Because of interactions among carbon dioxide, bicarbonate buffer, and phenol red, frozen or newly thawed GelNest™ Matrix may display different colors, ranging from straw yellow to dark red.

Phenol red appears bright yellow when frozen or under acidic conditions and turns red near physiological pH or above 0°C. Color variation in GelNest™ Matrix is normal and does not affect product quality. After equilibration with 5% CO₂, the color will become uniform.

Similarities:

a. Similar experimental methods are used, including Transwell assays, Boyden chamber migration assays, and wound-healing assays.

b. Both evaluate the ability of cells to move from one location to another.

c. The molecular mechanisms are similar and involve cytoskeletal remodeling, cell-cell and cell-matrix interactions, and regulation of signaling pathways.

Differences:

a. Experimental procedure: invasion assays require the upper side of the membrane to be coated with matrix to mimic the extracellular matrix in vivo.

b. Regulatory mechanisms: cell migration is mainly influenced by chemotactic factors and the extracellular matrix, and is achieved through cytoskeletal remodeling and changes in membrane fluidity. Cell invasion additionally requires cells to secrete proteases that degrade the basement membrane so they can cross the barrier.

c. Matrix interactions: during migration, repeated adhesion to and detachment from the matrix are essential for movement, with the extracellular matrix serving as structural support. During invasion, cells must secrete proteases to degrade the basement membrane and create a path through the barrier.

Both methods are used to study tumor invasion and metastasis. A Transwell invasion assay is an in vitro experiment, whereas a tumorigenicity study is performed in vivo, commonly using 4–6-week-old nude mice. Both can be used to investigate tumor formation and metastasis.

A Transwell invasion assay applies Transwell technology to the study of tumor-cell invasion. It is widely used because it is simple and reproducible. Membranes with 8.0 or 12.0 μm pores are commonly used. Tumor cells are seeded in the upper chamber, while FBS or specific chemoattractants are added to the lower chamber. The cells migrate toward the nutrient-rich lower chamber. Unlike a migration assay, however, the upper surface of the polycarbonate membrane is coated with matrix to mimic the extracellular matrix in vivo. To reach the lower chamber, cells must first secrete matrix metalloproteinases (MMPs) to degrade the matrix and then pass through the polycarbonate membrane. The number of cells entering the lower chamber reflects the invasive capacity of the tumor cells.

In an in vivo tumorigenicity study, immunodeficient mice serve as hosts for xenograft models. Tumor cells are injected into the mice, and biological changes are evaluated by monitoring tumor growth. Matrix may be added to accelerate tumor formation, using a 1:1 ratio of matrix to PBS or serum-free medium.

Human umbilical vein endothelial cells (HUVECs) are commonly selected for the following reasons:

A) Convenient source: HUVECs are isolated from neonatal umbilical cord tissue, which is readily available, involves no major ethical concerns, and can provide a sufficient number of cells.

B) Tube-forming capability: HUVECs have progenitor-like potential and can theoretically be passaged 50–60 times.

C) Primary HUVECs closely resemble human endothelial cells in vivo and reflect the characteristics of newly formed vascular endothelium.

Serum starvation limits the cells’ access to nutrients and proliferation factors, thereby reducing their growth rate.

It can arrest cells in the G0/G1 phase and synchronize cell growth and division.

It can also promote apoptosis, making changes in cell morphology and differentiation easier to observe.