Biomedical Engineering Reference
In-Depth Information
that patients can heal quickly and pain-free, returning to their normal
lives and, importantly for the economy, place of work, more quickly.
An artificial bone graft that can replace the need for grafts would have
a massive impact on the global economy. The device market itself is
thought to be worth $2 billion per year without taking into account the
economic impact of reduced operating costs and faster recovery times.
Many artificial bone grafts are designed to replace or augment the
bone and stay there for a long time rather than regenerate the bone
to its original state and function. Examples are porous titanium or
tantalum metal constructs. Metallic scaffolds have the advantage of high
strength and toughness. Toughness (resistance to crack propagation) is
important when the scaffold is to be exposed to cyclic loads, which are
commonplace in skeletal tissue. However, metals are usually bio-inert
and intrinsically not bioactive, so fibrous encapsulation may occur. The
metal will also stay in place long-term, meaning that naturally healthy
bone will never re-form. The body is likely eventually to reject the
implant, but time scales are variable.
12.3 DESIGN CRITERIA FOR AN IDEAL SYNTHETIC
BONE GRAFT
Surgeons ultimately want something that works and can be implanted
with ease. They would like to be able to take a packet off the shelf,
remove the implant, shape it, press or inject it into the defect, and watch
as it fills the space. They would like the implant to take load and share
load with the host bone, immediately. This is so the patient can load
their bones, keeping them healthy, but also so bed space is not occupied
for too long. Then, over time, they would like the scaffold to disappear
as the bone regrows.
An ideal synthetic bone graft would regenerate a bone defect and leave
no trace of an implant, and it must possess the following characteristics:
(a) be biocompatible and bioactive, promoting bone formation, and
bond to the bone without soft tissue encapsulation;
(b) act as a template for bone growth, with an interconnected porous
structure that allows cell migration and vascularisation;
(c) biodegrade safely in the body and have a controllable degrada-
tion rate;
(d) have mechanical properties similar to those of the host bone;
