A review of rapid prototyping techniques for tissue engineering purposes

Figures & data

Table

CAD	computer-aided design
CCD	charge-coupled device
CT	computerized tomography
FDM	fused deposition modeling
HA	hydroxyapatite
MRI	magnetic resonance imaging
Nd:YAG	neodymium-doped yttrium aluminum garnet
NIR	near-infrared
PCL	polycaprolactone
PLA	polylactide
PP	polypropylene
RP	rapid prototyping
SLA	stereolithography
SLS	selective laser sintering
TCP	tricalcium phosphate
TMJ	temporomandibular joint
TPA	two-photon absorption
TPP	two-photon polymerization
UV	ultraviolet

Figure 1.  MicroCT analysis of salt-leached, photopolymerized scaffold fabricated with Kerr dental lamp. The material was methacrylate end-capped poly(D,L-lactide), and camphorquinone has been used as photoinitiator.

Figure 2.  Pore size distribution of the photopolymerized scaffold visualized by microCT.

Figure 3.  Schematic representation of the stereolithography (SLA) system. An ultraviolet (UV) laser is used to solidify the model's cross-section while leaving the remaining areas in liquid form. The movable table then drops by a sufficient amount to cover the solid polymer with another layer of liquid resin.

Figure 4.  Example of a scaffold fabricated using stereolithography (SLA). A: Computer-aided design (CAD) image of the structure. B: Completed SLA-fabricated scaffold with very regular pore size distribution. C: Microcomputerized tomography (microCT) image of the scaffold.

Figure 5.  Scheme of 3D printing process. A stream of adhesive droplets is expelled through an inkjet printhead, selectively bonding a thin layer of powder particles to form a solid shape.

Figure 6.  Scheme of selective laser sintering (SLS) technique. The laser selectively fuses powdered material by scanning cross-sections generated from a 3D digital description of the part on the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed.

Figure 7.  Scheme of the fused deposition modeling (FDM) system. FDM uses a moving nozzle to extrude a fiber of polymeric material from which the physical model is built layer by layer.

Figure 8.  Sketch of the 3D Bioplotter® system. The material is plotted through the nozzle into a liquid medium with matching density. The material solidifies when it comes in contact with the medium. The liquid medium compensates for gravity, and hence no support structure is needed.

Figure 9.  The principle of the two-photon polymerization process. Overlap of photons from the ultrashort laser pulse leads to chemical reactions between monomers and starter molecules within the transparent matrix.

Table I.  Comparison of different rapid prototyping (RP) methods on the basis of their achievable resolution, advantages, and disadvantages.

RP technique	Resolution (µm)	Advantages	Disadvantages	Reference
SLA	70–250	Easy to remove support materials, easy to achieve small features	Limited choice of photopolymerizable and biocompatible liquid polymer materials	37, 43
3D printing	200	Low costs, no toxic components, fast processing	Weak bonding between powder particles, rough surface, postprocessing	38, 43
SLS	500	High accuracy, good mechanical strength, broad range of materials	High temperatures during process, trapped powder is difficult to be removed	39, 43
FDM	250	Low costs	Elevated temperatures during process, small range of materials	40, 43
3D plotting	250	Broad range of materials and conditions, incorporation of cells, proteins and fillers	Slow process, limited resolution	41, 43
Organ printing	300–400	Pattern flexibility, incorporation of cell aggregates, high throughput	Lack of structural support, dependence on self-assembly	30, 42
TPP	0,1	Simple, fast, true 3D process, high resolution	Requires a femtosecond laser, material has to be photosensitive	33, 34

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