3D nanoprinting of embryo microinjection needles with anti-clogging features.

Wide-ranging biomedical applications spanning both research and clinical settings rely on microinjection protocols that involve using a long, hollow microneedle to deliver foreign substances directly into biological targets, such as embryos. Unfortunately, conventional microneedles are prone to clogging-e.g., cytoplasmic material from an embryo becoming lodged inside the needle tip during penetration, thereby obstructing delivery-motivating researchers to use top-down microfabrication techniques to modify needle tips and reduce such failure modes. Recent advancements for the submicron-scale additive manufacturing approach, "Two-Photon Direct Laser Writing (DLW)", offer a new, bottom-up pathway for re-architecting microneedle tips to address clogging susceptibility via geometric means. Here, we investigate this potential by 3D printing monolithic 650-µm-tall, 15-µm-diameter hollow microneedles comprising architectural features designed to remediate clogging phenomena: (i) a solid, fine-point tip, (ii) multiple side ports (i.e., perpendicular to the insertion direction), and (iii) an internal microfilter. Serial microinjection experiments with live zebrafish embryos reveal that the 3D microneedles yield enhanced delivery performance without any instances of complete blockages that are pervasive among both standard glass and 3D-printed control microneedles. These findings suggest that DLW-based 3D printing holds distinctive promise for high-precision microinjection applications, particularly in scenarios involving extensive serial injections or critical payloads and targets.