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Research Papers

Microstructure and Mechanics of Collagen-Fibrin Matrices Polymerized Using Ancrod Snake Venom Enzyme

[+] Author and Article Information
Shaneen L. Rowe

 Rensselaer Polytechnic Institute, Troy, NY 12180

Jan P. Stegemann1

 Rensselaer Polytechnic Institute, Troy, NY 12180jpsteg@umich.edu

1

Corresponding author. Present address: Department of Biomedical Engineering, University of Michigan, 1101 Beal Avenue, Ann Arbor, MI 48109

J Biomech Eng 131(6), 061012 (May 08, 2009) (9 pages) doi:10.1115/1.3128673 History: Received November 19, 2008; Revised February 23, 2009; Published May 08, 2009

The relationship between microstructural features and macroscopic mechanical properties of engineered tissues was investigated in pure and mixed composite scaffolds consisting of collagen Type I and fibrin proteins containing embedded smooth muscle cells. In order to vary the matrix microstructure, fibrin polymerization in mixed constructs was initiated using either the blood-derived enzyme thrombin or the snake venom-derived enzyme ancrod, each at low and high concentrations. Microstructural features of the matrix were quantified by analysis of high resolution scanning electron micrographs. Mechanical properties of the scaffolds were assessed by uniaxial tensile testing as well as creep testing. Viscoelastic parameters were determined by fitting creep data to Burger’s four-parameter model. Oscillatory dynamic mechanical testing was used to determine the storage modulus, loss modulus, and phase shift of each matrix type. Mixed composite scaffolds exhibited improved tensile stiffness and strength, relative to pure collagen matrices, as well as decreased deformation and slower relaxation in creep tests. Storage and loss moduli were increased in mixed composites compared with pure collagen, while phase shift was reduced. A correlation analysis showed that the number of fiber bundles per unit volume was positively correlated with matrix modulus, strength, and dynamic moduli, though this parameter was negatively correlated with phase shift. Fiber diameter also was negatively correlated with scaffold strength. This study demonstrates how microstructural features can be related to the mechanical function of protein matrices and provides insight into structure-function relationships in such materials. This information can be used to identify and promote desirable microstructural features when designing biomaterials and engineered tissues.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of the fibrinogen molecule and its interactions with thrombin and ancrod. Adapted from Ref. 16.

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Figure 2

(a) Spring and dashpot representation of Burger’s four-parameter model. (b) Example of a creep plot and parameters that govern each region.

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Figure 3

Compaction as a percentage of the original volume for pure collagen and mixed composite scaffolds

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Figure 4

Scanning electron micrographs of (a) pure collagen and (b)–(e) mixed matrices prepared with varying enzyme and concentration. Scale bar in (a) is 200 nm.

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Figure 5

Quantitative measurements for collagen and mixed scaffolds. (a) Fiber diameter, (b) length between nodes, (c) number of bundles per volume, and (d) width of bundles. ∗ is the statistical difference from collagen, and † is the statistical difference from mixed thrombin low.

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Figure 6

(a) Material modulus, UTS, and (b) maximum force at failure for pure collagen and the mixed composites constructs. ∗ is the statistical difference from collagen, and † is the statistical difference from mixed thrombin low.

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Figure 7

Model parameters derived from creep testing of pure collagen and mixed composites constructs: (a) R1 (b) R2, (c) η2, and (d) η1 for ∗ is the statistical difference from collagen, and † is the statistical difference from mixed thrombin low

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Figure 8

(a) Storage and loss moduli, and (b) phase shift for pure collagen and the mixed composites constructs. ∗ is the statistical difference from collagen, and † is the statistical difference from mixed thrombin low.

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