Generating Large Tissues in the Lab: Advances in Bioreactor Cultivation and Micofluidics
Introduction
The field of tissue engineering is making significant strides in the ability to generate large tissues in the lab. This innovation is pivotal in the medical industry, offering potential solutions for regenerative medicine and personalized healthcare. One key advancement in this area is the use of bioreactors and microfluidics to culture tissues more effectively. In this article, we delve into the pioneering work conducted by researchers like Gordana Vunjak-Novakovic at Columbia, exploring the technical aspects and potential applications of these techniques.
Bioreactor Cultivation of Anatomically Shaped Human Bone Grafts
The work by Gordana Vunjak-Novakovic has been particularly insightful in this field. Her laboratory has developed a method for engineering bone grafts in vitro with a specific geometry using bioreactors. This technique begins by segmenting the anatomical geometry of the bone grafts from computed tomography (CT) scans and converting them into G-code for precise machining of decellularized trabecular bone scaffolds. Human bone marrow-derived mesenchymal stem cells (MSCs) are then seeded into these scaffolds using spinner flasks.
(Chapter image: Bioreactor with a decellularized trabecular bone scaffold)
The scaffolds are cultivated for up to 5 weeks in a custom-designed perfusion bioreactor system. The flow patterns through the complex scaffold geometry are modeled using SolidWorks to optimize the bioreactor design. This approach results in significantly higher cellular content, better matrix production, and increased bone mineral deposition compared to non-perfused static controls. This technology can be applicable for creating patient-specific bone grafts of various shapes and sizes, offering a promising avenue for personalized medicine.
Biomimetic Perfusion and Electrical Stimulation for Cardiac Tissue Engineering
While bone tissue engineering focuses on complex geometries, cardiac tissue engineering is concerned with mimicking the microenvironment of the heart. Work by Gordana Vunjak-Novakovic and co-authors has pioneered the use of scaffolds with parallel arrays of small-diameter (250 μm) channels, allowing for uniform seeding of cardiac cells. Perfusion of culture medium through these small channels decreases diffusional transport distances and protects cells from hydrodynamic shear, mimicking capillary flow in the heart.
(Bioreactor image: Scaffolds with parallel channels)
The researchers propose a bioreactor design to deliver both culture medium perfusion and electrical stimulation, while allowing the cultured tissues to freely contract. This combined approach aims to create a more viable and functional tissue, demonstrating that a combination of perfusion and electrical stimulation enhances tissue formation compared to either stimulus alone.
Nutrient Channels in Cartilage Tissue Engineering
Another significant challenge in tissue engineering is the delivery of nutrients to larger tissues, such as cartilage. A study by another research group demonstrated that nutrient transport limitations can be overcome by introducing channels in 10 mm diameter cartilage constructs. By extending this approach to 40 mm diameter constructs, the team was able to culture robust cartilage constructs that were 4 mm thick and 52 mm in diameter, representing a 100-fold increase in scale. These large constructs retained their functional properties, with Young's modulus reaching up to 623 kPa and GAG content up to 8.9/ww of wet weight.
(Cartilage construct image: Scaffolds with channels)
The introduction of nutrient channels in cartilage tissue engineering has been a significant step forward, proving effective for large tissues with low metabolic activity. This method can potentially be applied in the creation of larger, more realistic cartilage grafts, which are crucial for treating joint injuries and degenerative diseases.
Endothelial Cell Anastomosis in Microfluidic Systems
For tissues that require a blood supply, the linking up of endothelial cells to microfluidic flow channels is crucial. The work by Steven C. George exemplifies this with his vascularized microfluidic mini-tissues. Directed fluid flow in these systems stimulates the movement of endothelial cells towards nearby channels, promoting anastomosis.
(Microfluidic image: Perfusion flow in a microchannel system)
This finding is particularly relevant for generating large, vascularized tissues, as it ensures the formation of a continuous network of blood vessels within the engineered tissue.
Conclusion
The advancements in bioreactor cultivation and microfluidics are paving the way for the generation of complex, large-scale tissues in the lab. By optimizing the delivery of nutrients, oxygen, and other essential factors, researchers are making significant strides in the field of regenerative medicine. As these techniques continue to improve, they hold the potential to revolutionize how we treat a wide range of medical conditions, from bone and cartilage defects to heart disease.