Tissue Engineered Models of Brain Tumors and Their Applications

85

icon wafer with an altered strip width and complex design provided important

insights on cell adhesion and migration [132]. U251 cells on STEP fibers and

C6 cells on laminin coated linear grooves have serviced to exercise the impact

of geometry on the migration speed and dimensions, and cytoskeletal model-

ing [133, 134]. Aside from the role of topographic information on migration

and mechanisms behind, it can still be applied to proliferation, invasion, and

investigation of driving factors of gene expresssion pattern [135, 136].

3.3.3

3D Models

After 2.5D models, 3D models gained popularity as versatile tools to address

the bottlenecks of conventional 2D models on the simulation of the GBM com-

plexity. Currently, 3D models are formulated as scaffold-free, scaffold-based,

and hybrid strategies. Additionally, microfluidic/chip systems and organotypic

slices are of current interest, especially to harness native tumor tissue prop-

erties.

Scaffold-free models (Figure 3.3 and Table 3.1) in GBM are constructed

as organizations of (hetero)spheroids and organoids. During this process, cell-

cell cohesion is amplified by driving minimum interaction with any non-cell

surface. Thereby, it leads to spontaneous cell arrangements in 3D configu-

rations. This assembly is considered superior over 2D monolayer culture, as

it can imitate various features of solid tumors. Even certain aspects of the

animal models of the disease cannot match the development stages of hu-

mans where patient-derived organoids can be preferable to model disease

and even to discover patient-specific responses. The possibility of real-time

imaging, biobanking and high-throughput analysis are other benefits of these

technologies [137–139]. Besides, in vitro culture creates development of three

distinct zones (proliferative, quiescent and necrotic zones) within especially

spheroids with larger than 500 µm in diameter. Non-uniform features of pH,

gases, nutrients, and other soluble factors are further posed by 3D organiza-

tion of spheroids with high similarity to native tumor [140]. An organoid is

also 3D assembly of cells, but it is composed of different cell types mimick-

ing the cellular composition, function and physiology of the tissue/organ they

originate, as well as better imitate genetics and phenotype of tumor tissue.

Conversely, they require growth factor cocktails to sustain tissue architecture

and, tissue procurement and processing alterations hamper standardization

[122, 123, 141].

In hanging drop (Figure 3.3A), 20–40 µl drops of cell suspension stay on

the lid by surface tension and, gravity leads to aggregation and compaction of

cells into spheroids. This technique is relatively simple, cost-effective, provides

control over spheroid size and content, but it is labor-intensive, challenging in

scale-up and traditionally does not support the addition of a fresh medium or

soluble factors during the incubation period [122, 142, 143]. 384 well-hanging

drop arrays can overcome these major drawbacks, as they allow time-lapse

imaging, on-site staining and drug treatment, and culture of distinct types