Biomedical Engineering Reference
In-Depth Information
implant will not stay static, but indeed can grow with the patient. This is the case
as reported by several investigators using SIS implants in children (Smith and
Campbell, 2006; Murphy and Corbally, 2007; Hayn et al., 2009; Karpelowsky et
al., 2009). A living graft can also be defended from bacterial invaders and avoid
early- and late-term infections often seen in permanent synthetic implants
(Badylak et al., 1994; Butler et al., 2005; Shell et al., 2005).
6.3
Harvest from nature or build from scratch
Bringing an ECM biomaterial into widespread clinical use clearly requires a
source for sufficient quantities of raw material. ECMs traditionally have been
harvested from an animal or human source, but the idea of creating a useful
ECM from the `ground up' is very attractive. If this could be done, then the
exact composition, microstructure, macrostructure, and even release kinetics for
drugs and the like could be precisely specified.
6.3.1
ECM sources similarities and differences
ECM for clinical use has been harvested from a wide variety of sources. These
include dermis, pericardium, fascia lata, dura mater, intestinal submucosa, bone,
ligament, heart valve, blood vessel, and many others that have only been tested
in preclinical studies. Aside from the tissue location of ECM harvest, such
materials can originate from autograft (self), allograft (different individual of the
same species), or xenograft (different species) sources ± all of which have been
used widely in clinical medicine. Xenograft materials that have been used
clinically have been harvested from pigs, sheep, cows, and even horses.
ECMs that have proven most successful in clinical medicine have a few
important characteristics in common. First, they have a readily available and
economically accessible source for tissue acquisition and processing. Also, in
the case of soft-tissue repairs, they have relative mechanical strength that allows
them to be sutured in place and readily able to resist the stresses encountered in
load-bearing sites. In the case of bone, they have the ability to be placed in a
bony defect and stimulate a functional repair of osseous tissue. They are all
biocompatible, meaning that they will pass a standard battery of biological tests,
and can be processed aseptically, terminally sterilized, or both. Finally, success-
ful decellularized ECMs do not stimulate immune rejection, sensitization, or
promotion of neoplastic cell growth. In fact, some studies even show that some
ECMs can alter neoplastic cell phenotypes and even reduce neoplastic growth in
vivo (Hurst et al., 2003; Hodde et al., 2004).
Although each combination of tissue and source species can result in a
harvestable ECM, they are by no means equivalent in their structure, composi-
tion, availability, or utility (Table 6.1). Of course, each harvested ECM inherits
many of the characteristics that describe the original
tissue. Thus, ECM
