Proper brain function requires strict regulation of blood, oxygen, and metabolite levels. The Blood-Brain Barrier, or BBB, does exactly this to maintain homeostasis. The BBB is a highly selective semipermeable membrane that protects the brain from cerebral blood vessels that circulate the brain. It prevents solutes in the circulating blood, such as neurotransmitters and neurotoxins, from entering the brain where neurons reside. One essential structure of the BBB is the “Endothelial Tight Junction,” the uniform arrangement of endothelial cells lining the interior of blood capillaries. These cells are organized extremely closely so that it only creates a small, tight gap where substances can enter paracellularly. 

In the presence of brain tumors, however, the BBB transforms into a dysfunctional barrier known as the Blood-Tumor Barrier or BTB. The BTB rearranges the Endothelial Tight Junction into a non-uniform, highly permeable arrangement. This enables tumor cells to enter blood vessels that deliver blood to the brain, and thus enter the brain. As tumors continue to grow inside the brain, the pressure inside the cranium increases and tissue functions compromise, leading to detrimental consequences like seizures, memory loss, and motor impairment, depending on what area of the brain the tumor affects.

Despite the crucial role it plays in general human functions, the BBB has not been extensively studied due to the difficulty of producing BBB models. Although methods to produce BBB models currently exist, they present limitations such as low reproducibility and high cost. Thus, more complex models are needed to understand the specific biological process involving both the pathological and physiological responses of BBB and tumor cells. 

Nonetheless, recent studies have shown that 3D bioprinting may be a promising new technique to produce BBB models. 3D bioprinting enables a complex layout to be built, containing desired biological materials and cells, all while costs remain low. Further research on this issue may successfully confirm this hypothesis and give rise to a novel method of studying the BBB.

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