# Regeneration of Biomechanically Functional Tendon Tissue Following Injection of Uncultured, Autologous, Adipose-Derived Regenerative Cells into Partial Achilles Tendon Defects in Rabbits

## TL;DR

Injecting unmodified fat-derived cells into rabbit tendon injuries promotes tissue regeneration and improves biomechanical properties compared to untreated injuries.

## Contribution

This study demonstrates that uncultured, autologous adipose-derived regenerative cells can regenerate functional tendon tissue in a rabbit model.

## Key findings

- UA-ADRC-treated tendons showed new connective tissue formation, indicating regeneration rather than scarring.
- Biomechanical testing revealed higher viscoelasticity in UA-ADRC-treated tendons compared to controls.
- The results suggest UA-ADRC therapy could be a viable treatment for partial tendon tears.

## Abstract

Current treatment strategies for partial tendon tears often lack the capacity to promote true tissue regeneration and improve long-term clinical outcomes. This study tested the hypothesis that treatment of a partial defect in the rabbit common calcaneus tendon (CCT) with uncultured, unmodified, autologous, adipose-derived regenerative cells (UA-ADRCs) enables regenerative healing without scar formation. A full-thickness, 3 mm defect was produced in the midsubstance of the right gastrocnemius tendon, a component of the CCT, in adult female New Zealand white rabbits. Animals received either an injection of 28.3 × 106 UA-ADRCs in 0.5 mL Ringer’s lactated solution (RLS) or saline, or RLS or saline alone as sham treatment. Tendons were analyzed 4 or 12 weeks post-treatment using histology, immunohistochemistry and non-destructive biomechanical testing. UA-ADRC-treated tendons showed newly formed connective tissue consistent with tendon regeneration, whereas sham-treated tendons developed scar tissue. Biomechanical testing showed significantly higher percent relaxation in UA-ADRC-treated tendons compared to sham controls (p < 0.05), indicating greater viscoelasticity characteristic of healthy or well-integrated tissue. Together, these findings suggest that UA-ADRC therapy may provide a regenerative, structure-modifying treatment for partial tendon tears.