolds in culture for 6 weeks, and evaluation of two different polymers in osteogenic and chondrogenic differentiation. In this investigation, both temperature and pressure (along with time) were necessary to control during the CO2 sintering of PCL (higher temperature and pressure conditions with longer exposure time), as opposed to PLGA, which was sintered at ambient temperature and pressure conditions (for 1 hour exposure). The results obtained showed the feasibility of using these constructs for bone and cartilage tissue regeneration. Biochemical analysis, gene expression and histological staining were used to analyze the data. The mechanical integrity of the constructs was evaluated at the beginning and end of the culture period. The onset of PLGA degradation for the CO2 sintered microspheres in this study appeared at 1.5 weeks which affected chondrogenesis. With osteogenesis, the Osteogenic PLGA group showed greater calcium content value over the Osteogenic PCL group while PCL retained its shape, size and mechanical integrity and had twice as many cells per construct at 6 weeks. In conclusion, this thesis lays a foundation to explore numerous applications using subcritical carbon dioxide sintering for tissue engineering applications

ChainQueen: A Real-Time Differentiable Physical Simulator for Soft Robotics

Physical simulators have been widely used in robot planning and control. Among them, differentiable simulators are particularly favored, as they can be incorporated into gradient-based optimization algorithms that are efficient in solving inverse problems such as optimal control and motion planning. Simulating deformable objects is, however, more challenging compared to rigid body dynamics. The underlying physical laws of deformable objects are more complex, and the resulting systems have orders of magnitude more degrees of freedom and therefore they are significantly more computationally expensive to simulate. Computing gradients with respect to physical design or controller parameters is typically even more computationally challenging. In this paper, we propose a real-time, differentiable hybrid Lagrangian-Eulerian physical simulator for deformable objects, ChainQueen, based on the Moving Least Squares Material Point Method (MLS-MPM). MLS-MPM can simulate deformable objects including contact and can be seamlessly incorporated into inference, control and co-design systems. We demonstrate that our simulator achieves high precision in both forward simulation and backward gradient computation. We have successfully employed it in a diverse set of control tasks for soft robots, including problems with nearly 3,000 decision variables.Comment: In submission to ICRA 2019. Supplemental Video: https://www.youtube.com/watch?v=4IWD4iGIsB4 Project Page: https://github.com/yuanming-hu/ChainQuee

Conformation constraints for efficient viscoelastic fluid simulation

The simulation of high viscoelasticity poses important computational challenges. One is the difficulty to robustly measure strain and its derivatives in a medium without permanent structure. Another is the high stiffness of the governing differential equations. Solutions that tackle these challenges exist, but they are computationally slow. We propose a constraint-based model of viscoelasticity that enables efficient simulation of highly viscous and viscoelastic phenomena. Our model reformulates, in a constraint-based fashion, a constitutive model of viscoelasticity for polymeric fluids, which defines simple governing equations for a conformation tensor. The model can represent a diverse palette of materials, spanning elastoplastic, highly viscous, and inviscid liquid behaviors. In addition, we have designed a constrained dynamics solver that extends the position-based dynamics method to handle efficiently both position-based and velocity-based constraints. We show results that range from interactive simulation of viscoelastic effects to large-scale simulation of high viscosity with competitive performance

Biological applications of kinetics of wetting and spreading

Wetting and spreading kinetics of biological fluids has gained a substantial interest recently. The importance of these fluids in our lives has driven the pace of publications. Globally scientists have ever growing interest in understanding wetting phenomena due to its vast applications in biological fluids. It is impractical to review extremely large number of publications in the field of kinetics of complex biological fluids and cosmetic solutions on diverse surfaces. Therefore, biological and cosmetic applications of wetting and spreading dynamics are considered in the following areas: (i) Spreading of Newtonian liquids in the case of non-porous and porous substrates. It is shown that the spreading kinetics of a Newtonian droplet on non-porous and porous substrate can be defined through theoretical relations for droplet base radius on time, which agree well with the experimental results; (ii) Spreading of blood over porous substrates. It is shown that blood, which has a complex non-Newtonian rheology, can be successfully modelled with the help of simple power-law model for shear-thinning non-Newtonian liquids; (iii) Simultaneous spreading and evaporation kinetics of blood. This part enlightens different underlying mechanisms present in the wetting, spreading, evaporation and dried pattern formation of the blood droplets on solid substrates; (iv) Spreading over hair. In this part the wetting of hair tresses by aqueous solutions of two widely used by industry commercially available polymers, AculynTM 22 and AculynTM 33, are discussed. The influence of non-Newtonian rheology of these polymer solutions on the drainage of foams produced from these solutions is also briefly discussed