Quantification of Single Human Dermal Fibroblast Contraction

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Abstract
Contraction forces produced by single, human dermal fibroblasts (HDF), cultured on deformable silicone substrata, were quantified using video microscopy and image analysis. Cell contraction causes deformation of the substrate, which appears as a series of surface wrinkles perpendicular to the long axis of the cell. Local surface deformation was measured from the two-dimensional displacement of small latex beads embedded in the surface layer to which the HDF adhere. A calibrated glass microneedle was used to measure the force required to stretch the surface by a known amount (the surface stiffness).1 From the motion of the latex beads, the contractile forces of the cells were calculated.2 In vivo, such forces are thought to cause contraction of the dermis and hence promote wound closure. Normal contraction is vital to prevent infection and water loss. However, aberrant cellular behaviour is thought to be responsible for a variety of wound pathologies, such as hypertrophic and keloid scarring. We have found that contractile forces of 2.65 µN/cell were produced. This is similar to those produced by single smooth muscle cells3 and approximately 10 times greater than the forces measured for keratocytes and three orders of magnitude greater than previously published values for fibroblasts that had been cultured in a collagen gel.4 Our goal is to understand the mechanisms that determine the polarity and maximum force of contraction and also to study differences in the behavior of HDF and myofibroblasts.