P. Mainilvarlet et al., LONG-TERM SOFT-TISSUE REACTION TO VARIOUS POLYLACTIDES AND THEIR IN-VIVO DEGRADATION, Journal of materials science. Materials in medicine, 7(12), 1996, pp. 713-721
Cylindrical pins made from poly(L-lactide), poly(L/D-lactide) 95/5% an
d poly(L/DL-lactide) 95/5% were implanted in the subcutaneous tissue o
f sheep. The tissue reaction to the implanted materials and their in v
ivo degradation was investigated at 1, 3, 6 and 12 months. The capsule
formed around the polylactide implants consisted of fibroblasts, fibr
ocytes, phagocytes, a few foreign body giant cells and polymorphonucle
ar cells. For all three polylactides used, the cellular response was m
ost intensive during the first 6 months of implantation and significan
tly subsided at 1 year. The thickness of the capsule was 200 mu m at 1
month, increased to 200-600 mu m at 6 months, and decreased to 100 to
200 mu m at 1 year, depending on the material used. The tissue reacti
on was more intense for poly(L/D-lactide) than for poly(L/DL-lactide)
and poly(L-lactide). The drop in molecular weight of the implants was
highest after 1 month of implantation (70 to 95%). Irrespective of the
extensive reduction of the molecular weight at 1 month, none of the p
olymers used was completely resorbed at 1 year. The most advanced reso
rption was observed for poly(L/D-lactide). Despite molecular weight re
duction, the poly(L-lactide) implants had maintained 70% of their init
ial bending strength and 95% of their shear strength at 3 months. The
poly(L/D-lactide) and poly(L/DL-lactide) had maintained only 26 to 27%
of their initial bending strength and 26 to 31% of the initial shear
strength, respectively. The crystallinity of all the materials increas
ed after implantation as compared with nonimplanted materials. The ove
rall crystallinity increase and the final crystallinity reached by the
materials at 1 year was, however, lowest for poly(L/DL-lactide) as co
mpared with the other two polylactides.