Page 354 - Biodegradable Polyesters

332 13 Biodegradable Polyester-Based Blends and Composites

are developed for the production of plates and screws [1, 78]. As the bone healing
progresses, it is advantageous that the bone is subjected to a steady increase in
stress, thus reducing the stress-shielding effect. This is achievable only if the plate
loses inflexibility in the human body. To meet this requirement, researchers have
developed degradable polymer-based composites for bone plate applications
[7, 78, 79]. One of the merits often quoted for degradable composite prosthetic
implants is that they do not need to be removed with an operational procedure,
as needed with metallic or nondegradable composite implants. To upgrade the
mechanical properties, PLA is often reinforced with natural and synthetic fibers.
Carbon fiber/PLA composites show good mechanical properties prior to their
implantation, but they often lose their properties rapidly in the implant because
of delamination [1]. In the biomedical field, the medial collateral ligament of
adult male beagle dogs was chosen for replacement [39] as a demonstrator of
carbon fiber/PLA composite usage for prosthesis. In the medical equipment or
instrumentation areas, PLA was reinforced with PGA to manufacture two conical
co-rotating screws [40]. However, the long-term effects of degradable composite
materials and biostable (or slowly eroding) fibers in the host tissues have not been
fully explored yet, and some remaining concerns still need to be addressed [78].
Polyester-based blended biodegradable composites have engrossed significant
interest for applications in medical devices, and will play a significant role in the
design and functions of medical devices. The common criteria for polymer materi-
als used in medical applications comprise mechanical properties and degradation
time suitable to the medical purpose. In addition, the materials should not evoke
toxic or invulnerable responses, and they should be degraded in the body after
satisfying their tasks. To address this requirement, a range of synthesized ecologi-
cal polyesters have been designed and used. Some biodegradable polyester-based
composites that have been used or shown potential in particular fields are briefly
described in the following.
In the 1960s, PGA self-reinforced composites were used to prepare completely
biodegradable sutures [80]. Since then, PLA, PCL, and poly[D,L-(lactide-co-
glycolide)] have been extensively used for medical devices [81]. Many commercial
orthopedic fixation devices, such as rods and pins for bone fracture fixation and
plates and screws for maxillofacial repair are made of PLA, poly(glycolide), and
other biodegradable polyester-based composites [82]. Many orthopedic fixation
devices are available in the market. Composites made of PLA and PGA are used
in cartilage tissue engineering [80, 83]. Research on devices for load-bearing bone
repair and implantable medical devices is thus quite active.
In the twenty-first century, environment factors were considered by manu-
facturing industries. Many disposable medical devices, such as injection pipes,
syringes, surgical gloves, pads, are regularly made of nondegradable plastics,
resulting in serious environmental problems. The composites made of PLA/PU,
PLA/PHB, PLA/PBS, and self-reinforced PLA, PGA, and PCL are all biodegrad-
able [68, 84, 85]. Consequently, they are promising materials for use in disposable
medical devices fulfilling environmental friendly needs. These biodegradable