# Imaging‐Guided Microscale Photothermal Stereolithography Bioprinting

## TL;DR

A new bioprinting technique called ImPSB enables high-resolution printing in water using light-to-heat conversion, overcoming previous limitations in aqueous environments.

## Contribution

ImPSB introduces imaging-guided stereolithography, a unique near-infrared photothermal initiator, and a new bioink to achieve microscale bioprinting in aqueous conditions.

## Key findings

- ImPSB achieves a printing resolution of ≈47 µm and smooth lines with diameters as small as ≈104 µm.
- The technique demonstrates cellular biocompatibility for bioscaffold and cell-laden hydrogel printing.
- Feasibility of transdermal printing is shown, opening new applications in bioprinting.

## Abstract

Stereolithography bioprinting relies heavily on costly photoinitiators for polymerization, limiting its potential for further technical advancement to meet growing needs in tissue engineering and regenerative medicine. Thermal initiators, in contrast, are low cost, and rapid growth of the photothermal conversion field offers a wide range of materials and tools to convert light into heat. However, high‐resolution photothermal stereolithography bioprinting remains unattainable due to the difficulty of confining heat in an aqueous environment. Here, this challenge has been fully addressed by establishing imaging‐guided microscale photothermal stereolithography bioprinting (ImPSB). This technique is achieved through building a novel imaging‐guided stereolithography system that provides depth‐resolved visualization of the printing dynamics, creating a unique photothermal initiator in the second near‐infrared window, and developing a new bioink by seeing and controlling the photothermal gelation process. ImPSB achieves a printing resolution of ≈47 µm and generates smooth lines of arbitrarily designed shapes with a cross‐sectional diameter as small as ≈104 µm, representing an unprecedented scale from photothermal aqueous stereolithography. Its cellular biocompatibility in printing both bioscaffold and cell‐laden hydrogel is demonstrated, and its feasibility of transdermal printing is also shown. This work sets a new path for high‐resolution stereolithography bioprinting where the vast photothermal resources can be utilized.

This work establishes imaging‐guided microscale photothermal stereolithography bioprinting, achieving microscale photothermal aqueous printing for the first time. Key innovations include novel imaging‐guided stereolithography, unique NIR‐II photothermal initiator, and new bioink with viscosity modifier. This addresses the long‐standing challenge of confining heat in an aqueous environment during photothermal dynamics, opening the avenue for high‐resolution stereolithography bioprinting with the vast photothermal resources.