Jamming transitions in cancer

The traditional picture of tissues, where they are treated as liquids defined by properties such as surface tension or viscosity has been redefined during the last few decades by the more fundamental question: under which conditions do tissues display liquid-like or solid-like behaviour? As a result, basic concepts arising from the treatment of tissues as solid matter, such as cellular jamming and glassy tissues, have shifted into the current focus of biophysical research. Here, we review recent works examining the phase states of tissue with an emphasis on jamming transitions in cancer. When metastasis occurs, cells gain the ability to leave the primary tumour and infiltrate other parts of the body. Recent studies have shown that a linkage between an unjamming transition and tumour progression indeed exists, which could be of importance when designing surgery and treatment approaches for cancer patient

Collective force generation by groups of migrating bacteria

From biofilm and colony formation in bacteria to wound healing and embryonic development in multicellular organisms, groups of living cells must often move collectively. While considerable study has probed the biophysical mechanisms of how eukaryotic cells generate forces during migration, little such study has been devoted to bacteria, in particular with regard to the question of how bacteria generate and coordinate forces during collective motion. This question is addressed here for the first time using traction force microscopy. We study two distinct motility mechanisms of Myxococcus xanthus, namely twitching and gliding. For twitching, powered by type-IV pilus retraction, we find that individual cells exert local traction in small hotspots with forces on the order of 50 pN. Twitching of bacterial groups also produces traction hotspots, however with amplified forces around 100 pN. Although twitching groups migrate slowly as a whole, traction fluctuates rapidly on timescales <1.5 min. Gliding, the second motility mechanism, is driven by lateral transport of substrate adhesions. When cells are isolated, gliding produces low average traction on the order of 1 Pa. However, traction is amplified in groups by a factor of ~5. Since advancing protrusions of gliding cells push on average in the direction of motion, we infer a long-range compressive load sharing among sub-leading cells. Together, these results show that the forces generated during twitching and gliding have complementary characters and both forces are collectively amplified in groups

Jamming and Unjamming in Cancer Cells

Jamming' ist ein faszinierender, nicht vollständig verstandener Prozess in der Physik der weichen Materie. Zelluläres Jamming' tritt auch in biologischem Gewebe auf und muss sich im Fall von Krebszellen im Tumorgewebe aufgrund der dichten Packung der Zellen über der dichtesten Kugelpackung anders verhalten als die bekannten 'Jamming' Systeme. In meiner Dissertation skizziere ich wesentliche Ergebnisse zum Verständnis dieses neuen physikalischen Phänomens. Meine Erkenntnisse tragen dazu bei die Dichotomie zwischen den Theorien der dichteinduzierten und der forminduzierten 'Zelljamming' aufzulösen. Die gewonnenen Erkenntnisse weisen auf die Möglichkeit hin Krebszellformen und deren Zellkernformen als Tumormarker für die Metastasierung zu verwenden. Ich fand ein kritisches Skalierungsverhalten für die Dynamik der Neuanordnung von Zellen in der Nähe des Jamming-Übergangs, abhängig von der Zellform der Nachbarschaft. Dies ist der bisher stärkste Beweis dafür, dass die Zellformen als Kontrollparameter für das 'Zelljamming' fungieren können. Die Zellanzahldichte beeinflusst ebenfalls das 'Jamming', ihr Einfluss kann jedoch als eine Verlangsamung der Eigengeschwindigkeit der Zellen beschrieben werden. Eine hohe Zellanzahldichte allein würde also nur die Viskosität des Gewebes erhöhen und es nicht verfestigen. Darüber hinaus habe ich gezeigt, dass es in dicht gepackten dreidimensionalen Zellsphäroiden sowie in Primärtumorstücken einen mit der Zellform verbundenen 'Jamming'-Übergang gibt. Ich verbinde das 'Unjamming' von Zellen mit dem Fortschreiten des Krebses, indem ich zeigte, dass die Herunterregulierung des Adhäsionsmoleküls E-Cadherin, die ein typischer Schritt während der Krebentwicklung ist, einen 'Unjamming'-Übergang verursacht. Bei diesem 'Unjamming'-Übergang kommt es zu einem ausgeprägten Verlust der Kohäsion und einem reduzierten Volumenanteil der Zellen, was zeigt, dass das 'Zelljamming' einen hohen Volumenanteil erfordert

Mathematical and mechanical modeling of vaso-occlusion in sickle cell disease

Thesis (S.M.)--Harvard-MIT Division of Health Sciences and Technology, 2007.Includes bibliographical references.Vaso-occlusive crises cause most of the morbidity and mortality associated with sickle cell disease. The proximal causes of these occlusive events are not well understood. The risks and consequences of vaso-occlusion however are clear. Ten percent of sickle cell disease patients will have a stroke by the age of 20. Two thirds of sickle cell disease patients require more than one hospitalization per year for treatment of pain crises. The flow behavior of blood samples from sickle cell patients was studied in an artificial microfluidic environment. This microfluidic environment allowed modulation of the hydrostatic pressure causing flow, the ambient oxygen concentration, and the vascular channel geometry. A range of blood samples was evaluated by selecting specimens with various hematocrits and concentrations of sickle hemoglobin. Velocity profiles were calculated following sudden changes in oxygen concentration. From these profiles, it was possible to create a phase space of vaso-occlusion in the artificial microfluidic environment. This phase space characterizes the environmental conditions in which sickle cell blood will stop flowing within a given interval of time.(cont.) This work is a first step in characterizing the inter-relationships between some of the control parameters governing vaso-occlusion: pressure, oxygen concentration, channel size, hematocrit, and sickle hemoglobin concentration. This artificial device enables a quantification of the effect of a clinical therapy, red blood cell exchange, as performed on an actual sickle cell patient. Additionally, three sample small molecules known to alter rates of sickle hemoglobin polymerization were evaluated for their ability to perturb the tendency of sickle cell blood to stop flowing. These results suggest a possible application of this technique to the diagnosis and monitoring of sickle cell patients as well as to the investigation of new regimens of existing treatments and altogether novel therapies.by John M. Higgins.S.M

Exciter Jammer Berbasis Direct Digital Synthesizer

In this paper, we propose a radio transmitter jamming device modification developed. The transmitter is built by replacing Voltage Controled Oscillator (VCO) with modules for Direct Digital Synthesizer (DDS) as an exciter. Advantages of DDS is programmed with a computer and can produce a signal with a frequency stability and frequency accuracy is very high. The use of DDS allow setting the frequency of central and deviation with very easily using software. In addition, the period or sweep time designed to use only software can be reprogrammed with DDS to function on a Linear Sweep No Dwell mode and signaltrigger with a period equal to the period the minimum desired sweep. DDS allows to generate a signal jamming by narrow BW, so the power output of the Jammer could be higher and increased outreach of radio jamming. Another advantage with theuse of DDS is the dimension transmitter Jammer becomes smaller.keywords: Jamming devices, DDS, Eletronics warfare Pada tulisan ini, modifikasi perangkat pemancar radio jamming diusulkan, dengan mengganti Voltage Controled Oscilator (VCO) dengan modul Direct Digital Synthesizer (DDS) sebagai exciter. Kelebihan DDS adalah bisa diprogram dengan komputer dan menghasilkan sinyal dengan stabilitas dan akurasi frekuensi yang sangat tinggi. Penggunaan DDS memungkinkan pengaturan frekuensi tengah dan deviasi dengan sangat mudah menggunakan sofware. Di samping itu, periode atau waktu sweep dirancang untuk bisa diatur hanya menggunakan software dengan memprogram DDS untuk berfungsi pada mode Linear Sweep No Dwell dan memberikan sinyal trigger dengan periode sebesar periode sweep minimum yang diinginkan. DDS memungkinkan untuk menghasilkan sinyal jamming dengn BW yang sempit, sehingga power output Jammer bisa lebih tinggi dan daya jangkau radio jamming meningkat. Keuntungan lain dengan penggunaan DDS adalah dimensi pemancar Jammer menjadi lebih kecil.kata kunci: Perangkat Jamming, DDS, Perang elektroni

Unjamming and cell shape in the asthmatic airway epithelium

From coffee beans flowing in a chute to cells remodelling in a living tissue, a wide variety of close-packed collective systems— both inert and living—have the potential to jam. The collective can sometimes flow like a fluid or jam and rigidify like a solid. The unjammed-to-jammed transition remains poorly understood, however, and structural properties characterizing these phases remain unknown. Using primary human bronchial epithelial cells, we show that the jamming transition in asthma is linked to cell shape, thus establishing in that system a structural criterion for cell jamming. Surprisingly, the collapse of critical scaling predicts a counter-intuitive relationship between jamming, cell shape and cell–cell adhesive stresses that is borne out by direct experimental observations. Cell shape thus provides a rigorous structural signature for classification and investigation of bronchial epithelial layer jamming in asthma, and potentially in any process in disease or development in which epithelial dynamics play a prominent role