Assistant Professor University of Memphis, Tennessee, United States
Introduction: Porous scaffolds play an important role in tissue engineering by facilitating cell attachment and the formation of tissues and organs. These scaffolds function as the building blocks for the culture and propagation of cellular structures outside of the body, temporarily replacing the extracellular matrix (ECM). Since porosity of the structure influences migrations and spatial organization for different types of cells, the scaffold structures with tunable porosity across multiscale is critical to mimic natural tissue structures. New methods to produce porous scaffolds have shown great promise in tissue engineering, including deposition modeling, electrospinning, gas foaming, and 3D printing [1,2]. However, current techniques have limitations in fabrication across multiscale: (1) lack of precision controlling the size and distribution of the porous microstructures with high resolution (2) time consumption for printing complicated structures. In this research, we introduce a novel approach to fabricate scaffolds by integrating acoustic-controlled microbubbles and digital light processing (DLP) 3D printing technology. Using a microfluidic bubble generator, we generated microbubbles in hydrogel with controlled size. These microbubbles are collected and patterned by an acoustic field and porous materials are fabricated by DLP 3D printing. Our method allows enhanced control over scaffold porosity at micro and macro levels. The integration of microbubbles can be finely adjusted to mimic the specific needs of different tissue types, ranging from vascular to tumoral structures. This research not only addresses the limitations of current scaffold manufacturing techniques but also opens new avenues for the creation of advanced biomaterials for the future of regenerative medicine.
Materials and
Methods: This work introduced a novel method to fabricate porous scaffolds with controllable porosity by combining acoustic controlled microbubbles and 3D printing technology. The total process has three steps (1) microbubble generation and size control (2) acoustic control of microbubbles (3) 3D printing of biomimetic hydrogel scaffold for cell culture. In the first step, we use a valve-based microfluidic bubble generator to precisely form bubbles with controlled sizes (15-200 μm), to better mimic scaffold of the native ECM and to apply the technology to a wider range of tissue types. For example, 100-200 μm is commonly used for cancer cell cultures to facilitate tumor-like growth, a smaller range of 10-40 μm is preferred for endothelial cell cultures to support the formation of vascular structures. Then, we applied acoustic field to patterning the microbubbles to create patterns of microbubbles on a free surface that can then be layered to produce lattice structures in three dimensions. After the microbubbles are patterned, DLP techniques are applied to print the scaffold structure. Gelatin methacryloyl (GelMA) was chosen as the materials of scaffold for its advantages in extrusion printing and availability. To accomplish printing, the Wintec PRO4500 was used and controlled with Texas Instrument’s DLP® LightCrafter 4500 [1]. The method of fabrication of the chips was micromilling and PDMS replica techniques. This method allows for rapid, cheap prototype production with only about 2-3 hours from milling a mold to generation testing. A syringe pump supplies the GelMA, also allowing for careful control of the flow rate.
Results, Conclusions, and Discussions: R Results: Testing of the microvalve showed that while there was deformation within this passage, the walls separating the constriction channel from the pressure channel were too thick for deformation. There is a geometric limitation to the microvalve, but it was found that diameter variation is possible through the control of pressure/flowrates. The observed behavior is that when the dispersed phase has a higher flow rate, the bubble size is reduced. If the flow rate of the continuous phase is increased, foam generation increases. Through the manipulation of the flowrates, microbubbles within the desired range of 30-200μm were produced. Initial testing of our control of the micropatterning was conducted with batches of SDS foam composed of microbubbles within the desired range. Piezoelectric transducers provided the energy for the secondary acoustic radiation force which patterns bubbles and particles suspended in a medium. SDS foam formed larger, macroscopic patterns but could be more easily disrupted. Patterned GelMA produced no observable macroscopic patterns, but larger droplets tended to distance themselves from each other and pack smaller droplets around themselves creating a more densely packed foam. During the testing of the DLP 3D printing, we confirmed that exposure time deepens the print until the hydrogel forms a solid throughout. For layered crosslinking, short-duration cycles are required so the exposure layer can be patterned between each cycle. Three initial prints were made of the same shape at three different scales: 25, 5, and 1 mm. Each produced a solid porous structure suitable for the testing of cell culturing.
Discussion: This project’s main goal was to combine a recent development in tissue engineering with acoustic patterning and reducing the size of the valve-based flow-focusing chip to move the generation range from the upper end of the ECM to the lower. Continuing research on this subject hopes to introduce additional techniques to the printing processes scaffolds. In future, if the biocompatibility is verified, more exact replications of the ECM can be created with a reproducible accuracy, cell propagation in engineered tissue could studied with greater accuracy due to a reduction in random abnormalities in artificial tissue sample structures.
.jpg "Yuan Gao, PhD (she/her/hers) photo")