# Copper-ion releasing LDH nanosheets-hydrogel synergistically enhance subchondral bone repair

## TL;DR

A new nanocomposite hydrogel with copper-ion releasing properties is developed to improve subchondral bone repair and regeneration.

## Contribution

The study introduces CuAl-LDH nanosheets integrated into a hydrogel for enhanced mechanical and osteogenic properties.

## Key findings

- The nanocomposite hydrogel showed improved compressive modulus and rapid gelation suitable for implantation.
- Gel-CAL reduced reactive oxygen species and upregulated osteogenic markers in stem cells.
- In rat models, Gel-CAL significantly increased new bone volume compared to the control hydrogel.

## Abstract

Bone defects represent a significant clinical challenge, frequently resulting in nonunion and impaired function. Although autologous bone grafts are considered the gold standard owing to their excellent biocompatibility, their application is constrained by limited donor availability, thereby driving the need for alternative biomaterials. In this study, we report the synthesis of copper-aluminum layered double hydroxide (CuAl-LDH) nanosheets as a bioactive platform for bone regeneration. The nanosheets were systematically characterized using transmission electron microscopy, energy-dispersive spectroscopy and dynamic light scattering, confirming uniform morphology, precise elemental composition and colloidal stability. To enable localized therapeutic delivery, CuAl-LDH nanosheets were incorporated into gelatin methacryloyl (GelMA) hydrogels to form a nanocomposite hydrogel (Gel-CAL). Mechanical testing demonstrated that tuning the CuAl-LDH concentration (0.01–0.1 wt%) significantly enhanced the compressive modulus of the hydrogel, while rheological analysis revealed rapid light-induced gelation kinetics, making it suitable for minimally invasive, in situ implantation. The nanocomposite exhibited sustained release of Cu2+ ions over 40 days and displayed strong antibacterial activity against Escherichia coli. In vitro studies using rat bone marrow mesenchymal stem cells showed that Gel-CAL effectively reduced intracellular reactive oxygen species levels and upregulated key osteogenic markers, including alkaline phosphatase. In a rat subchondral bone defect model, micro-computed tomography and histological analyses at 5 weeks post-implantation revealed that Gel-CAL induced a significantly higher new bone volume fraction compared to GelMA alone. These results demonstrate that CuAl-LDH nanosheets serve as a multifunctional biomaterial that integrates mechanical reinforcement, antibacterial properties and osteogenic stimulation, offering a promising strategy for bone regeneration.

Graphical Abstract