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Research Papers

An Instrumented Bioreactor for Mechanical Stimulation and Real-Time, Nondestructive Evaluation of Engineered Cartilage Tissue

[+] Author and Article Information
Jenni R. Popp1

Materials Reliability Division,  National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305jenni.popp@nist.gov

Justine J. Roberts, Kristi S. Anseth, Stephanie J. Bryant

Department of Chemical and Biological Engineering,  University of Colorado, Boulder, CO 80309

Doug V. Gallagher, Timothy P. Quinn

Materials Reliability Division,  National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305

The full description of the procedures used in this paper requires the identification of certain commercial products and their suppliers. The inclusion of such information should in no way be construed as indicating that such products or suppliers are endorsed by NIST or are recommended by NIST or that they are necessarily the best materials, instruments, software or suppliers for the purposes described.

1

Corresponding author.

J. Med. Devices 6(2), 021006 (Apr 26, 2012) (7 pages) doi:10.1115/1.4006546 History: Received November 18, 2011; Revised February 29, 2012; Published April 26, 2012; Online April 26, 2012

Mechanical stimulation is essential for chondrocyte metabolism and cartilage matrix deposition. Traditional methods for evaluating developing tissue in vitro are destructive, time consuming, and expensive. Nondestructive evaluation of engineered tissue is promising for the development of replacement tissues. Here we present a novel instrumented bioreactor for dynamic mechanical stimulation and nondestructive evaluation of tissue mechanical properties and extracellular matrix (ECM) content. The bioreactor is instrumented with a video microscope and load cells in each well to measure tissue stiffness and an ultrasonic transducer for evaluating ECM content. Chondrocyte-laden hydrogel constructs were placed in the bioreactor and subjected to dynamic intermittent compression at 1 Hz and 10% strain for 1 h, twice per day for 7 days. Compressive modulus of the constructs, measured online in the bioreactor and offline on a mechanical testing machine, did not significantly change over time. Deposition of sulfated glycosaminoglycan (sGAG) increased significantly after 7 days, independent of loading. Furthermore, the relative reflection amplitude of the loaded constructs decreased significantly after 7 days, consistent with an increase in sGAG content. This preliminary work with our novel bioreactor demonstrates its capabilities for dynamic culture and nondestructive evaluation.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Instrumented bioreactor. (a) The loading mechanism consists of an actuator that applies force to the constructs through impermeable stainless steel platens attached to load cells to measure applied force. The portion labeled (A) corresponds to the cutout of the sample well. (b) A cross-sectional view depicts the linear displacement guide and mechanism. (c) Photograph of the bioreactor and additional instruments. A rotation stage is used to position the sample well over the ultrasonic transducer that is attached to a linear actuator or the video microscope located adjacent to the bioreactor. Scale bar: 5 cm.

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Figure 2

Representative force-displacement curve for a loaded sample. Samples (5 mm tall) are subjected to 1 h of sinusoidal compression at 1 Hz from 0% to 10% strain. The figure depicts force-displacement data for 200 s of the 1 h sinusoidal loading condition. Force measured by the load cell increases with increasing displacement of the platen. Inset depicts displacement versus time for a portion of the 1 h sinusoidal loading condition.

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Figure 3

The compressive modulus was measured (a) online in the bioreactor every 12 h and (b) offline in a standard mechanical testing machine on days 0 and 7. Data represent the mean plus or minus one standard deviation for n = 4 or n = 5 constructs.

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Figure 4

Sulfated glycosaminoglycan. Histological sections stained with safranin O on (a) day 0 control, (b) day 7 control, and (c) day 7 bioreactor. Scale bars are 100 μm. sGAG content was quantified with dimethylmethylene blue at days 0 and 7 (d). Data represent the mean plus or minus one standard deviation for n = 4 constructs. Asterisk denotes significant difference from day 0, p < 0.05.

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Figure 5

Representative ultrasonic amplitude maps of hydrogel constructs at (a) day 0 and (b) day 7. Two-dimensional acoustic images were constructed with the brightness of each pixel corresponding to the amplitude of the acoustic signal reflected from the stainless steel platen.

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Figure 6

Relative reflection amplitude for each construct on days 0 and 7. Data represent the mean plus or minus one standard deviation for n = 4 constructs. Asterisk denotes significant difference between day 0 and day 7 for the same construct, p < 0.05.

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