J. of Supercritical Fluids 41 (2007) 173–178 Carbon dioxide impregnation of electrospun polycaprolactone fibers Olukemi Ayodeji a , Emily Graham a , Douglas Kniss b , John Lannutti a , David Tomasko c,∗ a Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210, USA b College of Medicine, Laboratory of Perinatal Research, Ohio State University, Columbus, OH 43210, USA c Department of Chemical and Biomolecular Engineering, Ohio State University, Columbus, OH 43210, USA Received 1 August 2005; received in revised form 8 September 2006; accepted 10 September 2006 Abstract The electrospinning of polymers has become a potentially important process for the production of tissue engineering scaffolds. CO 2 impregnation of these scaffolds may provide a method for tailoring the chemistry of these relatively high surface area scaffolds without altering their biomimetic architecture. In pursuing this we found that electrospun polycaprolactone (PCL) fibers melt when exposed to supercritical CO 2 even at room temperature. However, CO 2 exposures ranging from 10 to 25 ◦ C and 1.0 to 3.44 MPa provided chemical impregnation without apparent changes in physical structure. A test compound, carboxytetramethylrhodamine, was embedded into electrospun PCL using CO 2 at 3.44 MPa and 25 ◦ C for 10 h. The subsequent release of carboxytetramethylrhodamine into phosphate buffered saline at 37 ◦ C was then monitored. Release was observed for 30 days after which the fibers were shown to retain 8.54 g of carboxytetramethylrhodamine/mg of PCL. Control samples not exposed to CO 2 showed no detectable release after 5 days. © 2006 Elsevier B.V. All rights reserved. Keywords: Electrospinning; Polycaprolactone; Carbon dioxide; Polymer 1. Introduction Electrospinning utilizes an electrical field to induce ejection of a charged jet from the surface of a solution; in biomedical applications this is typically a polymer (synthetic or naturally derived) solution. This jet elongates under the influence of tan- gential stresses and bending instabilities and as it falls the solvent evaporates. This can result in fibers having submicron diameters that are then collected on an electrical ground [1,2]. Electrospun poly(s-caprolactone) (PCL) has recently been extensively inves- tigated for potential use in tissue engineering and other biomedi- cal applications [3–17]. These novel biodegradable nanofibrous scaffolds closely mimic the normal extracellular matrix. The unique architecture produced by electrospinning can provide temporary structural support and guide tissue regeneration. Sev- eral investigations have involved the use of electrospun scaffolds to develop bone grafts [18,19] in a well-vascularized site using mesenchymal stem cells [16,13]. Other efforts targeted cartilage replacement and cardiac grafts [20–22]. Human smooth muscle cells [23] and endothelial cells can be seeded on these scaffolds ∗ Corresponding author. Tel.: +1 614 292 4249; fax: +1 614 292 3769. E-mail address: tomasko.l@osu.edu (D. Tomasko). to form a three-dimensional cellular network suggesting its use in blood vessel substitutes [24,25]. In this context it is well established that supercritical fluids (SCF) can be used to modify a broad range of polymer systems [26–33]. Advantages include the absence of organic solvents [34,35] and the ability to incorporate delicate biological com- pounds without loss of activity combined with the generation of possibly desirable porous internal architectures [36]. In contrast, the solution processing of many biodegradable polymers typi- cally involves organic solvents that could leave behind harmful residues. Residual CO 2 is inert, nontoxic and nonflammable. Under appropriate conditions CO 2 is a potent swelling agent for polymers and facilitates the absorption of desirable addi- tives. The swollen state is characterized by both increased free volume and greater chain motion enabling more rapid diffusion of large molecules into the polymer. Recent research has shown that biodegradable polymer matrix, poly-dl-lactide-co-glycolide (PLGA) can be impregnated with 5-fluorouracil and -estradiol, drugs that are used for chemotherapy and estrogen hormone therapy [37]. The use of CO 2 as a means of impregnating other solutes into various polymers [38–43] has been investigated. In this work, we extend the use of subcritical levels of car- bon dioxide (CO 2 ) previously demonstrated [44] to study the morphological effects on a common tissue engineering scaffold, 0896-8446/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.supflu.2006.09.011