Construction of fibroblast-collagen gels with orientated fibrils induced by static or dynamic stress: toward the fabrication of small tendon grafts.

As a step toward the fabrication of small tendon grafts, fibroblast-collagen gels were constructed with orientated fibrils induced by static or dynamic loading. Three groups of gel samples, each consisting of 1.0 x 10(6) fibroblasts and 2 mg type I collagen, were fabricated: freely contracted gels formed the control group; contraction-directed gels made up the static group (the gel contraction was directed perpendicular to an axis made by two anchors buried in the gels so that the constraint stress exerted by the two anchors was imposed on the gel); and for the dynamic group, a specific loading pattern (free contraction followed by cyclic stretching using a tensile bioreactor) was employed. Mechanical properties were evaluated by means of the uniaxial tension test. The gels of the static group had an ultimate stress of 350 +/- 43.6 kPa and a material modulus of 548.8 +/- 61.6 kPa, which were almost 5.2 times and 15.6 times, respectively, greater than those of the controls. The dynamic gels had an ultimate stress of 256.8 +/- 80.7 kPa and a material modulus of 118.6 +/- 23.5 kPa. These results show that the ultimate stress and material modulus of the static samples are much greater than those of the dynamic samples, which is the opposite of our expectations. Therefore, studies under other dynamic loading patterns and long-term culture are needed to clarify whether dynamic loading is superior to static loading.