BIOACTIVE IMPLANT COATING
Participants: Patil, P.V., Freiberg, A., Levy, R., Goldstein,
S.A.
Keywords: gene therapy, biomaterials, bone
Introduction
In wounds such as fractures or connective tissue tears,
medical devices or implants have substantially improved our
ability to affect therapy. Despite these advances, the interface
between the tissues and the implants has been inconsistent or
time limited. A need exists to enhance the tissue interface by
improving implant stability.
As recombinant proteins are becoming more popular as
osteoinductive treatments new concerns are raised. Relatively
large dose of such proteins are needed which raises the concerns
of expense and toxicity. Gene therapy may be a more efficient
means of delivery for such osteoinductive molecules. The purpose
of this study is to test a polymer based gene delivery system in
which intramedullary nails are coated with biologic factors to
alter the response of the interfacial tissue.
Materials and Methods
| In order to evaluate the
possibility of transferring a therapeutic gene from a
polymer coating into local cells, a reporter gene was
employed. In this model we have chosen to use plasmid DNA
that encodes for green fluorescent protein (GFP). GFP has
been used in many different applications as a reporter
gene due to ease of imaging. Fourteen adult male
Sprague-Dawley rats have been utilized for this study.
Four of these animals were used to establish histologic
protocols. The remaining ten animals were used to
statistically detect presence of the reporter gene. These
animals were chosen because of bone repair and remodeling
characteristics. A 1 cm incision was made lateral to the
patella and dissection continued until the patella was
dislocated medially and the condyles could be visualized.
A pilot hole was then surgically drilled in the femoral
notch between the femoral condyles. A sterile 0.045 mm
Kirschner wire coated by an emulsion dipping process with
plasmid DNA incorporated with PGLA copolymer or control
(coating done) was inserted retrograde up the femoral
canal and lodged in the trabecular bone of the femur. A
custom instrument was used to countersink the pin below
cortical bone so as to not interfere with knee flexion.
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Progress
All animals have been entered into the study. Based on the
initial four rats, we will be using immunoperoxidase staining for
GFP in frozen sections (pin removed) fixed in 4%
paraformaldehyde. Further GFP detection methods that will be
included are the following: broad-band UV fluorescence, confocal
microscopy, western blots, and/or RT-PCR. While the preliminary
findings look very promising, technical difficulties with
visualizing the GFP flourescence above background have slowed the
progress. The imaging evaluation is continuing.