Biomécanique et Bioingénierie

Electrospinning is a versatile technique used to create native tissue-like fibrous scaffolds. Recently, it has gained a large amount of attention for generation of bioactive dressing materials suitable for treatment of both chronic and acute wounds. In this Review, we focus on the latest advances made in the application of electrospun scaffolds for bioactive wound healing. We first provide a brief overview of the wound healing process and electrospinning approaches. We then discuss fabrication of scaffolds made from natural and synthetic polymers via electrospinning for effective wound treatment and management. Natural polymers used for wound healing included in our Review cover protein based polymers such as collagen, gelatin, and silk and polysaccharide based polymers such as chitosan, hyaluronic acid, and alginate. In addition, we discuss aliphatic polyesters, super hydrophilic polymers, and polyurethanes as some of the most commonly used synthetic polymers for wound healing and wound dressing applications. Next, we review multifunctional and "smart" scaffolds developed by electrospinning based approaches. We place an emphasis on how flexibility of the electrospinning process enables production of advanced scaffolds such as core-shell fibrous scaffolds, multilayer scaffolds, and surface modified scaffolds. Taken together, it is clear that electrospinning is an emerging technology that provides a unique opportunity for engineering more effective wound dressing, management, and care products.

A biomaterial-based vaccination system that uses minimal extracorporeal manipulation could provide in situ enhancement of dendritic cell (DC) numbers, a physical space where DCs interface with transplanted tumour cells, and an immunogenic context. Here we encapsulate GM-CSF, serving as a DC enhancement factor, and CpG ODN, serving as a DC activating factor, into sponge-like macroporous cryogels. These cryogels are injected subcutaneously into mice to localize transplanted tumour cells and deliver immunomodulatory factors in a controlled spatio-temporal manner. These vaccines elicit local infiltrates composed of conventional and plasmacytoid DCs, with the subsequent induction of potent, durable and specific anti-tumour T-cell responses in a melanoma model. These cryogels can be delivered in a minimally invasive manner, bypass the need for genetic modification of transplanted cancer cells and provide sustained release of immunomodulators. Altogether, these findings indicate the potential for cryogels to serve as a platform for cancer cell vaccinations. Immune responses are induced in the organized, cytokine-rich environment of lymph nodes, which can be mimicked by biomaterials. Here the authors show that injectable sponge-like gels decorated with immunostimulatory factors attract dendritic cells and boost antitumour immune responses in mice.

Abstract There exists a technological need for advanced materials with improved properties for emerging biomedical applications. Recent developments in macroporous materials have demonstrated their applicability as indispensable tools in biomedical research. Cryogels, which are materials with a macroporous 3D structure, are produced as a result of controlled freezing during polymerization with a highly interconnected polymer network. Cryogels’ interest lies in their ability to address some of the limitations of their hydrogel analogues. In this review, hydrogel and cryogel basic concepts are discussed as a short primer for readers unfamiliar with the cryogels literature. Next, a general overview of the methods for synthesis and characterization of cryogels is provided, highlighting key concepts relevant to cryogels and explaining their unique properties. Finally an in‐depth overview of specific technologies and fields where cryogels have been applied is given. It is argued that the latest advances in cryogel technologies are able to address challenges in bioseparation, tissue engineering, and other emerging bioengineering disciplines.

Three constitutive laws (Skalak et al.'s law extended to area-compressible interfaces, Hooke's law and the Mooney–Rivlin law) commonly used to describe the mechanics of thin membranes are presented and compared. A small-deformation analysis of the tension–deformation relation for uniaxial extension and for isotropic dilatation allows us to establish a correspondence between the individual material parameters of the laws. A large-deformation analysis indicates that the Mooney–Rivlin law is strain softening, whereas the Skalak et al. law is strain hardening for any value of the membrane dilatation modulus. The large deformation of a capsule suspended in hyperbolic pure straining flow is then computed for several membrane constitutive laws. A capsule with a Mooney–Rivlin membrane bursts through the process of continuous elongation, whereas a capsule with a Skalak et al. membrane always reaches a steady state in the range of parameters considered. The small-deformation analysis of a spherical capsule embedded in a linear shear flow is modified to account for the effect of the membrane dilatation modulus.

RATIONALE AND OBJECTIVES: To investigate and measure temporal and amplitude aspects of blood and cerebrospinal fluid (CSF) flow waveform relations. METHODS: A cine phase-contrast magnetic resonance imaging pulse sequence was used to measure blood and CSF flow in 16 healthy subjects aged 27 +/- 4 years. A semiautomated segmentation algorithm was developed to study CSF flow. RESULTS: Standard deviations of the aqueductal and cervical flow measurements carried out by five observers were 1% and 4%, respectively. The peak systolic arterial flow was 1087 +/- 169 mL/min, and the peak cervical CSF flush (173 +/- 59 mL/min) occurred at 5% +/- 3% of the cardiac cycle after the internal carotid systolic peak flow. Peak aqueductal flush flow (13 +/- 5 mL/min) occurred at 21% +/- 7% of the cardiac cycle after the internal carotid systolic peak flow. CONCLUSIONS: The CSF segmentation algorithm is reproducible. Brain expansion was quickly regulated by a major extracerebral CSF flush flow, whereas ventricular CSF made only a very small contribution.

The dynamic response of an initially spherical capsule subject to different externally imposed flows is examined. The neo-Hookean and Skalak et al. (Biophys. J., vol. 13 (1973), pp. 245–264) constitutive laws are used for the description of the membrane mechanics, assuming negligible bending resistance. The viscosity ratio between the interior and exterior fluids of the capsule is taken to be unity and creeping-flow conditions are assumed to prevail. The capillary number $\varepsilon $ is the basic dimensionless number of the problem, which measures the relative importance of viscous and elastic forces. The boundary-element method is used with bi-cubic B-splines as basis functions in order to discretize the capsule surface by a structured mesh. This guarantees continuity of second derivatives with respect to the position of the Lagrangian particles used for tracking the location of the interface at each time step and improves the accuracy of the method. For simple shear flow and hyperbolic flow, an interval in $\varepsilon $ is identified within which stable equilibrium shapes are obtained. For smaller values of $\varepsilon $ , steady shapes are briefly captured, but they soon become unstable owing to the development of compressive tensions in the membrane near the equator that cause the capsule to buckle. The post-buckling state of the capsule is conjectured to exhibit small folds around the equator similar to those reported by Walter et al. Colloid Polymer Sci. Vol. 278 (2001), pp. 123–132 for polysiloxane microcapsules. For large values of $\varepsilon $ , beyond the interval of stability, the membrane has two tips along the direction of elongation where the deformation is most severe, and no equilibrium shapes could be identified. For both regions outside the interval of stability, the membrane model is not appropriate and bending resistance is essential to obtain realistic capsule shapes. This pattern persists for the two constitutive laws that were used, with the Skalak et al. law producing a wider stability interval than the neo-Hookean law owing to its strain hardening nature.

Liver failure is associated with high morbidity and mortality without transplantation. There are two types of device for temporary support: artificial and bioartificial livers. Artificial livers essentially use non-living components to remove the toxins accumulated during liver failure. Bioartificial livers have bioreactors containing hepatocytes to provide both biotransformation and synthetic liver functions. We review here the operating principles, chemical effects, clinical effects and complications of both types, with specific attention paid to bioartificial systems. Several artificial support systems have FDA marketing authorisation or are CE labelled, but the improvement they provide in terms of patient clinical outcome has not yet been fully demonstrated. At present, different bioartifical systems are being investigated clinically on the basis of their promises and capacity to provide and replace most liver functions. However, important issues such as cost, cell availability, maintenance of cell viability and functionality throughout treatment, and regulatory issues, as well as difficult challenges, including implementing cell-housing devices at the patient's bedside on an emergency basis, have delayed their appearance in intensive care units and on the market. Bioreactors are, nevertheless, when combined with artificial components, a pragmatic approach for future treatment of liver failure.

This article reviews the mechanical behavior of a capsule under the influence of viscous deforming forces due to a flowing fluid. It focuses on artificial capsules and vesicles with an internal liquid core enclosed by a very thin membrane with different constitutive laws. The recent modeling strategies are outlined together with their respective advantages and limitations. I then consider the motion and deformation of a single, initially spherical capsule freely suspended in a simple shear or plane hyperbolic flow and discuss the effect of the membrane constitutive law, initial prestress, membrane buckling, and bulk or membrane viscosity. Finally, I consider the flow of spherical capsules in small pores and show how numerical models can be used to evaluate the mechanical properties of the membrane.

The rheology of rigid rod cellulose whisker suspensions has been investigated. The isotropic-at-rest suspension flow curves show two plateaus, one at low shear rates and another at high shear rates, that reflect the flow of isotropic (at low shear rates) or oriented (at high shear rates) suspensions. From the low shear rate viscosity plateau vs concentration, we see that the system is in the semidilute region above 0.02 wt %, in agreement with the theoretical predictions. From the same curve, we can estimate a maximum packing concentration of whiskers rods that corresponds to the experimentally measured isotropic-to-anisotropic transition. The high shear rate plateau viscosity data show that the suspension is still in the dilute state above 0.6 wt %. The critical concentration at the dilute−semidilute transition is thus strongly dependent on the state of order, which suggests that care has to be taken when measuring parameters extracted from flowing solutions or suspensions, as for example occurring with Ubbelhode viscometry. Above a certain critical concentration, the suspensions become anisotropic at rest. The viscosity vs concentration curve has a maximum that vanishes at high shear rates as for liquid crystalline polymer solutions. Rheological and rheo-optical observations show fast inception and relaxation of both the rheological functions and the texture, in complete contrast with liquid crystalline polymer solutions.

RATIONALE AND OBJECTIVES: Using magnetic resonance imaging (MRI), we investigated cerebral blood and cerebrospinal fluid (CSF) flows in patients with communicating hydrocephalus (CH) and in healthy volunteers to determine the contribution of CSF flow to brain pressure regulation in CH patients. METHODS: Cine phase-contrast MRI data from 16 healthy volunteers and 12 patients with CH characterized by hyperdynamic aqueductal CSF flow were analyzed using in-house image-processing software that automatically measured flow curves. Amplitude and temporal CSF and blood flow parameters were compared in the 2 groups. RESULTS: Jugular peak flow occurred significantly earlier (P < 0.01) in the CH patients than in the healthy volunteers. Cervical CSF oscillations were not significantly different between the 2 groups. CONCLUSION: Venous vessel compression and/or changes in intracranial subarachnoid CSF flow produce an increase in ventricular CSF flush that compensates for vascular brain expansion in patients with CH.

PURPOSE OF REVIEW: To review various methods for measuring body composition by bioimpedance and their limitations, as well as available impedance meters, including body fat analyzers for home use. RECENT FINDINGS: Bioimpedance spectroscopy, which requires multifrequency impedance meters, is preferable for fluid volume measurements, especially extracellular fluid, whereas bioimpedance analysis at 50 kHz is more widely used for measuring fat-free mass. A method for using bioimpedance spectroscopy equations with 50 kHz impedance meters has been recently proposed and successfully tested. Low cost foot-to-foot impedance meters (body fat analyzers) with plantar electrodes on a body scale, that are easy and fast to use, have been compared with medical impedance meters and with dual X-ray absorptiometry measurements and found reasonably accurate, except for individuals with very low or high BMI. SUMMARY: Body composition by bioimpedance is gaining acceptance in nutrition, hemodialysis, gerontology and sports medicine. Body fat analyzers that have been validated by comparison with dual x-ray absorptiometry could be useful to general practitioners, nutritionists and cardiologists.

Recently, much progress has been made to develop more physiologic in vitro models of the respiratory system and improve in vitro simulation of particle exposure through inhalation. Nevertheless, the field of nanotoxicology still suffers from a lack of relevant in vitro models and exposure methods to predict accurately the effects observed in vivo, especially after respiratory exposure. In this context, the aim of our study was to evaluate if exposing pulmonary cells at the air-liquid interface to aerosols of inhalable and poorly soluble nanomaterials generates different toxicity patterns and/or biological activation levels compared to classic submerged exposures to suspensions. Three nano-TiO 2 and one nano-CeO 2 were used. An exposure system was set up using VitroCell® devices to expose pulmonary cells at the air-liquid interface to aerosols. A549 alveolar cells in monocultures or in co-cultures with THP-1 macrophages were exposed to aerosols in inserts or to suspensions in inserts and in plates. Submerged exposures in inserts were performed, using similar culture conditions and exposure kinetics to the air-liquid interface, to provide accurate comparisons between the methods. Exposure in plates using classical culture and exposure conditions was performed to provide comparable results with classical submerged exposure studies. The biological activity of the cells (inflammation, cell viability, oxidative stress) was assessed at 24 h and comparisons of the nanomaterial toxicities between exposure methods were performed. Deposited doses of nanomaterials achieved using our aerosol exposure system were sufficient to observe adverse effects. Co-cultures were more sensitive than monocultures and biological responses were usually observed at lower doses at the air-liquid interface than in submerged conditions. Nevertheless, the general ranking of the nanomaterials according to their toxicity was similar across the different exposure methods used. We showed that exposure of cells at the air-liquid interface represents a valid and sensitive method to assess the toxicity of several poorly soluble nanomaterials. We underlined the importance of the cellular model used and offer the possibility to deal with low deposition doses by using more sensitive and physiologic cellular models. This brings perspectives towards the use of relevant in vitro methods of exposure to assess nanomaterial toxicity.

The new metastable epsilon-Bi2O3 polymorph has been prepared by hydrothermal treatment and structurally characterized. It shows strong relationships with the room temperature alpha form and the metastable beta form through rearrangements of [Bi2O3] columns formed by edge-sharing OBi4 tetrahedra. Its fully ordered crystal structure yields an ionic insulating character. It irreversibly transforms at 400 degrees C to the alpha form. The chemical analysis indicates its undoped bismuth oxide nature, then leading to the fifth characterized Bi2O3 polymorph to date.

Abstract We introduce a new numerical method to model the fluid–structure interaction between a microcapsule and an external flow. An explicit finite element method is used to model the large deformation of the capsule wall, which is treated as a bidimensional hyperelastic membrane. It is coupled with a boundary integral method to solve for the internal and external Stokes flows. Our results are compared with previous studies in two classical test cases: a capsule in a simple shear flow and in a planar hyperbolic flow. The method is found to be numerically stable, even when the membrane undergoes in‐plane compression, which had been shown to be a destabilizing factor for other methods. The results are in very good agreement with the literature. When the viscous forces are increased with respect to the membrane elastic forces, three regimes are found for both flow cases. Our method allows a precise characterization of the critical parameters governing the transitions. Copyright © 2010 John Wiley & Sons, Ltd.

Concentration polarization (CP) and membrane fouling are two major drawbacks for pressure-driven membrane filtration processes (PDMPs) because they cause severe flux decline, which requires effective control strategies. Many articles have proposed the diverse potential applications of various control strategies in reducing CP and membrane fouling. This paper reviews various mechanisms and influencing factors on flux decline, as well as their control strategies in PDMPs. Nine effective control strategies are summarized, generalized, and compared in this paper. On the basis of their functions and influences, they can be also classified as the following: (1) modification: pretreatment of feed, modification of feed characteristics, selection and modification of membrane; (2) design: shear-enhanced filtration modules, applied field enhancement and CP drawer; (3) operation: optimization of operating parameters, hydraulic flushing and two-phase flow. Then, the general and practical guidelines are given. On the basis of this review, future research perspectives related to flux decline control strategies are proposed.

Tissue engineering is a promising approach to repair tendon and muscle when natural healing fails. Biohybrid constructs obtained after cells’ seeding and culture in dedicated scaffolds have indeed been considered as relevant tools for mimicking native tissue, leading to a better integration in vivo. They can also be employed to perform advanced in vitro studies to model the cell differentiation or regeneration processes. In this review, we report and analyze the different solutions proposed in literature, for the reconstruction of tendon, muscle, and the myotendinous junction. They classically rely on the three pillars of tissue engineering, i.e., cells, biomaterials and environment (both chemical and physical stimuli). We have chosen to present biomimetic or bioinspired strategies based on understanding of the native tissue structure/functions/properties of the tissue of interest. For each tissue, we sorted the relevant publications according to an increasing degree of complexity in the materials’ shape or manufacture. We present their biological and mechanical performances, observed in vitro and in vivo when available. Although there is no consensus for a gold standard technique to reconstruct these musculo-skeletal tissues, the reader can find different ways to progress in the field and to understand the recent history in the choice of materials, from collagen to polymer-based matrices.

The effects of long-term spaceflight (90-180 days) on the contractile and elastic characteristics of the human plantarflexor muscles were studied in 14 cosmonauts before and 2-3 days after landing. Despite countermeasures practiced aboard, spaceflight was found to induce a decrease in maximal isometric torque (17%), whereas an index of maximal shortening velocity was found to increase (31%). In addition, maximal muscle activation evaluated during isokinetic tests decreased by 39%. Changes in musculotendinous stiffness and whole joint stiffness were characterized by means of quick-release movements and sinusoidal perturbations. Musculotendinous stiffness was found to be increased by 25%. Whole joint stiffness decreased under passive conditions (21%), whereas whole joint stiffness under active conditions remained unchanged after spaceflight (-1%). This invariance suggests an adaptive mechanism to counterbalance the decrease in stiffness of passive structures by an increased active stiffness. Changes in neural drive could participate in this equilibrium.

Magnetic resonance elastography (MRE) is capable of noninvasively quantifying the mechanical properties of skeletal muscles in vivo. This information can be clinically useful to understand the effects of pathologies on the mechanical properties of muscle and to quantify the effects of treatment. Advances in inversion algorithms quantify muscle anisotropy in two-dimensional (2D) and three-dimensional (3D) imaging. Databases of the shear stiffness of skeletal muscle have been presented in the relaxed and contracted states in the upper extremity (biceps brachii, flexor digitorum profundus, and upper trapezius), distal leg muscles (tibialis anterior, medial gastrocnemius, lateral gastrocnemius, and trapezius), and proximal leg muscles (vastus lateralis, vastus medialis, and sartorius). MRE measurements have successfully validated a mathematical model of skeletal muscle behavior in the biceps brachii, correlated to electromyographic data in the distal leg muscles and quantified the effects of pathologies on the distal and proximal leg muscles. Future research efforts should be directed toward improving one-dimensional (1D) and 3D MRE data acquisition and image processing, tracking the effects of treatment on pathologic muscle and correlating the shear stiffness with clinical measurements.

International audience

A covalently crosslinked methacrylated (MA)-alginate cryogel vaccine has been previously shown to generate a potent response against murine melanoma, but is not mechanically robust and requires a large 16G needle for delivery. Here, covalent and ionic crosslinking of cryogels are combined with the hypothesis that this will result in a tough MA-alginate cryogel with improved injectability. All tough cryogels can be injected through a smaller, 18G needle without sustaining any damage, while covalently crosslinked-only cryogels break after injection. Cytosine-phosphodiester-guanine (CpG)-delivering tough cryogels effectively activate dendritic cells (DCs). Granulocyte macrophage colony-stimulating factor releasing tough cryogels recruit four times more DCs than blank gels by day 7 in vivo. The tough cryogel vaccine induces strong antigen-specific cytotoxic T-lymphocyte and humoral responses. These vaccines prevent tumor formation in 80% of mice inoculated with HER2/neu-overexpressing DD breast cancer cells. The MA-alginate tough cryogels provide a promising minimally invasive delivery platform for cancer vaccinations.