A new form of 3D printing, called fusion electro-writing, has been used by researchers to produce scaffolds for artificial heart valves that mimic the different biomechanical properties of heart valve tissue. The fabrication platform allows researchers at the Technical University of Munich (TUM) in Germany to combine various precise custom designs into the scaffold and fine-tune its mechanical properties so that the patient’s own cells form new tissue as the scaffold biodegrades. The hope is that this technology will produce pediatric implants that will last a lifetime and will not require replacement surgery.
Four heart valves in the human body ensure that blood flows in the right direction, and it is essential that they open and close correctly, notes the press release on TUM’s website. To perform this function, heart valve tissue is heterogeneous, which means that heart valves exhibit different biomechanical properties within the same tissue.
A team of researchers working with Petra Mela, Professor of Medical Materials and Implants at TUM, and Professor Elena De-Juan Pardo of the University of Western Australia, have for the first time mimicked this heterogeneous structure using electro-writing by fusion.
The high voltage electric field produces extremely fine polymer fibers
Fusion electrowriting is a relatively new additive manufacturing technology that uses high voltage to create precise patterns of very fine polymer fibers. When the polymer is melted and pushed out of a printhead as a liquid jet, a high voltage electric field is applied which greatly reduces the diameter of the polymer jet by accelerating it and pulling it towards a collector. This results in a thin fiber with a diameter generally in the range of five to 50 micrometers. By comparison, a human hair is about 70 micrometers. The electric field also stabilizes the polymer jet, which is important for creating defined and precise patterns.
Image courtesy of Andreas Heddergott/TUM
|Close-up of a scaffold for artificial heart valves printed by fused electro-writing.|
The “writing” of the fiber jet according to predefined patterns is carried out using a computer-controlled mobile collector. The user specifies the path by programming his coordinates.
The researchers developed software that allows operators to easily assign patterns to different regions of the scaffold by choosing from a library of available patterns. Geometric specifications such as length, diameter and scaffold thickness can be easily adjusted via the GUI.
Biodegradable medical grade polycaprolactone (PCL) is used to print the scaffold. After implantation, the researchers believe that the patient’s own cells will grow on the porous scaffold, as was the case in early cell culture studies. The cells would then potentially form new tissue before the PCL-based scaffold degrades.
The PCL scaffold is embedded in an elastin-like material that mimics the properties of natural elastin found in real heart valves. According to the researchers, the micropores of the elastin-like material are smaller than the pores of the PCL structure, giving cells enough room to settle but sealing the valves adequately for blood flow.
Tests have shown that artificial heart valves work well
The designed valves were tested using a simulated flow circulatory system simulating physiological blood pressure and flow. The heart valves opened and closed correctly under the conditions examined, the press release said.
The PCL material was then developed and evaluated by adding iron oxide nanoparticles, which allowed the researchers to visualize the scaffolds via magnetic resonance imaging. The modified material remained printable and biocompatible. Being able to monitor scaffolds after implantation could make it easier to move research into clinical settings.
The researchers’ ultimate goal is to design bio-inspired heart valves that promote the formation of new functional tissues in patients. This would especially benefit children, as current artificial heart valves do not grow with the patient and need to be replaced over time. “Our heart valves, on the other hand, mimic the complexity of native heart valves and are designed to let a patient’s own cells seep into the scaffold,” Mela said.
Preclinical studies in animal models are forthcoming. Researchers are also focusing on improving technology and developing new biomaterials.