# The Effects of Ovine-Derived Reinforced Tissue Matrix Surrounding Silicone-Based Implants in a Rat Prepectoral Reconstruction Model

## TL;DR

This study explores how a tissue matrix affects silicone implants in rats, aiming to reduce complications like capsular contracture.

## Contribution

A novel rat model using 3D-printed silicone implants and ovine-derived matrix to study foreign body responses is introduced.

## Key findings

- RTM-covered implants showed reduced contractile fibroblasts and macrophages compared to controls.
- Implants were well-tolerated for 12 weeks with no difference in capsule thickness.
- Findings suggest RTM may improve capsule quality by affecting fibrosis-related cells.

## Abstract

Silicone-based implants have been widely used in breast reconstruction but have also been associated with poorly understood complications, including pathologic foreign body responses such as capsular contracture. In this study, we leveraged 3D-printing technology to generate silicone-based implants in a novel, anatomically relevant, prepectoral rat model. We used this model to evaluate the response to an extracellular matrix-based product: ovine-derived reinforced tissue matrix (RTM). Two-piece negative molds were developed through computer-aided design and 3D-printed. The molds were filled with various polydimethylsiloxane mixtures and dip-coated to fabricate implants. Implant material characterization revealed that the implants retained the original 3D-printed mold shape and qualitatively demonstrated a shell with an inner solid gel-like structure. Fabricated implants had smooth surfaces, as well as tunable features including implant stiffness (storage modulus). From initial studies in our rat model, placement of bilateral prepectoral implants allowed assessment of both muscle- and skin-facing capsules and were well-tolerated for at least 12 weeks. Comparison of the foreign body response between RTM-covered and uncovered (control) implants in this model revealed that the capsule thickness did not differ between groups at the 12-week endpoint. However, RTM reduced contractile fibroblasts (alpha-smooth muscle actin) and macrophages (Iba1) compared to the control. Our findings suggested that RTM may improve capsule quality by attenuating cells involved in fibrosis, even when total capsule thickness remains unchanged. However, these changes to cells involved in fibrosis were only observed at this early endpoint and may not predict long-term clinical outcomes.