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Research Papers

Mechanical Characterization of Electrospun Polycaprolactone (PCL): A Potential Scaffold for Tissue Engineering

[+] Author and Article Information
Ryan R. Duling, Noriko Katsube

Department of Mechanical Engineering, The Ohio State University, Columbus, OH 43210

Rebecca B. Dupaix1

Department of Mechanical Engineering, The Ohio State University, Columbus, OH 43210dupaix.1@osu.edu

John Lannutti

 Department of Materials Science, The Ohio State University, Columbus, OH 43210

1

Corresponding author.

J Biomech Eng 130(1), 011006 (Feb 05, 2008) (13 pages) doi:10.1115/1.2838033 History: Received August 28, 2006; Revised May 10, 2007; Published February 05, 2008

This paper investigates the mechanical behavior of electrospun polycaprolactone (PCL) under tensile loading. PCL in bulk form degrades slowly and is biocompatible, two properties that make it a viable option for tissue engineering applications in biomedicine. Of particular interest is the use of electrospun PCL tubes as scaffolds for tissue engineered blood vessel implants. Stress relaxation and tensile tests have been conducted with specimens at room temperature (21°C) and 37°C. Additionally, to probe the effects of moisture on mechanical behavior, specimens were tested either dry (in air) or submerged in water. In general, the electrospun PCL was found to exhibit rate dependence, as well as some dependence on the test temperature and on whether the sample was wet or dry. Two different models were investigated to describe the experimentally observed material behavior. The models used were Fung’s theory of quasilinear viscoelasticity (QLV) and the eight-chain model developed for rubber elastomers by Arruda and Boyce (1993, “A Three-Dimensional Constitutive Model for the Large Stretch Behavior of Rubber Elastic Materials  ,” J. Mech. Phys. Solids, 41(2), pp. 389–412). The implementation and fitting results, as well as the advantages and disadvantages of each model, are presented. In general, it was found that the QLV theory provided a better fit.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Comparison of collagen fibers (top) to electrospun PCL fibers (bottom). The top photo is from Ref. 10. The bottom image was taken via scanning electron microscopy (SEM).

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Figure 2

Block diagram and photo of electrospinning process

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Figure 3

Dogbone specimen geometry, dimensions in millimeters

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Figure 4

Reservoir in lowered position. Method used to connect to existing clamps can be seen in lower portion of picture.

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Figure 5

Typical stress relaxation test response for a specimen tested at room temperature at 0.8mm∕s

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Figure 6

Average loading response for dry room temperature tests. Notice the effects of extension rate on specimen loading response. Responses are averages for all samples tested at a given extension rate.

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Figure 7

Reduced relaxation function as a function of extension rate. Note that there is less variability than seen in loading curves.

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Figure 8

Reduced relaxation function as a function of strain amount. All tests were completed at 0.8mm∕s. Notice the decrease in slope that corresponds to lower maximum strains.

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Figure 9

Average loading response for dry 37°C testing with 20min exposure time. Rate dependence can still be seen. All specimens are from the same sheet. Dry room temperature 0.8mm∕s average (control) from the sheet is included for comparison.

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Figure 10

Dry 37°C loading response for various pretest exposure times. All specimens are from the same sheet. Dry room temperature 0.8mm∕s average (control) from the sheet is included for comparison. All tests completed at 0.8mm∕s.

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Figure 11

Loading response for wet room temperature testing. All specimens from the same sheet. All specimens subjected to 15min soak time before testing. Dry room temperature 0.8mm∕s average (control) from the sheet is included for comparison.

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Figure 12

Loading response for wet 37°C tests. All specimens subjected to 90min soak time before testing. Dry room temperature 0.8mm∕s average (control) from Fig. 6 is included for comparison.

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Figure 13

Average results for tensile tests to failure. The solid lines represent average dry room temperature tests, and the dashed lines represent average dry tests at 37°C with a 20min pretest exposure time. All samples from the same sheet.

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Figure 14

Cyclic stress relaxation response for electrospun PCL dogbones. Specimens were tested at 0.8mm∕s for a total of 15cycles. All four specimens are shown (however, they are quite coincidental).

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Figure 15

Sample stress response for preconditioning at 0.8mm∕s for 10cycles. Similar response seen for all preconditioned specimens.

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Figure 16

Reduced relaxation fit for 8mm∕s dry room temperature average using QLV theory

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Figure 17

Loading fit for 0.8mm∕s dry room temperature average using QLV theory

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Figure 18

0.8mm∕s failure fit using QLV theory (dry room temperature average)

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Figure 19

Overestimation of rate dependence seen when using Fung’s QLV theory. 0.8mm∕s experimental response and corresponding QLV fit are highly coincidental and are thus hard to distinguish from one another.

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Figure 20

Cyclical stress relaxation predictions at 0.8mm∕s using parameters for dry room temperature testing without preconditioning

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Figure 21

QLV fit for 0.8mm∕s average preconditioned loading response. Note that the negative stresses seen in Fig. 1 have been rezeroed for modeling purposes.

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Figure 22

Cyclical stress relaxation predictions using parameters for 0.8mm∕s dry room temperature average testing with preconditioning. Vastly improved predictive capability was noticed.

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Figure 23

Eight-chain fit for 8mm∕s dry room temperature average loading

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Figure 24

Eight-chain fit for 0.8mm∕s average preconditioned loading response

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