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Proceedings Paper

Correlations between second harmonic signal, microstructure, and mechanics of contracting collagen gels
Author(s): Christopher B. Raub; Peter D. Kim; Andrew J. Putnam; John S. Lowengrub; Bruce J. Tromberg; Steven C. George
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Paper Abstract

Second harmonic generation (SHG) from collagen provides an optical signal that can yield detailed information about collagen microstructure when imaged with laser scanning microscopy, from both collagen-based engineered tissue and connective tissues from animals. Therefore SHG images may provide information that correlates with bulk tissue mechanical properties, or at least a component of those properties resulting from collagen. In order to probe these correlations, we used multiphoton microscopy to gather SHG signal intensity and depth decay information from fibroblast-seeded contracting collagen hydrogels. These gels were polymerized at pH 6 to engineer a tissue with large diameter collagen fibers and large pores between fibers, and pH 9 to produce smaller diameter collagen fibers with smaller pores. Both gels initially contained 4 mg/ml collagen; after 16 days of floating culture, the pH 6-polymerized gels had contracted to 4.4 ± 0.6% of their original volume, and the pH 9-polymerized gels to 10.7 ± 2.7%. During this time period, the bulk compressive moduli (CM) of the gels increased ~9.2-fold and ~1.4-fold for the pH 6 and pH 9 polymerization conditions, respectively. Correspondingly, the SHG signal at the tissue surface increased ~25-fold and ~19-fold for the pH 6 and pH 9 gels, respectively; whereas the effective SHG attenuation coefficient increased ~4.5 and ~5.8-fold, respectively. Meaningful linear correlations only existed between the CM and surface SHG signal and the CM and SHG attenuation coefficient for pH 6-polymerized gels, indicating a possible influence of fibroblast activity on the CM of the pH-9 polymerized gels.

Paper Details

Date Published: 6 February 2008
PDF: 11 pages
Proc. SPIE 6858, Optics in Tissue Engineering and Regenerative Medicine II, 68580O (6 February 2008); doi: 10.1117/12.764110
Show Author Affiliations
Christopher B. Raub, Univ. of California/Irvine (United States)
Peter D. Kim, Univ. of California/Irvine (United States)
Andrew J. Putnam, Univ. of California/Irvine (United States)
John S. Lowengrub, Univ. of California/Irvine (United States)
Bruce J. Tromberg, Univ. of California/Irvine (United States)
Beckman Laser Institute (United States)
Steven C. George, Univ. of California/Irvine (United States)

Published in SPIE Proceedings Vol. 6858:
Optics in Tissue Engineering and Regenerative Medicine II
Sean J. Kirkpatrick; Ruikang K. Wang, Editor(s)

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