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Research Papers

In vitro Articular Cartilage Growth with Sequential Application of IGF-1 and TGF-β1 Enhances Volumetric Growth and Maintains Compressive Properties

[+] Author and Article Information
Nathan T. Balcom, Britta Berg-Johansen1

Mechanical Engineering Department,  California Polytechnic State University, San Luis Obispo, CA 93405

Kristin J. Dills, Jennifer R. Van Donk

Mechanical Engineering Department,  California Polytechnic State University, San Luis Obispo, CA 93405

Gregory M. Williams, Albert C. Chen

Department of Bioengineering,  University of California-San Diego, La Jolla, CA 92093

Scott J. Hazelwood

Biomedical and General Engineering Department,  California Polytechnic State University, San Luis Obispo, CA 93405

Robert L. Sah

Department of Bioengineering  University of California-San Diego, La Jolla, CA 92093; Department of Orthopaedic Surgery,  University of California-San Diego, La Jolla, CA 92093

Stephen M. Klisch2

Mechanical Engineering Department,  California Polytechnic State University, San Luis Obispo, CA 93405,sklisch@calpoly.edu

1

N. T. Balcom and B. Berg-Johansen contributed equally to this work.

2

Corresponding author.

J Biomech Eng 134(3), 031001 (Mar 19, 2012) (8 pages) doi:10.1115/1.4005851 History: Received August 22, 2011; Revised January 13, 2012; Posted February 01, 2012; Published March 16, 2012; Online March 19, 2012

In vitro cultures with insulin-like growth factor-1 (IGF-1) and transforming growth factor-β1 (TGF-β1) have previously been shown to differentially modulate the growth of immature bovine articular cartilage. IGF-1 stimulates expansive growth yet decreases compressive moduli and increases compressive Poisson’s ratios, whereas TGF-β1 maintains tissue size, increases compressive moduli, and decreases compressive Poisson’s ratios. The current study’s hypothesis was that sequential application of IGF-1 and TGF-β1 during in vitro culture produces geometric and compressive mechanical properties that lie between extreme values produced when using either growth factor alone. Immature bovine articular cartilage specimens were harvested and either untreated (D0, i.e., day zero) or cultured in vitro for either 6 days with IGF-1 (D6 IGF), 12 days with IGF-1 (D12 IGF), or 6 days with IGF-1 followed by 6 days with TGF-β1 (D12 SEQ, i.e., sequential). Following treatment, all specimens were tested for geometric, biochemical, and compressive mechanical properties. Relative to D0, D12 SEQ treatment enhanced volumetric growth, but to a lower value than that for D12 IGF. Furthermore, D12 SEQ treatment maintained compressive moduli and Poisson’s ratios at values higher and lower, respectively, than those for D12 IGF. Considering the previously described effects of 12 days of treatment with TGF-β1 alone, D12 SEQ induced both growth and mechanical property changes between those produced with either IGF-1 or TGF-β1 alone. The results suggest that it may be possible to vary the durations of select growth factors, including IGF-1 and TGF-β1, to more precisely modulate the geometric, biochemical, and mechanical properties of immature cartilage graft tissue in clinical repair strategies.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

Grahic Jump Location
Figure 1

Change in (a) wet weight, and (b) thickness for cultured explants. (c) Water content of D0 and cultured explants. Symbols indicate p < 0.05 versus *D0; #D6 IGF; + D12 IGF. Mean ± SE. n = 15.

Grahic Jump Location
Figure 2

(a, b) Glycosaminoglycan (GAG) content, (c, d) collagen (COL) content, and (e, f) cell content of D0 and cultured explants, normalized to initial wet weight WWi (a, c, e), and final wet weight WWf (b, d, f). For D0, WWi = WWf. Symbols indicate p < 0.05 versus *D0; #D6 IGF; + D12 IGF. Mean ± SE. n = 15.

Grahic Jump Location
Figure 3

Compressive mechanical properties of D0 and cultured explants measured at 15%, 30%, and 45% compressive strains. (a) Equilibrium confined compression (CC) modulus, HA , (b) unconfined compression (UCC) modulus, E, (c) UCC Poisson’s ratio, ν31 , and (d) UCC Poisson’s ratio, ν32 . Symbols indicate p < 0.05 versus *D0; #D6 IGF; + D12 IGF. Mean ± SE. n = 15.

Grahic Jump Location
Figure 4

Regression of (a-c) equilibrium CC modulus, (d-f) equilibrium UCC modulus, and (g-l) Poisson’s ratios at 30% with water, COL, and GAG concentrations (% of WWf). Data points correspond to individual D0 (♦), D6 IGF (),D12IGF(), and D12 SEQ (○) specimens. Trendlines shown correspond to significant relationships for all data points combined (ALL). See Table 1 for more details.

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