# Dual-Channel Extrusion-Based 3D Printing of a Gradient Hydroxyapatite Hydrogel Scaffold with Spatial Curved Architecture

## TL;DR

Researchers developed a 3D-printed cartilage scaffold with a graded HA composition and curved structure, mimicking natural cartilage for tissue engineering.

## Contribution

A dual-channel extrusion method enables precise fabrication of curved, compositionally graded cartilage scaffolds.

## Key findings

- The scaffold achieved a continuous HA gradient from bottom to top, mimicking native cartilage composition.
- The printed scaffolds showed improved compressive performance and stable swelling and degradation behavior.
- In vitro tests confirmed good cytocompatibility and biosafety for cartilage tissue engineering.

## Abstract

A biomimetic cartilage scaffold featuring a continuous hydroxyapatite (HA) concentration gradient and a spatially curved architecture was developed using a dual-channel mixing extrusion-based 3D printing approach. By dynamically regulating the feeding rates of two bioinks during printing, a continuous HA gradient decreasing from the bottom to the top of the scaffold was precisely achieved, mimicking the compositional transition from the calcified to the non-calcified cartilage region in native articular cartilage. The integration of gradient material deposition with synchronized multi-axis motion enabled accurate fabrication of curved geometries with high structural fidelity. The printed scaffolds exhibited stable swelling and degradation behavior and showed improved compressive performance compared with step-gradient counterparts. Rheological analysis confirmed that the bioinks possessed suitable shear-thinning and recovery properties, ensuring printability and shape stability during extrusion. In vitro evaluations demonstrated good cytocompatibility, supporting bone marrow mesenchymal stem cell (BMSC) adhesion and proliferation. Chondrogenic assessment based on scaffold extracts indicated that the incorporation of HA and its gradient distribution did not inhibit cartilage-related extracellular matrix synthesis, confirming the biosafety of the composite hydrogel system. Overall, this study presents a controllable and versatile fabrication strategy for constructing curved, compositionally graded cartilage scaffolds, providing a promising platform for the development of biomimetic cartilage tissue engineering constructs.