Development of Biodegradable Polymer Scaffolds using Co-Extrusion
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Development of Biodegradable Polymer Scaffolds using Co-extrusion Newell R. Washburn, Carl G. Simon, Jr., Alamgir Karim and Eric J. Amis National Institute of Standards and Technology, Gaithersburg, MD 20899, USA ABSTRACT A methodology for the preparation of porous scaffolds for tissue engineering using co-extrusion is presented. Poly(ε-caprolactone) is blended with poly(ethylene oxide) in a twin-screw extruder to form a two-phase material with micrometer-sized domains. Selective dissolution of the poly(ethylene oxide) with water results in a porous material. This method of polymer extrusion permits the preparation of scaffolds having continuous void space and controlled characteristic length scales without the use of potentially toxic organic solvents. A range of blend volume fractions results in co-continuous networks of polymer and void spaces. Annealing studies demonstrate that the characteristic pore size may be increased to larger than 100 µm. The mechanical properties of the scaffolds are characterized by a compressive modulus on the order of 1 MPa at low strains and approximately 10 MPa at higher strains. The results of osteoblast seeding suggest it is possible to use co-extrusion to prepare polymer scaffolds without the introduction of toxic contaminants. INTRODUCTION There is a continued interest in developing new methods for preparing porous, polymeric materials for use in tissue engineering. Techniques such as salt crystal dissolution, solid-liquid [1,2] or liquid-liquid [3,4] phase separation, microparticle aggregation [5], and others [6] have been investigated to generate scaffolds for medical applications. We present here a new methodology for preparing scaffolds using a commonly employed technique from polymer processing known as co-extrusion [7]. EXPERIMENTAL DETAILS Poly(ε-caprolactone) [8] (Aldrich) and poly(ethylene oxide) (Polysciences) were blended in a research-scale mini-compounder (Daca Instruments, California). A schematic of the interior of the mini-compounder is shown in Figure 1. The barrel is heated to the processing temperature, above the melting temperatures Tm and glass transition temperatures Tg of all the components. Blend components are added through the inlet and the twin screws rotate in tandem driving material from the top of the barrel to the bottom. The polymers return to the top of the barrel through the recirculation channel. As the blend circulates through the compounder it is subjected to strong extensional and rotational stresses that finely mix the components. The size scale of the as-mixed blend is generally on the order of a micrometer but may be controlled through the temperature and screw rotation rate. [9] Blends with a total mass of 3.5 g and a 30 % volume fraction poly(ε-caprolactone) (PCL) were mixed at 50 rpm and 100 °C for 10 min. These were recovered by opening the exit port at the bottom of the compounder barrel and extruded in the form of a tube roughly 3 mm in diameter. The tubes were
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twin screws inlet
recirculation 15 cm exit
Figure 1. Schema
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