Making Porous 3D Structures

The BioAssemblyBot® Platform can be used to fabricate mesh or weave-like patterns to generate constructs with varying porosity

3D tissue scaffolds that contain precise pore structures are necessary for a myriad of tissue engineering applications. Many engineered tissue scaffolds are porous to enable both the necessary biological interactions inherent in tissues to occur while also maintaining structure fidelity or strength through the connections contained within mesh-like materials. This also recapitulates the porous nature of native scaffolds within a variety of different tissues while simultaneously providing avenues for cell growth to occur. These mesh-like materials are also used for additional applications outside of the direct tissue engineering realm, such as being used as filters, screens, masks and patches. The BioAssemblyBot® technology platform provides the precision required to generate such porous constructs that can be made from a variety of biocompatible of materials through the tool-sets available in the platform.

The Process

To generate porous or mesh-like scaffold materials, the design of the structure can first be created within the fully-integrated software program, TSIM®, including the appropriate material controls for each component of the construct. In this case study, we demonstrate the ability of the platform to generate structures of varying porosity with two distinct material types. The first example assumes that the scaffold will need to maintain shape over extended periods of time. Therefore, the heat-controlled tool is utilized to extrude biodegradable materials, such polycaprolactone, or PCL. Due to the more rigid nature of PCL, this material requires a melt-extrusion process. To achieve this, PCL pellets are loaded into the heat-controlled syringe. This syringe can maintain temperature control beginning at the storage bay, which allows the tool and material to get up to a temperature that would enable extrusion. This temperature can then continue to be maintained as the tool is being utilized for its designed task as well as when it is returned to the storage bay. To maintain the structure generated with PCL, the print will need to cool down to ambient temperatures. The second example below utilizes hydrogel materials that can be extruded under ambient conditions.

Figure 1. PCL scaffold fabricated on the BioAssemblyBot® platform using the heat-controlled tool.

Porous Construct Made of PCL

After the desired parameters for the utilization of the tool are determined based on the construct as well as desired pore size of interest, the scaffold can then be printed on the BioAssemblyBot® platform as shown in the image below (Figure 1). This type of structure and fabrication strategy is also used to generate mimics of woven material.

Varying Porosities Made with Extreme Precision

Different tissue types and applications will require scaffolds that contain pores of varying size and density. Through the design work that can be done within TSIM® along with the precision enabled through using the 6-axis arm, the BioAssemblyBot® can generate structures with varying porosities. As seen in (Figure 2) below, different materials as well as design parameters resulted in unique pore dimensions that were repeated throughout the scaffold.

Figure 2. Magnified view of pores that contain varying dimension based upon design requirements as well as material composition.

The top image shown above contains a magnified view of the PCL structure shown in Figure 1. This illustrates how precisely the pattern was generated using a melt-extrusion process while also exhibiting how this pattern mimics that found in woven fabrics and constructs, which are often used as a supporting material for a variety of regenerative medicine-based applications. The next image illustrates the size of each pore of a construct made of pluronic hydrogel. This material can be extruded under ambient conditions and this structure includes unique porosity dimensions compared to the PCL example. Therefore, altogether these examples demonstrate the flexibility and precision that the BioAssemblyBot® technology contains to fabricate 3D structures with varying porosity.

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