Biomedical Engineering Reference
In-Depth Information
TABLE 4.2
Differences between Biological Tissue Development and Tissue Engineering Using Scaffolds
Tissue Development
RP Scaffold Approach
Not scaffold dependent
A porous biodegradable scaffold is necessary
Cells create their matrix and extend in three dimensions
from a “point source”
Takes place through pseudo-3-D fabrication: through
layer-by-layer assembly of 2-D
Environment and structure modulated in real time
Preprogrammed architecture
Complex multicomponent materials
Usually one material
Soft and wet
Often hard and dry
assemble and organize through a process of accumulation and accretion rather than degradation and
attrition. However, the differences between tissue development and scaffold-based tissue engineer-
ing, some of which are listed in Table 4.2, should be kept in mind. Cell assembly and organization is
an immensely complicated process and depends on the correct orchestration of biochemical signals
with spatial and other physical stimuli. Simply seeding cells on a porous scaffold with the same
shape as the end organ and hoping for a functional tissue to form has already been shown to be
insuffi cient. Indeed, despite the enormous economic resources injected into tissue engineering, very
few products are actually viable from a commercial [27] or even medical point of view [28].
In this sense, scaffold fabrication techniques through RP are not stand-alone tissue engineering
tools but, taking into account the intricate complexity of living systems, must be integrated with
other micro and macroscale techniques. For instance, that scaffolds must be accompanied by pre-
or postsurface modifi cation usually thorough the immobilization of adhesion proteins, which is
already well established. Other supporting elements such as soluble growth factors, incubators, or
bioreactors are also mandatory. We have already mentioned that the nature of the biomaterial as
well as its microstructure and topology are additional critical factors. It should not be forgotten that
even in mechanical terms, the microfabrication or biomaterial processing method must be matched
to each particular tissue to be engineered. Optimized solutions could be found by combining dif-
ferent RP methods and by following biomimetic design principles through the use of biomaterials,
which resemble biological materials as much as possible. This implies the development of hybrid
materials and structures with a composite nature and high water content and the integration of two
or more RP techniques, for example, with different resolutions and different types of polymers.
4.11 CONCLUSION
An overview of RP methods for biomaterial fabrication has been provided with the aim of illus-
trating the basic principles behind the scaffold-based tissue engineering. Rather than providing
exhaustive technical and comparative details, which are available in several excellent reviews that
the interested reader is encouraged to refer to Refs. 2,29,30, we have described aspects which must
be taken into consideration when realizing a scaffold such as the resolution time of manufacture
ratio, materials employed, and scaffold geometrical design. Furthermore, it is also important for the
RP engineer involved in tissue-engineering construct manufacture to be acutely aware of the differ-
ences between tissue development and the use of a scaffold to guide cells to appropriate locations
on a scaffold. High throughput production of tissue-engineered constructs is still a long way away
and not only requires great multidisciplinary effort but also a thorough understanding of the biol-
ogy, chemistry, and engineering of cells and biomaterials and above all their interaction in complex
3-D environments.
