Biofidelic simulations of embryonic joint growth and morphogenesis

During skeletal development, the opposing surfaces in the joint mould into interlocking and reciprocal shapes in a process called morphogenesis. Morphogenesis is critical to the health and function of the joint, and yet, little is known about the process of joint morphogenesis. For example, how do different joints acquire their specific shapes? Which cellular processes underlie joint shaping and how are they regulated? However, it is known that fetal movements are critical to joint development, with alterations or absences of movement being implicated in multiple pre- and post-natal musculoskeletal conditions. This doctorate explored the cell-level dynamics governing joint growth and the implication of movements in regulating them, using novel biofidelic and mechanobiological models of joint growth. Cell-level data from wild type zebrafish larvae were tracked and synthesised in a biofidelic simulation of zebrafish jaw joint growth. Growth characteristics were quantified revealing a strong anisotropy (Chapter 3). Next, zebrafish larvae were immobilised using drug treatment. The material properties of the zebrafish jaw cartilage were measured using nano-indentation in the presence or absence of movement showing a delay in cartilage stiffening in immobilised larvae (Chapter 4). Then, I developed a novel mechanobiological model of zebrafish jaw joint growth, which identified a correlation between growth characteristics and the dynamic patterns of mechanical stimuli experienced by joint elements over jaw motion (Chapter 5). Finally, local growth rates were characterised in the mouse elbow in the presence or absence of skeletal muscles. Spatial heterogeneity in the growth rates correlated with the emergence of specific shape features at the level of the condyles. Immobilisation led to disruption of the local growth rates correlated with failed shape differentiation of the condyles. The relative contribution of key cell activities to growth such as cell volume expansion, cell number increases and extracellular matrix expansion, were shown to vary over time in both wild types and muscleless-limbs and to be altered in the absence of skeletal muscles (Chapter 6). This research offers avenues for improvement in simulations of joint development and potentially other organs. It provides fundamental advance in our understanding of mechanoregulation in the developing joint and increases our understanding of the origins of musculoskeletal abnormalities.Open Acces

Pulse, polarization and topology shaping of polariton fluids

Here we present different approaches to ultrafast pulse and polarization shaping, based on a “quantum fluid” platform of polaritons. Indeed we exploit the normal modes of two dimensional polariton fluids made of strong coupled quantum well excitons and microcavity photons, by rooting different polarization and topological states into their sub-picosecond Rabi oscillations. Coherent control of two resonant excitation pulses allows us to prepare the desired state of the polariton, taking benefit from its four-component features given by the combination of the two normal modes with the two degrees of polarization. An ultrafast imaging based on the digital off-axis holography technique is implemented to study the polariton complex wavefunction with time and space resolution. We show in order coherent control of the polariton state on the Bloch sphere, an ultrafast polarization sweeping of the Poincaré sphere, and the dynamical twist of full Poincaré states such as the skyrmion on the sphere itself. Finally, we realize a new kind of ultrafast swirling vortices by adding the angular momentum degree of freedom to the two-pulse scheme. These oscillating topology states are characterized by one or more inner phase singularities tubes which spirals around the axis of propagation. The mechanism is devised in the splitting of the vortex into the upper and lower polaritons, resulting in an oscillatory exchange of energy and angular momentum and in the emitted time and space structured photonic packets