Tissue Scaffold Engineering by Micro-Stamping
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Tissue Scaffold Engineering by Micro-Stamping Eric C. Schmitt1, Robert D. White1, Amrit Sagar1, Thomas P. James1 1 Mechanical Engineering, Tufts University, Medford, MA 02155, U.S.A. ABSTRACT A hand operated benchtop stamping press was developed to conduct research on microscale hole fabrication in polymer membranes for applications as scaffolds in tissue engineering. A biocompatible and biodegradable polymer, poly(ε-caprolactone), was selected for micropunching. Membranes between 30 μm and 50 μm thick were fabricated by hot melt extrusion, but could not be stamped with a 200 μm circular punch at room temperature, regardless of die clearance due to excessive strain to fracture. This problem was overcome by cooling the membrane and die sets with liquid nitrogen to take advantage of induced brittle behavior below the polymer’s glass transition temperature. While cooled, 203 μm hole patterns were successfully punched in 33 μm thick poly(ε-caprolactone) membranes with 11% die clearance, achieving 71% porosity. INTRODUCTION Tissue engineering provides an opportunity to develop patient specific implants comprised of scaffolds seeded with donor cells. Conventional methods such as solvent-casting with particulate leaching, gas foaming, phase separation, melt molding, freeze drying, and solution casting are not adequate to produce an engineered microarchitecture [1][2][3]. Scaffolds with engineered pores and internal channels can direct cell growth and provide transport to and from seeded cells [4]. Solid freeform fabrication (SFF) methods developed to engineer microarchitecture include 3D printing, stereolithography, fused deposition modeling, and phase-change jet printing, however most SFF methods require an internal support structure that must be dissolved with solvents, where residuals pose a risk of toxicity to seeded cells. Scaffold engineering through multi-layer construction is a relatively new field where microarchitecture is created by stacking porous 2D membranes into 3D structures [5][6]. In general, these methods and the aforementioned SFF methods are time consuming, which is to say it takes hours rather than seconds to produce a single scaffold layer. One underlying reason for manufacturing inefficiency is the pursuit of scaffold material production at the same time as hole creation by rapid prototyping or molding methodologies. The novel approach presented in this paper is to separate these manufacturing processes by first pursuing high efficiency methods of material film production and then fabricating hole patterns via micromechanical punching. Micro-punching first emerged in 2001 with the development of a micro-punching machine by Joo et al., who punched 100 μm holes in 100 μm brass sheets using dies fabricated with micro electrical discharge machining [7]. Subsequent research has almost exclusively been focused on micro-punching various metals 1.5-200 μm thick [7-12]. Polymers, however, present a different set of challenges for microscale punching, the topic of the present study.
MATERIALS AND METHODS Th
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