Do Cells Contribute to Tendon and Ligament Biomechanics?

<div><p>Introduction</p><p>Acellular scaffolds are increasingly used for the surgical repair of tendon injury and ligament tears. Despite this increased use, very little data exist directly comparing acellular scaffolds and their native counterparts. Such a comparison would help establish the effectiveness of the acellularization procedure of human tissues. Furthermore, such a comparison would help estimate the influence of cells in ligament and tendon stability and give insight into the effects of acellularization on collagen.</p><p>Material and Methods</p><p>Eighteen human iliotibial tract samples were obtained from nine body donors. Nine samples were acellularized with sodium dodecyl sulphate (SDS), while nine counterparts from the same donors remained in the native condition. The ends of all samples were plastinated to minimize material slippage. Their water content was adjusted to 69%, using the osmotic stress technique to exclude water content-related alterations of the mechanical properties. Uniaxial tensile testing was performed to obtain the elastic modulus, ultimate stress and maximum strain. The effectiveness of the acellularization procedure was histologically verified by means of a DNA assay.</p><p>Results</p><p>The histology samples showed a complete removal of the cells, an extensive, yet incomplete removal of the DNA content and alterations to the extracellular collagen. Tensile properties of the tract samples such as elastic modulus and ultimate stress were unaffected by acellularization with the exception of maximum strain.</p><p>Discussion</p><p>The data indicate that cells influence the mechanical properties of ligaments and tendons in vitro to a negligible extent. Moreover, acellularization with SDS alters material properties to a minor extent, indicating that this method provides a biomechanical match in ligament and tendon reconstruction. However, the given protocol insufficiently removes DNA. This may increase the potential for transplant rejection when acellular tract scaffolds are used in soft tissue repair. Further research will help optimize the SDS-protocol for clinical application.</p></div

The osmotic stress technique was applied to partially plastinated iliotibial tract samples.

<p>Each sample pair consisting of one native tract and its corresponding acellular counterpart were submersed for 24 h in a 2.5 wt % polyethylene glycol solution before uniaxial tensile testing. Scale bar  = 10 mm</p

Summary of the study protocol and the amount of specimens that were used for the respective experiments.

<p>Summary of the study protocol and the amount of specimens that were used for the respective experiments.</p

Time-dependent decrease of the water content as a function of the polyethylene glycol (PEG) concentrations (2a, top) and correlation between polyethylene glycol (PEG) concentration and iliotbial tract water content after submersion for 24 h (2b, bottom) are shown.

<p>Applying the osmotic stress technique to iliotibial tract specimens caused a PEG- dependent decrease of their water content. PEG concentrations of 2.5 wt% (grey arrow) were most suitable for osmotically adjusting the water content of iliotibial tract samples and their corresponding acellular scaffolds.</p

Experimental setup for uniaxial stress-strain testing of an acellular iliotibial tract sample (4a) and partially plastinated tact sample (4b) with a sketch of the template used to taper the specimens (red figure with broken line).

<p>F =  fresh (unfixed) and P =  unfixed part of the tract sample; scale bar  = 50 mm (4a), 17 mm (4b)</p

Stress-strain curves of native and acellular iliotibial tract samples obtained from the same donors and anatomical site.

<p>Stress-strain curves of native and acellular iliotibial tract samples obtained from the same donors and anatomical site.</p

Hematoxylin-eosin stained histology samples were obtained from the native iliotibial tract and from acellular scaffolds.

<p>In the native samples (7a,b), nuclei are stained in an intensive blue color. In the acellular scaffolds, the nuclei vanished and the collagen appears to be washed out (7c,d). Scale bar 25 µm (7a,c) and 12 µm (7b,d).</p

Box plots are depicted for elastic modulus (6a, left), ultimate stress (6b, center) and for maximum strain (6c, right).

<p>Material properties were unaffected by acellularization with the exception of maximum strain.</p

Safranin-o staining of native (8a) and acellular (8b) iliotibial tract samples.

<p>Scale bar  = 1000 µm.</p

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