Biomedical Engineering Reference
In-Depth Information
Fig. 3
Mean spacing of fibronectin fibrils versus fibronectin anchorage strength on dif-
ferent maleic anhydride copolymer substrates in terms of time constant of fibronectin
heteroexchange
applied tension of the cytoskeleton towards the substrate can be assumed
with a similar strength because the cells adhere and spread similarly on the
different copolymer surfaces. As a different focal adhesion density was ob-
served for the different substrates, the local force at those adhesion sites
should scale indirectly proportional to their density, because focal adhesions
are thought of as primary adhesion sites. The observed dependence of fo-
cal adhesion density on the substrate physicochemistry can be interpreted as
the result of the cellular signalling mechanisms, which regulates the force ap-
plied on the adhesion ligands [99, 100]. Because of the different anchorage
strength of fibronectin to the substrates, the cells establish a local force on the
receptor-ligand pairs appropriate to the ligand-substrate anchorage strength.
Subsequently, the focal adhesion pattern will function as a template for fi-
bronectin fibrillogenesis, because the focal adhesions act as primary sites of
fibronectin fibril formation [101]. Thus, the overall process results in a fi-
bronectin fibril pattern with a spacing depending on the fibronectin substrate
anchorage strength—directly influenced by the substrate physicochemistry.
Additional investigations [102] on the nanoscale fibronectin fibril pat-
tern supported the hypothesis of cellular sensing of the fibronectin anchor-
age strength. Therein, a substrate-dependent spacing of paired fibronectin
nanofibrils was correlated to the force sensitive feedback mechanism of the
actin cytoskeleton and its inner structure. A larger spacing of the paired
nanofibrils in the range of 300 nmwasobservedonsubstrateswithahigher
fibronectin anchorage strength. The distinct spacings were concluded to
reflect the thickness of the actin stress fibres as template structures of fi-
bronectin fibrillogenesis. The inner structure of actin stress fibres with
α
-actinin cross-linked actin filaments lead to a repeating unit of 71 nm for
the spacing of the paired nanofibrils on the different copolymer substrates
