Quantitative Characterization of Liquid Photosensitive Bioink Properties for Continuous Digital Light Processing Based Printing

This study uses temperature and material composition to control the yield stress properties of yield stress fluids. The solid-like state of the ink can protect the printing structure, and the liquid-like state can continuously fill the printing position, realizing the digital light processing 3D printing of extremely soft bioinks.

My research mainly involves DLP 3D bio printing and tissue engineering. We tried to optimize and improve the DLP printing process and formula theory, so that the printed tissue engineering scaffold can better meet the actual clinic application needs. The printing conditions of the existing light-curable materials rely on manual experiments, and are obtained by feeding the data of multiple performing experiments.

Such experiments waste material and reduce printing efficiency. I constructed a theoretical working curve and determined the DLP printing pyramids of the material only based on the physical properties of the material. A dynamic fluid bath concept is proposed to be applied in DLP printing to realize DLP format of complex three-dimensional structures of extremely soft materials.

This method can improve the efficiency of determining the printing conditions of photocurable materials. This technology can provide technical support for the research and development of photocurable materials and the accurate printing of these materials. Begin by measuring the threshold time of the bio ink using a rheometer with a temperature control element.

Utilize a 365 nanometer light source to expose the testing platform of the rheometer, and set the light intensity to a certain value. In the rheometer software, go to the time settings option and set the rheometer to acquire the time moduli data for 300 data points, with each data point taken every 0.3 seconds. Click the Start Test button on the rheometer software to begin the test.

Simultaneously, click the Start button of the light source. To calculate the threshold time, record the corresponding time counting from the start of exposure when the storage modulus data is equal to the lost modulus data. Then build the absorbance test equipment by using upper and lower glass slides and the ring-shaped printed structure.

Clamp the ring between the glass slides so that the inner circle of the ring forms the chamber. Place the chamber on the test area of the light intensity meter, and set the light source to expose the chamber area. When the test chamber is not filled with material from the absorbance test equipment, measure the incident light intensity II by reading the display of the light intensity meter.

Next, fill the test chamber with 10 microliters of bio ink. Expose the test chamber containing bio ink to ultraviolet light at 365 nanometers. Obtain the light intensity IIH by reading the display.

When the value no longer changes on the light intensity meter, read the display to obtain the light intensity when the bio ink is cured. The value is the solid absorbance ISH. To achieve digital light processing or DLP printing, start by using a DLP software.

In the parameter settings, set the exposure time of the first single layer to the threshold time. Calculate the exposure time of curing 10 micrometer thick materials according to this equation, and subtract the threshold time to obtain the real exposure time for curing a single layer. In the software's parameter settings, set the time interval between adjacent layers to zero seconds.

Start the printer by clicking the Start button in the printing software. When the printing process ends, finish printing by clicking the Stop button. This protocol demonstrates that the continuous DLP printing method can accurately calculate the theoretical working curves of different materials.

A high degree of coincidence was observed between theoretical predictions and real printing results for three distinct materials. Compared to the traditional DLP printing method, this method showed improvement in printing efficiency, with decreasing printing layer thickness. Furthermore, a tenfold increase in curing efficiency was observed compared to traditional DLP printing, showing that the continuous DLP printing method can simultaneously achieve high efficiency and high fidelity.