Bioabsorbable orthopedic fixation devices are conceptually more attractive
than metallic devices in repairing damaged tissues or in fastening implants.
Our study focuses on investigating bioabsorbable composites for potential use
as materials for orthopedic appliances. The study focuses on Poly(l-lactic acid)
(PLLA), Polyglycolic acid (PGA), Poly-e-caprolactone (PCL), matrices with
Carbon fibers (AS4), Nylon fibers and PLLA fibers. Fiber coating effects have
also been investigated, with compliant polymers (1%, 50% and 100% of matrix
properties) and with hydroxyapatite (HA). Unidirectional, continuous fiber
plies, and multi-directional, random and quasi-random short-fiber
composites were considered in our study.
NDSANDS a concentric cylinder model computer software, was used to
evaluate the stiffness and strength of the bioabsorbable composites with unidirectional
fiber orientation. To achieve a better physical understanding, the
NDSANDS predictions were also compared with those given by a simple,
mechanics of materials approach. The theory for multidirectional short fiber
composites, recently developed by Giurgiutiu and Reifsnider was employed with three fiber-orientation distribution functions and three failure
mechanisms.
Stiffness and strength of bioabsorbable composites were predicted over a range
of fiber volume fraction. It was found that AS4/PLLA with 16% fiber volume
fraction can have properties close to the bone when used in short fiber
composite. Similar results are obtained using AS4/PLLA with hydroxyapatite
coating. PLLA/PGA and PLLA/PLLA also demonstrated properties close to
those of the bone in the range of 25% and 64%.
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