Biomedical Engineering Reference
In-Depth Information
many attempts have been made to increase the interaction of cells with the scaffolds
by precoating the scaffold surfaces with fibronectin or laminin.
The cells do not just probe the chemistry of an intended landing surface. There
is plenty of evidence that the surface roughness, or topography, and in particu-
lar, nanostructural features (10-100 nm) influence the way that cells explore the
attachment possibilities, for example by producing pseudopodia ([
414
,
415
]). Nan-
otopography might influence the diffusion process of important biomolecules that
may affect, in turn, the probing of the landscape by the cells. However, the mech-
anism(s) by which the cells “feel” the nanofeatures of surfaces is not clearly
understood.
13.3.4
Mechanical Properties
There are at least three different aspects associated with the significance of the
mechanical properties of the scaffolds, as they are related to the function of the cells
and the new tissue being built. First, from the moment of implantation the scaffold
must be integrated mechanically to the tissue/organ environment, i.e., it must stay
in place, bear the recurring loads, adapt to the deformations and fluid shear stresses.
In certain cases, it has to be fixed with internal fixation techniques (see Fig.
13.5
).
Second, the scaffold should operate at the implantation site in a way such as to pro-
vide the appropriate mechanical signals to the attached complexes of protein-cells
in order for the cells to produce the expected extracellular material. Furthermore, the
mechanical cues from the dynamical behavior of the scaffold should act as attrac-
tive signals for the desired flowing cells to become attached to the available scaffold
surface. Third, and this is related and amplified in the next subchapter, as the scaf-
fold degrades with time, its remaining mechanical properties (moduli of elasticity,
strength, toughness, etc.) in association with the mechanical properties of the newly
formed tissue should create the right mechanical environment for the continuation
of the regeneration process.
These mechanical requirements are desired of course, but little is known about
the time-dependent parameters (cellular interpretation of mechanical signals, degra-
dation kinetics in vivo, as well as of other biological reactions, such as inflammatory
responses, which are not dealt here) of the multiplex dynamic environment, which
is created during and after the implantation, involving also the wound healing pro-
cess. This is one of the main reasons why so many different materials, designs,
and processes are found in the literature: lack of detailed knowledge leads to the
trial-and-error approach. Nevertheless, the effort is continuing, and some aspects
of the particular problem, that of how the architectural structure of the scaffold at
all levels, from the nano- to the macroscopic one, modulates the material proper-
ties of the scaffold bulk materials is gaining both experimental and computational
attention [
412
].
