Mechanical Characterization of Frozen and Freshly‐Isolated Human Brain Tumors

Tissue banks are a common human tissue source for oncology researchers, and common pathobiological assays have been optimized to accommodate previously frozen tissue. However, emerging interest in tissue mechanics to motivate tissue‐on‐a‐chip applications necessitate additional optimization for and understanding of mechanical changes with prolonged storage. Here, we seek to compare the mechanical properties of previously frozen to freshly‐isolated human brain tumors. Methods All human tumor samples were collected and data analyzed under University of Florida Institutional Review Board‐approve protocols. Meningioma samples were isolated from patients and stored at −80°C for 2 or 5 years before thawing in DMEM at room temperature and characterizing with a custom‐built indentation system within 30 min after thawing. Indentation and subsequent analysis of samples was performed fresh, never frozen tissue (1). Briefly, samples were indented and allowed to undergo stress‐relaxation until a quasi‐static state was reached. The steady‐state modulus was then determined by fitting the data to the Standard Linear Solid viscoelastic model, which represents the quasi‐static properties of the sample. Freshly‐isolated human tumor and normal mouse brain data was originally published in PLoS ONE in 2017 (1). Statistics were performed with a Wilcoxon non‐parametric test with multiple comparisons. Values are reported as median ± median absolute deviation. Results and Discussion Freshly‐isolated human meningioma samples were about twice as stiff (2.83±1.26 kPa, Figure 1) as frozen meningiomas stored for 2 or 5 years (1.15±0.26 kPa and 0.97±0.54 kPa, respectively, p<0.0003). These findings are similar to those in the literature comparing showing that frozen tissue is softer than the freshly isolated counterparts (2, 3). The change in the mechanical properties of previously frozen tissue may reflect disruption of the extracellular matrix (ECM) architecture and cellular fidelity due to expansion and contraction of ice crystals during a freeze/thaw cycle (4). Future work will investigate changes in the ECM structure via SEM and immunostaining to correlate ECM structure and mechanical properties, allowing for a better understanding of cryogenically‐stored tissue. Support or Funding Information We gratefully acknowledge support from the Florida Center for Brian Tumor Research for human tissue coordination and collection, and funding support from Medtronic and NSF Award No. 1711543 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .