Barbieri Thesis - BioMedical Materials program (BMM)

Chapter 8 – General discussion
to control cell fate in vivo triggering their osteogenic differentiation into bone–
synthesizing cells without adding osteogenic (growth) factors to the material itself.
Then, when trying to improve mechanical properties, we increased the molecular
weight of the polymer phase and the biological characteristics of the composite
worsened and vice versa. Thus, we had to face with the challenge that either
excessively simplifying the system, or excessively complicating it, may be detrimental
for the performance efficacy of the biomaterial. This concept can be extended to a
more general view: a biomaterial approach should focus on a few simple mechanisms
occurring in nature that effectively influence and control cell fate and try to reproduce
them in a material. In particular, in view of a simple and effective approach we should
focus on simple and controllable ‘intrinsic’ properties of biomaterials that are then able
to interact with the biological environment by means of protein adsorption, surface
mineralization and release of certain ions that will influence on cell behaviour. For
example, the surface properties or the chemistry have been reported to play important
roles such biological phenomena and in instructing cells.
However, as mentioned earlier, we wanted to design a biomaterial that, upon
implantation, supports, or replaces, the tissue function by means of simple ‘physical’
mechanisms (in view of simplifying the system). The material, once implanted, may
degrade leaving room for the growing new tissue. In this scenario, the choice of
material factors is crucial to trigger biological phenomena involving tissue cells and
intrinsic properties of materials such as surface features or mechanical performance.
For instance, successful attempts to design an artificial vocal cord were
accomplished, [405] where the main issue was mimicking the viscoelastic properties of
the cord since it varies its dynamic viscosity with the frequency of stimulus (i.e. the
vibrational stress given by the air flush during the talk) for a proper phonation.
However, this material still has to demonstrate its effectiveness in driving cell fate and
supporting new cord tissue formation. This example demonstrates how challenging is
to design a biomaterial that have controllable ‘multiple’ characteristics.
The mechanisms of tissue formation and healing are still unknown, although new
discoveries in cell biology and medicine are contributing to the development of new
instructive materials that fully or partially mimic nature’s structures and regenerative
mechanisms. These new insights highlight the issues of (1) what is the minimum
level of material complexity required for the regeneration of specific tissues, and
(2) how to balance the feasibility of new biomaterial design with the regulatory
implications, costs of the final device and its ease of use by surgeons, design time
and, to a less extent, available funding.
As already seen, interest is growing in the exciting possibility of using simple material
properties that physically or chemically influence cell behavior. Current worldwide
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