The design of the synthetic scaffold enables the gradual dissolution of the synthetic material and promotes optimal ligament cell growth for formation of a neoligament, explains Laurencin. Using a process that he refers to as 3-D polymeric fiber braiding, the team of researchers fabricated a 3-D scaffold by braiding the fibers of the PLLA polymer. This method enables cells to efficiently maneuver around the synthetic material and produce collagen fibers and fresh blood vessels much faster than current methods do. Braiding the ligament also gives the structure strength.
To evaluate the newly bioengineered ligaments, Laurencin’s team conducted a study, published in the February 27 issue of Proceedings of the National Academy of Sciences, using rabbit subjects. The study tested two types of the scaffold: one seeded with cells from the rabbits’ ACLs and one consisting of only the synthetic material. The team surgically replaced each rabbit’s torn ACL with one of the two kinds of scaffolds, using the same surgical procedure that would be used on humans. Each scaffold was designed to be slightly smaller than the original rabbit ACL to permit tissue regeneration to take place: tissue growth in the intra-articular, or joint, portion and cell growth in the portion of the scaffold attached to the bone.
The study was performed using 32 rabbits examined at 4 and 12 weeks–the beginning and end of the crucial period of healing. The results for the seeded scaffold were deemed remarkable by Laurencin, who says that within 48 hours of surgery the rabbits were walking around normally. The study reported collagen and cellular infiltration in the implant at 4 weeks, and at 12 weeks the cells at the edge of the scaffold had generated collagen fibers for the formation of a new ligament. In addition to demonstrating faster, short-term recovery time, the neoligament showed sufficient mechanical strength.
“This is the first tissue-engineered matrix for ACL to demonstrate such substantial neoligament formation, in terms of both vascularity and collagen formation,” says Laurencin. “This provides hope for being able to regenerate the ACL in humans and will hopefully pave the way for new treatment paradigms of patients.”
Although Laurencin’s preliminary findings are promising, a few of the rabbits in the seeded group, and almost all of the rabbits in the unseeded group, suffered ruptured ligaments, possibly because rabbits, unlike humans, do not adhere to a physical-therapy schedule, nor are they used to protecting their ligaments. Laurencin plans on continuing to monitor the rabbits and will perform a follow-up study with larger animals and, eventually, humans.
For athletes like Palmer, the system could be the difference between having a great career and a mediocre one.