Release date: 2016-09-07
At the first Regenovo Bio 3D Printing Academic Forum, Professor Xu Shanhui, Director of Tissue Engineering and 3D Printing Center of Taiwan University, shared some of his team's research results on 3D bioprinting of waterborne polymer materials.
There are many 3D technologies in the industry, but not all can be applied to biomedicine. Therefore, in addition to using some hard tissue materials in biomedicine, it is some laser technology. The most common organic materials are SLAFDM and LFDM. The simplest method is extrusion molding. The general 3D printing materials can be roughly divided into two categories: inorganic materials and organic materials. Today I mainly focus on the organic materials.
The emergence of low temperature processing waterborne materials
The advantage of organic materials is that there are many processing methods. Currently, the most widely used in the industry is polylactic acid (PLA) and acrylonitrile-butadiene styrene (ABS). The difference is that ABS cannot be decomposed.
Polymer 3D printing material is the most popular ABS, his processing performance is very good, but his problem is that its general processing method is high temperature, there will be taste when printing, this taste is related to his volatility, so in recent years Less popular than PLA. If processed at high temperatures, both PLA and PCL will be hydrolyzed, so the printed matter is different from the raw materials, which limits the application in the medical field. Therefore, we decided to use PLA without high temperature to do PLA and PCL in 2001. Printing, because the degree of hydrolysis of the raw materials is different after printing. So we changed to a solvent method and processed it at low temperatures.
The advantage of the polymer is that in addition to melt processing, it can also be processed with a solvent. The solvent can be used at low temperatures, but most of the solvent is toxic. The solvent for PLA and PCL usually has 1,4-dioxane. Dichloromethane, chloroform. Water-based printing materials are environmentally friendly, not only environmentally friendly, but also safe for the human body. Do not worry about the safety of residual solvents when the bioprinting support has high porosity.
Among the commonly used water-based printing materials, natural polymers are chitosan, gelatin, etc. Chitosan is formed by liquid cryoprecipitation, but its properties are brittle. Gelatin is formed by photocuring. The advantage of curing with light is that it is easy to form. However, there will be free radicals. If the cells are printed, different cells eat different degrees of free radicals. Therefore, after the system is changed, the cells need to be adjusted, and the survival rate of the cells is affected by free radicals. Synthetic polymers are PEG and pluronic, which have the advantage of flexible modification, but they are not biodegradable and can only be dissolved, so they can be dissolved only in small molecules and then excreted.
Improvement plan
1. 3D printing technology of water-based biodegradable organic elastomer
We introduce PCL or PLA, a decomposable polyester, into the R end of PU polymer, and then self-emulsifying it through some small molecule synthesis techniques. Here we introduce a negatively charged substance, which can be made into a negatively charged nanometer. The elastomer can then be physically formed using a water-based, low-temperature system. This is our printing system, which can print quickly at temperatures as low as -20~-30°C.
Then why can we do this? The reason is that there are a lot of PU nano-elastomers in the printed matter. Each nano-elastomer has about 200-300 polymer chains. The molecular weight of each chain is 100,000, so the overall molecular weight is 10 million. So it is equivalent to a nano-rubber, although it is nano-scale, but still has the mechanical properties of the elastomer. One advantage of such a substance is that it is rendered water-insoluble after processing, and can print target materials of various sizes, all of which are aqueous printing materials, but are insoluble in water. Printed cartilage, its compressibility value, various mechanical values, dynamic mechanical values ​​are similar to natural cartilage.
The next question is whether cells can stay inside. From the results we obtained, cells can grow better in PU than PLGA because the surface of PLGA is a hydrophobic group, and our PU is an aqueous system, and cells are easier to grow. So overall, its biocompatibility is good, and the bigger benefit is that we can print growth factors, FTF or other drugs with cells at the same time, and then release them in the body over time.
Some people say that Y27632 does not cartilize when the cells are cultured in a plane, but it will be in three dimensions. So we used a printed matter containing Y27632 to examine changes in the release over time. The advantage of adding Y27632 to replace TGFβ is that since TGFβ is also a growth factor required during hard bone development, the release of TGFβ will progress to hard ossification, but it is not possible if Y27632 is used. The result we saw was that stem cells reached an effective concentration after three days, which meant that they could aggregate and then cartilize.
Gene expression also shows that after the cells are planted in the biological scaffolds we print, there will be the best cartilage, and the same level of protein expression.
2. Bio-printing materials for aqueous biodegradable hydrogels
One of the biggest drawbacks of the water-based materials we make is that when we want to print the cells together with the tissue, the cells are less resistant to freezing. Some teams tried to keep cells active with low temperature plus DMSO, but it was not very successful. We hope to use temperature or light curing to compromise or modify our materials, hoping to make it a hydrogel printing material.
There are many people who have talked about different techniques in the literature, but most of the materials are still not able to meet the requirements of printing when they are printed, and they are not deformed after printing.
We have previously changed the ratio of some R-ends to the same PU material and found that these nano-elastomers became gel, and the condition of this gel is irreversible and can contain cells. The advantage of the aqueous solution of PU is that it can directly adjust the solid content therein to change the overall chemical structure and thus the hardness. So we can see that rheology is definitely a very important parameter in the development of bio-printing technology, and our materials can change the rheological properties.
What problems need to be solved in the future development of bio-printing?
I think that in the future, multi-cell and multi-materials will of course be equipped with multi-nozzle design, which will make printing develop.
Another very important thing is the formation of vascular networks. Cartilage has no blood vessels, so it is good to do, but many tissues have blood vessels. This is also a direction for the future. If you want to print organs, especially large tissues such as kidneys and livers, the formation of vascular networks is a very important bottleneck.
There is still a lot of room for improvement in 3D bioprinting. I believe that organic polymer materials can contribute. The main reason is that it can be deformed when deformation is realized, and it can remain unchanged after printing. Protect cells to make them alive.
summary
1. The new organic polymer printing material ink is still in development, and it is hoped that the whole world will emerge in this field;
2, printing equipment, whether it is high temperature control or light cross-linking platform, in the design of the new ink materials can be matched with each other;
3, I hope to find a balance point in bio-ink rheology, so that bio-ink can print tissue and cells well one day.
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