Bipolymer Microthreads Regenerate Human Tissue

American researchers are developing a system that uses micro threads to regenerate human tissue and heal wounds.

George Pins, associate professor of biomedical engineering at WPI in Massachusetts, got the idea of using micro threads as the basis for tissue engineering when he wanted to find a better way to repair torn anterior cruciate ligaments (ACLs) in the knee, according to WPI press release. Currently, to repair ACLs, surgeons must remove a section of healthy tendon from another party of the body and graft it into the damaged tissue to replace it. Because the method harms one part of the body to repair another, the surgery is not considered ideal.

“The ACL, like other ligaments and tendons, is a fibrous cable-like structure,” Pins says. “So the original idea was to use thin collagen threads, bundled into cables that mimic the natural structures in the body, as a scaffold for the tissue engineering that would be used to replace the ACL.”

Collagen, a structural protein, is the building block for skin and connective tissues, such as tendons, ligaments, muscle, and cartilage. Pins and his colleagues theorized that thin threads of collagen would be tolerated by the body. As their work progressed, they also began making micro threads from fibrin, the main protein in blood clots. Because the body produces blood clots immediately in response to an injury, Pins thought that fibrin threads could become useful as “scaffolds” to help heal wounds.

Early in the research, Pins and the lab team made each thread by hand, using a large syringe to push out a bead of collagen or fibrin, pull it into a solution, and lift it out by hand to dry suspended over the edges of a cardboard box. Pins challenged several of his undergraduate students to develop an automated system to make the threads in a consistent manner.

Paul Vasiliadis, a member of the team, took the production of the threads to the next level. As a graduate student, he became the lead developer, and now uses a computer-controlled system capable of continuous extrusion with a range of specified thread diameters and quantities.

WPI explains some of the ways that the method has been improved:

The Pins lab continues to develop the microthread technology for use as potential ligament and tendon scaffolds while also working to optimize the composition and mechanical properties of the threads. For example, they are experimenting with ways to control the tensile strength of the threads, and to control the rate at which the threads dissolve once implanted in the body. They have also developed new technologies to tailor the surface topographies and biochemistries of the microthreads to provide specific signaling cues that they predict will direct cell-mediated tissue responses.

The threads also are being used as biological sutures to deliver bone marrow-derived adult stem cells known as human mesenchymal stem cells (hMSCs) to cardiac tissue damaged by disease or trauma. The research team has found that when hMSCs are delivered to damaged hearts, they moderately improve cardiac function.

Another application for the fibrin-based micro threads is as a platform to restore muscle tissue that was damaged by traumatic injury. Here, the micro threads are seeded with new cells that could regenerate muscle tissue, and they serve as a muscle-like scaffold to promote the body’s own healing and regenerative processes.

“This is becoming a platform technology, growing in ways we hadn’t imagined when we first began this line of research,” Pins says. “It’s exciting to see the clinical potential for this technology accelerating.”