Physical and biological aspects of renal vitrification

Cryopreservation would potentially very much facilitate the inventory control and distribution of laboratory-produced organs and tissues. Although simple freezing methods are effective for many simple tissues, bioartificial organs and complex tissue constructs may be unacceptably altered by ice formation and dissolution. Vitrification, in which the liquids in a living system are converted into the glassy state at low temperatures, provides a potential alternative to freezing that can in principle avoid ice formation altogether. The present report provides a brief overview of the problem of renal vitrification. We report here the detailed case history of a rabbit kidney that survived vitrification and subsequent transplantation, a case that demonstrates both the fundamental feasibility of complex system vitrification and the obstacles that must still be overcome, of which the chief one in the case of the kidney is adequate distribution of cryoprotectant to the renal medulla. Medullary equilibration can be monitored by monitoring urine concentrations of cryoprotectant, and urine flow rate correlates with vitrification solution viscosity and the speed of equilibration. By taking these factors into account and by using higher perfusion pressures as per the case of the kidney that survived vitrification, it is becoming possible to design protocols for equilibrating kidneys that protect against both devitrification and excessive cryoprotectant toxicity.     

Physical aspects of vitrification in aqueous solutions

Vitrification is the process by which a liquid solidifies at temperatures usually far below the normal freezing point, but without the formation of any crystalline phase. The liquid has formed a glass. Occasionally, when the liquid consists of a solution, one of the components freezes to form a crystalline phase during cooling, but the remainder of the solution vitrifies. The product is then a partially crystallized glass. Glass formation, as a feature of aqueous solutions, either of the whole solution or of the remaining fraction after crystallization of ice, is discussed. We focus on the general principles involved in glass formation and also discuss in detail the effect of pressure on the nucleation and vitrification of the solution. In particular we look at the physical processes involved as well as the chemical aspects of the solutes which can be used in vitrifiable aqueous solutions. In any application of vitrification of aqueous solutions the material properties of the resultant glass are also important; these are also briefly considered. Recent work concerning the nature of the devitrification (crystallization during warming) event at high pressures is detailed.     

Physical problems with the vitrification of large biological systems

Vitrification is an attractive potential pathway to the successful cryopreservation of mature mammalian organs, but modern cryobiological research on vitrification to date has been devoted mostly to experiments with solutions and with biological systems ranging in diameter from about 6 through about 100 microns. The present paper focuses on concerns which are particularly relevant to large biological systems, i.e., those systems ranging in size from approximately 10 ml to approximately 1.5 liters. New qualitative data are provided on the effect of sample size on the probability of nucleation and the ultimate size of the resulting ice crystals as well as on the probability of fracture at or below Tg. Nucleation, crystal growth, and fracture depend on cooling velocity and the magnitude of thermal gradients in the sample, which in turn depend on sample size, geometry, and cooling technique (environmental thermal history and thermal uniformity). Quantitative data on thermal gradients, cooling rates, and fracture temperatures are provided as a function of sample size. The main conclusions are as follows. First, cooling rate (from about 0.2 to about 2.5 degrees C/min) has a profound influence on the temperature-dependent processes of nucleation and crystal growth in 47-50% (w/w) solutions of propylene glycol. Second, fracturing depends strongly on cooling rate and thermal uniformity and can be postponed to about 25 degrees C below Tg for a 482-ml sample if cooling is slow and uniform. Third, the presence of a carrier solution reduces the concentration of cryoprotectant needed for vitrification (CV). However, the CV of samples larger than about 10 ml is significantly higher than the CV of smaller samples whether a carrier solution is present or not.     

Thermodynamic aspects of vitrification

Vitrification is a process in which a liquid begins to behave as a solid during cooling without any substantial change in molecular arrangement or thermodynamic state variables. The physical phenomenon of vitrification is relevant to both cryopreservation by freezing, in which cells survive in glass between ice crystals, and cryopreservation by vitrification in which a whole sample is vitrified. The change from liquid to solid behavior is called the glass transition. It is coincident with liquid viscosity reaching 10¹³ Poise during cooling, which corresponds to a shear stress relaxation time of several minutes. The glass transition can be understood on a molecular level as a loss of rotational and translational degrees of freedom over a particular measurement timescale, leaving only bond vibration within a fixed molecular structure. Reduced freedom of molecular movement results in decreased heat capacity and thermal expansivity in glass relative to the liquid state. In cryoprotectant solutions, the change from liquid to solid properties happens over a ∼10 °C temperature interval centered on a glass transition temperature, typically near −120 °C (±10 °C) for solutions used for vitrification. Loss of freedom to quickly rearrange molecular position causes liquids to depart from thermodynamic equilibrium as they turn into a glass during vitrification. Residual molecular mobility below the glass transition temperature allows glass to very slowly contract, release heat, and decrease entropy during relaxation toward equilibrium. Although diffusion is practically non-existent below the glass transition temperature, small local movements of molecules related to relaxation have consequences for cryobiology. In particular, ice nucleation in supercooled vitrification solutions occurs at remarkable speed until at least 15 °C below the glass transition temperature.     

Evolutional and biological aspects of placentophagia

Over the last 30 years it could be observed that a very small minority of modern humans consumes the human placenta that belongs to the afterbirth. This behavior, which is known by the technical term of placentophagia, is the focal point of the present essay. Placentophagia is a behavior common among almost all kinds of mammals, even primates can be observed ingesting at least amniotic fluid during the birth. However, humans of traditional human cultures consume the afterbirth only in rare cases. In detail, the present essay discusses the hypothesis that human placentophagia has a phylogenetic basis and the hypothesis that human placentophagia is physiologically reasonable. It is concluded that the behavior of the human placentophagia neither possesses a phylogenetic basis nor can be regarded as physiologically reasonable.     

Phytoecdysteroids: biological aspects

Phytoecdysteroids are a family of about 200 plant steroids related in structure to the invertebrate steroid hormone 20-hydroxyecdysone. Typically, they are C27, C28 or C29 compounds possessing a 14alpha-hydroxy-7-en-6-one chromophore and A/B-cis ring fusion (5beta-H). In the present review, the distribution, biosynthesis, biological significance and potential applications of phytoecdysteroids are summarised.     

Physical aspects of artificial diets

The physical properties of artificial diets, texture, hardness, homogeneity, and water content are regulated by the addition of cellulose, agar, polysaccharide gums, and other large molecules. These physical aspects are important in promoting good growth and development of insects.The development of the boll weevil, Anthonomus grandis Boheman, was improved by adding more cellulose to the diet. Additional agar did not improve growth. Polysaccharide gums made the diet too viscous and were poor substitutes for agar. This insect developed satisfactorily on diets with moderate ranges of water and nutrient content.The preparation of the diets is also important in regulating physical properties. Heating stops enzyme action in plant products, ruptures cells, and affects solubility of ingredients. The addition of stabilizers protects nutrients and keeps them mixed homogeneously.

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Zusammenfassung Die physikalischen Eigenschaften künstlicher Diäten für Insekten umfassen Struktur, Härte, Homogenität und Wassergehalt sowie Faktoren, die diese beeinflussen. Diese Gründsätze gelten für feste Diäten bei Insekten mit beißenden Mundwerkzeugen.Strukturelle Eigenschaften werden gewöhnlich durch Hinzufügen von Zellulose hervorgerufen, welche die Konsistenz liefert und zum Fraß anregt. In Diäten mit hohem Wassergehalt wird die Konsistenz durch Zugabe von Agar reguliert. Natürliche polysaccharide Gummis verleihen den Diäten Andickung, Stabilisierung, Gelierung und strukturelle Eigenschaften. Diäten für den Baumwollkapselbohrer, Anthonomus grandis Boheman, werden abgewandelt durch Hinzufügen zusätzlicher Zellulosemengen, Agar und Stärke sowie ersatzweise durch Carrageenan, Heuschrecken- Bohnen- Gummi und Guar-Gummi für die Gesamtheit oder Teile des Agars. In den beschriebenen Versuchen verkürzte Zellulose die Entwicklungszeit. Agar und Stärke verursachten wenig Veränderung. Im allgemeinen bildeten die Gummis visköse Gemische und gelierten nicht. Daher ergab sich eine schlechte Entwicklung für den Baumwollkapselkäfer. Carrageenan konnte als teilweiser Ersatz für Agar verwendet werden. Große Moleküle, wie Zellulose, Stärke, Pektin, Phospholipide und Proteine, die in natürlichen Produkten vorkommen, beeinflussen die physikalischen Eigenschaften der Diäten ebenfalls. Diese Eigenschaft der Naturstoffe ist oft übersehen worden, weil die Hauptbedeutung immer in ihrem Nährwert gesehen wurde.Obwohl die Nahrung pflanzenfressender Insekten einen hohen Wassergehalt hat, können viele mit Nahrung sehr unterschiedlicher Wasserkonzentrationen auskommen und einige vermögen trockene Nahrung zu verzehren und Wasser zu trinken. Die Herstellung der Diäten kann ihre physikalischen Eigenschaften ebenfalls beeinflussen. Die Bestandteile der Diät können chemische und enzymatische Veränderungen erfahren, welche die Diät und damit das Insekt beeinflussen. Hitze-Behandlung stoppt die enzymatischen Reaktionen in den Geweben, zerreißt die Zellen und löst ihre Inhaltsstoffe. Polysaccharide Gummis, Phospholipide und gelierende Mittel werden benutzt, um die Bestandteile der Diät in einem beständigen, homogenen Gemisch zu erhalten. Diese Substanzen können auch in flüssigen Diäten verwendet werden, um die Nährstoffe in Suspension zu halten.

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in cooperation with Texas Agricultural Experiment Station Texas A & M University, U.S.A.     

Physical aspects of organic evolution

The system composed of species of living organisms and their environment evolves under a stream of available energy from the sun. The differential survival of the components depends on the degree of success of each in securing its share of energy from this stream. This type of problem is familiar from the study of physicochemical systems in which the distribution and change in distribution of matter among specified components is examined in its relation to parameters of state. But whereas it is characteristic of physicochemical systems commonly considered that structure and mechanism play at most a subordinate role, in the study of organic evolution the structure and mechanical properties of the components, on which their aptitude for capturing energy depends, play the dominant role. Address delivered before the Symposium on Mathematical Biology held during the meeting of the A.A.A.S. in Chicago, December 26–27, 1947. Other papers presented at the Symposium are also being published inThe Bulletin. Those include: Rapoport, Anatol and Shimbel, Alfonso. 9, 169, 1947; Culbertson, J. T.10, 31, 1948; Rapoport, Anatol and Shimbel, Alfonso.10, 41, 1948; Hearon, John Z.10, 175, 1948; Morales, Manuel F. and Smith, Robert E.10, 191, 1948. For technical reasons the papers are not published in the same order as they were presented. A complete list of the papers presented at the Symposium on Mathematical Biology, together with abstracts is published inBiometrics,4, No. 2, 1948.Editor.     

Physical aspects of cancer invasion

Invasiveness, one of the hallmarks of tumor progression, represents the tumor's ability to expand into the host tissue by means of several complex biochemical and biomechanical processes. Since certain aspects of the problem present a striking resemblance with well-known physical mechanisms, such as the mechanical insertion of a solid inclusion in an elastic material specimen (G Eaves 1973 The invasive growth of malignant tumours as a purely mechanical process J. Pathol. 109 233; C Guiot, N Pugno and P P Delsanto 2006 Elastomechanical model of tumor invasion Appl. Phys. Lett. 89 233901) or a water drop impinging on a surface (C Guiot, P P Delsanto and T S Deisboeck 2007 Morphological instability and cancer invasion: a 'splashing water drop' analogy Theor. Biol. Med. Model 4 4), we propose here an analogy between these physical processes and a cancer system's invasive branching into the surrounding tissue. Accounting for its solid and viscous properties, we then arrive, as a unifying model, to an analogy with a granular solid. While our model has been explicitly formulated for multicellular tumor spheroids in vitro, it should also contribute to a better understanding of tumor invasion in vivo.     

Effect of conditioned media on three genotypes of Drosophila melanogaster: Physical,chemical, and biological aspects

The uric acid contents in larvae, pupae, and culture media were studied during larval and pupal development in three genotypes of Drosophila melanogaster reared in both crowded and noncrowded conditions. The uric acid content and the response of genotypes in media supplemented with 10 and 15 mg/ml of uric acid were correlated with the outcome obtained in conditioned media. In addition, the behavior of genotypes in conditioned media is explained in terms of the physicochemical properties of the conditioned media, which include uric acid content, the amount of food ingested, the degree of free water, the physical disturbance within the cultures, and the particular response of each genotype to uric acid.     

Physical models of biological information and adaptation

The bio-informational equivalence asserts that biological processes reduce to processes of information transfer. In this paper, that equivalence is treated as a metaphor with deeply anthropomorphic content of a sort that resists constitutive-analytical definition, including formulation within mathematical theories of information. It is argued that continuance of the metaphor, as a quasi-theoretical perspective in biology, must entail a methodological dislocation between biological and physical science. It is proposed that a general class of functions, drawn from classical physics, can serve to eliminate the anthropomorphism. Further considerations indicate that the concept of biological adaptation is central to the general applicability of the informational idea in biology; a non-anthropomorphic treatment of adaptive phenomena is suggested in terms of variational principles.     

Physical aspects of COPI vesicle formation

Abstract

Coat proteins orchestrate membrane budding and molecular sorting during the formation of transport intermediates. Coat protein complex I (COPI) vesicles shuttle between the Golgi apparatus and the endoplasmic reticulum and between Golgi stacks. The formation of a COPI vesicle proceeds in four steps: coat self-assembly, membrane deformation into a bud, fission of the coated vesicle and final disassembly of the coat to ensure recycling of coat components. Although some issues are still actively debated, the molecular mechanisms of COPI vesicle formation are now fairly well understood. In this review, we argue that physical parameters are critical regulators of COPI vesicle formation. We focus on recent real-time in vitro assays highlighting the role of membrane tension, membrane composition, membrane curvature and lipid packing in membrane remodelling and fission by the COPI coat.     

Physical aspects of COPI vesicle formation

Coat proteins orchestrate membrane budding and molecular sorting during the formation of transport intermediates. Coat protein complex I (COPI) vesicles shuttle between the Golgi apparatus and the endoplasmic reticulum and between Golgi stacks. The formation of a COPI vesicle proceeds in four steps: coat self-assembly, membrane deformation into a bud, fission of the coated vesicle and final disassembly of the coat to ensure recycling of coat components. Although some issues are still actively debated, the molecular mechanisms of COPI vesicle formation are now fairly well understood. In this review, we argue that physical parameters are critical regulators of COPI vesicle formation. We focus on recent real-time in vitro assays highlighting the role of membrane tension, membrane composition, membrane curvature and lipid packing in membrane remodelling and fission by the COPI coat.     

Physical aspects of dynamic stereotactic radiosurgery

Dynamic stereotactic radiosurgery is a radiosurgical technique based on a medium-energy isocentric linear accelerator and a stereotactic frame. The technique uses concurrent and continuous rotations of both the gantry (300 degrees, from 30 to 330 degrees) and the couch (150 degrees, from 75 to -75 degrees). It gives a uniform dose (+/- 5%) within the target volume and dose fall-offs outside the target volume comparable to those obtained from presently known radiosurgical techniques.