Jeffrey M Karp Seattle Poster.ppt

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Published on November 26, 2008

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Slide 1: Shaping 3-D Biodegradable Scaffolds for Tissue Engineering 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. 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. References 1. Holy CE, Davies JE, Shoichet MS. In Biomaterials, Carriers For Drug Delivery, And Scaffolds For 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). 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. Figure 1. SEM Images of Uncut and Cut Scaffolds (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). 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. Figure 3. Macroporous Scaffold Blocks 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. 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 the PLGA Scaffolds 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 Institute for Biomaterials and Biomedical Engineering, University of Toronto A B Jeffrey M. Karp, Kathy Rzeszutek, and John E. Davies through the scaffold blocks.

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