# Analysis of Interactions Between Pyomelanin and the Extracellular Matrix in an Ex Vivo Turkey Tendon Model

## TL;DR

This study examines how a melanin-like polymer interacts with tendon tissue in a turkey model to understand its impact on the extracellular matrix.

## Contribution

The study introduces a novel ex vivo model to investigate melanin–extracellular matrix interactions using multiple analytical techniques.

## Key findings

- PolyHGA deposition alters tendon collagen properties, similar to pathologies in alkaptonuria and calcific tendinitis.
- Combining spectroscopy and microscopy reveals subtle changes in ECM composition and melanin distribution.
- The turkey tendon model effectively mimics biological melanin deposition in connective tissues.

## Abstract

Melanins are conjugated biopolymers with varying compositions and functions, found in various tissues throughout the body. Here, the conjugated polymers derived from homogentisic acid (HGA), polyHGA (a simplified model of pyomelanin), formed in an ex vivo tendon model are examined with a view to understanding interactions between melanins and the extracellular matrix (ECM) using a selection of different analytical techniques, including spectroscopy (energy dispersive X‐ray, infrared, and Raman), X‐ray diffraction, and microscopy (electron, optical, and scanning electrochemical). The combination of techniques was used to facilitate an understanding of subtle differences in the composition and distribution of ECM components, hydroxyapatite, and melanin in the tendons for the first time. PolyHGA deposition in connective tissues in patients with alkaptonuria is a significant burden and causes multiple tendon ruptures due to the significant alterations in collagen properties. A similar pathology is seen in the wider population from calcific tendinitis because of hydroxyapatite crystal deposition in tendons of the shoulder and lower limbs, in particular.

Polymerization of homogentisic acid in the presence of extracellular matrix (ECM) components (an ex vivo turkey tendon model) yields simplified versions of biologically generated melanins in the ECM, facilitating studies of melanin–ECM interactions. A variety of techniques (X‐ray diffraction, microscopy, and spectroscopy) were employed to understand the potential influence of the ECM in the deposition of melanins in biological tissues.© 2025 WILEY‐VCH GmbH