While animal studies have long been a critical component of biomedical research, the value of such studies can be unpredictable: for example, the functioning of a drug in a mouse model may or may not indicate its value in humans. There is also tremendous value in the culturing of primary human cells for in vitro experimentation, but similarly, traditional cultures are not always representative of in vivo response. This is largely due to their lack of 3D structure, cell-matrix interactions, and physiological mechanical characteristics. For these reasons, interest in using engineered 3D cell culture constructs (organoids) as a platform for translational science is growing quickly.
A major translational goal for organoid technology is rapid parallel assessment, including drug testing. One route to addressing this is microfluidic technology, in which designed microchannels are fabricated on a chip and used to deliver fluids to discrete locations on demand. In collaboration with colleagues at the Wake Forest Institute for Regenerative Medicine, our group is developing innovative technologies approaches for incorporating tissue organoids with microfluidic devices.
For high throughput and increased design flexibility, we make microfluidic devices using patterned adhesive thin films sandwiched between milled laboratory slides (right) rather than conventional polymers like PDMS. Stacked film devices can be manufactured very quickly (in minutes) using inexpensive materials and instrumentation, and enable rapid system modification. Using this approach, we can implement passive fluidic devices (far right) as well as integrated control elements, like valves and mixers.
Most conventional methods of producing 3D cell culture is not easily compatible with microfluidic devices. For example, bioprinting requires access by a printing head, which is challenging with the intrinsically closed microfluidic system, and is largely serial, making the production of multiple independent organoids slow. Instead, we using the fabrication principles of photolithography to produce organoids in situ (far left): by introducing cell-laden and photopolymerizable hydrogel to the entire device channel, we can use ultraviolet exposure through a photomask to produce discrete 3D culture constructs of arbitrary shape. Additionally, iterative patterning (near left) enables the building of complex, multi-domain structures.
Our fabrication technique can be performed in multiple channels simultaneously using an appropriate photomask and a single ultraviolet light exposure. This ultimately allows for multiple, independent measurements to be carried out in parallel using a platform that is fabricated rapidly. In one potential approach, identical organoids may be circulated with media featuring a range of drug concentrations through a common pumping source (right) and then examined after treatment for response.
We have pursued exactly this type of investigation using a number of cell lines, but a major focus of our work has been expansion towards patient-derived primary cells: only with patient cells can we truly validate the predictive power of the technology. For example, we have incorporated into devices cells derived from the tumor biopsies of two patients with mesothelioma (below) and probed their responses to two common chemotherapy drug mixtures, carboplatin/pemetrexed and cisplatin/pemetrexed. Using cell viability as a metric of effectiveness, we observed that both drugs had some effectiveness for the two samples, but that cisplatin/pemetrexed was more effective for subject 1 while carboplatin/pemetrexed was more effective for subject 2. This correlated with the drug effects documented for the patients following biopsy collection.
Cell migration on a chip
In addition to the cell viability experiments and high-sensitivity biochemical assessments that our microfluidic systems support, we are also interested at looking at dynamic cell behavior. To that end, we developed a novel cell migration assay. The foundation of the approach is a multicomponent 3D cell culture construct (biofabricated in situ by photopatterning, figure below, top row) consisting of a cell-laden region and a cell-free region in a monolithic, shape-defined hydrogel. Our design allows the border between the two regions to be identified, enabling the number and speed of 'invading' cells to be quantified as a function of time. In our initial demonstration, we used the system to probe the effects of two types of chemotherapeutic - one antimigratory and one antiproliferative - on cancer cell migration (below, bottom row). We found that the former effectively reduces migration in a dose-dependent manner while the latter reduces migration only to a point; it prevents migration through cell death, but resistant cells maintain an unaltered migratory capacity. Currently, we are working to use this approach and variations on it to study metastasis and the factors that could prevent it in cancer progression.
"Drug compound screening in single and integrated multi-organoid body-on-a-chip systems", A. Skardal, J. Aleman, S. Forsythe, S. A. P. Rajan, S. Murphy, M. Devarasetty, Z. Pourhabibi Zarandi, G. Nzou, R. Wicks, H. Sadri-Ardekani, C. Bishop, S. Soker, A. R. Hall, T. Shupe, A. Atala, Biofabrication, 12, 025017, 2020 PDF
"Probing prodrug metabolism and reciprocal toxicity with an integrated and humanized multi-tissue organ-on-a-chip platform", S. A. P. Rajan, J. Aleman, M. Wan, N. Pourhabibi Zarandi, G. Nzou, S. Murphy, C. E. Bishop, H. Sadri-Ardekani, T. Shupe, A. Atala, A. R. Hall, A. Skardal, Acta Biomaterialia, doi: 10.1016/j.actbio.2020.02.015, 2020 PDF
"Multi-domain photopatterned 3D tumor constructs in a micro-physiological system for analysis, quantification, and isolation of infiltrating cells", S. A. P. Rajan, A. Skardal, A. R. Hall, Advanced Biosystems, doi:10.1002/adbi.201900273, 2020 PDF
"In vitro patient-derived 3D mesothelioma tumor organoids facilitate patient-centric therapeutic screening", A. R. Mazzocchi AR, S. A. P. Rajan, K. I. Votanopoulos, A. R. Hall, A. Skardal, Scientific Reports, 8, 2886, 2018 PDF
"Multi-tissue interactions in an integrated three-tissue organ-on-a-chip platform", A. Skardal, S. Murphy, M. Devarasetty, I. Mead, H.-W. Kang, Y.-J. Seol, Y. S. Zhang, S. R. Shin, L. Zhao, J. Aleman, A. R. Hall, T. Shupe, A. Kleensang, M. Dokmeci, S. J. Lee, J. Jackson, J. Yoo, T. Hartung, A. Khademhosseini, S. Soker, C. Bishop, A. Atala, Scientific Reports, 7, 8837, 2017 PDF
"In situ patterned micro 3-D liver constructs for parallel toxicology testing in a fluidic device", A. Skardal, M. Devarasetty, S. Soker, A. R. Hall, Biofabrication, 7 (3), 031001, 2015 PDF