Biomedical Engineering Reference
In-Depth Information
A successful outcome when decellularized biologic grafts are used in tissue
repair depends not only on adequate overlap of the mesh and the adjacent
tissues. It also depends on close and frequent tissue approximation. Tacks or
sutures spaced at as little as 2 mm intervals adequately secure decellularized
biologics into place and allow the patient's adjacent cells to invade the graft. If
relative motion between the implant and the surrounding tissues is not
minimized, the patient's cells will never populate the graft and it will become
walled off or dissolved, leaving a nidus or dead space that can serve as a pocket
for fluid accumulation or bacterial colonization.
Because decellularized biologics consist of ECM proteins, they are highly
susceptible to enzymatic breakdown by the body's own remodeling
mechanisms or by bacteria that may be present. Clearly, a risk of using
naturally derived, decellularized graft materials is their inherent susceptibility to
colonization by bacteria. Collagen is an excellent growth substrate for
microorganisms, and so any successful use of a biologic mesh should take
into consideration the effect that contamination may have on the implant. For
example, Helton et al. (2005) report that repair of the ventral abdominal wall
with porcine small intestinal submucosa is more successful and less prone to
complications in clean cases than in contaminated ones. Likewise, it is likely
that many of the early failures observed following placement of a collagen plug
in abscessed anal fistulas are due to contamination of the fistula tract with a
collagenase-producing, gram-negative bacterium. Preventing breakdown due to
colonization by bacteria is critical to the graft's success and can be achieved
only if the patient's adjacent cells bring in a new blood supply. Close and tight
approximation of the graft with the surrounding tissues ensures that
repopulation of the graft will occur and that the risk of premature degradation
due to bacterial colonization or liberation of matrix metalloproteases can be
minimized.
The most common areas for biologic graft use include ventral hernia repairs
in contaminated or potentially contaminated fields where synthetic grafts are
often contra-indicated. A recent systematic review of the literature for hernia
repair using biologic grafts found, somewhat surprisingly, that the published
experience with biologic grafts was much greater for clean cases than for
contaminated ones, and it verified that SIS can be used for a long-term repair
extending beyond 7 years (Hiles et al., 2009). Widespread use for ECMs also
has arisen in the treatment of chronic wounds, chronic fistulas, plastic surgery,
and dura mater repair; but everyday inguinal hernias, pelvic organ prolapse
repairs, and many other applications have yet to see much ECM use because of
concerns over cost and lack clinical evidence. Nonetheless, in many instances
where repeat surgeries for recurrent hernia, late infections or erosions from
synthetic incompatibilities, or long-term pain from chronic neuritis can be
avoided, ECM-based biologic grafts are growing in popularity and proving that
in many instances they can save costs in the long term.
