Name: a lab-on-a-chip platform for stimulating osteocyte mechanotransduction and analyzing functional outcomes of bone remodeling
Uploaded: 2020-05-21T14:30:00
Description: Watch this Scientific Journal Video about A Lab-On-A-Chip Platform for Stimulating Osteocyte Mechanotransduction and Analyzing Functional Outcomes of Bone Remodeling at JoVE.com

This work was supported by the National Science Foundation under Grant Nos. (CBET 1060990 and EBMS 1700299). Also, this material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. (2018250692). Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

1. Chip mask preparation
NOTE: Steps 1.1 - 1.3 only need to be performed once upon initial receipt of the chip mask. They ensure the mask does not bow during use. The design of the microfluidic masks was previously described11,14. Masks were designed in-house and commercially fabricated using high resolution stereolithography (Figure 1A).
<ol>
	<li>Cover the top surface of the mask with ...

<ol>
	<li>Hemmatian, H., Bakker, A. D., Klein-Nulend, J., van Lenthe, G. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aging,+Osteocytes,+and+Mechanotransduction.">Aging, Osteocytes, and Mechanotransduction.</a> Current Osteoporosis Reports. 15 (5), 401-411 (2017).</li><li>Bonewald, L. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+amazing+osteocyte.">The amazing osteocyte.</a> Journal of Bone and Mineral Research. 26 (2), 229-238 (2011).</li><li>Middleton, K., Al-Dujaili, S., Mei, X., Gunther, A., You, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+co-culture+platform+for+investigating+osteocyte-osteoclast+signalling+during+fluid+shear+stress+mechanostimulation.">Microfluidic co-culture platform for investigating osteocyte-osteoclast signalling during fluid shear stress mechanostimulation.</a> Journal of Biomechanics. 59, 35-42 (2017).</li><li>Kou, S., 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=A+multishear+microfluidic+device+for+quantitative+analysis+of+calcium+dynamics+in+osteoblasts.">A multishear microfluidic device for quantitative analysis of calcium dynamics in osteoblasts.</a> Biochemical and Biophysical Research Communications. 408 (2), 350-355 (2011).</li><li>Ma, H. 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W., Horton, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Variable+osteogenic+performance+of+MC3T3-E1+subclones+impacts+their+utility+as+models+of+osteoblast+biology.">Variable osteogenic performance of MC3T3-E1 subclones impacts their utility as models of osteoblast biology.</a> Scientific Reports. 9 (1), 8299 (2019).</li><li>Beier, E. E., Holz, J. D., Sheu, T. J., Puzas, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elevated+lifetime+lead+exposure+impedes+osteoclast+activity+and+produces+an+increase+in+bone+mass+in+adolescent+mice.">Elevated lifetime lead exposure impedes osteoclast activity and produces an increase in bone mass in adolescent mice.</a> Toxicological Sciences. 149 (2), 277-288 (2016).</li><li>Chaudhary, L. R., Hofmeister, A. M., Hruska, K. 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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+considerations+for+optimizing+bone+cell+culture+and+remodeling+in+a+lab-on-a-chip+platform.">Cellular considerations for optimizing bone cell culture and remodeling in a lab-on-a-chip platform.</a> Biotechniques. , (2019).</li><li>Truesdell, S. L., George, E. L., Seno, C. E., Saunders, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=3D+printed+loading+device+for+inducing+cellular+mechanotransduction+via+matrix+deformation.">3D printed loading device for inducing cellular mechanotransduction via matrix deformation.</a> Experimental Mechanics. 59 (8), 1223-1232 (2019).</li><li>George, E. L., Truesdell, S. L., Magyar, A. L., Saunders, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effects+of+mechanically+loaded+osteocytes+and+inflammation+on+bone+remodeling+in+a+bisphosphonate-induced+environment.">The effects of mechanically loaded osteocytes and inflammation on bone remodeling in a bisphosphonate-induced environment.</a> Bone. 127, 460-473 (2019).</li><li>George, E. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Quantifying the roles of stimulated osteocytes and inflammation in bone remodeling Doctor of Philosophy. , (2019).</li><li>York, S. L., Sethu, P., Saunders, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+osteocytic+microdamage+and+viability+quantification+using+a+microloading+platform.">In vitro osteocytic microdamage and viability quantification using a microloading platform.</a> Medical Engineering &amp; Physics. 38 (10), 1115-1122 (2016).</li><li>Hui, A. Y., Wang, G., Lin, B., Chan, W. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microwave+plasma+treatment+of+polymer+surface+for+irreversible+sealing+of+microfluidic+devices.">Microwave plasma treatment of polymer surface for irreversible sealing of microfluidic devices.</a> Lab Chip. 5 (10), 1173-1177 (2005).</li><li>Millare, B., 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=Dependence+of+the+quality+of+adhesion+between+poly(dimethylsiloxane)+and+glass+surfaces+on+the+conditions+of+treatment+with+oxygen+plasma.">Dependence of the quality of adhesion between poly(dimethylsiloxane) and glass surfaces on the conditions of treatment with oxygen plasma.</a> Langmuir. 24 (22), 13218-13224 (2008).</li><li>Lee, J. N., Park, C., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solvent+compatibility+of+poly(dimethylsiloxane)-based+microfluidic+devices.">Solvent compatibility of poly(dimethylsiloxane)-based microfluidic devices.</a> Analytical Chemistry. 75 (23), 6544-6554 (2003).</li><li>Regehr, K. J., 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=Biological+implications+of+polydimethylsiloxane-based+microfluidic+cell+culture.">Biological implications of polydimethylsiloxane-based microfluidic cell culture.</a> Lab Chip. 9 (15), 2132-2139 (2009).</li><li>Wang, Y., Burghardt, T. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Uncured+PDMS+inhibits+myosin+in+vitro+motility+in+a+microfluidic+flow+cell.">Uncured PDMS inhibits myosin in vitro motility in a microfluidic flow cell.</a> Analytical Biochemistry. 563, 56-60 (2018).</li><li>Millet, L. J., Stewart, M. E., Sweedler, J. V., Nuzzo, R. G., Gillette, M. U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+devices+for+culturing+primary+mammalian+neurons+at+low+densities.">Microfluidic devices for culturing primary mammalian neurons at low densities.</a> Lab Chip. 7 (8), 987-994 (2007).</li><li>Kilic, O., 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=Brain-on-a-chip+model+enables+analysis+of+human+neuronal+differentiation+and+chemotaxis.">Brain-on-a-chip model enables analysis of human neuronal differentiation and chemotaxis.</a> Lab Chip. 16 (21), 4152-4162 (2016).</li><li>Van Scoy, G. 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This article describes the foundations for fabricating a bone remodeling LOC platform for culturing osteocytes, osteoclasts, and osteoblasts. By altering the depth and size of the well within the chip, multiple configurations were developed for stimulating osteocytes with mechanical load and quantifying functional outcomes of bone remodeling (Figure 1B).
During chip assembly, optimizing the plasma oxidation protocol was critical for eliminating le...

Bone is a highly dynamic tissue that requires intricate coordination among the three major cell types: osteocytes, osteoblasts, and osteoclasts. Multicellular interactions among these cells are responsible for the bone loss that occurs during paralysis and long-term immobility and for the bone formation that occurs in response to growth and exercise. Osteocytes, the most abundant bone cell type, are highly sensitive to mechanical stimuli applied to the bone. Mechanical stimulation alters osteocyte metabolic activity and leads to an increase in key signaling molecules1,2. Through this process, known as mechanotransduction, osteocytes can directly coordinate the activities of osteoblasts (bone forming cells) and osteoclasts (bone resorbing cells). Maintaining bone homeostasis requires a tight regulation between bone formation and bone resorption rates; however, disruptions in this process can result in disease states such as osteoporosis or osteopetrosis.
The complexity of interactions between these three cell types lends itself well to investigation utilizing microfluidic and lab-on-a-chip (LOC) technologies. To that end, our lab has recently established proof of concept of a LOC platform for analyzing bone resorption and formation (functional outcomes) in the bone remodeling process. The platform can be used for the study of cellular interactions, altered loading environments, and investigational drug screening. In recent years, various microfluidic devices have been developed for investigating the molecular signaling pathways that regulate bone remodeling; however, many of these systems quantify remodeling through indirect markers that are indicative of functional activity3,4,5,6,7. An advantage of our system is that it can be used for direct quantification of functional outcomes. Bone remodeling is a long-term process. As such, direct quantification of bone resorption and formation requires a culturing system that can be maintained for a minimum of several weeks to months8,9,10,11. Thus, when developing the LOC platform, we established long-term culturing protocols necessary for formation and resorption and have maintained cells within the system for up to seven weeks11. Additionally, we incorporated appropriate culturing substrates for both cell types into the platform; osteoclasts were cultured directly on bone, and osteoblasts, which are known to be plastic adherent, were cultured on polystyrene discs. Further, we addressed issues concerning sterility, long-term cytotoxicity and chip disassembly for remodeling analysis11,12.
The LOC platform can also be used to induce osteocyte mechanotransduction through matrix deformation. A 3D printed mechanical loading device was developed to pair with the LOC and apply a static out of plane distention to stretch the cells13. To accommodate this mechanical load, the depth of the well within the LOC was increased. This small scale, simple mechanical loading device can be easily produced by labs with limited engineering experience, and we have previously shared drawings of the 3D printed components13. In the current work, we demonstrate some of the novel techniques necessary for the successful use of the LOC. Specifically, we demonstrate chip fabrication, cell seeding on functional substrates, mechanical loading and chip disassembly for remodeling quantification. We believe that the explanation of these techniques benefit from a visual format.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Acrylic sheet</td>
			<td>Optix</td>
			<td>--</td>
			<td>3.175 mm thick</td>
		</tr>
		<tr>
			<td>Angled dispensing tips</td>
			<td>Jensen Global</td>
			<td>JG18-0.5X-90</td>
			<td>Remove plastic connector prior to use</td>
		</tr>
		<tr>
			<td>Biopsy punch</td>
			<td>Robbins Instruments</td>
			<td>RBP-10</td>
			<td>1 mm diameter</td>
		</tr>
		<tr>
			<td>Bone wafers</td>
			<td>Boneslices.com</td>
			<td>0.4 mm thick</td>
			<td>Bovine cortical bone</td>
		</tr>
		<tr>
			<td>Bovine calf serum</td>
			<td>Hyclone</td>
			<td>SH30072</td>
			<td></td>
		</tr>
		<tr>
			<td>Calipers</td>
			<td>Global Industrial</td>
			<td>T9F534164</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell spatula</td>
			<td>TPP</td>
			<td>99010</td>
			<td></td>
		</tr>
		<tr>
			<td>Chip mask</td>
			<td>ProtoLabs</td>
			<td>Custom-designed</td>
			<td>Print material: Accura SL 5530</td>
		</tr>
		<tr>
			<td>Cork borer</td>
			<td>Fisher Scientific</td>
			<td>07-865-10B</td>
			<td></td>
		</tr>
		<tr>
			<td>Cotton tipped applicator</td>
			<td>Puritan</td>
			<td>806-WCL</td>
			<td></td>
		</tr>
		<tr>
			<td>Culture dish (100 mm)</td>
			<td>Corning</td>
			<td>430591</td>
			<td>Sterile, Non-tissue culture treated</td>
		</tr>
		<tr>
			<td>Culture dish (150 mm)</td>
			<td>Corning</td>
			<td>430597</td>
			<td>Sterile, Non-tissue culture treated</td>
		</tr>
		<tr>
			<td>Double sided tape</td>
			<td>3M Company</td>
			<td>Scotch 237</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum</td>
			<td>Hyclone</td>
			<td>SH30910</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>Fisher Scientific</td>
			<td>22-327379</td>
			<td></td>
		</tr>
		<tr>
			<td>Leveling box</td>
			<td>Custom-made</td>
			<td>--</td>
			<td>3D printed</td>
		</tr>
		<tr>
			<td>Masking tape</td>
			<td>3M Company</td>
			<td>Scoth 2600</td>
			<td></td>
		</tr>
		<tr>
			<td>MC3T3-E1 preosteoblasts</td>
			<td>ATCC</td>
			<td>CRL-2593</td>
			<td>Subclone 4</td>
		</tr>
		<tr>
			<td>Mechanical loading device</td>
			<td>Custom-made</td>
			<td>--</td>
			<td>3D printed</td>
		</tr>
		<tr>
			<td>Minimum essential alpha medium</td>
			<td>Gibco</td>
			<td>12571-063</td>
			<td></td>
		</tr>
		<tr>
			<td>MLO-Y4 osteocytes</td>
			<td>--</td>
			<td>--</td>
			<td>Gift from Dr. Lynda Bonewald</td>
		</tr>
		<tr>
			<td>Packaging tape</td>
			<td>Duck Brand</td>
			<td>--</td>
			<td>Standard packaging tape</td>
		</tr>
		<tr>
			<td>Paraffin film</td>
			<td>Bemis Parafilm</td>
			<td>PM999</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin/streptomycin</td>
			<td>Invitrogen</td>
			<td>p4333</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasma cleaner</td>
			<td>Harrick Plasma</td>
			<td>PDC-001</td>
			<td>Expanded plasma cleaner</td>
		</tr>
		<tr>
			<td>Polydimethylsiloxane kit</td>
			<td>Dow Corning</td>
			<td>Sylgard 184</td>
			<td></td>
		</tr>
		<tr>
			<td>Polystyrene coverslips</td>
			<td>Nunc Thermanox</td>
			<td>174942</td>
			<td>Sterile, tissue culture treated</td>
		</tr>
		<tr>
			<td>Oven</td>
			<td>Quincy Lab</td>
			<td>12-180</td>
			<td></td>
		</tr>
		<tr>
			<td>RAW264.7 preosteoclasts</td>
			<td>ATCC</td>
			<td>TIB-71</td>
			<td></td>
		</tr>
		<tr>
			<td>Scalpel</td>
			<td>BD Medical</td>
			<td>372611</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicone tubing</td>
			<td>Saint-Gobain Tygon</td>
			<td>ABW00001</td>
			<td>ID: 1/32&#34; (0.79 mm), OD: 3/32&#34; (2.38 mm)</td>
		</tr>
		<tr>
			<td>SolidWorks software</td>
			<td>Dassault Syst&#232;mes</td>
			<td>--</td>
			<td>Used to generate 3D printed models and perform FEA</td>
		</tr>
		<tr>
			<td>Spray adhesive</td>
			<td>Loctite</td>
			<td>2323879</td>
			<td>Multi-purpose adhesive</td>
		</tr>
		<tr>
			<td>Syringe (5 ml)</td>
			<td>BD Medical</td>
			<td>309646</td>
			<td>Sterile</td>
		</tr>
		<tr>
			<td>Syringe pump</td>
			<td>Harvard Apparatus</td>
			<td>70-2213</td>
			<td>Pump 11 Pico Plus</td>
		</tr>
		<tr>
			<td>Tapered laboratory spatula</td>
			<td>Fisher Scientific</td>
			<td>21-401-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Two-part expoxy</td>
			<td>Loctite</td>
			<td>1395391</td>
			<td>5 minute quick set</td>
		</tr>
		<tr>
			<td>Type I collagen</td>
			<td>Corning</td>
			<td>354236</td>
			<td>Rat tail collagen</td>
		</tr>
		<tr>
			<td>Vacuum desiccator</td>
			<td>Bel-Art</td>
			<td>F42010-0000</td>
			<td></td>
		</tr>
		<tr>
			<td>Waterproof sealant</td>
			<td>Gorilla</td>
			<td>8090001</td>
			<td>100% silicone sealant</td>
		</tr>
	</tbody>
</table>

a lab-on-a-chip platform for stimulating osteocyte mechanotransduction and analyzing functional outcomes of bone remodeling

Bone remodeling is a tightly regulated process that is required for skeletal growth and repair as well as adapting to changes in the mechanical environment. During this process, mechanosensitive osteocytes regulate the opposing responses between the catabolic osteoclasts and anabolic osteoblasts. To better understand the highly intricate signaling pathways that regulate this process, our lab has developed a foundationary lab-on-a-chip (LOC) platform for analyzing functional outcomes (formation and resorption) of bone remodeling within a small scale system. As bone remodeling is a lengthy process that occurs on the order of weeks to months, we developed long-term cell culturing protocols within the system. Osteoblasts and osteoclasts were grown on functional activity substrates within the LOC and maintained for up to seven weeks. Afterward, chips were disassembled to allow for the quantification of bone formation and resorption. Additionally, we have designed a 3D printed mechanical loading device that pairs with the LOC platform and can be used to induce osteocyte mechanotransduction by deforming the cellular matrix. We have optimized cell culturing protocols for osteocytes, osteoblasts, and osteoclasts within the LOC platform and have addressed concerns of sterility and cytotoxicity. Here, we present the protocols for fabricating and sterilizing the LOC, seeding cells on functional substrates, inducing mechanical load, and disassembling the LOC to quantify endpoint results. We believe that these techniques lay the groundwork for developing a true organ-on-a-chip for bone remodeling.

The shallow-well configuration can be used for analyzing functional activity of osteoblasts and osteoclasts. Bone formation via osteoblasts and resorption via osteoclasts requires culturing times on the order of several weeks to months. Bone formation from MC3T3-E1 pre-osteoblasts was quantified using alizarin red and von Kossa stains11,15. At day 49, the average surface area stained with alizarin red was 10.7% &#177; 2.2% (mean &...

Watch this Scientific Journal Video about A Lab-On-A-Chip Platform for Stimulating Osteocyte Mechanotransduction and Analyzing Functional Outcomes of Bone Remodeling at JoVE.com

A Lab-On-A-Chip Platform for Stimulating Osteocyte Mechanotransduction and Analyzing Functional Outcomes of Bone Remodeling

Here, we present protocols for analyzing bone remodeling within a lab-on-a-chip platform. A 3D printed mechanical loading device can be paired with the platform to induce osteocyte mechanostransduction by deforming the cellular matrix. The platform can also be used to quantify bone remodeling functional outcomes from osteoclasts and osteoblasts (resorption/formation).

Bone remodeling is a tightly regulated process that is required for skeletal growth and repair as well as adapting to changes in the mechanical ...

Here we present protocols for culturing bone cells within an adaptable lab-on-a-chip platform. These techniques can be used to further our understanding of the mechanisms that regulate mechanically-induced bone remodeling. Our system allows for long-term culturing of bone cells, which enables direct quantification of bone formation and resorption in response to altered mechanical loading environments.Use of these foundational techniques can lead to discoveries that extend to a number of bone-related issues such as osteoporosis, fracture healing, and periprosthetic osteolysis. To create the well and microchannel layer, combine the PDMS prepolymer and curing agent at a ratio of 10 to one in a plastic cup and mix vigorously, then degas the polymer for 30 minutes. Slowly pour the mixture over the appropriate pre-leveled mask.Let it sit for 30 minutes and bake it at 45 degrees Celsius for 18 hours. Loosen the edges of the PDMS with a tapered laboratory spatula and carefully peel it away from the mask, then cut out individual chips with a scalpel and a 3D-printed template and surface clean them with packaging tape. To make the PDMS membrane layer, repeat the previous steps for mixing, pouring, and baking the PDMS.Remove the PDMS sheet from the leveling box and cut individual membranes that match the dimensions of the well and microchannel layer. Use calipers to measure the membrane thickness at the center and discard any membranes that are outside of the desired thickness, then carefully clean the membranes with packaging tape and place them on a piece of paraffin film. To make the PDMS lid layer, repeat the previous steps for mixing, pouring, and baking the PDMS.After cutting individual lids to size, punch access holes through the PDMS with a one millimeter biopsy punch and then surface clean them with packaging tape. Activate the surfaces of layers one and two with a plasma cleaner for 30 seconds on a medium radio frequency power setting, then align the access holes in layer one with the microchannels in layer two and firmly press the two layers together. For the deep-well design, repeat this process with layers two and three using double-sided tape to attach the paraffin film of layer three to a flat surface during plasma treatment.Trim off excess material from the PDMS membrane and carefully peel away the sheet of paraffin film from the bottom of the chip. Bake the chip at 65 degrees Celsius for 10 minutes to increase bond strength between the PDMS layers, then insert angle dispensing tips into the access holes in the lid and secure them with a two-part epoxy using a micropipette tip to apply the epoxy around each tip. After the epoxy has fully cured, surface clean the chip with 70%ethanol and transfer it to a biosafety cabinet.Connect a five milliliter syringe to the dispensing tips with sterile silicone tubing and fill the entire chip with 70%ethanol for at least 30 seconds. Remove the ethanol from the chip and sterilize it with UV light overnight. On the next day, wash the chip three times with distilled water, fill it with water, and remove the tubing from the dispensing tips.Incubate the chip for at least 48 hours at 37 degrees Celsius. Place a compression spring around the shaft of the platen and insert it into the central hole on the bottom of the base, then attach the dial block to the bottom of the base with four self-tapping screws. Place a second compression spring around the central screw.Insert the screw into the hexagonal-shaped hole in the bottom of the dial and screw the assembly into the threaded hole in the center of the dial block. Screw four male-female standoffs into the bottom of the base. Remove slack from the device by turning the dial counterclockwise until the top of the platen is below the top of the base, then slowly turn the dial clockwise until the top of the platen is level with the top of the base.Use a five milliliter syringe to remove the water from the deep-well chip and coat the bottom of the well with 200 microliters of type I collagen in acetic acid for an hour. Rinse the chip three times using DPBS with calcium and magnesium and place it into the chip holder. Seed the chip with MLO-Y4 osteocytes in MEM alpha medium supplemented with calf serum, FBS, and penicillin/streptomycin.Remove the tubing from the dispensing tips, place the chip into a deep-well culture dish, and incubate the cells at 37 degrees Celsius and five percent carbon dioxide for 72 hours. After the incubation, attach sterile tubing to dispensing tips and use a five milliliter syringe to remove the spent culture medium from the chip, then slowly refill the chip with fresh medium. Place the chip holder into the rectangular inset on the top of the loading device base, feed the tubing through the slots located on the lid, and secure the lid to the base.Apply load to the cells by turning the dial clockwise until the desired platen displacement is reached, then place the loading device into an empty P1000 micropipette tip box and incubate the cells with the load for 15 minutes. After the incubation, remove the load from the cells by turning the dial counterclockwise to the original starting position, then remove the lid from the device, place the chip holder into the deep-well culture plate, and incubate the cells for a 90-minute post load recovery period. Use a five milliliter syringe to remove the conditioned medium from the chip and remove the chip from the chip holder, then use a tapered spatula to break the bond between the PDMS lid and well layer.The cells are now ready to be analyzed. The shallow-well configuration can be used for analyzing functional activity of osteoblasts and osteoclasts. Bone formation from preosteoblasts was quantified using alizarin red and von Kossa stains.Bone resorption from osteoclasts was quantified using toluidine blue staining and scanning electron microscopy was used to verify the presence of resorption pits. The deep-well chip configuration was used to induce osteocyte mechanotransduction by stretching the cells via a static out of plane distension. Images of osteocyte seeded in chips demonstrate that the 48-hour incubation of the chip with distilled water is critical for maintaining cell viability in typical morphology.During bouts of loading, osteocytes were exposed to a strain gradient induced on the PDMS membrane. The relationship between average equivalent strain and platen displacement for values between one and two millimeters was determined and a representative heat map of the induced strain was generated. Following loading, cell viability was analyzed with lactate dehydrogenase staining and the annexin V and dead cell assay.Lactate dehydrogenase stain of stretched osteocytes showed a lighter staining near the outer edge of the well, which corresponds to the location of higher strain values. Our platform provides a high degree of versatility and can be used to investigate a variety of factors that regulate bone remodeling such as load-induced mechanotransduction, inflammation, and drug effects. The techniques presented here provide a foundation for developing a true bone organ on a chip that could greatly enhance our understanding of the multicellular intricacies that regulate bone health.

Research

JoVE Journal

Bioengineering

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