New 3D Printing Technology Makes “Heart Bandage” Possible

Despite the rapid advancement of 3D printing technology, the field of biomedical engineering often faces challenges with strength and toughness when printing certain materials. Two universities in the United States have now introduced a new method that not only addresses these issues but also expands the application of 3D printing in the biomedical field.

3D printers work by depositing layers of plastic, metal, or even living cells to create objects in three dimensions. Some scientists have used special materials like hydrogels (similar to those in contact lenses) to print artificial tissues, organs, and implants. However, transitioning these materials from the lab to medical use has proven difficult.

The primary issue lies in conventional Digital Light Processing (DLP) 3D printing technology, which utilizes light exposure to quickly solidify liquid hydrogels. This method often leads to premature termination or incomplete reactions of polymer chains, affecting the overall strength and toughness of the materials.

To overcome these challenges, researchers at the University of Colorado Boulder (CU) and the University of Pennsylvania developed a technique known as “Continuously Localized Reconstruction and Yield” (CLEAR) technology. This innovation enhances the toughness, plasticity, and adhesion of printed products.

Their findings were published on August 2nd in the journal “Science,” garnering coverage from 24 news outlets and over 5,300 downloads.

The CLEAR technology involves incorporating a special oxidation-reduction initiator into the hydrogel material (acrylamide) used in 3D printing. This allows the material to continue polymerizing after light exposure, forming additional polyacrylamide polymer chains that intertwine to create a highly tangled network structure.

Furthermore, the entire curing process of the hydrogel with CLEAR is continuous and can be conducted at room temperature without the need for additional steps involving light or heat.

In their experiments, the researchers compared the 3D printing of polyacrylamide materials using traditional DLP methods with the CLEAR approach. The results showed that the hydrogels printed using the CLEAR method exhibited superior toughness and compressive strength compared to those printed using the DLP method. This is due to the significantly higher degree of intermolecular chain entanglement in the CLEAR-printed hydrogels.

Additionally, CLEAR-printed hydrogels demonstrated lower dissolution rates when exposed to water compared to DLP-printed hydrogels. They were also less prone to deformation and expansion, thanks to the crowded molecular structure resulting from chain entanglement, effectively reducing water infiltration.

The research team intentionally printed porous geometric shapes using the CLEAR method, creating products with both hardness and flexibility. For instance, printing supramaterial lattice structures like octahedral trusses and spring-like patterns allows these hydrogels to withstand significant compressive or tensile forces and revert to their original state when the external force is removed.

By pouring the hydrogel into waved molds and allowing slow cooling, multiple wave-shaped hydrogels could merge to form a polymer network with high toughness and mechanical performance.

After characterizing the basic properties of the CLEAR hydrogel, the researchers tested its adhesion on pig hearts, wet pig lungs, and stomachs. The hydrogels adhered firmly to these organs, demonstrating high interfacial toughness and strength. Even after washing with phosphate-buffered saline (simulating gastro fluids), the hydrogels did not detach.

This indicates that the CLEAR hydrogel can not only be rapidly shaped but can also adapt to curved organs. It can securely adhere to moist organs and withstand changes in organ size without detachment or rupture.

Moreover, the hydrogel can withstand compressive loads of up to 43 kPa, making it suitable for printing joint components in different body positions of patients, potentially paving the way for a new generation of biomaterials.

The researchers believe that the advantages of the CLEAR hydrogel could make it a valuable tool in repairing heart defects by serving as heart bandages for patients. It could also aid doctors in delivering tissue regeneration drugs directly to patients’ organs or cartilage, reducing the need for cartilage patches and sutures.

Professor Jason Burdick from the University of Colorado Boulder’s BioFrontiers Institute stated, “Since the self-repair capabilities of heart and cartilage tissues are very limited, once damaged, they are challenging to restore to their previous state. With our newly developed materials, we can enhance the repair processes of these organs, which will have a profound impact on patients.”

Matt Davidson, a researcher at the Burdick Lab at the University of Pennsylvania and one of the first authors, commented, “The mechanically robust adhesive material we can now print with this method is strong enough to support tissues, which was something we couldn’t achieve before.”

Abhishek Dhand, another researcher at the same lab, added, “This is a simple 3D processing method that can be used in academic labs and industry to enhance the mechanical properties of materials for various applications. It addresses significant issues in 3D printing.”

The team has applied for a provisional patent and plans to conduct further research to better understand how human tissues respond to such materials. They emphasize that this new method has implications beyond the medical field, as it eliminates the need for additional energy for curing or hardening parts.