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1.
Sci Adv ; 9(2): eade2522, 2023 01 13.
Article in English | MEDLINE | ID: mdl-36630495

ABSTRACT

Mechanical properties of soft biological tissues play a critical role in physiology and disease, affecting cell behavior and fate decisions and contributing to tissue development, maintenance, and repair. Limitations of existing tools prevent a comprehensive characterization of soft tissue biomechanics, hindering our understanding of these fundamental processes. Here, we develop an instrument for high-fidelity uniaxial tensile testing of soft biological tissues in controlled environmental conditions, which is based on the closed-loop interaction between an electromagnetic actuator and an optical strain sensor. We first validate the instrument using synthetic elastomers characterized via conventional methods; then, we leverage the proposed device to investigate the mechanical properties of murine esophageal tissue and, individually, of each of its constitutive layers, namely, the epithelial, connective, and muscle tissues. The enhanced reliability of this instrument makes it an ideal platform for future wide-ranging studies of the mechanics of soft biological tissues.


Subject(s)
Elastomers , Models, Biological , Animals , Mice , Reproducibility of Results , Muscles , Biomechanical Phenomena , Stress, Mechanical , Tensile Strength
2.
Acta Biomater ; 78: 111-122, 2018 09 15.
Article in English | MEDLINE | ID: mdl-30099199

ABSTRACT

Recreating tissue-specific microenvironments of the extracellular matrix (ECM) in vitro is of broad interest for the fields of tissue engineering and organ-on-a-chip. Here, we present biofunctional ECM protein fibres and suspended membranes, with tuneable biochemical, mechanical and topographical properties. This soft and entirely biologic membrane scaffold, formed by micro-nano-fibres using low voltage electrospinning, displays three unique characteristics for potential cell culture applications: high-content of key ECM proteins, single-layered mesh membrane, and flexibility for in situ integration into a range of device setups. Extracellular matrix (ECM) powder derived from urinary bladder, was used to fabricate the ECM-laden fibres and membranes. The highest ECM concentration in the dry protein fibre was 50 wt%, with the rest consisting of gelatin. Key ECM proteins, including collagen IV, laminin, and fibronectin, were shown to be preserved post the biofabrication process. The single fibre tensile Young's modulus can be tuned for over two orders of magnitude between ∼600 kPa and 50 MPa depending on the ECM content. Combining the fibre mesh printing with 3D printed or microfabricated structures, culture devices were constructed for endothelial layer formation, and a trans-membrane co-culture formed by glomerular cell types of podocytes and glomerular endothelial cells, demonstrating feasibility of the membrane culture. Our cell culture observation points to the importance of membrane mechanical property and re-modelling ability as a factor for soft membrane-based cell cultures. The ECM-laden fibres and membranes presented here would see potential applications in in vitro assays, and tailoring structure and biological functions of tissue engineering scaffolds. STATEMENT OF SIGNIFICANCE: Recreating tissue-specific microenvironments of the extracellular matrix (ECM) is of broad interest for the fields of tissue engineering and organ-on-a-chip. Both the biochemical and biophysical signatures of the engineered ECM interplay to affect cell response. Currently, there are limited biomaterials processing methods which allow to design ECM membrane properties flexibly and rapidly. Solvents and additives used in many existing processes also induced unwanted ECM protein degradation and toxic residues. This paper presents a solution fibre spinning technique, where careful selection of the solution combination led to well-preserved ECM proteins with tuneable composition. This technique also provides a highly versatile approach to fabricate ECM fibres and membranes, leading to designable fibre Young's modulus for over two orders of magnitude.


Subject(s)
Extracellular Matrix/metabolism , Nanofibers/chemistry , Animals , Cells, Cultured , Elastic Modulus , Elements , Humans , Membranes , Podocytes/cytology , Solutions , Spectroscopy, Fourier Transform Infrared , Stress, Mechanical , Swine , Tensile Strength , Tissue Engineering
3.
Biophys J ; 115(1): 139-149, 2018 07 03.
Article in English | MEDLINE | ID: mdl-29972805

ABSTRACT

Tracking Brownian particles is often employed to map the energy landscape they explore. Such measurements have been exploited to study many biological processes and interactions in soft materials. Yet video tracking is irremediably contaminated by localization errors originating from two imaging artifacts: the "static" errors come from signal noise, and the "dynamic" errors arise from the motion blur due to finite frame-acquisition time. We show that these errors result in systematic and nontrivial biases in the measured energy landscapes. We derive a relationship between the true and the measured potential that elucidates, among other aberrations, the presence of false double-well minima in the apparent potentials reported in recent studies. We further assess several canonical trapping and pair-interaction potentials by using our analytically derived results and Brownian dynamics simulations. In particular, we show that the apparent spring stiffness of harmonic potentials (such as optical traps) is increased by dynamic errors but decreased by static errors. Our formula allows for the development of efficient corrections schemes, and we also present in this work a provisional method for reconstructing true potentials from the measured ones.


Subject(s)
Optical Tweezers , Thermodynamics , Time Factors
4.
R Soc Open Sci ; 5(12): 181579, 2018 Dec.
Article in English | MEDLINE | ID: mdl-30662758

ABSTRACT

Metastatic tumours often invade healthy neighbouring tissues by forming multicellular finger-like protrusions emerging from the cancer mass. To understand the mechanical context behind this phenomenon, we here develop a minimalist fluid model of a self-propelled, growing biological tissue. The theory involves only four mechanical parameters and remains analytically trackable in various settings. As an application of the model, we study the evolution of a two-dimensional circular droplet made of our active and expanding fluid, and embedded in a passive non-growing tissue. This system could be used to model the evolution of a carcinoma in an epithelial layer. We find that our description can explain the propensity of tumour tissues to fingering instabilities, as conditioned by the magnitude of active traction and the growth kinetics. We are also able to derive predictions for the tumour size at the onset of metastasis, and for the number of subsequent invasive fingers. Our active fluid model may help describe a wider range of biological processes, including wound healing and developmental patterning.

5.
Chem Soc Rev ; 45(24): 6698-6724, 2016 Dec 21.
Article in English | MEDLINE | ID: mdl-27510041

ABSTRACT

Nature has mastered the construction of nanostructures with well-defined macroscopic effects and purposes. Structural colouration is a visible consequence of the particular patterning of a reflecting surface with regular structures at submicron length scales. Structural colours usually appear bright, shiny, iridescent or with a metallic look, as a result of physical processes such as diffraction, interference, or scattering with a typically small dissipative loss. These features have recently attracted much research effort in materials science, chemistry, engineering and physics, in order to understand and produce structural colours. In these early stages of photonics, researchers facing an infinite array of possible colour-producing structures are heavily inspired by the elaborate architectures they find in nature. We review here the recent technological strategies employed to artificially mimic the structural colours found in nature, as well as some of their current and potential applications.


Subject(s)
Biomimetic Materials/chemistry , Color , Nanostructures/chemistry , Light , Molecular Structure , Optics and Photonics , Particle Size , Polymers/chemistry , Silicon Dioxide/chemistry , Surface Properties
6.
Phys Rev E ; 93(5): 052803, 2016 May.
Article in English | MEDLINE | ID: mdl-27300960

ABSTRACT

Interfacial thermodynamics has deep ramifications in understanding the boundary conditions of transport theories. We present a formulation of local equilibrium for interfaces that extends the thermodynamics of the "dividing surface," as introduced by Gibbs, to nonequilibrium settings such as evaporation or condensation. By identifying the precise position of the dividing surface in the interfacial region with a gauge degree of freedom, we exploit gauge-invariance requirements to consistently define the intensive variables for the interface. The model is verified under stringent conditions by employing high-precision nonequilibrium molecular-dynamics simulations of a coexisting vapor-liquid Lennard-Jones fluid. We conclude that the interfacial temperature is determined using the surface tension as a "thermometer," and it can be significantly different from the temperatures of the adjacent phases. Our findings lay foundations for nonequilibrium interfacial thermodynamics.

7.
Soft Matter ; 12(2): 562-73, 2016 Jan 14.
Article in English | MEDLINE | ID: mdl-26497051

ABSTRACT

When red blood cells (RBCs) move through narrow capillaries in the microcirculation, they deform as they flow. In pathophysiological processes such as sickle cell disease and malaria, RBC motion and flow are severely restricted. To understand this threshold of occlusion, we use a combination of experiment and theory to study the motion of a single swollen RBC through a narrow glass capillary of varying inner diameter. By tracking the movement of the squeezed cell as it is driven by a controlled pressure drop, we measure the RBC velocity as a function of the pressure gradient as well as the local capillary diameter, and find that the effective blood viscosity in this regime increases with both decreasing RBC velocity and tube radius by following a power-law that depends upon the length of the confined cell. Our observations are consistent with a simple elasto-hydrodynamic model and highlight the role of lateral confinement in the occluded pressure-driven slow flow of soft confined objects.


Subject(s)
Erythrocytes/cytology , Hemorheology , Pressure , Cell Adhesion , Hydrodynamics , Models, Biological
8.
Biophys J ; 103(9): 1909-18, 2012 Nov 07.
Article in English | MEDLINE | ID: mdl-23199919

ABSTRACT

Inspired by molecular mechanisms that cells exploit to sense mechanical forces and convert them into biochemical signals, chemists dream of designing mechanochemical switches integrated into materials. Using the adhesion protein fibronectin, whose multiple repeats essentially display distinct molecular recognition motifs, we derived a computational model to explain how minimalistic designs of repeats translate into the mechanical characteristics of their fibrillar assemblies. The hierarchy of repeat-unfolding within fibrils is controlled not only by their relative mechanical stabilities, as found for single molecules, but also by the strength of cryptic interactions between adjacent molecules that become activated by stretching. The force-induced exposure of cryptic sites furthermore regulates the nonlinearity of stress-strain curves, the strain at which such fibers break, and the refolding kinetics and fraction of misfolded repeats. Gaining such computational insights at the mesoscale is important because translating protein-based concepts into novel polymer designs has proven difficult.


Subject(s)
Fibronectins/chemistry , Microfibrils/chemistry , Amino Acid Motifs , Amino Acid Sequence , Biomechanical Phenomena , Molecular Dynamics Simulation , Molecular Sequence Data , Polymers , Protein Folding , Repetitive Sequences, Amino Acid
10.
Langmuir ; 27(22): 13796-805, 2011 Nov 15.
Article in English | MEDLINE | ID: mdl-21977962

ABSTRACT

Using computational modeling, we investigate the mechanical properties of polymeric materials composed of coiled chains, or "globules", which encompass a folded secondary structure and are cross-linked by labile bonds to form a macroscopic network. In the presence of an applied force, the globules can unfold into linear chains and thereby dissipate energy as the network is deformed; the latter attribute can contribute to the toughness of the material. Our goal is to determine how to tailor the labile intra- and intermolecular bonds within the network to produce material exhibiting both toughness and strength. Herein, we use the lattice spring model (LSM) to simulate the globules and the cross-linked network. We also utilize our modified Hierarchical Bell model (MHBM) to simulate the rupture and reforming of N parallel bonds. By applying a tensile deformation, we demonstrate that the mechanical properties of the system are sensitive to the values of N(in) and N(out), the respective values of N for the intra- and intermolecular bonds. We find that the strength of the material is mainly controlled by the value of N(out), with the higher value of N(out) providing a stronger material. We also find that, if N(in) is smaller than N(out), the globules can unfold under the tensile load before the sample fractures and, in this manner, can increase the ductility of the sample. Our results provide effective strategies for exploiting relatively weak, labile interactions (e.g., hydrogen bonding or the thiol/disulfide exchange reaction) in both the intra- and intermolecular bonds to tailor the macroscopic performance of the materials.


Subject(s)
Biomimetics , Models, Molecular , Polymers/chemistry , Hydrogen Bonding
11.
Nature ; 476(7358): 57-62, 2011 Aug 03.
Article in English | MEDLINE | ID: mdl-21814276

ABSTRACT

The developing vertebrate gut tube forms a reproducible looped pattern as it grows into the body cavity. Here we use developmental experiments to eliminate alternative models and show that gut looping morphogenesis is driven by the homogeneous and isotropic forces that arise from the relative growth between the gut tube and the anchoring dorsal mesenteric sheet, tissues that grow at different rates. A simple physical mimic, using a differentially strained composite of a pliable rubber tube and a soft latex sheet is consistent with this mechanism and produces similar patterns. We devise a mathematical theory and a computational model for the number, size and shape of intestinal loops based solely on the measurable geometry, elasticity and relative growth of the tissues. The predictions of our theory are quantitatively consistent with observations of intestinal loops at different stages of development in the chick embryo. Our model also accounts for the qualitative and quantitative variation in the distinct gut looping patterns seen in a variety of species including quail, finch and mouse, illuminating how the simple macroscopic mechanics of differential growth drives the morphology of the developing gut.


Subject(s)
Intestines/anatomy & histology , Intestines/embryology , Models, Anatomic , Models, Biological , Animals , Biomechanical Phenomena , Chick Embryo , Computer Simulation , Elasticity , Female , Finches/embryology , Mesentery/anatomy & histology , Mesentery/embryology , Mice , Quail/embryology , Rotation , Rubber
12.
Phys Rev E Stat Nonlin Soft Matter Phys ; 76(2 Pt 1): 021501, 2007 Aug.
Article in English | MEDLINE | ID: mdl-17930038

ABSTRACT

Video microscopy can be used to simultaneously track several microparticles embedded in a complex material. The trajectories are used to extract a sample of displacements at random locations in the material. From this sample, averaged quantities characterizing the dynamics of the probes are calculated to evaluate structural and/or mechanical properties of the assessed material. However, the sampling of measured displacements in heterogeneous systems is singular because the volume of observation with video microscopy is finite. By carefully characterizing the sampling design in the experimental output of the multiple particle tracking technique, we derive estimators for the mean and variance of the probes' dynamics that are independent of the peculiar statistical characteristics. We expose stringent tests of these estimators using simulated and experimental complex systems with a known heterogeneous structure. Up to a certain fundamental limitation, which we characterize through a material degree of sampling by the embedded probe tracking, these estimators can be applied to quantify the heterogeneity of a material, providing an original and intelligible kind of information on complex fluid properties. More generally, we show that the precise assessment of the statistics in the multiple particle tracking output sample of observations is essential in order to provide accurate unbiased measurements.

13.
Soft Matter ; 3(9): 1194-1202, 2007 Aug 14.
Article in English | MEDLINE | ID: mdl-32900041

ABSTRACT

Hydrogels formed from the self-assembly of oligopeptides are being extensively studied for biomedical applications. The kinetics of their gelation, as well as a quantitative description of the forces controlling the rate of assembly has not yet been addressed. We report here the use of multiple particle tracking to measure the self-assembly kinetics of the model peptide FKFEFKFE (KFE8). KFE8 forms well-defined ß-sheet intermediates and is often used as a model peptide system that forms a fibrous network in aqueous solvent. We find that increasing the pH of this system from 3.5 to 4.0 decreases the time of KFE8 gelation by almost hundredfold, from hours to minutes. A remarkable self-similarity between measurements performed at different pH suggests that, although accelerated by the pH increase, gelation follows an invariable mechanism. We propose a semi-quantitative interpretation for the order of magnitudes of gelation time using a simple model for the interaction driving the self-assembly in terms of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Such understanding is important for the development of current and future therapeutic applications ( drug delivery).

14.
Phys Rev E Stat Nonlin Soft Matter Phys ; 71(4 Pt 1): 041106, 2005 Apr.
Article in English | MEDLINE | ID: mdl-15903656

ABSTRACT

The role of a finite exposure time sigma on measuring rheological properties using microrheology techniques is theoretically investigated. We concentrate on studying fluid models displaying a plateau in the mean-squared displacement (MSD) of the embedded probe particle. A model is developed to compare the resulting experimentally measured MSD of the particle to its expected value in the fluid model. A plateau MSD is greatly modified in a measurement when sigma is greater than the plateau onset time. Moreover, apparent dynamics drastically differ from the true dynamics at frequencies omega less than or approximately equal sigma(-1) . These results quantify when and how a finite exposure time effects the measured MSD of a probe particle which can then alter the extracted rheological properties and physical interpretations.

15.
Biophys J ; 88(1): 623-38, 2005 Jan.
Article in English | MEDLINE | ID: mdl-15533928

ABSTRACT

Particle tracking techniques are often used to assess the local mechanical properties of cells and biological fluids. The extracted trajectories are exploited to compute the mean-squared displacement that characterizes the dynamics of the probe particles. Limited spatial resolution and statistical uncertainty are the limiting factors that alter the accuracy of the mean-squared displacement estimation. We precisely quantified the effect of localization errors in the determination of the mean-squared displacement by separating the sources of these errors into two separate contributions. A "static error" arises in the position measurements of immobilized particles. A "dynamic error" comes from the particle motion during the finite exposure time that is required for visualization. We calculated the propagation of these errors on the mean-squared displacement. We examined the impact of our error analysis on theoretical model fluids used in biorheology. These theoretical predictions were verified for purely viscous fluids using simulations and a multiple-particle tracking technique performed with video microscopy. We showed that the static contribution can be confidently corrected in dynamics studies by using static experiments performed at a similar noise-to-signal ratio. This groundwork allowed us to achieve higher resolution in the mean-squared displacement, and thus to increase the accuracy of microrheology studies.


Subject(s)
Biophysics/methods , Algorithms , Diffusion , Elasticity , Microscopy, Video/methods , Models, Molecular , Models, Statistical , Models, Theoretical , Normal Distribution , Oscillometry , Photons , Reproducibility of Results , Time Factors , Water/chemistry
16.
Arq. bras. cardiol ; 47(2): 97-100, ago. 1986. tab, ilus
Article in Portuguese | LILACS | ID: lil-38702

ABSTRACT

Valvuloplastia aórtica transluminar percutânea (VTP) foi realizada em 10 pacientes de 68 a 85 anos (média 78), com estenose aórtica calcificada. O gradiente transvalvar aórtico diminuiu, em média, de 50 mmHg + ou - 17 (p < 0,001) e foi de 33 mmHg depois da VTP. A superfície valvar aórtica era, em média, no início, de 0,38 + ou - 0,10 cm2, e passou a 0,78 + ou - 0,12 cm2, depois da VTP. O débito cardíaco aumentou de 4,28 + ou - 1,12 l/min para 4,81 + ou - 1,23 l/min, depois da VTP. Um dos pacientes faleceu em decorrência de problemas ligados à via de acesso do cateter munido de baläo. A VTP parece uma alternativa válida do tratamento da estenose aórtica grave nos pacientes idosos


Subject(s)
Humans , Male , Female , Aged , Aortic Valve Stenosis/therapy , Angioplasty, Balloon , Aged, 80 and over , Cardiac Output , Age Factors , Angioplasty, Balloon/mortality
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