Shaping 3-D Biodegradable Scaffolds for Tissue Engineering
Jeffrey M. Karp, Kathy Rzeszutek, and John E. Davies
Institute for Biomaterials and Biomedical Engineering, University of Toronto
Figure 2. Large Scaffold
Mold
A Large Teflon®FEP coated
aluminum mold (10.0cm x 10.0cm
x 3.0cm) was custom made for
producing the initial scaffold
blocks.
Figure 3. Macroporous
Scaffold Blocks
Overview
Shaping tissue engineering scaffolds is of great importance for in vivo applications
to fit specific defects, and for in vitro applications where consistent and reproducible
samples must be used to perform controlled experiments. One method to
manufacture scaffolds of a desired shape involves the use of individual molds.
However, the porosity at the outer margins of the created scaffolds, which are in
contact with the mold surface, is often compromised by the creation of an area with
significantly reduced porosity or a polymer “skin” [1,2] (Figure 1A). Many
biodegradable polymeric scaffolds are soft and delicate. Perhaps for this reason,
methods for reproducibly cutting these scaffolds, in a manner which retains the
original scaffold porosity and geometry to the margins of the material, have not yet
been explicitly described.
We have created a simple proprietary system that can be used to quickly and
accurately cut cylindrical shapes from delicate polymeric scaffold materials that
maintain their morphological features to the margins of the shapes produced. This
technology is of particular benefit for reproducibly shaping soft macroporous
scaffolds and creating channels in such scaffolds.
Large PLGA scaffold blocks
(10.0cm x 10.0cm x 1.2cm) were
created using the Teflon®FEP
coated aluminum mold. These
scaffold blocks have a high
degree
of
interconnected
macroporosity, which mimics the
structure of trabecular bone.
(A) An outer edge of the large scaffold block that was in contact with the
Teflon®FEP mold surface has a PLGA “skin”. (B) Once cut, the resultant
scaffolds maintain their morphological features to the outer margins of
the shapes produced.
Discussion
Scaffold blocks (10.0cm x 10.0cm x 1.2cm) (Figure 3) were created using
large molds (Figure 2) only as a means of obtaining the starting scaffolds
of which shape is unimportant. By doing this, one can cut out many
small-sized highly porous scaffolds, using the device described, while
maintaining porosity to the outer margins of these scaffolds (Figure 1B
and Figure 6).
Figure 4. Stainless Steel
Cutting Tools
Proprietary cutting devices having
various
diameters
were
fabricated. From left to right the
diameters of the devices are 10.0
mm, 4.4mm and 2.4mm. Smaller
diameter devices can be used to
cut scaffolds with a reduced pore
size. (patent application pending)
Figure 5. Cutting
PLGA Scaffolds
the
Many cylindrical scaffolds were
cut from one PLGA scaffold block
by placing the cutting tools into a
digitally controlled high speed
Dremel® housed in a Dremel®
press. This allowed for precisely
controlled rotational speed and
travel of the cutting device
through the scaffold blocks.
A
B
Figure 1. SEM Images of Uncut and Cut Scaffolds
Figure 6. Samples of Cut Scaffolds
The proprietary cutting device can cut a wide variety of sizes of cylindrical scaffolds
from larger scaffold blocks. In addition, the device can be used to create channels,
both radial and axial, within scaffolds for promoting cell migration and vascular
ingrowth. These channels can also be used for incorporation of drug delivery
devices, other organic and inorganic materials, and for seeding such scaffolds with
cells. (the ruler represents cm)
Materials and Methods
Poly(lactide-co-glycolide) (PLGA) 75/25 scaffolds were produced by modifying a previously described
technology [Holy et al 1997]. Briefly, the starting PLGA 75:25 3-D scaffold blocks were prepared by dispersing
glucose crystals having 0.85 to 1.18mm dimensions in a solution of PLGA 75:25 in dimethysulfoxide (5%, 6%,
7%, 8%, 9% and 10% PLGA (w/v)). The sugar/polymer mixture was then placed in a Teflon®FEP coated
aluminum mold (Figure 2) and allowed to set. When the polymer precipitated, the glucose crystals were
extracted from the polymer, which resulted in a 3-D scaffold block having macroporous interconnected
porosity. The dimensions of the resultant scaffold were 10.0cm x 10.0cm x 1.2cm (Figure 3).
The cutting device was turned on a lathe from a stainless steel (316 grade) rod. Three different cylinder sizes
10.0 mm, 4.4 mm, and 2.4 mm in diameter were manufactured (Figure 4). One end of the cylinder was used
to create the cutting edge, while the other end was reduced in diameter to 1/5 in or 1/8 in to fit either a
standard drill or Dremel® (Model 398) respectively. A Multipro Deluxe drill press stand Model 212 type II was
used with the Dremel® for enhanced control and precision (Figure 5). The cylindrical scaffolds were cut to the
desired length using a custom-made Teflon® guiding device and a standard double-edged razor blade. The
cutting devices were ultrasonically cleaned with acetone and Decon™, and then rinsed with double distilled
water and ethanol ( 70% and 100%) prior to use.
In order to determine the limitations of the device with respect to the
physical strength of the scaffold, PLGA scaffold blocks having 5%, 6%,
7%, 8%, 9% and 10% (w/v) were cut. The limiting factor during
manufacturing of the final cylindrical scaffold was found to be the physical
strength of the initial scaffold block. The 5% PLGA in DMSO (w/v) scaffold
blocks were found to be very fragile to handle and collapsed during the
cutting process. All of the other scaffolds that were made with 6%-10%
(w/v) maintained the interconnected macroporosity throughout the
scaffold after cutting. It was also found that cutting pre-wetted scaffold
blocks improved the dimensional stability of the cylindrical scaffolds.
In order to determine the cutting precision of the device, the mass
deviation was obtained for one hundred 10.0mm diameter scaffolds that
were randomly selected. The scaffolds weighed 23.0 ± 3.0mg and the
standard deviation in mass was 5.3%, which can be considered an
acceptable value of error.
Acknowledgements
The authors would like to thank Keith Porter for custom making the
stainless steel cutting tools. This work was supported by a grant from the
ORDCF.
References
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Tissue Engineering (Peppas, N.A., Mooney, D.J., Mikos, A.G., Brannon-Peppas, L., Eds.) AiChE
Press, NY, 1997: 272-274.
2. Agrawal CM, Ray RB. Biodegradable polymeric scaffolds for musculoskeletal tissue engineering.
J Biomed Mater Res 2001;55(2):141-50.
3. Mikos AG, Temenoff JS. Formation of highly porous biodegradable scaffolds for tissue
engineering. EJB Electronic J Biotech 2000;3(2).