Biomedical Engineering Reference
In-Depth Information
All samples
20
15
10
S1
S2
S3
S4
S5
5
0
0
−
10
10
20 30
Strain (%)
40
50
60
70
5
−
FIGURE 2.10
The second-generation FDM scaffolds for bone engineering are now made of polymers and
ceramics.
11
Polymer/CaP composites confer favorable mechanical (pictures top row) and biochemical proper-
ties, including strength via the ceramic phase, toughness and plasticity via the polymer phase, more favorable
degradation and resorption kinetics, and graded mechanical stiffness. Other advantages include improved
cell seeding, and enhanced control and simplifi cation of the incorporation and immobilization of biological
factors PCL-TCP composite scaffolds (see white window left and middle picture lower row) placed as bone
graft in a high load bearing application in a pig spinal fusion model. Three-month postoperative x-ray analysis
shows no spinal bone fusion due to the scaffold becoming encapsulated with fi brous tissue (micro-CT, bottom
right picture).
Mondrinos et al.
13
used indirect SFF by applying a drop on demand printing (DDP) fabrica-
tion process. A single universal porogen material was used to build a negative mold, which could
then be injected with a wide range of biomaterials. Scaffolds comprising homogenous composites
of PCL and calcium phosphate (10% or 20% w/w) were fabricated using injection molding of mol-
ten polymer-ceramic composites, followed by porogen dissolution with ethanol creating scaffold
pore sizes as low as 200 µm. An inherent advantage of this technique is the ability to use multiple
biomaterials for injection molding with a single ubiquitous porogen. Furthermore this technique
circumvents the need to use cytotoxic solvents, which are common with many other polymer fab-
rication routes.
Yaszemski et al.
34
used poly(propylene fumarate) (PPF) as an injectable, biodegradable poly-
mer, which has been used for fabricating preformed scaffolds in tissue engineering applications
because of
in situ
crosslinking characteristics in combination with an SFF technique. To understand
the effects of pore structure parameters on bone tissue in growth, 3-D PPF scaffolds with controlled
pore architecture have been produced in this study from CAD models. The authors created origi-
nal scaffold models with three pore sizes (300, 600, and 900 µm) and randomly closed 0%, 10%,
20%, or 30% of total pores from the original models in three planes. PPF scaffolds were fabricated
by a series of steps involving 3-D printing of support/build constructs, dissolving build materials,
injecting PPF, and dissolving support materials. To investigate the effects of pore size and intercon-
nectivity on scaffolds, the authors compared the porosities between the models and PPF scaffolds
fabricated thereby examined pore morphologies in surface and cross-section using scanning elec-
tron microscopy, and measured permeability using the falling head conductivity test.
