# Solid Microneedles from Poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate): A Solvent-Free, Biodegradable Platform for Drug Delivery

## TL;DR

This study introduces a biodegradable, solvent-free method to create solid microneedles for drug delivery using a new biopolyester material.

## Contribution

A novel biodegradable thermoplastic is proposed for solvent-free fabrication of solid microneedles with good mechanical and drug delivery properties.

## Key findings

- PHBHVHHx microneedles had sharp, well-defined structures and withstood compressive forces up to 0.25 N/needle.
- The needles achieved insertion depths of 396 µm in a skin simulant and released 73% of the drug within 10 minutes.
- The material supports sustainable, solvent-free fabrication and coated drug delivery.

## Abstract

Background: Solid microneedles (MNs) are effective transdermal delivery devices but are commonly fabricated from metallic or non-biodegradable materials, raising concerns related to sustainability, waste management, and processing constraints. This study aimed to evaluate the suitability of the biodegradable biopolyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (PHBHVHHx) as a structuring material for solvent-free fabrication of solid MN arrays and to assess their mechanical performance, insertion capability, and drug delivery potential. Methods: PHBHVHHx MN arrays were fabricated by solvent-free micromolding at 200 °C. The resulting MNs were morphologically characterized by scanning electron microscopy. Mechanical properties were assessed by axial compression testing, and insertion performance was evaluated using a multilayer Parafilm skin simulant model. Diclofenac sodium was used as a model drug and applied via surface coating using a FucoPol-based formulation. In vitro drug release was assessed in phosphate-buffered saline under sink conditions and quantified by UV–Vis spectroscopy. Results: PHBHVHHx MN arrays consisted of sharp, well-defined conical needles (681 ± 45 µm length; 330 µm base diameter) with micro-textured surfaces. The MNs withstood compressive forces up to 0.25 ± 0.03 N/needle and achieved insertion depths of approximately 396 µm in the Parafilm model. Drug-coated MNs retained adequate mechanical integrity and exhibited a rapid release profile, with approximately 73% of diclofenac sodium released within 10 min. Conclusions: The results demonstrate that PHBHVHHx is a suitable biodegradable thermoplastic for the fabrication of solid MN arrays via a solvent-free process. PHBHVHHx MNs combine adequate mechanical performance, reliable insertion capability, and compatibility with coated drug delivery, supporting their potential as sustainable alternatives to conventional solid MN systems.