Programmable acoustofluidic engineering for creating gradient biomaterials.

Gradient biomaterials that exhibit spatially varying physical, chemical, or biological properties can be used in various applications such as tissue engineering, organoid development, mechanobiology, and spatially controlled drug delivery. However, current fabrication methods often suffer from limited gradient precision, restricted material compatibility, and poor reproducibility. Here, we introduced gradient regulation via acoustofluidic dynamic engineering (GRADE), a programmable system to generate high-fidelity gradient biomaterials across different material systems. By incorporating focused interdigital transducers with the pulsed surface acoustic wave actuation, GRADE can achieve tunable and directional acoustic streaming (0 to 22 millimeters per second), which allows accurate regulation of the gradient magnitude and length. Its open microchannel design enables nondestructive extraction of centimeter-scale gradients and supports device reuse, enhancing practicality and scalability. In contrast to magnetic or electrospinning techniques that are limited to specific material types, the GRADE approach supports composition-independent fluid manipulation of a diverse group of biomaterials and cross-linking methods, thus providing greater versatility and translational potential. Furthermore, we demonstrate stiffness-dependent mechanosensation in stem cells cultured on customized gradient substrates, which validates the platform's usability. The experimental results show that GRADE has the ability to uncover mechanobiological responses in physiologically relevant contexts. All these results establish GRADE as a powerful and versatile platform for gradient biomaterial fabrication. It shows broad potential to advance both fundamental research and translational biomedical applications.