Effects of orthopedic implants with a polycaprolactone polymer coating containing bone morphogenetic protein-2 on osseointegration in bones of sheep.
OBJECTIVE
To determine elution characteristics of bone morphogenetic protein (BMP)-2 from a polycaprolactone coating applied to orthopedic implants and determine effects of this coating on osseointegration.


METHODS
6 sheep.


METHODS
An in vitro study was conducted to determine BMP-2 elution from polycaprolactone-coated implants. An in vivo study was conducted to determine the effects on osseointegration when the polycaprolactone with BMP-2 coating was applied to bone screws. Osseointegration was assessed via radiography, measurement of peak removal torque and bone mineral density, and histomorphometric analysis. Physiologic response was assessed by measuring serum bone-specific alkaline phosphatase activity and uptake of bone markers.


RESULTS
Mean +/- SD elution on day 1 of the in vitro study was 263 +/- 152 pg/d, which then maintained a plateau at 59.8 +/- 29.1 pg/d. Mean peak removal torque for screws coated with polycalprolactone and BMP-2 (0.91 +/- 0.65 dN x m) and screws coated with polycaprolactone alone (0.97 +/- 1.30 dN.m) did not differ significantly from that for the control screws (2.34 +/- 1.62 dN x m). Mean bone mineral densities were 0.535 +/- 0.060 g/cm(2), 0.596 +/- 0.093 g/cm(2), and 0.524 +/- 0.142 g/cm(2) for the polycaprolactone-BMP-2-coated, polycaprolactone-coated, and control screws, respectively, and did not differ significantly among groups. Histologically, bone was in closer apposition to the implant with the control screws than with either of the coated screws.


CONCLUSIONS
BMP-2 within the polycaprolactone coating did not stimulate osteogenesis. The polycaprolactone coating appeared to cause a barrier effect that prevented formation of new bone. A longer period or use of another carrier polymer may result in increased osseointegration.
Niehaus
Andrew J
AJ
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210, USA. niehaus.25@osu.edu
Anderson
David E
DE
Samii
Valerie F
VF
Weisbrode
Steven E
SE
Johnson
Jed K
JK
Noon
Mike S
MS
Tomasko
David L
DL
Lannutti
John J
JJ
D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology*; D001863:Bone Screws / Q000662:veterinary*; D020099:Coated Materials, Biocompatible / Q000378:metabolism; D005260:Female; D008297:Male; D016348:Osseointegration / Q000187:drug effects*; D011091:Polyesters / Q000494:pharmacology*; D012756:Sheep / Q000378:metabolism*; D013997:Time Factors
D055396:Bone Morphogenetic Protein 2; D020099:Coated Materials, Biocompatible; D011091:Polyesters; C016240:polycaprolactone