# Biodistribution and Biodegradation of an Osteoinductive Supramolecular Polymer Implant in a Rat Spinal Fusion Model

## TL;DR

A new biodegradable implant for spinal fusion was tested in rats, showing it breaks down safely with minimal side effects.

## Contribution

The study demonstrates the biodegradation and tissue clearance of a supramolecular polymer implant in a rat spinal fusion model.

## Key findings

- Gadolinium concentration at the fusion site decreased from 71% to 19.5% over 13 weeks.
- Peak Gd accumulation in the liver was 3% at 4 weeks, declining to 1.4% by 13 weeks.
- MRI showed complete loss of Gd signal enhancement by 8 weeks, indicating implant degradation.

## Abstract

Recombinant human bone morphogenic protein-2 (rhBMP-2) use in spinal fusion is limited by dose-dependent complications. Peptide amphiphile (PA) supramolecular polymers presenting a BMP-2–binding epitope have previously been developed to reduce the rhBMP-2 dose required for successful fusion. We evaluated PA implant biodegradation and tissue clearance in a rat posterolateral spinal fusion model as a prerequisite to clinical safety studies. Twenty-three female Sprague–Dawley rats underwent L4–L5 fusion with gadolinium (Gd)-labeled PA implants. Longitudinal magnetic resonance imaging (MRI) was performed up to 13 weeks postoperatively, while the spine and filter organs were harvested for inductively coupled plasma mass spectrometry (ICP-MS) quantification of Gd at multiple time points. Gd concentration at the fusion site decreased from 71% of maximum to 19.5% at 13 weeks, and MRI showed a complete loss of Gd signal enhancement by 8 weeks. In peripheral organs, peak Gd accumulation was 3% in the liver at 4 weeks, declining to 1.4% at 13 weeks, while Gd remained below 0.05% in the spleen, lung, and blood at all time points. These data indicate PA implant localization, with robust degradation and clearance and minimal off-target accumulation, supporting its translational potential for spinal fusion applications.