Biointerfaces Between Cells and Substrates in Three Dimensions - Biointerfaces: Where Material Meets Biology - page 134

Traditionally, plastic Petri dishes and welled plates have been used as the
artificial growth environment for most in vitro cell studies, offering only a
two-dimensional (2D) interface for cell attachment and growth (along the XY
plane). Whilst this approach has proved an extremely practical and access-
ible method of cell growth in the past, it is now regarded as highly un-
realistic compared to the complex 3D scenario described above. 1,2 Cells in a
2D monolayer are unable to form multi-directional tight junctions with their
neighbours and become polarised, given that the majority of the cell surface
is spread out along the plastic interface. In addition, a cell's cytoskeleton
and delicate organelles are forced into a severely flattened shape when
cultured in two dimensions. This can cause unnecessary stress, making it
artificially vulnerable to external stimuli and mechanical forces. Un-
surprisingly, many primary cells, such as hepatocytes, cultured at the 2D
interface rapidly lose their native phenotype and viability after just a few
days in culture.
Recognising the limitations of 2D culture substrates there is now a strong
demand for materials that can offer cells a 3D interface for growth (XYZ
plane). 3 By adding the third dimension to the growth substrate, cells can
more readily approximate their native 3D organisation and cell density. This
in turn encourages cell communication and anchorage, making cells less
susceptible to trauma and thus prolonging a more representative in vitro
phenotype. Indeed, the advantages of 3D interfaces for cell growth are al-
ready evident. 3D biointerfaces are now helping to progress our under-
standing of the molecular mechanisms involved in cancer. 4,5 They are also
opening up exciting opportunities in the fields of tissue engineering and
regenerative medicine, where 3D constructs grown in vitro or ex vivo can later
be implanted into the body for organ repair. 6,7 This chapter will therefore
briefly describe some of the materials used to create 3D interfaces for cells
and tissues, with a particular emphasis on materials used in 3D cell culture
applications. Some general methodologies used to examine cells in the 3D
microenvironment will also be discussed, with the intention of merely
highlighting to the reader the techniques available, rather than providing
detailed experimental conditions or specific procedures.

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6.2 Using Natural and Synthetic Materials to Create
Three-dimensional Biointerfaces
There is now a variety of different materials that can offer a 3D interface for
cell and tissue growth, with the choice of material depending on the appli-
cation required. Natural-based materials such as protein hydrogels or
alginate scaffolds are particularly attractive for tissue engineering or
regenerative medicine applications, as the biocompatibility and biodegrad-
ability of these materials makes them suitable for eventual implantation into
the body. These materials are also useful for studying cell-ECM interactions,
given that natural-based materials are more likely to mimic specific