Name: a reliable and reproducible critical-sized segmental femoral defect model in rats stabilized with a custom external fixator
Uploaded: 2019-03-24T15:00:00
Description: Watch this Scientific Journal Video about A Reliable and Reproducible Critical-Sized Segmental Femoral Defect Model in Rats Stabilized with a Custom External Fixator at JoVE.com

This work was supported by an NIH Equipment Grant 1S10OD023676-01 with additional support provided through the University of Wisconsin&#8217;s Departments of Orthopedics and Rehabilitation and School of Medicine and Public Health. We wish to acknowledge the UW&#8217;s Carbone Cancer Center Support Grant P30 CA014520 and use of their Small Animal Imaging Facility, as well as NIH Training Grant 5T35OD011078-08 for support of H. Martin. We also thank Michael and Mary Sue Shannon for their support of the Musculoskeletal Regeneration Partnership.

The rats used in this study received daily care in accordance with the AVMA Guidelines for the Euthanasia of Animals: 2013 Edition16. The Institutional Animal Care and Use Committee at the University of Wisconsin-Madison evaluated and approved this experimental protocol before the project began.
1. Animals
<ol>
	<li>Use the outbred Sprague-Dawley male rats weighing approximately 350 g.</li>
</ol>
2. Preparation of Bone Morphogenetic Protein-2 (rh...

<ol>
	<li>Filipowska, J., Tomaszewski, K. A., Nied&#378;wiedzki, &. #. 3. 2. 1. ;., Walocha, J. A., Nied&#378;wiedzki, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+vasculature+in+bone+development,+regeneration+and+proper+systemic+functioning.">The role of vasculature in bone development, regeneration and proper systemic functioning.</a> Angiogenesis. 20 (3), 291-302 (2017).</li><li>Charalambous, C. P., Akimau, P., Wilkes, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hybrid+monolateral-ring+fixator+for+bone+transport+in+post-traumatic+femoral+segmental+defect:+A+technical+note.">Hybrid monolateral-ring fixator for bone transport in post-traumatic femoral segmental defect: A technical note.</a> Archives of Orthopaedic and Trauma Surgery. 129 (2), 225-226 (2009).</li><li>Xing, 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=Establishment+of+a+bilateral+femoral+large+segmental+bone+defect+mouse+model+potentially+applicable+to+basic+research+in+bone+tissue+engineering.">Establishment of a bilateral femoral large segmental bone defect mouse model potentially applicable to basic research in bone tissue engineering.</a> The Journal of Surgical Research. 192 (2), 454-463 (2014).</li><li>Chadayammuri, V., Hake, M., Mauffrey, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Innovative+strategies+for+the+management+of+long+bone+infection:+A+review+of+the+Masquelet+technique.">Innovative strategies for the management of long bone infection: A review of the Masquelet technique.</a> Patient Safety in Surgery. 9 (32), (2015).</li><li>Koettstorfer, J., Hofbauer, M., Wozasek, G. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Successful+limb+salvage+using+the+two-staged+technique+with+internal+fixation+after+osteodistraction+in+an+effort+to+treat+large+segmental+bone+defects+in+the+lower+extremity.">Successful limb salvage using the two-staged technique with internal fixation after osteodistraction in an effort to treat large segmental bone defects in the lower extremity.</a> Archives of Orthopaedic and Trauma Surgery. 132 (19), 1399-1405 (2012).</li><li>Fragomen, A. T., Rozbruch, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mechanics+of+external+fixation.">The mechanics of external fixation.</a> The Musculoskeletal Journal of Hospital for Special Surgery. 3 (1), 13-29 (2007).</li><li>O&#8217;Toole, R. V., 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+prospective+randomized+trial+to+assess+fixation+strategies+for+severe+open+tibia+fractures:+Modern+ring+external+fixators+versus+internal+fixation+(FIXIT+Study).">A prospective randomized trial to assess fixation strategies for severe open tibia fractures: Modern ring external fixators versus internal fixation (FIXIT Study).</a> Journal of Orthopaedic Trauma. 31, S10-S17 (2017).</li><li>F&#252;rmetz, 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=Bone+transport+for+limb+reconstruction+following+severe+tibial+fractures.">Bone transport for limb reconstruction following severe tibial fractures.</a> Orthopedic Reviews. 8 (1), 6384 (2016).</li><li>Dohin, B., Kohler, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Masquelet&#8217;s+procedure+and+bone+morphogenetic+protein+in+congenital+pseudarthrosis+of+the+tibia+in+children:+A+case+series+and+meta-analysis.">Masquelet&#8217;s procedure and bone morphogenetic protein in congenital pseudarthrosis of the tibia in children: A case series and meta-analysis.</a> Journal of Children's Orthopaedics. 6 (4), 297-306 (2012).</li><li>Einhorn, T. A., Gerstenfeld, L. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fracture+healing:+Mechanisms+and+interventions.">Fracture healing: Mechanisms and interventions.</a> Nature Reviews Rheumatology. 11, 45-54 (2015).</li><li>Pascher, A., 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=Gene+delivery+to+cartilage+defects+using+coagulated+bone+marrow+aspirate.">Gene delivery to cartilage defects using coagulated bone marrow aspirate.</a> Gene Therapy. 11 (2), 133-141 (2004).</li><li>Glatt, V., Matthys, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adjustable+stiffness,+external+fixator+for+the+rat+femur+osteotomy+and+segmental+bone+defect+models.">Adjustable stiffness, external fixator for the rat femur osteotomy and segmental bone defect models.</a> Journal of Visualized Experiments. (92), (2014).</li><li>Betz, O. 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=Direct+percutaneous+gene+delivery+to+enhance+healing+of+segmental+bone+defects.">Direct percutaneous gene delivery to enhance healing of segmental bone defects.</a> The Journal of Bone and Joint Surgery. 88 (2), 355-365 (2006).</li><li>Fang, 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=Stimulation+of+new+bone+formation+by+direct+transfer+of+osteogenic+plasmid+genes.">Stimulation of new bone formation by direct transfer of osteogenic plasmid genes.</a> Proceedings of the National Academy of Sciences of the United States of America. 93 (12), 5753-5758 (1996).</li><li>Kaspar, K., Schell, H., Toben, D., Matziolis, G., Bail, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+easily+reproducible+and+biomechanically+standardized+model+to+investigate+bone+healing+in+rats,+using+external+fixation.">An easily reproducible and biomechanically standardized model to investigate bone healing in rats, using external fixation.</a> Biomedizinische Technik. 52 (6), 383-390 (2007).</li><li>Leary, 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=AVMA+guidelines+for+the+euthanasia+of+animals:+2013+edition.">AVMA guidelines for the euthanasia of animals: 2013 edition.</a> American Veterinary Medical Association. , (2013).</li><li>McKay, W. F., Peckham, S. M., Badura, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+comprehensive+clinical+review+of+recombinant+human+bone+morphogenetic+protein-2+(INFUSE+Bone+Graft).">A comprehensive clinical review of recombinant human bone morphogenetic protein-2 (INFUSE Bone Graft).</a> International Orthopaedics. 31 (6), 729-734 (2007).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Living lmage Software. , (2006).</li><li>Bassett, J. H. D., Van Der Spek, A., Gogakos, A., Williams, G. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+X-ray+imaging+of+rodent+bone+by+faxitron.">Quantitative X-ray imaging of rodent bone by faxitron.</a> Methods in Molecular Biology. , 499-506 (2012).</li><li>Histing, T., 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=Small+animal+bone+healing+models:+Standards,+tips,+and+pitfalls+results+of+a+consensus+meeting.">Small animal bone healing models: Standards, tips, and pitfalls results of a consensus meeting.</a> Bone. 49 (4), 591-599 (2011).</li><li>Lieberman, J. R., 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=The+effect+of+regional+gene+therapy+with+bone+morphogenetic+protein-2-producing+bone-marrow+cells+on+the+repair+of+segmental+femoral+defects+in+rats.">The effect of regional gene therapy with bone morphogenetic protein-2-producing bone-marrow cells on the repair of segmental femoral defects in rats.</a> The Journal of Bone and Joint Surgery. 81 (7), 905-917 (1999).</li><li>Tsuchida, H., Hashimoto, J., Crawford, E., Manske, P., Lou, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineered+allogeneic+mesenchymal+stem+cells+repair+femoral+segmental+defect+in+rats.">Engineered allogeneic mesenchymal stem cells repair femoral segmental defect in rats.</a> Journal of Orthopaedic Research. 21 (1), 44-53 (2003).</li><li>Jiang, H., 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=Novel+standardized+massive+bone+defect+model+in+rats+employing+an+internal+eight-hole+stainless+steel+plate+for+bone+tissue+engineering.">Novel standardized massive bone defect model in rats employing an internal eight-hole stainless steel plate for bone tissue engineering.</a> Journal of Tissue Engineering and Regenerative Medicine. 12 (4), 2162-2171 (2018).</li><li>Baltzer, A. W., 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=Genetic+enhancement+of+fracture+repair:+Healing+of+an+experimental+segmental+defect+by+adenoviral+transfer+of+the+BMP-2+gene.">Genetic enhancement of fracture repair: Healing of an experimental segmental defect by adenoviral transfer of the BMP-2 gene.</a> Gene Therapy. 7 (9), 734-739 (2000).</li><li>Li, Y., 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=Bone+defect+animal+models+for+testing+efficacy+of+bone+substitute+biomaterials.">Bone defect animal models for testing efficacy of bone substitute biomaterials.</a> Journal of Orthopaedic Translation. 3 (3), 95-104 (2015).</li></ol>

Small animal models of orthopedic injuries such as complete bone fractures enable research that explores the mechanisms of osteogenesis and assessing the therapeutic potential of biomaterials20. This study introduces a rat segmental defect model stabilized by a custom external fixator that a lab and biomedical engineering team can readily reproduce for further studies of load-bearing osteosynthetic bone repair.
Previous studies using critical-sized defects in rat models...

Orthopedic trauma surgery focuses on treating a wide range of complex fractures. Critical diaphyseal segmental bone defects have proven difficult to treat clinically due to the decreased regenerative ability of the surrounding muscle and periosteum as well as the failure of localized angiogenesis1. Modern treatment techniques include operative fixation with bone grafting, delayed bone (Masquelet) grafting, bone transport, fusion, or amputation2,3,4. In most patients who have ambulatory function preserved after their trauma, with well-functioning distal limbs, limb salvage is clearly a better treatment option5. These salvage treatments often require staged surgical interventions over a long treatment course. Some authors have suggested that external fixation is superior as compared to the internal fixation for these applications due to the decreased tissue damage during implantation, decreased implanted surface area, and increased postoperative adjustability of the fixator6. However, a prospective randomized controlled trial is currently underway to help clarify this controversy of internal versus external fixation in severe open fractures of the tibia7. Unfortunately, with either treatment selected, significant complication and failure rates persist8,9. With either treatment method, with respect to the segmental bone loss, the surgeon must contend with segmental diaphyseal defects that present significant challenges. Corrections of segmental defects must maximize bone stabilization and simultaneously enhance the osteogenic process10,11.
Due to the clinical importance, yet the lower volume, of critical-sized diaphyseal segmental defects, an effective, reproducible animal model is necessary to enable research teams to advance treatment techniques and ultimately improve clinical outcomes. Researchers need to study in vivo physiologic healing mechanisms in a mammalian animal model. While such models of external fixation already exist12,13,14,15, we hope to provide a more reliable method for non-unions in the untreated animals, decrease costs through the choice of affordable fixator materials, and outline a straightforward surgical protocol for the easy application to future studies. The primary goal of this protocol is to establish a reliable and reproducible model of a critical diaphyseal defect in rats. The procedure was evaluated by assessing the stabilization and bone healing in rat femurs over 12 weeks. The secondary goals included: making an affordable model as a cost effective as possible, simplifying the surgical approach and stabilization, and ensuring ethical care of the animals. The authors and research team conducted preliminary experiments with a range of different biomaterials and potential regenerative therapies to improve healing in this segmental defect.

<table>
	<tbody>
		<tr>
			<td>0.9% Sterile Saline</td>
			<td>Baxter</td>
			<td>2F7124</td>
			<td>Used for irrigating wound and rehydration</td>
		</tr>
		<tr>
			<td>10% Iodine/Povidone</td>
			<td>Carefusion</td>
			<td>1215016</td>
			<td>Used to prep skin</td>
		</tr>
		<tr>
			<td>10% Neutral Buffered Formalin</td>
			<td>VWR</td>
			<td>89370094</td>
			<td>Used as fixative</td>
		</tr>
		<tr>
			<td>1mm non-threaded kirschner wire</td>
			<td>DePuy Synthes</td>
			<td>VW1003.15</td>
			<td>Sterilized, used for the most proximal pin</td>
		</tr>
		<tr>
			<td>1mm threaded kirschner wire</td>
			<td>DePuy Synthes</td>
			<td>VW1005.15</td>
			<td>Sterilized, used for the 3 most distal pin slots</td>
		</tr>
		<tr>
			<td>2x2 gauze</td>
			<td>Covidien</td>
			<td>4006130</td>
			<td>Sterilized, used to prep skin and absorb blood</td>
		</tr>
		<tr>
			<td>4-0 Vicryl Suture</td>
			<td>Ethicon</td>
			<td>4015304</td>
			<td>Used to close muscle and skin layers</td>
		</tr>
		<tr>
			<td>4-40 x 0.25&#34;,18-8 stainless steel button head cap screws</td>
			<td>Generic</td>
			<td></td>
			<td>External fixator assembly</td>
		</tr>
		<tr>
			<td>4200 Cordless Driver</td>
			<td>Stryker</td>
			<td>OR-S-4200</td>
			<td>Used to drill kirschner wires</td>
		</tr>
		<tr>
			<td>4x4 gauze</td>
			<td>Covidien</td>
			<td>1219158</td>
			<td>Sterilized, used to absorb blood</td>
		</tr>
		<tr>
			<td>70 % Ethanol</td>
			<td></td>
			<td></td>
			<td>Used to prep skin</td>
		</tr>
		<tr>
			<td>Baytril</td>
			<td>Bayer Healthcare LLC, Animal health division</td>
			<td>312.10010.3</td>
			<td>Added to water as an antibiotic</td>
		</tr>
		<tr>
			<td>Cefazolin</td>
			<td>Hikma Pharmaceuticals</td>
			<td>8917156</td>
			<td>Pre-op antibiotic</td>
		</tr>
		<tr>
			<td>CleanCap Gaussia Luciferase mRNA (5moU)</td>
			<td>TriLink Biotechnologies</td>
			<td>L-7205</td>
			<td>Modified mRNA encoding for Gaussia Luciferase, keep on ice during use</td>
		</tr>
		<tr>
			<td>Coelenterazine native</td>
			<td>NanoLight Technology</td>
			<td>303</td>
			<td>Substrate for Guassia Luciferase, used to assess luciferase activity in vivo</td>
		</tr>
		<tr>
			<td>Double antibiotic ointment</td>
			<td>Johnson &#38; Johnson consumer Inc</td>
			<td>8975432</td>
			<td>Applied to pin sites post-op as wound care</td>
		</tr>
		<tr>
			<td>Dual Cut Microblade</td>
			<td>Stryker</td>
			<td>5400-003-410</td>
			<td>Used to create 5mm defect in femur</td>
		</tr>
		<tr>
			<td>Ethylenediamine Tetraacetic Acid (EDTA)</td>
			<td>Fisher</td>
			<td>BP120-500</td>
			<td>Used to decalcify bone to prep for histology</td>
		</tr>
		<tr>
			<td>Extended Release Buprenorphine</td>
			<td>ZooPharm</td>
			<td></td>
			<td>Used as 3 day pain relief</td>
		</tr>
		<tr>
			<td>Fenestrated drapes</td>
			<td>3M</td>
			<td>1204025</td>
			<td>Used to establish sterile field</td>
		</tr>
		<tr>
			<td>Handpiece cord for TPS</td>
			<td>Stryker</td>
			<td>OR-S-5100-4N</td>
			<td>Used to create 5mm defect in femur</td>
		</tr>
		<tr>
			<td>Heating pad</td>
			<td>K&#38;H Pet Products</td>
			<td>121239</td>
			<td>Rat body temperature maintenance</td>
		</tr>
		<tr>
			<td>Hexagonal head screwdriver</td>
			<td>Wiha</td>
			<td>263/1/16 &#34; X 50</td>
			<td>External fixator tightening</td>
		</tr>
		<tr>
			<td>Induction chamber</td>
			<td>Generic</td>
			<td></td>
			<td>Anesthesia for rats</td>
		</tr>
		<tr>
			<td>Infuse collagen sponge with recombinant human Bone Morphogenic Protein-2</td>
			<td>Medtronic</td>
			<td>7510200</td>
			<td>Clinically relevant treatment used as positive control</td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>Clipper</td>
			<td>10250</td>
			<td>Anesthesia for rats</td>
		</tr>
		<tr>
			<td>IVIS</td>
			<td>Perkin Elmer</td>
			<td>124262</td>
			<td>Bioluminescence imaging modality</td>
		</tr>
		<tr>
			<td>Jig</td>
			<td>Custom</td>
			<td></td>
			<td>Used to place bicortical pins</td>
		</tr>
		<tr>
			<td>Lipofectamine MessengerMAX</td>
			<td>Fisher Scientific</td>
			<td>LMRNA003</td>
			<td>mRNA complexing agent that enables mRNA delivery</td>
		</tr>
		<tr>
			<td>Sensorcaine-MPF (Bupivicane (0.25%) and Epinephrine (1:200,000))</td>
			<td>APP Pharmaceuticals, LLC</td>
			<td>NDC 63323-468-37</td>
			<td>Applied to surgical site for pain relief and vasoconstriction</td>
		</tr>
		<tr>
			<td>Sterile water</td>
			<td>Hospira</td>
			<td>8904653</td>
			<td>Used as solvent for cefazolin powder</td>
		</tr>
		<tr>
			<td>Titanium external fixator plates</td>
			<td>Custom</td>
			<td></td>
			<td>Prepared in house with scrap titanium and milling machine</td>
		</tr>
		<tr>
			<td>Total Performance System (TPS) Console</td>
			<td>Stryker</td>
			<td>OR-S-5100-1</td>
			<td>Used to create 5mm defect in femur</td>
		</tr>
		<tr>
			<td>TPS MicroSaggital Saw</td>
			<td>Stryker</td>
			<td>OR-S-5100-34</td>
			<td>Used to create 5mm defect in femur</td>
		</tr>
		<tr>
			<td>Ultrafocus Faxitron with DXA</td>
			<td>Faxitron</td>
			<td></td>
			<td>High resolution radiographic imaging modality</td>
		</tr>
		<tr>
			<td>Uniprim rat diet</td>
			<td>Envigo</td>
			<td>TD.06596</td>
			<td>Medicated rat diet</td>
		</tr>
		<tr>
			<td>Universal Handswitch for TPS</td>
			<td>Stryker</td>
			<td>OR-S-5100-9</td>
			<td>Used to create 5mm defect in femur</td>
		</tr>
		<tr>
			<td>Vetbond Tissue Adhesive</td>
			<td>3M</td>
			<td>1469</td>
			<td>Skin closure</td>
		</tr>
	</tbody>
</table>

a reliable and reproducible critical-sized segmental femoral defect model in rats stabilized with a custom external fixator

Orthopedic research relies heavily on animal models to study mechanisms of bone healing in vivo as well as investigate the new treatment techniques. Critical-sized segmental defects are challenging to treat clinically, and research efforts could benefit from a reliable, ambulatory small animal model of a segmental femoral defect. In this study, we present an optimized surgical protocol for the consistent and reproducible creation of a 5 mm critical diaphyseal defect in a rat femur stabilized with an external fixator. The diaphyseal ostectomy was performed using a custom jig to place 4 Kirschner wires bicortically, which were stabilized with an adapted external fixator device. An oscillating bone saw was used to create the defect. Either a collagen sponge alone or a collagen sponge soaked in rhBMP-2 was implanted into the defect, and the bone healing was monitored over 12 weeks using radiographs. After 12 weeks, rats were sacrificed, and histological analysis was performed on the excised control and treated femurs. Bone defects containing only collagen sponge resulted in non-union, while rhBMP-2 treatment yielded the formation of a periosteal callous and new bone remodeling. Animals recovered well after implantation, and external fixation proved successful in stabilizing the femoral defects over 12 weeks. This streamlined surgical model could be readily applied to study bone healing and test new orthopedic biomaterials and regenerative therapies in vivo.

Surgeries were performed in approximately one hour by one surgeon with the help of one assistant. After surgical optimization, intra- and postoperative complications were greatly minimized and use of the jig apparatus ensured consistent size (5 x 3 x 3 mm) and localization of femoral defects. Rats were ambulatory immediately following recovery from anesthesia and did not appear to have any altered behavioral patterns; their gait was not antalgic, and they did not appear to be disturbed by...

Watch this Scientific Journal Video about A Reliable and Reproducible Critical-Sized Segmental Femoral Defect Model in Rats Stabilized with a Custom External Fixator at JoVE.com

A Reliable and Reproducible Critical-Sized Segmental Femoral Defect Model in Rats Stabilized with a Custom External Fixator

In vivo mammalian models of critical-sized bone defects are essential for researchers studying healing mechanisms and orthopedic therapies. Here, we introduce a protocol for the creation of reproducible, segmental, femoral defects in rats stabilized using external fixation.

Orthopedic research relies heavily on animal models to study mechanisms of bone healing in vivo as well as investigate the new treatment techniques. ...

This surgical protocol uses a consistent and reproducible externally fixed segmental defect model to evaluate the healing mechanisms of bone and the use of potential regenerative therapies. We have streamlined a challenging surgery for the creation and stabilization of a segmental bone defect model that is accessible and cost effective while remaining appropriate for longitudinal healing studies. This technique is particularly translatable to the treatment of traumatic critical-sized diaphysial bone defects that may benefit from stabilization with external fixation, although the model requires further study.To prevent a fracture while drilling the pins, use high rotations per minute and a low pressure to puncture the lateral cortex, then decrease the rotations per minute to advance. After preparing the scaffold from a bone morphogenetic protein tube bone graft kit, according to the manufacturer's instructions, use sterile scissors and a sterile ruler to trim the collagen sponge to fit a five by three by three millimeter defect. Then use a syringe to distribute the bone morphogenetic protein-2 solution evenly over the surface of the sponge, until the entire volume of solution is absorbed.Next, shave the area around the hind leg of an anesthetized rat using the 13th rib, hind paw, and dorsal and ventral midlines as margins, followed by four sequential alternating scrubs of the exposed skin with sterile gauze soaked in 10%povidone-iodine and 70%ethanol. To induce the femoral defect, extend the shaved leg through a fenestrated clear sticky drape, and cover the surgical bench in sterile towels to create a sterile field. Palpate the femur and use a number 15 blade to create an anterolateral incision through the skin extending from the patella to the greater trochanter at the proximal femur.Carefully incise the lateral leg fascia along the intermuscular septum to separate the vastus lateralis muscle of the quadriceps anteriorly from the hamstrings posteriorly until the lateral femur is exposed. Keeping a number 15 scalpel blade parallel against the contour of the bone surface, gently cut the muscle away from the underlying bone to perform a careful, atraumatic circumferential soft tissue dissection, and start on the lateral surface, expose the femur at its mid-diaphysis. Use a periosteal elevator to lift the muscle away from the exposed bone as it is dissected, and proceed around the femoral shaft until seven to 10 milliliters of central diaphysis has been cleared of soft tissue on all sides.Next, place one pin just at the level of the lateral epicondyl, followed by placement of a jig flush to the lateral distal femur, and insert one one-millimeter threaded tip Kirschner wire. Next, maintaining the position of the jig on the bone, identify where the most proximal pin will enter the bone based on the jig holes. Carefully incise parallel to the fibers of the gluteal tendon as needed to create a small gap in the tissue for the proximal pin to pass through, minimizing iatrogenic damage to the tendon.Drill a one-millimeter non-threaded k-wire into the gap, and compare the height of the drilled pin with the loose pin to confirm that the pin engages both cortices. Maintain the position of the jig in contact with the bone and drill two one-millimeter threaded k-wires, one on either side of the future defect site, ensuring that the pins engage both cortices, and place the external fixator bar level one centimeter above the skin. Screw tightly, locking the bar in place, and clip the excess pin lengths.Place a small curved retractor around the anterior and posterior femur to protect the surrounding soft tissue, muscle, and neurovascular bundle, and use an approximately five millimeter sagittal oscillating saw blade, and light, even pressure, to very carefully create a five millimeter segmental defect through the mid-diaphysis. Flush the wound with 10 milliliters of 0.9%normal saline after creating the defect, and administer 0.1 milliliters of 0.25%bupivacaine with epinephrine to the wound as an analgesic and vasoconstrictor. Insert the bone morphogenetic protein-2 soaked sponge scaffold into the defect, and use a 4-0 absorbable suture in the simple interrupted pattern to close the muscle plane.Then close the skin layer using a 4-0 absorbable suture in a running subcuticular pattern, then skin glue to close any gaps around the protruding pins, and obtain an anterior-posterior radiographic image of the femur immediately, and four and 12 weeks after surgery. Negative control defects containing only a collagen sponge show no evidence of bridging osteogenesis between the proximal and distal bone edges. A small amount of new bone remodeling can be seen directly adjacent to the cut femur edge, while the defect itself shows a lack of bony material, the presence of cartilage, and some residual hematoma.Defects containing bone morphogenetic protein-2 soaked sponge demonstrate significant bone healing as early as four weeks after surgery, as evidenced by the radiopaque callous bridging across the defect. By 12 weeks, significant new mineral deposition has formed throughout the defect. Significant new periosteal bone can be observed in the callous extending from the cut femur edge and the spicules of woven and lamellar bone have developed throughout the defect.Further, cartilage deposition is not seen. Imaging via In Vivo Imaging System after the removal of the external fixator allows visualization of the bioluminescent transfected cells within the defect. For example, cells in the medullary cavity luminesce after transfection with complexed mRNA encoding for Gaussia luciferase, and could be used to measure biological changes in the expression of a gene or protein of interest during the healing process.Pin placement is important for ensuring a stable, lasting external fixation. The pins should be directly perpendicular to the femur, and parallel to each other, to minimize breakage and infection. Using this model, biological mechanisms, such as specific protein expressions, may be monitored to better understand healing, and different scaffold biomaterials or therapies may also be tested for therapeutic efficacy.We hope this technique will allow future researchers to more efficiently and effectively study orthopedic healing with external fixation so that their findings may be translated to improved clinical successes. Avoid inhaling anesthetic gases, wear proper personal protective equipment when handling formalin and EDTA, and take care when handling surgical instruments, particularly the drill and oscillating bone saw.

a-reliable-reproducible-critical-sized-segmental-femoral-defect-model

Research

JoVE Journal

Bioengineering

Creating Two-Dimensional Patterned Substrates for Protein and Cell Confinement

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1 While microcontact printing can be employed to directly print a large number of molecules, including proteins,2 DNA,3 and silanes,4 the formation of self-assembled monolayers (SAMs) from long chain alkane thiols on gold provides a simple way to confine proteins and cells to specific patterns containing adhesive and resistant regions. This confinement can be used to control cell morphology and is useful for examining a variety of questions in protein and cell biology. Here, we describe a general method for the creation of well-defined protein patterns for cellular studies.5 This process involves three steps: the production of a patterned master using photolithography, the creation of a PDMS stamp, and microcontact printing of a gold-coated substrate. Once patterned, these cell culture substrates are capable of confining proteins and/or cells (primary cells or cell lines) to the pattern.
The use of self-assembled monolayer chemistry allows for precise control over the patterned protein/cell adhesive regions and non-adhesive regions; this cannot be achieved using direct protein stamping. Hexadecanethiol, the long chain alkane thiol used in the microcontact printing step, produces a hydrophobic surface that readily adsorbs protein from solution. The glycol-terminated thiol, used for backfilling the non-printed regions of the substrate, creates a monolayer that is resistant to protein adsorption and therefore cell growth.6 These thiol monomers produce highly structured monolayers that precisely define regions of the substrate that can support protein adsorption and cell growth. As a result, these substrates are useful for a wide variety of applications from the study of intercellular behavior7 to the creation of microelectronics.8
While other types of monolayer chemistry have been used for cell culture studies, including work from our group using trichlorosilanes to create patterns directly on glass substrates,9 patterned monolayers formed from alkane thiols on gold are straight-forward to prepare. Moreover, the monomers used for monolayer preparation are commercially available, stable, and do not require storage or handling under inert atmosphere. Patterned substrates prepared from alkane thiols can also be recycled and reused several times, maintaining cell confinement.10

Self-assembled monolayers (SAMs) formed from long chain alkane thiols on gold provide well-defined substrates for the formation of protein patterns and cell confinement. Microcontact printing of hexadecanethiol using a polydimethylsiloxane (PDMS) stamp followed by backfilling with a glycol-terminated alkane thiol monomer produces a pattern where protein and cells adsorb only to the stamped hexadecanethiol region.

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1  While microcontact printing ...

A Full Skin Defect Model to Evaluate Vascularization of Biomaterials In Vivo

Insufficient vascularization is considered to be one of the main factors limiting the clinical success of tissue-engineered constructs. In order to evaluate new strategies that aim at improving vascularization, reliable methods are required to make the in-growth of new blood vessels into bio-artificial scaffolds visible and quantify the results. Over the past couple of years, our group has introduced a full skin defect model that enables the direct visualization of blood vessels by transillumination and provides the possibility of quantification through digital segmentation. In this model, one surgically creates full skin defects in the back of mice and replaces them with the material tested. Molecules or cells of interest can also be incorporated in such materials to study their potential effect. After an observation time of one&#8217;s own choice, materials are explanted for evaluation. Bilateral wounds provide the possibility of making internal comparisons that minimize artifacts among individuals as well as of decreasing the number of animals needed for the study. In comparison to other approaches, our method offers a simple, reliable and cost effective analysis. We have implemented this model as a routine tool to perform high-resolution screening when testing vascularization of different biomaterials and bio-activation approaches.

A Full Skin Defect Model to Evaluate Vascularization of Biomaterials In Vivo

Vascularization is key to approaches in successful tissue engineering. Therefore, reliable technologies are required to evaluate the development of vascular networks in tissue-constructs. Here we present a simple and cost-effective method to visualize and quantify vascularization in vivo.

Insufficient vascularization is considered to be one of the main factors limiting the clinical success of tissue-engineered constructs. In order to ...

Custom-designed Laser-based Heating Apparatus for Triggered Release of Cisplatin from Thermosensitive Liposomes with Magnetic Resonance Image Guidance

Liposomes have been employed as drug delivery systems to target solid tumors through exploitation of the enhanced permeability and retention (EPR) effect resulting in significant reductions in systemic toxicity. Nonetheless, insufficient release of encapsulated drug from liposomes has limited their clinical efficacy. Temperature-sensitive liposomes have been engineered to provide site-specific release of drug in order to overcome the problem of limited tumor drug bioavailability. Our lab has designed and developed a heat-activated thermosensitive liposome formulation of cisplatin (CDDP), known as HTLC, to provide triggered release of CDDP at solid tumors. Heat-activated delivery in vivo was achieved in murine models using a custom-built laser-based heating apparatus that provides a conformal heating pattern at the tumor site as confirmed by MR thermometry (MRT). A fiber optic temperature monitoring device was used to measure the temperature in real-time during the entire heating period with online adjustment of heat delivery by alternating the laser power. Drug delivery was optimized under magnetic resonance (MR) image guidance by co-encapsulation of an MR contrast agent (i.e.,&#160;gadoteridol) along with CDDP into the thermosensitive liposomes as a means to validate the heating protocol and to assess tumor accumulation. The heating protocol consisted of a preheating period of 5 min prior to administration of HTLC and 20 min heating post-injection. This heating protocol resulted in effective release of the encapsulated agents with the highest MR signal change observed in the heated tumor in comparison to the unheated tumor and muscle. This study demonstrated the successful application of the laser-based heating apparatus for preclinical thermosensitive liposome development and the importance of MR-guided validation of the heating protocol for optimization of drug delivery.

AN MRI-compatible&#160;custom-designed laser-based heating apparatus has been developed to provide local heating of subcutaneous tumors in order to activate release of agents from thermosensitive liposomes specifically at the tumor region.

Liposomes have been employed as drug delivery systems to target solid tumors through exploitation of the enhanced permeability and retention (EPR) effect ...

Method and Instrumented Fixture for Femoral Fracture Testing in a Sideways Fall-on-the-Hip Position

Mechanical testing of femora brings valuable insights into understanding the contribution of clinically-measureable variables such as bone mineral density distribution and geometry on the femoral mechanical properties. Currently, there is no standard protocol for mechanical testing of such geometrically complex bones to measure strength, and stiffness. To address this gap we have developed a protocol to test cadaveric femora to fracture and to measure their biomechanical parameters. This protocol describes a set of adaptable fixtures to accommodate the various load magnitudes and directions accounting for possible bone orientations in a fall on the hip configuration, test speed, bone size, and left leg-right leg variations. The femora were prepared for testing by cleaning, cutting, scanning, and potting the distal end and greater trochanter contact surfaces in poly(methyl methacrylate) (PMMA) as presented in a different protocol. The prepared specimens were placed in the testing fixture in a position mimicking a sideways fall on the hip and loaded to fracture. During testing, two load cells measured vertical forces applied to the femoral head and greater trochanter, a six-axis load cell measured forces and moments at the distal femoral shaft, and a displacement sensor measured differential displacement between the femoral head and trochanter contact supports. High speed video cameras were used to synchronously record the sequence of fracture events during testing. The reduction of this data allowed us to characterize the strength, stiffness, and fracture energy for nearly 200 osteoporotic, osteopenic, and normal cadaveric femora for further development of engineering-based diagnostic tools for osteoporosis research.

In this manuscript, we present a protocol to fracture test cadaveric proximal femora in a sideways fall on the hip configuration using instrumented fixtures mounted on a standard servo hydraulic frame. Nine digitized signals comprising forces, moments, and displacement along with two high speed video streams are acquired during testing.

Mechanical testing of femora brings valuable insights into understanding the contribution of clinically-measureable variables such as bone mineral density ...

An Efficient and Reproducible Protocol for Distraction Osteogenesis in a Rat Model Leading to a Functional Regenerated Femur

This protocol describes the use of a newly developed external fixator for distraction osteogenesis in a rat femoral model. Distraction osteogenesis (DO) is a surgical technique leading to bone regeneration after an osteotomy. The osteotomized extremities are moved away from each other by gradual distraction to reach the desired elongation. This procedure is widely used in humans for lower and upper limb lengthening, treatment after a bone nonunion, or the regeneration of a bone defect following surgery for bone tumor excision, as well as in maxillofacial reconstruction. Only a few studies clearly demonstrate the efficiency of their protocol in obtaining a functional regenerated bone, i.e., bone that will support physiological weight-bearing without fracture after removal of the external fixator. Moreover, protocols for DO vary and reproducibility is limited by lack of information, making comparison between studies difficult. The aim of this study was to develop a reproducible protocol comprising an appropriate external fixator design for rat limb lengthening, with a detailed surgical technique that permits physiological weight-bearing by the animal after removal of the external fixator.

This study describes a reproducible and detailed protocol using a newly developed external fixator for distraction osteogenesis (DO) in a femoral rat model which permits physiological weight-bearing by the animal after removal of the external fixator.

This protocol describes the use of a newly developed external fixator for distraction osteogenesis in a rat femoral model. Distraction osteogenesis (DO) ...

Fabrication of Custom Agarose Wells for Cell Seeding and Tissue Ring Self-assembly Using 3D-Printed Molds

Engineered tissues are being used clinically for tissue repair and replacement, and are being developed as tools for drug screening and human disease modeling. Self-assembled tissues offer advantages over scaffold-based tissue engineering, such as enhanced matrix deposition, strength, and function. However, there are few available methods for fabricating 3D tissues without seeding cells on or within a supporting scaffold. Previously, we developed a system for fabricating self-assembled tissue rings by seeding cells into non-adhesive agarose wells. A polydimethylsiloxane (PDMS) negative was first cast in a machined polycarbonate mold, and then agarose was gelled in the PDMS negative to create ring-shaped cell seeding wells. However, the versatility of this approach was limited by the resolution of the tools available for machining the polycarbonate mold. Here, we demonstrate that 3D-printed plastic can be used as an alternative to machined polycarbonate for fabricating PDMS negatives. The 3D-printed mold and revised mold design is simpler to use, inexpensive to produce, and requires significantly less agarose and PDMS per cell seeding well. We have demonstrated that the resulting agarose wells can be used to create self-assembled tissue rings with customized diameters from a variety of different cell types. Rings can then be used for mechanical, functional, and histological analysis, or for fabricating larger and more complex tubular tissues.

This protocol describes a platform for fabricating self-assembled tissue rings in variable sizes using a customized 3D-printed plastic mold. PDMS negatives are cured in the 3D-printed mold; then agarose is cast in the cured PDMS negatives. Cells are seeded into the resulting agarose wells where they aggregate into tissue rings.

Engineered tissues are being used clinically for tissue repair and replacement, and are being developed as tools for drug screening and human disease ...

Perfusable Vascular Network with a Tissue Model in a Microfluidic Device

A spheroid (a multicellular aggregate) is regarded as a good model of living tissues in the human body. Despite the significant advancement in the spheroid cultures, a perfusable vascular network in the spheroids remains a critical challenge for long-term culture required to maintain and develop their functions, such as protein expressions and morphogenesis. The protocol presents a novel method to integrate a perfusable vascular network within the spheroid in a microfluidic device. To induce a perfusable vascular network in the spheroid, angiogenic sprouts connected to microchannels were guided to the spheroid by utilizing angiogenic factors from human lung fibroblasts cultured in the spheroid. The angiogenic sprouts reached the spheroid, merged with the endothelial cells co-cultured in the spheroid, and formed a continuous vascular network. The vascular network could perfuse the interior of the spheroid without any leakage. The constructed vascular network may be further used as a route for supply of nutrients and removal of waste products, mimicking blood circulation in vivo. The method provides a new platform in spheroid culture toward better recapitulation of living tissues.

The protocol describes how to engineer a perfusable vascular network in a spheroid. The spheroid's surrounding microenvironment is devised to induce angiogenesis and connect the spheroid to the microchannels in a microfluidic device. The method allows the perfusion of the spheroid, which is a long-awaited technique in three-dimensional cultures.

A spheroid (a multicellular aggregate) is regarded as a good model of living tissues in the human body. Despite the significant advancement in the ...

Repressing Gene Transcription by Redirecting Cellular Machinery with Chemical Epigenetic Modifiers

Regulation of chromatin compaction is an important process that governs gene expression in higher eukaryotes. Although chromatin compaction and gene expression regulation are commonly disrupted in many diseases, a locus-specific, endogenous, and reversible method to study and control these mechanisms of action has been lacking. To address this issue, we have developed and characterized novel gene-regulating bifunctional molecules. One component of the bifunctional molecule binds to a DNA-protein anchor so that it will be recruited to an allele-specific locus. The other component engages endogenous cellular chromatin-modifying machinery, recruiting these proteins to a gene of interest. These small molecules, called chemical epigenetic modifiers (CEMs), are capable of controlling gene expression and the chromatin environment in a dose-dependent and reversible manner. Here, we detail a CEM approach and its application to decrease gene expression and histone tail acetylation at a Green Fluorescent Protein (GFP) reporter located at the Oct4 locus in mouse embryonic stem cells (mESCs). We characterize the lead CEM (CEM23) using fluorescent microscopy, flow cytometry, and chromatin immunoprecipitation (ChIP), followed by a quantitative polymerase chain reaction (qPCR). While the power of this system is demonstrated at the Oct4 locus, conceptually, the CEM technology is modular and can be applied in other cell types and at other genomic loci.

Regulation of the chromatin environment is an essential process required for proper gene expression. Here, we describe a method for controlling gene expression through the recruitment of chromatin-modifying machinery in a gene-specific and reversible manner.

Regulation of chromatin compaction is an important process that governs gene expression in higher eukaryotes. Although chromatin compaction and gene ...

A Tripeptide-Stabilized Nanoemulsion of Oleic Acid

We describe a method to produce a nanoemulsion composed of an oleic acids-Pt(II) core and a lysine-tyrosine-phenylalanine (KYF) coating (KYF-Pt-NE). The KYF-Pt-NE encapsulates Pt(II) at 10 wt. %, has a diameter of 107 &#177; 27 nm and a negative surface charge. The KYF-Pt-NE is stable in water and in serum, and is biologically active. The conjugation of a fluorophore to KYF allows the synthesis of a fluorescent nanoemulsion that is suitable for biological imaging. The synthesis of the nanoemulsion is performed in an aqueous environment, and the KYF-Pt-NE forms via self-assembly of a short KYF peptide and an oleic acids-platinum(II) conjugate. The self-assembly process depends on the temperature of the solution, the molar ratio of the substrates, and the flow rate of the substrate addition. Crucial steps include maintaining the optimal stirring rate during the synthesis, permitting sufficient time for self-assembly, and pre-concentrating the nanoemulsion gradually in a centrifugal concentrator.

This protocol describes an efficient method to synthesize a nanoemulsion of an oleic acids-platinum(II) conjugate stabilized with a lysine-tyrosine-phenylalanine (KYF) tripeptide. The nanoemulsion forms under mild synthetic conditions via self-assembly of the KYF and the conjugate.

We describe a method to produce a nanoemulsion composed of an oleic acids-Pt(II) core and a lysine-tyrosine-phenylalanine (KYF) coating (KYF-Pt-NE). The ...

Establishing Single-Cell Based Co-Cultures in a Deterministic Manner with a Microfluidic Chip

Cell co-culture assays have been widely used for studying cell-cell interactions between different cell types to better understand the biology of diseases including cancer. However, it is challenging to clarify the complex mechanism of intercellular interactions in highly heterogeneous cell populations using conventional co-culture systems because the heterogeneity of the cell subpopulation is obscured by the average values; the conventional co-culture systems can only be used to describe the population signal, but are incapable of tracking individual cells behavior. Furthermore, conventional single-cell experimental methods have low efficiency in cell manipulation because of the Poisson distribution. Microfabricated devices are an emerging technology for single-cell studies because they can accurately manipulate single cells at high-throughput and can reduce sample and reagent consumption. Here, we describe the concept and application of a microfluidic chip for multiple single-cell co-cultures. The chip can efficiently capture multiple types of single cells in a culture chamber (~46%) and has a sufficient culture space useful to study the cells&#39; behavior (e.g., migration, proliferation, etc.) under cell-cell interaction at the single-cell level. Lymphatic endothelial cells and oral squamous cell carcinoma were used to perform a single-cell co-culture experiment on the microfluidic platform for live multiple single-cell interaction studies.

This report describes a microfluidic chip-based method to set up a single cell culture experiment in which high-efficiency pairing and microscopic analysis of multiple single cells can be achieved.

Cell co-culture assays have been widely used for studying cell-cell interactions between different cell types to better understand the biology of diseases ...