Scanning electron microscopy study including maceration techniques of an absorbable alloplastic implant designed for the reconstruction of ventral abdominal wall defects.

The interposition of synthetic material represents the most generally acknowledged method for achieving a tension-free surgical repair of major abdominal wall defects. As permanent materials are frequently associated with severe complications (rejection, peritonitis, enterocutaneous fistula, erosive invasion into the intestine), a newly designed absorbable prosthetic (polydioxanone, PDS) has been developed. The ellipsoid implant is composed of a knitted envelope and a filling of loosely arranged filaments. Interpositioning of the implant into an artificial circular abdominal wall defect was carried out on 30 Wistar rats. Explantation was performed 21 days post implantationem (p.i.), 42 days p.i. and 180 days p.i. The aim of the study was to evaluate the use of scanning electron microscopy (SEM) combined with maceration techniques (2 N NaOH for 1, 3 and 5 days) for a spatial assessment of the interactions between the implanted material and the ingrowing tissue components. Application of 2 N NaOH caused the complete dissolution of the PDS-material and a concomitant gradual disappearance of cellular and amorphous tissue components, thereby unmasking the remaining collageneous network. SEM of non-macerated specimens demonstrated that 21 days p.i. the entire implant has been filled with connective tissue components. Additionally, the ventral and dorsal surfaces of the implant were covered by a collageneous layer (neo-fascia). 21 days p.i. the PDS-filaments had developed minor clefts, which increased in number and depth 42 days p.i., and were transformed into small remnants 180 days p.i. Alkali treatment revealed the three-dimensional arrangement of collagen fibers, which ensheathed the PDS-filaments and formed interconnecting networks between them. At the ventral portion of the implant the fibrous network was more elaborate and densely distributed. 180 days p.i. the implant has been transformed into a membranous structure (neo-membrane) composed of the ventral and dorsal neofascia, remnants of PDS-filaments and a continuous connective tissue layer containing wave-like collagenous structures. Whereas 21 and 42 days p.i. no herniation was observed, 130 days p.i. the implant began to bulge out of the ventral abdominal wall. It is therefore concluded that inspite of the advantages of absorbable materials, longer resorption times may be required to allow a sufficient consolidation of the ingrowing connective tissue to resist the tensile forces of the abdominal muscle coat. SEM combined with 2N NaOH maceration proved to be a usefull tool in addition to conventional histological techniques for a three-dimensional assessment of fibrous connective tissue components ingrowing into alloplastic implants.