Endogenous means relating to or produced by metabolic synthesis in the body.

Tamoxifen is an estrogen receptor antagonist.

Although microglia do not form in mice lacking a CSF-1 receptor, they are present in mice with a mutation in the CSF-1 gene that codes for the ligand.

As it turns out, presence of another ligand IL-34 (cytokine interleukin 34) is sufficient to activate CSF-1R on microglial cells to compensate for the loss of CSF-1. In contrast, some tissue macrophages fail to form in mice with a mutated ligand.

The op/op (osteopetrotic) mutant mouse possesses an inactivating mutation in the colony-stimulating factor-1 (CSF-1) gene, which results in the absence of certain macrophages, including defective osteoclasts (macrophages of the bone), resulting in osteopetrosis.

Osteopetrosis ("marble bone disease") is an extremely rare inherited disorder whereby the bones become thick, but their increased size does not improve their strength. Instead, their disordered architecture results in weak and brittle bones.

CSF-1R is required for the development of yolk sac macrophages and microglia.

A gate is a numerical or graphical boundary that can be used to define the characteristics of cells.

Both yolk sac macrophages and microglia depend on the presence of CSF-1R receptor on their surface for their differentiation. Absence of this receptor did not affect development of circulating monocytes.

This suggests that CSF-1R expression is not essential for monocyte differentiation outside the central nervous system (CNS).

However, it does not exclude the possibility that monocytes require CSF-1R after they enter the CNS and could serve as microglial precursors.

It was shown that the expression of colony stimulating factor-1 ligand (CSF-1) and its receptor CSF-1R is a prerequisite for the differentiation of macrophages in the adult animal.

Similarity in phenotype between two cell types suggests they have common origin.

During embryogenesis, the three germ layers (endoderm, mesoderm, and ectoderm) are formed, from which all body tissues will later develop.

Neuroepithelium is the part of the embryonic ectoderm that gives rise to the nervous system .

Cephalic means relating to the head or the head end of the body. From the Latin "cephalicus," and from the Greek "kephalikos," meaning head.

The head mesenchyme is a type of undifferentiated connective tissue, which primarily originates from a mixture of cranial neural crest and head mesoderm cells.

These cells eventually give rise to the skeletal elements (skull and facial bones), connective tissue, and musculature of the vertebrate head.

To be able to detect myeloid cells expressing the CX3CR1 receptor (aka fractalkine receptor) in the brain, the authors used a reporter mouse with an inserted, or knocked in, gene that codes for a green fluorescent protein in the locus of CX3CR1 gene. This way, every time the CX3CR1 gene is expressed, the cell fluoresces in green color.

Read more here about how specific genes are targeted:

http://studentreader.com/gene-targeting/

Yolk sac is a membranous sac of most vertebrates that encloses the yolk. It is attached in most animals (as in humans) through the yolk stalk with the intestinal cavity of the embryo, and is supplied with blood vessels that transport nutritive yolk products to the developing embryo.

Located outside an embryo.

Being able to survival high radiation levels.

Using parabiotic models, previous research showed that cells from the bone marrow and those that are circulating in the blood are not able to enter the brain in the absence of irradiation, which causes inflammation and disrupts the blood-brain barrier (BBB). In addition, intravenous injection of bone marrow cells in the circulation creates a pool of bone marrow cells that are not present in the blood under natural conditions, increasing their chances of reaching the brain.

This indicated that previous findings reporting that monocytes enter the brain and differentiate into microglia in the adult brain could be attributed either to the loss of the BBB integrity in irradiated animals or increased numbers of bone marrow cells in the blood, or both.

Previous reports showed that in parabiotic mice recruitment of monocytes by the recipient mouse was more limited than the recruitment of B and T cells.

Read more about parabiotic mice here:

http://www.jove.com/video/50556/parabiosis-in-mice-a-detailed-protocol

Research of microglial turnover in adulthood used irradiation for bone marrow reconstitution and produced conflicting results: Some authors suggested that, similarly to the perinatal period, monocytes circulating in the blood can contribute to microglial turnover in the adult brain, whereas others found no influx of blood precursors into the brain in an adult animal.

Bone marrow is the soft, organic, spongelike material in the cavities of bones. It is a network of blood vessels and special connective tissue fibers that hold together a composite of fat and blood-producing cells.

Its chief function is to manufacture blood cells including erythrocytes, leukocytes, and platelets.

In contrast to this paper's and other recent findings, early research of microglial origin in the brain indicated that microglia arise from blood monocytes that migrate into the brain around the time of birth and continue influx throughout the adult life, replacing embryonic microglia and contributing to microglial pool in adulthood.

Leukocytes encompass all white blood cells, including monocytes, lymphocytes, granulocytes, and macrophages

Congenic bone marrow chimeras are mice that are genetically identical with the exception of one gene.

The authors exposed recipient C57BL/6 newborn mice to a slightly less than lethal dose of irradiation to obliterate their developing bone marrow and any blood cell progenitors present outside the bone marrow such as in the fetal liver or spleen. They then restored their bone marrow and hematopoietic system by injecting bone marrow cells or fetal liver cells that contained hematopoietic progenitors from the donor mice.

The donor mice were genetically identical to the recipient mice with the exception of the CD45 allele (CD45.1), which codes for a transmembrane protein expressed on all white blood cells.

Using flow cytometry the authors were able to distinguish resident CD45.2+ (positive, or expressing) cells from donor CD45.1+ cells stained with an allele-specific antibody.

http://www.jove.com/video/4208/differentiating-functional-roles-gene-expression-from-immune-non

Hematopoeisis refers to the process of production and differentiation of all blood cell types .

A hematopoietic wave is an influx of cells that can originate from different sites of hematopoiesis such as the yolk sac, the fetal liver, and the bone marrow, or from the same site at different times under certain conditions (e.g., inflammation).

Time immediately before or after birth.

As opposed to polynuclear phagocytes (ex.: neutrophils), monocytes, macrophages. and dendritic cells have one nucleus and are called mononuclear phagocytes.

Ontogeny refers to the complete developmental history of an individual organism, or, here in this study, of a cell population.

Myeloid cells are differentiated descendants of common myeloid progenitors of hematopoietic stem cells in the bone marrow. They include granulocytes, monocytes, macrophages, and dendritic cells.

Initially, the adjective“myeloid” defined cells related or derived from the bone marrow. However, it also defines cells that are not “lymphoid,” i.e., cells related to lymphocytes that include T and B cells, as well as NK cells and innate lymphoid cells.

Performed in a living organism, from the Latin for "within the living."

Lineage tracing is the identification of all progeny, i.e., descendants, of a defined cell population or a single cell.

Homeostasis is the state of balance or equilibrium from the Greek "homœos," meaning "similar," and "stasis," meaning "standing still."

Hematopoietic cells are all blood cells that derive from hematopoietic stem cells present in the adult bone marrow.

Pathogenesis refers to the cause or origin of the pathology of a disease.

Macrophages are a type of white blood cell.

As scavengers of the immune system, macrophages engulf and destroy self-antigens, foreign pathogens (such as bacteria and viruses), cancer cells, and other cellular debris via a process called phagocytosis.

Microglia are a type of glial cell that are the resident macrophages of the brain and spinal cord, and thus act as the first and main form of active immune defense in the central nervous system.

The Next Generation Science Standards, LS1.C: Organization for Matter and Energy Flow in Organisms

Guiding question: How do organisms obtain and use the matter and energy they need to live and grow?

http://www.nap.edu/read/13165/chapter/10#147

The Next Generation Science Standards, LS1.D: Information Processing

Guiding question: How do organisms detect, process, and use information about the environment?

http://www.nap.edu/read/13165/chapter/10#149

The Next Generation Learning Standards, Crosscutting Concept 2: Cause and Effect

http://www.nap.edu/openbook.php?record_id=13165&page=88

The Next Generation Science Standards, LS1.A: Structure and Function

Guiding question: How do the structures of organisms enable life's functions?

http://www.nap.edu/openbook.php?record_id=13165&page=144

The cerebral vasculature is the collection of blood vessels that supplies blood to the brain.

There are two types of cerebral vasculature: anterior and posterior, which supply blood to the front and back portions of the brain, respectively.

The arteries carry oxygenated blood with glucose and other nutrients; whereas the veins carry deoxygenated blood back to the heart.

Similar to this study, which showed that a young systemic factor could improve neurogenesis in old mice, Sinha et al. 2014 tested the same concept in muscle.

Exposure of GDF-11 in old mice led to improved muscle structure, restored genomic integrity in adult muscle stem cells, increased strength, and increased capacity for exercise.

This study, conducted in 1999, was one of the first to study the effects of age on brain networks. At the time, little was known about the relationship between age and brain mechanisms of changes in memory.

This study showed that age is related to changes in verbal memory, and not picture memory.

Neurogenesis is restricted to two main areas of the brain (subventricular zone and dentate gyrus) by precursor cell proliferation and differentiation. BM88/Cend1 is a neuronal lineage specific regulator. In this study, Katsimpardi et al. studied the effects of this regulator in postnatal neurogenesis.

They found that BM88 is important for cell cycle control and neuronal differentiation in the neonatal subventricular zone, in the transition from neuroblast to mature neurons in mouse brains.

Here, the authors study the subventricular zone (SVZ) to investigate the decline in neurogenesis during aging. By conducting electron microscopy imaging, and labeling cells, they examine the cytoarchitecture of the SVZ.

They found a specific dorsolateral aspect of the SVZ, which retains features of a neurogenic stem cell niche in elderly mice.

This study shows the effects of systemic factors on the decline of age-related neurogenesis. They found that chemokines CCL1/Eotaxin is present in aging mice, and is associated with reduced neurogenesis. Similar to this Katsimpardi et al. study, increasing the levels of the blood-borne factor CCL1 in young mice led to decreased neurogenesis and impaired learning and memory.

Exposure to an enriched environment increases neurogenesis in adult mice. Examples of enriched environments include larger housing, voluntary exercise, social interactions, and learning opportunities. Enhanced neurogenesis in enriched environments is also linked to improved spatial memory capabilities.

This study shows that voluntary exercise alone can improve enhanced neurogenesis in adult mice.

Here, endothelial cells were identified as critical components of the neural stem cell niche.

Factors derived from endothelial cells promote neural stem cell self-renewal and promotes neurogenesis.

The possibility of introducing systemic factors present in young blood to remodel vasculature and increase neurogenesis is an exciting prospect for many neurodegenerative disorders.

Treatment with GDF11, along with other key factors, may be able to reverse numerous detrimental effects associated with the decline of neural activity.

Learn more about a new scientific initiative, which uses physics to design a method of measuring neural activity in the brain, in this Science News story:

http://www.sciencemag.org./content/344/6187/954.full

The microvascular network is the vasculature consisting of small blood vessels (diameter less than 100 microns). A large amount of oxygen is supplied throughout the brain by these networks.

GDF11, is a key systemic factor that contributes to neurogenesis and declines with increased age. However, exposing this circulating factor in old mice improves vascular remodeling and increases neural stem cell populations.

This Science Perspective provides a review about the process of neurogenesis in the hippocampal dentate gyrus:

http://www.sciencemag.org./content/339/6127/1534.full.pdf?sid=ca66d276-ff72-4c2a-8db8-4b174aa4ee06

The authors conducted an in vitro experiment to test the specific downstream effects of GDF11. They treated brain capillary endothelial cells with GDF11, as well as a TGF-beta inhibitor, for 6 days.

GDF11-treated cells did not increase cell proliferation in the presence of the inhibitor.

This indicates that GDF11 acts directly on the TGF-beta SMAD pathway, in order to have an effect on blood vessels.

SMAD proteins are signaling molecules located in the cytoplasm of a cell.

Phosphorylation of SMAD proteins indicates the activation of these proteins.

Activated SMADs lead to a cascade of signaling events for gene transcription in the nucleus to regulate diverse biological functions.

The BMP/TGF-beta signaling pathway has an important role in cell growth, differentiation, and development of biological systems.

Pericytes are contracting cells that wrap around endothelial cells in the blood vessels. These cells are capable of constricting blood vessels.

The young mice were transgenic for green fluorescent protein, so all the cells of the young mice were green. The authors didn't see any green blood vessels in the old mice, meaning that the endothelial progenitor cells didn't travel from the young mice to the old.

Green fluorescent protein is a fluorescent protein marker used to tag a protein of interest, allowing visualization of movement of the protein of interest.

Endothelial progenitors are a rare population of cells in the blood that give rise to endothelial cells. Endothelial cells form the lining of blood vessels.

In addition to the formation of new blood vessels in the vascular nervous system, the formation of new neurons is an interesting area of neuroscience research.

Read more in Science Magazine:

http://www.sciencemag.org/news/2003/06/another-fountain-new-neurons-found

Compared to young adults, old adults had less regional cerebral blood flow associated with a delayed response. Therefore, a reduction in cerebral blood flow is associated with increased age in certain regions of the brain.

Magnetic resonance imaging (MRI) is a radiological imaging technique to observe the anatomy and physiology of the body. MRI uses magnetic fields and radiowaves (there is no ionizing radiation) to form images of the body.

Currently, MRI is considered to be the better method (compared with CT scans) for brain imaging.

Typically, an angiogram is an imaging test that uses x-rays to visualize blood vessels in the body. In this case the word "angiogram" is used to denote the 3D reconstruction of the z-stacks. They did not do x-rays.

To measure the volume of blood vessels, and to create an "angiogram," the authors imaged mouse blood vessels on a confocal microscope and captured z-plane stacks over the total thickness of the section. The z-stacks were added to create 3D angiograms for calculation of total blood vessel volume.

Cerebrovasculature refers to the blood vessels in the brain, especially the arteries that supply blood to the brain.

An increased sense of smell.

Because heterochronic old (Het-O) mice and isochronic young mice indicated similar levels of high smell sensitivity in the olfaction assay, this indicates that Het-O mice have increased functional olfaction due to being exposed to young systemic factors.

The goal of this experiment is to test any difference in sensitivity of smell between heterochornic old, isochronic old, and young mice. If there is a change in smell sensitivity, this is due to increased neurogenesis.

Bromodeoxyuridine (BrdU) is a synthetic nucleoside that is incorporated into DNA of replicating cells.

NeuN+ denotes neuronal nuclei.

The authors use BrdU and NeuN double-positive staining to identify and track newborn neurons in hetero-chronic old mice.

This is an in vivo study to complement the results of increased neurogenesis observed in their in vitro study (Fig. 1). The in vitro study is in the supplemental data.

There are three types of neurons in the central nervous system: sensory neurons, interneurons, and motor neurons.

Interneurons enable communication between sensory and motor neurons.

Rostral and caudal are directionality terms used for the brain.

Rostral, or anterior, refers to the front end (near nose) and caudal, or posterior, refers to the back end.

Neural stem cells differentiate into neuroblasts. A neuroblast is a dividing cell, which gives rise to a neuron.

Exposure of old mice to young systemic factors restores the neurogenic potential of neural stem cells and increases their ability to proliferate and differentiate into neurons in the olfactory bulb.

The authors of reference 10 studied the decline of neurogenesis caused by blood-borne factors present in old mice.

They created heterochronic parabiosis mice between young-old mice, and observed that systemic factors from old mice caused a decrease in synaptic plasticity of neurons, as well as a decline in spatial learning and memory skills in young mice.

The hippocampus is a C-shaped structure in the brain that functions for learning, memory, and spatial navigation.

The dendate gyrus is a subsection of the hippocampus. Neurogenesis also occurs in the dentate gyrus of the hippocampus.

Ki67 is a cellular marker for proliferating cells.

Sox2 is a transcription factor that marks stem cells.

Olig2 is a transcription factor that is a marker for progenitor cells. Progenitor cells give rise to differentiated cells.

The brain can be sectioned into three different planes called coronal, sagittal, and horizontal/axial.

Coronal sections are vertical dissections, similar to slices from a loaf of bread.

The authors report a novel finding of the possibility of reversing and remodeling the neural stem niche of old mice, by exposing them to systemic factors present in young mice.

The authors report a novel finding of the possibility of reversing and remodeling the neural stem niche of old mice, by exposing them to systemic factors present in young mice.

Reference 13 describes a study similar to the one described in this paper, where heterochronic parabiotic mouse pairs were generated between young and old mice, to discover a reversal in the process of age-related cardiac hypertrophy.

In this study, they observed a dramatic reduction in cardiac hypertrophy in old mice, due to being exposed to a blood-borne factor in young mice. In order to identify the special systemic factor, they profiled the proteome of young mice, and found that GDF11 declines with age, and exposure to GDF11 in old mice restored age-related cardiac hypertrophy.

The subventricular zone is located in the walls of the lateral ventricles. This zone is one of the two main sites of neurogenesis in the adult mammalian brain. The lateral ventricles contain cerebrospinal fluid and are part of the ventricular system in the body.

Parabiosis means “living beside.” Parabiosis can be between animals of different strains or different weight, age, or any other parameter.

In this study, parabiosis is the process of sewing an old mouse and a young mouse together so they share one vascular system.

Heterochronic parabiosis is when parabiosis is performed between animals of different ages. Isochronic is same age.

Chemokines are chemical signaling molecules secreted by cells that induce changes in signaling pathways of another neighboring cell(s).

'Re-wiring' of neuronal synaptic connections in oder to adapt to environmental changes.

Neurogenic potential is the ability to generate mature neurons for the process of neurogenesis.

Reference 6 studies the effects of stress and anxiety on neurogenesis.

Here, they found that a small subset of neurons in the dentate gyrus, which is responsible for the negative control of the hypothalamic-pituitary-adrenal axis. Elevation of stress hormones and anxiety are correlated with decreased neurogenesis.

In reference 4, the authors recapitulate a mouse model of Alzheimer's disease and find that calorie restriction for 4 months could increase the expression of neurogenesis-related genes and decrease inflammatory-related genes in the hippocampus of these mice.

Proliferation refers to the continuous division of a cell, and differentiation is the process where a stem cell acquires a specialized cell fate.

Neurovascular diseases occur from sudden blockage of the normal blood flow to the brain or deterioration of the vasculature.

Examples include ischemic strokes or brain aneurysms.

Neurodegenerative diseases result primarily in the loss of function and death of neurons leading to progressive loss of structure in a region of the brain.

Examples include amyotrophic lateral sclerosis, Parkinson’s, and Huntington disease.

Vascular remodeling is the process of altering the 3D structure and architecture of blood vessels.

Generation of neurons from neural stem cells and neural progenitor cells.

Neural stem cells are cells that are able to self-renew, and are capable of differentiating into any cell type in the central nervous system.

A specialized microenvironment favorable to the regulation of stem cells in the nervous system.

The central nervous system is a complex network of nerve tissues that control functions of the body. It consists of the brain and spinal cord.

SitC, but again won't change the meaning of the post

I would describe this as an "educational resource"

This should be in italics, Science in the Classroom, but it won't change the meaning of your post if not.

Instead of coating the base polymer lattice after microstereolithography, nanoparticles can be added to the resin bath and thus create ceramic lattices.

The authors created solid alumina ceramic lattices by using a resin bath containing alumina nanoparticles.

The elastic properties of cellular materials with random porosity degrade when the density decreases. This is because of a nonlinear relationship between strength and density.

That is why, in this paper, the authors proposed materials with a linear relationship, which maintain mechanical performance for a broad range of densities.

Cellular materials (materials with a significant amount of porosity) present a number of properties (namely low weight, high sound absorption, crashworthiness, high permeability, thermal properties) that make them suitable for a large range of applications.

Metamaterials are a class of objects whose properties are related to the geometrical properties of the constituting structure and not to the mechanical properties of the constituting material.

These metamaterials present properties not obtained with regular materials.

This article reports the design of the high-resolution projection microstereolithography technique used by the authors.

This technique is used in the present article to manufacture the different cellular solids (see Fig.2 A).

The authors of this article investigated the compressive behavior of a random cell structure, a metallic foam.

This structure was also manufactured by the authors of the present article and served for comparison purposes against the new ultralight and ultrastiff structures.

This book presents the basic theory and tools needed to study the behavior of elastic structures.

The goal of this article is to analyze the properties of the octet-truss unit cell using mechanical theory, simulations, and experiments.

The octet-truss unit cell is the basic building block chosen by the authors of the present article to design their ultralight and ultrastiff materials.

In this article, the authors explain the process of manufacturing an ultralight fractal structure to obtain either hollow or solid objects. The potential applications are described.

This chapter of a book describes the processing and the properties of a specific cellular class of solids: the metallic honeycombs.

This text reviews the contents of a special issue of the MRS bulletin, dedicated to cellular solids.

This article describes the behavior of nanoporous silica aerogels: these objects are super compressible for ultralow densities.

In this article, the authors have fabricated ultralight metallic microlattices and have performed mechanical testing on these objects.

The elasticity of this material is proportional to the square of the density.

Hence, the linear law desired by the authors of the present paper is not reached in this article.

This book about cellular solids summarizes the theory needed to understand the structural properties and the mechanical behavior of cellular solids.

The applications of these kinds of materials are also reviewed.

In this article, the authors report the design of a new biocompatible material in the vascular tissue engineering field.

This article describes the use of carbon microlattices as a catalyst support for chemistry applications.

This article presents the optimization process in the design of metallic sandwiches for active cooling applications.

This article describes the design of metallic microlattices for energy-absorbing applications.

This article is a review of the manufacturing techniques available to produce microarchitectured materials.

The conclusion of the review is that the technology is mature for the development, characterization, and optimal design of a novel class of multifunctional materials with the potential to achieve unprecedented combination of properties.

In this paper, the authors presented a new class of materials based on a specific microlattice.

These materials exhibit interesting mechanical properties for a range of constituent materials and densities.

That made them suitable for a wide range of applications.

Composite materials with the desired behavior have already been developed by another team.

However, this behavior was only available under specific conditions and a narrow density range.

Unlike previously developed materials, the proposed new materials present a higher specific stiffness (stiffness per unit of mass density), which remains nearly constant.

The properties of a bend-dominated structure were shown to degrade significantly as the density is reduced.

The differences in compressive behavior between the different objects (hollow-tube compared with solid ceramic microlattices) observed by the authors of this study have been reported and explained previously by other teams.

Buckling is a phenomenon of instability: A slender structure submitted to a compressive load can bend and deform in the direction perpendicular to the compression axis.

The structure will then be submitted to a bending load rather than a compression load.

Ductile is the opposite of brittle. A ductile material can deform plastically without breaking when subjected to a load.

A brittle material submitted to a stress breaks without significant deformation.

The elastic behavior of the materials, for the ultralow densities, depends on the fabrication process: Hollow-tube microlattices and solid ceramic lattices present different responses to a compression load.

The marked difference is a result of nanoscale wall thickness in microscale hollow tubes as apposed to solid microscale struts in higher density samples.

The developed materials also present the valuable specificity of being isotropic.

The structures created by the authors present two interesting properties: They are both ultralight and ultrastiff, and the stiffness-to-weight ratio is not strongly affected by the density.

What do you think about the material properties achieved by the proposed objects? Do they satisfy the criteria indicated as desired in the introduction of the article?

Next Generation Science Standards, Science and Engineering Practice 4: Analyzing and interpreting data

A tetrakaidecahedron, also called tetradecahedron (from the Greek words tetra, four, and deca, 10) is a polyhedron with 14 faces.

These movies can be accessed on this page:

http://www.sciencemag.org/content/344/6190/1373/suppl/DC1

A material is said to present hysteresis if its behavior depends on the current loads applied and on the history of the past loads.

For example, a material that presents hysteresis will not sustain the same stresses if the strains are increasing or decreasing: The stress-strain curve will present a loop.

A viscoelastic behavior is an intermediate between a purely elastic behavior (like a spring) and a purely viscous behavior (like an absorber).

Polymers are known to exhibit a viscoelastic behavior, and the authors actually observed this phenomenon in the microlattices they produced.

This parameter characterizes the ability of a material to withstand loads tending to reduce its size in one dimension.

It is defined as the maximum force per unit area of a material to withstand loadings before it fails plastically (i.e., in a permanent and irreversible way) or fractures.

Young's modulus is a parameter used to characterize the stiffness of a material.

It is defined as the ratio between the stress (force per unit area) and the strain (displacement normalized by the initial length) and it is expressed in Pa.

The samples were mechanically tested to obtain their properties.

The authors estimated the densities of the created samples by measuring their weights and volumes (dimensions).

Sintering is the process of forming a solid mass of material by heating or pressuring particles of this material without reaching the melting point.

The stereolithography process applied using a resin bath with nanoparticles results in an hybrid microlattice (made of a mixture of solid polymer and nanoparticles).

An additional step is needed to obtain a microlattice made of pure alumina.

Atomic Layer Deposition is a method to deposit a thin film on a substrate. It consists of exposing the surface of the substrate to gaseous species.

A different coating process was applied to generate hollow-tube lattices with a different material (alumina). This process is called atomic layer deposition.

After covering the initial polymer microlattice with a nickel alloy, the polymer base was destroyed by heating the lattice. A hollow-tube nickel microlattice was thus obtained.

Electroless nickel plating is a chemical technique to deposit a layer of nickel alloy on a solid piece made of another metal or of plastic.

The base polymer lattice obtained through the microstereolithography was transformed in a metallic lattice by first covering the formed polymer with a nickel alloy.

The projection microstereolithography technique was used to generate a base polymer lattice.

This template is then converted into the desired metallic or ceramic microlattices using nanoscale coating techniques.

Scanning electron microscopy is a technique used to image the surface of a sample with a high resolution. (The resolution is in the nanometer scale.)

The first step to manufacture a piece with 3D printing techniques consists of designing a numerical or analytical model of it.

Software called computer-aided design software can help create a 3D model of the desired piece.

A photomask defines the area that will be illuminated. For the stereolithography technique, this area corresponds to a 2D cross section of the object.

To get the complete 3D object, different photomasks must be generated for each slice, each 2D cross-section.

A spatial light modulator is a device that allows one to modify the characteristics (phase, intensity, or polarization) of a light beam.

In this article, the spatial light modulator is used to define the mask, the area that will be illuminated.

The photosensitivity is the ability of some materials to react to the light. In this example, when the liquid polymer resin is exposed to light, it cures and becomes solid.

The different samples were created using two combined techniques.

First, a base polymer lattice was generated with projection microstereolithography.

This template was then converted into metallic and ceramic microlattices using nanoscale coating methods.

Rapid prototyping is a family of techniques used to quickly create models and prototypes, using 3D computer-aided design data. The most "famous" technique is 3D printing.

The structure proposed by the authors is based on a stretch-dominated lattice. A series of foams based on the other type of lattice, bend-dominated lattice, was fabricated to compare with the new proposed structure.

The behavior of a material can depend on the direction of the applied load. It also depends on the orientation of its architecture.

To investigate the relationship between the elastic response and the orientation and load direction, different samples with varying orientations were created and they were tested with different loading directions.

What experiment can you propose to answer this question?

AP Biology Science Practices:

• Practice 3: The student can engage in scientific questioning to extend thinking or to guide investigations within the context of the AP course. • Practice 4: The student can plan and implement data collection strategies appropriate to a particular scientific question.

The tessellation of a surface consists of tiling this surface using one or more geometric patterns (called tiles) without overlaps or gaps.

Loading a piece of material with an uniaxial compressive load means that the load applied tends to reduce the size of the sample in one specific direction.

FCC structure means a face-centered cubic structure. A structure is said to have an FCC architecture if its joints are located on the eight corners of a cube and in the center of each of the eight faces of the cube.

The aspect ratio is a parameter used to define the shape of a structure. For example, the aspect ratio of an image is the ratio of the width to the height.

Here, for the struts, the aspect ratio refers to the ratio of the length of the strut to its diameter.

The superiority of the stretch-dominated over the bend-dominated structure in regard to the mechanical efficiency has been suggested.

Deshpande and his team have analyzed the criterion for the construction of a stretch-dominated structure (Maxwell's criterion). They have also investigated the mechanical properties of an octet-truss unit cell and shown its efficiency.

Maxwell suggested a rule to set out the condition of rigidity for a cell structure with b struts and j frictionless joints.

A joint designates the connection between two struts. This connection is supposed to be frictionless, which means that there is no force resisting the relative motions of the two connected parts.

A strut is a structural component designed to resist longitudinal compression. Struts are the rod parts Fig1 A, B, C.

The authors created samples with a wide range of densities to investigate the evolution of the elastic properties when the density changes.

The critical features, in this case, refer to the dimensions of the smallest controllable feature size of the structure (for example, the length or the diameter of a strut).

A structure is said to have a face-centered cubic face if its joints are located on the eight corners of a cube and in the center of each of the eight faces of the cube.

Cellular materials can be classified in two categories: the bend-dominated structures and the stretch-dominated structures.

If a compressive loading is applied to a bend-dominated cellular structure, the cell's edges bend. If a tensile loading is applied to a stretch-dominated cellular structure, the material responds by an elastic stretching of its struts.

If a compressive loading is applied to a stretch-dominated cellular structure, no bending deformation exists in structural members. The material responds by an elastic stretching of its struts.

Authors designed and realized samples of ultralight mechanical metamaterials with a specific set of properties (namely, the coupling between stiffness and weight density is reduced to the theoretical limit).

The fracture toughness is a property of a material that describes the ability of this material to resist fracture.

The common idea behind these new designs and processes proposed to build new materials with improved mechanical properties is that the material must present a structural hierarchy at different scales (micro, nano, etc.).

Generally, an object does not behave the same way when a load is applied to it along a direction or when the load is applied along another direction. Thus it is important to know what the loading direction is.

This is especially true among previous works, such as structural honeycombs and sandwich panels.

The problem of the dependence of the mechanical properties on the density has been addressed by different teams.

They proposed various new designs and new fabrication processes, and they evaluated the relation between the relative density of the material and its mechanical properties.

Even if an improvement was shown with these new processes, they can only be used to build materials in a small density range and often this improvement was only applicable in certain loading directions.

Bending = flexure. It describes the way a slender structure behaves when a load is applied perpendicularly to its longitudinal axis.

Stochastic means random, unorganized.

According to what you have read so far, can you explain the goal of the present study?

Next Generation Science Standards Science and Engineering Practice 1: Asking questions (for science) and defining problems (for engineering)

http://www.nextgenscience.org/get-to-know

The material properties (Young's modulus, yield strength) of a solid with a high porosity are not the same as those of a solid bar of the same material but with no porosity.

The properties of the material with no porosity, the intrinsic properties of the material, are called bulk properties.

The yield strength is the stress at which a material begins to deform plastically.

Below this value, the deformation of the material is elastic: once the applied stress is removed, the material returns to its initial shape. Above this value, the deformation becomes permanent and irreversible.

Young's modulus is a parameter used to characterize the stiffness of a material. It is defined as the ratio between the stress (force per unit area) and the strain (displacement normalized by the initial length) and it is expressed in Pa.

Because of the number of potential applications, several teams recently carried out research to propose new designs of lightweight materials.

One inconvenience of these designs resides in the significant decrease of mechanical properties when the density is low.

Stiffness is a parameter describing the rigidity of a given piece of material, i.e., the way this piece resists deformation when a force is applied to it.

An object with low stiffness (such as a piece of rubber) will exhibit large deformation in response to an applied force. On the other hand, a material with high stiffness (like a metallic piece) will deform less if the same force is applied.

Stiffness-to-weight ratio means the stiffness per unit mass density. This parameter characterizes the mechanical efficiency of a material.

Assembly of basic cells (either open or closed) with solid edges and faces packed together to form a material with specific properties.

The authors designed and characterized a new category of light structures presenting ultrastiff properties for a wide range of densities and for different materials.

Stereolithography is a method of 3D printing. Objects are printed one layer at a time by curing a photosensitive resin with a UV source.

Microstereolithography is the same technique applied to fabricate structures with microscale feature resolutions.

A microlattice is a connected network of struts of microscopic size.

The connectivity characterizes the degree by which each individual structural element is connected to others.

For example, a connectivity of eight means each node inside the unit cell is connected with eight structural filaments.

An isotropic object is an object whose properties are the same whatever the considered direction.

Microarchitected materials are composed of elements of microscopic size organized in a designed topology.

The mechanical properties of a material are indices used to describe the way this material behaves when submitted to a load.

Check out ImmiFlex's video on Neutrophil Phagocytosis

https://www.youtube.com/watch?v=Z_mXDvZQ6dU

A rapid process that involves change in the distribution of cell surface receptors on leukocytes. This aids in the process of extravasation into the tissue from blood vessels.

This paper details the process of how neutrophils, with the help of platelets, are able to trap bacteria in the blood and play an important role in controlling sepsis.

In this study, the deltaCD knock-in mice were prepared, whereas the cytoplamsic domain (CD) of PSGL-1 is removed.

In this paper, the authors show that neutrophils deficient in Cdc42 cannot maintain polarity (distinct leading edge and uropod).

This is a review of the immune functions of platelets, the underdog cell type for most immunologists, This review highlights the essential roles platelets play in several immune functions.

This paper has been discussed in The Scientist magazine:

http://www.the-scientist.com/?articles.view/articleNo/41581/title/Platelets-Fan-Inflammation/

Neutrophil extracellular traps are one of the mechanisms employed by neutrophils to trap extracellular pathogens. They are known to be induced when neutrophils come in contact with a pathogen or other cell types, including platelets.

http://www.actabp.pl/pdf/3_2013/277.pdf

These experiments conclude that even in the brain, interactions between neutrophils and platelets is mediated by PSGL-1.

Death of tissue when blood and oxygen supply gets blocked is an infarction. In this case, the authors observed that tissue death/infarction in the brain was decreased when neutrophils were depleted.