Generating a Continuous Gradient Through Extrusion-Based 3D Bioprinting

Fabrication of a continuous gradient between two hydrogel materials

A major limitation in the field of 3D bioprinting to date has been the ability to create and utilize complex biomaterials. This also relates to the concentration or level of different materials and components across an area or tissue. These concentrations or gradients are important for recapitulating native gradients of signaling molecules as well as varying levels of matrix stiffness that occurs in tissues. A new fabrication methodology developed by the team at Advanced Solutions Life Sciences enables the incorporation of materials that can be mixed at the point of extrusion. Thereby providing a method for a new set of materials to be incorporated into 3D tissue structures by specifically fabricating 3D structures that contain a continuous gradient mixture between two materials.

The Process

A structure of interest is created using sketching tools within TSIM®. After a structure with the desired parameters are created, a gradient is generated using the “set material gradient” tool. The ratios and the length of the gradient can then be altered based upon the design requirements of the structure or the properties of the materials that are to be mixed. After a gradient is set, a priming process occurs on the mixing tool to ensure that the 3D structure fabricated contains the appropriate gradient that is designated in the digital design. This process illustrates the functionality within TSIM® that has been designed around the 3D Dual Syringe | Mix BioAssemblyTool™.

Creating a continuous gradient around a sketch in TSIM®

In this example workflow, a structure is created de novo using the “create a sketch” functionality within TSIM®. The number of dots within the line will serve as gradient starting points once the gradient is created, as indicated below in the left panel. After the sketch is complete, a tube is created around the line at the desired dimensions for this experiment as shown in the right panel below.

Figure 1 - Left: Starting points for the gradient. Right: The tube is created around the line at the desired dimensions.

Then, with the tube highlighted, the “set material gradient” is selected, and it is here that the percentage of the primary material across the gradient is designated, where the initiation of the gradient is each point along the sketch (pick a sketch point on TSIM®). In this example, a gradient of 100% primary material, to 0% primary material, back to 100% primary material will be fabricated. The gradient between the two materials is also visible in TSIM® as shown in the image below. After the parameters in the gradient are finalized, this information is sent to the BioAssemblyBot® to complete utilizing the 3D Dual Syringe | Mix BioAssemblyTool™.

Figure 2 - Creating the gradient in TSIM

Creating a gradient using the 3D Dual Syringe | Mix on the BioAssemblyBot

The workflow at the BioAssemblyBot® to create a continuous gradient starts with priming the 3D Dual Syringe | Mix, where the primary material (right hand side material) and the secondary material (left-hand side) are pushed through the mixing chamber. This priming step is included in the print workflow as it is necessary for the ability to ensure that the entire mixing chamber is filled so that once the print begins, the desired percentage gradient between the materials is present at the start of the print. After priming, the continuous gradient is printed as a single fabrication step.

Figure 3 - Left: Gradient in TSIM. Right: 3D Dual Syringe | Mix printing the gradient.

Figure 4 - The gradient as printed by BioAssemblyBot.

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The 3D Dual Syringe | Mix seen in Figure 3 is a preproduction version of the tool.