135 research outputs found
Chemotaxis-based spatial self-organization algorithms
Self-organization is a process that increases the order of a system as a result of local interactions among low-level, simple components, without the guidance of an outside source. Spatial self-organization is a process in which shapes and structures emerge at a global level from collective movements of low level shape primitives. Spatial self-organization is a stochastic process, and the outcome of the aggregation cannot necessarily be guaranteed. Despite the inherent ambiguity, self-organizing complex systems arise everywhere in nature. Motivated by the ability of living cells to form specific shapes and structures, we develop two self-organizing systems towards the ultimate goal of directing the spatial self-organizing process. We first develop a self-sorting system composed of a mixture of cells. The system consistently produces a sorted structure. We then extend the sorting system to a general shape formation system. To do so, we introduce morphogenetic primitives (MP), defined as software agents, which enable self-organizing shape formation of user-defined structures through a chemotaxis paradigm.
One challenge that arises from the shape formation process is that the process may form two or more stable final configurations. In order to direct the self-organizing process, we find a way to characterize the macroscopic configuration of the MP swarm. We demonstrate that statistical moments of the primitives' locations can successfully capture the macroscopic structure of the aggregated shape. We do so by predicting the final configurations produced by our spatial self-organization system at an early stage in the process using features based on the statistical moments. At the next stage, we focus on developing a technique to control the outcome of bifurcating aggregations. We identify thresholds of the moments and generate biased initial conditions whose statistical moments meet the thresholds. By starting simulations with biased, random initial configurations, we successfully control the aggregation for a number of swarms produced by the agent-based shape formation system. This thesis demonstrates that chemotaxis can be used as a paradigm to create an agent- based spatial self-organization system. Furthermore, statistical moments of the swarm can be used to robustly predict and control the outcomes of the aggregation process.Ph.D., Computer Science -- Drexel University, 201
Adhesion and volume constraints via nonlocal interactions determine cell organisation and migration profiles
The description of the cell spatial pattern and characteristic distances is fundamental in a wide range of physio-pathological biological phenomena, from morphogenesis to cancer growth. Discrete particle models are widely used in this field, since they are focused on the cell-level of abstraction and are able to preserve the identity of single individuals reproducing their behavior. In particular, a fundamental role in determining the usefulness and the realism of a particle mathematical approach is played by the choice of the intercellular pairwise interaction kernel and by the estimate of its parameters. The aim of the paper is to demonstrate how the concept of H-stability, deriving from statistical mechanics, can have important implications in this respect. For any given interaction kernel, it in fact allows to a priori predict the regions of the free parameter space that result in stable configurations of the system characterized by a finite and strictly positive minimal interparticle distance, which is fundamental when dealing with biological phenomena. The proposed analytical arguments are indeed able to restrict the range of possible variations of selected model coefficients, whose exact estimate however requires further investigations (e.g., fitting with empirical data), as illustrated in this paper by series of representative simulations dealing with cell colony reorganization, sorting phenomena and zebrafish embryonic development
Self-organized collective cell behaviors as design principles for synthetic developmental biology
Over the past two decades, molecular cell biology has graduated from a mostly analytic science to one with substantial synthetic capability. This success is built on a deep understanding of the structure and function of biomolecules and molecular mechanisms. For synthetic biology to achieve similar success at the scale of tissues and organs, an equally deep understanding of the principles of development is required. Here, we review some of the central concepts and recent progress in tissue patterning, morphogenesis and collective cell migration and discuss their value for synthetic developmental biology, emphasizing in particular the power of (guided) self-organization and the role of theoretical advances in making developmental insights applicable in synthesis
Lattice-Gas Cellular Automata In Modeling Biological Pattern Formation
There are several phenomena present in the physical world which can be defined or predicted by specific models. Cellular automata are basic mathematical models for characterization of natural systems by generating simple components and their local interactions. These models are specified on simple updating rules yet demonstrate complex behavior of physical phenomena. Besides this, lattice-gas cellular automata models go one step further and differ from cellular automata by having split updating rule into two parts as collision and propagation. In this study, the goal is to analyze hexagonal lattice-gas cellular automata with single cell type by using agent-based modeling and simulate the model with NetLogo to observe pattern formation. The model examination is focused on the two parameters for stability analysis. The results show that if there is a pattern formation in the model, the system is unstable, and if the patches are smaller and lighter patches, it is stable. Furthermore, the analysis for the choice of particle density and adhesion coefficient displayed that they are the main decision-mechanisms for general structure
Bioengineering strategies for cancer therapy and modelling
Tese de doutoramento em Engenharia de Tecidos, Medicina Regenerativa e CĂ©lulas EstaminaisCancer is a global pandemic with a high incidence among the world population and effective
treatments are for the most part elusive. The tumor microenvironment is a highly complex and heterotypic
mixture of cells that interact to regulate central control mechanisms, driving immunosuppression and
promoting both survival and invasion of cancer cells into surrounding tissues. It has been this complexity
that has made finding effective therapeutics such a demanding task and therefore cancer still remains a
burden worldwide in health as well as in economic terms. While the progression in the field of cancer
research has been clear over the years, there are still several challenges that need to be addressed.
Herein, two different sides to this disease are explored: treatment and in vitro models. Adoptive T
cell therapy has shown impressive results, however not without its limitations. The use of the T cell
mitogen IL-2 within culture systems is known to lead to early exhaustion of T cell subsets while high
density of co-stimulating molecules has been linked to undesired immune responses. As an alternative,
a nanoparticle system based on the natural polymer gellan-gum was proposed, with tailorable surface
functionalization with co-stimulatory molecules. High levels of T cell expansion were observed over the
studied period, with secreted IL-2 levels overcoming those of commercial alternatives. With this system,
increased expression of cytotoxic molecules Granzyme B and Perforin were also detected in vitro. On the
other spectrum, 3D cancer models have sustained a great number of developments observed by an
increase in similarity towards native tissues; however, a requirement for even more complex architectures
capable of better mimicking cellular interactions is still present. Therefore, an assembloid-based approach
was proposed to develop a 3D in vitro melanoma model to further study cellular interactions. These
heterotypic tumor assembloids presented a complex architecture capable of sustaining endothelial cell
function as well as a high expression of stemness-related markers. These models were subjected to
functionality assays where they showed a capacity for âcooperative invasionâ which was coincident with
an observed increased production of MMP-2. To further unravel the role of stromal cells in the invasive
potential of cancer cells a 3D chemotaxis chamber was developed to study cellular interactions observed
in the tumor microenvironment, where stem cells and fibroblasts showed to have a crucial role. Ultimately,
this thesis allowed to explore biomedical engineering approaches to further contribute to the knowledge
in the field opening new doors to be explored in the future.O cancro Ă© uma pandemia global com uma elevada incidĂȘncia e cujo desenvolvimento de
tratamentos eficazes continua a ser difĂcil. O microambiente tumoral Ă© uma mistura altamente complexa
e heterotĂpica de cĂ©lulas que interagem para regular mecanismos centrais que provocam
imunossupressĂŁo promovendo a sobrevivĂȘncia e invasĂŁo de cĂ©lulas tumorais para os tecidos
circundantes. Ă esta complexidade que tem tornado desafiante encontrar terapias eficazes, tornando
esta doença um fardo a nĂvel global em termos de saĂșde e economia. Enquanto a progressĂŁo na ĂĄrea
da investigação oncológica tem sido clara ao longo dos anos, existem ainda vårios desafios que precisam
de serem encarados para permitir futuros desenvolvimentos.
Aqui, foram exploradas duas vertentes diferentes desta doença: o tratamento e os modelos in vitro.
A terapia celular adotiva tem demonstrado resultados impressionantes, no entanto nĂŁo sem as suas
limitaçÔes. O uso do mitogĂ©nio IL-2 nestes sistemas de cultura Ă© conhecido por levar rapidamente Ă
exaustão das células T, enquanto o uso de moléculas co-estimulatórias em elevadas densidades estå
associado a respostas imunes nĂŁo desejadas. Como alternativa, foi proposto um sistema de
nanopartĂculas baseado no polĂmero natural goma gelana e funcionalizado com molĂ©culas co estimulatĂłrias. Foram observados elevados nĂveis de expansĂŁo de cĂ©lulas T e quantidade de IL-2
secretada superior Ă de alternativas comerciais. Foi ainda verificado in vitro um aumento de expressĂŁo
das molĂ©culas citotĂłxicas Grazima B e Perforina. No outro espectro, tĂȘm sido desenvolvidos modelos
tumorais 3D com uma cada vez maior similaridade para tecidos nativos; no entanto, a necessidade de
arquiteturas ainda mais complexas capazes de melhor representar interaçÔes celulares persiste. Assim,
foi proposta uma abordagem baseada em âassemblĂłidesâ para obter modelos 3D in vitro de melanoma
para estudar interaçÔes celulares. Estes âassemblĂłidesâ tumorais heterotĂpicos apresentaram uma
arquitetura complexa capaz de suportar a função de células endoteliais, bem como a elevada expressão
de marcadores de pluripotĂȘncia. Estes modelos foram sujeitos a ensaios de funcionalidade onde
mostraram a capacidade de âinvasĂŁo cooperativaâ que foi coincidente com uma produção aumentada
de MMP-2. Para tornar mais claro o papel das células estaminais no potencial invasivo de células
tumorais, uma cùmara 3D de quimiotaxia foi desenvolvida para estudar as interaçÔes celulares
observadas no microambiente tumoral onde as células estaminais e fibroblastos mostraram ter um papel
determinante. Em Ășltima anĂĄlise, esta tese permitiu explorar abordagens da engenharia biomĂ©dica de
forma a contribuir para o conhecimento da ĂĄrea e abrir novas portas a serem exploradas no futuro
Using Differential Adhesion to Control Self-Assembly and Self-Repair of Collections of Modular Mobile Robots
Institute of Perception, Action and BehaviourThis thesis presents a novel distributed control method which allows a collection
of independently mobile robotic units, with two or three dimensional movement, to
self-assemble into self-repairing hierarchical structures. The proposed method utilises
a simple model of the cellular adhesion mechanisms observed in biological cells, allowing
the robotic units to form virtually bonded aggregates which behave as predicted
by Steinbergâs differential adhesion hypothesis.
Simulated robotic units based on the design of the subaquatic HYDRON module
are introduced as a possible platform on which the model can be implemented. The
units are used to carry out a detailed investigation of the model behaviour and parameter
space focusing on the two main tasks of rounding and sorting in both two and
three dimensions. These tasks assess the modelâs ability to reach a thermodynamically
stable configuration when the aggregates consist of either a single population of units
or multiple populations of units with differing adhesive properties. The results are
analysed in detail with particular attention given to the role of random movements in
determining the overall performance, and demonstrate that this model provides a very
robust solution to these complex tasks.
Finally, a possible extension of this work is presented in which the original model
is combined with a genetic regulatory network controller. The performance of this
composite is evaluated, and the benefits of this hybrid approach, in which a powerful
control system manipulates a robust self-organising behaviour, are discussed
Multi-scale models of ovarian cancer
In ovarian cancer, disease and treatment can be examined across multiple spatial scales including molecules, cells, intra-tumor vasculature, and body-scale dynamics of circulating drugs. Survival of primary tumor cells and their development into disseminated tumors is related to adhesion between the cells, attachment, and invasion. Growth of new tumors depends on the delivery of nutrients, which depends on the tumor diameter and the tumors vasculature. Drug delivery also depends on tumor diameter and vasculature, and molecular- and gross-scale drug processes. A cellular Potts simulation integrated data at these multiple scales to model microscopic residual disease during relapse after a primary surgery. The model generated new hypotheses about tumor cell behavior, and the effectiveness of drug delivery to tumors disseminated in the peritoneal cavity. First, the model required high intra-tumor adhesion in ovarian tumors, the existence of an unknown factor that drew tumor cells to vessels, a threshold of vascular endothelial growth factor (VEGF) for initiation of endothelial sprouting, and constitutive expression of angiogenic chemical messengers by tumor cells prior to needing oxygen. Alteration of the model incorporated drug delivery by the two standard routes, intraperitoneal and intravenous, from tumor vasculature parameterized from real patient data. Delivery of both small- and large-molecular weight therapies was superior during intraperitoneal therapy. Finally, empirical and theoretical distributions of vessel radii were considered. Samples from tumors with each type of vascular morphology were run as though too distant from the peritoneal cavity to receive peritoneal delivery, with three results: first, intravenous delivery was superior to the secondary delivery into the circulatory system from a primary intraperitoneal delivery. Second, small molecules penetrated homogeneously across all cells, regardless of vascular volume or morphology, while antibodies penetrated heterogeneously, particularly in low-vessel-volume samples. Third, when each of the whole tumors was considered, this heterogeneity resulted in a large sub-population of cells that accumulated non-therapeutic levels of antibody, even during the best delivery scenario (IV). Fourth, delivery of antibodies was poorest in the empirical distribution. Finally, hypotheses were generated about the impact of heterogeneity of drug delivery, to be addressed as future questions
Creation of a Pioneer-Neuron Axonal Pathfinding Model for Future Applications in Developmental Neurotoxicity Testing
The developing central nervous system is a unique target for environmental toxicants both pre- and postnatal. Exposure to industrial chemical toxicants at various stages throughout development are known to contribute to injuries that result in autism, attention-deficit hyperactivity disorder (ADHD), dyslexia, and other cognitive impairments [81]. The damage caused by these exposures is often untreatable and frequently permanent, resulting in reduced intelligence (expressed in terms of lost IQ points) or behavioral abnormalities. It is now reported that 10-15% of all births are associated with disorders of neurobehavioral development [81], where 1 in 68 children in the United States is diagnosed with some form of an autism spectrum disorder (ASD) [7, 93, 188] and 14% of the roughly 4 million children born each year suffer from ADHD [124]. It is estimated that 3% of developmental disabilities are the direct result of environmental exposure, and that another 25% stem from interactions between environmental factors and genetic susceptibility [80, 146]. With more diagnosed cases and rising costs, the identification of the chemicals responsible for the deleterious effects on the developing nervous system has become significant topic of research. Current developmental neurotoxicity (DNT) testing relies heavily on whole animal approaches for hazard identification and dose-response evaluations. These methods are not practical for screening the over 82,000 chemicals already used in commerce with an additional 700 new chemicals introduced annually [24]. Following the first workshop on ĂąâŹĆIncorporating In Vitro Alternative Methods for Developmental Neurotoxicity (DNT) Testing into International Hazard and Risk Assessment Strategiesù⏠in 2005, it was determined that in vitro DNT testing methods should be included as part of a tiered approach to help create a reference list of potential developmentally neurotoxic chemicals and catalog the effects they have on various developmental mechanistic endpoints [40, 127]. Using directionality of pioneer-neuron axonal pathfinding as the mechanism for evaluation, we developed a biochip-based single-neuron axonal pathfinding assay to subjugate extending axons to simultaneous geometric and chemical guidance. To achieve this we devised a laser cell-micropatterning system to facilitate the placement of individual-neurons to exact locations on a PDMS substrate. The cell-culture conditions were optimized to promote single-neuron axonal extension through and beyond the confinements of a geometric guidance microchannel. Evaluation of the pathfinding direction in response to geometric guidance was compared to that of geometric and chemical stimuli. We found using our system that the addition of a chemical guidance component 1) increased the number of individual-neurons extending an axon at least 20 Ă”m beyond the end of a guidance microchannel structure and 2) showed the potential to elicit a growth cone turning event by abruptly changing the initial pathfinding trajectory of an axon. Based on our previous study that single-neuron axonal pathfinding under geometric guidance is one order of magnitude more sensitive to a chemical toxicant, our research data demonstrate that we have created a platform that can be used to test the possible effects that low dose (nM concentrations) chemical exposures may have on pioneer-neuron axonal pathfinding
Spatial quantification and mathematical modelling of tissue development
In this thesis, we study biological tissue development, during which cells
organise themselves into structures which perform a specific function. Understanding
how particular types of mechanisms lead to the emergence of
various cell patterns in tissues is the main motivation of this research. Quantifying
the tissue patterns is a first step towards understanding which mechanisms
are at work in particular experiments. For this purpose, we develop
pair-correlation functions (PCFs) which quantify how a spatial distribution
of cells deviates from complete spatial randomness over specified directions.
We evaluate the usefulness of PCFs for studying the three-dimensional organisation
of cells in tumour spheroids and show that the PCFs robustly
reveal information about their spatial structure. In particular, we demonstrate
that the boundary that separates the necrotic and viable zones in
the tumour spheroids can be detected using the PCF with a high degree of
accuracy.
We then turn to development of mathematical models to investigate the
types of patterns that can arise from simple hypothesised interactions between
cells. We begin in Chapter 3 by developing an on-lattice agent-based
model (ABM) to investigate tumour spheroid growth using two different culture
methods: suspension culture, and culture within a microgel. Our results
suggest that stratifying the seeded cells into multiple layers and also reducing
cell death are the key effects of the microgel that enable it to produce
more uniformly-sized spheroids. In Chapter 4, we extend the ABM to study
systems with two interacting species. A huge variety of aggregation patterns
can arise in these systems, depending upon the underlying attractive-repulsive
mechanisms. More specifically, we show that the run-and chase
mechanism can produce a striped pattern, similar to that observed on the
skin of zebrafish.
Finally, we develop a non-local continuous model, approximating the
mean behaviour of the ABM. This provides a connection between the cell-level
and population-level models of tissue development. A linear stability
analysis of the continuous model allows us to investigate parameter regimes that produce striped patterns. Importantly, we also point out the disparities
that may arise between the behaviours of the continuous and discrete models,
which highlights the importance of considering the underlying biological
constraints in using the continuous approximated models. In particular, we
show that the derivation of the approximate continuum model from the ABM
introduces terms representing cell-size effects. These terms can lead to the
emergence of stripes in cases where they would not be predicted in the similar
continuum model of Painter et al. (2015), which does not include these
terms.
The combination of spatial quantification and mathematical modelling
(using both continuous and discrete methods) developed in this work helps
us to gain a better understanding of tissue development. Our approach
provides a novel means to investigate the underpinning mechanisms of tissue
development by combining model simulations with analysis of biological and
synthetic data using the pair-correlation functions.Thesis (Ph.D.) -- University of Adelaide, School of Mathematical Sciences, 201
Cell adhesion and cell mechanics during zebrafish development
During vertebrate development, gastrulation leads to the formation of three distinct germlayers. In zebrafish a central process is the delamination and the ingression of single cells from a common ancestor tissue - that will lead to the formation of the germlayers. Several molecules have been identified to regulate this process but the precise cellular mechanisms are poorly understood. Differential adhesiveness, a concept first introduced by Steinberg over 40 years ago, has been proposed to represent a key phenomena by which single hypoblast cells separate from the epiblast to form the mesendoderm at later stages. In this work it is shown that differential adhesion among the germlayer progenitor cells alone cannot predict germlayer formation. It is a combination of several mechanical properties such as cell cortex tension, cell adhesion and membrane mechanical properties that influence the migratory behavior of the constituent cells
- âŠ