# Spectroscopic and Rheological Characterization of Polyvinyl Alcohol/Hyaluronic Acid-Based Systems: Effect of Polymer Ratio and Riboflavin on Hydrogel Properties

## TL;DR

This paper studies how mixing ratios of PVA and HA, along with riboflavin and UV light, affect hydrogel properties like swelling and self-repair.

## Contribution

The novel contribution is the systematic analysis of PVA/HA hydrogel properties influenced by polymer ratios, crosslinking agents, and riboflavin under UV-A.

## Key findings

- Hydrogels with PVA/HA ratios above 1/1 form successfully with crosslinking agents.
- The PVA/HA 4/1 ratio shows the highest water uptake and potential self-repair behavior.
- Riboflavin and UV-A induce reactive oxygen species without significantly altering hydrogel mechanics.

## Abstract

We report a systematic investigation on the physicochemical properties of polymer systems consisting of polyvinyl alcohol (PVA) and hyaluronic acid (HA) mixed in various volume ratios (1/4, 2/3, 1/1, 3/2, and 4/1). At PVA/HA ratios above 1/1, in the presence of glutaraldehyde and divinyl sulfone as crosslinking agents, hydrogels are formed. Their swelling behavior is dependent on the polymer ratio, with the highest water uptake determined for PVA/HA 4/1. The in situ generation of reactive oxygen species (HO• radicals) under UV-A irradiation, in the presence of riboflavin as a photoinitiator, is evidenced by electron paramagnetic resonance (EPR) spectroscopy. The diffusion of small paramagnetic molecules across the interface of two PVA/HA 4/1 gel pieces placed in direct contact reveals the occurrence of molecular exchange, which could indicate some degree of self-repair of the hydrogel network. When the paramagnetic moiety is attached to the HA polymer by spin labeling, the absence of diffusion demonstrates the stability of the crosslinked HA chains within the PVA/HA network. The structural modifications induced by crosslinking, by the presence of riboflavin, and by exposure to UV-A light, and the resulting alterations in the mechanical behavior of the hydrogels are monitored by infrared spectroscopy and rheology. Only a slight decrease in the viscoelastic moduli values is noted, indicating that the formation of HO• radicals has minimal impact on the macroscopic properties of the hydrogels.