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International Journal of Bioprinting Bioprinted tissue-on-a-chip in drug screening

It has been reported that partial tumor environments do 2.3. Tumor behaviors
exist with permanent or temporary hypoxia. Pericytes Relentless proliferation (replication immortality),
surrounding endothelial cells control vasoconstriction. drug resistance, abnormal vessel formation, invasion,
Hypoxia and ischemia in TME are promoted by pericyte and metastasis are fundamental tumor behaviors.
abscission, increased permeability of vessel, as well Research confirmed that reprogramming of tumor
as abnormal angiogenesis, thereby promoting tumor energy metabolism and immune evasion are also tumor
metastasis and invasion. The energy metabolism pathway behaviors. Some of these behaviors have been reproduced
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of tumors is affected by HIF activity in a hypoxic state. In in vitro via 3D bioprinting and microfluidic technology.
an attempt to help tumor cells adapt to hypoxic conditions,
glycolysis serves as a common energy metabolism pathway 2.3.1. Metastasis and invasion
in tumor cells. Glycolysis with great glucose consumption Invasion and metastasis are the most representative
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and significant lactate formation is accompanied by the behaviors of therioma in comparison with benign tumors.
generation of pyruvic acid and hydrion, which gives rise Invasion and metastasis are inextricably linked, but in
to low potential of hydrogen (pH) that is regarded as general, tumors should acquire an invasive phenotype
another characteristic of TME. In addition, one of the first. Tumor cells internally infiltrate into blood vessels
critical mechanisms undermining tumor immunity is the after migrating on the tumor–stromal surface. Although
restriction of immunocyte functions by hypoxia. Thus, most cells will succumb to death in blood stream, a
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physiological characteristics, including hypoxia/oxygen minority of the cells survive and successfully exosmose
gradient, acidity, and abnormal vessel formation, should from blood vessels to target organs, where metastatic cells
be recapitulated in tumor models (Figure 2). spoliate nutrients from target organs for proliferation and

Figure 2. Schematic diagram depicting various cell types (neutrophil, NK cell, T cell, B cell, macrophage, fibroblast) and physiological features (hypoxia,
oxygen gradient, abnormal vasculum) associated with tumor microenvironment. Abbreviations: NK cell, natural killer cells; T cell, thymus-dependent
lymphocyte; B cell, bursa-dependent lymphocyte.

Volume 10 Issue 3 (2024) 176 doi: 10.36922/ijb.1951