Holographic Feedback Controlled Micro-Stereolithography for Constructing Microstructures with Tuned Mechanical Property

The fabrication of biocompatible scaffolds mimicking the stiffness of real human tissues holds paramount significance in the fields of tissue engineering and cell biology. However, existing stereolithography technologies still face challenges in precise control of the mechanical stiffness distribution of biological microstructures due to the difficulty in real-time monitoring of their mechanical properties during printing. In this study, we propose an innovative projection-based micro-stereolithography control method based on real-time holographic phase feedback to achieve high-precision fabrication of microstructures with region-specific mechanical stiffness distributions. Employing the minimum mean square error method, we calculate the optimal single mapping transformation matrix from holograph to DMD (digital micromirror device) mask for the corresponding calibration. The real-time holographic phase serves as feedback data to correct and modify the dynamic DMD mask. Additionally, adjusting the sampling interval and threshold parameters in feedback control enhances precision. Through this method, we constructed a complex mechanical property distribution of a windmill-shaped hydrogel microstructure. Experimental results demonstrate that our control method reduces the error in mechanical stiffness from 19.2 kPa in the case of no feedback control to 3.68 kPa, representing an 80.8% improvement in accuracy. The novel approach for constructing complex mechanical property distributions of microstructures in vitro has significant potential in tissue engineering in the future.