26 research outputs found
The discrete multi-physics method applied to biomechanics
In this thesis, a fully Lagrangian approach called the Discrete Multi-Physics is adopted and applied to biomechanics. The Discrete Multi-Physics combines the Smoothed Particle Hydrodynamics, the Mass and Spring Model and the Discrete Element Method in a common particle-based framework. In the Discrete Multi-Physics, high deformations and contact of solid structures (e.g. valve’s leaflets during closing phase or colloid contact) can be easily modelled. In biological valve simulations, for instance, we were able to account for repeated opening-closing cycles and to introduce an agglomeration algorithm to model clotting. Besides cardiovascular and venous flows, we also applied the Discrete Multi-Physics to respiratory tracts for modelling (i) cilia motion and drug diffusion in the periciliary layer (ciliated epithelium) and (ii) the release of active ingredients in powder inhalers for drug delivery in the lungs
The duality between particle methods and artificial neural networks
The algorithm behind particle methods is extremely versatile and used in a variety of applications that range from molecular dynamics to astrophysics. For continuum mechanics applications, the concept of ‘particle’ can be generalized to include discrete portions of solid and liquid matter. This study shows that it is possible to further extend the concept of ‘particle’ to include artificial neurons used in Artificial Intelligence. This produces a new class of computational methods based on ‘particle-neuron duals’ that combines the ability of computational particles to model physical systems and the ability of artificial neurons to learn from data. The method is validated with a multiphysics model of the intestine that autonomously learns how to coordinate its contractions to propel the luminal content forward (peristalsis). Training is achieved with Deep Reinforcement Learning. The particle-neuron duality has the advantage of extending particle methods to systems where the underlying physics is only partially known, but we have observations that allow us to empirically describe the missing features in terms of reward function. During the simulation, the model evolves autonomously adapting its response to the available observations, while remaining consistent with the known physics of the system
Modelling and simulation of the hydrodynamics and mixing profiles in the human proximal colon using Discrete Multiphysics
The proximal part of the colon offers opportunities to prolong the absorption window following oral administration of a drug. In this work, we used computer simulations to understand how the hydrodynamics in the proximal colon might affect the release from dosage forms designed to target the colon. For this purpose, we developed and compared three different models: a completely-filled colon, a partially-filled colon and a partially-filled colon with a gaseous phase present (gas-liquid model). The highest velocities of the liquid were found in the completely-filled model, which also shows the best mixing profile, defined by the distribution of tracking particles over time. No significant differences with regard to the mixing and velocity profiles were found between the partially-filled model and the gas-liquid model. The fastest transit time of an undissolved tablet was found in the completely-filled model. The velocities of the liquid in the gas-liquid model are slightly higher along the colon than in the partially-filled model. The filling level has an impact on the exsisting shear forces and shear rates, which are decisive factors in the development of new drugs and formulations
Discrete multi physic model for the Rayleigh collapse of a single cavity
In this thesis, a Discrete Multi-Physics model based on Smoothed Particle Hydrodynamics is developed to simulate a Rayleigh collapse of a single bubble. All the simulations were run on a modified version of the open source software LAMMPS and visualised on OVITO. Initially a 2D model is validated by simulating a phenomenon that shares many similarities with a collapse mechanism, the interaction of a shock wave with a discrete gas inhomogeneity, showing similar performance to classic mesh based CFD. The model is then used to simulate a 2D Rayleigh collapse and validated against the 2D Rayleigh-Plesset equation for both empty and gas filled cavity. The validated model is used to investigate the role of heat diffusion at the gas-liquid interface of the cavity, and to study non-symmetrical collapse induced by the presence of a nearby surface. Enabling heat diffusion at the gas-liquid interface allowed to identify five different possible behaviours that range from isothermal to adiabatic, while the results of non symmetric collapse show that the surface is hit by a stronger shock when distance between the center of the cavity and the surface is zero while showing more complex double peaks behaviour for other distances. In the final chapter a 3D model is used to model an attached non-symmetrical collapse and its hydrodynamic is compared with the equivalent 2D case
Development of a digital twin of a tablet that mimics a real solid dosage form : differences in the dissolution profile in conventional mini-USP II and a biorelevant colon model
The performance of colon-targeted solid dosage forms is commonly assessed using standardised pharmacopeial dissolution apparatuses like the USP II or the miniaturised replica, the mini-USP II. However, these fail to replicate the hydrodynamics and shear stresses in the colonic environment, which is crucial for the tablet's drug release process. In this work, computer simulations are used to create a digital twin of a dissolution apparatus and to develop a method to create a digital twin of a tablet that behaves realistically. These models are used to investigate the drug release profiles and shear rates acting on a tablet at different paddle speeds in the mini-USP II and biorelevant colon models to understand how the mini-USP II can be operated to achieve more realistic (i.e., in vivo) hydrodynamic conditions. The behaviour of the tablet and the motility patterns used in the simulations are derived from experimental and in vivo data, respectively, to obtain profound insights into the tablet's disintegration/drug release processes. We recommend an "on-off" operating mode in the mini-USP II to generate shear rate peaks, which would better reflect the in vivo conditions of the human colon instead of constant paddle speed
Combined peridynamics and discrete multiphysics to study the effects of air voids and freeze-thaw on the mechanical properties of asphalt
This paper demonstrates the use of peridynamics and discrete multiphysics to assess micro crack formation and propagation in asphalt at low temperatures and under freezing conditions. Three scenarios are investigated: (a) asphalt without air voids under compressive load, (b) asphalt with air voids and (c) voids filled with freezing water. The first two are computed with Peridynamics, the third with peridynamics combined with discrete multiphysics. The results show that the presence of voids changes the way cracks propagate in the material. In asphalt without voids, cracks tend to propagate at the interface between the mastic and the aggregate. In the presence of voids, they ‘jump’ from one void to the closest void. Water expansion is modelled by coupling Peridynamics with repulsive forces in the context of Discrete Multiphysics. Freezing water expands against the voids’ internal surface, building tension in the material. A network of cracks forms in the asphalt, weakening its mechanical properties. The proposed methodology provides a computational tool for generating samples of ‘digital asphalt’ that can be tested to assess the asphalt properties under different operating conditions
Microfluidic disturbances on synthetic patterned surfaces and their impact on microorganisms in relation to biofouling control
Biofouling, the unwanted growth of sessile microorganisms on submerged surfaces, presents a serious problem for underwater structures, water vessels and medical devices. It is ubiquitous in nature and readily develops on any unprotected surfaces in both the marine and physiological environments. Conventionally the underwater structures and water vessels are being protected against biofouling by metal based antifouling paints. The use of antifouling paints, in particular those containing Copper and Tributyltin (TBT), have been extremely successful for the hulls of ships by killing the majority of fouling species. Similarly, antibacterial medical coatings containing silver or antibiotics are being used frequently. These coatings have many detrimental effects including the mutation of bacteria which enables antibiotic-resistant biofilm development, failure of medical devices such as hip and knee implants, cause of catheter-associated urinary tract infection (CAUTI) and other hospital-acquired infections. The use of biocide-based metallic paints in the ocean and the silver-based antibacterial medical coating are posing more ecological and toxicity concerns and thus led to a mounting interest in developing non-toxic and no-kill alternatives for these systems. One of the non-toxic approaches to control biofouling is to modify the settlement surface. This usually entails altering the surface topography and roughness, and developing a surface with a microstructured pattern. Studies showed that patterned surfaces inhibit the initial settlement of microorganisms and prolong the subsequent biofilm formation process. Though it is well documented that biofouling can be controlled to various degrees with different microstructure-based patterned surfaces, the understanding of the underlying mechanism is still imprecise. The present study considered that microtopographies might influence near-surface microfluidic conditions, thus microhydrodynamically preventing the settlement of microorganisms. It is therefore aimed to characterize the microfluidic environment developed on patterned surfaces and its relation with the antifouling behaviour of those surfaces. In this study, patterned surfaces with microwell arrays were assessed experimentally with a real-time biofilm development monitoring system using a novel microchannel-based flow cell reactor. The dynamic interaction of a motile bacterium ( Escherichia coli ) with microtopographies was investigated by observing and assessing the trajectories of individual cells across an array of microwells using a time-lapse imaging module and image processing software. The effects of the solid boundaries on the dynamic stability of E. coli cells were assessed numerically using computational fluid dynamics (CFD) simulations. From this study, it is evident that patterned surfaces develop fluctuating stress-strain rates around microorganisms, alter their swimming depths, make them dynamically unstable and thus exhibit antifouling characteristics in a submerged condition. It is also stated that microstructures, capable of developing high wall shear bounded zones, keeping microorganisms away from the base surface, and giving no shelter against fluctuating microfluidic forces, could be considered effective in biofouling control. Finally, this study suggested a few optimized design patterns of microstructure-based antifouling surfaces, to develop effective microfluidic conditions capable of inhibiting the initial settlement of microorganisms