Nicholas John Cotton

Long-term in vivo Degradation of Poly-L-lactide (PLLA) in Bone

The use of absorbable orthopedic implants has increased substantially during the last decade. Currently, most of them are fabricated from poly-L-lactide (PLLA), its co-polymers, or mixtures with other constituents. In vivo, PLLA persists for years after its surgical role has ended, which is confirmed by a long-term histological study of PLLA implanted in sheep either as functional interference screws or nonfunctional rods. The first tissue reaction is the sequestration of the implant within new bone during the initial 3 months. After a nonreactive period, a second tissue reaction is associated with the early signs of structural disintegration of the PLLA at 1 year. Subsequently, as the polymer mass reduces, it is replaced by a relatively avascular fibrous tissue containing macrophages and having an occasional multinucleated giant cell on the implant surface. After 3 years much of the polymer is still present, although as isolated fragments. The tissue reactions can be explained in terms of the physical chemistry of PLLA degradation. Though biocompatible, the excessive longevity of PLLA and the absence of its replacement by bone, indicates that despite being satisfactory clinically, it is not an ideal implant material, and that improved absorbable materials need to be developed.

FlaCeramic-loaded mineralizing bioresorbable polymers for orthopaedic applications

Bioresorbable polymers are widely used in biomedical applications, for example in surgical sutures and orthopaedic screws. One class of these materials is broadly based on poly(lactide)-poly(glycolide) copolymers, whose proportions govern the rate of physiological resorption. One difficulty encountered in implantation of resorbable polymers into bone is local acidification as the polymer breaks down and the body mounts an inflammatory response. Another is that resorbable polymers are usually neither bioactive nor osteoconductive. This presentation explores a novel bioresorbable polymer-inorganic particulate composite implant that both buffers local acidity and promotes osteoconductive replacement of the implant by bone over a one-year time span.