Author: Zhang Bin, Gao Lei, Xue Qian, Cui Zhanfeng, Ma Liang, YANG Hua-yong
Source: Zhejiang University News
In 2019, Kelly et al. Were inspired by computer tomography (CT) and reported a “volume additive manufacturing” technology based on computational axial lithography and applied for related patents. This technology solidifies the material in a specific target area by accumulating light, thereby printing out a pre-designed three-dimensional component. This technology significantly improves the ability of digital light processing (DLP) technology.
In 2016, Wu Xiang also proposed a lithography technology based on a similar algorithm in the patent (application number PCT / CN2016 / 080097). Although this method can achieve very high resolution in theory, it is similar to the traditional DLP method, and it still has the following three problems.
“Science” revolutionary high-speed “volume 3D printing technology” was questioned by the Chinese to copy their own patents
(1) This technology is only compatible with photosensitive materials, so its ability to manufacture components containing multiple materials or microstructures is limited. For example, the material in the target area is suspended in the liquid during the curing process. High viscosity or solid precursor materials are then added to reduce the blur caused by displacement and geometric misalignment. This may cause the precursor material to remain in the finished component.
(2) The effect of the attenuation of oxygen content and the diffusion of oxygen or inhibitory molecules on the accuracy of the technology is for further study. The author proposes an oxygen suppression method to delay the curing time. By fully dissolving oxygen or other inhibitory molecules in the printed material, the free radicals generated by the photoinitiator preferentially react with the inhibitor to ensure that sufficient light intensity accumulates in the target area to cure the material. However, during the printing process, the effect of the nonlinear attenuation of the liquid oxygen content at the target position on the material response needs further study. The author believes that the reaction between the photoinitiator and oxygen consumes the most time in the process of “calculating axial lithography”. In the final stage of the reaction, the oxygen content at the target location is below the threshold and the material solidifies quickly. In this liquid-solid conversion process, the diffusion of oxygen or other inhibitory molecules will require in-depth research to further improve manufacturing accuracy.
(3) The scattering and superposition of light will affect the manufacturing accuracy. The bandwidth of incident light is limited by the added dye, and the blur caused by light refraction is reduced by the amount of normal incidence. However, due to the physical characteristics of the container wall and the existence of the liquid-solid interface, the incident light must refract, reflect and attenuate to a certain extent. Since the depth of focus of the projection system is much greater than the diameter of the printed component, the change in optical path is ignored. When molecules are polymerized, the liquid-solid interface will also cause changes in the optical path, resulting in energy loss and imaging errors. Therefore, taking these factors into consideration may further improve printing accuracy.
Although computational axial lithography is controversial, through improved algorithms and in-depth analysis of light, this technology will likely achieve technological breakthroughs, especially in the fields of biological 3D printing and regenerative medicine. The author has long been studying 3D printing of corneal, skin and heart patches, aiming to develop transplantable tissue substitutes for the treatment of diseases and injuries such as corneal blindness, skin burns and myocardial infarction. As one of the founders of “Bio-Design and Manufacturing” magazine, we track the development of various cutting-edge biomanufacturing technologies. We believe that CAL has many advantages over traditional additive manufacturing technologies.
First, the technology has natural advantages in manufacturing tissues or organs in liquid materials. Currently, at least 15 types of tissues or organs can be performed using viscous liquid materials (bone, cartilage, cornea, nerves, muscles, blood vessels, lymphoid tissues, endocrine glands, uterus, ovaries, cervical tissues, lungs, airways, liver, kidneys) 3D printing [5, 6], 3 of them (corneal, liver, blood vessels) have adopted DLP technology [7–9]. Secondly, CAL can realize the construction of smooth surfaces, and has the potential to manufacture most tissues and organs. For example, a transparent cornea with a smooth surface can be manufactured and transplanted to animals, even human patients. Finally, the manufacturing speed of CAL is at the forefront of all 3D printing technologies, which can significantly accelerate the process from experiment to clinic.
The volume-based additive manufacturing technology based on CAL has become an important advancement in the field of additive manufacturing due to its unprecedented manufacturing speed and resolution. If the technology can be more adapted to the actual needs of biomedical applications, the technology will provide a transformative tool for tissue engineering and regenerative medicine.
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