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Surface Tension: The force acting on the surface of a liquid, tending to minimize the area of the surface. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)


JoVE 10673

Cohesion is the attraction between molecules of the same type - such as water molecules. The partially charged negative oxygen of one water molecule binds to the partially charged positive hydrogen of a second water molecule via hydrogen bonding. Each water molecule can form up to four hydrogen bonds with other water molecules.

On a surface, when multiple water molecules come together through cohesion, a droplet is formed. Water does not typically spread out across the surface. This is because the water molecules are more attracted to each other than to molecules that make up the surface or the surrounding air. Surface tension results from cohesion. Pond skaters, also known as water striders, are insects that use this phenomenon to walk on water. Surface tension occurs at the interface between water and air (i.e., the water’s surface). Again, water molecules are more attracted to each other than they are to molecules in the air. Thus, the water molecules at the surface form bonds with neighboring water molecules beside and below them. Since the surface water molecules cannot form bonds with other water molecules on one side (the side next to the air), they form stronger bonds with their neighboring water molecules. The strongly-bonded molecules have a compressed surface area, creating spherical droplets of water molecules. The high surface tension of

 Core: Chemistry of Life


JoVE 10882

The process of breathing, inhaling and exhaling, involves the coordinated movement of the chest wall, the lungs, and the muscles that move them. Two muscle groups with important roles in breathing are the diaphragm, located directly below the lungs, and the intercostal muscles, which lie between the ribs. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity and creating more room for the lungs to expand. When the intercostal muscles contract, the ribs move upward and the rib cage expands, similarly expanding the thoracic cavity. Each lung is surrounded by two membranes called plurae, which are separated by fluid. This fluid creates an adhesive force that causes the lungs to stretch as the thoracic cavity expands. The increased volume in the lungs reduces the pressure. When the pressure drops below atmospheric pressure, this produces a pressure gradient that moves air from the higher-pressure atmosphere into the lower-pressure lungs. When the diaphragm and intercostal muscles relax, the volume of the lungs decreases, increasing the pressure in the lungs. As pressure increases beyond atmospheric pressure, the resulting pressure gradient pushes air out of the body. In this way, the cycle of inhaling and exhaling is maintained. Boyle’s law states that, at a given temperature in a closed space, the press

 Core: Circulatory and Pulmonary Systems

Hydrogen Bonds

JoVE 10666

Hydrogen bonds are weak attractions between atoms that have formed other chemical bonds. One of these atoms is electronegative, like oxygen, and has a partial negative charge. The other is a hydrogen atom that has bonded with another electronegative atom and has a partial positive charge.

Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are unequally shared. The other atom pulls the electrons to itself, sharing them with the hydrogen atom a smaller amount of the time. This gives the hydrogen atom a partial positive charge, causing it to be attracted to atoms with a partial negative charge. The cumulative effect of these weak bonds is life-altering, endowing water with high heat capacity, high heat of vaporization, ability to dissolve polar molecules, adhesion, cohesion, and strong surface tension.

 Core: Chemistry of Life

Porosimetry of a Silica Alumina Powder

JoVE 10383

Source: Kerry M. Dooley and Michael G. Benton, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA

Surface area and pore size distribution are attributes used by adsorbent and catalyst manufacturers and users to ensure quality control and to determine when products are at the end of their useful lives. The…

 Chemical Engineering

Buoyancy and Drag on Immersed Bodies

JoVE 10392

Source: Alexander S Rattner and Sanjay Adhikari; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA

Objects, vehicles, and organisms immersed in fluid mediums experience forces from the surrounding fluid in the form of buoyancy- a vertical upward force due to fluid weight,…

 Mechanical Engineering

Determination of Moisture Content in Soil

JoVE 10011

Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - Arizona University
Demonstrating Author: Bradley Schmitz

Soils normally contain a finite amount of water, which can be expressed as the “soil moisture content.” This moisture exists within the pore spaces in between soil aggregates (inter-aggregate pore space) …

 Environmental Microbiology

Electrospinning of Silk Biomaterials

JoVE 5798

Silk fibers have been processed and used to create fabrics and threads for centuries. However, the solubilizing of silk fibers, thereby turning it into a versatile pre-polymer solution is a much newer technology. Solubilized silk can be processed in many different ways to create a biocompatible material with controllable mechanical properties.


The Effect of Reflux Ratio on Tray Distillation Efficiency

JoVE 10432

Source: Kerry M. Dooley and Michael G. Benton, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA

Tray and packed columns are both commonly used for distillation, absorption, and stripping separation operations.1,2 The goal of this experiment is to distill a mixture of alcohols (methanol, isopropanol) and water …

 Chemical Engineering

Degassing Liquids with Freeze-Pump-Thaw Cycling

JoVE 5639

Source: Laboratory of Dr. Neil Branda — Simon Fraser University

Degassing refers to the process by which dissolved gases are removed from a liquid. The presence of dissolved gases such as oxygen or carbon dioxide can impede chemical reactions that utilize sensitive reagents, interfere with spectroscopic measurements, or can…

 Organic Chemistry

Drosophila Larval IHC

JoVE 5106

Immunohistochemistry (IHC) is a technique used to visualize the presence and location of proteins within tissues. Drosophila larvae are particularly amenable to IHC because of the ease with which they can be processed for staining. Additionally, the larvae are transparent, meaning that some tissues can be visualized without the need for dissection.

In IHC, proteins are…

 Biology I

Using a Hemacytometer to Count Cells

JoVE 5048

Many biomedical experiments require manipulation of a known quantity of cells, in order to achieve accurate, reproducible, and statistically-relevant data. Therefore, learning how to count cells is a particularly essential technique for any successful biomedical scientist. The most common way to count cells is by using a hemacytometer - an instrument that bears two laser-etched grids, which…

 Basic Methods in Cellular and Molecular Biology

Introduction to the Spectrophotometer

JoVE 5038

The spectrophotometer is a routinely used instrument in scientific research. Spectrophotometry is the quantitative measurement of how much a chemical substance absorbs light by passing a beam of light through the sample using a spectrophotometer.

In this video, basic concepts in spectrophotometry, including transmittance, absorbance and the Beer-Lambert Law …

 General Laboratory Techniques

Understanding Concentration and Measuring Volumes

JoVE 5026

Solutions are utilized to some degree in almost all biological research applications. Therefore understanding how to measure and manipulate them is imperative to any experiment. In this video, concepts in preparing solutions are introduced.

Solutions consist of a solute dissolved in solvent to yield a homogeneous mixture of molecular substances. …

 General Laboratory Techniques

Pulling Membrane Nanotubes from Giant Unilamellar Vesicles

1Laboratoire Physico Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, 2Department of Genetics and Complex Diseases, T. H. Chan School of Public Health, Harvard Medical School, 3Department of Cell Biology, Harvard Medical School, 4Sorbonne Universités, UPMC University Paris 06, 5Center for Studies in Physics and Biology, The Rockefeller University

JoVE 56086


Covalent Immobilization of Proteins for the Single Molecule Force Spectroscopy

1Center for Applied Tissue Engineering and Regenerative Medicine, Munich University of Applied Sciences, 2FG Protein Biochemistry & Cellular Microbiology, Munich University of Applied Sciences, 3Center for Nano Science, Ludwig-Maximilians-Universität München, 4Klinik für Unfallchirurgie, Orthopädie und Plastische Chirurgie, University Medical Center Göttingen

JoVE 58167


Patterning the Geometry of Human Embryonic Stem Cell Colonies on Compliant Substrates to Control Tissue-Level Mechanics

1Graduate Program in Bioengineering, University of California San Francisco and University of California Berkeley, 2Center for Bioengineering and Tissue Regeneration, Department of Surgery, University of California San Francisco, 3Department of Mechanical Engineering, University of California Berkeley, 4Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, University of California San Francisco, 5UCSF Comprehensive Cancer Center, Helen Diller Family Cancer Research Center, University of California San Francisco, 6Department of Anatomy, Department of Bioengineering and Therapeutic Sciences, and Department of Radiation Oncology, University of California San Francisco

JoVE 60334


Polymer Microarrays for High Throughput Discovery of Biomaterials

1Laboratory of Biophysics and Surface Analysis, University of Nottingham, 2School of Molecular Medical Sciences, University of Nottingham, 3David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology

JoVE 3636


The Subventricular Zone En-face: Wholemount Staining and Ependymal Flow

1Department of Neurosurgery, The Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, University of California, San Francisco - UCSF, 2Department of Pathology and Cell Biology, College of Physicians and Surgeons, Columbia University, 3Department of Neuroscience and Neurology, College of Physicians and Surgeons, Columbia University, 4Department of Developmental and Regenerative Biology, Nagoya City University Graduate School of Medical Sciences, 5Center for Motor Neuron Biology and Disease, College of Physicians and Surgeons, Columbia University

JoVE 1938


Construction of Defined Human Engineered Cardiac Tissues to Study Mechanisms of Cardiac Cell Therapy

1Cardiovascular Research Center, Icahn School of Medicine at Mount Sinai, 2The Mindich Child Health and Development Institute, Icahn School of Medicine at Mount Sinai, 3Stem Cell & Regenerative Medicine Consortium, LKS Faculty of Medicine, University of Hong Kong

JoVE 53447


An Enzyme- and Serum-free Neural Stem Cell Culture Model for EMT Investigation Suited for Drug Discovery

1Dept. of Biomedicine, Pharmacenter, University of Basel, 2Molecular Signalling and Gene Therapy, Narayana Nethralaya Foundation, Narayana Health City, 3Brain Ischemia and Regeneration, Department of Biomedicine, University Hospital Basel, 4Department of Neurosurgery, Klinikum Idar-Oberstein, 5Department of Neurosurgery and Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, 6Department of Neurology, Laboratory of Molecular Neuro Oncology, University Hospital of Zurich

JoVE 54018

 Developmental Biology

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

1Center for Free Electron Laser Science, DESY, 2Department of Physics, University of Hamburg, 3Institute for Biochemistry and Molecular Biology, Laboratory for Structural Biology of Infection and Inflammation, University of Hamburg, 4The Hamburg Center for Ultrafast Imaging, University of Hamburg, 5Integrated Biology Infrastructure Life-Science Facility at the European XFEL (XBI), 6European Molecular Biology Laboratory, EMBL c/o DESY, 7Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry

JoVE 57133


Characterizing Multiscale Mechanical Properties of Brain Tissue Using Atomic Force Microscopy, Impact Indentation, and Rheometry

1Department of Materials Science and Engineering, Massachusetts Institute of Technology, 2Department of Biological Engineering, Massachusetts Institute of Technology, 3Department of Mechanical Engineering, Massachusetts Institute of Technology, 4Department of Neurology, The F.M. Kirby Neurobiology Center, Boston Children’s Hospital, Harvard Medical School

JoVE 54201


Chronic Implantation of Multiple Flexible Polymer Electrode Arrays

1Medical Scientist Training Program and Neuroscience Graduate Program, University of California San Francisco, 2Kavli Institute for Fundamental Neuroscience, Center for Integrative Neuroscience, and Department of Physiology, University of California San Francisco, 3Bioengineering Graduate Program, University of California San Francisco, 4Center for Micro- and Nanotechnology, Lawrence Livermore National Laboratory, 5Neuralink Corp., 6Howard Hughes Medical Institute

JoVE 59957


Assembly and Characterization of Biomolecular Memristors Consisting of Ion Channel-doped Lipid Membranes

1Joint Institute for Biological Sciences, Oak Ridge National Laboratory, 2Department of Mechanical, Aerospace and Biomedical Engineering, University of Tennessee, 3Bredesen Center for Interdisciplinary Research, University of Tennessee, 4Department of Biosystems and Agriculture Engineering, University of Kentucky, 5Department of Electrical Engineering and Computer Science, University of Tennessee, 6Computer Science and Mathematics Division, Oak Ridge National Laboratory, 7Center for Nanophase Materials Sciences, Oak Ridge National Laboratory

JoVE 58998

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