Osmotic Exchange Research Articles

Aspects of a Suspended Bioprinting System Affect Cell Viability and Support Bath Properties.

Suspended hydrogel printing is a growing method for fabricating bioprinted hydrogel constructs, largely due to how it enables nonviscous hydrogel inks to be used in extrusion printing. In this work, a previously developed poly(N-isopropylacrylamide)-based thermogelling suspended bioprinting system was examined in the context of chondrocyte-laden printing. Material factors such as ink concentration and cell concentration were found to have a significant effect on printed chondrocyte viability. In addition, the heated poloxamer support bath was able to maintain chondrocyte viability for up to 6 h of residence within the bath. The relationship between the ink and support bath was also assessed by measuring the rheological properties of the bath before and after printing. Bath storage modulus and yield stress decreased during printing as nozzle size was reduced, indicating the likelihood that dilution occurs over time through osmotic exchange with the ink. Altogether this work demonstrates the promise for printing high-resolution cell-encapsulating tissue engineering constructs, while also elucidating complex relationships between the ink and bath, which must be taken into consideration when designing suspended printing systems.

Philosophy of Gurukula education: Personal education and practical democracy

Abstract Education, which is as old as humanity, has existed in various personal forms in non-western societies, where an osmotic exchange of wisdom, values and life skills within families, tribes and communities was instrumental in the formation and continuation of diverse wisdom traditions all over the world. A personal system of education, called Gurukula (Sanskrit guru, teacher; kula, family) education, thrived in pre-colonial South Asia for centuries before it was replaced by colonial education. This article discusses the philosophy and science behind Gurukula education, where education was a personal process involving an osmotic exchange of essences between teacher and taught, giving wide scope for the celebration of the natural diversity and variability of human behaviour and personality leading to an education that provides equal opportunity in the real sense—as an equal fit between individuals and their environment(s), giving rise to a practical democracy.

Spraying treatment of fresh-cut apples as a sustainable alternative to dipping for browning inhibition: a preliminary lab-scale study

Several fresh-cut apple snacks are available on the market, and their color is highly relevant for consumers. As apple slices brown very quickly after cutting, dipping them in an antioxidant solution for a few minutes is common to avoid this phenomenon. However, this procedure has some limitations. Using the same solution for several immersion cycles over several hours can lead to cross-contamination and microbial growth. In addition, osmotic exchange phenomena in the immersion tank lead to a reduction in the concentration of the active ingredients of the antioxidant solution over time, which requires continuous readjustment of the concentrations. These aspects, together with the large quantities of exhausted antioxidant solution to be disposed of, are limiting factors that drive the search for alternative and more sustainable methods than dipping. In this work, a comparison between a conventional dipping treatment of fresh-cut apples and spraying at increasing volume of antioxidant solution was performed. Color, considered as the quality reference parameter, was visually assessed (occurrance of dark spots) and CIE Lab colorimetric indices were measured over a five-day experimental period. Based on dark spots and the changes in brightness (Δ L*), hue angle (Δ h) and chroma (Δ C*), some of the spraying treatments applied were found to be comparable to dipping in controlling browning. For all treatments, high intra- and inter-batch variability and within slices of the same apple was observed concerning both instrumental data and dark spots development, indicating that further investigation is needed to validate this result and to apply this procedure at an industrial level.

Edelman Revisited: Concepts, Achievements, and Challenges.

The key message from the 1958 Edelman study states that combinations of external gains or losses of sodium, potassium and water leading to an increase of the fraction (total body sodium plus total body potassium) over total body water will raise the serum sodium concentration ([Na]S), while external gains or losses leading to a decrease in this fraction will lower [Na]S. A variety of studies have supported this concept and current quantitative methods for correcting dysnatremias, including formulas calculating the volume of saline needed for a change in [Na]S are based on it. Not accounting for external losses of sodium, potassium and water during treatment and faulty values for body water inserted in the formulas predicting the change in [Na]S affect the accuracy of these formulas. Newly described factors potentially affecting the change in [Na]S during treatment of dysnatremias include the following: (a) exchanges during development or correction of dysnatremias between osmotically inactive sodium stored in tissues and osmotically active sodium in solution in body fluids; (b) chemical binding of part of body water to macromolecules which would decrease the amount of body water available for osmotic exchanges; and (c) genetic influences on the determination of sodium concentration in body fluids. The effects of these newer developments on the methods of treatment of dysnatremias are not well-established and will need extensive studying. Currently, monitoring of serum sodium concentration remains a critical step during treatment of dysnatremias.

Hormonal Regulation of Fish Adaptation to Atypical Fluctuations in Temperature and Oxygen Regime of a Water Body

Recently, the water temperature significantly exceeded the climatic norms for the studied region of Ukraine. Water is heated to 30ºC with a decrease in the concentration of dissolved oxygen in shallow water. In this connection, the change in the hormone content in the blood plasma of carp, roach, rudd, perch and ruff in response to these factors has been studied. Most of the fish species studied in June respond by increasing the cortisol content in the blood by 1.2–3.3 times to an increase in water temperature. Fish quite successfully adapts after a month's stay in conditions of high water temperature to 31ºC, and the level of cortisol is reduced. The content of thyroid hormones in the blood of the rudd, roach and ruff is quite high and after a month of adaptation to the existing factors. This indicates an increased activity in their metabolic processes. The content of somatotropin and prolactin in the blood of the studied fish species decreases 2.4–5.0 and 1.9–7.7 times, respectively, in response to an increase in temperature and a decrease in the oxygen concentration in water. This should lead to a decrease in the rate of fish growth and change in the activity of osmotic exchange. However, hormonal reactions are species-specific in nature to the existing factors. Perch and roach are less plastic to increase water temperature. Carp most favorably tolerates an increase in water temperature and a decrease in oxygen concentration.

Artificial muscles driven by the cooperative actuation of electrochemical molecular machines. Persistent discrepancies and challenges

ABSTRACTHere we review the persisting conceptual discrepancies between different research groups working on artificial muscles based on conducting polymers and other electroactive material. The basic question is if they can be treated as traditional electro-mechanical (physical) actuators driven by electric fields and described by some adaptation of their physical models or if, replicating natural muscles, they are electro-chemo-mechanical actuators driven by electrochemical reaction of the constitutive molecular machines: the polymeric chains. In that case the charge consumed by the reaction will control the volume variation of the muscular material and the motor displacement, following the basic and single Faraday’s laws: the charge consumed by the reaction determines the number of exchanged ions and solvent, the film volume variation to lodge/expel them and the amplitude of the movement. Deviations from the linear relationships are due to the osmotic exchange of solvent and to the presence of parallel reactions from the electrolyte, which originate creeping effects. Challenges and limitations are underlined.

A recursive microfluidic platform to explore the emergence of chemical evolution.

We propose that a chemically agnostic approach to explore the origin of life, using an automated recursive platform based on droplet microfluidics, could be used to induce artificial chemical evolution by iterations of growth, speciation, selection, and propagation. To explore this, we set about designing an open source prototype of a fully automated evolution machine, comprising seven modules. These modules are a droplet generator, droplet transfer, passive and active size sorting, splitter, incubation chamber, reservoir, and injectors, all run together via a LabVIEWTM program integration system. Together we aim for the system to be used to drive cycles of droplet birth, selection, fusion, and propagation. As a proof of principle, in addition to the working individual modules, we present data showing the osmotic exchange of glycylglycine containing and pure aqueous droplets, showing that the fittest droplets exhibit higher osomolarity relative to their neighbours, and increase in size compared to their neighbours. This demonstrates the ability of our platform to explore some different physicochemical conditions, combining the efficiency and unbiased nature of automation with our ability to select droplets as functional units based on simple criteria.

MODELING OF LOW SALINITY WATERFLOODING IN CLAY-CONTAINING OIL RESERVOIRS

Analysis of osmotic and ion exchange processes between injected agent and clay-containing rock has been carried out. The analysis allowed to obtain reservoir properties depending on ionic composition and salinity of the injected water and ratio of clay-content of reservoir. It’s been shown that change of hydrochemicalmode of formation development leads to transformation of structure of porous medium, and as a result to changes in reservoir porosity and permeability properties. Analytical dependencies of porosity and relative phase permeability on the salt concentration and ion composition of injected fluid have been obtained on the basis of micromechanical description of fluid flow process in porous medium. The modeling of two-phase Newtonian fluids flow in clay-containing porous medium has been carried out. Influence of parameters of porous medium and injected saline liquid on oil production has been researched. Efficiency of low salinity solutions and highactive metals solutions injection in clay containing reservoir has been shown.

Evaluation of the osmotic dehydration process of two varieties of mango (Mangifera indica L.)

Osmotic dehydration (DO) is a postharvest handling technique, widely used for the conservation and transformation of agricultural products, it consists of extracting water from a food by subjecting it to a temporary immersion in a solution with a greater quantity of soluble solids, which generates an osmotic exchange between the food and the solution. The mango constitutes one of the tropical fruits with greater volumes of production in Colombia and the lack of ideas for its conservation and transformation; generates losses close to 5000 tons. In this investigation, the effect of the osmotic dehydration process (DO) of a solution of sucrose at 45 ° Brix on the physicochemical properties of the Creole varieties of mango heart and yarn after having been immersed in the osmotic solution for 133 h was evaluated. The fruits used were different degrees of maturity: 2 the mango heart and the mango yarn in a degree of maturity 4. During the DO process, the first 18 h presented the greatest water loss for the two varieties. However, the yarn handle showed greater water loss and higher solids gain. The similar behavior during the DO process between the varieties of mango criollas in comparison with the improved varieties, shows that the landraces have potential and competitive characteristics in the processes of transformation of the fruit. In the same way, agronomically the criollo varieties present better productive capacity since they are adapted to the conditions of the region.

Assessment of Rauvolfia nukuhivensis: from uses to biological ac-tivities and chemodiversity

Rauvolfia genus, biogeographically widespread in tropical areas, includes many species used in traditional medicine. Studies of these species showed that their uses are related to their bioactive content mostly composed by alkaloid compounds. Rauvolfia nukuhivensis, called locally “tueiao”, is an endemic species grown in Nuku-Hiva island located in Marquesas archi-pelago where the bark is used for intimate woman care [1]. Ethnopharmacological approach was adopted to assess this plant. For that purpose, firstly, we checked if the plant extract played an antiseptic role within antimicrobial effects by testing the extract and contents on bacterial and fungi strains (Escherichia coli, Staphylococcus aureus, Candida albicans and Aspergillus niger) and bioassay results showed moderate to low activities. Then, we supposed that traditional medicinal uses of this plant may be linked to biological activities having close relationship with secretory mechanisms regulation. This hypothesis was investigated by the ion channels inhibition related to osmotic exchanges and then, inhibiting effects on hNav1.6 currents and hERG channel were so investigated. Some alkaloidal constituents, and more especially nukuhivensiums, were shown to significantly induce a reduction of IKr amplitude (hERG current). According to these biological activities, a computational study through docking was performed in order to illustrate these results [2,3]. The chemodiversity of the alkaloids from the bark of this plant was assessed by three inte-grated approaches mainly: structural elucidation, phylogenetic analysis and a putative biosynthesis hypothesis statement. Structural elucidation by spectroscopic means (MS, NMR) led to the identification of 13 major constituents belonging to four distinct indole alkaloid skeletons (ajmalane, sarpagane, macroline and β-carboline) within six new naturally occuring compounds. As the Rauvolfia genus is well distributed in the Pacific region, we carried out a phylogenetic study (using DNA barcoding method) of Rauvolfia species, endemic or indigenous in Oceania, as a second approach, aiming to a better understanding of the occurence and distribution of these alkaloids. The very rare co-occurence of these alkaloids belonging to four different skeletons inspired to set up a putative biosynthesis of these components, as a third way of investigation of their chemodiversity

Decoupling of mass transport mechanisms in the stagewise swelling of multiple emulsions.

This contribution reports on the mass transport kinetics of osmotically imbalanced water-in-oil-in-water (W1/O/W2) emulsions. Although frequently studied, the control of mass transport in W1/O/W2 emulsions is still challenging. We describe a microfluidics-based method to systematically investigate the impact of various parameters, such as osmotic pressure gradient, oil phase viscosity, and temperature, on the mass transport. Combined with optical microscopy analyses, we are able to identify and decouple the various mechanisms, which control the dynamic droplet size of osmotically imbalanced W1/O/W2 emulsions. So, swelling kinetics curves with a very high accuracy are generated, giving a basis for quantifying the kinetic aspects of transport. Two sequential swelling stages, i.e., a lag stage and an osmotically dominated stage, with different mass transport mechanisms are identified. The determination and interpretation of the different stages are the prerequisite to control and trigger the swelling process. We show evidence that both mass transport mechanisms can be decoupled from each other. Rapid osmotically driven mass transport only takes place in a second stage induced by structural changes of the oil phase in a lag stage, which allow an osmotic exchange between both water phases. Such structural changes are strongly facilitated by spontaneous water-in-oil emulsification. The duration of the lag stage is pressure-independent but significantly influenced by the oil phase viscosity and temperature.

Investigation of Cyclic Electrolytic Solutions Injection in Clay-Containing Oil Reservoirs

Analysis of osmotic and ion exchange processes at the interface between injected agent and clay-containing rock has been carried out. The analysis allowed to obtain reservoir properties depending on ionic composition of the injected water and clay-content of reservoir. It’s been shown that decrease of salinity of the injected agent leads to the transformation of the structure of the porous medium: share of «thin» pores increases, whereas the share of «thick» pores reduces, resulting in reduced porosity. Analytical relative permeabilities depending on the salt concentration and ion composition of injected fluid have been obtained on the basis of micromechanical description of fluid flow process in frame of the lattice model of porous medium. The modeling of two-phase Newtonian fluids flow in clay-containing porous medium has been carried out. The influence of parameters of porous medium, injected saline fluid also injection frequency on efficiency of oil displacement has been analyzed.

Effects of osmo-air dehydration treatments on chemical, antioxidant and morphological characteristics of blueberries

Osmo-air dehydration treatments are widely applied to fruits in order to prolong shelf-life, reduce packaging and logistic costs, and to improve both sensory and nutritional quality of the end products. In this work, osmo-air dehydration was applied to blueberries (Vaccinium corymbosum); blanched blueberries were dipped in sucrose (60 °Bx) and fructose/glucose (48.6 °Bx) osmotic solutions (aw = 0.90) for 24 h, and the osmotic exchanges were determined by mass balances (water loss, solid gain, sugar intake, changes in total phenolics and anthocyanins). Untreated and infused berries were subsequently air dried at 70 °C to final moisture content of 10–14%, and drying kinetics as well as compositional and morphological changes of berries were followed in the course of drying. Data show that the osmotic treatment causes significant losses in the antioxidant components (total phenolics, total and individual anthocyanins) and in the antioxidant activity. Losses in the antioxidant components also occur in the course of air drying, with similar kinetics in untreated and infused blueberries. Glucose/fructose infusion gives better results in terms of morphological changes, with lower shrinkage and wrinkling of the berries.

Hydrodynamics of steady state phloem transport with radial leakage of solute.

Long-distance phloem transport occurs under a pressure gradient generated by the osmotic exchange of water associated with solute exchange in source and sink regions. But these exchanges also occur along the pathway, and yet their physiological role has almost been ignored in mathematical models of phloem transport. Here we present a steady state model for transport phloem which allows solute leakage, based on the Navier-Stokes and convection-diffusion equations which describe fluid motion rigorously. Sieve tube membrane permeability Ps for passive solute exchange (and correspondingly, membrane reflection coefficient) influenced model results strongly, and had to lie in the bottom range of the values reported for plant cells for the results to be realistic. This smaller permeability reflects the efficient specialization of sieve tube elements, minimizing any diffusive solute loss favored by the large concentration difference across the sieve tube membrane. We also found there can be a specific reflection coefficient for which pressure profiles and sap velocities can both be similar to those predicted by the Hagen-Poiseuille equation for a completely impermeable tube.

Near infrared (NIR) spectroscopy as a tool for monitoring blueberry osmo–air dehydration process

Osmo–air dehydration treatments are widely applied to fruits in order to prolong shelf-life, reduce packaging and logistic costs, and improve both sensory and nutritional quality of the end products. In this work osmo–air dehydration was applied to blueberries (Vaccinium corymbosum), a fruit that is gaining increasing attention due to its high content of dietary antioxidants. In particular, the aim of this study was to investigate the performance of near infrared (NIR) spectroscopy as a tool for monitoring blueberry osmo and air dehydration processes.Blanched blueberries were dipped in sucrose and fructose+glucose osmotic solutions for 24h, and the osmotic exchanges were determined by mass balances (water loss, solid gain, sugar intake, changes in total phenolics and anthocyanins); NIR spectra were collected in order to study modifications due to the osmotic treatments. Untreated and infused berries were subsequently air-dried at 70°C to final moisture content of 10–14%. During drying chemical, nutritional and structural changes were monitored and NIR spectra were acquired on whole berries, using an optic probe working in diffuse reflectance. Spectral data were standardized, transformed into first derivative and processed by Principal Component Analysis. Results show that NIR spectroscopy was able to follow the osmotic and the air-drying processes and to discriminate untreated and osmo-dehydrated berries. Spectral differences reflect the main molecular modifications associated with water absorption bands due to OH stretch+OH bending and sugar absorption bands due to CH stretch+CH bending and OH stretch+OH bending. In order to investigate the variation of main constituents (sugars and water) involved in the osmo-dehydration process, two-dimensional correlation analysis of spectral data was also carried out.

Adhesive interactions between vesicles in the strong adhesion limit.

We consider the adhesive interaction energy between a pair of vesicles in the strong adhesion limit, in which bending forces play a negligible role in determining vesicle shape compared to forces due to membrane stretching. Although force−distance or energy−distance relationships characterizing adhesive interactions between fluid bilayers are routinely measured using the surface forces apparatus, the atomic force microscope, and the biomembrane force probe, the interacting bilayers in these methods are supported on surfaces (e.g., mica sheet) and cannot be deformed. However, it is known that, in a suspension, vesicles composed of the same bilayer can deform by stretching or bending, and can also undergo changes in volume. Adhesively interacting vesicles can thus form flat regions in the contact zone, which will result in an enhanced interaction energy as compared to rigid vesicles. The focus of this paper is to examine the magnitude of the interaction energy between adhesively interacting, deformed vesicles relative to free, undeformed vesicles as a function of the intervesicle separation. The modification of the intervesicle interaction energy due to vesicle deformability can be calculated knowing the undeformed radius of the vesicles, R0, the bending modulus, k(b), the area expansion modulus, k(a), and the adhesive minimum, W(P)(0), and separation, D(P)(0), in the energy of interaction between two flat bilayers, which can be obtained from the force−distance measurements made using the above supported-bilayer methods. For vesicles with constant volumes, we show that adhesive potentials between nondeforming bilayers such as |W(P)(0)| 5 × 10(−4) mJ/m2, which are ordinarily considered weak in the colloidal physics literature, can result in significantly deep (>10×) energy minima due to increase in vesicle area and flattening in the contact region. If the osmotic expulsion of water across the vesicles driven by the tense, stretched membrane in the presence of an osmotically active solute is also taken into account, the vesicles can undergo additional deformation (flattening), which further enhances the adhesive interaction between them. Finally, equilibration of ions and solutes due to the concentration differences created by the osmotic exchange of water can lead to further enhancement of the adhesion energy. Our result of the progressively increasing adhesive interaction energy between vesicles in the above regimes could explain why suspensions of very weakly attractive vesicles may undergo flocculation and eventual instability due to separation of vesicles from the suspending fluid by gravity. The possibility of such an instability is an extremely important issue for concentrated vesicle-based products and applications such as fabric softeners, hair therapeutics and drug delivery.

The behavior of the human erythrocyte as an imperfect osmometer: A hypothesis

The human erythrocyte does not behave as a perfect osmometer that is its volume does not change as predicted with the change of the tonicity of the medium, as if there was a fraction of the cell water not participating in the osmotic exchange. A mechanism of control of the erythrocyte shape has been previously proposed in which Band 3 (AE1), the protein anion exchanger of Cl − and HCO 3 −, plays a central role. Specifically, decrease and increase of the ratio of its outward-facing conformation and inward-facing conformation (Band 3 o /Band 3 i ) contract and relax the membrane skeleton, thus favoring echinocytosis and stomatocytosis, respectively. The equilibrium Band 3 o /Band 3 i ratio is determined by the Donnan equilibrium ratio of anions and protons, increasing with it ( r = Cl i - / Cl o - = HCO 3 i - / HCO 3 o - = H o + / H i + ). The Donnan ratio is influenced by the erythrocyte transport and metabolic activities. The volume change of the human erythrocyte alters the skeleton conformation as it is accompanied by a change of the membrane curvature. Thus, the mechanism could be a hypothesis for explaining the behavior of the human erythrocyte as an imperfect osmometer since the Donnan ratio controls the Band 3 o /Band 3 i ratio which controls the volume by a control of the degree of contraction or relaxation of the skeleton. Predictions made by the hypothesis on the Ponder's coefficient R′ values in the presence of sucrose or Band 3 substrates slowly transported as well as on the participation of Band 3 in the osmotic hemolysis appear to be corroborated by previous observations. If the hypothesis was valid, it would follow that there is a pressure gradient across the erythrocyte membrane. The equilibrium volume is antagonistically determined by the Donnan ratio per se and Band 3. Band 3, rather than the ratio of surface-to-volume, primarily controls the osmotic hemolysis.

A physical model of muscle working to evaluate the work ability

It was well known that work ability included a wide kind of related aspects, involving both mental and physical well-being. When mechanical works were taken into account, it was necessary to refer to muscular structure and its consistency, for assessing the work ability and employability; i.e. efficiency of performances of the muscles has to be expressed in terms of physiological parameters representing the best expression of physical health. To enhance the existence of idoneous relationships between the muscle operation and the work ability, it should be necessary to point out a specific physical model of muscle motor enabling to correlate physiological parameters involved in the muscle operation to the physical quantities usually employed for estimating the work made by a machine. The authors have evaluated a mechanical model of the muscle motor, which allowed them to include the isometric and isotonic contractions, the primitive role of osmotic exchanges and the presence of energy dissipation, also in the presence of elastic forces, avoiding the so constructed model to have conservative nature. The so developed model, virtually animated using specific interactive software to reproduce the effective muscular behaviour during limbs' movements, has appeared extremely suitable both for educational and scientific aim.

Hydration and thermodynamic equilibrium of non-ionic surfactant in solution

In this article we present a combined analysis of volumetric [1] and molecular dynamics (MD) [2] determinations of the interfacial properties of non-ionic surfactant aggregates belonging to the family of the oligooxyethylene glycol (C iEj). The volumetric experiments were made on surfactant having i = 12 and j ranging from 5 to 8 EO unit and concern the density, and the sound velocity measurements on aqueous solutions of the surfactants. For concentrations up to about 40 wt.% the density of the solutions cross that of pure solvent at given temperatures. The presence of crossing temperatures T ρ allows us to describe the surfactant solutions in terms of an ideal mixture of pure solvent and an effective solute. On the ground of a simple hydration model for the micellar aggregate, we obtained the dependence of the degree of hydration and of the osmotic compressibility on the solute molar volumes and on the temperature. On the other hand, the compressibility embodies a term associated with a local osmotic exchange between the aggregates and the external solvent. To obtain a microscopic resolution of the interfacial properties, MD simulations were performed on a spherical C 12 E 6 micelle. The dependence of the aggregate hydration on the temperature obtained by MD agrees with the results from density experiment. However, the MD clearly indicates that dehydration mainly occurs at the exposed hydrophobic area. Besides the MD results have shown that the micellar interface is characterized by significative interaction among the hydrophilic termination. These interactions leave a large hydrophobic area exposed to the solvent. Despite the complexity of the problem, in the context of our hydration model and within 40 wt.%, the properties of these solutions can be defined by their specific hydration numbers.

Solvent-dehydrated calvarial allografts in craniofacial surgery.

Craniofacial surgery almost always requires the use of bone grafting. Although autografts are the standard procedure for bone grafting, it is sometimes not possible to harvest bone, and autografts have particular risks. The use of allograft bone provides a reasonable alternative to meet the need for graft material. Solvent dehydration is a multistage procedure in which human cadaveric bone is processed by osmotic exchange baths and gamma sterilization. This processing avoids the risk of infection transmission, decreases antigenicity, and does not weaken the mechanical properties of the bone. Solvent-dehydrated, gamma-irradiated human calvarial bone allografts were used for reconstruction of craniofacial deformities in 24 patients between 1988 and 2002. Resorption of the allografts and results of the surgical intervention were evaluated with plain radiographs and three-dimensional computed tomography 12 months after surgery, in 21 patients. Serologic tests for human immunodeficiency virus-1 antibody, hepatitis B surface antigen, and hepatitis C antigen were also performed. Biopsy specimens were taken from the allografts. Average follow-up in this group was 30 months (range, 8 to 60 months), and results of serologic tests were negative in all patients. Seventy-one percent of the patients (15 of 21) showed no resorption, with partial and complete allograft fusion. One patient had nearly total graft loss and the remaining five patients had 10 to 25 percent graft resorption. Rigid fixation of the allograft, contact with the dura and periosteum, and prevention of dead spaces around the allograft are the most important factors in achieving a satisfactory result. In solvent-dehydrated bone allografts, sterilization and antigenic tissue cleaning are achieved after several steps with a minimal dose of radiation. The result is a nonantigenic, sterile mechanical scaffold that can tolerate external forces. Although autografts are the standard in craniofacial surgery, solvent-dehydrated calvarial bone allografts produced successful results in selected cases.