Biointerfaces Between Cells and Substrates in Three Dimensions - Biointerfaces: Where Material Meets Biology - page 135

carbohydrate motifs or peptide anchorage points present on the native ECM.
In contrast, applications such as high-throughput laboratory models as a
replacement for 2D plastic plates will more likely require synthetic sub-
strates that are reproducible, chemically stable and easy to use. Many
natural-based materials are often too variable in composition and structure
for this application. Their biodegradability also adds an unwanted time-
dependent variable into laboratory experiments.
Whilst it is not possible to list every natural and synthetic material used
for 3D cell growth, broad categories of materials have been described below.
Within each category, a brief description of the technology is available, along
with any important advantages and disadvantages.

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6.2.1 Sandwiching Cells with Extracellular Matrix Proteins
Extracellular matrix (ECM) proteins such as collagen or the sarcoma-derived
protein mixture Matrigel t (BD Biosciences) have long been used to coat Petri
dishes and welled plates to improve the physiological relevance of the 2D
interface and thus promote cell adhesion and function. Taking this further,
researchers in the field of liver biology found that applying a second layer of
ECM protein directly above the monolayer, to create a sandwich of protein-
cell-protein, helped to keep cells in a more upright morphology during the
culture period (Figure 6.1). As a result, cells were less flattened and could
sustain a polarised state that led to enhanced functional capacity. 8 Con-
sequently this approach is a popular method of culturing hepatocyte cells,
particularly to monitor hepatobiliary mechanisms in vitro. 9

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Figure 6.1 Schematic of a collagen sandwich culture compared to a conventional 2D

culture. Top: conventional 2D culture where cells flatten out along the
plastic surface. Bottom: collagen sandwich culture where the collagen
above and below the cells helps to maintain a more appropriate upright
morphology. Notice the reduction in cell-cell contact in the 2D culture
whilst in 3D sandwich culture there is greater opportunity for intercellu-
lar interactions (stars).