3D Printing of Customized Biomedical Scaffolds and Implants

Powder-bed 3D printing (3DP) is a versatile additive manufacturing technique that uses ink binder deposition to bind loose powder particles together. This paper evaluates the work using powder-bed 3DP technology as a low-cost manufacturing system to print non-proprietary materials for biomedical scaffold and implant applications. The work presents development of suitable binder-powder feedstock coupled with the suitable printing and post-processing methodologies for respective biomaterial. INTRODUCTION Additive manufacturing (AM) is an alternative manufacturing process that is capable of producing near net-shape products directly from their 3D computer models without the use of a mold. The ease in design modification is earning this technology favorable notion to fabricate products that require customization or are produced in low volume, such as biomedical implants and scaffolds. There are still engineering challenges and opportunities in provisions of 3D biomedical scaffolds with porous microstructures mimicking the tissue architecture, fabricated using suitable biomaterials (Griffith & Naughton, 2002). Both AM and non-AM techniques have been attempted to produce such scaffolds. Non-AM methods include gas foaming (Yoon et al. 2001), solvent casting and particulate leaching (Kawanishi et al. 2004, Sato et al. 2004), and freeze-drying (Whang et al. 1995). These methods are typically good to obtain random porosity, as the porosity is process-dependent or resultant from pore forming agents. Consequently, these methods typically produce pores in irregular shape and size, with limited interconnectivity of the porous network. Proc. of the Intl. Conf. on Progress in Additive Manufacturing Edited by Chua Chee Kai, Yeong Wai Yee, Tan Ming Jen and Liu Erjia Copyright © 2014 by Research Publishing Services. ISBN: 978-981-09-0446-3 :: doi:10.3850/978-981-09-0446-3 069 411 Chua Chee Kai, Yeong Wai Yee, Tan Ming Jen and Liu Erjia (Eds.) Porous scaffold and implant fabrication by AM have been reported in various publications (Yang et al. 2002, Yeong et al. 2004, Bártolo et al. 2009, Peltola et al. 2008), reporting scaffolds and implants with regularly structured pores and porosity, in customizable overall shape and size. Powder-based AM systems are considered as the most versatile AM technology, as various materials are directly available in powder form. Compared to other commercially available powder-based AM systems, such as selective laser sintering, selective laser melting and electron beam melting, powder-bed 3DP is regarded as a low-cost system, therefore reducing the initial investment cost of owning a powder-based AM system. A powder-bed 3DP builds part based on inkjet printing deposition concept. The system consists of a part building chamber, a powder supply chamber, a roller and an inkjet printer depositor. The ink depositor mechanism selectively drops the ink binder onto the loose powder in the part-building chamber, corresponding to that particular layer’s cross-sectional area. This action produces a layer of bonded powder material at the selected regions. Parts printed by powder-bed 3DP are naturally porous. This is mainly due to the 3DP inkjetprinting manner, whereby the powder particles are bound together by the ink binder with minimal heating at temperature much lower than the powder’s melting or glass-transition temperature. Therefore the bound powder particles still maintain their original size and shape, with highly porous printed parts produced. Combining the design flexibility that is a common feature in AM technologies, 3DP products can have dual porosity that is a combination of the inherent and predesigned porosity (Maleksaeedi et al. 2013). This paper elaborates the studies conducted using powder-bed 3DP to print non-proprietary biomaterials, namely poly(lactide-co-glycolide and polyglycolide biopolymers and titanium. The studies encompass analysis of selecting suitable ink binder material and development of suitable printing process. Exploration of post-processing methodologies, such as thermal debinding, sintering and infiltration, were conducted for the respective biomaterials to enhance the scaffold mechanical performance. 3D PRINTING OF BIOPOLYMER SCAFFOLDS 50/50 poly(DL-lactide-co-glycolide) (PLGA) and polyglycolide (PGA) (Purasorb PDLG, Purac Asia Pacific Pte Ltd) pellets were pulverized in cryogenic environment (SPEX CertiPrep 6850 freezer/mill) to obtain particles size less than 212 m. Binder materials evaluated were poly(ethylene glycol) (PEG) (30,902-B, Sigma-Aldrich), poly(ethylene oxide) (PEO) (18,945-6, Sigma-Aldrich) and poly(vinyl alcohol) (PVA) (GL-05S, Nippon Gohsei). Ink binders evaluated were water, ethanol and acetone. The compatibility between the polymer materials (PLGA, PGA and various binders) and ink binder was established by dissolving the polymer in the respective ink binders. The solubility of each material is provided in Table 1. Although ethanol was not able to dissolve the PLGA, it was included in the ink formulation to dilute the corrosive effect of acetone on the printer components. Test printing (ZCorp Z402 system) was conducted to examine the solvent-binder-polymer compatibility by overprinting the same area of polymer/binder mixture with acetone/ethanol/water