Positionally Stable Smooth Implants: An In Vivo Submuscular Model

Following the voluntary recall of certain textured implants due to recognized association with BIA-ALCL, plastic surgeons lost the major benefit of textured surfaces-positional stability. We have engineered a novel smooth-surface breast implant design featuring small millimeter-dimension cylindrical surface wells that promote tissue ingrowth and stabilize the implant. These Positionally Stable Smooth Implants (PSSI) previously demonstrated superior positional stability versus smooth implants (and comparable to textured) in a subcutaneous in vivo model. Here, we investigate PSSI in a submuscular model.

Hemispherical miniature breast implants were fabricated with polydimethylsiloxane. PSSI implants featured wells 2mm wide by 1mm deep with 26, 52, or 70 wells/implant. Miniature smooth and textured implants served as controls. Six implants per group were placed under bilateral latissimus dorsi muscles of female Sprague-Dawley rats. Implant position was evaluated at 2, 4, 8, and 12 weeks, then explanted.

Over 12 weeks, PSSI exhibited significantly less rotation than smooth implants (p<0.001) and comparable to that of textured implants. Textured and some PSSI capsules had significantly lower collagen density and smooth muscle actin expression compared to smooth implants (p<0.05). PSSI and smooth capsules had lower pro-inflammatory M1 macrophage expression and a lower M1/M2 macrophage ratio than textured capsules (p<0.01).

PSSI implants demonstrated significantly increased rotational stability and reduced collagen density and myofibroblast presence compared to smooth implants, as well as significantly decreased expression of pro-inflammatory macrophages compared to textured implants. These data suggest a promising alternative to texturing for providing positional stability of implants in the submuscular plane.