Biomedical Engineering Reference
In-Depth Information
First, micro- and nanofabrication technologies are rapidly expand-
ing the accessibility of test platforms that measure events at cell-relevant
length scales (Toh
et al.
, 2010; Voldman
et al.
, 1999; Toetsch
et al.
, 2009).
For instance, nanopatterning has been used to study the effects of integ-
rin receptor clustering on cell adhesion and motility (Maheshwari
et al.
,
2000; Selhuber-Unkel
et al.
, 2010). Furthermore, microfabrication processes
have been used to design microfl uidic devices that are capable of direct-
ing cell adhesion and cell separation in small volume samples over wide
ranges of shear stress (Green
et al.
, 2009; Plouffe
et al.
, 2008; Radisic
et al.
,
2006). Following this model, as fl ow chamber designs are miniaturized from
macro- to microscale this technology is poised to impact cell migration in
similar ways.
Our own work provides a key example of employing microfabrication
to quantitatively analyze cell adhesion. It was previously demonstrated,
using the spinning disk apparatus, that initially, cell adhesion strength is
proportional to the number of integrin-matrix bonds (Garcia
et al.
, 1998).
However, the subsequent processes, including receptor clustering, focal
adhesion assembly and association with the cytoskeleton, and dramatic
cell shape changes, complicate long-term (>15 min) analyses of adhesion
strengthening. Recently we addressed this challenge by using microcontact
printing to regulate cell shape and spreading. This permitted the investiga-
tion of the contribution of focal adhesion assembly to strengthening inde-
pendently of cell spreading (Gallant
et al.
, 2002, 2005; Gallant and Garcia,
2007). This approach revealed that cell adhesion strength was strongly
dependent on the contact time and available adhesive area. By combining
mechanical measurements of adhesion strength with biochemical quanti-
fi cation methods we were able to demonstrate that the anisotropic spatial
distribution of integrin bonds and the assembly of focal adhesions results in
a large and rapid cell adhesion strengthening response. Our current work
includes using this experimental and theoretical platform to independently
analyze the individual contributions of focal adhesion assembly parameters
including composition, size and position (Elineni and Gallant 2011), as well
as the regulatory effects of matrix elasticity.
Another technique to quantify the adhesion strength of cells on biomate-
rials that has been introduced recently is laser spallation (Shim
et al.
, 2008).
This technique was adapted from a method originally developed to deter-
mine the tensile strength of thin fi lm interfaces. This technique provides an
interesting new quantitative cell adhesion assay, but it has not yet been used
in an application that demonstrates its advantages over existing methods.
Traction force microscopy (TFM) is a technique that facilitates the mea-
surement of force vectors in static and migrating cells (Oliver
et al.
, 1999).
This technique is not new, but it is being used by numerous laboratories
to measure the dependence of cell adhesion strength on adhesion complex
