Speaker
Description
Introduction: Melt electrowriting (MEW) has gained considerable popularity in the field of biofabrication due to the unique capabilities it offers to fabricate biologically relevant architectures. Most MEW-generated scaffolds have fiber sizes within the range of 5-50 microns and inter-fiber distances as low as 100 microns. However, that is just close to the maximum pore size where cells uniformly show maximal spreading during their initial attachment. However, no matter how densely woven a MEW layer is, achieving the adequate mechanical properties to withstand suturing is a significant challenge. Additional strength can be provided by using thicker fibers to survive suture stress (e.g., tension, shear, etc.). Eventually, the goal is to have a confluent sheet of cells with the cell’s extracellular matrix capable of supporting physiological loads. In the pursuit of this goal, having fiber-bound pores with a predictable geometry that is small enough to allow cells to fully span to two or more polymer filaments becomes crucial. To demonstrate these mechanical and geometric requirements, we tested the hybridization of MEW with Fused Deposition Modeling (FDM) to fabricate reinforced scaffolds that can withstand suturing and at the same time offer an appropriate environment for cell proliferation.
Methods: The hybrid scaffolds used in this study were fabricated in a custom-built printer. It incorporates a dual printhead that uses PID (Proportional–Integral–Derivative)-controlled cartridge heaters to melt polymer contained in a glass reservoir (MEW printhead). For the fabrication of the FDM borders we adapted a pellet extruder mechanism to an Ender Pro hot end (Creality, Shenzen, China) that served as the FDM printhead. Purasorb® PC 12 medical grade polycaprolactone pellets (Corbion, Netherlands) were used for the fabrication of both MEW and FDM fibers. For the fabrication of the MEW textile with a 50-micron pore size, the pellets were melted for 1-hour prior to printing at 80°C and then extruded at a pressure of 0.72 Bar. The high voltage and translating speed of the collector was set to 5 kV and 12.5 mm/s, respectively. For the FDM borders, the extrusion rate and translating speed of the collector was adjusted so that a 0.4-mm thick fiber was printed. The toolpath design and postprocessing of G-Codes for both was done in Fusion 360 (Autodesk, California, US). L929 cells were then seeded on the hybrid scaffolds to study cell viability and confluence during a 7-day period.
Results: Preliminary data on suture retention using the ISO 7198 showed a 166% increase in the peak load (0.655 vs 1.741 N) when comparing a MEW-alone textile vs. the MEW+FDM textile. Moreover, by optimizing the MEW process to print a 50-micron pore size that was reliably and uniformly small, we were able to rapidly achieve cell confluence by day 7 (Figure 1C).
Discussion: FDM fiber incorporation and full confluence of our hybrid textile scaffolds portends future achievement of our mechanical and biological goals. We anticipate that cells stimulated by load carrying FDM borders will thicken and strengthen. The original MEW and FDM fibers will become less relevant over time and eventually resorb.
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