Chitosan-based hyaluronan hybrid polymer fibre scaffold for ligament and tendon tissue engineering.

T Majima, T Irie, N Sawaguchi, T Funakoshi, N Iwasaki, K Harada, A Minami, S-I Nishimura

In the event of a tendon injury, the preferred method of treatment is an autograft. But this requires additional surgery and healing at the donor site. The authors of my selected paper have been working on a method to grow tendon tissue on a three-dimensional scaffold. The scaffold acts as a temporary template for the cells and provides the biomechanical characteristics that they would be exposed to in vivo. The difficulty is in finding a biomaterial that possesses those characteristics. Collagen can cause immunogenic reactions and polyglycolic acid does not possess the proper mechanical properties, making them poor candidates. It was known to the authors that glycoaminoglycans, specifically their main component hyaluronan (HA), improved tissue healing. Chitosan was also an excellent biomaterial for tissue repair. The authors decided to create hybrid polymer-fibers using the two and a hyaluronan-like material, alginate. They developed a chitosan-based hyaluronan hybrid and an alginate-based chitosan hybrid. The polymer-fibers were made using wetspinning using the base material and adding either 0, .05 percent, or 0.1 percent of the other material. The selected control was polyglactin, a material used for wound closure.

The authors tested various properties of the polymer-fibers in-vitro. A tensile strength test showed that adding HA to chitosan fibers increased tensile strength while adding chitosan to alginate did not. A cell adhesion test showed that adding HA to chitosan fibers and adding chitosan to alginate fibers decreased cell adhesion, with the addition of HA to chitosan fibers causing a more significant difference. From these tests, the authors decided to continue their study using chitosan-based 0.1 percent HA material. The fibers were incubated for 0, 2 hours, 14 days, or 28 days and tested for tensile strength again and it was discovered that tensile strength drops before 2 hours but is maintained between 2 hours and 28 days. In a test of cell proliferation, fibroblasts were loaded into scaffolds and it was found that chitosan-based 0.1 percent HA material had significantly greater amounts of DNA content that 0.05 percent or 0 percent. After 14 days, they were observed producing ECM.
The authors then began testing the chitosan-based 0.1 percent HA hybrid polymer-fibers in-vivo. First, they tested biodegradability by implanting the scaffolds into rats and measuring failure load at 0, 2, 4, 6, 12, and 16 weeks. After two weeks, maximum failure load had significantly dropped but gradually increased afterwards. To test the feasibility of repairing tendons with the scaffold, defects in a rabbit's rotator cuff tendon model were created and covered with a fibroblast-seeded scaffold. After 4 and 12 weeks, the engineered tendons were tested. In the fibroblast-seeded scaffolds, collagen I was detected and tensile strength was increased compared to a non-cell-seeded scaffold. To test the feasibility of repairing ligaments with the scaffold, the medial collateral ligament was injured, removed, and reconstructed using the engineered scaffold. After 12 weeks, the engineered ligaments were tested. Two of the engineered ligaments actually did not break in the ligament but where it was bound to bone. The other three engineered ligaments and all ligaments repaired with scar tissue broke in the ligament. This means that the engineered ligaments are an improvement over normal healing with scar tissue.

I chose this paper because ligament injuries, especially of the knee, are a fairly common sports injury and an injury that can result from normal wear-and-tear as life expectancy increases. In addition, ligament injuries are relatively difficult to heal because of the low number of active cells present in a ligament with most of it consisting of ECM but also because ligaments are constantly in tension which prevent the damaged ends of a torn ligament from ever meeting. The current treatment of autograft can be extremely painful because of the secondary surgery to remove ligament from the donor site, which also increases the healing time. If ligament tissue could be successfully grown on a scaffold, such treatments would not be needed anymore thus improving the recovery process and increasing quality of life for those who suffer from ligament injuries.