The authors acknowledge funding support NIH/NIDCR R00DE018212 (SPH), NIH/NIDCR-R01DE022032 (SPH), NIH/NIDCR T32 DE07306 (AJ, JDL), NIH/NCRR S10RR026645, (SPH) and Departments of Preventive and Restorative Dental Sciences and Orofacial Sciences, UCSF.&#160; In addition, the authors acknowledge Xradia Graduate Fellowship (AJ), Xradia Inc., Pleasanton, CA.&#160;
The authors thank Dr. Kathryn Grandfield, UCSF for her assistance with post processing of data; Drs. Stephen Weiner and Gili Naveh, Weizmann Institute of Science, Rehovot, Israel; Dr. Ron Shahar, The Hebrew University of Jerusalem, Israel for their insightful discussions specific to the in situ loading device.&#160; The authors would also like to thank Biomaterials and Bioengineering MicroCT Imaging Facility at UCSF for the use of Micro XCT and the in situ loading device.

Animal housing and euthanasia: All animals used in this demonstration were housed under pathogen-free conditions in accordance to the guidelines of the Institutional Animal Care and Use Committee (IACUC) and the National Institute of Health (NIH).
Provide animals with standard hard-pellet rat chow and water ad lib. Euthanize animals via a two-step method of carbon dioxide asphyxiation, bilateral thoracotomy in accordance with the standard protocol of UCSF as approved by IACUC. Perform biomechanical testing within 24 hours of animal sacrifice to avoid tissue degradation.
1. Preparation and Dissection of a Rat Mandible or Maxilla
<ol>
	<li>Remove rat mandibles by gently severing membranous tissue and muscle tissue attachments while preserving the entire mandible, including the coronoid process and the condylar process (Figure 1)15.</li>
	<li>Separate hemimandibles by carefully cutting the fibrous tissue of mandibular symphysis with a scalpel blade. 
	Note: The coronary and condylar processes, and ramus of the mandible (Figure 1) should be removed if they physically obstruct biomechanical testing of the 2nd molar.</li>
	<li>Cut the incisors without exposing the pulp chamber as not to hinder loading of the molar.</li>
</ol>
2. Specimen Preparation for in situ Compressive Loading (Figure 2)
<ol>
	<li>Immobilize the specimen on a steel stub by using a material that is significantly stiffer than the experimental specimen prior to loading it in an in situ loading device (Figure 2A). 
	Note: Polymethylmethacrylate (PMMA) was used to immobilize the specimen in this study and excess, if any, was removed using a dental explorer.</li>
	<li>Align the occlusal surface of the molar(s) of interest parallel with the AFM metal specimen disc using a straight edge in both planes (i.e. mesial-distal and buccal-lingual).</li>
	<li>Create a trough with a blunt instrument surrounding the molars. 
	Note: This space should serve as a &#8220;moat&#8221; to contain excess liquid and maintain tissue hydration during in situ loading.</li>
	<li>Prepare the tooth surface to build up for concentric (Figure 2B) or eccentric (Figure 2C) loading using a dental composite. Etch the surface of the tooth of interest with 35% phosphoric acid gel on occlusal surface for 15 sec.</li>
	<li>Rinse the etchant thoroughly with deionized water and dry the surface using an air/water syringe or a compressed-air canister. With an explorer, spread a drop of the bonding agent into open cusps in a thin layer. Cure the composite with a dental curing light. 
	Note: All steps involving composites should be performed without direct light from a lamp. Such conditions would undesirably accelerate the polymerization process, and could prevent proper placement of the composite. Room lighting is acceptable.</li>
	<li>Remove excess bonding agent from adjacent teeth with a fine scalpel or razor blade.</li>
	<li>Place flowable dental composite on the surface following the preparation of the surface and spread it into grooves of the molar(s) of interest using a dental explorer.</li>
	<li>Expose the composite to dental curing light for 30 sec.</li>
	<li>Mold an occlusal buildup of about 3-4 mm using a dental resin composite, from the occlusal plane of the molar(s) of interest and light cure for 30 sec.</li>
	<li>Reduce the top of the composite buildup to a flat surface parallel to enable a consistent loading scheme across all specimens by using a straight edge and a high speed hand piece. 
	Note: During biomechanical testing, other specimens should be stored in tris-phosphate buffered solution (TBS) with 50 mg/ml penicillin, and streptomycin15.</li>
</ol>
3. Loading Device Drift and Stiffness, Material Property Differentiating Capability, in situ Loading of the Fibrous Joint
<ol>
	<li>Secure the specimen with the composite buildup on the anvil of the loading stage, and test for uniform loading as shown in Figure 2B.</li>
	<li>Place an articulating paper on the surface of the composite followed by loading the specimen to a finite load to check for concentric or eccentric loading (Figures 2B and&#160;2C).</li>
	<li>Place TBS-soaked Kimwipe around the specimen to ensure specimen hydration. Make a trough around the specimen and fill it with TBS to keep the organ hydrated during imaging.</li>
	<li>Input peak load and displacement rate into the Deben software to compress the molar to a desired peak load at a displacement rate following immobilization of the hemimandible. 
	Note: Typical readouts should include a reactionary load as the material is compressed over time (load transducer sensitivity = 0.1 N). From load-time and displacement-time, a load-displacement curve for the compressed material should be obtained16-18. Using the data collected from the loading cycles, various properties of the joint can also be determined. The stiffness of the joint should be calculated by taking the slope of the linear portion (approximately the last 30% of the data) of the loading phase of the load vs. displacement curve19.</li>
</ol>
4. Staining of Soft Tissue, the PDL, with Phosphotungstic Acid (PTA)
Note: To enhance X-ray attenuation contrast, the PDL should be stained with 5% PTA solution20.
<ol>
	<li>Backfill PTA staining solution into a clean 1.8 ml glass carpule and place loaded carpule into syringe.</li>
	<li>Inject solution slowly (5 min/carpule) into the PDL-space of adjacent teeth to prevent structural damage to periodontal tissues surrounding molar of interest. 
	Note: The above steps should be repeated until about 5 full carpules (9 ml) of solution are injected and allowed to flow into the surrounding tissues. The prepped specimens can also be soaked overnight in the remaining PTA solution (8 hr).</li>
</ol>
5. Recommended &#956;-XCT Scanning Settings
Perform m-XCT with the following scanning settings:
<table border="1" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Objective Magnification</td>
			<td>4X, 10X</td>
		</tr>
		<tr>
			<td></td>
			<td>1,800 images</td>
		</tr>
		<tr>
			<td>X-ray tube voltage</td>
			<td>75 kVp (50 kVp for PTA stained samples)</td>
		</tr>
		<tr>
			<td></td>
			<td>8 W</td>
		</tr>
		<tr>
			<td>Exposure Time</td>
			<td>~8-25 sec*</td>
		</tr>
		<tr>
			<td></td>
			<td>~4 &#956;m (4X objective),~2 &#956;m (10X objective) **</td>
		</tr>
	</tbody>
</table>
* exposure time can vary based on the geometry and optical density of the specimen and X-ray tube voltage. 
** actual pixel resolution will slightly differ based on the configuration of the source, specimen, and detector.

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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MicroCT+for+comparative+morphology:+simple+staining+methods+allow+high-contrast+3D+imaging+of+diverse+non-mineralized+animal+tissues.">MicroCT for comparative morphology: simple staining methods allow high-contrast 3D imaging of diverse non-mineralized animal tissues.</a> BMC Physiol. 9, 11 (2009).</li><li>Carrillo, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoindentation+of+polydimethylsiloxane+elastomers:+Effect+of+crosslinking,+work+of+adhesion,+and+fluid+environment+on+elastic+modulus+(vol+20,+pg+2820).">Nanoindentation of polydimethylsiloxane elastomers: Effect of crosslinking, work of adhesion, and fluid environment on elastic modulus (vol 20, pg 2820).</a> J. Mater. Res. 21, 535-537 (2006).</li><li>Hiiemae, K. 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The authors have nothing to disclose.&#160;

The first step in establishing this protocol involved evaluating the stiffness of the loading frame by using a rigid body. Based on the results, the stiffness was significantly higher enabling the use of the loading device for further testing of specimens with significantly lower stiffness values. The second step highlighted the ability of the instrument to distinguish different stiffness values by using two phases of the loading-unloading curve generated by using a rigid body, PDMS materials of different crosslink densi...

Several experimental methods continue to be used to investigate the biomechanics of diarthrodial and fibrous joints. Methods specific to the tooth organ biomechanics include the use of strain gauges1-3, photoelasticity methods4,5, Moir&#233; interferometry6,7, electronic speckle pattern interferometry8, and digital image correlation (DIC)9-14. In this study, the innovative approach includes noninvasive imaging using X-rays to expose the internal structures of a fibrous joint (mineralized tissues and their interfaces consisting of softer zones, and interfacing tissues such as ligaments) at loads equivalent to in vivo conditions. An in situ loading device coupled to a micro-X-ray microscope will be used. The load-time and load-displacement curves will be collected as the molar of interest within a freshly harvested rat hemi-mandible is loaded. The main goal of the approach presented in this study is to emphasize the effect of three-dimensional morphology of tooth-bone by comparing conditions at: 1) no load and when loaded, and when 2) concentrically and eccentrically loaded. Eliminating the need for cut specimens, and to perform experiments on whole intact organs under wet conditions will allow for maximum preservation of the 3D stress state. This opens a new area of investigation in understanding dynamic processes of the complex under various loading scenarios.
In this study, the methods for testing PDL biomechanics within an intact fibrous joint of a Sprague Dawley rat, a joint considered as an optimum bioengineering model system will be detailed. Experiments will include simulation of mastication loads under hydrated conditions in order to highlight three important features of the joint as they relate to organ level biomechanics. The three points will include: 1) reactionary force vs. displacement: tooth displacement within the alveolar socket and its reactionary response to loading, 2) three-dimensional (3D) spatial configuration and morphometrics: geometric relationship of the tooth with the alveolar socket, and 3) changes in readouts 1 and 2 due to a change in loading axis, i.e. from concentric to eccentric loads. The three fundamental readouts of the proposed technique can be applied to investigate the adaptive nature of joints in vertebrates either due to changes in functional demands, and/or disease. Changes in the aforementioned readouts, specifically the correlation between reactionary loads with displacement, and resulting reactionary load-time and load-displacement curves at different loading rates can be applied to highlight overall changes in joint biomechanics. Efficacy of the proposed protocol will be evaluated by coupling mechanical testing readouts to 3D morphometrics and overall biomechanics of the joint.

<table border="0" cellpadding="0" cellspacing="0" width="652">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:169px;">Bard Parker Blade</td>
			<td style="width:101px;">BD</td>
			<td style="width:123px;">MEDC-001054</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:169px;">AFM metal disk</td>
			<td style="width:101px;">Ted Pella</td>
			<td style="width:123px;">16218</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:169px;">Polymethyl methacrylate&#160;</td>
			<td style="width:101px;">GC America</td>
			<td style="width:123px;">N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:169px;">Uni-Etch</td>
			<td style="width:101px;">Bisco</td>
			<td style="width:123px;">E5502EBM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:169px;">Optibond Solo Plus</td>
			<td style="width:101px;">Kerr Corp</td>
			<td style="width:123px;">N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:169px;">Filtek Flow</td>
			<td style="width:101px;">3M</td>
			<td style="width:123px;">N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:169px;">Hurculite Ultra</td>
			<td style="width:101px;">Kerr</td>
			<td style="width:123px;">34346</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:169px;">Tris buffer</td>
			<td style="width:101px;">Mediatech Inc.</td>
			<td style="width:123px;">N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:169px;">Articulating paper</td>
			<td style="width:101px;"></td>
			<td style="width:123px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:169px;">Phosphotungstic Acid</td>
			<td style="width:101px;">Sigma Aldrich</td>
			<td style="width:123px;">HT152</td>
			<td></td>
		</tr>
	</tbody>
</table>

in situ compressive loading and correlative noninvasive imaging of the bone-periodontal ligament-tooth fibrous joint

This study demonstrates a novel biomechanics testing protocol. The advantage of this protocol includes the use of an in situ loading device coupled to a high resolution X-ray microscope, thus enabling visualization of internal structural elements under simulated physiological loads and wet conditions. Experimental specimens will include intact bone-periodontal ligament (PDL)-tooth fibrous joints. Results will illustrate three important features of the protocol as they can be applied to organ level biomechanics: 1) reactionary force vs. displacement: tooth displacement within the alveolar socket and its reactionary response to loading, 2) three-dimensional (3D) spatial configuration and morphometrics: geometric relationship of the tooth with the alveolar socket, and 3) changes in readouts 1 and 2 due to a change in loading axis, i.e. from concentric to eccentric loads. Efficacy of the proposed protocol will be evaluated by coupling mechanical testing readouts to 3D morphometrics and overall biomechanics of the joint. In addition, this technique will emphasize on the need to equilibrate experimental conditions, specifically reactionary loads prior to acquiring tomograms of fibrous joints. It should be noted that the proposed protocol is limited to testing specimens under ex vivo conditions, and that use of contrast agents to visualize soft tissue mechanical response could lead to erroneous conclusions about tissue and organ-level biomechanics.

Estimation of loading device &#8220;backlash&#8221;, &#8220;pushback&#8221;, stiffness, and system drift under a constant load
Backlash: Between loading and unloading portions of the cycle, there exists a pause of 3 sec during which gears reverse within the motor before true unloading commences, i.e. as the specimen pulls away from the top jaw (Figure&#160;3). This period is referred to as a backlash in the system, which represents a ...

Watch this Scientific Journal Video about In situ Compressive Loading and Correlative Noninvasive Imaging of the Bone-periodontal Ligament-tooth Fibrous Joint at JoVE.com

In situ Compressive Loading and Correlative Noninvasive Imaging of the Bone-periodontal Ligament-tooth Fibrous Joint

In this study, the use of an in situ loading device coupled with micro-X-ray computed tomography for fibrous joint biomechanics will be discussed. Experimental readouts identifiable with an overall change in joint biomechanics will include: 1) reactionary force vs. displacement, i.e. tooth displacement within the alveolar socket and its reactionary response to loading, 2) three-dimensional (3D) spatial configuration and morphometrics, i.e.&#160;geometric relationship of the tooth with the alveolar socket, and 3) changes in readouts 1 and 2 due to a change in loading axis, i.e. concentric or eccentric loads.

In situ Compressive Loading and Correlative Noninvasive Imaging of the Bone-periodontal Ligament-tooth Fibrous Joint

This study demonstrates a novel biomechanics testing protocol. The advantage of this protocol includes the use of an in situ loading device coupled to a ...

in-situ-compressive-loading-correlative-noninvasive-imaging-bone

Research

JoVE Journal

Bioengineering

13.3K Views.  University of California San Francisco.  In questo studio, sarà discusso l'uso di un dispositivo in situ loading accoppiato con tomografia micro-computerizzata a raggi X per la biomeccanica articolare fibrosi. Letture sperimentali identificabili con una variazione complessiva delle biomeccanica articolare saranno: 1) forza reazionaria contro lo spostamento, vale a dire lo spostamento del dente nella presa alveolare e la sua risposta reazionaria a carico, 2) tridimensionale (3D) configuraz...

Video: In situ Compressive Loading and Correlative Noninvasive Imaging of the Bone-periodontal Ligament-tooth Fibrous Joint

High-resolution Fiber-optic Microendoscopy for in situ Cellular Imaging

Many biological and clinical studies require the longitudinal study and analysis of morphology and function with cellular level resolution. Traditionally, multiple experiments are run in parallel, with individual samples removed from the study at sequential time points for evaluation by light microscopy. Several intravital techniques have been developed, with confocal, multiphoton, and second harmonic microscopy all demonstrating their ability to be used for imaging in situ 1. With these systems, however, the required infrastructure is complex and expensive, involving scanning laser systems and complex light sources. Here we present a protocol for the design and assembly of a high-resolution microendoscope which can be built in a day using off-the-shelf components for under US$5,000. The platform offers flexibility in terms of image resolution, field-of-view, and operating wavelength, and we describe how these parameters can be easily modified to meet the specific needs of the end user.
We and others have explored the use of the high-resolution microendoscope (HRME) in in vitro cell culture 2-5, in excised 6 and living animal tissues 2,5, and in human tissues in vivo 2,7. Users have reported the use of several different fluorescent contrast agents, including proflavine 2-4, benzoporphyrin-derivative monoacid ring A (BPD-MA) 5, and fluoroscein 6,7, all of which have received full, or investigational approval from the FDA for use in human subjects. High-resolution microendoscopy, in the form described here, may appeal to a wide range of researchers working in the basic and clinical sciences. The technique offers an effective and economical approach which complements traditional benchtop microscopy, by enabling the user to perform high-resolution, longitudinal imaging in situ.

High-resolution Fiber-optic Microendoscopy for in situ Cellular Imaging

In many biological and clinical situations it is advantageous to study cellular processes as they evolve in their native microenvironment. Here we describe the assembly and use of a low-cost fiber-optic microscope which can provide real time imaging in cell culture, animal studies, and clinical patient studies.

Many biological and clinical studies require the longitudinal study and analysis of morphology and function with cellular level resolution.  ...

Demonstrating the Uses of the Novel Gravitational Force Spectrometer to Stretch and Measure Fibrous Proteins

The study of macromolecular structure has become critical to the elucidation of molecular mechanisms and function. There are several limited, but important bioinstruments capable of testing the force dependence of structural features in proteins. Scale has been a limiting parameter on how accurately researchers can peer into the nanomechanical world of molecules, such as nucleic acids, enzymes, and motor proteins that perform life-sustaining work. Atomic force microscopy (AFM) is well tuned to determine native structures of fibrous proteins with a distance resolution on par with electron microscopy. However, in AFM force studies, the forces are typically much higher than a single molecule might experience 1, 2. Optical traps (OT) are very good at determining the relative distance between the trapped beads and they can impart very small forces 3. However, they do not yield accurate absolute lengths of the molecules under study. Molecular simulations provide supportive information to such experiments, but are limited in the ability to handle the same large molecular sizes, long time frames, and convince some researchers in the absence of other supporting evidence2, 4.
The gravitational force spectrometer (GFS) fills a critical niche in the arsenal of an investigator by providing a unique combination of abilities. This instrument is capable of generating forces typically with 98% or better accuracy from the femtonewton range to the nanonewton range. The distance measurements currently are capable of resolving the absolute molecular length down to five nanometers, and relative bead pair separation distances with a precision similar to an optical trap. Also, the GFS can determine stretching or uncoiling where the force is near equilibrium, or provide a graded force to juxtapose against any measured structural changes. It is even possible to determine how many amino acid residues are involved in uncoiling events under physiological force loads 2. Unlike in other methods where there is extensive force calibration that must precede any assay, the GFS requires no such force calibration 5. By complementing the strengths of other methods, the GFS will bridge gaps in understanding the nanomechanics of vital proteins and other macromolecules.

This is a step-by step guide showing the purpose, operation, and representative results from the novel gravitational force spectrometer.

The study of macromolecular structure has become critical to the elucidation of molecular mechanisms and function. There are several limited, but ...

In vitro Synthesis of Native, Fibrous Long Spacing and Segmental Long Spacing Collagen

Collagen fibrils are present in the extracellular matrix of animal tissue to provide structural scaffolding and mechanical strength. These native collagen fibrils have a characteristic banding periodicity of ~67 nm and are formed in vivo through the hierarchical assembly of Type I collagen monomers, which are 300 nm in length and 1.4 nm in diameter. In vitro, by varying the conditions to which the monomer building blocks are exposed, unique structures ranging in length scales up to 50 microns can be constructed, including not only native type fibrils, but also fibrous long spacing and segmental long spacing collagen. Herein, we present procedures for forming the three different collagen structures from a common commercially available collagen monomer. Using the protocols that we and others have published in the past to make these three types typically lead to mixtures of structures. In particular, unbanded fibrils were commonly found when making native collagen, and native fibrils were often present when making fibrous long spacing collagen. These new procedures have the advantage of producing the desired collagen fibril type almost exclusively. The formation of the desired structures is verified by imaging using an atomic force microscope.

In vitro Synthesis of Native, Fibrous Long Spacing and Segmental Long Spacing Collagen

Simple and reproducible procedures are described for making three structurally distinct collagen assemblies from a common commercially available Type I collagen monomer. Native type, fibrous long spacing or segmental long spacing collagen can be constructed by varying the conditions to which the 300 nm long and 1.4 nm diameter monomer building block is exposed.

Collagen fibrils are present in the  extracellular matrix of animal tissue to provide structural scaffolding and  mechanical strength. These native ...

Design of a Biaxial Mechanical Loading Bioreactor for Tissue Engineering

We designed a loading device that is capable of applying uniaxial or biaxial mechanical strain to a tissue engineered biocomposites fabricated for transplantation. While the device primarily functions as a bioreactor that mimics the native mechanical strains, it is also outfitted with a load cell for providing force feedback or mechanical testing of the constructs. The device subjects engineered cartilage constructs to biaxial mechanical loading with great precision of loading dose (amplitude and frequency) and is compact enough to fit inside a standard tissue culture incubator. It loads samples directly in a tissue culture plate, and multiple plate sizes are compatible with the system. The device has been designed using components manufactured for precision-guided laser applications. Bi-axial loading is accomplished by two orthogonal stages. The stages have a 50 mm travel range and are driven independently by stepper motor actuators, controlled by a closed-loop stepper motor driver that features micro-stepping capabilities, enabling step sizes of less than 50 nm. A polysulfone loading platen is coupled to the bi-axial moving platform. Movements of the stages are controlled by Thor-labs Advanced Positioning Technology (APT) software. The stepper motor driver is used with the software to adjust load parameters of frequency and amplitude of both shear and compression independently and simultaneously. Positional feedback is provided by linear optical encoders that have a bidirectional repeatability of 0.1 &mu;m and a resolution of 20 nm, translating to a positional accuracy of less than 3 &mu;m over the full 50 mm of travel. These encoders provide the necessary position feedback to the drive electronics to ensure true nanopositioning capabilities. In order to provide the force feedback to detect contact and evaluate loading responses, a precision miniature load cell is positioned between the loading platen and the moving platform. The load cell has high accuracies of 0.15% to 0.25% full scale.

We designed a novel mechanical loading bioreactor that can apply uniaxial or biaxial mechanical strain to a cartilage biocomposite prior to transplantation into an articular cartilage defect.

We  designed a loading device that is capable of applying uniaxial or biaxial  mechanical strain to a tissue engineered biocomposites fabricated for  ...

FIBS-enabled Noninvasive Metabolic Profiling

In the era of computational biology, new high throughput experimental systems are necessary in order to populate and refine models so that they can be validated for predictive purposes. Ideally such systems would be low volume, which precludes sampling and destructive analyses when time course data are to be obtained. What is needed is an in situ monitoring tool which can report the necessary information in real-time and noninvasively. An interesting option is the use of fluorescent, protein-based in vivo biological sensors as reporters of intracellular concentrations. One particular class of in vivo biosensors that has found applications in metabolite quantification is based on F&#246;rster Resonance Energy Transfer (FRET) between two fluorescent proteins connected by a ligand binding domain. FRET integrated biological sensors (FIBS) are constitutively produced within the cell line, they have fast response times and their spectral characteristics change based on the concentration of metabolite within the cell. In this paper, the method for constructing Chinese hamster ovary (CHO) cell lines that constitutively express a FIBS for glucose and glutamine and calibrating the FIBS in vivo in batch cell culture in order to enable future quantification of intracellular metabolite concentration is described. Data from fed-batch CHO cell cultures demonstrates that the FIBS was able in each case to detect the resulting change in the intracellular concentration. Using the fluorescent signal from the FIBS and the previously constructed calibration curve, the intracellular concentration was accurately determined as confirmed by an independent enzymatic assay.

A description of how to calibrate F&#246;rster Resonance Energy Transfer integrated biological sensors (FIBS) for in situ metabolic profiling is presented.&#160;The FIBS can be used to measure intracellular levels of metabolites noninvasively aiding in the development of metabolic models and high throughput screening of bioprocess conditions.

In the era of computational biology, new high throughput experimental systems are necessary in order to populate and refine models so that they can be ...

Studying the Stoichiometry of Epidermal Growth Factor Receptor in Intact Cells using Correlative Microscopy

This protocol describes the labeling of epidermal growth factor receptor (EGFR) on COS7 fibroblast cells, and subsequent correlative fluorescence microscopy and environmental scanning electron microscopy (ESEM) of whole cells in hydrated state. Fluorescent quantum dots (QDs) were coupled to EGFR via a two-step labeling protocol, providing an efficient and specific protein labeling, while avoiding label-induced clustering of the receptor. Fluorescence microscopy provided overview images of the cellular locations of the EGFR. The scanning transmission electron microscopy (STEM) detector was used to detect the QD labels with nanoscale resolution. The resulting correlative images provide data of the cellular EGFR distribution, and the stoichiometry at the single molecular level in the natural context of the hydrated intact cell. ESEM-STEM images revealed the receptor to be present as monomer, as homodimer, and in small clusters. Labeling with two different QDs, i.e.,&#160;one emitting at 655 nm and at 800 revealed similar characteristic results.

This protocol describes the labeling of epidermal growth factor receptor (EGFR) on COS7 fibroblast cells, and subsequent correlative light- and electron microscopy of whole cells in hydrated state. The label contained fluorescent quantum dots. The protocol can be used to study the stoichiometry of EGFR at the single molecule level.

This protocol describes the labeling of epidermal growth factor receptor (EGFR) on COS7 fibroblast cells, and subsequent correlative fluorescence ...

Characterizing Cell Migration Within Three-dimensional In Vitro Wound Environments

Currently, most in vitro models of wound healing, such as well-established scratch assays, involve studying cell migration and wound closure on two-dimensional surfaces. However, the physiological environment in which in vivo wound healing takes place is three-dimensional rather than two-dimensional. It is becoming increasingly clear that cell behavior differs greatly in two-dimensional vs. three-dimensional environments; therefore, there is a need for more physiologically relevant in vitro models for studying cell migration behaviors in wound closure. The method described herein allows for the study of cell migration in a three-dimensional model that better reflects physiological conditions than previously established two-dimensional scratch assays. The purpose of this model is to evaluate cell outgrowth via the examination of cell migration away from a spheroid body embedded within a fibrin matrix in the presence of pro- or anti-migratory factors. Using this method, cell outgrowth from the spheroid body in a three-dimensional matrix can be observed and is easily quantifiable over time via brightfield microscopy and analysis of spheroid body area. The effect of pro-migratory and/or inhibitory factors on cell migration can also be evaluated in this system. This method provides researchers with a simple method of analyzing cell migration in three-dimensional wound associated matrices in vitro, thus increasing the relevance of in vitro cell studies prior to the use of in vivo animal models.

Characterizing Cell Migration Within Three-dimensional In Vitro Wound Environments

The goal of this protocol is to evaluate the effect of pro- and anti-migratory factors on cell migration within a three-dimensional fibrin matrix.

Currently, most in vitro models of wound healing, such as well-established scratch assays, involve studying cell migration and wound closure on ...

Optimized Setup and Protocol for Magnetic Domain Imaging with In Situ Hysteresis Measurement

This paper elaborates the sample preparation protocols required to obtain optimal domain patterns using the Bitter method, focusing on the extra steps compared to standard metallographic sample preparation procedures. The paper proposes a novel bespoke rig for dynamic domain imaging with in situ BH (magnetic hysteresis) measurements and elaborates the protocols for the sensor preparation and the use of the rig to ensure accurate BH measurement. The protocols for static and ordinary dynamic domain imaging (without in situ BH measurements) are also presented. The reported method takes advantage of the convenience and high sensitivity of the traditional Bitter method and enables in situ BH measurement without interrupting or interfering with the domain wall movement processes. This facilitates establishing a direct and quantitative link between the domain wall movement processes&#8211;microstructural feature interactions in ferritic steels with their BH loops. This method is anticipated to become a useful tool for the fundamental study of microstructure&#8211;magnetic property relationships in steels and to help interpret the electromagnetic sensor signals for non-destructive evaluation of steel microstructures.

Optimized Setup and Protocol for Magnetic Domain Imaging with In Situ Hysteresis Measurement

This paper elaborates the sample and sensor preparation procedures and the protocols for using the test rig particularly for dynamic domain imaging with in situ BH measurements in order to achieve optimal domain pattern quality and accurate BH measurements.

This paper elaborates the sample preparation protocols required to obtain optimal domain patterns using the Bitter method, focusing on the extra steps ...

Nanosensors to Detect Protease Activity In Vivo for Noninvasive Diagnostics

Proteases are multi-functional enzymes that specialize in the hydrolysis of peptide-bonds and control broad biological processes including homeostasis and allostasis. Moreover, dysregulated protease activity drives pathogenesis and is a functional biomarker of diseases such as cancer; therefore, the ability to detect protease activity in vivo may provide clinically relevant information for biomedical diagnostics. The goal of this protocol is to create nanosensors that probe for protease activity in vivo by producing a quantifiable signal in urine. These protease nanosensors consist of two components: a nanoparticle and substrate. The nanoparticle functions to increase circulation half-life and substrate delivery to target disease sites. The substrate is a short peptide sequence (6-8 AA), which is designed to be specific to a target protease or group of proteases. The substrate is conjugated to the surface of the nanoparticle and is terminated by a reporter, such as a fluorescent marker, for detection. As dysregulated proteases cleave the peptide substrate, the reporter is filtered into urine for quantification as a biomarker of protease activity. Herein we describe construction of a nanosensor for matrix metalloproteinase 9 (MMP9), which is associated with tumor progression and metastasis, for detection of colorectal cancer in a mouse model.

Nanosensors to Detect Protease Activity In Vivo for Noninvasive Diagnostics

Proteases are tightly regulated enzymes involved in fundamental biological processes, and dysregulated protease activity drives progression of complex diseases such as cancer. This method&#39;s goal is to create nanosensors that measure protease activity in vivo by producing a cleavage signal that is detectable from host urine and discriminates disease.

Proteases are multi-functional enzymes that specialize in the hydrolysis of peptide-bonds and control broad biological processes including homeostasis and ...

Correlative Light Electron Microscopy (CLEM) for Tracking and Imaging Viral Protein Associated Structures in Cryo-immobilized Cells

Due to its high resolution, electron microscopy (EM) is an indispensable tool for virologists. However, one of the main difficulties when analyzing virus-infected or transfected cells via EM are the low efficiencies of infection or transfection, hindering the examination of these cells. In order to overcome this difficulty, light microscopy (LM) can be performed first to allocate the subpopulation of infected or transfected cells. Thus, taking advantage of the use of fluorescent proteins (FPs) fused to viral proteins, LM is used here to record the positions of the "positive-transfected" cells, expressing a FP and growing on a support with an alphanumeric pattern. Subsequently, cells are further processed for EM via high pressure freezing (HPF), freeze substitution (FS) and resin embedding. The ultra-rapid freezing step ensures excellent membrane preservation of the selected cells that can then be analyzed at the ultrastructural level by transmission electron microscopy (TEM). Here, a step-by-step correlative light electron microscopy (CLEM) workflow is provided, describing sample preparation, imaging and correlation in detail. The experimental design can be also applied to address many cell biology questions.

Correlative Light Electron Microscopy CLEM for Tracking and Imaging Viral Protein Associated Structures in Cryo-immobilized Cells

A correlative light electron microscopy (CLEM) method is applied to image virus-induced intracellular structures via electron microscopy (EM) in cells that are previously selected by light microscopy (LM). LM and EM are combined as a hybrid imaging approach to achieve an integrated view of virus-host interactions.

Due to its high resolution, electron microscopy (EM) is an indispensable tool for virologists. However, one of the main difficulties when analyzing ...