The Development of Computer-Aided System for Tissue Scaffolds (CASTS) System for Functionally Graded Tissue-Engineering Scaffolds

Abstract

Computer-aided system for tissue scaffolds (CASTS) is an in-house parametric library of polyhedral units that can be assembled into customized tissue scaffolds. Thirteen polyhedral configurations are available to select, depending on the biological and mechanical requirements of the target tissue/organ. Input parameters include the individual polyhedral units and overall scaffold block as well as the scaffold strut diameter. Taking advantage of its repeatability and reproducibility, the scaffold file is then converted into .STL file and fabricated using selective laser sintering, a rapid prototyping system. CASTS seeks to fulfill anatomical, biological, and mechanical requirements of the target tissue/organ. Customized anatomical scaffold shape is achieved through a Boolean operation between the scaffold block and the tissue defect image. Biological requirements, such as scaffold pore size and porosity, are unique for different type of cells. Matching mechanical properties, such as stiffness and strength, between the scaffold and target organ is very important, particularly in the regeneration of load-bearing organ, i.e., bone. This includes mimicking the compressive stiffness variation across the bone to prevent stress shielding and ensuring that the scaffold can withstand the load normally borne by the bone. The stiffness variation is tailored by adjusting the scaffold porosity based on the porosity-stiffness relationship of the CASTS scaffolds. Two types of functional gradients based on the gradient direction include radial and axial/linear gradient. Radial gradient is useful in the case of regenerating a section of long bones while the gradient in linear direction can be used in short or irregular bones. Stiffness gradient in the radial direction is achieved by using cylindrical unit cells arranged in a concentric manner, in which the porosity decreases from the center of the structure toward the outside radius, making the scaffold stiffer at the outer radius and more porous at the center of the scaffold. On the other hand, the linear gradient is accomplished by varying the strut diameter along the gradient direction. The parameters to vary in both gradient types are the strut diameter, the unit cell dimension, and the boundaries between two scaffold regions with different stiffness.

Graded Cellular Bone Scaffolds

“…CAD-based methods [28,29] and implicit surface modeling (ISM) methods [18,30] are common to create the cellular structures with porosity-graded structures, since the internal architectures are fully controlled with no hanging edge [18,31]. For the CAD-based methods, graded structures of the pillar octahedral scaffolds could be attained by varying the architectural parameters, such as lattice diameter (t) and unit size (L) (Figure 7).…”

Influence of Tomographic Slice Thickness and Field of View Variation on the Reproduction of Thin Bone Structures for Rapid Prototyping Purposes —An <i>in</i> <i>Vitro</i> Study

“…Dental implantology has been using these models for surgical planning, especially in more complex cases [10][11][12][13]. There are also applications of MRP in tissue engineering and regenerative medicine [14][15][16].…”

Software for Bioprinting

“…It is used to import and export file formats such as ACIS, IGES, and Parasolid formats, which are specialized widely-used general file formats for solid modeling but not for bioprinting. The platform for the CAD system for tissue scaffolds (CASTS) has been developed later based on Pro/Engineer[ 47 , 48 ]. For the input model, CASTS uses imaging software such as materialize interactive medical image control system (MIMICS) to convert the patient data from magnetic resonance imaging (MRI) or computer tomography (CT) to the IGES, neutral CAD file format.…”