ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

was observed several millimeters away from the location of the physical constraints
indicating that ECM fibers are effective conduits for long-range mechanical force
transmission (Karamichos, et. al, 2007).
A demonstration of collagen fiber alignment between two fibroblasts that can occur 24
hours after seeding is shown in Fig. 1. Here an initially random fiber orientation (not
shown) is reorganized by the fibroblasts over 24 hours into a network that connects two
cells ~100 um apart.
a. b.
Fig 1. a) Differential interference contrast (DIC) and b) confocal reflectance microscopy
images of fibroblasts and bovine collagen gels, 24 hours after initial seeding. (Images
courtesy of Maureen Weber; see Ma et. al, 2011 a, b.)
Inspired by these images we used idealized and simplified finite element models of cells
and randomly oriented collagen fibers embedded in a thin slab of surrounding matrix
material for the current computational study.
3. METHODS
The COMSOL (Burlington, MA) finite element program (version 4.2a) was used for all
analyses and simulations. A MATLAB (Mathworks, Natick, MA) script was written to
generate geometric primitives for fibers, based on user input parameters for: the number
of fibers, fiber length, fiber diameter, fiber orientation, fiber material properties, and the
geometry and material properties of the surrounding matrix materials. All of the models
presented here have the same general parameter values as in the table below.
Table 1. Characteristics of the idealized Collagen fiber gels
Number of fibers 25
Fiber Diameter 1 µm
Fiber length 100 µm
Fiber Orientation Random
Fiber Properties Linear elastic: 300 MPa, ν = 0.45
Matrix Dimensions 600 x 600 x 15 µm
Matrix Properties Linear elastic: 197 Pa; ν = 0.49
In addition, empty circular cylinders, 15 µm in diameter, were generated using
COMSOL’s Boolean geometry difference operation to simulate two cells in the matrix.