BIOMATERIAL APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 535

Through the design and expression of artifi cial genes, it is possible to prepare
artifi cial ECM proteins with controlled mechanical properties and with domains
chosen to modulate cellular behaviour. This approach avoids several important
limitations encountered in the use of natural ECM proteins, including batch-to-
batch (or source-to-source) variation in materials isolated from tissues, restricted
fl exibility in the range of accessible materials properties, and concerns about
disease transmission associated with materials isolated from mammalian sources.
Elastin-based systems have been of special interest in this regard. Urry and co-
workers have shown over many years that simple repeating polypeptides related
to elastin can be engineered to exhibit mechanical behaviour reminiscent of the
intact protein.
The understanding that the natural ECM is a multifunctional nanocomposite
motivated researchers to develop nanofi brous scaffolds through electrospinning
or self-assembly. Nanocomposites containing nanocrystals have been shown to
elicit active bone growth. Incorporation of cell adhesion ligands allows attach-
ment and spreading of cultured cells, and in the specifi c case of materials for vas-
cular grafts, retention of endothelial cell adhesion in the face of shear stresses is
characteristic of the normal circulation.
Recent progress in the development of methods for incorporation of non-
natural amino acids into recombinant proteins points the way to an alternative
strategy for preparing artifi cial ECM proteins with diverse chemical, physical, and
biological properties. Substantially more experience has been gained in evaluat-
ing the in vivo performance of engineered biomaterials based on polysaccharides.
Alginate hydrogels bearing cell-adhesion ligands have been used as scaffolds for
cell encapsulation and transplantation, and have yielded promising results in
experiments directed towards the engineering of bone tissue capable of growth
from small numbers of implanted cells. The prospect of growing tissues from
small numbers of precursor cells is an attractive alternative to harvesting and
encapsulating large cell masses before transplantation. Molecular self assembly
of peptides or peptide-amphiphiles may also lead to unique biomaterials. A
number of self assembled peptide systems have been developed, including
systems that can potentially be used in tissue engineering and nanotechnology.
An alternative to synthesizing polymers composed of natural components is
the synthesis of biomimetic polymers, which combine the information content
and multifunctional character of natural materials (such as a particular amino
acid sequence that might be desirable for cell attachment) with the tailorability of
a synthetic polymer, such as control of molecular mass or polymer degradation,
and the ability to impart appropriate mechanical properties. An example of
this concept has been the synthesis of polymers composed of lactic acid and
lysine.
15.3.10 Array Technologies and Specifi c Medical Applications
A related challenge arises in the engineering of materials for diagnostics and
array technologies, in which large numbers (typically hundreds or thousands) of