# Solution Extrusion Additive Manufacturing of Biodegradable Polycaprolactone
## 1 Introduction  
Polycaprolactone (PCL) is a biodegradable semicrystalline poly(\(\alpha\)-hydroxyester) that resorbs slowly by hydrolysis due to its high crystallinity and hydrophobic nature [1; 2]. It is synthesized by ring-opening polymerization of \(\varepsilon\)-caprolactone. The material is semi-crystalline, its melting temperature is 59-64 \({}^{\circ}\)C, and its glass transition temperature is \(-\)60 \({}^{\circ}\)C. PCL is extremely hydrophobic, so it has longer degradation periods than polylactide, making it appropriate for applications requiring long degradation times. In the human body, PCL is resorbed via hydrolysis of the ester linkages. Thus, it has gained much attention as a material for implantable devices. The polymer has also found applications in many fields, such as implantable biomaterials, biodegradable scaffolds, and micro-/nano-particles for drug delivery [3]. Various pharmaceuticals have been incorporated into PCL for drug delivery and targeted release. PCL scaffolds have also been developed for tissue engineering of bone and cartilage. Additive manufacturing [4; 5], which is also called 3D printing, is an easy and adaptable method for the fabrication of products of intricate geometry. The advantages of additive manufacturing include manufacturing options, short time to market, customization, and intricacy, making the process oneof the most favored techniques. Through continuous deposition of filaments and layers, additive manufacturing provides a brand new method for product fabrication. The most commonly employed additive manufacturing method is called fused deposition modeling (FDM) [6]. The process expels thermoplastic melts from a nozzle and lays them onto the developing product. The extrusion nozzle moves in the x and y directions to compose one material layer each time. The nozzle then shifts in the z direction in tiny consecutive steps to make a fresh layer. The moving of the extruding nozzle is controlled by a microprocessor to eventually form a three-dimensional product. The additive manufacturing of pure PCL or filled PCL composites, however, remains as a challenge, mainly due to the restricted availability of PCL filaments for FDM manufacturing [7; 8]. To overcome this limitation, various works have been done. [PERSON] and [PERSON] [9] developed a fused filament fabrication (FFF)-based printer for additive manufacturing of polycaprolactone stents. [PERSON] et al. [10] investigated the morphology and mechanical properties of hydroxyapatite/PCL scaffolds fabricated by a self-developed melt differential FDM 3D printer. [PERSON] et al. [11] employed FDM printing of PCL implants for the delivery of micronized indomethacin. [PERSON] et al. [12] combined FDM with a salt leaching method to develop a 3D printed PCL scaffold with dual micro- and macro-porosity. Despite these efforts, all these works were based on the FDM method, which employs high-temperature extrusions during the manufacturing process. Such a polymer extrusion process poses some restrictions, particularly when the fabricated product is employed as a device for drug delivery. Compounding polymers with pharmaceuticals at high temperatures in the melt extrusion of an additive manufacturing process can destroy or deteriorate the drugs [13]. This study proposed a novel method for additive manufacturing of PCL products using a solution extrusion layer-by-layer scheme. PCL materials and solvent were first mixed and expelled from a feeder equipped with a syringe and a dispensing tip (nozzle). The dispensing tip was controlled and moved by a computer and microprocessor. As soon as the solvent volatilized, the solution was driven from the dispensing tip, solidified, and was piled in continuous layers to make parts of desired geometries. A single factor experimental design was carried out to evaluate the influence of different processing parameters on the tensile properties of additive manufactured parts.