Researchers at Rice University and Baylor College of Medicine have overcome an important challenge to using endothelial cells sourced from induced pluripotent stem cells to generate bioengineered blood vessels. Specifically, the investigators were able to watch and guide the formation of tiny blood vessels within specially built molds that promote cellular ingrowth. This development should help eventually lead to lab-grown organ replacements suffused with a complex network of vessels, just as within our natural organs.
The team used both fibrin and gelatin methacrylate, a synthetic material, to create the molds. Gelatin methacrylate is 3D printable, which means it may be suitable for creating customized molds for generation of patient specific replacement vessels.
Rice University has some details:
[Gisele Calderon, the lead author of the study], said the first step in the experiments was to develop a third-generation lentivirus reporter to genetically modify the cells to produce two types of fluorescent protein, one located only in the nucleus and another throughout the cell. This permanent genetic modification allowed the team to noninvasively observe the cell morphology and also identify the action of each individual cell for later quantitative measurements. Next, the cells were mixed with fibrin and incubated for a week. Several times per day, Calderon and Thai used microscopes to photograph the growing samples. Thanks to the two fluorescent markers, time-lapse images revealed how the cells were progressing on their tubulogenic odyssey.
Calderon conducted advanced confocal microscopy at the Optical Imaging and Vital Microscopy Core facility at Baylor College of Medicine. Calderon and [undergrad student Patricia Thai] then used an open-source software called FARSIGHT to quantitatively analyze the 3-D growth patterns and development character of the tubulogenenic networks in each sample. In fibrin, the team found robust tubule formation, as expected. They also found that endothelial cells had a more difficult time forming viable tubules in GelMA, a mix of denatured collagen that was chemically modified with methacrylates to allow rapid photopolymerization.
Over several months and dozens of experiments the team developed a workflow to produce robust tubulogenesis in GelMA, Calderon said. This involved adding mesenchymal stem cells, another type of adult human stem cell that had previously been shown to stabilize the formation of tubules.
Here’s Gisele Calderon giving an excellent 90 second summary presentation of her work: