Question

How could you change the scaffold mechanical properties through the design ?

Answer 1

Scaffold design requirements must be addressed on both macroscopic and microscopic scales.

On a macroscopic scale (defined as >1 mm), a scaffold design must replicate human anatomy while on a microscopic level, it must fulfill temporary tissue function and simultaneously enhance tissue regeneration.

These two scales must be integrated to produce a single design that can be embodied in a format appropriate for SFF methods.

Data for macroscopic design is typically derived from computed tomography (CT) or magnetic resonance imaging (MRI) that represents anatomical shape and topology by density distributions within a three-dimensional volume element (voxel) database.

Image processing techniques, including basic thresholding, noise filtering, edge detection, morphological filtering and region of interest selection, are needed to process the data into a form suitable for design purposes.

Once the image data is processed, there are two ways to utilize it for scaffold design.

For traditional computer aided design (CAD) techniques the image data must first be converted to a geometric form such as points, lines or surfaces.

Geometric representations of anatomy can then be further manipulated to control the exterior scaffold shape.

A second method directly creates topology within the voxel data structure, a process known as image-based design (IBD).

This technique creates an external design by altering the density distribution within the voxel dataset.

Requirements for microscopic design are more complex and much less defined than macroscopic requirements.

Both physical properties (including stiffness, permeability and conductivity) and tissue regeneration enhancement (related to scaffold porosity, pore diameter, interconnectivity, and permeability) depend directly on scaffold microstructure.

Although these general requirements are agreed upon (LeBaron and Athanasiou 2000, Butler et al. 2000, Hollister et al. in press, Yang et al. 2001), the most critical requirement for successful tissue regeneration is yet to be determined, but must entail the concurrent design of scaffold microstructure, material, and tissue interface.

A widely proposed design principle, although lacking substantive experimental evidence, is that scaffold microstructure should render effective properties that match those of native tissue and yet maintain high permeability or porosity for biofactor delivery.

Three design approaches have been employed in accordance with this principle:

(i)-material process-defined design,

(ii)-periodic cell-based design and

(iii)-biomimetic design.