Biointerfaces Between Cells and Substrates in Three Dimensions - Biointerfaces: Where Material Meets Biology - page 136

6.2.2 Hydrogels
Hydrogels derived from natural or synthetic polymers can be used to im-
mobilise cells within a 3D gel matrix that mimics certain physical, mech-
anical and/or biochemical aspects of the native ECM. Within the gel, cells
aggregate into 3D structures that promote cell contact and interaction across
multiple surfaces (Figure 6.2). Many hydrogels are made from biodegradable
polymers, such as natural proteins or synthetic polypeptides, enabling good
suitability for tissue engineering or regenerative medicine applications. 10
Also, being approximately 90% water, hydrogels can display some of the
mechanical properties of soft tissue, which for certain organs such as the
bladder, is an important factor in maintaining normal cell function.
Whilst hydrogels do go a long way to mimic several components of the
ECM and are therefore an attractive choice for many researchers, there are
some notable limitations. Mass-transfer issues have long been a concern for
hydrogels, in that the diffusion of nutrients and waste through the gel may
be too slow to accommodate dense 3D structures. Another limitation is gel
formation. Many hydrogels require some form of external switch to gel, such
as a change in temperature, pH or exposure to UV radiation. Hence if cells
are dispersed into the material prior to gelation, which is common practice,
care needs to be taken to ensure that the gelation process does not have any
detrimental effect on cell viability.

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6.2.3 Electrospun Polymer Fibres
Electrospinning is a technique that converts polymeric liquids (natural and
synthetic) into micro- or nanoscale fibres creating a 3D mesh topography.

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Figure 6.2 3D cell growth in hydrogels. Left: schematic showing how a gel will

encapsulate a 3D aggregate of cells. Right: glioma (brain cancer) cells
growing in a 3D hydrogel. The green fluorescent dye reflects the cyto-
skeletons of the cells. Scale bar is 50 mm.
Image taken from www.medgadget.com (original

image courtesy of

Brendan Harley).