Biomedical Engineering Reference
In-Depth Information
triggers long-term inflammatory response. To circumvent this,
scientists have attempted to develop biomaterials which will slowly
degrade over time, ideally at the same pace as the ligamentization
occurs. Hence, several artificial ligaments utilizing well-known
biodegradable materials have emerged as potential candidates for
ACL reconstruction. This is the case for the artificial ligament
developed by Laurencin's group, which was fabricated by twisting
and braiding various aliphatic polyester fibers (known to degrade via
hydrolysis and enzymatic degradation) such as polyglycolic acid
(PGA), poly-glycolic-co-lactic acid (PLGA) and poly-L-lactic acid
(PLLA) into a dense and robust structure (Figure 7.1(b)) [FRE 07,
LAU 05, LU 05]. These structures would initially present enough
mechanical strength in order to supply the normal function of the
ligament. Particular attention was paid to the degradation rate of these
structures, which was an essential component of the fabrication
strategy. To this end Lu
et al
. systematically tested PGA, PLGA, and
PLLA braided scaffold and demonstrated that, despite initial adequate
mechanical properties the PGA scaffold was degrading at a very high
rate even inducing in vitro toxicity due to the excessive release of
acidic degradation by-products [LU 05]. As the PLLA could maintain
high mechanical properties for a long period of time, the authors
claimed it was the most suitable biodegradable polymer for ACL
replacement. This was consistent with the literature as PLLA has
already been utilized for long-term biomedical application such as
fixation screws or pins. However, PLLA has also been associated with
late inflammatory response due to an enrichment in highly crystalline
micro-particles with an extremely slow degradation rate [BER 95].
Another strategy involving the utilization of a very slow
degradable material, that is, silk, has been implemented by Kaplan's
group which were amongst the pioneers to utilize silk in biomedical
applications [ALT 02]. In this approach, silk fibers extracted from
Bombyx mori
are assembled in a parallel manner and thereafter
twisted into a bundle (Figure 7.1(c)). The same procedure is repeated
with 6 bundles in order to create a strand and 3 strands are arranged in
parallel fashion to form a cord and finally 6 parallel cords are
necessary for creating the artificial ligament matrix. This multiscale
organization strongly resembles the architecture and organization of
