Rate of tendon gap closure in an in vitro collagen gel matrix

Tendon gap closure was examined in a tissue culture model and found to have a similar time course as skin wound closure . Foot tendons from White Rock chickens were mounted in a collagen gel matrix and maintained with the use of Dulbecco's modified Eagle medium, containing fetal calf serum and antibiotics, for 4 weeks at 37°C in an incubator . Gap distances between tendons were measured every 1 to 3 days and plotted against time as the contraction curve . After an initial lag period of 4 to 8 days, gap distance showed a progressive decrease, Gap closure rate was defined as the slope of the contraction curve, and it was found to be a function of initial gap distance (r = 0.643, p 0,045) . The time necessary to reduce the initial gap distance by half had a significant correlation with the initial gap distance (r = 0.986, p < 0.001). Fibroblast migration began on days 2 to 3 after a 1-to 2-day lag period . Fibroblasts were visible in the tendon gap region before the start of collagen gel contraction . At this time, the fibroblast migration rate was 0.33 mm/day . A critical density of fibroblasts was necessary to start collagen gel contraction. Once the gap distance began to diminish, fibroblast migration measurements were hampered because the measurable area was decreasing . Collagen gel contraction reduced the measurable fibroblast migration rate by nearly half to 0.18 mm/day . A linear correlation was found between fibroblast distance traveled and time in culture during both the gel lag and gel contraction time periods, This tendon culture model may be potentially useful for wound healing studies because it allows for studies of fibroblast activity in the early lag phase when the cells populate the collagen lattice but before contraction of the gel occurs . (WOUND REP REG 1997;5:62-8) Culturing fibroblasts in hydrated collagen gel lattices was introduced in 1972 by Elsdale and Bard' and expanded on in 1979 by Bell et al .2 as a technique for assessing fibroblast activity. These authors added fibroblast suspensions to collagen solutions and then allowed the collagen to gel into a native fibril lattice. Fibroblasts were found to migrate throughout the collagen gel lattice and shrink the lattice. 1,2 Lattice contraction served as a monitor of fibroblast activity, and this phenomenon has subsequently been used as an in vitro model of skin wound contraction. 2-4 One problem with the Bell model is that the initial seeding of the collagen gel with fibroblasts is homoge- neous with a high cell density in the range of 10 5 to 10 6 fibroblasts per milliliter of gel.5-6 The presence of such initially high fibroblast numbers is different from a real wound where fibroblast numbers are initially low at the wound site and increase after 3 to 4 days .' In the present study, we report on a new in vitro model for the examination of fibroblast activity in collagen gel lattices . The fibroblasts are initially packaged inside a tendon and subsequently allowed to grow out and multiply in the collagen gel. This produces a lag time before contraction of the collagen gel. This sequence of events more closely mimics the events of real wound contraction. Using a culture model containing two separated tendons, we studied the effect of initial tendon gap distance on the rate of collagen gel contraction and on the rate of fibroblast outgrowth into the collagen gel from the cut tendon ends