This research was funded by N&#214; Forschungs- und Bildungsges.m.b.H. and the provincial government of Lower Austria through the Life Science Calls (Project ID: LSC15-019) and by the Austrian COMET Program (Project K2 XTribology, Grant No. 849109).

1. Preparation of metal cylinders
<ol>
	<li>Analyze cylindrical cobalt-chromium-molybdenum (CoCrMo) rods fulfilling the standard specifications for surgical implants for their chemical composition using scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy per manufacturer&#8217;s protocol to confirm provided values. 
	NOTE: The elemental composition of the CoCrMo alloy used for this experiment is 65% Co, 28% Cr, 5% Mo and 2% others.</li>
	<li>Wet grind the samples with silicon carbide grinding paper starting with a grain size of 500. Use grinding paper in increasing order up to a grain size of 4000.</li>
	<li>Polish the cylinder with 3 &#181;m and 1 &#181;m paste to achieve a surface roughness that is within the tolerance level of surface finish requirements for metallic surgical implants (ISO 5832-12:2019) and total and partial joint replacement implants (ISO 21534:2007). 
	NOTE: The average surface roughness is determined using a confocal microscope.</li>
	<li>Cut CoCrMo rods (&#216; of 6 mm) to cylinders with a length of 10 mm.</li>
</ol>
2. Harvesting of osteochondral cylinders
<ol>
	<li>Use bovine stifle joints from skeletally mature animals (aged 18-24 months at the time of sacrifice) and keep them contained and cooled until dissection within 24 h after sacrifice. 
	NOTE: Joints are purchased from the local butcher. The joint remains closed until dissection.</li>
	<li>To harvest cylindrical osteochondral plugs under aseptic conditions, disinfect the knee and perform an arthrotomy and expose the medial femoral condyle. 
	NOTE: The dissection has to be performed with caution not to damage the articular surface.</li>
	<li>Inspect the articular surface for macroscopic damages. 
	NOTE: Discard the sample if the cartilage lacks its whitish, smooth and glossy appearance or if there is blistering, fissures or larger defects.</li>
	<li>Align the cutting tube perpendicular to the articular surface of the weight-bearing area and drive the device into the cartilage and subchondral bone by firm strokes with a hammer. At 15 mm penetration depth, twist the device clockwise with a sudden motion.</li>
	<li>Remove the device, insert the white knob and screw it in until the bottom end of the osteochondral plug is visible.</li>
	<li>Mark the anteroposterior orientation of the samples with a sterile marker in order to arrange the osteochondral cylinder accordingly during testing. 
	NOTE: The three-dimensional collagen network and its complex architecture facilitate the unique mechanical properties of articular cartilage and should be considered in the orientation of the samples.</li>
	<li>Rinse the sample with phosphate-buffered saline (PBS) to wash off blood and fat tissue.</li>
	<li>Repeat the steps mentioned above to harvest the desired number of osteochondral plugs (8 mm diameter, 15 mm length). 
	NOTE: Typically, 9 to 12 osteochondral cylinders can be harvested from the weight bearing area on the medial femoral condyle.</li>
	<li>Place the samples in Dulbecco&#8217;s modified Eagle&#8217;s medium containing 10% fetal bovine serum, supplemented with antibiotics (penicillin 200 U/mL; streptomycin 0.2 mg/mL) and amphotericin B 2.5 &#181;g/mL and store them at 4 &#176;C until testing to maintain viability.</li>
	<li>Analyze control osteochondral plugs immediately after harvesting to establish baseline values (see analysis section).</li>
</ol>
3. Tribological testing
<ol>
	<li>Perform the experiments using a commercially available reciprocating tribometer with a cylinder-on-plate configuration. Requirements for the device are vertical loading and adjustable load and sliding speed. Furthermore, a liquid cell enables to perform the tests in a lubricating solution.</li>
	<li>Determine the contact pressure in the CoCrMo-on-cartilage system using a pressure measurement film. Place the pressure measurement film at the interface and apply static load for 30 s to determine initial contact pressure, contact size and shape. Owing to the convexity of the metal cylinder and the articular cartilage, the initial contact area has an elliptical shape in this configuration. 
	NOTE: The pressure measurement film reacts to the applied pressure showing red discoloration of zones where the threshold pressure is reached or exceeded. For 1 N of load, the contact pressure was determined around 2 MPa by visual comparison with defined contact pressures.</li>
	<li>Fix the osteochondral cylinders on the bottom sample holder with the marking aligned with the sliding direction, and mount the CoCrMo cylinders onto the upper load cell.</li>
	<li>Add the testing solution (PBS with 3 g/L hyaluronic acid) into the liquid cell that results in submerging the osteochondral cylinder and covering the metal-cartilage sliding interface.</li>
	<li>Set the testing parameters (prescribed normal force, stroke and sliding speed), which are then applied and maintained throughout the test. 
	NOTE: The stroke length of the reciprocating motion must be set according to the contact area to create a migrating contact area (MCA). For plugs that are 8 mm in diameter, a 2 mm stroke allows adequate rehydration of the cartilage.</li>
	<li>Start reciprocal sliding of the CoCrMo cylinder against the articular cartilage immersed in the lubricating solution with the set loading parameters.</li>
	<li>Monitor the coefficient of friction (COF) during the experiments. 
	NOTE: The COF is assessed automatically but can be calculated using the equation &#956;=F/W (&#956; - coefficient of friction; F - frictional force; W - normal load applied by the system).</li>
	<li>Terminate the experiment after the desired testing period.</li>
	<li>Remove the osteochondral plug from the sample holder, rinse it with PBS and store it in medium until further biological analysis (see below).</li>
	<li>Submerge control samples in the testing solution at room temperature for the duration of the test and analyze together with samples that have been exposed to mechanical loading.</li>
</ol>
4. Analysis
NOTE: Osteochondral cylinder are analyzed for metabolic activity and gene expression to investigate biological activity; histology is performed to study cartilage surface integrity and the underlying matrix.
<ol>
	<li>Histology
	<ol>
		<li>For histological analysis, immerse the osteochondral plugs in 4% buffered formaldehyde solution at room temperature until further processing.</li>
		<li>Rinse the samples with PBS and place them into a plastic vessel.</li>
		<li>Add an excess of the ready-to-use decalcifier-solution so that all samples are covered.</li>
		<li>Apply constant agitation for 4 weeks for complete decalcification.</li>
		<li>After decalcification, embed the samples in water soluble glycols and resins and store them at &#8722;80 &#176;C.</li>
		<li>Obtain 6 &#181;m sections by cryosectioning transversal to the contact area.</li>
		<li>Subsequently, prepare the samples for Safranin O staining and Fastgreen counterstaining using a manufacturer&#8217;s protocol.</li>
		<li>Capture histological images using a microscope and process using imaging processing software.</li>
	</ol>
	</li>
	<li>Metabolic activity 
	NOTE: The metabolic activity of chondrocytes in the articular cartilage are investigated with an XTT-based ex vivo toxicology assay.
	<ol>
		<li>Rinse the osteochondral plug using PBS and place the sample in a Petri dish.</li>
		<li>Place a 24-well plate on a scale and zero the scale.</li>
		<li>Cut off the cartilage from the osteochondral graft with a scalpel in one piece.</li>
		<li>Bisect the cartilage in two equal pieces so that the contact area is equally distributed onto both cartilage pieces and mince one half to 1 mm&#179; pieces. The second half is used for gene expression analysis.</li>
		<li>Transfer the minced cartilage into one well of the prepared 24-well plate and determine the tissue weight.</li>
		<li>Repeat the steps mentioned above for each sample and add 1 mL of growth medium to each well of the plate.</li>
		<li>Add the XTT solution (490 &#181;L of XTT labelling reagent and 10 &#181;L of activation reagent) according to the manufacturer&#8217;s instruction and mix.</li>
		<li>Incubate the plate at 37 &#176;C and 5% CO2 for 4 h.</li>
		<li>After incubation, remove the supernatant and transfer it to a 5 mL tube.</li>
		<li>Extract the tetrazolium product by adding 0.5 mL of dimethyl sulfoxide (DMSO) to the cartilage tissue in the 24-well plate and apply continuous agitation for 1 h at room temperature.</li>
		<li>Remove the DMSO solution and pool it with the previously collected XTT solution.</li>
		<li>Transfer 100 &#181;L of the sample in triplicates in a 96-well plate on a plate reader and measure the absorbance at a wavelength of 492 nm and a reference wavelength at 690 nm.</li>
		<li>Normalize the resulting absorbance values to the wet weight of each sample and perform analysis using software.</li>
	</ol>
	</li>
	<li>Gene expression analysis
	<ol>
		<li>RNA isolation 
		NOTE: RNA isolation is carried out using a commercial kit (Table of Materials) according to the instructions provided by the manufacturer with small amendments.
		<ol>
			<li>Mince the second half of the cartilage tissue obtained from the osteochondral plug into small pieces.</li>
			<li>Transfer them to a tube containing ceramic beads and 300 &#181;L of Lysis Buffer (containing 1% &#946;-mercaptoethanol). 
			NOTE: The samples can be frozen in liquid nitrogen until further processing.</li>
			<li>Thaw the samples for 2 min and use the commercial lyser for homogenization of the tissue. Apply 6500 rpm for 20 s (homogenization step) four times with a 2 min cooling phase after each run (at 4 &#176;C using the commercial lyser cooling device) to fully disrupt the tissue.</li>
			<li>Add 20 &#181;L of proteinase K and 580 &#181;L of RNase-free water to each tube and incubate them at 55 &#176;C for 30 min.</li>
			<li>Centrifuge the samples for 3 min at 10,000 x g and transfer the supernatant to a 1.5 mL tube.</li>
			<li>Add 0.5 volumes of 90% ethanol to each tube and mix.</li>
			<li>Transfer 700 &#181;L of the sample to an RNA binding column placed in a 2 mL collection tube and centrifuge at 8,000 x g for 15 s.</li>
			<li>Discard the flow-through and repeat the centrifugation step for the complete lysate.</li>
			<li>Add 350 &#181;L of Buffer RW1 to the column, centrifuge at 8,000 x g for 15 s, and discard the flow-through.</li>
			<li>Mix 10 &#181;L of DNase stock solution and 70 &#181;L of Buffer RDD. Add the solution to the RNA purification membrane and incubate it at room temperature for 15 min.</li>
			<li>Add 350 &#181;L of Buffer RW1 to the column and centrifuge at 8,000 x g for 15 s. Discard the flow-through.</li>
			<li>Add 500 &#181;L of Buffer RPE and centrifuge at 8,000 x g for 15 s. Discard the flow-through.</li>
			<li>Add 500 &#181;L of Buffer RPE to the RNA purification column and centrifuge at 8,000 x g for 2 min.</li>
			<li>Place the column in a 1.5 mL collection tube and add 30 &#181;L of RNase-free water. Centrifuge at 8,000 x g for 1 min.</li>
			<li>Store the isolated RNA at -80 &#176;C until cDNA synthesis.</li>
		</ol>
		</li>
		<li>cDNA synthesis 
		NOTE: To synthesize complementary DNA (cDNA) from messenger RNA (mRNA) a commercial kit (Table of Materials) was used. RNA from bacteriophage MS2 was added to stabilize isolated RNA during cDNA synthesis.
		<ol>
			<li>Thaw and mix the reagents. The composition for a single reaction is shown in Table 1.</li>
			<li>Add 16 &#181;L of RNA sample to the volume for a single reaction (14 &#181;L).</li>
			<li>Perform cDNA synthesis in a thermal cycler using the following parameters: 10 min at 25 &#176;C (primer annealing), 60 min at 50 &#176;C (DNA synthesis), 5 min at 85 &#176;C (denaturation) and 5 min at 20 &#176;C (cooling phase).</li>
			<li>Store cDNA at -20 &#176;C until real-time quantitative polymerase chain reaction (RT-qPCR).</li>
		</ol>
		</li>
		<li>RT-qPCR 
		NOTE: For RT-qPCR of bovine samples, primers and probes were designed by using commercial Real-Time qPCR software (e.g., IDT) for the genes GAPDH (Glyceraldehyde 3-phosphate dehydrogenase), COL2A1 (Collagen type 2), ACAN (Aggrecan), COL1A1 (Collagen type 1), MMP-1 (Matrix Metalloproteinase-1), and MMP-13 (Matrix Metalloproteinase-13). Bovine primers and double quenched probes were provided by IDT. The reagents used for a single reaction to evaluate the efficiency and gene expression are displayed in Table 2.
		<ol>
			<li>Dispense the master mix of a single reaction (9 &#181;L) to each well of a 96-well PCR plate and add 1 &#181;L of cDNA to each reaction. Perform tests for each sample in triplicates.</li>
			<li>Close the PCR plate using sealing oil and centrifuge at 877 x g for 10 min at 4 &#176;C.</li>
			<li>Perform RT-qPCR using a precision thermal cycler with the following protocol: 95 &#176;C for 10 min, 45 cycles of amplification (95 &#176;C for 10 s, annealing for 30 s, cDNA synthesis), and 37 &#176;C for 30 s. 
			NOTE: Specific annealing temperatures are required for each primer.</li>
			<li>Use GAPDH along with the target genes to confirm efficiency.</li>
			<li>Use the provided software to calculate the efficiency of each gene.</li>
			<li>Normalize the cycle threshold (CT) values to the expression of the reference gene GAPDH and use the &#916;&#916;CT method for quantification.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>

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The authors declare that they have no competing interests.

Focal metallic implants represent a salvage procedure for osteochondral defects, especially in middle-aged patients and after failed primary treatment. Although clinical studies demonstrated promising short-term results, one observed complication is damage to the opposing, native cartilage10. Cadaver and biomechanical studies show clear evidence that proper implantation with flat or slightly recessed positioning maintains natural contact pressures19. Tribological experiments provide a possibility to test various cartilage pairings in vitro. In such, loading conditions, lubrication, material pairings and duration might be adjusted as desired.
Bovine cartilage is available in high quantity at the local abattoir. The cellularity and the zonal structure are very similar to the human femoral condyles20. However, proteoglycan content is site-specific, whereas gene expression levels have been shown to be uniform over the articular surface. In this protocol, osteochondral plugs were harvested from the weight bearing area. Cartilage thickness, collagen architecture and resulting tribological properties show regional differences over the articular surface16. The limitation of using osteochondral plugs in an unconfined loading setup with a disrupted collagen network and changed fluid pressurization compared with whole joint models need to be considered.
In the majority of tribological studies, PBS alone is used as testing solution to generate more robust data. PBS is a buffer solution with isotonic osmolarity and helps to maintain a constant pH during biological experiments. Using PBS with hyaluronic acid provides boundary lubrication and reduced friction21. Accordingly, synovial fluid reduces the friction coefficient and improves fluid pressurization compared with saline22. The friction coefficient depends on various system properties, demonstrated by the classic Stribeck Curve. The Stribeck Curve relates the friction coefficient and viscosity, speed and load and presents the basic lubrication regimes: boundary, mixed, and hydrodynamic lubrication. Boundary lubrication can be obtained with PBS alone as lubricating fluid, but loading parameters would need to be adjusted accordingly. The COF delivered from the tests are average values over the stroke. Thus, it can be assumed that different lubrication conditions occur during the cycle. During standstill at reversal position, boundary conditions might be prevailing, while mixed lubrication might be predominant during sliding. Based on absolute duration during the sliding cycle, the latter would have had more influence on the mean COF value.
To investigate physiological conditions occurring in joints during daily activities, loading conditions can be adjusted accordingly in the tribometer software. Pressure sensitive measurements should be used to confirm the desired contact pressures. Reported femorotibial contact pressures range between 1 MPa during standing and up to 10 MPa during downhill running23. With a focal resurfacing, implant pressures are just slightly elevated compared with healthy joints24. Reported relative sliding velocities during the gait cycle are reported up to 100 mm/s with high variations during the different phases. This means that relative joint movements exceed the velocities that can be applied in this tribological setup. To mimic natural kinematic conditions and contact pressures in healthy knee joints, loading conditions range from 1 to 10 MPa contact pressure and 5 to 100 mm/s sliding speed. However, while high loads can be applied in this experimental setup, the range of sliding velocities is limited. Pathological loading conditions, both overload and inadequate loads, might also be simulated. Low sliding velocities or static loading equate immobilization, while higher loads represent nonphysiological mechanical stimulation.
As enzymatic digestion can affect the expression of cartilage-specific genes, a nonenzymatic tissue homogenization is described in this protocol. During cDNA synthesis, in addition to the instructions, RNA from bacteriophage MS2 is added for stabilization purposes. Gene expression levels, but not proteins, were analyzed to detect early changes in the biosynthetic activity of articular chondrocytes. In addition to histological sections and metabolic activity, these assays provide comprehensive information on the effects of mechanical loading on articular cartilage.

The treatment of osteochondral defects is demanding and requires surgery in many cases. For focal osteochondral lesions in middle-aged patients, focal metallic implants are a viable option, especially after the failure of primary treatment, like bone marrow stimulation (BMS) or autologous chondrocyte implantation (ACI)1. Partial surface replacements can be considered salvage procedures that can reduce pain and improve the range of motion2. These implants are typically composed of a CoCrMo alloy and are available in different sizes and offset configurations to match the normal anatomy3. While initially developed for defects on the medial femoral condyle in the knee, such implants are now available and in use for the hip, ankle, shoulder, and elbow4,5,6. For a satisfactory outcome, it is crucial to assess the mechanical joint alignment and condition of the opposing cartilage. Furthermore, correct implantation without protrusion of the implant has been shown to be fundamental7.
Clinical studies demonstrated excellent short-term results in terms of pain reduction and improvement of function in middle-aged patients for various locations5,6,8. Compared with allograft implantation, focal metal implants allow early weight bearing. However, the opposing articular cartilage showed accelerated wear in a considerable number of patients9,10. Hence, even with proper placement, in many cases degeneration of the native cartilage seems inevitable, while the underlying mechanisms remain unclear. Similar degenerative changes have been observed after bipolar hemiarthroplasty of the hip11 and are increased with activity and loading12.
Tribological experiments provide the possibility to study such pairings in vitro and simulate different loading situations occurring under physiological conditions13. The use of osteochondral pins offers a simple geometry model to investigate the tribology of articular cartilage sliding against native cartilage or any implant material14 and might further be used in whole joint simulation models15. Metal-on-cartilage pairings show accelerated cartilage wear, extracellular matrix disruption, and decreased cell viability in the superficial zone compared with a cartilage-on-cartilage pairing16. Damage to the cartilage occurred mainly in the form of delamination between the superficial and middle zones17. However, the mechanisms leading to cartilage degeneration are not fully understood. This protocol provides a comprehensive analysis of the biosynthetic activity of articular cartilage. By the determination of metabolic activity and gene expression levels of catabolic genes, early indications for cartilage breakdown might be identified. The advantage of in vitro tribological experiments is that loading parameters can be adjusted to imitate various loading conditions.
Hence, the following protocol is suitable to simulate a metal-on-cartilage pairing, representing an experimental hemiarthroplasty model.

<table border="0" cellpadding="0" cellspacing="0" style="width:773px;" width="772">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:297px;">Amphotericin B</td>
			<td style="width:191px;">Sigma&#8208;Aldrich Chemie GmbH</td>
			<td style="width:119px;">A-2942-100ML</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">buffered formaldehyde solution 4%</td>
			<td style="width:191px;">VWR</td>
			<td style="width:119px;">97131000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cell Proliferation Kit II (XTT)</td>
			<td>Roche Diagnostics</td>
			<td style="width:119px;">11465015001</td>
			<td>XTT-based ex vivo toxicology assay</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">CoCrMo raw material</td>
			<td style="width:191px;">Acnis International</td>
			<td style="width:119px;"></td>
			<td>CoCrMo rods 6mm in diameter</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CryoStar NX70 Cryostat</td>
			<td>Thermo Fischer Scientific</td>
			<td style="width:119px;"></td>
			<td>cryosectioning device</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">dimethyl sulfoxide (DMSO)</td>
			<td style="width:191px;">Sidma-Aldrich Chemie</td>
			<td style="width:119px;">D 2438-10ML</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Dulbecco&#8217;s modified Eagle&#8217;s medium</td>
			<td style="width:191px;">Sigma&#8208;Aldrich Chemie GmbH</td>
			<td style="width:119px;"></td>
			<td>medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">fetal bovine serum</td>
			<td style="width:191px;">Gibco</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Hyaluronic acid</td>
			<td style="width:191px;">Anika Therapeutics Inc.</td>
			<td style="width:119px;"></td>
			<td>component of lubricating solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">iCycler</td>
			<td>BioRad</td>
			<td style="width:119px;"></td>
			<td>thermal cycler</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Leica microscope DM&#8208;1000</td>
			<td>Leica</td>
			<td style="width:119px;"></td>
			<td>microscope for histology</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">LightCycler 480 Sealing Foil</td>
			<td style="width:191px;">Roche Diagnostics</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">LightCycler 96</td>
			<td>Roche Diagnostics</td>
			<td style="width:119px;"></td>
			<td>thermal cycler for PCR</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MagNA Lyser Green Beads</td>
			<td>Roche Diagnostics</td>
			<td style="width:119px;">3358941001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Osteochondral Autograft Transfer System (OATS)</td>
			<td style="width:191px;">Arthrex Inc.</td>
			<td style="width:119px;"></td>
			<td>cutting tube for harvesting osteochondral cylinders</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">osteosoft</td>
			<td style="width:191px;">Merck</td>
			<td style="width:119px;">1017279010</td>
			<td>decalcifier-solution</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Penicillin /Streptomycin</td>
			<td style="width:191px;">Sigma&#8208;Aldrich Chemie GmbH</td>
			<td style="width:119px;">P4333-100ML</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:297px;">phosphate&#8208;buffered saline</td>
			<td style="width:191px;">Sigma&#8208;Aldrich Chemie GmbH</td>
			<td style="width:119px;"></td>
			<td>PBS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Prescale Low Pressure</td>
			<td style="width:191px;">Fujifilm</td>
			<td style="width:119px;"></td>
			<td>pressure indicating film</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">RNeasy Fibrous Tissue Kit</td>
			<td style="width:191px;">QIAGEN</td>
			<td style="width:119px;">74404</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Synergy 2</td>
			<td>BioTek Instruments</td>
			<td style="width:119px;"></td>
			<td>plate reader</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:297px;">Tetra&#8208;Falex MUST</td>
			<td style="width:191px;">Falex Tribology</td>
			<td style="width:119px;"></td>
			<td>Tribometer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tissue&#8208; Tek O.C.T.</td>
			<td style="width:191px;">SAKURA</td>
			<td style="width:119px;">4583</td>
			<td>embedding formulation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Transcriptor First Strand cDNA Synthesis Kit</td>
			<td>Roche Diagnostics</td>
			<td style="width:119px;">40897030001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">&#946;-mercaptoethanol</td>
			<td style="width:191px;">Sidma-Aldrich Chemie</td>
			<td style="width:119px;">M3148</td>
			<td></td>
		</tr>
	</tbody>
</table>

biotribological testing and analysis of articular cartilage sliding against metal for implants

Osteochondral defects in middle-aged patients might be treated with focal metallic implants. First developed for defects in the knee joint, implants are now available for the shoulder, hip, ankle and the first metatarsalphalangeal joint. While providing pain reduction and clinical improvement, progressive degenerative changes of the opposing cartilage are observed in many patients. The mechanisms leading to this damage are not fully understood. This protocol describes a tribological experiment to simulate a metal-on-cartilage pairing and comprehensive analysis of the articular cartilage. Metal implant material is tested against bovine osteochondral cylinders as a model for human articular cartilage. By applying different loads and sliding speeds, physiological loading conditions can be imitated. To provide a comprehensive analysis of the effects on the articular cartilage, histology, metabolic activity and gene expression analysis are described in this protocol. The main advantage of tribological testing is that loading parameters can be adjusted freely to simulate in vivo conditions. Furthermore, different testing solutions might be used to investigate the influence of lubrication or pro-inflammatory agents. By using gene expression analysis for cartilage-specific genes and catabolic genes, early changes in the metabolism of articular chondrocytes in response to mechanical loading might be detected.

The contact area and contact pressure must be confirmed using a pressure measurement film (Figure 1). Physiological loading condition can be confirmed by comparing with reference imprints for defined contact pressures. During testing, the coefficient of friction is monitored constantly. With a migrating contact area, a low friction coefficient can be maintained for at least 1 h (Figure 2). Using Safranin O staining the extracellular matrix composition and structure can be determined (Figure 3). The intensity of Safranin O staining is proportional to the proteoglycan content. Fast Green counterstains the non-collagen sites and provides a clear contrast to the Safranin O staining. The proteoglycan content varies over the articular surface but should be uniform throughout the tissue section in baseline samples (Figure 3A). Control samples submerged in the testing solution show extraction of GAGs, which can be counteracted by mechanical loading (Figure 3B, 3C). Metabolic activity of the bovine articular chondrocytes is independent of the harvesting site, but shows an increase with mechanical loading compared with unloaded controls (Figure 4). The gene expression levels of cartilage-specific genes (COL2A1, ACAN) increase with physiological loading conditions, whereas catabolic genes (COL1A1 and MMP13) are upregulated with stationary contact area (Figure 5).
<table border="1" fo:keep-together.within-page="1">
	<tbody>
		<tr>
			<td></td>
			<td>Volume (&#181;l)</td>
		</tr>
		<tr>
			<td>Transcriptor RT Reactions Buffer 5x conc.</td>
			<td>6</td>
		</tr>
		<tr>
			<td>Protector RNase Inhibitor 40U/&#181;l</td>
			<td>0.75</td>
		</tr>
		<tr>
			<td>Deoxynucleotide Mix 10 mM each</td>
			<td>3</td>
		</tr>
		<tr>
			<td>Random Hexamer Primer 600 &#181;M</td>
			<td>3</td>
		</tr>
		<tr>
			<td>Transcriptor Reverse Transcriptase 20 U/&#181;l</td>
			<td>0.75</td>
		</tr>
		<tr>
			<td>MS2 RNA (0,8 &#181;g/&#181;l)</td>
			<td>0.375</td>
		</tr>
		<tr>
			<td>Nuclease free distilled water</td>
			<td>0.125</td>
		</tr>
		<tr>
			<td>Total volume</td>
			<td>14</td>
		</tr>
	</tbody>
</table>
Table 1: Reagents for a single reaction for cDNA synthesis.
<table border="1" fo:keep-together.within-page="1">
	<tbody>
		<tr>
			<td></td>
			<td>Volume (&#181;l)</td>
		</tr>
		<tr>
			<td>FastStart Probe Master 2X</td>
			<td>5</td>
		</tr>
		<tr>
			<td>Hydrolysis Probe 2,5 &#181;M</td>
			<td rowspan="3">1</td>
		</tr>
		<tr>
			<td>Left PrimerGAPDH 5 &#181;M</td>
		</tr>
		<tr>
			<td>Right Primer GAPDH 5 &#181;M</td>
		</tr>
		<tr>
			<td>Nuclease free distilled water</td>
			<td>3</td>
		</tr>
		<tr>
			<td>Total Master Mix</td>
			<td>9</td>
		</tr>
	</tbody>
</table>
Table 2: Reagents for the Master Mix for a single PCR.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61304/61304fig1.jpg" /> 
Figure 1: Pressure measurement of the initial contact area at the metal-cartilage interface before testing. Due to the convexity of the metal cylinder and the articular surface and its elastic properties, the initial contact area is elliptical. During sliding, this initial contact area moves with a stroke of 2 mm, resulting in a larger area that is exposed to mechanical loading; scale bar = 2 mm. <a href="https://www.jove.com/files/ftp_upload/61304/61304fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61304/61304fig2.jpg" /> 
Figure 2: Time-depended coefficient of friction (duration 1 hour) for seven samples tested at 8 mm/s sliding speed and 1 N load (2 MPa contact pressure). Each colored line represents the COF of one osteochondral cylinder. The observed variability is within the limits for biological samples. <a href="https://www.jove.com/files/ftp_upload/61304/61304fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61304/61304fig3.jpg" /> 
Figure 3: Histological cross-sections of bovine osteochondral samples stained with Safranin-O and Fast Green. (A) Baseline samples show high GAG content throughout the articular cartilage. (B) Control sample submerged in testing solution without mechanical loading show less Safranin-O staining in the middle zone, indication an extraction of proteoglycans. (C) Tested samples show higher GAG content compared with controls, indicating mechanical stimulation; scale bar = 250 &#181;m <a href="https://www.jove.com/files/ftp_upload/61304/61304fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61304/61304fig4.jpg" /> 
Figure 4: Metabolic activity of bovine articular chondrocytes after tribological testing with different loading variations and controls. The horizontal dotted line represents baseline levels. The nonparametric Kruskal&#8211;Wallis test was performed for comparison between testing groups followed by Dunn&#8217;s post hoc test in case of significance. *p &#60; 0.05. This figure has been modified from Stotter et al.18. <a href="https://www.jove.com/files/ftp_upload/61304/61304fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61304/61304fig5.jpg" /> 
Figure 5: Gene expression of cartilage-specific genes after tribological testing with different loading conditions and controls. COL2A1=collagen type 2; ACAN=aggrecan; COL1A1= collagen type 1; MMP13= matrix metalloproteinase 13. The expression levels were normalized to the housekeeping gene GAPDH (glyceraldehyde 3-phosphate dehydrogenase). The horizontal dotted lines represent baseline expression levels. The nonparametric Kruskal&#8211;Wallis test was performed for comparison between testing groups followed by Dunn&#8217;s post hoc test in case of significance. *p &#60; 0.05. This figure has been modified from Stotter et al.18. <a href="https://www.jove.com/files/ftp_upload/61304/61304fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Biotribological Testing and Analysis of Articular Cartilage Sliding against Metal for Implants at JoVE.com

Biotribological Testing and Analysis of Articular Cartilage Sliding against Metal for Implants

This protocol describes the preparation, biotribological testing, and analysis of osteochondral cylinders sliding against metal implant material. Outcome measures included in this protocol are metabolic activity, gene expression and histology.

Osteochondral defects in middle-aged patients might be treated with focal metallic implants. First developed for defects in the knee joint, implants are ...

biotribological-testing-analysis-articular-cartilage-sliding-against

Nanyang Technological University

Research

JoVE Journal

Medicine

3.8K Views.  Danube University Krems. This protocol describes the preparation, biotribological testing, and analysis of osteochondral cylinders sliding against metal implant material. Outcome measures included in this protocol are metabolic activity, gene expression and histology.

Video: Biotribological Testing and Analysis of Articular Cartilage Sliding against Metal for Implants

A Novel Application of Musculoskeletal Ultrasound Imaging

Ultrasound is an attractive modality for imaging muscle and tendon motion during dynamic tasks and can provide a complementary methodological approach for biomechanical studies in a clinical or laboratory setting. Towards this goal, methods for quantification of muscle kinematics from ultrasound imagery are being developed based on image processing. The temporal resolution of these methods is typically not sufficient for highly dynamic tasks, such as drop-landing. We propose a new approach that utilizes a Doppler method for quantifying muscle kinematics. We have developed a novel vector tissue Doppler imaging (vTDI) technique that can be used to measure musculoskeletal contraction velocity, strain and strain rate with sub-millisecond temporal resolution during dynamic activities using ultrasound. The goal of this preliminary study was to investigate the repeatability and potential applicability of the vTDI technique in measuring musculoskeletal velocities during a drop-landing task, in healthy subjects. The vTDI measurements can be performed concurrently with other biomechanical techniques, such as 3D motion capture for joint kinematics and kinetics, electromyography for timing of muscle activation and force plates for ground reaction force. Integration of these complementary techniques could lead to a better understanding of dynamic muscle function and dysfunction underlying the pathogenesis and pathophysiology of musculoskeletal disorders.

We describe a new ultrasound-based vector tissue Doppler imaging technique to measure muscle contraction velocity, strain and strain rate with sub-millisecond temporal resolution during dynamic activities. This approach provides complementary measurements of dynamic muscle function and could lead to a better understanding of mechanisms underlying musculoskeletal disorders.

Ultrasound is an attractive modality for imaging muscle and tendon  motion during dynamic tasks and can provide a complementary methodological  approach ...

Techniques for Processing Eyes Implanted with a Retinal Prosthesis for Localized Histopathological Analysis: Part 2 Epiretinal Implants with Retinal Tacks

Retinal prostheses for the treatment of certain forms of blindness are gaining traction in clinical trials around the world with commercial devices currently entering the market. In order to evaluate the safety of these devices, in preclinical studies, reliable techniques are needed. However, the hard metal components utilised in some retinal implants are not compatible with traditional histological processes, particularly in consideration for the delicate nature of the surrounding tissue. Here we describe techniques for assessing the health of the eye directly adjacent to a retinal implant secured epiretinally with a metal tack.
Retinal prostheses feature electrode arrays in contact with eye tissue. The most commonly used location for implantation is the epiretinal location (posterior chamber of the eye), where the implant is secured to the retina with a metal tack that penetrates all the layers of the eye. Previous methods have not been able to assess the proximal ocular tissue with the tack in situ, due to the inability of traditional histological techniques to cut metal objects. Consequently, it has been difficult to assess localized damage, if present, caused by tack insertion.
Therefore, we developed a technique for visualizing the tissue around a retinal tack and implant. We have modified an established technique, used for processing and visualizing hard bony tissue around a cochlear implant, for the soft delicate tissues of the eye. We orientated and embedded the fixed eye tissue, including the implant and retinal tack, in epoxy resin, to stabilise and protect the structure of the sample. Embedded samples were then ground, polished, stained, and imaged under various magnifications at incremental depths through the sample. This technique allowed the reliable assessment of eye tissue integrity and cytoarchitecture adjacent to the metal tack.

Here we describe histological techniques for visualising ocular tissue directly adjacent to a metal epiretinal tack and retinal prosthesis.

Retinal prostheses for the treatment of certain forms of blindness are gaining traction in clinical trials around the world with commercial devices ...

Proximal Cadaveric Femur Preparation for Fracture Strength Testing and Quantitative CT-based Finite Element Analysis

Cadaveric fracture testing is routinely used to understand factors that affect proximal femur strength. Because ex vivo biological tissues are prone to lose their mechanical properties over time, specimen preparation for experimental testing must be performed carefully to obtain reliable results that represent in vivo conditions. For that reason, we designed a protocol and a set of fixtures to prepare the femoral specimens such that their mechanical properties experienced minimal changes. The femora were kept in a frozen state except during preparation steps and mechanical testing. The relevant clinical measures of total hip and femoral neck bone mineral density (BMD) were obtained with a clinical dual X-ray absorptiometry (DXA) bone densitometer, and the 3D geometry and distribution of bone mineral were obtained using CT with a calibration phantom for quantitative estimations based on the greyscale values. Any possible bone disease, fracture, or the presence of implants or artifacts affecting the bone structure, was ruled out with X-ray scans. For preparation, all bones were carefully cleaned of excess soft tissue, and were cut and potted at the internal rotation angle of interest. A cutting fixture allowed the distal end of the bone to be cut off leaving the proximal femur at a desired length. To allow positioning of the femoral neck at prescribed angles during later CT scanning and mechanical testing, the proximal femoral shafts were potted in polymethylmethacrylate (PMMA) using a fixture designed specifically for desired orientations. The data collected from our experiments were then used for validation of quantitative computed tomography (QCT)-based finite element analysis (FEA), as described in a different protocol. In this manuscript, we present the protocol for the precise bone preparation for mechanical testing and subsequent QCT/FEA modeling. The current protocol was successfully applied to prepare about 200 cadaveric femora over a 6-year time period.

We present a robust protocol on how to carefully preserve and prepare cadaveric femora for fracture testing and quantitative computed tomography imaging. The method provides precise control over input conditions for the purpose of determining relationships between bone mineral density, fracture strength, and defining finite element model geometry and properties.

Cadaveric fracture testing is routinely used to understand factors that affect proximal femur strength.  Because ex vivo biological tissues are prone to ...

Oral Biofilm Formation on Different Materials for Dental Implants

Dental implants and their prosthetic components are prone to bacterial colonization and biofilm formation. The use of materials that provides low microbial adhesion may reduce the prevalence and progression of peri-implant diseases. In view of the oral environment complexity and oral biofilm heterogeneity, microscopy techniques are needed that can enable a biofilm analysis of the surfaces of teeth and dental materials. This article describes a series of protocols implemented for comparing oral biofilm formation on titanium and ceramic materials for prosthetic abutments, as well as the methods involved in oral biofilms analyses at the morphological and cellular levels. The in situ model to evaluate oral biofilm formation on titanium and zirconia materials for dental prosthesis abutments as described in this study provides a satisfactory preservation of the 48 h biofilm, thereby demonstrating methodological adequacy. Multiphoton microscopy allows the analysis of an area representative of the biofilm formed on the test materials. In addition, the use of fluorophores and the processing of the images using multiphoton microscopy allows the analysis of the bacterial viability in a very heterogeneous population of microorganisms. The preparation of biological specimens for electron microscopy promotes the structural preservation of biofilm, images with good resolution, and no artifacts.

Here, we present a protocol to evaluate oral biofilm formation on titanium and zirconia materials for dental prosthesis abutments, including the analysis of bacterial cells viability and morphological characteristics. An in situ model associated with powerful microscopy techniques is used for the oral biofilm analysis.

Dental implants and their prosthetic components are prone to bacterial colonization and biofilm formation. The use of materials that provides low ...

Handheld Metal Detector Screening for Metallic Foreign Body Ingestion in Children

Coins are the most common ingested metallic foreign bodies among children. The goal of this protocol is to assess the accuracy and feasibility of using a handheld metal detector to detect ingested metallic foreign bodies in children. We propose that by introducing handheld metal detector screening early in the triage process of children with high suspicion of metallic foreign body ingestion, the number of radiographs being ordered to localize the metallic foreign body can be reduced in this radio-sensitive population. The study protocol requires the screening of the participants for history of foreign body ingestion and exclusion of patients with respiratory distress or metallic implants. The patient changes to hospital gown and items that could contain metal like eyeglasses, earrings, pendants, and ornaments are removed. The patient is positioned in the center of the room away from other metallic interferences. The working status of the handheld metal detector is first confirmed by eliciting a positive audio-visual signal. Then the screening is done in an erect position with head in extension to expose the neck, from the level of the chin to the level of the hip joint, to cover the anatomical areas from neck to pelvis in a zig-zag manner both anteriorly and posteriorly. A positive audio-visual signal is carefully noted during the scanning for the presence of metallic foreign body. Relevant radiographs are ordered as per the area detected on the metal detector screening. The handheld metal detector was able to precisely identify all the coins among the ingested metallic foreign bodies in our study. The handheld metal detector could not consistently detect non-coin metallic foreign bodies. This protocol demonstrates the accuracy of handheld metal detector in the identification and localization of coins and coin like metallic foreign bodies.

Here, we present a protocol to use the handheld metal detector, to screen for the presence of ingested metallic foreign bodies in children who present to the pediatric emergency medicine department with a history of foreign body ingestion.

Coins are the most common ingested metallic foreign bodies among children. The goal of this protocol is to assess the accuracy and feasibility of using a ...

Hemocompatibility Testing of Blood-Contacting Implants in a Flow Loop Model Mimicking Human Blood Flow

The growing use of medical devices (e.g., vascular grafts, stents, and cardiac catheters) for temporary or permanent purposes that remain in the body&#39;s circulatory system demands a reliable and multiparametric approach that evaluates the possible hematologic complications caused by these devices (i.e., activation and destruction of blood components). Comprehensive in vitro hemocompatibility testing of blood-contacting implants is the first step towards successful in vivo implementation. Therefore, extensive analysis according to the International Organization for Standardization 10993-4 (ISO 10993-4) is mandatory prior to clinical application. The presented flow loop describes a sensitive model to analyze the hemostatic performance of stents (in this case, neurovascular) and reveal adverse effects. The use of fresh human whole blood and gentle blood sampling are essential to avoid the preactivation of blood. The blood is perfused through a heparinized tubing containing the test specimen by using a peristaltic pump at a rate of 150 mL/min at 37 &#176;C for 60 min. Before and after perfusion, hematologic markers (i.e., blood cell count, hemoglobin, hematocrit, and plasmatic markers) indicating the activation of leukocytes (polymorphonuclear [PMN]-elastase), platelets (&#946;-thromboglobulin [&#946;-TG]), the coagulation system (thombin-antithrombin III [TAT]), and the complement cascade (SC5b-9) are analyzed. In conclusion, we present an essential and reliable model for extensive hemocompatibility testing of stents and other blood-contacting devices prior to clinical application.

This protocol describes a comprehensive hemocompatibility evaluation of blood-contacting devices using laser-cut neurovascular implants. A flow loop model with fresh, heparinized human blood is applied to mimic blood flow. After perfusion, various hematologic markers are analyzed and compared to the values gained directly after blood collection for hemocompatibility evaluation of the tested devices.

The growing use of medical devices (e.g., vascular grafts, stents, and cardiac catheters) for temporary or permanent purposes that remain in the ...

Novel Percutaneous Approach for Deployment of 3D Printed Coronary Stenosis Implants in Swine Models of Ischemic Heart Disease

Minimally invasive methods for creating models of focal coronary narrowing in large animals are challenging. Rapid prototyping using three-dimensionally (3D) printed coronary implants can be employed to percutaneously create a focal coronary stenosis. However, reliable delivery of the implants can be difficult without the use of ancillary equipment. We describe the use of a mother-and-child coronary guide catheter for stabilization of the implant and for effective delivery of the 3D printed implant to any desired location along the length of the coronary vessel. The focal coronary narrowing was confirmed under coronary cineangiography and the functional significance of the coronary stenosis was assessed using gadolinium-enhanced first-pass cardiac perfusion MRI. We showed that reliable delivery of 3D printed coronary implants in swine models (n = 11) of ischemic heart disease can be achieved through repurposing mother-and-child coronary guide catheters. Our technique simplifies the percutaneous delivery of coronary implants to create closed-chest swine models of focal coronary artery stenosis and can be performed expeditiously, with a low procedural failure rate.

We describe a novel, cost-effective, and efficient technique for percutaneous delivery of three-dimensionally printed coronary implants to create closed-chest swine models of ischemic heart disease. The implants were fixed in place using a mother-and-child extension catheter with high success rate.

Minimally invasive methods for creating models of focal coronary narrowing in large animals are challenging. Rapid prototyping using three-dimensionally ...

3D Planning and Printing of Patient Specific Implants for Reconstruction of Bony Defects

We are in the midst of the 3D era in most aspects of life, and especially in medicine. The surgical discipline is one of the major players in the medical field using the constantly developing 3D planning and printing capabilities. Computer-assisted design (CAD) and computer assisted manufacturing (CAM) are used to describe the 3D planning and manufacturing of the product. The planning and manufacturing of 3D surgical guides and reconstruction implants is performed almost exclusively by engineers. As technology advances and software interfaces become more user-friendly, it raises a question regarding the possibility of transferring the planning and manufacturing to the clinician. The reasons for such a shift are clear: the surgeon has the idea of what he wants to design, and he also knows what is feasible and could be used in the operating room. It allows him to be prepared for any scenario/unexpected results during the operation and allows the surgeon to be creative and express his new ideas using the CAD software. The purpose of this method is to provide clinicians with the ability to create their own surgical guides and reconstruction implants. In this manuscript, a detailed protocol will provide a simple method for segmentation using segmentation software and implant planning using a 3D design software. Following the segmentation and stl file production using segmentation software, the clinician could create a simple patient specific reconstruction plate or a more complex plate with a cradle for bone graft positioning. Surgical guides can be created for accurate resection, hole preparation for proper reconstruction plate positioning or for bone graft harvesting and re-contouring. A case of lower jaw reconstruction following plate fracture and nonunion healing of a trauma sustained injury is detailed.

This protocol describes the use of 3D planning and printing for reconstruction of bony defects. We use segmentation tools to create 3D models followed by 3D design software to create patient specific implants for reconstruction purposes concomitant to ablative surgery or as a second stage.

We are in the midst of the 3D era in most aspects of life, and especially in medicine. The surgical discipline is one of the major players in the medical ...

Development and Evaluation of 3D-Printed Cardiovascular Phantoms for Interventional Planning and Training

Catheter-based interventions are standard treatment options for cardiovascular pathologies. Therefore, patient-specific models could help training physicians&#39; wire-skills as well as improving planning of interventional procedures. The aim of this study was to develop a manufacturing process of patient-specific 3D-printed models for cardiovascular interventions.
To create a 3D-printed elastic phantom, different 3D-printing materials were compared to porcine biological tissues (i.e., aortic tissue) in terms of mechanical characteristics. A fitting material was selected based on comparative tensile tests and specific material thicknesses were defined. Anonymized contrast-enhanced CT-datasets were collected retrospectively. Patient-specific volumetric models were extracted from these datasets and subsequently 3D-printed. A pulsatile flow loop was constructed to simulate the intraluminal blood flow during interventions. Models&#39; suitability for clinical imaging was assessed by x-ray imaging, CT, 4D-MRI and (Doppler) ultrasonography. Contrast medium was used to enhance visibility in x-ray-based imaging. Different catheterization techniques were applied to evaluate the 3D-printed phantoms in physicians&#39; training as well as for pre-interventional therapy planning.
Printed models showed a high printing resolution (~30 &#181;m) and mechanical properties of the chosen material were comparable to physiological biomechanics. Physical and digital models showed high anatomical accuracy when compared to the underlying radiological dataset. Printed models were suitable for ultrasonic imaging as well as standard x-rays. Doppler ultrasonography and 4D-MRI displayed flow patterns and landmark characteristics (i.e., turbulence, wall shear stress) matching native data. In a catheter-based laboratory setting, patient-specific phantoms were easy to catheterize. Therapy planning and training of interventional procedures on challenging anatomies (e.g., congenital heart disease (CHD)) was possible.
Flexible patient-specific cardiovascular phantoms were 3D-printed, and the application of common clinical imaging techniques was possible. This new process is ideal as a training tool for catheter-based (electrophysiological) interventions and can be used in patient-specific therapy planning.

Here we present development of a mock circulation setup for multimodal therapy evaluation, pre-interventional planning, and physician-training on cardiovascular anatomies. With the application of patient-specific tomographic scans, this setup is ideal for therapeutic approaches, training, and education in individualized medicine.

Catheter-based interventions are standard treatment options for cardiovascular pathologies. Therefore, patient-specific models could help training ...

A Non-Invasive Method for Generating the Cyclic Loading-Induced Intra-Articular Cartilage Lesion Model of the Rat Knee

The pathophysiology of primary osteoarthritis (OA) remains unclear. However, a specific subclassification of OA in relatively younger age groups is likely correlated with a history of articular cartilage damage and ligament avulsion. Surgical animal models of OA of the knee play an important role in understanding the onset and progression of post-traumatic OA and aid in the development of novel therapies for this disease. However, non-surgical models have been recently considered to avoid traumatic inflammation that could affect the evaluation of the intervention. 
In this study, an intra-articular cartilage lesion rat model induced by in vivo cyclic compressive loading was developed, which allowed researchers to (1) determine the optimal magnitude, speed, and duration of load that could cause focal cartilage damage; (2) assess post-traumatic spatiotemporal pathological changes in chondrocyte vitality; and (3) evaluate the histological expression of destructive or protective molecules that are involved in the adaptation and repair mechanisms against joint compressive loads. This report describes the experimental protocol for this novel cartilage lesion in a rat model.

Here, we present the cyclic loading-induced intra-articular cartilage lesion model of the rat knee, generated by 60 cyclic compressions over 20 N, resulting in damage to the femoral condylar cartilage in rats.

The pathophysiology of primary osteoarthritis (OA) remains unclear. However, a specific subclassification of OA in relatively younger age groups is likely ...