Orthopaedic Research Laboratory Alumni Council

Alumni Laboratories

Visit the research laboratories of the alumni of Dr. Woo.

Board of Directors

Richard Debski, Ph.D. President
Caroline Wang, M.S. Secretary
Jamie Pfaeffle, M.D., Ph.D. Treasurer
Doug Boardman, M.D.
Thay Lee, Ph.D.
Patrick McMahon, M.D.
Karen Ohland, M.S.
Christos Papgeorgiou, M.D.
Masataka Sakane, M.D.
Sven Scheffler, M.D.
Jennifer Wayne, Ph.D.

2004 Erin McGurk Grant Recipient

Karin Wartella
Virginia Commonwealth University

Tissue Engineering Cartilage -
Application of Controlled Loads to Cell Seeded Scaffolds

Karin with her advisor, Dr. Jennifer Wayne

Final Report

The design criteria for development of a suitable bioreactor for biaxial mechanical stimulation to a cell/scaffold (construct) were as follows: Bioreactor-composed of a stage, tension assembly, compression assembly, and tissue stimulation chamber (tsc), components made of a non-corrosive material that survives 99% humidity, 37°C, and 5% CO2, and dimensions to fit within the confines of an incubator. The bioreactor was primarily composed of clear plastic material to prevent corrosion of assembly components and ease of viewing (see Figure 1 for drawing).

Figure 1 Bioreactor design (Solidworks 2001)

The compression and tension assemblies had an acrylic tension piston with a model 31 load cell (A) (Honeywell Sensotec, Inc., Columbus, OH) interposed to monitor the applied loads. The load cell was chosen for its capacity (250 grams), miniature size, ability to survive high humidity, and ease of computer interface with a LabVIEW DAQ. Each piston was connected to an M-227.10 DC-Mike actuator (B) (Phyiks Instrument, Inc., Auburn, MA) to provide linear movement along the vertical and horizontal axes. The actuator was chosen for its 10 mm range, minimal movement increments of 0.05 mm, backlash of 2 mm, maximum velocity of 0.875 mm/sec, and a resolution of 0.0035 mm (1 count). The actuator was rigidly held in position within a polycarbonate housing, which was attached to the two vertical upright supports or a base stage for compression and tension assemblies, respectively.

The tsc (C) was constructed of acrylic and had a platform centrally located inside for compression support (Figure 2). On either side of the platform were tissue grips (a) erected from polycarbonate for clamping of the construct. The lid (b) was constructed from acrylic with a T-75 flask bottleneck replicated out of acrylic and a T-75 cap (c). The compression piston connected to the compression platen (d) through the lid. A latex bellows was attached to both the interior and exterior piston and a wall lip (e) to keep the chamber sealed. All control and data collection was performed by LabVIEW programming.

Figure 2 Drawing of Tissue Stimulation Chamber(Solidworks 2001)

Upon completion of the device construction, a preliminary test was run to check for contamination and control accuracy of the components through LabVIEW. During the pre-testing, the tsc was filled with ~50 ml Dulbecco’s Modified Eagles Medium (DMEM) (Gibco, Carlsbad, CA) supplemented with 1% antibiotic/antimyotic (Sigma-Aldrich, St. Louis, MO), and 10% fetal bovine serum (Invitrogen, Carlsbad, CA). The tension assembly was not attached only the compression actuator was available at the time of testing. The bioreactor was placed in an incubator at 370C with 5% CO2.

Compression displacement was applied for 0.5 h with a 2 min rest period prior to a second application of compression. Compression was applied cyclically with a triangular waveform at 0.1 Hz, at a rate of 0.875 mm/sec. The initial values were chosen so the bioreactor setup could be closely monitored during testing for any movement problems. The bioreactor was tested for 3 days. Upon completion of testing, the data from positioning showed variation by less than 0.65 mm, and the chamber was found free of contaminants.

An additional test was run on a chondrocyte seeded porous type I collagen scaffolds (Collagen Matrix, Inc, Franklin Lakes, NJ) with dimensions of 13mm diameter by 3 mm thickness (Figure 3).

Figure 3 Picture of bioreactor in incubator applying displacement to a tissue engineered construct

The scaffold was subjected to two consecutive days of testing for 3 h of compression and 3 h of tension, with a 1 h rest period between the cycles, per day. The chamber was visually evaluated periodically during the testing period for movement problems. The test ran well with no slippage of the construct between the grips. Towards the end of the tension sequence on the first day, a small leak developed from the tension piston latex connection on the outside of the chamber. Additional banding was added on the piston and latex and the leakage stopped. On day two of testing, there were no problems with the assembly.

The purpose of this study was to develop a biaxial mechanical stimulation bioreactor for application of both compressive and tensile forces to a tissue construct. The bioreactor design was successful in satisfying all the design criteria. The tissue stimulation chamber allowed for application of forces with an environment that was suitable for cell viability and prevention of contamination. SEM pictures of the tested construct showed cells were
adherent to the scaffold after mechanical stimulation. Positioning evaluation showed minimal inaccuracy of displacement position, with position values varying by less than 0.65 micrometer. Use of this biaxial mechanical stimulation bioreactor for cartilage tissue engineering is underway.

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