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Design Innovation

Morphological Characterization of a Novel Scaffold for Anterior Cruciate Ligament Tissue Engineering

[+] Author and Article Information
Cédric P. Laurent1

 LEMTA, Nancy-Université, CNRS UMR 7563, 2 avenue Forêt de Haye, 54504 Vandœuvre-lès-Nancy, Francecedric.laurent@ensem.inpl-nancy.fr

Jean-François Ganghoffer, Rachid Rahouadj

 LEMTA, Nancy-Université, CNRS UMR 7563, 2 avenue Forêt de Haye, 54504 Vandœuvre-lès-Nancy, France

Jérôme Babin, Jean-Luc Six

 LCPM, Nancy-Université, UMR CNRS-INPL 7568, 1 rue Grandville, BP 20541, 54001 Nancy, France

Xiong Wang

 PPIA, Nancy-Université, CNRS UMR 7561, Faculté de Médecine, 54504 Vandœuvre-lès-Nancy, France

1

Corresponding author.

J Biomech Eng 133(6), 065001 (Jun 22, 2011) (9 pages) doi:10.1115/1.4004250 History: Received December 17, 2010; Revised May 06, 2011; Posted June 22, 2011; Published June 22, 2011; Online June 22, 2011

Tissue engineering offers an interesting alternative to current anterior cruciate ligament (ACL) surgeries. Indeed, a tissue-engineered solution could ideally overcome the long-term complications due to actual ACL reconstruction by being gradually replaced by biological tissue. Key requirements concerning the ideal scaffold for ligament tissue engineering are numerous and concern its mechanical properties, biochemical nature, and morphology. This study is aimed at predicting the morphology of a novel scaffold for ligament tissue engineering, based on multilayer braided biodegradable copoly(lactic acid-co-(e-caprolactone)) (PLCL) fibers The process used to create the scaffold is briefly presented, and the degradations of the material before and after the scaffold processing are compared. The process offers varying parameters, such as the number of layers in the scaffold, the pitch length of the braid, and the fibers’ diameter. The prediction of the morphology in terms of pore size distribution and pores interconnectivity as a function of these parameters is performed numerically using an original method based on a virtual scaffold. The virtual scaffold geometry and the prediction of pore size distribution are evaluated by comparison with experimental results. The presented process permits creation of a tailorable scaffold for ligament tissue engineering using basic equipment and from minimum amounts of raw material. The virtual scaffold geometry closely mimics the geometry of real scaffolds, and the prediction of the pore size distribution is found to be in good accordance with measurements on real scaffolds. The scaffold offers an interconnected network of pores the sizes of which are adjustable by playing on the process parameters and are able to match the ideal pore size reported for tissue ingrowth. The adjustability of the presented scaffold could permit its application in both classical ACL reconstructions and anatomical double-bundle reconstructions. The precise knowledge of the scaffold morphology using the virtual scaffold will be useful to interpret the activity of cells once it will be seeded into the scaffold. An interesting perspective of the present work is to perform a similar study aiming at predicting the mechanical response of the scaffold according to the same process parameters, by implanting the virtual scaffold into a finite element algorithm.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Determination of the virtual fiber trajectories based upon the kinematics of the circular braiding process. Two groups of fibers (even and odd) move in opposite directions in an interlacing circular motion. (a) Even fibers are rotated clockwise of the angle θ. (b) Odd fibers are rotated counterclockwise of the angle θ. A fiber goes alternatively from Dint to D and from D to Dext . Steps (a) and (b) are done iteratively. (c) Example of a seven-layer virtual scaffold issued from this procedure.

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Figure 2

(a) Binarized section of the virtual scaffold. The center of mass (Cm ) is marked, and a few equidistant segments of interest (SOI) have been represented. (b) Variations of the average gray level intensity along the radius, represented in three and two dimensions. (c) Variations of the average gray level intensity along the angle, represented in three and two dimensions.

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Figure 3

Network of pores computed from the virtual scaffold (a) alone and (b) into the virtual scaffold. The color of each pore corresponds to its diameter. The interconnection of pores has been emphasized by drawing links (solid lines) between spheres considered as connected.

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Figure 4

Biggest circles included the free regions of a particular section of a real scaffold consisting of nine layers of 16 fibers (diameter = 200 μm, pitch length = 16 mm). The color of each circle corresponds to its diameter.

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Figure 5

Experimental and theoretical diameters of the extruded fibers for different couples (Vp , Ωr ). The theoretical values are issued from Eq. 1.

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Figure 6

External diameters of real scaffolds (dashed line) and virtual scaffolds (box-and-whisker diagrams)

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Figure 7

Comparison between gray level intensity profiles along the radial and angular direction in sections of real scaffolds (dark) and virtual scaffolds (light). Profiles along the angular direction have been represented in a Fourier diagram to emphasize the periodicities. Results are given in terms of mean value and confidence interval.

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Figure 8

Distributions of pore sizes issued from the mercury porosimetry (black line), from the computation of biggest circles in cross-sectional pictures of a real scaffold (blue bars) and from the computation of the biggest spheres in the virtual scaffold (yellow bars)

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Figure 9

Influence of the pitch length, the fiber diameter, and the number of layers on the pore size distribution computed from the virtual scaffold

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