The authors gratefully acknowledge the support provided by the National Natural Science Foundation of China (Grant Nos. 12125205, 12072316, 12132014), and the China Postdoctoral Science Foundation (Grant No. 2022M712754).

1. Theoretical preparation
<ol>
	<li>Define three parameters: liquid absorbance (Al), solid absorbance (As), and threshold time (tT)17.</li>
	<li>Rewrite the traditional Jacobs working curve using these three parameters17 according to Equation 1: 
	<img alt="Equation 1" src="/files/ftp_upload/65277/65277eq01.jpg" style="margin: auto;" />&#160; &#160; &#160;(Equation 1) 
	Here, tH is th...

Quantitative Characterization of Bioink Properties for Continuous DLP Printing

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The critical steps of this protocol are described in section 2. It is necessary to unify the light intensity used in the photorheology test and the printing light intensity in the actual tests. The absorbance testing equipment is the most important part. The shape of the test chamber should be the same as the photosensitive area of the light intensity meter. Due to the properties of the materials that continuously change during the whole UV light exposure process, the light intensity needs to continue to change<sup class...

Tissue engineering1 is important in the field of organ repair. Due to the lack of organ donation, some diseases, such as liver failure and kidney failure, cannot be cured well, and many patients do not receive timely treatment2. Organoids with the required function of the organs may solve the problem caused by the lack of organ donation. The construction of organoids depends on the progress and development of bioprinting technology3.
Compared with extrusion-type bioprinting4 and inkjet-type bioprinting5, the printing speed and printing accuracy of the digital light processing (DLP) bioprinting method are higher6,7. The printing module of the extrusion-type method is line-by-line, while the printing module of the inkjet-type method is dot-by-dot, which is less efficient than the layer-by-layer printing module of DLP bioprinting. The modulated ultraviolet (UV) light exposure to a whole layer of material to cure a layer in DLP bioprinting and the feature size of the image determines the accuracy of DLP printing. This makes DLP technology very efficient8,9,10. Due to overcuring of the UV light, the precise relationship between the curing time and the printing size is important for high-accuracy DLP bioprinting. Furthermore, continuous DLP printing is a modification of DLP printing method that can greatly improve the printing efficiency11,12,13. For continuous DLP printing, precise printing conditions are the most important factors.
The relationship between the curing time and the printing size is called the Jacobs working curve, which is widely used in DLP printing14,15,16. The traditional method to obtain the relationship is to expose the material for a certain time and measure the curing thickness to obtain a data point about the exposure time and curing thickness. Repeating this operation at least five times and fitting the data points obtains the Jacobs working curve. However, this method has obvious disadvantages; it needs to consume a lot of material to achieve the curing, the results are highly dependent on the printing conditions, the bioinks used in DLP bioprinting are expensive and rare, and the formability of the bioinks is usually not good, which can lead to inaccurate measurements of curing thickness.
This article provides a new method to obtain the curing relationship according to the physical properties of the bioink. Using this theory can optimize continuous DLP printing. This method can be used to obtain the curing relationship more quickly and accurately; the continuous DLP curing can therefore be better determined.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Brilliant Blue</td>
			<td>Aladdin (Shanghai, China).</td>
			<td>6104-59-2&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>DLP software</td>
			<td>Creation Workshop</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Lithium phenyl-2,4,6-trimethylbenzoylphosphinate</td>
			<td></td>
			<td>N/A</td>
			<td>LAP; synthesized</td>
		</tr>
		<tr>
			<td>Light source</td>
			<td>OmniCure</td>
			<td>https://www.excelitas.com/product-category/omnicure-s-series-lamp-spot-uv-curing-systems</td>
			<td>365 nm</td>
		</tr>
		<tr>
			<td>Polyethylene (glycol) diacrylate</td>
			<td>Sigma-Aldrich</td>
			<td>455008</td>
			<td>PEGDA Mw ~700</td>
		</tr>
		<tr>
			<td>Rheometer&#160;</td>
			<td>Anton Paar, Austria</td>
			<td>MCR302</td>
			<td></td>
		</tr>
	</tbody>
</table>

quantitative characterization of liquid photosensitive bioink properties for continuous digital light processing based printing

Precise printing fabrication of bioinks is a prerequisite for tissue engineering; the Jacobs working curve is the tool to determine the precise printing parameters of digital light processing (DLP). However, the acquisition of working curves wastes materials and requires high formability of materials, which are not suitable for biomaterials. In addition, the reduction of cell activity due to multiple exposures and the failure of structural formation due to repeated positioning are both unavoidable problems in conventional DLP bioprinting. This work introduces a new method of obtaining the working curve and the improvement process of continuous DLP printing technology based on such a working curve. This method of obtaining the working curve is based on the absorbance and photorheological properties of the biomaterials, which do not depend on the formability of the biomaterials. The continuous DLP printing process, obtained from improving the printing process by analyzing the working curve, increases the printing efficiency more than tenfold and greatly improves the activity and functionality of cells, which is beneficial to the development of tissue engineering.

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

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

My research mainly involves DLP 3D bio printing and tissue engineering. We try 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 reduced printing efficiency. I constructed a theoretical working curve and determined the DLP printing pyramids only based on the physical properties of the material. Dynamics both best concept is proposed to be applied in DLP printing to realize DLP format of complex dimensional structures of extremely soft materials.This method can improve the efficiency of determining the printing conditions of photo curable materials. This technology can provide technical support for the research and development of photo curable materials and the accurate printing of these materials.

This article shows a new method to obtain curing parameters and introduces a new way to achieve continuous DLP printing, demonstrating the efficiency of this method in determining the working curve.
We used three different materials in DLP printing to verify the accuracy of the theoretical working curve obtained by the method introduced in this article. The materials are 20% (v/v) polyethylene (glycol) diacrylate (PEGDA), 0.5% (w/v) lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) with d...

Watch this Scientific Journal Video about Quantitative Characterization of Liquid Photosensitive Bioink Properties for Continuous Digital Light Processing Based Printing at JoVE.com

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.

Precise printing fabrication of bioinks is a prerequisite for tissue engineering; the Jacobs working curve is the tool to determine the precise printing ...

quantitative-characterization-liquid-photosensitive-bioink-properties