Biomedical Engineering Reference
In-Depth Information
structures have distinct cellular and matrix properties so that individualized
methods are necessary to achieve antigenic neutrality and preserve matrix struc-
ture. However, once the tissues are prepared, further processing can yield unique
formulations and constructs. As an example, the sheet AlloDerm RTM prepared
from allograft dermis can be micronized in a cryofracture process that produces
particles of intact matrix with an average diameter of 123 µm, allowing for delivery
by injection (Sclafani
et al.
, 2002). The same particulate matrix, marketed as
Cymetra, can be mixed with allograft demineralized bone to create an easily
moldable and injectable putty that retains the cellular ingrowth and osteoinductive
properties of the materials which it comprises. Thus, the resulting putty, marketed
as AlloCraft DBM, is suitable for the repair of irregular bone defects which have
no load-bearing requirement (Qiu
et al
., 2007).
The intact matrix scaffold strategy can also be applied to tissues sourced from
non-human species. Owing to its similarities to human skin (Lavker
et al
., 1991;
Wollina
et al.
, 1991) and wound healing properties (Rigal
et al
., 1992), much of
LifeCell's technology platform and early knowledge base pertaining to a matrix's
regenerative potential was developed using porcine skin (Livesey
et al
., 1995). As
the uses for products that support regeneration have grown, LifeCell has come full
circle with the introduction of the porcine-derived tissue reconstructive matrix
device, Strattice. The unique processing in the manufacture of Strattice yields an
intact ECM that extends the possible applications and markets for intact matrix
products. While Strattice represents the future of soft-tissue reconstruction de-
vices, the foundation of this technology was laid with AlloDerm, the characterization
and performance of which will be the focus for the remainder of this chapter.
10.2.3 Processing affects biological responses
Because the methods used to prepare a matrix scaffold from existing tissues have
a significant impact on the retention and integrity of matrix components, they
ultimately dictate the body's response to the implanted material. These responses
are likely to fall into one of three general categories (
Fig. 10.2
). Processing that
causes damage, such as protein denaturation, cleavage or extraction, tends to
induce an inflammatory response resulting in a reparative wound healing mecha-
nism characterized by resorption of the matrix, deposition of a provisional matrix,
and formation of scar. Cross-linking of matrix components, either intentionally to
prevent degradation caused by the presence of hidden antigenic epitopes or
unintentionally as the result of poor preservation or incompatible sterilization
modalities, can elicit a foreign body response resulting in matrix encapsulation. In
contrast to these undesirable outcomes, a properly prepared matrix that maintains
the bioinductive, mechanical, constitutional and functional properties of a native
intact ECM is likely to support the body's intrinsic regenerative potential. While
these responses are most notable in applications where the biomaterial is used as an
implant (Valentin
et al
., 2006), they are similar in consequence to those found for
