The Use of Acellular Dermal Matrix to Prevent Capsular Formation Around Implants in a Primate Model
Amy Stump, MD1, Luther H. Holton, III, MD1, Jerome Connor, PhD2, John R. Harper, PhD2, Sheri Slezak, MD1, Ronald P. Silverman, MD1.
1University of Maryland Medical Center, Baltimore, MD, USA, 2LifeCell Corporation, Branchburg, NJ, USA.
Background: Implant-based breast reconstruction is a popular option after mastectomy, but capsular contracture may detract from long-term outcomes. We have observed that when breasts are reconstructed with the use of acellular dermal matrix (AlloDerm, LifeCell Corp. Branchburg, NJ), a capsule does not typically form in the area where the implant is in direct contact with the acellular matrix. We decided to test this observation experimentally by comparing capsular formation around implants in the presence and absence of AlloDerm in a primate model.
Methods: Eight smooth-surfaced tissue expanders were implanted into 8 African green monkeys (Chlorocebus aethiops). A subcutaneous pocket was created on the animal's back so that the implant could be placed directly above the fascia of the back musculature. In four experimental animals, a sheet of AlloDerm was draped over the tissue expander and sutured to the muscle so as to cover the implant. Four control animals underwent placement of a tissue expander only. Animals were euthanized after 10 weeks, and specimens were removed and subject to histological and immunohistochemical analysis.
Results: H&E and Masson's trichrome staining of control specimens revealed the presence of a distinct layer of wavy, parallel arrays of collagen fibers consistent with the typical appearance of a capsule. Immunostaining for alpha-smooth muscle actin identified abundant myofibroblasts, a pro-fibrotic cell found in breast capsules. In the experimental (AlloDerm-covered) specimens, no capsule layer was visible. Instead, we saw a layer of collagen bundles in the omnidirectional, dermal layer-like appearance of AlloDerm. Experimental specimens stained weakly for myofibroblasts. The difference in myofibroblast staining intensity was statistically significant.
Conclusions: Chlorocebus aethiops is an effective model for studying capsule formation. The use of AlloDerm to partially enclose implants prevented the formation of a capsule in areas where AlloDerm contacted the implant. We postulate that by sequestering the implant beneath a layer of acellular tissue which does not induce chronic inflammation, we are able to prevent the foreign body response, thus preventing the formation of a dense, fibrous capsule. Long-term studies will be required to determine whether this is a durable result that can be reproduced in humans.
Images: H&E stain of control (upper image) and experimental (AlloDerm-covered) specimens (lower image) at 20x. A capsule is visible in the control specimen. AlloDerm is visible in the experimental specimen, but no capsule layer has formed above or below it.