Microfluidic Vasculature for Cell Culture - Evelyn Moore
Introduction
It is extremely important to create in vitro models of vasculature in order to study cancer (including metastasis and tumor cell circulation), drug delivery, diseases, and to supply oxygen and remove waste to systems too large to depend on diffusion. Vascular diseases are the leading cause of death worldwide causing around 17 million deaths per year. There are limited treatments, and therefore a dire need to better understand the vascular system [1]. Blood vessels are responsible for delivering nutrients and oxygen and for disposing wastes to and from all parts of the body. Vessels therefore end up controlling the microbiome. [2]. Currently, the best experiments are conducted on animal models and/or cell culture, but even these methods are poor indicators for what occurs in vivo [1].
Cell culture experiments fail to consider the complex, diverse, vascular system. Rather than being a single type of cell, capillaries and arteries are composed with different layers of cells. The inner layer is made up of endothelial cells (ECs) which act as a semipermeable membrane between the vessel wall and the fluid from the outside. The middle layer is comprised of smooth muscle cells (SMCs), which give the vessels their mechanical properties and provide structure by producing collagen. Fibroblasts and connective tissue line the outer layer [1]. Depending on what researchers are investigating, all of the layers of the blood vessels may need to be included. If the goal is to supply oxygen or deliver waste or maybe includes topics not associated with the actual biology of the blood vessel, then simpler fabrication methods can be used.
The vascularization of microfluidic devices is the creation of channels within a device capable of transporting blood in one end and completely out the other. As blood vessels range in size from the smallest capillaries of 5 micrometers to the aorta of 25 mm, microfluidic devices are excellent tools in order to provide the proper channels for blood flow [4]. The first generation of these devices relied on 2D manufactured devices stacked on top of one another in order to create a 3D vascularized device [5]. Now technology allows for the creation of detailed 3D vascularized microfluidic devices with the proper channel size for the type of blood vessel being recreated and type of tissue being replaced.
The vascularization of microfluidic devices has a vast number of applications as the ability to successfully move blood in an artificial tissue construct is important in the effectiveness of the device. Vascularized microfluidic devices can be used in both the medical field as a tissue implant in a number of areas of the body or for more research applications as a way of studying blood flow in vitro [3]. A number of considerations must be taken into account when creating these devices because of their use within the body. Biocompatibility of the materials used in these devices is very important as cells must adhere to the surface of the device and each device should accurately model the body [4]. Over the past few decades, several different techniques for the construction of vascularized microfluidic devices have been developed including traditional methods of construction using photolithography[1] and soft lithography[2] as well as emerging technologies of 3D printing through both dissolvable sacrificial moldings and hybrid method bioprinting. As these technologies continue to develop, vascularized microfluidic devices will continue to grow in importance for organ and tissue repair.
There are several challenges that must be considered when using microfluidics to create a vascular system. For example, many microfluidic devices are inexpensive and easy to make because of the heat curing polymer polydimethylsiloxane (PDMS). It is typically considered a great material for biological applications because it is gas permeable, bio-compatible, and clear. However, PDMS adsorbs hydrophobic molecules, making it difficult to study drugs. Some decide to work with thermoplastic materials in place of PDMS for drug studies, but these are expensive, auto-fluorescent (bad for imaging), and not gas permeable (so cells will die quicker than in PDMS) [1].
Additionally, the geometry of the channels may not always be perfect with lithographic techniques. Even though chips can function on the micro and nano scale, the vessel walls in vivo are extremely thin, and consequently difficult to study. Soft lithography also typically will create rectangular channels by adhering a design to a flat surface [1]. This may cause discrepancies between fluid interaction with cells in vivo and in vitro. Molding the channels a new way or taking advantage of 3D printing technologies can help create cylindrical channels.
Applications for Understanding Tumor Metastasis
When cancer cells spread from their origin to other areas in the body, it is referred to as tumor metastasis. This event is responsible for the greatest percentage of cancer deaths and therefore is an important area of study for improving cancer understanding and improving patient outcomes. [6] One way that researchers are looking to understand the molecular processes of metastasis is with microfluidic models of the tumor and its microenvironment.
The primary mechanism by which metastasis occurs is through the bloodstream, so in microfluidic devices aimed to model metastasis, vascularization must be properly represented. Referred to as angiogenesis, the development of new blood vessels occurs in tandem with cancer metastasis and is a primary area of study. [7]
An example of such device can be seen in Figure 2. This in vitro model was designed for high-throughput screening of new drugs to protect against microvascular destabilization and provides an excellent example of three-dimension tissue modeling in a microfluidic device. Three channels are shown, a blue collagen extracellular matrix, endothelial cells in the top perfusion lane to form a microvessel, and a third channel to which perfusion of the culture spread towards when the angiogenic factors were stimulated.[8]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Gold, K., Gaharwar, A.K., & Jain A.J. (2019). Emerging trends in multiscale modeling of vascular pathophysiology: Organ-on-a-chip and 3D printing. Elsevier, 196, pp. 2-17. http://doi.org/10.1016/j.biomaterials.2018.07.029
- ↑ Lee, S., Ko, J., Park, D., Lee, S., Chung, M., Lee, Y., & Jeon, N.L. (2018). Microfluidic-based vascularized microphysiological systems. Lab on a Chip, (18), pp. 2686-2709. http://doi:10.1039/C8LC00285A
- ↑ 3.0 3.1 Kolesky, D.B.; Truby, R.L.; Gladman, A.S.; Busbee, T.A.; Homan, K.A.; Lewis, J.A. 3D bioprinting of vascularized, heterogeneous cell‐laden tissue constructs. Advanced materials, 2014, 26(19), 3124-3130. https://doi.org/10.1002/adma.201305506
- ↑ 4.0 4.1 Hasan, A.; Paul, A.; Vrana, N.E.; Zhao, X.; Memic, A.; Hwang, Y.S.; Dokmeci, M.R.; Khademhosseini, A. Microfluidic techniques for development of 3D vascularized tissue. Biomaterials, 2014, 35(26), 7308-7325. https://doi.org/10.1016/j.biomaterials.2014.04.091
- ↑ He, Y.; Wu, Y.; Fu, J.Z.; Gao, Q.; Qiu, J.J. Developments of 3D printing microfluidics and applications in chemistry and biology: a review. Electroanalysis, 2016, 28(8), 1658-1678. https://doi.org/10.1002/elan.201600043
- ↑ Fares, J.; Fares, M. Y.; Khachfe, H. H.; Salhab, H. A.; Fares, Y. Molecular Principles of Metastasis: A Hallmark of Cancer Revisited. Sig Transduct Target Ther 2020, 5 (1), 1–17. https://doi.org/10.1038/s41392-020-0134-x.
- ↑ Zhang, Q.-Z.; Zhu, Y.-P.; Rahat, M. A.; Kzhyshkowska, J. Editorial: Angiogenesis and Tumor Metastasis. Front. Oncol. 2023, 12. https://doi.org/10.3389/fonc.2022.1129736.
- ↑ 8.0 8.1 Kramer, B.; Corallo, C.; van den Heuvel, A.; Crawford, J.; Olivier, T.; Elstak, E.; Giordano, N.; Vulto, P.; Lanz, H. L.; Janssen, R. A. J.; Tessari, M. A. High-Throughput 3D Microvessel-on-a-Chip Model to Study Defective Angiogenesis in Systemic Sclerosis. Sci Rep 2022, 12 (1), 16930. https://doi.org/10.1038/s41598-022-21468-x.
